Device and method for controlling pulsed laser beam during laser shock peening

Abstract

The present application provides a device for pulsed laser beam control, which includes: (i) a diode pumped solid-state laser oscillator configured to generate and output a pulsed laser beam having predefined beam characteristics corresponding to a current setting selection of a controller; and (ii) an amplifier configured to amplify energy and modify the beam distribution of the pulsed laser beam. A beam detector is coupled to the generated laser beam to monitor the following combination: (i) the width of the pulsed laser beam; (ii) the diameter of the pulsed laser beam; and (iii) the energy level, and generates an error signal as a feedback signal to send back to the controller. The controller is configured with a current source to output a correction current to tune the DPSSL oscillator, wave plate and first polarizer to rotate the correction polarization angle and adjust the energy amplification or time distribution to within a defined performance tolerance.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims priority to U.S. Provisional Patent Application No. 62 / 987,172 filed on March 9, 2020, the entire contents of which are hereby incorporated by reference as if incorporated herein. Technical Field

[0003] The present application relates to a device and method for controlling a pulsed laser beam during laser shock peening, and belongs to the technical field of pulsed laser beam control. Background Art

[0004] Laser shock peening, also known as "laser peening" and "LSP", is an alternative or complementary method to traditional shot peening. It is a cold working method used to produce a deep (e.g., greater than 1 mm) residual compressive stress layer and change the mechanical properties of the material by impacting the material with sufficient force to cause it to plastically deform. The residual stress generated by laser peening increases the fatigue and stress resistance of the material, thereby significantly improving the service life of laser peened parts. Laser peening uses high-energy laser pulses to generate a plasma plume and cause a rapid increase in pressure on the surface of the part. The pressure generates and maintains a high-intensity shock wave that propagates to the surface of the part. The shock wave generated by laser peening causes cold working of the microstructure of the part and helps to improve the performance of the part.

[0005] When the shock wave propagates into the part, some of the energy in the wave is absorbed during plastic deformation of the part material. This is also known as cold working. Laser peening typically uses laser pulse widths of about 8 nanoseconds (ns) to about 40 ns. In laser peening, a commonly used spot diameter of the laser beam is about 1.0 mm to about 8.0 mm.

[0006] Laser pulse width is usually defined by the pulse width, which is measured at half the peak intensity of the pulse. For Gaussian-shaped pulses, the pulse energy is approximated as the integral of the area under the pulse (i.e., the change in power over time). Therefore, for a fixed energy output, a narrower pulse width laser beam with a sharper rise time at the leading edge of the pulse can provide higher impact pressure on the surface of the component in laser shot peening. Summary of the invention

[0007] In one aspect, an apparatus for pulsed laser beam control is provided, the apparatus comprising: a diode pumped solid-state laser (DPSSL) oscillator configured to generate and output a pulsed laser beam having predefined beam characteristics corresponding to a current setting selection of a controller, wherein the controller, in response to the current setting selection, controls a current source to output a current to tune the DPSSL oscillator to generate a first beam having a pulse width within a defined tolerance, a first energy, a first spatial distribution, and a first temporal distribution; and an optical filter configured to modify a received modified first beam having a modified pulse width (PW2) using a second temporal distribution. A beam to output a second beam with a second energy, a second spatial distribution and a second temporal distribution; and a multi-stage amplifier configured to output an output beam after beam energy amplification and beam distribution modification, the multi-stage amplifier comprising: a first-stage amplifier configured to amplify and modify the second beam to output a third beam with a third energy and a third temporal distribution; and a second-stage amplifier configured to amplify and modify the third beam to output a fourth beam with a fourth energy and a fourth temporal distribution, wherein the fourth beam substantially maintains the pulse width (PW1) or the modified pulse width (PW2) within the defined tolerance.

[0008] On the other hand, a method for pulsed laser beam control is provided, the method comprising: generating and outputting a pulsed laser beam having predefined beam characteristics corresponding to a current setting selection of a controller by a diode pumped solid-state laser (DPSSL) oscillator; in response to the current setting selection, the controller controlling a current source to output a current to tune the DPSSL oscillator to produce a first beam (PW1) having a pulse width within a defined tolerance, a first energy, a first spatial distribution, and a first temporal distribution; modifying, through a filter, receiving the modified first beam having a modified pulse width (PW2) having a second temporal distribution to output a second beam A beam having a second energy, a second spatial distribution, and a second time distribution, and amplifying the beam energy and modifying the beam distribution through a multi-stage amplifier to output an output beam; the multi-stage amplifier amplifying the beam energy and modifying the beam distribution includes: amplifying and modifying the second beam through a first-stage amplifier to output a third beam having a third energy and a third time distribution; and amplifying and modifying the third beam through a second-stage amplifier to output a fourth beam having a fourth energy and a fourth time distribution, wherein the fourth beam substantially maintains the pulse width (PW1) or the modified pulse width (PW2) within the defined tolerance. BRIEF DESCRIPTION OF THE DRAWINGS

[0009] The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate various exemplary systems and are used only to illustrate various exemplary aspects. In the drawings, the same elements have the same reference numerals.

[0010] Figure 1A It is a schematic diagram of a device for generating and adjusting a pulsed laser beam for laser shot peening.

[0011] Figure 1B An example method of pulsed laser beam generation and conditioning for laser peening of a target component is provided.

[0012] Figure 2 is a schematic diagram of an example diode pumped solid-state laser (DPSSL) oscillator.

[0013] Figure 3 is a graph of an example output of a DPSSL oscillator.

[0014] Figure 4 is a graph describing the variable pulse width current and attenuation characteristics of a DPSSL oscillator.

[0015] Figure 5 is a graph describing the variable pulse width current and power characteristics of a DPSSL oscillator.

[0016] Figure 6 is a graph of example time modifications to the laser beam.

[0017] Figure 7 is a schematic diagram of an example filter.

[0018] Figure 8 is a graph of example spatial distribution modifications to the laser beam.

[0019] Fig. 9 is a schematic diagram of an example amplifier.

[0020] Fig.10 is a schematic diagram of an example beam delivery apparatus and laser peening unit. DETAILED DESCRIPTION

[0021] Figure 1A An example apparatus 100 for laser peening is shown. The apparatus 100 is operable to generate a pulsed laser beam and output it to a target component 101 for laser peening the target component 101.

[0022] The apparatus 100 for generating a pulsed laser beam may include a DPSSL oscillator 102 configured to generate and output a pulsed laser beam having predefined beam characteristics corresponding to a current setting selection (e.g., based on a lookup table LUT 141) of a controller 140, wherein the controller 140, in response to the current setting selection, controls a current source 142 to output a current 143 (or a correction current) to tune the DPSSL oscillator 102 to generate a pulse having a pulse width PW1 within a defined tolerance (e.g., 12-30 nanoseconds), a first energy, a first spatial distribution (substantially Gaussian, see Figure 3 and 6 ) and the first light beam 108 of the first temporal distribution. The filter 112 can be arranged after the DPSSL oscillator 102 to modify the received modified first light beam 110 with the modified pulse width with the second temporal distribution to output a light beam with the second energy, the second spatial distribution (flat top shape, see Figure 8 ) and a second light beam 118 with a second time distribution. The multi-stage amplifier 106 is configured to output an outgoing light beam 126 after beam energy amplification and beam profile modification. The multi-stage amplifier 106 may include at least a first stage amplifier 901 (see Fig. 9 ), configured to amplify and modify the second light beam 118 to output a third light beam 915 having a third energy and a third time distribution; and a second stage amplifier 902, configured to amplify and modify the third light beam 915 to output a fourth light beam 941 having a fourth energy and a fourth time distribution, wherein the fourth light beam 941 substantially maintains a pulse width (PW1) or a modified pulse width (PW2) within a defined tolerance.

