Title of Invention	OPTICAL ELEMENT AND METHOD FOR RECORDING BEAM PARAMETERS, COMPRISING A TEMPERATURE SENSOR PROVIDED IN THE FORM OF A PIXEL MATRIX
Abstract	The invention relates to an optical element for guiding and forming a laser beam, and to a method for recording beam parameters, particularly in a laser system, comprising a carrier substrate (40) and a coating (39), which is applied to at least one side of the carrier substrate (40), and comprising at least one temperature sensor (38). The temperature sensor (38) is comprised of a number of pixels arranged in a matrix, and each respective pixel has at least one temperature sensitive element (39). The at least one temperature sensitive element (39) of the pixel is constructed inside the carrier substrate (40) made of silicon.

Title of Invention

OPTICAL ELEMENT AND METHOD FOR RECORDING BEAM PARAMETERS, COMPRISING A TEMPERATURE SENSOR PROVIDED IN THE FORM OF A PIXEL MATRIX

Abstract

The invention relates to an optical element for guiding and forming a laser beam, and to a method for recording beam parameters, particularly in a laser system, comprising a carrier substrate (40) and a coating (39), which is applied to at least one side of the carrier substrate (40), and comprising at least one temperature sensor (38). The temperature sensor (38) is comprised of a number of pixels arranged in a matrix, and each respective pixel has at least one temperature sensitive element (39). The at least one temperature sensitive element (39) of the pixel is constructed inside the carrier substrate (40) made of silicon.

