Device for laser protection

Abstract

The invention relates to a device (14a, 14b) for laser protection, having an optical element (16a, 16b) for reflecting and / or absorbing a laser beam (18), and having a sensor (30a, 30b) which is arranged on or at a distance from the optical element (16a, 16b) in order to detect the situation in which the laser beam (18) penetrates the optical element (16a, 16b). The sensor (30a, 30b) has a substrate (42), on the surface of which conductor tracks (44a, 44b) are arranged, the conductor tracks (44a, 44b) extending in the shape of a labyrinth.

Description

Technical Field

[0001] The invention relates to a device for laser protection and also to a laser protection system. Background Art

[0002] Devices for protecting laser beams, for example in the event of incorrect orientation of the laser beam, are known from the prior art.

[0003] WO 2015 / 172816 A1 discloses a temperature sensor connected to a temperature monitoring unit for monitoring the correct orientation of a laser beam when passing through an opening.

[0004] EP 2 119 531 A1 discloses a laser protection window in which a sensor detects secondary radiation generated by a laser beam in the laser protection window.

[0005] EP 2 338 635 B1 discloses a laser protection wall which is designed to detect the sound caused by a laser beam in the laser protection wall.

[0006] DE 20 2016 008 509 U1 relates to a rolling door for a building opening with a sensor for detecting laser radiation.

[0007] Optical components can be penetrated and destroyed by laser beams, in particular short-pulse laser beams, without the optical component itself heating up as a result. In many of these cases, the destruction of the optical component and the subsequent undesired radiation direction of the laser beam cannot be detected by sensors for detecting the laser beam at the optical component, which are usually based on temperature measurement. Summary of the invention

[0008] Therefore, the object of the present invention is to provide a device for laser protection which can reliably detect penetration of optical elements, in particular without significant heating of the optical element during penetration. Another object of the present invention is to provide a laser protection system with such a device.

[0009] Description of the invention

[0010] This object is achieved by the device according to claim 1. The laser protection system according to the invention is characterized by what is disclosed in claim 8 .

[0011] The device of the present invention comprises the following elements:

[0012] a) Optical elements that can be irradiated by laser beams and have a reflective and / or absorbing effect;

[0013] b) A sensor having a substrate and a first electrical conductor track arranged on a first side of the substrate in a meandering manner;

[0014] The sensor is indirectly arranged on the optical element or directly arranged or constructed on the optical element to detect damage to the optical element caused by the laser beam.

[0015] The sensor can be used to reliably determine whether the laser beam strikes an undesired location in the surroundings of the optical element, for example whether the laser beam penetrates the optical element. As a follow-up to the detection, the laser beam can be switched off to prevent further damage. Advantageously, the sensor is compact and has a simple structure.

[0016] Due to its meandering extension, the conductor track is designed to cover a larger part of the surface of the substrate. When the laser beam irradiates the conductor track, a part of the conductor track will be removed or destroyed. In particular, part of the conductor track will melt, peel off or evaporate. This leads to a change in the electrical characteristic parameters of the conductor track, in particular the resistance. In the case of a current passing through the conductor, changes in the characteristic parameters outside the predetermined control range can be detected, and the laser beam can be turned off before the laser beam causes damage to the surroundings of the optical element. In particular, the current interruption caused by the laser beam destroying the conductor track can be simply and reliably detected as a sudden increase in the resistance of the conductor track. The detection of the laser beam is advantageously achieved independently of the temperature measurement. Preferably, the laser beam is prevented from being turned back on.

[0017] Adjacent sections of the conductor track preferably have a sufficiently large spacing such that adjacent sections of the conductor track do not connect to one another when the laser beam causes a local widening of the conductor track (eg due to melting).In certain embodiments, a plurality of sensors are connected in series.

[0018] The optical element is designed in particular as a reflector, a beam guide and / or an aperture. The laser beam is generated in a laser source. The laser source comprises in particular a solid-state laser for generating a laser beam, preferably a laser beam with a wavelength of 1030 nm. The substrate is designed in particular as a non-carbonized substrate, for example made of ceramic. The sensor preferably forms part of a detection device, in particular part of a safety circuit.

[0019] The conductor tracks are preferably arranged on the substrate by vapor deposition, ablation, etching and / or adhesive bonding, in particular using a carrier film, wherein, in the case of electrically conductive substrates, in particular additional electrically insulating layers are used in the application method.

[0020] In a preferred embodiment of the device, the sensor has a meander-shaped second electrical conductor track, wherein the first conductor track and the second conductor track are arranged in particular perpendicular to one another. The second conductor track covers an additional section on the surface of the substrate that is not covered by the first conductor track. This increases the probability that a laser beam impinging on the substrate surface also impinges on the conductor track, thereby increasing the probability that the sensor detects the laser beam.