[0023] The apparatus 100 may further include a first optical isolator 114 and a second optical isolator 120, a first pair of wave plates 116 and a first polarizer 115, and a second pair of Pockels cells 104 and a second polarizer 117, a beam delivery device 122, and a laser peening unit 124. The second optical isolator 120 may deliver the modified amplified light beam 126 from the amplifier 106 to the beam delivery device 122, and the beam delivery device 122 may deliver the modified amplified light beam 126 to the laser peening unit 124. The wave plate 116 may be a half-wave plate or a quarter-wave plate as required by the application.

[0024] A first pair of wave plates 116 and a first polarizer 115 can be disposed at the output end of the DPSSL oscillator 102, wherein the first pair of wave plates 116 and the first polarizer 115 can be configured to rotate a certain amount of polarization angle relative to the first light beam 108 to attenuate the first energy of the first light beam 108 to generate an attenuated first light beam 109 that does not exceed the defined first energy level, which is safe for the system. The attenuated first light beam 109 does not exceed the defined polarization angle. Therefore, the attenuated first light beam 109 can retain most of the beam characteristics, such as the pulse width (PW1), beam diameter d1, and time distribution of the first light beam 108.

[0025] A second pair of Pockels cells 104 and a second polarizer 117 may be disposed between the first pair of wave plates 116 and the first polarizer 115, and further include an optical filter 112, wherein the second pair of Pockels cells 104 and the second polarizer 117 may be configured to perform nanosecond duration switching on the first light beam 108 or the attenuated first light beam 109 from the first polarizer 115 by allowing or preventing the first light beam 108 or the attenuated first light beam 109 from leaving the Pockels cell 104, wherein the output light beam is a modified first light beam having a modified pulse width (PW2) and a second time distribution.

[0026] In one embodiment, the Pockels cell 104 may include a crystalline material containing one of barium borate (BBO) or potassium dideuterium phosphate (KD*P). In the case where the Pockels cell 104 includes a crystalline material containing KD*P, the Pockels cell 104 may also be configured to perform pulse slicing of the leading edge 656 of the first light beam 108 or the attenuated first light beam 109 (see Figure 6 ) (alternatingly pulse slicing the leading edge 656 and the trailing edge 660) to output a modified first light beam 110 having a modified pulse width 662 (PW2, see Figure 6 ), and having a second time distribution.

[0027] In one embodiment (see Figure 7-8 ), the first light beam 108 output from the DPSSL oscillator 102 may have a first diameter d1 and a wing (878), and the filter 112 may include: a beam expander 766 configured to expand the first light beam 108 or the modified first light beam 110 to a diameter d2 greater than the first diameter d1; and a tracer 768 configured to receive the expanded first light beam or the expanded modified first light beam 770 from the beam expander 766 to remove the wing 878 to output a second light beam 118 having a second spatial distribution, the second light beam 118 having a flat top 881 without the wing 878.

[0028] In one embodiment, the multi-stage amplifier 106 may further include: a third-stage amplifier 903, configured to amplify and modify the fourth light beam 941 to output a fifth light beam 959 having a fifth energy and a fifth time distribution; and a fourth-stage amplifier 904, configured to amplify and modify the fifth light beam 959 to output a sixth light beam or an output light beam 126 having a sixth energy and a sixth time distribution.

[0029] In one embodiment (see Fig.10 ), the outgoing beam 126 from the multi-stage amplifier 106 to the beam delivery device 122 can have a near-field value and a measurement value, and the laser beam delivery device 122 can include a vacuum relay imaging module (VRIM) 1091, which is configured to maintain the near-field value and the measurement value of the outgoing beam 126 and deliver the outgoing beam 126 to the target component 101.

[0030] The apparatus 100 may include a feedback mechanism for monitoring beam characteristics to detect beam stability (e.g., pulse width, beam diameter, energy level, etc.), and adjusting certain beam settings (e.g., current settings, wave plate and polarizer rotation angles, Pockels cell bias voltages, amplifier gain, etc.) to ensure that the pulsed laser beam operates within a specified performance matrix. In one embodiment, a beam detector 130 (including a photodetector and a high-speed oscilloscope 131) may be coupled to one or a combination of the first polarizer 115 and the second polarizer 117 and the beam delivery device 122 disposed after the multi-stage amplifier 106 for monitoring one or a combination of the beam pulse width, beam diameter, and energy level.

[0031] The beam detector 130 may generate an error signal 128 from the monitoring process, which is sent back to the controller 140 as a feedback signal. If the magnitude of the error signal 128 exceeds the defined error range, the error signal 128 may cause the controller 140 to perform one or a combination of the following: configure the current source 142 to output a correction current 143 to tune the DPSSL oscillator 102 to cancel the error signal of the pulse width until the pulse width (PW1) remains within a defined tolerance according to the current setting; configure the first pair of wave plates 116 and the first polarizer 115 to rotate a certain amount of the correction polarization angle 144 relative to the first beam 108 to increase or decrease the attenuation of the first energy of the first beam 108 so as to remain within a defined first energy level; configure the Pockels cell 104 to be turned on or off, or adjust the modified pulse width (PW2) by a certain amount 145 to remain within a defined tolerance; and configure the multi-stage amplifier 106 through the correction gain signal 146 to adjust one or a combination of beam energy amplification and beam profile modification to remain within a defined output energy level and a defined beam profile.

[0032] In one embodiment, the device 100 may include a first isolator 114 disposed between the DPSSL oscillator 102 and the wave plate 116, and a second isolator 120 disposed between the multi-stage amplifier 106 and the beam delivery device 122, wherein the first isolator 114 and the second isolator 120 can prevent the light beam from being reflected in the opposite direction.

[0033] Figure 1B An example method 160 for generating and adjusting a pulsed laser beam for laser peening a target component by the apparatus 100 is shown. The method 160 includes using a controller 140, which may be a general purpose controller having at least one processor (PROC 148) that executes algorithmic code stored in a memory (MEM 147) to perform operations on a current source 142, a wave plate 116, a Pockels cell 104, and a multi-stage amplifier 106 (see Figure 1A ) or a combination thereof to perform the aforementioned functions in device 100.

[0034] The method 160 may include step 162, in which the DPSSL oscillator 102 in the apparatus 100 generates a pulsed laser beam having predefined beam characteristics corresponding to a current setting selection stored in the controller 140 (e.g., from the lookup table LUT 141). In response to the current setting selection, the controller 140 may control the current source 142 to output a current 143 (or a correction current) to tune the DPSSL oscillator 102 to produce a first beam 108 having a pulse width (PW1) within a defined tolerance, a first energy, a first spatial distribution, and a first temporal distribution.

[0035] In step 170, the filter 112 after the DPSSL oscillator 102 may be configured to modify the received modified first light beam 110 with the modified pulse width (PW2) and the second temporal distribution to output a second energy, a second spatial distribution (flat top shape, see Figure 8 ), a second light beam 118 with a second time distribution.

[0036] In step 172, the multi-stage amplifier 106 can perform beam amplification and beam profile modification to output an output beam 126, the amplification and modification including: amplifying and modifying the second beam 118 by the first stage 901 to output a third beam 915 having a third energy and a third time profile; amplifying and modifying the third beam 915 by the second stage 902 to output a fourth beam 941 (which can be the output beam 126) having a fourth energy and a fourth time profile, wherein the fourth beam 941 substantially maintains the pulse width (PW1) or the modified pulse width (PW2) within a defined tolerance. In one embodiment, step 172 can include performing further energy amplification and beam time profile modification by additional amplifiers. For example, the multi-stage amplifier 106 may also include: a third-stage amplifier 903, configured to amplify and modify the fourth light beam 941 to output a fifth light beam 959 having a fifth energy and a fifth time distribution; and a fourth-stage amplifier 904, configured to amplify and modify the fifth light beam 959 to output a sixth light beam having a sixth energy and a sixth time distribution as an output light beam 126.

[0037] In step 174, the outgoing beam 126 can be delivered by the beam delivery device 122 to the target component 101 for performing laser peening. Fig.10 ), the outgoing beam 126 from the multi-stage amplifier 106 to the beam delivery device 122 can have a near-field value and a measurement value, and the beam delivery device 122 can include a VRIM 1091, which is configured to maintain the near-field value and the measurement value of the outgoing beam 126 and transmit the outgoing beam 126 to the target component 101.

