LASER SYSTEMS AND METHODS FOR PROVIDING HIGH-FREQUENCY AND LOW-FREQUENCY LASER PULSE TRAINS

Abstract

Laser systems are described that each include at least one excitation laser, a high frequency laser pulse source, and a beam switchover device. The beam switchover device is configured to be switched, in order a) in a high-frequency functional position to guide at least one GHz laser pulse train with a pulse repetition rate of individual pulses in the GHz laser pulse train of at least 0.5 GHz from the high frequency laser pulse source to a target position, and b) in a low-frequency functional position to guide at least one low-frequency laser pulse train with a pulse repetition rate of individual pulses in the low-frequency laser pulse train of less than 0.5 GHz from the at least one excitation laser to the target position.

Claims

1. A laser system, comprising: at least one excitation laser configured to generate laser pulses in a low-frequency laser pulse train with a pulse repetition rate of individual pulses in the low-frequency laser pulse train of less than 0.5 GHz; a high frequency laser pulse source configured to generate a GHz laser pulse train with a pulse repetition rate of individual pulses in the GHz laser pulse train of at least 0.5 GHz; an amplifier configured to amplify laser light; and a beam switchover device arranged upstream of the amplifier in a light propagation direction, wherein the beam switchover device is switchable between a high-frequency functional position and a low-frequency functional position and is configured: a) to feed at least one GHz laser pulse train of the high frequency laser pulse source to the amplifier for amplification in the high-frequency functional position, and b) to feed at least one low-frequency laser pulse train of the at least one excitation laser to the amplifier for amplification in the low-frequency functional position.

2. The laser system of claim 1, wherein the high frequency laser pulse source comprises a laser diode.

3. The laser system of claim 1, wherein the beam switchover device comprises at least one of: at least one beam selector or at least one beam distributor.

4. The laser system of claim 1, wherein the high frequency laser pulse source is configured to generate the GHz laser pulse train based on the laser pulses from the at least one excitation laser.

5. The laser system of claim 1, wherein the high frequency laser pulse source comprises a repetition rate multiplier.

6. The laser system of claim 5, wherein the repetition rate multiplier is configured to: receive a plurality of individual laser pulses from the at least one excitation laser; and multiply an individual pulse repetition rate of the plurality of individual laser pulses.

7. The laser system of claim 5, wherein the beam switchover device comprises: a beam distributor configured to split laser light of the at least one excitation laser temporally or spatially or both temporally and spatially between the repetition rate multiplier and an individual pulse section; and a beam selector configured to feed to the amplifier at least one GHz laser pulse train from the repetition rate multiplier in the high-frequency functional position and laser pulses from the individual pulse section in the low-frequency functional position.

8. The laser system of claim 7, wherein the beam distributor comprises: a) a passive beam splitter, b) an active beam switching device, or c) a combination of a passive beam splitter and an active beam switching device.

9. The laser system of claim 7, wherein the beam selector comprises: a) an active beam switching device, b) a passive beam combiner, or c) a combination of a passive beam combiner and at least one active beam influencing device.

10. The laser system of claim 7, comprising a mode change device having: the beam distributor, the repetition rate multiplier, the individual pulse section and the beam selector.

11. The laser system of claim 10, wherein the mode change device is arranged, in the light propagation direction, at least one of: a) upstream of a pulse selection device for selecting individual pulses or individual laser pulse trains, b) upstream of a preamplifier, c) upstream of a pulse stretcher, d) downstream of the preamplifier, or e) downstream of the pulse selection device.

12. The laser system of claim 1, wherein the beam switchover device comprises at least one of a) an acousto-optical modulator, b) an electro-optical modulator, or c) a micro-electro-mechanical system.

13. The laser system of claim 1, wherein, downstream of the excitation laser in the light propagation direction, the laser system further comprises at least one of: a) a pulse stretcher; b) at least one preamplifier; c) the amplifier; or d) a pulse compressor.