Full Text	WO 2006/103104 PCT/EP2006/003019 OPTICAL ELEMENT AND METHOD FOR RECORDING BEAM PARAMETERS, COMPRISING A TEMPERATURE SENSOR PROVIDED IN THE FORM OF A PIXEL MATRIX The invention relates to an optical element for guiding and shaping a laser beam in accordance with the preamble of claim 1, and to a method for recording beam parameters with such an optical element in accordance with the preamble of claim 14. The use of laser beams for machining materials is widespread in industrial manufacturing. For monitoring the machining and for quality assurance it is necessary that a constant power of an electromagnetic radiation be generated by a laser arrangement and be output with constant parameters. A laser arrangement is provided with a plurality of optical elements that guide and shape the beam. At the same time, the power of the beam is also influenced thereby. The quality of the laser arrangement is essentially determined by the beam orientation, the beam profiling and the beam power. These parameters are to be optimized for the machining processes and can be adversely influenced by aging, incipient destruction and/or contamination of the optical elements. Such influences in turn adversely affect the beam parameters of the electromagnetic radiation or of the laser beam. In order to record or monitor said parameters, there is the possibility of producing a so-called mode shot of a laser beam. The laser beam generated by the laser arrangement; i s coupled out from the customary beam path and directed onto a plexiglass cube, where material vaporizes upon impingement of the laser beam and the remaining contour enables a statement about the quality of the beam. This technique is time-consuming and requires an interruption of production. WO 2006/103104 PCT/EP2006/003019 - 2 - A brochure from the company Prometec entitled "Laserscope UFC60" discloses a cevice that enables a continuous measurement and monitoring of unfocused laser radiation from lasers with high power that is principally used in laser machining. The device operates according to the measurement principle according to which a wire increases its electrical resistance if its temperature increases on account of absorbed radiation. In order to determine measurement data, a plurality of grids arranged one above another with extremely thin wires arranged next to one another are provided. An apparatus with two grids mounted one above another is proposed for bean monitoring, wherein this device receiving the grids is to be positioned in a beam path in such a way that the laser beam passes through said grids. This device is not possible in routine operation of a laser arrangement on account of a housing receiving the grids. As a result, no online measurements can be carried out. Furthermore, the wires provided for recording information are extremely sensitive since they have a diameter in the lower micrometers range and can break very easily. In particular, a cooling of the grids for an exact measurement is possible with difficulty since the wires break even more easily when there is a strong air flow. Without cooling of the grids, however, the recorded values are beset with errors as a result of continuous heating of the grids. Furthermore, dirt particles can deposit on the grid and additionally corrupt the measurement results. Moreover, the device cannot be used within a laser apparatus, a beam source or a beam generator. The contamination, aging and beginning of the destruction of optical elements cannot be recorded either. FR 2 698 4 95 A1 reveals a method for measuring a temperature of a lens provided in a laser arrangement. WO 2006/103104 PCT/EP2006/003019 - 3 - A first thermoelement fitted at the edge of the lens is provided for recording the temperature of the lens. A further temperature element is arranged on a front side of an exit of the lens outside the beam path. A third thermoelement is fitted at a shoulder of the receptacle. These three thermoelenents are respectively arranged in a manner offset by 120° relative to one another and forward the recorded temperature to an evaluation unit. As soon as the recorded temperature has exceeded a threshold value, an alarm signal is output. By virtue of the arrangement of the thermoelements on the lens and the lens receptacle, individual measurements at the respective contact locations of the thermoelements relative to the lens are carried out by the thermoelements. This does net enable a statement about the determination of the degree of contamination or an incipient destruction or aging and the power of the beam or further beam parameters. US-A 4,692,623 discloses a device provided for recording a situation and a position of a laser beam. Said device has a grid of conductor tracks on a glass substrate, the conductor tracks being insulated from one another at the crossover points. Said conductor tracks can be covered with a reflective coating. A detector and a display device for recording the change in the electrical resistance on account of the absorbed heat are connected to the conductor tracks. An analogous arrangement is disclosed in CH 690 796 A5. The mirror disclosed in this document differs from the previous device by virtue of the fact that the grid of conductor tracks is formed in two planes isolated by an insulation. A first layer of a multiplicity of conductor tracks arranged parallel to one another is provided on an insulation on the carrier material of WO 2006/103104 PCT/EP2006/003019 - 4 - the mirror. Said layer is covered with an insulation which, in turn, receives a second layer of conductor tracks running parallel to one another. The second layer of conductor tracks is oriented in a manner rotated by 90° relative to the first layer. The second layer of conductor tracks is also covered by an insulation. Contact areas for connection to an evaluation unit are provided in each case at the outer-ends of the conductor tracks. EP 1 310 7 82 A1 has disclosed an optical element having a coating on a carrier material. Such optical elements are used for guiding and shaping a laser beam. For recording a situation and a. position of a laser beam, it is provided that the optical element has a grid structure composed of thin conductive material on or in the coating or the carrier material. Via contact elements acting on the optical element, the recorded measured values can be forwarded into a measuring device or evaluation unit. What the three abovementioned devices in accordance with US-A 4,692,623, CK 690 796 A5 and EP 1 31.0 782 A1 all have in common is that a temperature change is brought about in the carrier materials on account of the absorbed radiation, which temperature change is in turn transmitted to the conductor tracks in order to record a change in the electrical resistance in the conductor tracks. However, said temperature change can only be recorded integrally by means of the respective conductor track, or the length thereof between the two end points. As a result, an evaluation with respect to the beam position and beam size can only be effected approximately. An evaluation of an intensity distribution of the beam, as is made visible by a mode shot, is not possible. Therefore, the invention is based on the object of WO 2006/103104 PCT/EP2006/003019 - 5 - proposing an optical element for guiding and shaping a laser beam which enables a precise recording of the beam position, the beam diameter and the intensity distribution of the beam whilst maintaining the beam guiding properties of an electromagnetic beam. This object is achieved according to the invention by means of an optical element for guiding and shaping a laser beam in accordance with the features of claim 1. The optical element formed according to the invention has the advantage that an exact evaluation of the beam parameters, such as, for example, the beam position, the beam diameter and the intensity distribution of the beam, is made possible. The configuration of the temperature sensor as a matrix composed of a multiplicity of pixels enables a spatial resolution of the intensity for the laser beam impinging on the optical element. On account of such a spatial resolution of the intensity, it is possible to record a beam alteration during the operation of a laser system without the laser beam being coupled out. The beam alteration represents an image about the state of the laser, with the result that not only optical elements but also further components of the laser systems can be monitored. The so-called mode shot can be replaced by the configuration of the optical element according to the invention. It is no longer necessary to couple out the laser beam in order to generate a mode shot. The measured values recorded by the temperature sensor furthermore enable an evaluation of a thermal loading of the optical element and also about the state of tne optical element with regard to aging and contamination or incipient destruction. At the same time, the use of at least one optical element according to the invention can afford a permanent monitoring of the laser system without intervention in routine production. WO 2006/103104 PCT/EP2006/003019 - 6 - According to one advantageous configuration of the invention, it is provided that the optical element comprises a matrix of temperature-sensitive elements as carrier material. By virtue of the arrangement of the temperature-sensitive elements in a matrix as temperature sensor, a statement can simultaneously be made about further bean parameters such as, for example, the position of the impingement area and the size or the diameter of the electromagnetic beam, the local resolution of the intensity distribution, the absolute beam power, the temporal resolution capability. The recording of the position makes it possible to record the beam orientation or the beam course with respect to the optical element and, consequently, misalignments possibly present. The recording of the beam diameter and/or the temperature profile makes it possible to determine the present power in comparison with the known desired power of the beam. According to a further advantageous configuration of the method, it is provided that the at least one temperature-sensitive element is constructed in a silicon wafer, in particular as a diode. When the semiconductor material is used as a carrier substrate, it is possible in particular to implement the diodes as temperature-sensitive elements directly into the carrier substrate. CMOS processes are preferably used to produce the diodes. Further known production processes can likewise be used. The temperature-sensitive elements are preferably embedded in so-called P- or N-doped depressions or wells ("p-wells" or "n-wells"). This provides an electrical insulation between the individual diodes, thereby reducing or preventing a crosstalk between the different temperature-sensitive elements. WO 2006/103104 PCT/EP2006/003019 - 7 - Preferably, the temperature-sensitive elements are thermally insulated from one another. For this purpose, for example trenches are provided in the carrier substrate, in particular silicon wafer, in order to insulate said temperature-sensitive elements from one another. Said trenches are filled with an insulating layer and are referred to as "deep-trench isolation". The recording and localizing of the electromagnetic beam impinging on the optical element can thereby be localized exactly. At the same time, ar. improved temperature recording can thereby be made possible for each temperature-sensitive element, whereby the beam profiling can be recorded more precisely. In one preferred embodiment, a plurality of temperature-sensitive elements are connected in series in a pixel. It is thereby possible to measure one or a plurality of time-dependent features or characteristic curves within the sensor chain, such as, for example, a voltage drop in the case of a specific current or a specific current drop in the case of a known voltage. By virtue of the fact that a pixel of the matrix advantageously comprises a plurality of temperature-sensitive elements, the measurement accuracy of a pixel and hence the performance of the temperature sensor comprising a plurality of pixels can be increased. As an alternative, it can be provided that the temperature-sensitive elements of a pixel are connected in parallel, whereby an averaged statement about a temperature of the pixel is likewise made possible. One preferred embodiment provides for a coating to be provided at a side of the carrier substrate which faces the temperature sensor, and a carrier material to be provided at a side of the carrier substrate which is remote from the temperature sensor. This construction enables in particular very thin silicon wafer's to be usable for the implementation of the diodes for WO 2006/103104 PCT/EP2006/003019 - 8 - producing the pixels as a matrix for forming a temperature sensor. Moreover, a multiplicity of carrier materials can be applied which have a high thermal conductivity and/or mechanical stiffness in order to receive the carrier substrate. By way of example, an adhesive-bonding connection can be provided between the carrier