[0038] In one embodiment, the method 160 may include an additional step 164, wherein the first pair of wave plates 116 and the first polarizer 115 may be disposed at the output of the DPSSL oscillator 102, wherein the first pair of wave plates 116 and the first polarizer 115 may be configured to attenuate the first energy of the first beam 108 by a certain amount of polarization angle relative to the rotation of the first beam 108, so as to generate an attenuated first beam 109 that does not exceed a defined first energy level, which is safe for the system. Therefore, the attenuated first beam 109 may retain most of the beam characteristics of the first beam 108, such as pulse width (PW1), beam diameter d1, and time distribution.

[0039] In one embodiment, method 160 may include an additional step 166, wherein a second pair of Pockels cells 104 and a second polarizer 117 may be disposed between the first pair of wave plates 116 and the first polarizer 115, and further comprising an optical filter 112, wherein the second pair of Pockels cells 104 and the second polarizer 117 may be configured to perform nanosecond duration switching on the first light beam 108 or the attenuated first light beam 109 from the first polarizer 115 by allowing or preventing the first light beam 108 or the attenuated first light beam 109 from leaving the Pockels cell 104, wherein the output light beam is a modified first light beam having a modified pulse width (PW2) and a second time distribution.

[0040] In one embodiment, the method 160 may include performing an additional step 168 of pulse slicing the leading edge of the attenuated first light beam 109. The Pockels cell 104 may include a crystalline material containing one of: BBO or KD*P. In the case where the Pockels cell 104 includes a crystalline material containing KD*P, the Pockels cell 104 may also be configured to perform pulse slicing on at least one wing 678 of the leading edge 656 of the first light beam 108 or the attenuated first light beam 109 (see Figure 6 ) (alternatingly pulse slicing the leading edge 656 and the trailing edge 660) or pulse slicing at least one wing portion 678 of the first light beam 108 or the attenuated first light beam 109 to output a modified pulse width 662 (PW2, see Figure 6 ) and a modified first light beam 110 having a second temporal distribution.

[0041] In one embodiment, the method 160 may include implementing a feedback mechanism in one or more combinations of steps 165, 169, and 175 for monitoring beam characteristics to detect beam stability (e.g., beam pulse width, beam diameter, energy level, etc.) and adjusting certain beam settings (e.g., current settings, wave plate and polarizer rotation angles, Pockels cell bias voltages, amplifier gain, etc.) to ensure that the pulsed laser beam operates within a specified performance matrix. In one embodiment, a beam detector 130 (including: a photodetector and a high-speed oscilloscope 131) may be coupled to one or a combination of the first polarizer 115, the second polarizer 117, and the beam delivery device 122 disposed after the multi-stage amplifier 106 for monitoring one or a combination of the beam pulse width, beam diameter, and energy level.

[0042] The beam detector 130 can generate an error signal 128 from the monitoring, which is sent back to the controller 140 as a feedback signal. If the magnitude of the error signal 128 exceeds the defined error range, the error signal 128 can cause the controller 140 to perform one or a combination of the following: configure the current source 142 to output a correction current 143 to tune the DPSSL oscillator 102 to offset the error signal of the pulse width until the pulse width (PW1) remains within the defined tolerance according to the current setting; configure the first pair of wave plates 116 and the first polarizer 115 to rotate a certain amount of the correction polarization angle 144 relative to the first beam 108 to increase or decrease the attenuation of the first energy of the first beam 108 so as to remain within the defined first energy level; configure the Pockels cell 104 to be turned on or off, or adjust the modified pulse width (PW2) by a certain amount 145 to remain within the defined tolerance; and configure the multi-stage amplifier 106 through the correction gain signal 146 to adjust one or a combination of beam energy amplification and beam profile modification to maintain it within the defined output energy level and the defined beam profile.

[0043] The method 160 may include providing a first isolator 114 between the DPSSL oscillator 102 and the wave plate 116, and providing a second isolator 120 between the multi-stage amplifier 106 and the beam delivery device 122 to prevent the beam from being reflected in the opposite direction.

[0044] refer to Figure 2 , a schematic diagram of a DPSSL oscillator 102 is shown. The DPSSL oscillator 102 may include an optical cavity 228, a gain medium 230 within the optical cavity 228, and a laser diode array 232, the laser diode array 232 pumping the gain medium 230 with light and energy 233 to generate a pulsed laser first beam 108. The oscillator 102 may also include a seed injector 234, and a variable aperture / limiting aperture 238, the seed injector 234 being configured to output a seed laser beam 236 into the optical cavity 228 to help stabilize the first beam 108.

[0045] The gain medium 230 can be a laser rod with a diameter of 2 mm (Nd:YLF) and can be a solid gain medium that can be optically pumped by one or more laser diodes (i.e., a diode array) 232. The gain medium 230 can be a single crystal or glass material and can be doped with trivalent rare earth ions or transition metal ions. In one aspect, the laser rod 230 used in the oscillator 102 can be doped with neodymium (Nd 3+ The gain medium 230 may be a synthetic yttrium aluminum garnet crystal (Y 3 Al 5 O 12), also known as "YAG". On the other hand, the gain medium 230 can be a synthetic yttrium lithium fluoride (YLiF) doped with neodymium (Nd:YLF). 4 ) crystal, or "YLF". The first beam 108 generated by the (Nd:YLF) laser rod 230 can have a wavelength of 1053 nm. The YLF crystal can generate a laser beam with better beam quality, has a longer lifetime, and allows for the extraction of longer beam pulse widths, which can allow for a smaller design of the device 100. Both YAG and YLF crystals can be grown using known methods, such as the Czochralski method. The crystals can be grown into a variety of geometries and configurations in order to vary factors of the gain medium, such as gain and energy storage.

[0046] The laser diode array 232 can pump the gain medium 230 with light energy 233 for amplification of the gain medium 230. In one aspect, the laser diode array 232 includes an array of 9 diode bars to pump the gain medium 230 to generate a 10 mJ (millijoule) laser output 108. For example, the laser diode array 232 can have a QCW (quasi-continuous wave) power output of about 6000 W and operate at a current of about 15 A with an electro-optical efficiency of about 57%. For example, the laser diode array 232 can have an operating voltage of about 60 V. In one aspect, the laser diode array 232 emits electromagnetic radiation having a wavelength of about 805.5 ± 2 nm; in another aspect, the laser diode array 232 emits electromagnetic radiation having a wavelength between about 750 nm and about 900 nm. A universal controller (UCC) 242 can be used to control the pumping of the gain medium 230 by the laser diodes 232. Specifically, the UCC 242 can control the timing of the laser diode 232 so that the laser diode 232 only pumps the gain medium 230 when the first light beam 108 passes through the gain medium 230 to optimize the gain and amplification of the first light beam 108 .

[0047] The oscillator 102 may also include a modulator 240 (i.e., a Q switch) configured to generate a pulsed laser beam 108. In one aspect, the Q switch 240 is used to generate the first beam 108 with a pulse width in the nanosecond range. The UCC 242 for the device 100 can feed a trigger signal 243 to the Q switch 240 to control the generation and generation frequency of the first beam 108. In one aspect, a repetition rate of about 20 Hz is used for pulse generation for laser peening applications. In another aspect, a repetition rate between about 25 Hz and about 30 Hz is used to generate pulses. In another aspect, a repetition rate of about 50 Hz or more is used to generate pulses. The repetition rate can be changed and selected by the user so that a repetition rate slower than the 20 Hz base rate can be used. For example, repetition rates of 20 Hz, 19 Hz, 18 Hz, 17 Hz, 16 Hz, 15 Hz, 14 Hz, 13 Hz, 12 Hz, 11 Hz, 10 Hz, 9 Hz, 8 Hz, 7 Hz, 6 Hz, 5 Hz, 4 Hz, 3 Hz, 2 Hz, and 1 Hz are considered. For the Q-switched optical cavity 228 on the oscillator 102 described herein, repetition frequencies of, for example, 20 Hz, 10 Hz, 6.67 Hz, 5 Hz, 4 Hz, 3.33 Hz, 2.857 Hz, 2.5 Hz, 2.22 Hz, 2 Hz, and 1 Hz may be considered. These example frequencies are created by selecting each pulse to achieve a frequency of 20 Hz, selecting each second pulse to achieve a frequency of 10 Hz, selecting each third pulse to achieve a frequency of 6.67 Hz, and so on.

