Assembly for laser protection

Abstract

The invention relates to an assembly (14a, 14b) for laser protection with an optical element (16a, 16b) for reflecting and / or absorbing a laser beam (18), and with a sensor (30a, 30b) which is arranged on the optical element (16a, 16b) or spaced apart from the optical element (16a, 16b), in order to detect trans-illumination of the laser beam (18) through the optical element (16a, 16b). The sensor (30a, 30b) has a substrate (42) with a conductor track (44a, 44b) which is arranged on the surface of the substrate (42), wherein the conductor track (44a, 44b) is routed in a labyrinth shape.

Description

[0001] Laser protection arrangement Background of the invention

[0002] The invention relates to a laser protection arrangement. The invention further relates to a laser protection system.

[0003] Arrangements for protection against laser beams, for example in the event of incorrect alignment of the laser beams, are known from the state of the art.

[0004] WO2015 / 172816A1 discloses temperature sensors connected to a temperature monitoring unit to monitor the correct alignment of the laser beam as it passes through openings.

[0005] EP 2 119 531 A1 discloses a laser protection window in which sensors detect secondary radiation generated by laser beams in the laser protection window. EP 2 338 635 B1 discloses a laser protection wall designed to detect sound generated by a laser beam in the laser protection wall.

[0006] DE 20 2016 008 509 Ul concerns a rolling gate of a building opening with a sensor for detecting laser radiation.

[0007] Optical elements can be penetrated and destroyed by laser beams, especially short-pulse laser beams, without the optical elements heating up. In many such cases, the destruction of an optical element and the subsequent undesired beam direction of the laser beam are not detected by the sensors used to detect laser beams on optical elements, which are typically based on temperature measurement.

[0008] It is therefore an object of the present invention to provide an arrangement for protection against laser radiation that reliably detects irradiation through an optical element, particularly when the optical element does not heat up significantly during irradiation. It is also an object of the invention to provide a laser protection system with such an arrangement.

[0009] This object is achieved according to the invention by an arrangement according to claim 1. The features of a laser protection system according to the invention are specified in claim 8.

[0010] The arrangement according to the invention comprises the following elements: a) a reflective and / or absorbing optical element that can be irradiated by a laser beam; b) a sensor having a substrate and a meandering electrical first conductor track arranged on a first side of the substrate; wherein the sensor is arranged indirectly on the optical element or is arranged or configured directly on the optical element to detect damage to the optical element by the laser beam.

[0011] The sensor can be used to reliably determine whether the laser beam is irradiating undesirable areas around the optical element, for example, whether the laser beam is penetrating the optical element. Following detection, the laser beam can be switched off to prevent further damage. Advantageously, the sensor is compact and has a simple structure.

[0012] Due to its meandering shape, the conductor track is designed to cover a comparatively large portion of the substrate's surface. When the laser beam hits the conductor track, part of the conductor track is ablated or destroyed. In particular, a portion of the conductor track melts, bursts off, or evaporates. This changes the electrical characteristics, particularly the electrical resistance, of the conductor track. If a current flows through the conductor track, a change in these characteristics that lies outside a predetermined control range can be detected, and the laser can be switched off before it causes damage to the area surrounding the optical element. In particular, an interruption in the current flow as a result of the conductor track being destroyed by the laser beam can be easily and reliably detected as a sudden increase in the resistance of the conductor track.The laser beam is advantageously detected independently of temperature measurements. Preferably, the laser beam is prevented from being switched on again.

[0013] Adjacent sections of the conductor track are preferably sufficiently spaced apart so that if a point on the conductor track is widened by the laser beam, for example by melting, the adjacent sections of the conductor track are not connected to one another. In some embodiments, several sensors are connected in series. The optical element is designed, in particular, as a mirror, beam guide tube, and / or aperture. The laser beam is generated in a laser source. This laser source comprises, in particular, a solid-state laser for generating a laser beam, preferably with a wavelength of 1030 nm. The substrate is designed, in particular, as a non-carbonizing substrate, for example, made of ceramic. The sensor preferably forms part of a detector device, in particular of a safety circuit.