substrate and the carrier material- Such carrier materials can be provided from metal, in particular copper, and also other materials such as e.g. silicon. An alternative embodiment of the optical element provides for a carrier material to be provided at a side of the carrier substrate which is remote from the temperature sensor, and a coating to be applied at the opposite side of the carrier material. This construction makes it possible e.g. for an increased reflection cr reduced transmission of the laser beam to be provided depending on the carrier material, such that the carrier material acts as a filter, a sufficient radiation energy still acting on the temperature sensor. In the case of the last-mentioned embodiment, the carrier material is preferably formed in highly transmissive or fully transmissive fashion. By way of example, the carrier material has a transmittance of at least 97%. Preferably, a passivation layer is provided between a coating and the carrier substrate in order to separate the highly reflective coating from the connections of the temperature sensor and also the temperature-sensitive elements. This arrangement is provided in a first embodiment of a layer construction for the optical element. In the second alternative embodiment, the temperature sensor is assigned in a manner remote with respect to the incident laser beam in the beam WO 2006/103104 PCT/EP2006/003019 - 9 - path and preferably receives an absorber layer on its rear side. According to a further advantageous configuration of the invention, it is provided that a stress-compensating layer is applied on a rear side of the carrier material, opposite to the coating, said stress-compensating layer preferably comprising a silicon nitride or similar materials. Such a layer can be applied for example by plasma-enhanced or chemical vapor deposition methods. According to a further advantageous configuration of the invention, it is provided that the coating of the optical element has a reflectance of the laser radiation of at least 98%. As a result, on the one hand, the imaging properties, in particular the guiding and/or shaping of the laser beam, are preserved and, on the other hand, the temperature sensor is protected from the intensity of the incident laser beam. The coating has the effect that the laser beam acts on the temperature sensor in attenuated fashion and therefore has a filter function. The non-reflected radiation or the waste heat thereof is used for the measurement. Furthermore, it is preferably provided that at least one multiplexer and preferably electronic components for the temperature sensor are constructed or embedded adjacent to the matrix comprising pixels in the carrier substrate. As a result, it is possible to provide a fully integrated configuration of a temperature sensor in which both the temperature-sensitive elements and the associated circuit and signal conversion are effected in the optical element, thereby enabling a signal to be output in a simple manner. The object according to the invention is furthermore achieved by means of a method for recording beam WO 2006/103104 PCT/EP2006/003019 - 10 - parameters in which one or a plurality of optical elements in accordance with one of the preceding advantageous embodiments are interrogated in a beam path of an electromagnetic beam and the recorded signals are recorded in an evaluation unit. In the evaluation unit, the data of the individual pixels are taken up and evaluated, thereby, enabling an exact-determination of the beam position, of the beam diameter and of the intensity distribution. Even with a single optical element according to the invention arranged in the beam path, it is possible to record the information important for monitoring purposes, such as the beam position, the beam diameter and the intensity distribution of the beam. In the case of monitoring carried out over a longer time duration, an alteration of the beam parameters can simultaneously be effected by means of a comparison with different time intervals. If a plurality of optical elements are provided in a beam path of a laser system, the recorded beam parameters at each individual optical element can be compared with one another, whereby for example an alteration of the beam profile along the beam path and also an alteration of the beam position and a decrease of a beam power can be recorded. As a result, it is also possible simultaneously to draw conclusions about incipient destruction, aging and contamination of the optical element or optical elements. In addition, the evaluation unit can enable independent readjustment of parameters in the laser arrangement in order to optimize the beam parameters. It is advantageously provided that the data recorded by the optical elements are provided by the evaluation unit for. remote interrogation via a remote data transmission unit. This ena.bles a remote diagnosis or a teleservice and a remote servicing. It is advantageously provided that a plurality of laser systems are monitored in a central recording location. WO 2006/103104 PCT/EP2006/003019 - 11 - In the event of deviations of the desired values determined for optimum operation, the recording location, which is established in a manner spatially separated from the laser systems, can access the respective laser system in order to set the laser system to the optimum parameters. The invention and also further advantageous embodiments and developments thereof are described and explained in more detail below on the basis of the examples illustrated in the drawings. The features that can be inferred from the description and the drawings can be applied individually by themselves or as a plurality in any desired combination according to the invention. In the figures: figure 1 shows a schematic construction of a laser machining machine, figure 2 shows a perspective view of an optical element according to the invention, figure 3 shows a schematic plan view of a temperature sensor provided in an optical element without coating, figure 4 shows a schematic sectional illustration of a temperature-sensitive element of a temperature sensor in an optical element, figure 5 shows a schematic sectional illustration of a temperature-sensitive element of a temperature sensor in an optical element with an alternative construction, figure 6 shows a schematically enlarged sectional illustration of temperature-sonsitivn WO 2006/103104 PCT/EP2006/003019 - 12 - elements arranged in the carrier substrate, figure 7 shows a schematic illustration of a pixel of a temperature sensor which comprises a matrix of temperature-sensitive elements, and figure 8 shows a schematic illustration of a pixel of a temperature sensor with two matrices of temperature-sensitive elements - Figure 1 illustrates a laser system 11, for example, which is used for the machining of materials and workpieces 12. The laser system 11 comprises a laser arrangement with a laser apparatus 13, in particular a CO2 laser, which generates an electromagnetic radiation, in particular a laser beam 14. The wavelength of the laser beam 14 preferably lies in the far infrared range. A beam telescope 16 is provided at the laser apparatus 13, via which beam telescope the laser beam 14 generated in the laser apparatus 13 is coupled out. From the beam telescope 16 as far as the machining location 17, the laser beam 14 is guided by an external optical unit 18. The external optical unit 18 is provided on a basic machine frame 19 embodied in single- or multi-axis fashion depending on the instances of use. In the present exemplary embodiment, the external optical unit 18 is moved in an X, Y and Z direction. A single-or multi-axis optical unit is also referred to as a floating optical unit. As an alternative, the workpiece 12 and/or the optical unit 18 can also be moved. The laser system 11 has a multiplicity of optical elements 23 in accordance with figure 2. The optical elements 23 required in the laser apparatus 13 are also WO 2006/103104 PCT/EP2006/003019 - 13 - referred to as internal optical elements and comprise, for example, rear mirrors, coupling-out mirrors, deflection mirrors and partly transmissive mirrors and also partly transmissive optical units, such as lenses, which are not illustrated in any greater detail. The external optical unit has for beam guiding and beam shaping at least one first deflection mirror 23' end, in the machining head 24, at least one further deflection mirror 23' and a focusing optical unit 23', which is formed as a lens, for example. A concave mirror can also be provided instead of the further-deflection mirror 23' and the focusing optical unit 23'. The beam path of the laser beam 14 from the beam telescope 16 as far as the focusing optical unit 23' is closed by a bellows. The optical element 23 in accordance with figure 2 comprises a carrier substrate 40 composed of metallic material, an alloy or composed of semiconductor material. A coating 32 is provided on the carrier substrate 40. Said coating 32 can comprise different metals or metal alloys and semiconductor materials. The set of arrows 34 is representative of the laser beam 14. An optical element 2.3 in accordance with figure 2 without coating 32 is illustrated in plan view in figure 3. A temperature sensor 38 is provided or embedded in the carrier substrate 40. Said temperature sensor 38 comprises a multiplicity of pixels 36 which are arranged in a matrix and which in each case comprise at least one temperature-sensitive element 39. By way of example, an arrangement is provided in which a plurality of temperature-sensitive elements 39 are arranged in a plurality of rows and columns alongside one another at predetermined spacings with respect to one another. WO 2006/103104 PCT/EP2006/003019 - 14 - The temperature-sensitive elements 3 9 can be embodied in the form of diodes which are connected to one another in a matrix, for example in rows and columns, in order to output a received signal via symbolically illustrated connections 42 to an evaluation unit 30 in a laser system 11. Such connections 42 can be formed for example by vapor deposition, as matrices, by coating or implantation of connection pieces. Wires or other connecting pieces can furthermore be used. The temperature sensor 38 can additionally comprise electronic circuits, such as multiplexers or amplifiers, for example, which enable, simplify or improve the signal pick-up. These elements are preferably embedded in the carrier substrate 4C. The circle 37 illustrated in figure 2 symbolizes the impinging laser beam 14. Figure 4 shows a schematic sectional illustration of a first embodiment according to the invention of a construction of an optical element 23 with a temperature-sensitive element 39 integrated in the carrier substrate 40, which element is part of a temperature sensor 38. Said temperature-sensitive element 3 9 is formed as a diode, for example, and introduced in a layer comprising silicon or into a silicon wafer by means of a CMOS-compatible process. Said temperature-sensitive element 39 is connected via connecting lines 43 to further temperature-sensitise elements 39 in a matrix in the form of rows and 'columns. A passivation layer 4 4 is preferably applied on the temperature-sensitive elements 3 9 in order to reduce or prevent a crosstalk. The coating 32 is applied to said passivation layer 44. In this embodiment, the silicon wafer or the carrier substrate 40 is made very thin and applied on a layer of a carrier material 31. Carrier materials 31 composed of metal such as, for example, copper and also silicon WO 2006/103104 PCT/EP2006/003019 - 15 - can be provided for receiving the carrier substrate 40. This configuration has the advantage that different carrier materials can be selected for different instances of use and be combined with the carrier substrate 40 in order for example to select a thermal conductivity or mechanical strength adapted to the application. An alternative embodiment of figure 3 provides for the carrier substrate to comprise a thicker layer composed of silicon, such that the additional use of a carrier material is not required. Figure 5 illustrates an alternative embodiment of an optical element 23. This embodiment has a construction in which a coating 32 is applied on the carrier material 31. The carrier substrate 40 is applied on the opposite side of the carrier material 31 to the coating 32, the temperature sensor 38 pointing toward the rear-side of the optical element 23. The temperature sensor 38 is covered by an absorption layer 45. In this embodiment, the carrier material 31 is formed in highly or fully transmissive fashion. By way of example, materials such as ZnSe can be used. These have a 'transmittance of at least 97%. The coating 32 is preferably provided with a trarsmissiviry of less than 2%. The coating 32 on the carrier substrate 4 0 or the carrier material 31 covers the temperature sensor 39 over the whole area and can extend over the whole area over the entire surface of the carrier substrate 40 and the carrier material 31 with the exception of the connections 42 for fitting contact elements. The coating 32 has