[0048] like Figure 2 As shown, the optical cavity 228 may further include a first reflector 244 and a second reflector 246. When the light beam 108 is output from the oscillator 102, the reflectors 244 and 246 reflect the coherent light emitted by the gain medium 230 in the optical cavity 228 to amplify the light beam 108. The piezoelectric converter 248 may be mounted to the second reflector 246.

[0049] The seed injector 234 can be configured to output a seed laser beam 236 into the optical cavity 228 to help stabilize the first light beam 108. The seed injector 234 can be a single longitudinal mode (SLM) fiber laser that injects the seed laser beam 236 into the optical cavity 228 to generate a single longitudinal mode first light beam 108 in the optical cavity 228.

[0050] The seed injector 234 may include a seed controller 252. The seed controller 252 may interface with the UCC controller 242 of the apparatus 100 for controlling a seed reset function. The seed controller 252 may also be used to control the position of the PZT 248, thereby controlling the position of the second reflector 246. A feedback line 254 connects the PZT 248 to the seed controller 252. An output line 256 connects the seed controller 252 to the PZT 248.

[0051] In use, a seed reset signal and a PZT control signal may be sent from the seed controller 252 via the output line 256 to control the position of the PZT 248. The PZT 248 outputs a voltage to the feedback line 254 based on its position, which corresponds to its current position and the current position of the second reflector 246. The seed controller 252 may adjust the position of the second reflector 246 to control the phase shift of the first light beam 108 within the optical cavity 228 and maintain a desired phase of the first light beam 108 relative to a single longitudinal mode (SLM). In other words, the seed controller 252 may control the position of the PZT 248 and the second reflector 246 to maintain the first light beam 108 in the SLM.

[0052] The PZT 248 has a starting position. The starting position of the PZT 248 occurs during startup of the device 100 and after a seed reset signal is sent from the seed controller 252 to the PZT 248. As the oscillator 102 generates and outputs the beam 108, the PZT continuously adjusts and moves to a new position away from its starting position to keep the subsequent beam 108 in the SLM. The seed controller 252 can store a reference voltage corresponding to the position of the PZT 248 that can generate the SLM first beam 108. The reference voltage is compared with a voltage from the PZT 248, which corresponds to the current position of the PZT 248 relative to the starting position. If the difference in the comparison value falls outside a predetermined range, the seed controller 252 can send a PZT control signal via the output line 256 to adjust the position of the PZT 248 and the second mirror 246. After a period of time, the PZT 248 will reach a limit of movement, after which the PZT 248 will no longer move to adjust the position of the second mirror 246. At this point, the seed controller 252 performs a "seed reset" to return the PZT 248 to its starting position. The seed controller 252 sends a reset signal to the PZT 248 via output line 256, and upon receiving the seed reset signal, the PZT 248 moves from its current position to the starting position.

[0053] The seed controller 252 may also be used to control when a reset of the PZT 248 is performed. One problem with the seed may be that a reset of the PZT 248 may occur automatically and may occur during a full system laser shot. Manual control of the seed may be modified and integrated into the seed controller 252 and the UCC controller 242 in order to anticipate the need for a seed reset and perform a seed reset when appropriate.

[0054] like Figure 2As shown, the oscillator 102 may also include a variable iris / limiting aperture 238. The variable iris 238 may include an aperture opening to allow the laser beam 108 to pass through before the laser beam 108 is output from the oscillator 102. The size of the aperture on the variable iris 238 may adjust the amount of the light beam 108 output from the oscillator 102. The light beam 108 passes through the variable iris 238 to generate a TEMoo single transverse mode light beam.

[0055] As described herein, "single transverse mode" (STM) means that the oscillator 102 operates in a single transverse resonator mode, typically a Gaussian mode, such that the quality of the laser beam 108 is diffraction limited, such that the beam 108 can be focused to a very small spot. Here, the transverse resonator mode will be a transverse electromagnetic mode (TEM) mode, such that there is neither a magnetic field nor an electric field in the direction of beam propagation. "Single longitudinal mode" (SLM) refers to a longitudinal beam of a single frequency and a single wavelength. The main sources of noise in the laser system can be fluctuations in the pump source 232, changes in the length of the optical cavity 228, or the alignment of the optical cavity 228. By limiting the beam 108 output from the oscillator 102 to STM and SLM, noise in the beam 108 can be eliminated. Therefore, the oscillator 102 is operable to output a pulsed laser beam 108 in STM and SLM modes.

[0056] Beam uniformity is a beam distribution measurement that represents the normalized RMS (root mean square) deviation of the energy density at or above the central 90% of the beam 108 from its mean. Data outside the central 90% is not included in the RMS calculation. In one aspect, the beam uniformity of the pulsed laser beam 108 output from the oscillator 102 is less than about 0.2.

[0057] The beam quality is determined by M 2 The value is given and is called the beam quality factor. 2 The numerical value is used to quantify the degree of variation between the actual beam 108 and the ideal beam. For a single transverse mode, TEM oo Gaussian laser beam, M 2 is exactly 1.0. On the one hand, the oscillator 102 outputs M 2 The value of the light beam 108 is about 1.2 or less. On the other hand, the oscillator 102 outputs M 2 The value of the beam 108 is less than about 1.3. On the other hand, the oscillator 102 outputs M 2 The SLM beam 108 may have a spectral width of about 1 pm. The modifier "substantially" is used multiple times herein. Whether explicit or not, the terms "single transverse mode" and "single longitudinal mode" should be understood as "substantially a single transverse mode" and "substantially a single longitudinal mode", with reference to M. 2 Such deviations from the ideal value are readily understood by those skilled in the art.

[0058] In addition to the output beams in STM and SLM modes, the pulsed laser beam 108 output from the oscillator 102 can have a first energy of about 10 mJ to about 20 mJ, have a first beam diameter of up to about 4 mm in diameter, have a first temporal distribution (e.g., a Gaussian shape), and have a first spatial distribution (e.g., a Gaussian shape).

[0059] Reference Figure 1A , the modulator 104 may receive the pulsed laser beam 108 from the oscillator 102. The modulator 104 may be a pulse shearer for sharpening the leading edge and / or trailing edge of the pulsed laser beam 108 to modify the temporal distribution of the pulsed laser beam 108, and outputting a modified beam 110 having a second energy, a first diameter, a second temporal distribution, and a first spatial distribution.

[0060] In one aspect, the pulse shearer 104 is an SBS unit for changing the temporal distribution of the laser beam 108. In another aspect, the pulse shearer 104 is a Pockels cell for changing the temporal distribution of the laser beam 108.

[0061] The modulator 104 may include a crystal material, such as BBO or KD*P, through which the pulsed laser beam 108 passes. In one aspect, the pulse shearer 104 includes a BBO material to provide faster pulse slicing of the beam 108. In one aspect, the pulse shearer 104 modifies the leading edge of the laser pulse 108. In another aspect, the pulse shearer 104 modifies the leading edge and the trailing edge of the laser pulse 108. The pulsed laser beam 108 may be sliced ​​and output as a modified beam 110 having a rise time less than about 5 ns. In one aspect, the rise time of the modified beam 110 is less than 3 ns. In another aspect, the rise time of the modified beam 110 is less than about 2 ns. In one aspect, the pulse width of the beam 108 is adjusted to between about 5 ns and 16 ns to be output as the modified beam 110. In another aspect, the pulse width of the beam 108 is adjusted to between about 8 ns and 16 ns to be output as the modified beam 110. In another aspect, the pulse width of the modified beam 110 is less than or equal to about 5 ns. A short rise time provides a laser beam that produces better laser shock peening results.