[0021] In a preferred configuration, the second conductor track is arranged on a second side of the substrate opposite to the first side of the substrate. As a result, if the conductor track on one side of the substrate is damaged, in particular by a laser beam, the conductor track on the other side of the substrate is better protected. In addition, the sensor can be used more flexibly with respect to its orientation.

[0022] In a preferred variant, the first conductor track and the second conductor track are connected in parallel. In this configuration, it is possible to detect which side of the substrate the laser beam strikes or whether it penetrates the substrate. In particular, the two conductors can be contacted by the detection device independently of each other. In this case, the sensor is dual-channel.

[0023] The invention also includes a configuration of the device in which the first conductor track and the second conductor track are connected in series. In this case, the sensor is single-channel. A change in the electrical characteristic variable of the conductor track at one point in the conductor track leads to a change in the electrical characteristic variable of the entire sensor. This increases the reliability of the detection. In particular, an interruption of the current at a certain point in the conductor track leads to an interruption of the current in the entire sensor.

[0024] In a preferred embodiment, the sensor is arranged or formed directly on the optical element, wherein in particular the substrate is formed as part of the optical element. As a result, the device for laser protection is designed to be particularly compact and can be easily transported.

[0025] The sensor advantageously has a housing which surrounds at least the first conductor track and the substrate. The housing preferably surrounds the two conductor tracks and the substrate of the sensor. The housing is preferably made of aluminum. The advantage of a housing made of aluminum is that it is easy to process and relatively inexpensive. The housing can also be made of copper. The advantage of a copper housing is that the housing is particularly robust, in particular for radiation with a wavelength of 1030 nm. The housing prevents the laser beam from penetrating the sensor, even if the laser beam penetrates the substrate. In addition, the housing serves to fix other parts of the sensor. In some embodiments, the housing has a protective glass to reduce the risk that particles generated when the sensor is irradiated by the laser beam flow into the environment surrounding the sensor. The protective glass is particularly designed to transmit the laser beam used.

[0026] The laser protection system of the present invention comprises the above-mentioned device for laser protection and a laser source for emitting a laser beam, wherein an optical element is arranged in the optical path of the laser beam. In such a laser protection system, it is possible to reliably detect whether the laser penetrates the optical element or is reflected by the optical element to an undesired position by a sensor. The laser source is particularly configured to generate laser pulses (e.g. short pulses or ultrashort pulses). The sensor is preferably connected to the laser source in terms of signal technology so as to shut down the laser source in the case of a predetermined sensor signal (predetermined change of the electrical characteristic variable of the sensor).

[0027] In a preferred embodiment, the laser protection system is preferably arranged in a laser housing. In this case, the laser source is additionally arranged in the laser housing. The laser source is preferably designed as a solid-state laser.

[0028] In a preferred embodiment of the laser protection system, the sensor is arranged on the back side of the optical element in the beam direction of the laser beam, wherein the beam direction points toward the optical element. By arranging the sensor directly on the back side of the optical element, the sensor detects promptly and with high precision whether the laser beam penetrates the back side of the optical element and thus whether the laser beam penetrates the optical element from the front to the back side. The beam direction refers in particular to the (extended) beam direction of the laser beam in the section of the beam path of the laser beam between the optical element and a further optical element which is closest to the optical element in the beam path and is located upstream of the optical element. In particular, the sensor is mounted on the back side of the reflector, wherein the back side can have one layer or a plurality of layers.

[0029] In an alternative configuration of the laser protection system, the sensor is arranged behind and spaced apart from the optical element in the beam direction of the laser beam, wherein the beam direction points toward the optical element. This allows the positioning of the sensor to be carried out relatively flexibly, for example to achieve a better signal connection to the detection device.

[0030] 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 directed toward the optical element. The absorber absorbs the portion of the laser radiation that is transmitted through the optical element (for example due to the different frequencies of the laser pulses). The absorber also absorbs radiation emitted by the optical element in the direction of the sensor due to the heating of the optical element due to the irradiation with 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.

[0031] In another configuration, the laser protection system has an EUV (extreme ultraviolet) light source in the beam path of the laser beam. An optical element is arranged in the beam path of the laser beam between the laser source and the EUV light source or after the EUV light source to steer the laser beam in the desired direction. Here, the sensor reliably indicates whether the laser beam penetrates the optical element and thus does not pass through the desired beam path. Preferably, the laser pulses generated by the laser source are used to illuminate the EUV light source, in particular tin droplets.