14. The laser system of claim 1, wherein the excitation laser comprises a fiber oscillator.

15. The laser system of claim 1, further comprising a controller configured to drive the beam switchover device.

16. A method of operating a laser system, the method comprising: generating, by at least one excitation laser of the laser system, laser pulses in a low-frequency laser pulse train with a pulse repetition rate of individual pulses in the low-frequency laser pulse train of less than 0.5 GHz; generating, by a high frequency laser pulse source of the laser system, a GHz laser pulse train with a pulse repetition rate of individual pulses in the GHz laser pulse train of at least 0.5 GHz; switching a beam switchover device of the laser system into a high-frequency functional position to guide at least one GHz laser pulse train from the high frequency laser pulse source to a target position; and switching the beam switchover device into a low-frequency functional position to guide at least one low-frequency laser pulse train from the at least one excitation laser to the target position, wherein switching the beam switchover device into the high-frequency functional position and the low-frequency functional position is in order.

17. A laser system, comprising: at least one excitation laser configured to generate laser pulses in a low-frequency laser pulse train with a pulse repetition rate of individual pulses in the low-frequency laser pulse train of less than 0.5 GHz; a high frequency laser pulse source configured to generate a GHz laser pulse train with a pulse repetition rate of individual pulses in the GHz laser pulse train of at least 0.5 GHz; and a beam switchover device configured to be switched: a) in a high-frequency functional position to guide at least one GHz laser pulse train from the high frequency laser pulse source to a target position, and b) in a low-frequency functional position to guide at least one low-frequency laser pulse train from at least one excitation laser to the target position, wherein the beam switchover device is configured to be switched in order in the high-frequency functional position and the low-frequency functional position.

18. The laser system of claim 17, further comprising: an amplifier configured to amplify laser light, wherein the beam switchover device is arranged upstream of the amplifier in a light propagation direction, and the amplifier is at the target position.

19. The laser system of claim 17, wherein the high frequency laser pulse source comprises a repetition rate multiplier configured to: receive a plurality of individual laser pulses from the at least one excitation laser; and multiply an individual pulse repetition rate of the plurality of individual laser pulses.

20. The laser system of claim 19, wherein the beam switchover device comprises: a beam distributor configured to split laser light of the at least one excitation laser temporally or spatially or both temporally and spatially between the repetition rate multiplier and an individual pulse section; and a beam selector configured to feed to the amplifier at least one GHz laser pulse train from the repetition rate multiplier in the high-frequency functional position and laser pulses from the individual pulse section in the low-frequency functional position, wherein the beam distributor comprises: a) a passive beam splitter, b) an active beam switching device, or c) a combination of a passive beam splitter and an active beam switching device, and wherein the beam selector comprises: a) an active beam switching device, b) a passive beam combiner, or c) a combination of a passive beam combiner and at least one active beam influencing device.

Description

DESCRIPTION OF DRAWINGS

[0081] FIG. 1 is a schematic illustration of a first example of an embodiment of a laser system, as described herein.

[0082] FIG. 2 is a schematic illustration of an example of an embodiment of a mode change device as described herein.

[0083] FIG. 3 is a schematic illustration of a second embodiment of the laser system.

[0084] FIG. 4 shows a schematic illustration of a third embodiment of the laser system.

[0085] FIG. 5 shows a schematic illustration of a fourth embodiment of the laser system.

[0086] FIG. 6 shows a schematic illustration of a fifth embodiment of the laser system.

[0087] FIG. 7 shows a schematic illustration of a functional mode of a laser system according to the present disclosure.