[0062] Figure 3 An example of a temporal distribution of the first light beam 108 is shown as a normal output from the DPSSL oscillator 102. The first light beam 108 shows a Gaussian-shaped temporal distribution, which may be output from the oscillator 102 between seed resetting operations without having a substantial effect on the first light beam 108.

[0063] Figure 4Current settings and wave plate 116 rotation settings are shown over different pulse width ranges. Figure 5 A measured graph showing the relationship of energy and power (before amplification) over a range of different pulse widths is shown. Figure 4 and 5 A graph of the curve can be stored in a lookup table (LUT141) which can be used for programmable settings and can be used as reference data to compare with the measurement values ​​detected by the beam detector 130 to generate an error signal 128 for a feedback mechanism.

[0064] For example, Figure 4 A relatively rapid change in pulse width modulation is shown between the current range from 85 to about 68 amps. Below 68 amps, the change is more moderate. Figure 5 It is shown that the first beam 108 can reach an energy peak at a pulse width of about 17-18 nanoseconds. Figure 4 and 5 In the embodiment, the rotation of the wave plate 116 can present a relatively linear region with the smallest attenuation change within the pulse width range of 13-18 nanoseconds, and the energy decay is faster when the pulse width exceeds 18 nanoseconds.

[0065] Reference Figure 6 , showing a time profile 600 of a modified beam 110. As described above, as shown in the figure, the time profile of the pulsed laser first beam 108 output from the oscillator 102 is substantially Gaussian in appearance. When the first beam 108 is modified into the modified first beam 110 by the Pockels cell 104 including the KD*P crystal, the leading edge 656 can be cut off by the Pockels cell 104 including the KD*P crystal to produce a sharper leading edge 658 of the laser pulse. The sharp leading edge 658 of the laser pulse can provide a faster rise time for the modified first beam 110. The trailing edge 660 of the laser pulse can also be cut off by the Pockels cell 104 including the KD*P crystal to change the pulse width 662 of the modified first beam 110.

[0066] Reference Figure 1A, the modified first light beam 110 can be output from the Pockels cell 104 containing the KD*P crystal and pass through the optical isolator 120. In one aspect, the optical isolator 120 is a Faraday isolator that transmits the modified first light beam 110 in a forward direction while blocking light in the opposite direction, such as reflected laser energy from optical surfaces of components in the device 100 or from the target component 101. The optical isolator 120 can be used to protect the oscillator 102 and the Pockels cell 104 containing the KD*P crystal from the interaction between the modified light beam 110 and other components in the device 100 to limit and prevent back reflections, that is, to prevent and limit light reflected from other components from passing back through the optical isolator 120 and damaging the oscillator 102 and the KD*P crystal contained in the Pockels cell 104. In one aspect, the Faraday isolator 120 is configured to pass the modified first light beam 110 having a first beam diameter d1 of up to about 4 mm.

[0067] The wave plate 116 can be, for example, a half-wave plate (λ / 2 plate) for rotating the polarization state of a linearly polarized laser pulse, such as the first light beam 108. When the laser pulse interacts with the optical components of the device 100, the polarization state of the laser pulse may change. The wave plate 116 can be used to fine-tune the device 100 by rotating the polarization state of the first polarizer 115 and the first light beam 108 to optimize the pulse energy transmission through the device 100. The rotation of the first pair of wave plates 116 and the first polarizer 115 can output an attenuated first light beam 109 having an optimal energy level for amplification. In another embodiment, additional wave plates can be added to the device 100 to optimize the transmission of laser pulses through the optical components in the device 100. The additional wave plates used can be combined with Figure 1A The wave plates 116 shown are identical, or they may be different. For example, such different wave plates may be quarter wave plates (λ / 4 plates).

[0068] The filter 112 can receive the modified first light beam 110 from the second polarizer 117 arranged after the wave plate 116, and the filter 112 can further modify the modified first light beam 110 from having second energy, second time distribution and first spatial distribution to a second light beam 118 having second energy, second time distribution and second spatial distribution, and output the second light beam 118.

[0069] Reference Figure 7, shows a schematic diagram of an exemplary optical filter 112, which may include a beam expander 766 and a beam shaping element 768. The beam expander 766 may be used to increase the diameter of the modified first beam 110 to be greater than the first diameter d1 of the first beam 108 generated by the oscillator. By increasing the diameter d1 of the modified first beam 110 with the beam expander 766, the expanded modified first beam 770 may overflow the hole 772 on the beam shaping element 768. In one aspect, the beam shaping element 768 is an apodizer. The apodizer 768 may include an hole 772 having a sandblasted or serrated edge 774. By expanding the modified first beam 110 with the beam expander 766, and the expanded modified first beam 770 overflowing the apodizer 768, the wings of the expanded modified first beam 770 may be removed to further improve the modified first beam 110 having the first spatial distribution to the second beam 118 having a second spatial distribution with a more flat top, top hat appearance. Other beam shaping devices may be used for the beam shaping element 768. In one aspect, a pi shaper manufactured by Adioptica Optical Systems GmbH of Berlin, Germany Used as a beam shaping element 768 to produce a flat-top (or pi-shaped) second beam 118.

[0070] Reference Figure 8 , shows an exemplary spatial distribution 800 of the second light beam 118. Figure 1A As shown in Figure 1A The pulsed laser beam 108 and the modified first beam 110 shown in FIG. 1 can both have a substantially Figure 8 The first spatial distribution of Gaussian is shown. The beam shaping element can be used to produce a substantially top-hat shaped flat top beam from the beam center portion 876. After removing the wings 878, when the second beam 118 having the flat top center portion 876 passes through the amplifier, the circular portion 880 of the substantially top-hat shaped flat top beam can continue to flatten, as approximated by the dashed line 881.

[0071] Reference Figure 1A , a second light beam 118 having a second energy, a second time distribution, and a second spatial distribution can be output from the filter 112 and input to the multi-stage amplifier 106 to amplify the second light beam 118. The amplifier 106 can output an amplified and modified output light beam 126. On the one hand, the pulsed laser first light beam 108 output from the oscillator 102 has a first energy, a first beam diameter d1, a first time distribution, and a first spatial distribution. At the same time, the modified and amplified output light beam 126 output from the multi-stage amplifier 106 has an energy greater than the first energy, a beam diameter d2 greater than the first beam diameter d1, a time distribution different from the first time distribution, and a spatial distribution different from the first spatial distribution.

[0072] refer to Fig. 9 , shows an exemplary multi-stage amplifier 106. Fig. 9 As shown, the amplifier 106 has four amplifier stages 901, 902, 903, and 904. As shown here, the second light beam 118 can enter the first amplifier stage 901, and the modified and amplified output light beam 126 can be output from the fourth amplifier stage 904.

[0073] The second light beam 118 may be input into an input 905 on the first amplifier stage amplifier 901 and pass through an optical isolator 907. From the optical isolator 907, the second light beam 118 may further pass through a VRIM 909, which focuses the second light beam 118 and then re-collimates the second light beam 118 to an increased diameter d3 before outputting a collimated light beam 911 to an amplifier module 913. The amplifier module 913 may amplify the collimated light beam 191 and output an amplified third light beam 915 to the first amplifier stage amplifier output 917.

[0074] The optical isolator 907 can function similarly to the optical isolators 114 or 120 described above. The optical isolator 907 can be a Faraday isolator that transmits the second light beam 118 in the forward direction while blocking backscattered light and other reverse energy from the second light beam 118. In one aspect, the optical isolator 907 is used to protect the above-mentioned components of the device 100 from the reverse energy from the second light beam 118 after the second light beam 118 passes through the optical isolator 907. The optical isolator 907 can provide a passage for the second light beam 118 with a beam diameter of up to about 8 mm.