[0032] In a preferred embodiment, the laser protection system has a switching element for switching off the laser beam when the resistance of one of the conductor tracks of the sensor exceeds a predefined control value, in particular when the current flowing through one of the conductor tracks of the sensor is interrupted. Advantageously, the switching element prevents the laser beam from being detrimentally coupled out into the surroundings of the optical element by switching off the laser beam.

[0033] Further advantages of the present invention are apparent from the description and the accompanying drawings. Likewise, the features described above and in the following can be used alone or in any combination. The embodiments shown and described are not to be understood as exhaustive, but rather have an exemplary character to illustrate the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 The laser protection system is shown schematically;

[0035] Figure 2 A cross section of a detection area of ​​a sensor of a laser protection system is schematically shown;

[0036] Figure 3 A top view of the substrate and conductor tracks of the sensor is schematically shown;

[0037] Figure 4 A cross section of the sensor is shown. DETAILED DESCRIPTION

[0038] Figure 1 Schematically shown is a laser protection system 10 having a laser source 12 and a first device 14a and a second device 14b for protecting the surroundings of a first and a second optical element 16a, 16b from a laser beam 18 from the laser source 12. The two devices 14a, 14b can be provided either one or together. The optical elements 16a, 16b are designed as mirrors and are arranged in a beam path 20 of the laser beam 18 from the laser source 12. The laser beam 18 is deflected by the optical elements 16a, 16b to an EUV light source ("target", in particular in the form of tin droplets) 22, which emits EUV radiation 24.

[0039] In order to absorb the laser radiation transmitted by the first optical element 16a, an absorber 28, for example in the form of a copper plate, is provided on the back side 26a of the first optical element 16a in a first direction RL1 of the laser beam 18. On the back side 26c of the absorber 28, a first sensor 30a is arranged at a distance from the first optical element 16a for detecting laser radiation that undesirably penetrates both the first optical element 16a and the absorber 28. The first sensor 30a is positioned after the first optical element 16a in the beam direction RL1 of the laser beam 18. A current flows through the first sensor 30a, wherein an electrical characteristic variable of the first sensor 30a changes when the laser beam 18 impinges on the first sensor 30a.

[0040] Changes in the electrical characteristic variable and changes in the current can be detected by a detection device 32, which is connected to the first sensor 30a via a first signal channel 34a. When the change in the characteristic variable is outside a predetermined control range, the detection device 32 sends a signal to the 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 concerns the conductor track of the first sensor 30a through which the current flows (see Figure 3 This prevents the laser beam 18 from irradiating an undesired location in the surroundings of the first optical element 16a and causing damage.

[0041] The laser beam 18 is deflected by the first optical element 16a to the second optical element 16b, which is configured as part of the second device 14b for laser protection. On the back side 26b of the second optical element 16b (in terms of the second direction RL2 of the laser beam 18 toward the second optical element 16b), there is a second sensor 30b for detecting whether the laser beam 18 undesirably penetrates the second optical element 16b. Like the first sensor 30a, a current flows through the second sensor 30b. Here, when the laser beam 18 penetrates the second optical element 16b and irradiates the second sensor 30b, the electrical characteristic parameter of the second sensor 30b changes. This change sends a signal to the detection device 32 via the fourth signal channel 34d, and the detection device 32 causes the laser source 12 to be turned off when the change exceeds the control range.

[0042] Figure 2 The detection area 38 of the sensor is schematically shown (see Figure 4 ) cross section, here taking sensor 30a as an example. A first conductor track 44a is arranged on a first side 40a of a substrate 42 of the sensor 30a, and when the laser beam 18 (see Figure 1 ) irradiates it, its electrical characteristic parameters will change. In order to improve the detection reliability, a second conductor track 44b is arranged on the second side 40b of the substrate 42 opposite to the first side 40a. The conductor tracks 44a and 44b can be connected in parallel or in series. The substrate 42 can be constructed as an optical element 16a, 16b (see Figure 1 ), for example on the back side of a reflector. The detection region 38 comprises in particular a substrate 42 and conductor tracks 44a, 44b.

[0043] Figure 3 The schematic diagram shows a top view of a substrate 42 and conductor tracks 44a, 44b of a sensor, taking the sensor 30a as an example. The first conductor track 44a is arranged in a meandering shape 46 on a first side 40a of the substrate 42 (see FIG. Figure 2) from the first electrical connector 48a to the second electrical connector 48b. Through the first and second connectors 48a, 48b, current can be conducted through the first conductor track 44a to measure the change of the electrical characteristic parameter of the first conductor track 44a. Accordingly, the second conductor track 44b is formed in a meandering shape 46 on the second side 40b (see Figure 2 ) extends from the third electrical connection 48c to the fourth electrical connection 48d. Via the third and fourth connections 48c, 48d, a current can be conducted through the second conductor track 44b to measure a change in an electrical characteristic variable of the second conductor track 44b. Here, the first and second conductor tracks 44a, 44b are arranged at an angle to each other, in particular perpendicularly. In particular, corresponding sections of the conductor tracks (for example sections of the same length) extend at right angles to each other.