DETAILED DESCRIPTION

[0088] FIG. 1 shows a schematic illustration of a first embodiment of a laser system 100. The laser system 100 includes an excitation laser 10 configured for generating laser pulses, e.g., with an individual pulse repetition rate of less than 0.5 GHz, of from at least 0.01 MHz to at most 100 MHz, of from at least 1 MHz to at most 90 MHz, or of from at least 5 MHz to at most 15 MHz or at most 10 MHz. The excitation laser 10 can be a fiber laser or a diode laser or any other suitable excitation laser. The laser system 100 also includes an amplifier 80 configured for amplifying laser light. The amplifier 80 can be a fiber amplifier, a rod amplifier, a slab amplifier, a disk amplifier, a solid state amplifier, or any other suitable laser amplifier. The laser system 100 additionally includes a high frequency laser pulse source 40, which is illustrated in FIG. 2 and which is part of a mode change device 30 in the embodiment in accordance with FIG. 1. The high frequency laser pulse source 40 is configured for generating a GHz laser pulse train with an individual pulse repetition rate in the GHz laser pulse train of at least 0.5 GHz, e.g., of from at least 1 GHz to at most 100 GHz, or of from at least 2 GHz to at most 10 GHz, such as 3.5 GHz or 5 GHz.

[0089] A beam switchover device 31, 33, which is likewise illustrated in FIG. 2 and which is likewise part of the mode change device 30 here in the embodiment in accordance with FIG. 1, is arranged upstream of the amplifier 80 in the light propagation direction. The beam switchover device 31, 33 is switchable between a high-frequency functional position and a low-frequency functional position and is configured to feed at least one GHz laser pulse train of the high frequency laser pulse source 40, e.g., a plurality of GHz laser pulse trains, to the amplifier 80 for amplification in the high-frequency functional position, and to feed at least one low-frequency laser pulse train of the at least one excitation laser 10, e.g., a plurality of low-frequency laser pulse trains, with an individual pulse repetition rate of individual laser pulses in the low-frequency laser pulse train of less than 0.5 GHz to the amplifier 80 for amplification in the low-frequency functional position. In the case of the laser system 100, as described herein, it is thus advantageously possible to switch over between the generation of GHz laser pulse trains, on one hand, and the generation of low-frequency laser pulse trains, on the other hand, and thus to provide a plurality of processing modes for processing workpieces, e.g., workpiece surfaces, in a simple and comparatively cost-effective manner.

[0090] The laser system 100 in accordance with the first embodiment in FIG. 1 can additionally include, downstream of the excitation laser 10 in the light propagation direction, a pulse stretcher 20, the mode change device 30, a first preamplifier 50, a second preamplifier 70, the amplifier 80, and a pulse compressor 110. Each of the first preamplifier 50 and the second preamplifier 70 can be a fiber preamplifier, rod preamplifier or any other suitable preamplifier.

[0091] The laser system 100 can additionally include a pulse selection device (or pulse selector) 60, which can be arranged between the first preamplifier 50 and the second preamplifier 70, as illustrated in FIG. 1. Furthermore, the laser system 100 can include a further, second pulse selection device (or pulse selector) 90, which can be arranged downstream of the amplifier 80 and upstream of the pulse compressor 110.

[0092] With the aid of at least one of the pulse selection devices 60, 90, in the low-frequency functional position it is possible to generate low-frequency pulse packets having at least two individual pulses and an individual pulse repetition rate of the individual pulses (micropulses) within such a low-frequency pulse packet (micropulse repetition rate) of less than 0.5 GHz, e.g., of from at least 0.01 MHz to at most 100 MHz, or from at least 1 MHz to at most 90 MHz, or of from at least 5 MHz to at most 15 MHz, or at most 10 MHz. The low-frequency pulse packets can temporally succeed one another with a low-frequency pulse packet repetition rate (macropulse repetition rate) of a few 100 kHz, a few 10 kHz or a few kHz.

[0093] With the aid of at least one of the pulse selection devices 60, 90, the GHz laser pulse trains can also be trimmed as GHz pulse packets having an individual pulse repetition rate of at least 0.5 GHz, e.g., of more than 0.5 GHz, or of from at least 1 GHz to at most 100 GHz, or of from at least 2 GHz to at most 20 GHz, or to at most 10 GHz, such as 1 GHz, 3.5 GHz or 5 GHz. The GHz pulse packets can succeed one another with a GHz pulse packet repetition rate (macropulse repetition rate) which can be more than 1 kHz or lies in the MHz range, where the GHz pulse packet repetition rate can also be less than 1 kHz.