[0075] The second light beam 118 may pass through the isolator 907 and be input to the VRIM 909. The VRIM 909 may focus and recollimate the second light beam 118 and output a collimated light beam 911. The VRIM 909 may include a first lens 921, a vacuum tube 923, and a second lens 925. The second light beam 118 enters the VRIM 909 and passes through the first lens 921, which focuses the second light beam 118 near the center of the inside of the vacuum tube 923 and passes through. When the second light beam 118 leaves the vacuum tube 923, the second light beam 118 is recollimated by the second lens 925. The collimated light beam 911 is output from the VRIM 909 with a reduced beam intensity and a third beam diameter d3 greater than the second beam diameter d2 of the pulsed laser second light beam 118. The VRIM 909 relays the second light beam 118 into a collimated light beam 191 having a larger third diameter d3. The vacuum tube 923 is used to prevent the second light beam 118 from being broken through by air at the focus. Air breakdown of the second beam 118 will result in a loss of beam quality and beam energy.

[0076] VRIM 909 can maintain the spatial distribution of second light beam 118 while increasing the size of second light beam 118 to optimally fill gain medium 927 of amplifier module 913. Optimally filling gain medium 927 optimizes amplification of collimated light beam 191 by amplifier module 913.

[0077] The light beam 911 enters the gain medium 927 of the amplifier module 913. The amplifier module 913 includes the gain medium 927 and a pump source 929. The pump source optically pumps the light beam 911 as it passes through the gain medium 927. The gain medium 927 may be a Nd:YLF crystal laser rod pumped by a laser diode array 929. As the light beam 911 passes through the laser rod 927, the light beam 911 is amplified and output as an amplified third light beam 915. In one aspect, the diameter of the laser rod 927 is about 5 mm. In another aspect, the diameter of the laser rod 927 is about 4-6 mm. In another aspect, the diameter of the laser rod 927 is about 3-7 mm. The gain medium 927 may have a filling factor of about 80% - that is, about 80% of the area of ​​the gain medium will be filled by the light beam 911. Generally, a gain medium with a larger filling factor will have a higher gain and more energy stored in the gain medium can be extracted. In one aspect, the laser rod 927 has a filling factor of 85%.

[0078] The first amplifier stage 901 with the amplifier module 913 can be used as a small preamplifier to amplify the energy of the second light beam 118 input at the input end 905 and output the amplified third light beam 915 at the output end 917. In the given example, the amplified light beam 915 can have a third energy of about 40mJ to 100mJ, a third beam diameter d3 of about 4.5mm, a third temporal distribution, and a third spatial distribution.

[0079] The amplified third light beam 915 may be input into an input 931 on the second amplifier stage amplifier 902. The second amplifier stage amplifier 902 may be similar to the first amplifier stage amplifier 901 and include a VRIM 933, and an amplifier module 935 having a gain medium 937 and a pump source 939. An amplified light beam 941 may be output from the amplifier module 935 to a second amplifier stage output 943.

[0080] The VRIM 933 may be similar in operation to the VRIM 909 and include lenses and vacuum tubes to focus the amplified beam 915, re-collimate the third beam 915, and output a collimated beam 945. The VRIM 933 prevents breakdown of the amplified beam 915 and increases the diameter d3 of the amplified third beam 915 to increase the fill factor of the collimated beam 945 on the gain medium 937. The lenses of the VRIM 933 may have larger diameters than the lenses 921 and 923 in the VRIM 909 (i.e., beams with higher energy and larger beam diameters, such as the amplified beam 915, may use larger diameter lenses), and the length of the vacuum tubes in the VRIM 933 may be longer than the vacuum tubes 923 in the VRIM 909. In general, the size of the lenses used in a VRIM and the length of the vacuum tubes in the VRIM increase as the beam energy and beam diameter increase. The VRIM 933 can relay image the amplified beam 915 into a collimated beam 945 having a certain diameter to provide a fill factor of approximately 80% to 85% to the gain medium 937.

[0081] Similar to the amplifier module 913 described above, the amplifier module 935 may include a gain medium 937 and a pump source 939. When the gain medium 937 is pumped by the pump source 939, the light beam 945 may pass through the gain medium 937 to amplify the light beam 945 before the light beam 945 is output from the amplifier module 935 as an amplified fourth light beam 941. The gain medium 937 may be a Nd:YLF crystal laser rod pumped by a laser diode array 939. In one aspect, the diameter of the laser rod 937 is about 9 mm. In another aspect, the diameter of the laser rod 937 is about 8-10 mm. In another aspect, the diameter of the laser rod 937 is about 7-11 mm. The second amplifier stage amplifier 902 with the amplifier module 935 may be used as a small preamplifier to amplify the energy of the third light beam 915 input at the input end 931 and output the amplified fourth light beam 941 at the output end 943. In the given example, the amplified fourth light beam 941 can have a fourth energy of about 1 J, a fourth beam diameter d4 of about 8.1 mm, a fourth temporal distribution, and a fourth spatial distribution.

[0082] like Fig. 9 As shown, amplifier stages 901 and 902 can operate in a small signal gain range, which can further sharpen the leading edge of the temporal profile of the beam by gain sharpening. The pulse width of the beam can also be narrowed as the beam passes through these amplifier stages.

[0083] The amplified fourth light beam 941 may be input to an input 947 on the third amplifier stage amplifier 903. The third amplifier stage amplifier 903 may be similar to the previous amplifier stages amplifiers 901 and 902 and include an optical isolator 949, a VRIM 951, and an amplifier module 953 having a gain medium 955 and a pump source 957. The amplified fifth light beam 959 may be output from the amplifier module 953 to a third amplifier stage output 961.

[0084] The optical isolator 949 can be similar in operation to the optical isolator 907 described above. In one aspect, the optical isolator 949 is configured to provide a passage for the amplified fourth light beam 941 having a diameter of up to about 12 mm.

[0085] The VRIM 951 can be similar in operation to the VRIMs 909 and 933 described above, including a lens and a vacuum tube to focus the amplified fourth beam 941, re-collimate the amplified fourth beam 941, and output a collimated beam 963. The VRIM 951 prevents breakdown of the amplified fourth beam 941 after it is focused, and re-collimates the fourth beam 941 to increase the diameter of the amplified fourth beam 941, thereby increasing the filling factor of the collimated beam 963 on the gain medium 955. The diameter of the lens of the VRIM 951 can be larger than the diameter of the lens in the VRIMs 909 and 933, and the length of the vacuum tube in the VRIM 951 can be larger than the length of the vacuum tube in the VRIMs 909 and 933. The VRIM 951 can relay image the amplified fourth beam 941 into a collimated beam 963 having a certain diameter to provide a filling factor of about 80% to 85% to the gain medium 955.

[0086] Similar to the amplifier modules 913 and 935 described above, the amplifier module 953 may include a gain medium 955 and a pump source 957. Before the light beam 963 is output from the amplifier module 953 as an amplified light beam 959, the collimated light beam 963 may pass through the gain medium 955 when the gain medium 955 is pumped by the pump source 957 to amplify the light beam 963. The gain medium 955 may be a Nd:YLF crystal laser rod pumped by a laser diode array 957. In one aspect, the diameter of the laser rod 955 is about 15 mm. In another aspect, the diameter of the laser rod 955 is about 14-18 mm. In another aspect, the diameter of the laser rod 955 is about 12-18 mm. The third amplifier stage amplifier 903 with the amplifier module 953 may be used as a small amplifier to amplify the energy of the light beam input at the input end 947 and output a fifth amplified light beam 959 at the output end 961. In the given example, the amplified light beam 959 can have a fifth energy of approximately 4.3 J, a fifth beam diameter d5 of approximately 13.5 mm, a fifth temporal distribution, and a fifth spatial distribution.

[0087] The amplified fifth light beam 959 can be input to an input terminal 965 on the fourth amplifier stage amplifier 904. The fourth amplifier stage amplifier 904 can be similar to the previous amplifier stage amplifiers 901, 902 and 903, and include a VRIM 967, a wave plate 969 and an amplifier module 971 having a gain medium 973 and a pump source 975. The amplified output light beam 126 can be output from the amplifier module 971 to a fourth amplifier stage output terminal 977.