a dual function in order to enable the laser beam to be guided and/or shaped and also to ensure an attenuation of the laser beam for the temperature-sensitive elements 3 9 for the protection WO 2006/103104 PCT/EP2006/003019 - 16 - thereof and for measured value recording. Figure 6 illustrates a schematic enlarged sectional illustration of two pixels 36 - arranged alongside one another - of the temperature sensor 38 in the optical element 23 in accordance with figure 3. Each pixel 3 6 comprises a diode as temperature-sensitive element 39 in a p- or n-doped well 4 6 with an oppositely doped diffusion layer 4 7 in the silicon wafer. A CMOS process can advantageously be used for this purpose. The p- or n-doped wells 4 6 bring about an electrical insulation between the two adjacent temperature-sensitive elements 39 and enable, a reduction of the crosstalk behavior between the temperature-sensitive elements 39. Structures such as trenches 48, for example, can additionally be introduced into the optical element 23, and increase the thermal insulation between the temperature-sensitive elements 39 arranged in a matrix in order to form a temperature sensor 38. Said trenches 4 8 are closed with a thermally insulating layer 49. For this purpose, separating cuts or etchings are introduced into the surface of the wafer, and are subsequently filled with an insulating material. This considerably reduces the thermal crosstalk. In order to increase the planarity of silicon wafers, a stress-compensating layer can advantageously be applied on the rear side of the silicon wafer. Said stress-compensating layer can be provided for example from SiRN (silicon-rich nitride) or silicon nitride or similar materials, which is applied by means of a plasma enhanced vapor deposition method (PECVD) or a low pressure vapor deposition method (LPCVD). In order to reduce the surface roughness of the silicon wafer and therefore in order to increase the reflective properties, the surface of the carrier substrate 40 in which the temperature sensor 38 is provided or embedded WO 2006/103104 PCT/EP2006/003019 - 17 - is polished. Reflective layers, for example gold layers and/or dielectric layers, can additionally be applied. Figure 7 illustrates a pixel 36 of a temperature sensor 38 in enlarged fashion. In this exemplary embodiment, by way of example, five temperature-sensitive elements 39 are connected in series with one another and form the pixel 36. This arrangement has the advantage that a plurality of temperature-dependent features or characteristic curves can be recorded, whereby "he measurement accuracy of each pixel 36 is increased. As an alternative, it can be provided that the temperature-sensitive elements 39 are arranged in a parallel connection with respect to one another. An alternative configuration of a pixel 3 6 for a temperature sensor 38 is illustrated in figure 8. Jr. this exemplary embodiment, two series of temperature-sensitive elements 39 are provided in a pixel 36. These can again be connected in series or else in parallel with one another in accordance with the exemplary embodiment. A plurality of signals can thereby be recorded, a higher-quality statement about the value recorded on average being made possible for an event. The optical elements 23 are arranged in holders or receptacles of the laser system 11. These receptacles or holding elements can have contact elements which act on the connections 42 when the optical elements 23 are inserted into the holding devices, such that a contact-connection is effected. As an alternative, it can be provided that other contacts are bonded or adhesively bonded prior to the insertion on the optical elements 23 or are formed as plug connections, in order to read out the recorded measured values from the optical element 23 and forward them to the evaluation unit. Furthermore, it can be provided that a contactless transmission of the measurement data from the optical. WO 2006/103104 PCT/EP2006/003019 - 18 - element 23 to the holding device,, to the controller or to further components of the laser system 11 is made possible instead of mechanical connections. The optical element 23 is provided with a transponder, that is to say an IC memory element and an antennar which enabJ.es a contactless transmission of the measurement data by means of RFID technology. Such a transponder can be provided in or on the carrier substrate 40, the carrier material 41 or the coating 32. The abovementioned exemplary embodiments comprising diodes as temperature-sensitive elements 39 can have different characteristics in order to record the temperature of the laser beam 14. Such characteristics can have for example a forward or reverse voltage drop in the case of a known or constant current or a forward or reverse current in the case of a known or constant voltage applied to the temperature-sensitive elements 39. The temperature dependencies can be recorded by means of said characteristics. The fact that the voltage difference is directly proportional to the temperature of the pixel can be derived therefrom. Consequently, direct conclusions can be drawn about the beam parameters depending on the laser 14 acting on the optical element 23. The temperature sensor 38 integrated or embedded in the carrier substrate 40 and also its configuration from temperature elements 39 arranged in the form of rows and columns make it possible for a plurality of parameters to be able to be simultaneously recorded and evaluated. These include the beam power, for example. The beam power or the changes thereof can be recorded by means of the proportional change in the voltage depending on the temperature distribution. The output power of a laser beam 14 generated by the laser WO 2006/103104 PCT/EP2006/003019 - 19 - apparatus 13 is known in this case. Consequently, along a beam path, for example, it is possible to record an alteration of the beam power by means of a comparison of the recorded data at a plurality of measurement locations. Furthermore, the beam position and the deviation thereof can be recorded by means of the multiplicity of temperature-sensitive elements 39. Consequently, it is possible to record conclusions about misalignments or incorrect alignments or alterations in the position of the optical elements 23 in the beam path. Beam profiles can furthermore be determined. On account of the direct dependence of the voltage on the temperature, beam profiles can be recorded by means of the pixel resolution. The remote diagnosis or telediagnosis can furthermore be modified to the effect that, remote from the laser system 11, a comparison of the actual and desired values of the parameters, such as, for example, beam position, power, beam profile, is effected and a correction of the actual values or an approximation to desired values is effected externally. Such a remote control enables a plurality of laser systems 11 to be monitored and controlled from a central workstation. This information is forwarded to an evaluation unit 30. The evaluation unit 30 can be integrated in the laser apparatus 13, be arranged on said laser apparatus or, remote from the latter, be connected to an external optical unit 18. Said evaluation, unit 30 can output the recorded data via a data line, via radio or the like, such that a remote diagnosis or telediagnosis is made possible. Furthermore, the interrogation of the present parameters of a laser beam 14 that is made possible at any time has the advantage that an interruption of the work process is not required and a complete monitoring of the laser system 11 during operation is made possible. As a result of the recording of the WO 2006/103104 PCT/EP2006/003019 - 20 - temperature distribution in the optical element 23, a beam profile can be determined by means of the deconvolution method. Furthermore, the beam profile can be determined from the temperature distribution by applying the maximum entropy method. By comparing the recorded values with the total power, it is furthermore possible to identify incipient contamination, aging or damage of nhe optical elements 23. At the same time, a so-called mode shot can be dispensed with as a result of this recording of the data. The required data can be determined by means of the temperature sensor 38 integrated in the optical element 23. Consequently, a time-consuming shutdown of the laser system 11 and also a complicated coupling-out of a laser beam 14 are not required. Moreover, a remote diagnosis, remote servicing and remote control of laser systems can be made possible. - 21 -Claims 1. An optical element for guiding and shaping a laser beam (14) , which can be arranged in particular in a laser system (11), comprising a carrier substrate (40) and a coating (39), which is applied to at least one side of the carrier substrate (40) and comprising at least one temperature sensor (38), characterized in that the temperature sensor (38) comprises a plurality of pixels (36) arranged in a matrix and the respective pixel (36) comprises at least one temperature-sensitive element (39), and in that the at least one temperature-sensitive element (39) of the pixel (36) i.s constructed in a carrier substrate (40) comprising silicon and in that the coating (32) has a reflectance of the radiation of at least 98%. 2. The optical element as claimed in claim 1, characterized in that the at least one temperature- sensitive element (39) is applied in a silicon wafer, in particular as a diode. 3. The optical element as claimed in claim 1, characterized in that the temperature-sensitive elements (39) are provided in so-called p- or n-doped depressions or wells (46). 4. The optical element as claimed in claim 1, characterized in that the temperature-sensitive elements (39) are thermally insulated from one another by insulating sections (48, 49) . 5. The optical element as claimed in claim 1, characterized in that a plurality of temperature- sensitive elements (3,9) are connected in series in a pixel (36). - 22 - 6. The optical element as claimed in claim 1, characterized in that a plurality of temperature- sensitive elements (39) are connected in parallel in a pixel (36). 7. The optical element as claimed in claim 1, characterized in that a coating (32) is provided at a side of the carrier substrate (40) which faces the temperature sensor (38), and a carrier material (31) is provided on a side of the carrier substrate (40) which is remote from the temperature sensor (38). 8. The optical element as claimed in claim 1, characterized in that a carrier material (31) is provided at a side of the carrier substrate (40) which is remote from the temperature sensor (38), and a coating (32) is provided on an opposite side of the carrier material (31). 9. The optical element as claimed in claim 1, characterized in that the carrier material (31) is formed in highly transmissive fashion. 10. The optical element as claimed in claim 1, characterized in that a passivation layer (44) is provided between the carrier substrate (40) receiving the temperature-sensitive elements (39) and the coating (32) provided at the carrier substrate, or in that an absorber layer (45) is provided at the carrier substrate (40) receiving the temperature-sensitive elements (39). 11. The optical element as claimed in claim 1, characterized in that a stress-compensating layer is applied on a side of the carrier material (31) or of the carrier substrate (40) which is remote from the coating (32). - 23 - 12. The optical element as claimed in claim 1, characterized in that at least one multiplexer and preferably electronic components are constructed adjacent to the matrix comprising pixels (36) in the carrier substrate (40). 13. A method for recording and monitoring beam parameters of a laser beam (14) in a laser system (11) with one or a plurality of optical elements as claimed in claim 1, characterized in that the data recorded by the optical element or optical elements (23) are forwarded to an evaluation unit (30) of the laser system (11), the data of the individual pixels (36) being recorded and evaluated by an actual/desired value comparison. 14. The method as claimed in claim 13, characterized in that the recorded data are output by the evaluation unit (30) for remote data transmission to a central recording location. 15. The method as claimed in claim 14, characterized in that beam parameters of the laser system (11) are set and monitored by the recording location, which is provided in a manner spatially separated from the laser system (11). The invention relates to an optical element for guiding and forming a laser beam, and to a method for recording beam parameters, particularly in a laser system, comprising a carrier substrate (40) and a coating (39), which is applied to at least one side of the carrier substrate (40), and comprising at least one temperature sensor (38). The temperature sensor (38) is comprised of a number of pixels arranged in a matrix, and each respective pixel has at least one temperature sensitive element (39). The at least one temperature sensitive element (39) of the pixel is constructed inside the carrier substrate (40) made of silicon.