[0094] It is also possible, however, to generate the laser pulse trains, whether they be GHz or low-frequency laser pulse trains, as individual pulse trains without a defined pulse packet repetition rate.

[0095] In some embodiments, it is possible to arrange downstream of the pulse compressor 110 one or more nonlinear optical components 120 configured for frequency conversion of the laser light of the excitation laser 10, e.g., for frequency multiplication, for example, frequency doubling or frequency tripling, for example, for generating a second harmonic of the excitation wavelength. The nonlinear optical components 120 can include frequency conversion crystals, e.g., Beta Barum Borate (BBO) or Lithium Triborate (LBO) crystals, or any other suitable type of crystals or elements for frequency multiplication.

[0096] In addition, the laser system 100 can include a control device (or controller) 130 configured for driving the beam switchover device 31, 33 to switch over from the high-frequency functional position to the low-frequency functional position—or vice versa.

[0097] The excitation laser 10 can be embodied as a fiber oscillator.

[0098] In the first embodiment illustrated here, the mode change device 30 is arranged upstream of the pulse selection device 60 and also upstream of the first preamplifier 50 and upstream of the second preamplifier 70. In some cases, the mode change device 30 is arranged directly downstream of the pulse stretcher 20 and upstream of the first preamplifier 50.

[0099] FIG. 2 shows an embodiment of the mode change device 30. The mode change device can include the beam switchover device 31, 33, which for its part includes a beam selector 33, embodied here as a beam changeover switch, and also a beam distributor 31. In this case, the beam distributor 31 is configured to split a laser beam or laser pulse between two beam sections, e.g., between the high frequency laser pulse source 40, on one hand, and an individual pulse section 32, on the other hand. The beam selector 33 is configured to guide laser light or laser pulses from the two beam sections onto a common path, e.g., to a common target position.

[0100] The high frequency laser pulse source 40 can be embodied here as a repetition rate multiplier 47, where laser pulses from the excitation laser 10 are able to be fed to the repetition rate multiplier 47. The repetition rate multiplier 47 is configured to multiply an individual pulse repetition rate of the individual pulses of the excitation laser 10.

[0101] The mode change device 30 can include the beam distributor 31, the repetition rate multiplier 47, the individual pulse section 32 and the beam selector 33.

[0102] The beam distributor 31 is configured here to split laser light of the excitation laser 10 temporally and/or spatially between the repetition rate multiplier 47, on one hand, and the individual pulse section 32, on the other hand. The beam selector 33 is configured to feed to the amplifier 80 at least one GHz laser pulse train from the repetition rate multiplier 47 in the high-frequency functional position, and laser pulses from the individual pulse section 32 in the low-frequency functional position.

[0103] In some embodiments, the beam distributor 31 is embodied as a passive beam splitter, e.g., with a constant splitting ratio. Alternatively, the beam distributor 31 can also be embodied as an active beam switching device, e.g., as an acousto-optical modulator, as an electro-optical modulator, or as a micro-electro-mechanical system.

[0104] Finally, it is also possible for the beam distributor 31 to be embodied as a combination of a passive beam splitter and an active beam switching device.

[0105] The beam selector 33 can be embodied as an active beam switching device, e.g., as an acousto-optical modulator, as an electro-optical modulator, or as a micro-electro-mechanical system. Alternatively, it is also possible for the beam selector 33 to be embodied as a combination of a passive beam combiner with at least one active beam influencing device, e.g., with a respective active beam influencing device of each beam section, that is to say here in the individual pulse section 32, on one hand, and the repetition rate multiplier 47, on the other hand.

[0106] If the beam selector 33 is not embodied as an active beam changeover switch, then it can alternatively also be embodied as a passive beam combiner. This is possible in particular if the beam distributor 31 is embodied as an active beam switching device or as a combination of a passive beam splitter and an active beam switching device.