[0088] VRIM 967 can be similar in operation to VRIM 909, 933, and 951 described above, including a lens and a vacuum tube to focus the amplified fifth beam 959, re-collimate the amplified fifth beam 959, and output a collimated beam 979, VRIM 967 prevents breakdown of the amplified fifth beam 959, and re-collimates the amplified fifth beam 959 to increase the diameter of the amplified fifth beam 959, thereby increasing the filling factor of the output beam 979 on the gain medium 973. The lens of VRIM 967 can have a larger diameter than the lens in VRIM 909, 933, and 951, and the length of the vacuum tube in VRIM 967 can be longer than the tube in VRIM 909, 933, and 951. VRIM 967 can relay image the amplified fifth beam 959 into a collimated beam 979 having a certain diameter to provide a filling factor of about 80% to 85% to the gain medium 973.

[0089] Similar to the amplifier modules 913, 935, and 953 described above, the amplifier module 971 can include a gain medium 973 and a pump source 975. When the gain medium 973 is pumped by the pump source 975 to amplify the light beam 979 output from the amplifier module 971, the collimated light beam 979 can pass through the gain medium 973 as an amplified output light beam 126. The gain medium 973 can be a Nd:YLF crystal laser rod pumped by a laser diode array 975. In one aspect, the diameter of the laser rod 973 is about 25 mm. The fourth amplifier stage 904 with the amplifier module 971 can be used as an amplifier to amplify the energy of the light beam input at the input end 965 and output the amplified output light beam 126 at the output end 977. In one aspect, the fourth amplifier stage amplifier 904 includes one amplifier module 971. In another aspect, the fourth amplifier stage amplifier 904 includes one or more amplifier modules 971. In the given example, the amplified exit beam 126 may have a sixth energy of about 7 J to 13 J, a sixth beam diameter d6 of about 20 mm to 25 mm, a sixth temporal distribution, and a sixth spatial distribution. The amplified exit beam 126 output from the amplifier 106 may be a modified amplified beam.

[0090] The characteristics of the light beam passing through the amplifier 106 may change due to the amplification of the light beam. For example, as the light beam is amplified, the diameter of the light beam may be increased by the optical elements in the amplifier 106 to more efficiently fill each gain medium (e.g., laser rod), which may provide optimized amplified laser light output from the gain medium while also fully utilizing the capabilities of certain components within the amplifier 106.

[0091] As the beam passes through the amplifier 106, the beam diameter may increase to match the gain medium size (e.g., laser rod diameter), such as the laser rods 927, 937, 955, and 973 used in the respective amplifier stages 901, 902, 903, and 904. As the beam energy increases throughout the amplifier 106, if the beam diameter remains too small, the risk of damage to the optical components within the amplifier 106 increases. The power density on the gain medium may be maintained below the damage threshold by increasing the beam size as the beam energy increases.

[0092] Due to the amplification of the beam, other characteristics of the beam passing through the amplifier 106 may change. For example, the leading edge of the temporal distribution of the beam may be sharpened when the beam is amplified.

[0093] like Figure 2 As shown, the UCC controller 242 can be used to control the timing of the amplification modules 913, 935, 953 and 971, as shown in FIG. Fig. 9 Specifically, the UCC controller 242 can control when the pump source in the amplifier module pumps the gain medium in the amplifier module to optimize the amplification of the light beam passing through the gain medium. In this way, the amplification of the light beam passing through the amplifier module can be controlled.

[0094] Reference Figure 1A , after the outgoing light beam 126 is output from the amplifier 106, the optical isolator 120 can be used to prevent the outgoing light beam 126 from interacting with existing optical components of the device 100 once it passes through the optical isolator 120. For example, once the outgoing light beam 126 passes through the optical isolator 120, the optical isolator 120 prevents backscattered light from the outgoing light beam 126 from interacting with any existing optical components from the oscillator 102 to the amplifier 106 in the device 100. In one aspect, the optical isolator 120 is a Faraday isolator and can allow a light beam 126 of up to about 35 mm in diameter to pass through.

[0095] Additional elements can be used with the apparatus 100 to deliver a modified and amplified laser exit beam 126 to the target component 101 for laser peening applications. The exit beam 126 can pass through the optical isolator 120 and reach the beam delivery device 122 for delivery to the target component 101 alone, or to the target component 101 contained in the peening unit 124.

[0096] like Fig.10 As shown. The beam delivery device 122 may include one or more reflective mirrors 1081, one or more optical cables 1083, and a multi-axis articulated arm 1085. The beam delivery device 122 may include a focusing optic 1087 to focus the larger size exit beam 126 into a smaller spot size of about 2-3 mm for laser peening applications. In one aspect, the focusing optic 1087 of the beam delivery device 122 focuses and adjusts the spot size of the exit beam 126 to between about 3 mm and 8 mm. The beam delivery device 122 may also include additional safety devices, such as a shutter 1089, to prevent the exit beam 126 from entering the beam delivery device 122 unless the delivery device 122 is positioned to deliver the beam 126 to the target part 101 or the peening unit 124. An additional VRIM assembly 1091 may be used with the beam delivery device 122 to maintain near-field values ​​and measurement values ​​of the modified amplified exit beam 126 output from the amplifier 106. In one aspect, the VRIM 1091 is used to relay the beam 126 to the target component 101 .

[0097] The laser peening cell 124 may include a target component 101 to be laser peened. The robotic manipulation system 1093 may be adapted to manipulate the beam delivery device 122 to change the position of the beam delivery device, thereby changing the position of the outgoing beam 126 output from the delivery device 122 to the target component 101. The robotic manipulation system 1093 may also be used to introduce components to and from the laser peening cell 124. The laser peening cell 124 may provide a light-tight environment to confine hazardous laser light from the outgoing beam 126 within the laser peening cell 124. The laser peening cell 124 may be equipped with additional options, such as lighting, an air filtration system and exhaust system for removing effluent and debris generated during laser peening, and an interface 1095 (i.e., entry / exit) for the robot 1093 to move components into and out of the laser peening cell 124, as well as other safety systems. In one aspect, the laser peening unit 124 can be approximately 4.5 m x 4.5 m x 3.0 m (height) in size to allow the robot 1093 to manipulate larger target components therein. The laser peening unit 124 can include a target isolation system 1096, such as an optical isolator, to prevent laser energy backscattered from the target component 101 from entering the conveyor 122 or other optical elements of the device. In one aspect, the laser peening unit 124 can optionally include an opaque cover applicator 1097 to apply an opaque cover to the target component 101, and a transparent cover applicator 1099 to apply a transparent cover to the target component 101. The opaque cover layer and the transparent cover layer can be applied to the target component 101 so that during the laser peening process, the amplified modified beam 126 contacts the opaque and transparent cover layers on the target component 101.

[0098] In one aspect, near-field values ​​of the modified and amplified light beam 126 include energy of about 7-13 J, pulse width up to about 16 ns, average power of 200 W, and spot size of at least 3 mm. In this aspect, the apparatus 100 generates the modified and amplified light beam 126 having these parameters at a repetition rate of 20 Hz.

[0099] On the other hand, near-field values ​​of the modified and amplified beam 126 include energy of about 5 J to about 10 J, average power of about 5 W to about 200 W, beam uniformity less than about 0.2 (20%), and beam focusing to a spot size of about 3 mm to about 8 mm. In this regard, the oscillator 102 of the device 100 can generate a beam having a beam quality of less than about 1.3 M2 in the oscillator, and the beam having these parameters and initial beam quality can be generated at a variable repetition rate between about 1 Hz and 20 Hz, for example, depending on the surface of the target component 101, and optionally "dynamically" variable.

[0100] On the other hand, there may be a working distance of about 5-10 m between the final focusing optics 1087 and the target component 101. A large working distance may adequately isolate the optical components of the apparatus 100 from debris and effluent generated during the LSP process.