Full Text

WO 2006/103104 PCT/EP2006/003019
OPTICAL ELEMENT AND METHOD FOR RECORDING BEAM PARAMETERS, COMPRISING A TEMPERATURE SENSOR PROVIDED IN THE FORM OF A PIXEL MATRIX
The invention relates to an optical element for guiding and shaping a laser beam in accordance with the preamble of claim 1, and to a method for recording beam parameters with such an optical element in accordance with the preamble of claim 14.
The use of laser beams for machining materials is widespread in industrial manufacturing. For monitoring the machining and for quality assurance it is necessary that a constant power of an electromagnetic radiation be generated by a laser arrangement and be output with constant parameters. A laser arrangement is provided with a plurality of optical elements that guide and shape the beam. At the same time, the power of the beam is also influenced thereby. The quality of the laser arrangement is essentially determined by the beam orientation, the beam profiling and the beam power. These parameters are to be optimized for the machining processes and can be adversely influenced by aging, incipient destruction and/or contamination of the optical elements. Such influences in turn adversely affect the beam parameters of the electromagnetic radiation or of the laser beam. In order to record or monitor said parameters, there is the possibility of producing a so-called mode shot of a laser beam. The laser beam generated by the laser arrangement; i s coupled out from the customary beam path and directed onto a plexiglass cube, where material vaporizes upon impingement of the laser beam and the remaining contour enables a statement about the quality of the beam. This technique is time-consuming and requires an interruption of production.

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A brochure from the company Prometec entitled "Laserscope UFC60" discloses a cevice that enables a continuous measurement and monitoring of unfocused laser radiation from lasers with high power that is principally used in laser machining. The device operates according to the measurement principle according to which a wire increases its electrical resistance if its temperature increases on account of absorbed radiation. In order to determine measurement data, a plurality of grids arranged one above another with extremely thin wires arranged next to one another are provided. An apparatus with two grids mounted one above another is proposed for bean monitoring, wherein this device receiving the grids is to be positioned in a beam path in such a way that the laser beam passes through said grids.
This device is not possible in routine operation of a laser arrangement on account of a housing receiving the grids. As a result, no online measurements can be carried out. Furthermore, the wires provided for recording information are extremely sensitive since they have a diameter in the lower micrometers range and can break very easily. In particular, a cooling of the grids for an exact measurement is possible with difficulty since the wires break even more easily when there is a strong air flow. Without cooling of the grids, however, the recorded values are beset with errors as a result of continuous heating of the grids. Furthermore, dirt particles can deposit on the grid and additionally corrupt the measurement results. Moreover, the device cannot be used within a laser apparatus, a beam source or a beam generator. The contamination, aging and beginning of the destruction of optical elements cannot be recorded either.
FR 2 698 4 95 A1 reveals a method for measuring a temperature of a lens provided in a laser arrangement.

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A first thermoelement fitted at the edge of the lens is provided for recording the temperature of the lens. A further temperature element is arranged on a front side of an exit of the lens outside the beam path. A third thermoelement is fitted at a shoulder of the receptacle. These three thermoelenents are respectively arranged in a manner offset by 120° relative to one another and forward the recorded temperature to an evaluation unit. As soon as the recorded temperature has exceeded a threshold value, an alarm signal is output.
By virtue of the arrangement of the thermoelements on the lens and the lens receptacle, individual measurements at the respective contact locations of the thermoelements relative to the lens are carried out by the thermoelements. This does net enable a statement about the determination of the degree of contamination or an incipient destruction or aging and the power of the beam or further beam parameters.
US-A 4,692,623 discloses a device provided for recording a situation and a position of a laser beam. Said device has a grid of conductor tracks on a glass substrate, the conductor tracks being insulated from one another at the crossover points. Said conductor tracks can be covered with a reflective coating. A detector and a display device for recording the change in the electrical resistance on account of the absorbed heat are connected to the conductor tracks.
An analogous arrangement is disclosed in CH 690 796 A5. The mirror disclosed in this document differs from the previous device by virtue of the fact that the grid of conductor tracks is formed in two planes isolated by an insulation. A first layer of a multiplicity of conductor tracks arranged parallel to one another is provided on an insulation on the carrier material of

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the mirror. Said layer is covered with an insulation which, in turn, receives a second layer of conductor tracks running parallel to one another. The second layer of conductor tracks is oriented in a manner rotated by 90° relative to the first layer. The second layer of conductor tracks is also covered by an insulation. Contact areas for connection to an evaluation unit are provided in each case at the outer-ends of the conductor tracks.
EP 1 310 7 82 A1 has disclosed an optical element having a coating on a carrier material. Such optical elements are used for guiding and shaping a laser beam. For recording a situation and a. position of a laser beam, it is provided that the optical element has a grid structure composed of thin conductive material on or in the coating or the carrier material. Via contact elements acting on the optical element, the recorded measured values can be forwarded into a measuring device or evaluation unit.
What the three abovementioned devices in accordance with US-A 4,692,623, CK 690 796 A5 and EP 1 31.0 782 A1 all have in common is that a temperature change is brought about in the carrier materials on account of the absorbed radiation, which temperature change is in turn transmitted to the conductor tracks in order to record a change in the electrical resistance in the conductor tracks. However, said temperature change can only be recorded integrally by means of the respective conductor track, or the length thereof between the two end points. As a result, an evaluation with respect to the beam position and beam size can only be effected approximately. An evaluation of an intensity distribution of the beam, as is made visible by a mode shot, is not possible.
Therefore, the invention is based on the object of

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proposing an optical element for guiding and shaping a laser beam which enables a precise recording of the beam position, the beam diameter and the intensity distribution of the beam whilst maintaining the beam guiding properties of an electromagnetic beam.
This object is achieved according to the invention by means of an optical element for guiding and shaping a laser beam in accordance with the features of claim 1.
The optical element formed according to the invention has the advantage that an exact evaluation of the beam parameters, such as, for example, the beam position, the beam diameter and the intensity distribution of the beam, is made possible. The configuration of the temperature sensor as a matrix composed of a multiplicity of pixels enables a spatial resolution of the intensity for the laser beam impinging on the optical element. On account of such a spatial resolution of the intensity, it is possible to record a beam alteration during the operation of a laser system without the laser beam being coupled out. The beam alteration represents an image about the state of the laser, with the result that not only optical elements but also further components of the laser systems can be monitored. The so-called mode shot can be replaced by the configuration of the optical element according to the invention. It is no longer necessary to couple out the laser beam in order to generate a mode shot. The measured values recorded by the temperature sensor furthermore enable an evaluation of a thermal loading of the optical element and also about the state of tne optical element with regard to aging and contamination or incipient destruction. At the same time, the use of at least one optical element according to the invention can afford a permanent monitoring of the laser system without intervention in routine production.

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According to one advantageous configuration of the invention, it is provided that the optical element comprises a matrix of temperature-sensitive elements as carrier material. By virtue of the arrangement of the temperature-sensitive elements in a matrix as temperature sensor, a statement can simultaneously be made about further bean parameters such as, for example, the position of the impingement area and the size or the diameter of the electromagnetic beam, the local resolution of the intensity distribution, the absolute beam power, the temporal resolution capability. The recording of the position makes it possible to record the beam orientation or the beam course with respect to the optical element and, consequently, misalignments possibly present. The recording of the beam diameter and/or the temperature profile makes it possible to determine the present power in comparison with the known desired power of the beam.
According to a further advantageous configuration of the method, it is provided that the at least one temperature-sensitive element is constructed in a silicon wafer, in particular as a diode. When the semiconductor material is used as a carrier substrate, it is possible in particular to implement the diodes as temperature-sensitive elements directly into the carrier substrate. CMOS processes are preferably used to produce the diodes. Further known production processes can likewise be used.
The temperature-sensitive elements are preferably embedded in so-called P- or N-doped depressions or wells ("p-wells" or "n-wells"). This provides an electrical insulation between the individual diodes, thereby reducing or preventing a crosstalk between the different temperature-sensitive elements.