[0107] Both the individual pulse section 32 and the repetition rate multiplier 47 can be embodied as fiber-optic components or include fiber-optic components. The individual pulse section 32 can include an individual pulse delay section 34 for compensating for dispersion.

[0108] On the input side, the repetition rate multiplier 47 includes a multiplier beam splitter 41, which splits the incoming laser pulses between a delay section 42, on one hand, and a passage section 43, on the other hand. In this case, the delay section 42 has a longer light path than the passage section 43, such that the laser pulse passing through the delay section 42 is delayed relative to the laser pulse passing through the passage section 43.

[0109] The repetition rate multiplier 47 additionally includes a plurality of combination elements 44, which each combine a beam combiner and a beam splitter with one another, where here in each case the laser radiation from the passage section 43, on one hand, and the delay section 42, on the other hand, is firstly combined with one another and then once again split between a downstream delay section 42 and a downstream passage section 43. This can be repeated as often as desired, in principle, where successive delay sections 42 can each have, depending on the configuration of the repetition rate multiplier 47, a doubling or—as in the embodiment illustrated here—halving length, such that as a result either laser pulse trains passing through the repetition rate multiplier 47 are multiplied or—as in the embodiment illustrated here—the individual pulse repetition rate is multiplied, namely by a factor of 2 per delay section passed through. On the output side, the repetition rate multiplier 47 includes a multiplier beam combiner 45, which combines the laser radiation from a last passage section 43 with the laser radiation from a last delay section 42 and forwards the combined laser radiation as a GHz laser pulse train to the beam selector 33.

[0110] FIG. 3 shows a schematic illustration of a second embodiment of the laser system 100.

[0111] Identical and functionally identical elements are always provided with identical reference signs in all of the figures, and so in this respect reference is made in each case to the preceding description.

[0112] The second embodiment in accordance with FIG. 3 differs from the first embodiment in accordance with FIG. 1 insofar as here the mode change device 30 is arranged downstream of the first preamplifier 50, here, for example, directly downstream of the first preamplifier 50 and directly upstream of the pulse selection device 60. Moreover, it is arranged upstream of the second preamplifier 70.

[0113] In the embodiments in accordance with FIGS. 1 and 3, the mode change device 30 is arranged in each case downstream of the pulse stretcher 20 and upstream of the pulse selection device 60. In this case, there is relatively much signal, but with the use of a slow pulse selection device 60 such as an acousto-optical modulator, for example, the problem arises that the GHz laser pulse trains generated by the high frequency laser pulse source 40 can be temporally shaped by the pulse selection device 60, giving rise to flat edges. This is not critical with GHz laser pulse trains of sufficient temporal length. Furthermore, it is not critical if a fast modulator such as an electro-optical modulator, for example, is used as the pulse selection device 60.

[0114] FIG. 4 shows a schematic illustration of a third embodiment of the laser system 100. In this case, the mode change device 30 is arranged upstream of the pulse stretcher 20, for example, directly upstream of the pulse stretcher 20. In this case, the high frequency laser pulse source 40, e.g., the repetition rate multiplier 47, can generate short pulses that may possibly have an excessively high peak pulse power, and so a small signal of the excitation laser 10 can be advantageously employed.

[0115] FIG. 5 shows a schematic illustration of a fourth embodiment of the laser system 100. In this case, the mode change device 30 is arranged downstream of the pulse selection device 60, for example, directly downstream of the pulse selection device 60, and, for example, directly upstream of the second preamplifier 70 in the light propagation direction. The arrangement downstream of the pulse selection device 60 has the advantage that a GHz laser pulse train having very steep edges, but in return less signal, can be generated from a single laser pulse.

[0116] Alternatively, it is also possible, in a manner not illustrated here, for the mode change device 30 to be arranged downstream of the second preamplifier 70, for example, directly downstream of the second preamplifier 70, e.g., upstream of the amplifier 80, for example, directly upstream of the amplifier 80.