[0014] The conductor tracks are preferably arranged on the substrate by vapor deposition, doctoring, etching and / or gluing (inter alia using a carrier film), wherein in the case of electrically conductive substrates, additional electrically insulating layers are used in particular in application processes.

[0015] In an advantageous embodiment of the arrangement, the sensor has a meandering electrical second conductor track, wherein the first conductor track and the second conductor track are particularly perpendicular to each other. The second conductor track covers additional sections on the surface of the substrate that are not covered by the first conductor track. This increases the probability that a laser beam impinging on the surface of the substrate will also irradiate a conductor track. This increases the probability of the sensor detecting the laser beam.

[0016] In a preferred embodiment, the second electrical conductor track is arranged on a second side of the substrate, which is opposite the first side of the substrate. This provides better protection for the conductor track on one side of the substrate if the conductor track on the other side of the substrate is subjected to damaging influences, particularly from the laser beam. Furthermore, the sensor is flexible in its orientation.

[0017] In an advantageous variant, the first conductor track and the second conductor track are connected in parallel. In this embodiment, it is possible to detect which side of the substrate a laser beam hits or whether the laser beam penetrates the substrate. In particular, both conductor tracks can be contacted independently of each other by a detector device. In this case, the sensor is designed with two channels.

[0018] The invention also encompasses configurations of the arrangement in which the first conductor track and the second conductor track are connected in series. In this case, the sensor is designed as a single-channel device. A change in the electrical characteristics of the conductor track at one point on the conductor track leads to a change in the electrical characteristics of the entire sensor. This increases detection reliability. In particular, an interruption in the current flow at one point on the conductor track leads to an interruption in the current flow throughout the entire sensor.

[0019] In a preferred embodiment, the sensor is arranged or formed directly on the optical element, with the substrate, in particular, being formed as part of the optical element. This makes the laser protection arrangement particularly compact and easy to transport.

[0020] The sensor advantageously has a housing that surrounds at least the first conductor track and the substrate. The housing preferably surrounds both of the aforementioned conductor tracks and the substrate of the sensor. The housing is preferably made of aluminum. A housing that includes aluminum as a material has the advantage that it is easy to process and is comparatively inexpensive. The housing can also be made of copper. This has the advantage that the housing is particularly robust, particularly against radiation with a wavelength of 1030 nm. The housing prevents the laser beam from penetrating the sensor, even if it passes through the substrate. Furthermore, the housing serves to hold the other components of the sensor. In some embodiments, the housing has protective glass to reduce the risk of particles that are generated when the sensor is irradiated by a laser beam flowing into the environment of the sensor.The protective glass is designed in particular to transmit the laser radiation used.

[0021] A laser protection system according to the invention comprises the aforementioned laser protection arrangement and a laser source for emitting the laser beam, wherein the optical element is arranged in the beam path of the laser beam. In such a laser protection system, the sensor can reliably detect whether the laser penetrates the optical element or is reflected by the optical element to an undesired location. The laser source is designed, in particular, to generate laser pulses (for example, short pulses or ultrashort pulses). The sensor is preferably connected to the laser source via signaling in order to deactivate the laser source in response to a predetermined sensor signal (in response to predetermined changes in the electrical characteristics of the sensor).

[0022] In an advantageous embodiment, the laser protection system is preferably arranged in a laser housing. The laser source is also arranged in the laser housing. The laser source is preferably a solid-state laser.

[0023] In an advantageous embodiment of the laser protection system, the sensor is arranged in a beam direction of the laser beam on a rear side of the optical element, wherein the beam direction is directed towards the optical element. Due to the direct spatial arrangement of the sensor on the rear side of the optical element, the sensor detects promptly and with high accuracy whether the laser beam radiates through the rear side of the optical element and thus through the optical element from its front side to its rear side. The beam direction refers in particular to an (extended) beam direction of the laser beam in a section of the beam path of the laser beam between the optical element and another optical element which is closest to the optical element in the beam path and is arranged upstream of the optical element.In particular, the sensor is applied to the back of a mirror, whereby this back can have one or more layers. In an alternative embodiment of the laser protection system, the sensor is arranged behind the optical element in a beam direction of the laser beam and at a distance from the optical element, with the beam direction directed toward the optical element. This allows for comparatively flexible positioning of the sensor, for example, to achieve a better signal connection to a detector device.