[0044] Figure 4 A cross section of a sensor is shown, here taking sensor 30a as an example. With conductor tracks 44a, 44b (see Figure 3 ) is surrounded by a housing 50 for protection, wherein the housing 50 has an opening 52 at the lower end and a cover 54 at the upper end. Through the opening 52, the laser beam 18 (see Figure 1 ) can enter the housing 50 in order to irradiate the substrate 42. Sealing rings 56a, 56b are arranged on both sides on the substrate 42, and protective glasses 58a, 58b are arranged on the sealing rings to additionally protect the conductor tracks 44a, 44b on the substrate 42. In particular, the protective glasses 58a, 58b and the housing 50 surround the detection area 38 of the sensor. The protective glasses 58a, 58b also reduce the influx of particles into the surroundings of the sensor 30a when the substrate 42 is irradiated by the laser beam 18. Preferably, the protective glasses 58a, 58b are transmissive to the radiation of the laser beam 18 used in the laser protection system 10.

[0045] In summary, the present invention relates to a device 14a, 14b for laser protection, which has 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 arranged at a distance from the optical element 16a, 16b to detect the penetration of the laser beam 18 through the optical element 16a, 16b. The sensor 30a, 30b has a substrate 42, on the surface of which conductor tracks 44a, 44b are arranged, wherein the conductor tracks 44a, 44b extend in a labyrinth shape.

[0046] Reference numerals list

[0047] 10 Laser protection system

[0048] 12 Laser Source

[0049] 14a,b Devices for laser protection

[0050] 16a,bOptical elements

[0051] 18 Laser Beam

[0052] 20 Light Path

[0053] 22 EUV light source

[0054] 24 EUV Radiation

[0055] 26a-c Back side of structural element

[0056] 28 Absorber

[0057] 30a,b sensor

[0058] 32 Detection device

[0059] 34a-d signal channel

[0060] 36 Switchgear

[0061] 38 Sensor detection area

[0062] 40a, b Side of the substrate

[0063] 42 substrate

[0064] 44a,b conductor rail

[0065] 46 Meandering

[0066] 48a-d connector

[0067] 50 Shell

[0068] 52 Opening

[0069] 54 Lid

[0070] 56a,b Sealing ring

[0071] 58a,b Protective glass

[0072] RL1,2 Direction of laser beam

Claims

1. A device (14a, 14b) for laser protection, comprising: a) an optical element (16a, 16b) capable of being irradiated by a laser beam (18) and having a reflective and / or absorbing effect; b) a sensor (30a, 30b) having a substrate (42) and a first electrical conductor track (44a) arranged in a meandering manner on a first side (40a) of the substrate; The sensor (30a, 30b) is indirectly arranged on the optical element (16a, 16b) or directly arranged or constructed on the optical element (16a, 16b) to detect damage to the optical element (16a, 16b) caused by the laser beam (18).

2. The device 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 arranged in particular perpendicular to one another.

3. The device according to claim 2, wherein: The second conductor track (44b) is arranged on a second side (40b) of the substrate (42) opposite the first side (40a) of the substrate (42).

4. The device according to claim 2 or 3, wherein: The first conductor track (44a) and the second conductor track (44b) are connected in parallel with each other.

5. The device according to claim 2 or 3, wherein: The first conductor track (44a) and the second conductor track (44b) are connected in series.

6. A device according to any one of the preceding claims, wherein: The sensor (30a, 30b) is arranged or formed directly on the optical element (16a, 16b), wherein in particular a substrate (42) is formed as part of the optical element (16a, 16b).

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

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

9. The laser protection system according to claim 8, wherein: A sensor (30a, 30b) is arranged on the back side (26a, 26b) of an optical element (16a, 16b) along a beam direction (RL1, RL2) of a laser beam (18), wherein the beam direction (RL1, RL2) points toward the optical element (16a, 16b).

10. The laser protection system according to claim 8, wherein: The sensor (30a, 30b) is arranged behind the optical element (16a, 16b) and spaced apart from the optical element (16a, 16b) along a beam direction (RL1, RL2) of a laser beam (18), wherein the beam direction (RL1, RL2) points to the optical element (16a, 16b).

11. The laser protection system according to claim 10, wherein: An absorber (28) is arranged between the sensor (30a, 30b) and the optical element (16a, 16b) along a beam direction (RL1, RL2) of the laser beam (18) directed toward the optical element (16a, 16b).

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

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

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