[0117] FIG. 6 shows a schematic illustration of a fifth embodiment of the laser system 100. In this case, the high frequency laser pulse source 40 is configured as a laser diode 46, which can be configured for generating picosecond pulses. For example, the laser diode 46 can be configured to generate laser pulses with an individual pulse repetition rate in the GHz range. However, it is also possible to combine the laser diode 46 with a diode repetition rate multiplier assigned thereto.

[0118] In this embodiment, the beam switchover device 31, 33 can include only the beam selector 33, which is embodied as a beam changeover switch and which here can receive light on one hand from the excitation laser 10 and the pulse stretcher 20 and on the other hand from the laser diode 46—optionally combined with a diode repetition rate multiplier. This light is fed to a common further light path. In the latter there then follow, in a configuration, the first preamplifier 50, the pulse selection device 60, the second preamplifier 70, the amplifier 80, for example, the second pulse selection device 90, the pulse compressor 110, and if appropriate—optionally—the at least one nonlinear optical component 120, if appropriate in this or any other suitable order.

[0119] FIG. 7 shows a schematic illustration of a functional mode of the laser system 100.

[0120] In this case, here an instantaneous laser power P, for example, on the output side of the laser system 100 is plotted against time tin a diagram. In this case, an operating mode of the laser system 100 in the high-frequency functional position of the beam switchover device 31, 33 is illustrated at A. In this case, GHz laser pulse trains 140 are generated, where here a GHz individual pulse train 190 is illustrated by way of example here. The GHz individual pulse train 190 includes individual pulses 150 which succeed one another with an individual pulse repetition rate of at least 0.5 GHz within the GHz laser pulse train 140. In some examples, a plurality of such GHz laser pulse trains 140 can be generated as GHz pulse packets which in turn succeed one another with a GHz pulse packet repetition rate of more than one kHz, or else in the MHz range.

[0121] A first configuration of an operating mode of the laser system 100 in the low-frequency functional position of the beam switchover device 31, 33 is illustrated at B, where here at least one low-frequency laser pulse train 180 having individual laser pulses 160 with an individual pulse repetition rate of less than 0.5 GHz, for example, with an individual pulse repetition rate of a few kHz, or else in the MHz range, is generated as a low-frequency individual pulse train.

[0122] A second configuration of the operating mode of the laser system 100 in the low-frequency functional position is illustrated at C, where two low-frequency laser pulse trains 180, 180′ are illustrated, and where here the laser pulses 160 are combined to form low-frequency pulse packets 170, 170′, of which a first low-frequency pulse packet 170 and a second low-frequency pulse packet 170′ are illustrated here. An individual pulse repetition rate of the individual laser pulses within the low-frequency pulse packets 170, 170′ can be from at least 0.01 MHz to at most 100 MHz, or from at least 1 MHz to at most 90 MHz, or from at least 5 MHz to at most 15 MHz, or at most 10 MHz. The low-frequency pulse packets 170, 170′ can temporally succeed one another with a low-frequency pulse packet repetition rate of a few kHz, a few 10 kHz or a few 100 kHz.

[0123] A method for operating the laser system 100 can include: the beam switchover device 31 33 of the laser system 100 is optionally switched into the high-frequency functional position or into the low-frequency functional position to guide at least one GHz laser pulse train 140 with an individual pulse repetition rate of individual pulses 150 in the GHz laser pulse train 140 of at least 0.5 GHz from the high frequency laser pulse source 40 to a target position in the high-frequency functional position, and to guide at least one low-frequency laser pulse train 180, 180′ with an individual pulse repetition rate of less than 0.5 GHz from the excitation laser 10 to the target position in the low-frequency functional position.

[0124] In this respect, a laser system 100 can also include the high frequency laser pulse source 40, the excitation laser 10 and the beam switchover device 31, 33 and which is configured for carrying out such a method.

Other Embodiments

[0125] A number of embodiments of the present disclosure have been described. Nevertheless, it will be understood that various modifications may be made without departing from the spirit and scope of the present disclosure. Accordingly, other embodiments are within the scope of the following claims.