[0024] In a preferred variant of the laser protection system, an absorber is arranged between the sensor and the optical element in the beam direction of the laser beam, which is directed towards the optical element. The absorber absorbs a portion of the laser radiation that is transmitted through the optical element, for example due to different frequencies of a laser pulse. The absorber also absorbs radiation that the optical element emits in the direction of the sensor due to its heating as a result of irradiation by the laser radiation. This protects the sensor. In particular, the sensor and the optical element are arranged directly on the absorber. The absorber is designed, for example, as a copper plate, wherein the absorber is particularly preferably thermally connected to a cooling system for cooling purposes.

[0025] In a further embodiment, the laser protection system has an EUV light source in the beam path of the laser beam. The optical element is arranged in the beam path of the laser beam between the laser source and the EUV (extreme ultraviolet radiation) light source, or behind the EUV light source, to direct the laser beam in a desired direction. The sensor reliably indicates whether the laser beam penetrates the optical element and thus does not follow the desired beam path. Laser pulses generated by the laser source are preferably used to irradiate the EUV light source, especially tin droplets.

[0026] In an advantageous embodiment, the laser protection system comprises a switching element for switching off the laser beam if the electrical resistance of one of the sensor's conductor tracks exceeds a predetermined control value, in particular if the current flow through one of the sensor's conductor tracks is interrupted. By switching off the laser beam, the switching element advantageously prevents the laser beam from being harmfully coupled into the vicinity of the optical element.

[0027] Further advantages of the invention will become apparent from the description and the drawings. Likewise, the features mentioned above and those further described can be used individually or in combination. The embodiments shown and described are not intended to be exhaustive, but rather are exemplary in nature for describing the invention.

[0028] Detailed description of the invention and drawing

[0029] Fig. 1 shows a schematic diagram of a laser protection system;

[0030] Fig. 2 shows a schematic cross section through a detection area of ​​a sensor of the laser protection system;

[0031] Fig. 3 shows a schematic plan view of the substrate and the conductor tracks of the sensor;

[0032] Fig. 4 shows a cross-section through the sensor.

[0033] Fig. 1 schematically shows a laser protection system 10 with a laser source 12 and a first arrangement 14a and a second arrangement 14b for protecting the surroundings of a first and second optical element 16a, 16b from a laser beam 18 from the laser source 12. The two arrangements 14a, 14b can be provided alternatively or together. The optical elements 16a, 16b are designed as mirrors and arranged in the beam path 20 of the laser beam 18 from the laser source 12. The optical elements 16a, 16b direct the laser beam 18 to an EUV light source ("target", in particular in the form of a tin droplet) 22, which emits EUV radiation 24. In order to absorb laser radiation transmitted by the first optical element 16a, an absorber 28, for example in the form of a copper plate, is located in a first direction RL1 of the laser beam 18 on the back side 26a of the first optical element 16a.A first sensor 30a is arranged on the rear side 26c of the absorber 28 at a distance from the first optical element 16a to detect laser radiation that undesirably passes through both the first optical element 16a and the absorber 28. The first sensor 30a is positioned behind the first optical element 16a in the beam direction RL1 of the laser beam 18. A current flows through the first sensor 30a, whereby the electrical characteristics of the first sensor 30a change when the laser beam 18 strikes the first sensor 30a.

[0034] The change in the electrical parameters and thus in the current flow can be detected by a detector device 32, which is connected to the first sensor 30a via a first signal channel 34a. If the parameters change outside a predetermined control range, the detector device 32 sends a signal to a switching device 36 via a second signal channel 34b to switch off the laser source 12 and thus the laser beam 18 via a third signal channel 34c. This particularly affects the electrical resistance of a conductor track of the first sensor 30a (see Fig. 3), through which the current flows. This prevents the laser beam 18 from irradiating an undesired location in the vicinity of the first optical element 16a and causing damage.