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Preferably, the temperature-sensitive elements are thermally insulated from one another. For this purpose, for example trenches are provided in the carrier substrate, in particular silicon wafer, in order to insulate said temperature-sensitive elements from one another. Said trenches are filled with an insulating layer and are referred to as "deep-trench isolation". The recording and localizing of the electromagnetic beam impinging on the optical element can thereby be localized exactly. At the same time, ar. improved temperature recording can thereby be made possible for each temperature-sensitive element, whereby the beam profiling can be recorded more precisely.
In one preferred embodiment, a plurality of temperature-sensitive elements are connected in series in a pixel. It is thereby possible to measure one or a plurality of time-dependent features or characteristic curves within the sensor chain, such as, for example, a voltage drop in the case of a specific current or a specific current drop in the case of a known voltage. By virtue of the fact that a pixel of the matrix advantageously comprises a plurality of temperature-sensitive elements, the measurement accuracy of a pixel and hence the performance of the temperature sensor comprising a plurality of pixels can be increased. As an alternative, it can be provided that the temperature-sensitive elements of a pixel are connected in parallel, whereby an averaged statement about a temperature of the pixel is likewise made possible.
One preferred embodiment provides for a coating to be provided at a side of the carrier substrate which faces the temperature sensor, and a carrier material to be provided at a side of the carrier substrate which is remote from the temperature sensor. This construction enables in particular very thin silicon wafer's to be usable for the implementation of the diodes for

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producing the pixels as a matrix for forming a temperature sensor. Moreover, a multiplicity of carrier materials can be applied which have a high thermal conductivity and/or mechanical stiffness in order to receive the carrier substrate. By way of example, an adhesive-bonding connection can be provided between the carrier substrate and the carrier material- Such carrier materials can be provided from metal, in particular copper, and also other materials such as e.g. silicon.
An alternative embodiment of the optical element provides for a carrier material to be provided at a side of the carrier substrate which is remote from the temperature sensor, and a coating to be applied at the opposite side of the carrier material. This construction makes it possible e.g. for an increased reflection cr reduced transmission of the laser beam to be provided depending on the carrier material, such that the carrier material acts as a filter, a sufficient radiation energy still acting on the temperature sensor.
In the case of the last-mentioned embodiment, the carrier material is preferably formed in highly transmissive or fully transmissive fashion. By way of example, the carrier material has a transmittance of at least 97%.
Preferably, a passivation layer is provided between a coating and the carrier substrate in order to separate the highly reflective coating from the connections of the temperature sensor and also the temperature-sensitive elements. This arrangement is provided in a first embodiment of a layer construction for the optical element. In the second alternative embodiment, the temperature sensor is assigned in a manner remote with respect to the incident laser beam in the beam

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path and preferably receives an absorber layer on its rear side.
According to a further advantageous configuration of the invention, it is provided that a stress-compensating layer is applied on a rear side of the carrier material, opposite to the coating, said stress-compensating layer preferably comprising a silicon nitride or similar materials. Such a layer can be applied for example by plasma-enhanced or chemical vapor deposition methods.
According to a further advantageous configuration of the invention, it is provided that the coating of the optical element has a reflectance of the laser radiation of at least 98%. As a result, on the one hand, the imaging properties, in particular the guiding and/or shaping of the laser beam, are preserved and, on the other hand, the temperature sensor is protected from the intensity of the incident laser beam. The coating has the effect that the laser beam acts on the temperature sensor in attenuated fashion and therefore has a filter function. The non-reflected radiation or the waste heat thereof is used for the measurement.
Furthermore, it is preferably provided that at least one multiplexer and preferably electronic components for the temperature sensor are constructed or embedded adjacent to the matrix comprising pixels in the carrier substrate. As a result, it is possible to provide a fully integrated configuration of a temperature sensor in which both the temperature-sensitive elements and the associated circuit and signal conversion are effected in the optical element, thereby enabling a signal to be output in a simple manner.
The object according to the invention is furthermore achieved by means of a method for recording beam

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parameters in which one or a plurality of optical elements in accordance with one of the preceding advantageous embodiments are interrogated in a beam path of an electromagnetic beam and the recorded signals are recorded in an evaluation unit. In the evaluation unit, the data of the individual pixels are taken up and evaluated, thereby, enabling an exact-determination of the beam position, of the beam diameter and of the intensity distribution. Even with a single optical element according to the invention arranged in the beam path, it is possible to record the information important for monitoring purposes, such as the beam position, the beam diameter and the intensity distribution of the beam. In the case of monitoring carried out over a longer time duration, an alteration of the beam parameters can simultaneously be effected by means of a comparison with different time intervals. If a plurality of optical elements are provided in a beam path of a laser system, the recorded beam parameters at each individual optical element can be compared with one another, whereby for example an alteration of the beam profile along the beam path and also an alteration of the beam position and a decrease of a beam power can be recorded. As a result, it is also possible simultaneously to draw conclusions about incipient destruction, aging and contamination of the optical element or optical elements. In addition, the evaluation unit can enable independent readjustment of parameters in the laser arrangement in order to optimize the beam parameters.
It is advantageously provided that the data recorded by the optical elements are provided by the evaluation unit for. remote interrogation via a remote data transmission unit. This ena.bles a remote diagnosis or a teleservice and a remote servicing. It is advantageously provided that a plurality of laser systems are monitored in a central recording location.

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In the event of deviations of the desired values determined for optimum operation, the recording location, which is established in a manner spatially separated from the laser systems, can access the respective laser system in order to set the laser system to the optimum parameters.
The invention and also further advantageous embodiments and developments thereof are described and explained in more detail below on the basis of the examples illustrated in the drawings. The features that can be inferred from the description and the drawings can be applied individually by themselves or as a plurality in any desired combination according to the invention. In the figures:
figure 1 shows a schematic construction of a laser machining machine,
figure 2 shows a perspective view of an optical element according to the invention,
figure 3 shows a schematic plan view of a temperature sensor provided in an optical element without coating,
figure 4 shows a schematic sectional illustration of a temperature-sensitive element of a temperature sensor in an optical element,
figure 5 shows a schematic sectional illustration of a temperature-sensitive element of a temperature sensor in an optical element with an alternative construction,
figure 6 shows a schematically enlarged sectional illustration of temperature-sonsitivn

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elements arranged in the carrier substrate,
figure 7 shows a schematic illustration of a pixel of a temperature sensor which comprises a matrix of temperature-sensitive elements, and
figure 8 shows a schematic illustration of a
pixel of a temperature sensor with two
matrices of temperature-sensitive elements -
Figure 1 illustrates a laser system 11, for example, which is used for the machining of materials and workpieces 12. The laser system 11 comprises a laser arrangement with a laser apparatus 13, in particular a CO2 laser, which generates an electromagnetic radiation, in particular a laser beam 14. The wavelength of the laser beam 14 preferably lies in the far infrared range. A beam telescope 16 is provided at the laser apparatus 13, via which beam telescope the laser beam 14 generated in the laser apparatus 13 is coupled out. From the beam telescope 16 as far as the machining location 17, the laser beam 14 is guided by an external optical unit 18. The external optical unit 18 is provided on a basic machine frame 19 embodied in single- or multi-axis fashion depending on the instances of use. In the present exemplary embodiment, the external optical unit 18 is moved in an X, Y and Z direction. A single-or multi-axis optical unit is also referred to as a floating optical unit. As an alternative, the workpiece 12 and/or the optical unit 18 can also be moved.
The laser system 11 has a multiplicity of optical elements 23 in accordance with figure 2. The optical elements 23 required in the laser apparatus 13 are also