[0035] The laser beam 18 is directed from the first optical element 16a to the second optical element 16b, which is formed as part of the second arrangement 14b for laser protection. A second sensor 30b is located on the rear side 26b of the second optical element 16b (in a second beam direction RL2 of the laser beam 18 toward the second optical element 16b) to detect whether the laser beam 18 undesirably penetrates the second optical element 16b. A current flows through the second sensor 30b, like the first sensor 30a. The electrical characteristics of the second sensor 30b change when the laser beam 18 strikes the second sensor 30b after penetrating the second optical element 16b. This change is signaled via a fourth signal channel 34d to the detector device 32, which in turn causes the laser source 12 to be switched off if a control range is exceeded due to these changes.

[0036] Fig. 2 schematically shows a cross-section through a detection region 38 (cf. Fig. 4) of a sensor, here by way of example the sensor 30a. On a first side 40a of a substrate 42 of the sensor 30a, a first conductor track 44a is arranged, the electrical characteristics of which change when it is irradiated by the laser beam 18 (see Fig. 1). To increase the detection reliability, a second conductor track 44b is arranged on a second side 40b of the substrate 42, which is opposite the first side 40a. The conductor tracks 44a, 44b can be connected in parallel or in series. The substrate 42 can be formed as part of an optical element 16a, 16b (see Fig. 1), for example on the back of a mirror. The detection region 38 has in particular the substrate 42 and the conductor tracks 44a, 44b.

[0037] Fig. 3 schematically shows a top view of the substrate 42 and the conductor tracks 44a, 44b of a sensor, here by way of example the sensor 30a. The first conductor track 44a is guided with a meander shape 46 along the first side 40a of the substrate 42 (see Fig. 2) from a first electrical connection 48a to a second electrical connection 48b. Current can be conducted through the first conductor track 44a via the first and second connections 48a, 48b in order to measure a change in the electrical characteristics of the first conductor track 44a. Accordingly, the second conductor track 44b is guided with a meander shape 46 along the second side 40b of the substrate 42 (see Fig. 2) from a third electrical connection 48c to a fourth electrical connection 48d. Current can be conducted through the second conductor track 44b through the third and fourth terminals 48c, 48d in order to measure a change in the electrical characteristics of the second conductor track 44b.The first and second conductor tracks 44a, 44b are angled, in particular perpendicular, to each other. In particular, corresponding sections of the conductor tracks 44a, 44b (e.g., sections of equal length) extend at a right angle to each other.

[0038] Fig. 4 shows a cross-section through a sensor, here the sensor 30a as an example. The substrate 42 with the conductor tracks 44a, 44b (see Fig. 3) is surrounded by a housing 50 for protection, wherein the housing 50 has an opening 52 at a lower end and a cover 54 at an upper end. A laser beam 18 (see Fig. 1) can penetrate into the housing 50 through the opening 52 in order to irradiate the substrate 42. Sealing rings 56a, 56b are applied to both sides of the substrate 42, on which sealing rings 56a, 56b are arranged protective glasses 58a, 58b in order to additionally protect the conductor tracks 44a, 44b on the substrate 42. In particular, the protective glasses 58a, 58b and the housing 50 delimit the detection area 38 of the sensor. The protective glasses 58a, 58b also reduce a flow of particles into the environment of the sensor 30a when the substrate 42 is hit by a laser beam 18.Preferably, the protective glasses 58a, 58b are permeable to the radiation of a laser beam 18 used in the laser protection system 10.

[0039] Taking all figures of the drawing together, the invention relates to a laser protection arrangement 14a, 14b comprising an optical element 16a, 16b for reflecting and / or absorbing a laser beam 18 and a sensor 30a, 30b arranged on the optical element 16a, 16b or spaced apart from the optical element 16a, 16b to detect the laser beam 18 passing through the optical element 16a, 16b. The sensor 30a, 30b comprises a substrate 42 with a conductor track 44a, 44b arranged on the surface of the substrate 42, wherein the conductor track 44a, 44b is guided in a labyrinth shape. List of Reference Symbols

[0040] 10 Laser protection system

[0041] 12 Laser source

[0042] 14a, b Laser protection regulations

[0043] 16a, b optical elements

[0044] 18 laser beam

[0045] 20 Beam path

[0046] 22 EUV light source

[0047] 24 EUV radiation

[0048] 26a-c Backs of the components

[0049] 28 absorbers

[0050] 30a, b Sensors

[0051] 32 Detector device

[0052] 34a-d signal channels

[0053] 36 Switching device

[0054] 38 Detection range of the sensor

[0055] 40a, b Sides of the substrate

[0056] 42 Substrat

[0057] 44a, b Conductor tracks

[0058] 46 Meander shape

[0059] 48a-d connections

[0060] 50 housings

[0061] 52 Opening

[0062] 54 Cover

[0063] 56a, b Sealing rings

[0064] 58a, b protective glasses

[0065] RL1,2 directions of the laser beam

Claims

Patent claims Arrangement (14a, 14b) for laser protection, comprising: a) a reflective and / or absorbing optical element (16a, 16b) which can be irradiated by a laser beam (18); b) a sensor (30a, 30b) with a substrate (42) and a meandering electrical first conductor track (44a) which is arranged on a first side (40a) of the substrate (42); wherein the sensor (30a, 30b) is arranged indirectly on the optical element (16a, 16b) or is arranged or designed directly on the optical element (16a, 16b) in order to detect damage to the optical element (16a, 16b) by the laser beam (18). Arrangement according to claim 1, wherein the sensor (30a, 30b) has a meandering electrical second conductor track (44b), wherein the first conductor track (44a) and the second conductor track (44b) are in particular perpendicular to one another.Arrangement according to claim 2, wherein the second conductor track (44b) is arranged on a second side (40b) of the substrate (42), which is opposite the first side (40a) of the substrate (42). Arrangement according to claim 2 or 3, wherein the first conductor track (44a) and the second conductor track (44b) are connected in parallel to one another. Arrangement according to claim 2 or 3, wherein the first conductor track (44a) and the second conductor track (44b) are connected in series. Arrangement according to one of the preceding claims, wherein the sensor (30a, 30b) is arranged or formed directly on the optical element (16a, 16b), wherein in particular the substrate (42) is formed as a part of the optical element (16a, 16b).

7. Arrangement according to one of the preceding claims, wherein the sensor (30a, 30b) has a housing (50) which surrounds at least the first conductor track (44a) and the substrate (42).

8. Laser protection system (10), comprising an arrangement (14a, 14b) for laser protection according to one of claims 1 to 7 and a laser source (12) for emitting the laser beam (18), wherein the optical element (16a, 16b) is arranged in the beam path (20) of the laser beam (18).

9. Laser protection system according to claim 8, wherein the sensor (30a, 30b) is arranged in a beam direction (RL1, RL2) of the laser beam (18) on a rear side (26a, 26b) of the optical element (16a, 16b), the beam direction (RL1, RL2) being directed towards the optical element (16a, 16b).

10. Laser protection system according to claim 8, wherein the sensor (30a, 30b) is arranged in a beam direction (RL1, RL2) of the laser beam (18) behind the optical element (16a, 16b) and at a distance from the optical element (16a, 16b), the beam direction (RL1, RL2) being directed towards the optical element (16a, 16b).

11. Laser protection system according to claim 10, wherein in the beam direction (RL1, RL2) of the laser beam (18) directed towards the optical element (16a, 16b), an absorber (28) is arranged between the sensor (30a, 30b) and the optical element (16a, 16b).

12. Laser protection system according to one of claims 8 to 11, comprising an EUV light source (22) in the beam path of the laser beam (18).

13. Laser protection system according to one of claims 8 to 12, comprising a switching element (36) for switching off the laser beam (18) when the electrical resistance of one of the conductor tracks (44a, 44b) of the sensor (30a, 30b) exceeds a predetermined control value, in particular, when the current flow through one of the conductor tracks (44a, 44b) of the sensor (30a, 30b) is interrupted.

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