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referred to as internal optical elements and comprise, for example, rear mirrors, coupling-out mirrors, deflection mirrors and partly transmissive mirrors and also partly transmissive optical units, such as lenses, which are not illustrated in any greater detail. The external optical unit has for beam guiding and beam shaping at least one first deflection mirror 23' end, in the machining head 24, at least one further deflection mirror 23' and a focusing optical unit 23', which is formed as a lens, for example. A concave mirror can also be provided instead of the further-deflection mirror 23' and the focusing optical unit 23'. The beam path of the laser beam 14 from the beam telescope 16 as far as the focusing optical unit 23' is closed by a bellows.
The optical element 23 in accordance with figure 2 comprises a carrier substrate 40 composed of metallic material, an alloy or composed of semiconductor material. A coating 32 is provided on the carrier substrate 40. Said coating 32 can comprise different metals or metal alloys and semiconductor materials. The set of arrows 34 is representative of the laser beam 14.
An optical element 2.3 in accordance with figure 2 without coating 32 is illustrated in plan view in figure 3. A temperature sensor 38 is provided or embedded in the carrier substrate 40. Said temperature sensor 38 comprises a multiplicity of pixels 36 which are arranged in a matrix and which in each case comprise at least one temperature-sensitive element 39. By way of example, an arrangement is provided in which a plurality of temperature-sensitive elements 39 are arranged in a plurality of rows and columns alongside one another at predetermined spacings with respect to one another.

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The temperature-sensitive elements 3 9 can be embodied in the form of diodes which are connected to one another in a matrix, for example in rows and columns, in order to output a received signal via symbolically illustrated connections 42 to an evaluation unit 30 in a laser system 11. Such connections 42 can be formed for example by vapor deposition, as matrices, by coating or implantation of connection pieces. Wires or other connecting pieces can furthermore be used. The temperature sensor 38 can additionally comprise electronic circuits, such as multiplexers or amplifiers, for example, which enable, simplify or improve the signal pick-up. These elements are preferably embedded in the carrier substrate 4C. The circle 37 illustrated in figure 2 symbolizes the impinging laser beam 14.
Figure 4 shows a schematic sectional illustration of a first embodiment according to the invention of a construction of an optical element 23 with a temperature-sensitive element 39 integrated in the carrier substrate 40, which element is part of a temperature sensor 38. Said temperature-sensitive element 3 9 is formed as a diode, for example, and introduced in a layer comprising silicon or into a silicon wafer by means of a CMOS-compatible process. Said temperature-sensitive element 39 is connected via connecting lines 43 to further temperature-sensitise elements 39 in a matrix in the form of rows and 'columns. A passivation layer 4 4 is preferably applied on the temperature-sensitive elements 3 9 in order to reduce or prevent a crosstalk. The coating 32 is applied to said passivation layer 44.
In this embodiment, the silicon wafer or the carrier substrate 40 is made very thin and applied on a layer of a carrier material 31. Carrier materials 31 composed of metal such as, for example, copper and also silicon

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can be provided for receiving the carrier substrate 40. This configuration has the advantage that different carrier materials can be selected for different instances of use and be combined with the carrier substrate 40 in order for example to select a thermal conductivity or mechanical strength adapted to the application.
An alternative embodiment of figure 3 provides for the carrier substrate to comprise a thicker layer composed of silicon, such that the additional use of a carrier material is not required.
Figure 5 illustrates an alternative embodiment of an optical element 23. This embodiment has a construction in which a coating 32 is applied on the carrier material 31. The carrier substrate 40 is applied on the opposite side of the carrier material 31 to the coating 32, the temperature sensor 38 pointing toward the rear-side of the optical element 23. The temperature sensor 38 is covered by an absorption layer 45. In this embodiment, the carrier material 31 is formed in highly or fully transmissive fashion. By way of example, materials such as ZnSe can be used. These have a 'transmittance of at least 97%. The coating 32 is preferably provided with a trarsmissiviry of less than 2%.
The coating 32 on the carrier substrate 4 0 or the carrier material 31 covers the temperature sensor 39 over the whole area and can extend over the whole area over the entire surface of the carrier substrate 40 and the carrier material 31 with the exception of the connections 42 for fitting contact elements. The coating 32 has a dual function in order to enable the laser beam to be guided and/or shaped and also to ensure an attenuation of the laser beam for the temperature-sensitive elements 3 9 for the protection

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thereof and for measured value recording.
Figure 6 illustrates a schematic enlarged sectional illustration of two pixels 36 - arranged alongside one another - of the temperature sensor 38 in the optical element 23 in accordance with figure 3. Each pixel 3 6 comprises a diode as temperature-sensitive element 39 in a p- or n-doped well 4 6 with an oppositely doped diffusion layer 4 7 in the silicon wafer. A CMOS process can advantageously be used for this purpose. The p- or n-doped wells 4 6 bring about an electrical insulation between the two adjacent temperature-sensitive elements 39 and enable, a reduction of the crosstalk behavior between the temperature-sensitive elements 39. Structures such as trenches 48, for example, can additionally be introduced into the optical element 23, and increase the thermal insulation between the temperature-sensitive elements 39 arranged in a matrix in order to form a temperature sensor 38. Said trenches 4 8 are closed with a thermally insulating layer 49. For this purpose, separating cuts or etchings are introduced into the surface of the wafer, and are subsequently filled with an insulating material. This considerably reduces the thermal crosstalk.
In order to increase the planarity of silicon wafers, a stress-compensating layer can advantageously be applied on the rear side of the silicon wafer. Said stress-compensating layer can be provided for example from SiRN (silicon-rich nitride) or silicon nitride or similar materials, which is applied by means of a plasma enhanced vapor deposition method (PECVD) or a low pressure vapor deposition method (LPCVD).
In order to reduce the surface roughness of the silicon wafer and therefore in order to increase the reflective properties, the surface of the carrier substrate 40 in which the temperature sensor 38 is provided or embedded

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is polished. Reflective layers, for example gold layers and/or dielectric layers, can additionally be applied.
Figure 7 illustrates a pixel 36 of a temperature sensor
38 in enlarged fashion. In this exemplary embodiment, by way of example, five temperature-sensitive elements
39 are connected in series with one another and form the pixel 36. This arrangement has the advantage that a plurality of temperature-dependent features or characteristic curves can be recorded, whereby "he measurement accuracy of each pixel 36 is increased. As an alternative, it can be provided that the temperature-sensitive elements 39 are arranged in a parallel connection with respect to one another.
An alternative configuration of a pixel 3 6 for a temperature sensor 38 is illustrated in figure 8. Jr. this exemplary embodiment, two series of temperature-sensitive elements 39 are provided in a pixel 36. These can again be connected in series or else in parallel with one another in accordance with the exemplary embodiment. A plurality of signals can thereby be recorded, a higher-quality statement about the value recorded on average being made possible for an event.
The optical elements 23 are arranged in holders or receptacles of the laser system 11. These receptacles or holding elements can have contact elements which act on the connections 42 when the optical elements 23 are inserted into the holding devices, such that a contact-connection is effected. As an alternative, it can be provided that other contacts are bonded or adhesively bonded prior to the insertion on the optical elements 23 or are formed as plug connections, in order to read out the recorded measured values from the optical element 23 and forward them to the evaluation unit. Furthermore, it can be provided that a contactless transmission of the measurement data from the optical.

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element 23 to the holding device,, to the controller or to further components of the laser system 11 is made possible instead of mechanical connections. The optical element 23 is provided with a transponder, that is to say an IC memory element and an antennar which enabJ.es a contactless transmission of the measurement data by means of RFID technology. Such a transponder can be provided in or on the carrier substrate 40, the carrier material 41 or the coating 32.
The abovementioned exemplary embodiments comprising diodes as temperature-sensitive elements 39 can have different characteristics in order to record the temperature of the laser beam 14. Such characteristics can have for example a forward or reverse voltage drop in the case of a known or constant current or a forward or reverse current in the case of a known or constant voltage applied to the temperature-sensitive elements 39.
The temperature dependencies can be recorded by means of said characteristics. The fact that the voltage difference is directly proportional to the temperature of the pixel can be derived therefrom. Consequently, direct conclusions can be drawn about the beam parameters depending on the laser 14 acting on the optical element 23.
The temperature sensor 38 integrated or embedded in the carrier substrate 40 and also its configuration from temperature elements 39 arranged in the form of rows and columns make it possible for a plurality of parameters to be able to be simultaneously recorded and evaluated. These include the beam power, for example. The beam power or the changes thereof can be recorded by means of the proportional change in the voltage depending on the temperature distribution. The output power of a laser beam 14 generated by the laser

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apparatus 13 is known in this case. Consequently, along a beam path, for example, it is possible to record an alteration of the beam power by means of a comparison of the recorded data at a plurality of measurement locations. Furthermore, the beam position and the deviation thereof can be recorded by means of the multiplicity of temperature-sensitive elements 39. Consequently, it is possible to record conclusions about misalignments or incorrect alignments or alterations in the position of the optical elements 23 in the beam path. Beam profiles can furthermore be determined. On account of the direct dependence of the voltage on the temperature, beam profiles can be recorded by means of the pixel resolution.
The remote diagnosis or telediagnosis can furthermore be modified to the effect that, remote from the laser system 11, a comparison of the actual and desired values of the parameters, such as, for example, beam position, power, beam profile, is effected and a correction of the actual values or an approximation to desired values is effected externally. Such a remote control enables a plurality of laser systems 11 to be monitored and controlled from a central workstation.
This information is forwarded to an evaluation unit 30. The evaluation unit 30 can be integrated in the laser apparatus 13, be arranged on said laser apparatus or, remote from the latter, be connected to an external optical unit 18. Said evaluation, unit 30 can output the recorded data via a data line, via radio or the like, such that a remote diagnosis or telediagnosis is made possible. Furthermore, the interrogation of the present parameters of a laser beam 14 that is made possible at any time has the advantage that an interruption of the work process is not required and a complete monitoring of the laser system 11 during operation is made possible. As a result of the recording of the

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temperature distribution in the optical element 23, a beam profile can be determined by means of the deconvolution method. Furthermore, the beam profile can be determined from the temperature distribution by applying the maximum entropy method.
By comparing the recorded values with the total power, it is furthermore possible to identify incipient contamination, aging or damage of nhe optical elements 23. At the same time, a so-called mode shot can be dispensed with as a result of this recording of the data. The required data can be determined by means of the temperature sensor 38 integrated in the optical element 23. Consequently, a time-consuming shutdown of the laser system 11 and also a complicated coupling-out of a laser beam 14 are not required. Moreover, a remote diagnosis, remote servicing and remote control of laser systems can be made possible.

- 21 -Claims
1. An optical element for guiding and shaping a laser beam (14) , which can be arranged in particular in a laser system (11), comprising a carrier substrate (40) and a coating (39), which is applied to at least one side of the carrier substrate (40) and comprising at least one temperature sensor (38), characterized in that the temperature sensor (38) comprises a plurality of pixels (36) arranged in a matrix and the respective pixel (36) comprises at least one temperature-sensitive element (39), and in that the at least one temperature-sensitive element (39) of the pixel (36) i.s constructed in a carrier substrate (40) comprising silicon and in that the coating (32) has a reflectance of the radiation of at least 98%.
2. The optical element as claimed in claim 1,
characterized in that the at least one temperature-
sensitive element (39) is applied in a silicon wafer,
in particular as a diode.
3. The optical element as claimed in claim 1,
characterized in that the temperature-sensitive
elements (39) are provided in so-called p- or n-doped
depressions or wells (46).
4. The optical element as claimed in claim 1,
characterized in that the temperature-sensitive
elements (39) are thermally insulated from one another
by insulating sections (48, 49) .
5. The optical element as claimed in claim 1,
characterized in that a plurality of temperature-
sensitive elements (3,9) are connected in series in a
pixel (36).

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6. The optical element as claimed in claim 1,
characterized in that a plurality of temperature-
sensitive elements (39) are connected in parallel in a
pixel (36).
7. The optical element as claimed in claim 1,
characterized in that a coating (32) is provided at a
side of the carrier substrate (40) which faces the
temperature sensor (38), and a carrier material (31) is
provided on a side of the carrier substrate (40) which
is remote from the temperature sensor (38).
8. The optical element as claimed in claim 1,
characterized in that a carrier material (31) is
provided at a side of the carrier substrate (40) which
is remote from the temperature sensor (38), and a
coating (32) is provided on an opposite side of the
carrier material (31).
9. The optical element as claimed in claim 1,
characterized in that the carrier material (31) is
formed in highly transmissive fashion.
10. The optical element as claimed in claim 1,
characterized in that a passivation layer (44) is
provided between the carrier substrate (40) receiving
the temperature-sensitive elements (39) and the coating
(32) provided at the carrier substrate, or in that an
absorber layer (45) is provided at the carrier
substrate (40) receiving the temperature-sensitive elements (39).
11. The optical element as claimed in claim 1,
characterized in that a stress-compensating layer is
applied on a side of the carrier material (31) or of
the carrier substrate (40) which is remote from the
coating (32).

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12. The optical element as claimed in claim 1,
characterized in that at least one multiplexer and
preferably electronic components are constructed
adjacent to the matrix comprising pixels (36) in the
carrier substrate (40).
13. A method for recording and monitoring beam
parameters of a laser beam (14) in a laser system (11)
with one or a plurality of optical elements as claimed
in claim 1, characterized in that the data recorded by
the optical element or optical elements (23) are
forwarded to an evaluation unit (30) of the laser
system (11), the data of the individual pixels (36)
being recorded and evaluated by an actual/desired value
comparison.
14. The method as claimed in claim 13, characterized
in that the recorded data are output by the evaluation
unit (30) for remote data transmission to a central
recording location.
15. The method as claimed in claim 14, characterized
in that beam parameters of the laser system (11) are
set and monitored by the recording location, which is
provided in a manner spatially separated from the laser
system (11).

The invention relates to an optical element for guiding and forming a laser beam, and to a method for recording beam parameters, particularly in a laser system, comprising a carrier substrate (40) and a coating (39), which is applied to at least one side of the carrier substrate (40), and comprising at least one temperature sensor (38). The temperature sensor (38) is comprised of a number of pixels arranged in a matrix, and each respective pixel has at least one temperature sensitive element (39). The at least one temperature sensitive element (39) of the pixel is constructed inside the carrier substrate (40) made of silicon.

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Patent Number

269909

Indian Patent Application Number

3725/KOLNP/2007

PG Journal Number

47/2015

Publication Date

20-Nov-2015

Grant Date

18-Nov-2015

Date of Filing

03-Oct-2007

Name of Patentee

TRUMPF WERKZEUGMASCHINEN GMBH & CO. KG.

Applicant Address

JOHANN-MAUS-STRASSE 2 71254 DITZINGEN

Inventors:

#	Inventor's Name	Inventor's Address
1	HORN, ARMIN	ELTINGER WEG 5/1 71272 RENNINGEN
2	WEICK, JURGEN-MICHAEL	EBERHARDSTRASSE 17/3 71679 ASPERG
3	HAMMANN, GERHARD	AUF DEM ROSSBUHL 7 70825 KORNTAL-MUNCHINGEN
4	LAITENBERGER, PETER	23 HERBERT STREET CB4 1 AG CAMBRIDGE
5	COLLIER, NICK	9 NESS ROAD CB5 0 AA BURWELL
6	JONES, ROSS PETER	84 WULFSTAN WAY CB1 8 QH CAMBRIDGE

PCT International Classification Number

B23K 26/42

PCT International Application Number

PCT/EP2006/003019

PCT International Filing date

2006-04-03

PCT Conventions:

#	PCT Application Number	Date of Convention	Priority Country
1	05007148.9	2005-04-01	EPO