[0101] As described herein, robotic controls, control systems, and instruction sets stored on computer-readable media may be used, which, when executed, can perform the exemplary methods described herein. For example, a robot can be used to manipulate a target part and direct a pulsed laser beam to different locations on the target part. A robot can be used to move a target part in and out of a laser peening cell for laser peening. A robot can move parts in batches for efficient laser peening. The robot can interface with a control system to manipulate parts for laser peening; that is, the robot can control the positioning of the parts so that the parts can be positioned to receive a transparent cover and laser pulses for laser peening. The robotic arm can reposition the same part for subsequent laser peening on the part. In one aspect, the robot repositions the same part at a rate of about 20 Hz for subsequent laser peening on the part. In another aspect, the robot has a position repeatability accuracy of less than about 0.2 mm. In addition, the robot can be used to interact with tools or sensors to generate feedback for system adjustment or calibration. As Fig.10 As shown, a robot such as a robot arm 1093 can be equipped with components of the beam delivery device 122, so that the robot 1093 and the beam delivery device 122 can be repositioned relative to the fixed part 101 to deliver laser pulses to the target component 101 for laser shock peening. In this way, the robot can control the position of the target component 101 relative to the outgoing beam 126, or control the position of the outgoing beam 126 relative to the target component 101.

[0102] An apparatus for an LSP process may be coupled to one or more controllers for controlling the functions of the apparatus. The controller may be calibrated or adjusted automatically, or there may be a user interface for a user to interface with the control interface of the apparatus. For automatic control, various sensors may be used to collect various beam parameters as the beam travels through the device. The sensor readings may be collected in real time or at intervals and used as feedback for control of the apparatus. For example, temperature measurements may be taken at regular intervals within the apparatus to ensure that the apparatus is operating within a specified temperature range. The pulse energy, pulse width, and spatial distribution of one or more pulses may be measured and monitored, and when the measured values ​​fall outside of a user-selected range, the control system may adjust components of the apparatus so that the measured values ​​fall within the user-selected range.

[0103] Data related to laser beam parameters can be acquired from within the machine and from the beam delivery path (e.g., as partial reflections from optics or energy leakage through mirrors). Machine data can be periodically acquired and cross-calibrated against target data to ensure that laser peening conditions are within user-selected tolerances.

[0104] The beam position and spot size have very tight tolerances and can be determined by a camera in the beam path. A camera can be used to capture an image of the beam, and the parameters extracted from the beam image can be compared to the ideal parameters. For example, if the beam position is not centered as indicated by the ideal position parameters, the reflector can be automatically adjusted to move the beam closer to the position defined by the ideal parameters. Adjusting the movement of the beam can be done in small increments, and multiple measurements and adjustments may be required until the beam is positioned as defined by the ideal position parameters. Cameras can also be used to measure spot area and spot size. The controller can automatically adjust the lens to adjust the target lens to set the spot size.

[0105] Although not exhaustive or limiting, control systems used with laser shot peening equipment may be used to: configure and monitor the electric drive system / oscillator (e.g., timing, pump current); configure and monitor the timing generator; control and monitor laser safety; control and monitor laser output; control and monitor laser temperature (e.g., housing temperature, cooling water temperature, etc.); control output energy by adjusting laser head timing; control coating application; control and monitor the final focusing lens; control and monitor the final rotating mirror; integrate with external control systems such as robots; store component configurations in the device; store data collected by the device for post-processing; and control access to the device (e.g., limiting access to the device to authorized users).

[0106] Although not exhaustive or limiting, the sensor components of a control system used with equipment for laser peening can sense and monitor: pulse width, pulse energy, spatial distribution of the beam, diode voltage, pump current, housing temperature, cooling water temperature, laser safety systems, and health of the equipment.

[0107] The control system as described herein can be used to automatically adjust: laser head timing, final focusing lens position; final tuning mirror position; coating application timing, cooling system operation, and data collection. The control system can automatically adjust the energy of the output laser beam. The control system can automatically adjust the diode voltage. The diode current can be automatically controlled by the electric drive system.

[0108] The method may also include repeatedly adjusting the laser parameters through an open loop or through a closed loop mechanism by adjusting the final focusing lens, adjusting the position of a mirror in the beam delivery device, and adjusting the pulse shearer, and re-measuring the spot size, beam position and pulse width until the spot size, beam position and pulse width are within the user-defined tolerances of the spot size, beam position and pulse width.

[0109] Unless specifically indicated to the contrary, the numerical parameters set forth in the specification, including the attached claims, are approximations that can vary depending upon the desired properties sought to be obtained by the exemplary aspects. At the very least, and not as an attempt to limit the application of the doctrine of equivalents to the scope of the claims, each numerical parameter should at least be construed in light of the number of reported significant digits and by applying ordinary rounding techniques.

[0110] Although the numerical ranges and parameters setting forth the broad scope of the invention are approximations, the numerical values ​​set forth in the specific examples are reported as precisely as possible. Any numerical value, however, inherently contains certain errors necessarily resulting from the standard deviation found in their respective testing measurements.

[0111] Furthermore, although the systems, methods and devices have been described by describing exemplary aspects, and although the exemplary aspects have been described in considerable detail, it is not the intention of the applicant to limit or in any way restrict the scope of the appended claims to these details if these details are not listed in the claims. Of course, it is not possible to describe every possible combination of components or methods for describing the systems, methods and devices. Additional advantages and improvements will be apparent to those skilled in the art with the aid of this application. Therefore, the present invention in its broader aspects is not limited to the specific details, embodiments and exemplary aspects shown and described. Therefore, these details may be deviated from without departing from the spirit and scope of the general inventive concept. Therefore, the present application is intended to include changes, modifications and variations that fall within the scope of the appended claims. The foregoing description is not meant to limit the scope of the present invention. On the contrary, the scope of the present invention is determined by the appended claims and their equivalents.

[0112] As used in the specification and claims, the singular forms "a", "an", and "the" include the plural. In addition, if the term "or" is used in the claims (e.g., A or B), it means "A or B or both". When the applicant intends to mean "only A or B, but not both", "only A or B, but not both" will be used; similarly, when the applicant means "one and only one" of A, B, or C, the applicant will use the phrase "one and only one"; and, in the scope of the use of the term "in" or "into" in the specification or claims, it can also mean "on" or "on"; in the scope of the use of the term "selectively" in the specification or claims, it means a state of a component, in which the user of the device can activate or deactivate the feature or function of the component as needed or desired when using the device. In the scope of the use of the term "operably connected" in the specification or claims, it means that the identified components are connected in a manner to perform the specified function. Finally, the term "about" is used in conjunction with a number, and its intention is to include ±10% of this number. In other words, "about 10" could be from 9 to 11.

Claims

1. A device for controlling a pulsed laser beam, the device comprising: a diode pumped solid-state laser (DPSSL) oscillator configured to generate and output a pulsed laser beam having predefined beam characteristics corresponding to a current setting selection of a controller, wherein the controller, in response to the current setting selection, controls a current source to output a current to tune the diode pumped solid-state laser oscillator to generate a first beam having a pulse width within a defined tolerance, a first energy, a first spatial distribution, and a first temporal distribution; a filter configured to modify the received modified first light beam having a modified pulse width PW2 using a second temporal distribution to output a second light beam having a second energy, a second spatial distribution, and a second temporal distribution; and A multi-stage amplifier is configured to output an output light beam after amplifying the light beam energy and modifying the light beam distribution, the multi-stage amplifier comprising: a first stage amplifier configured to amplify and modify the second light beam to output a third light beam having a third energy and a third temporal distribution; and a second stage amplifier configured to amplify and modify the third light beam to output a fourth light beam having a fourth energy and a fourth temporal distribution, wherein the fourth light beam substantially maintains the pulse width PW1 or the modified pulse width PW2 within the defined tolerance; Also included is a first pair of wave plates and a first polarizer disposed at an output end of the diode-pumped solid-state laser oscillator, wherein the first pair of wave plates and the first polarizer are configured to rotate a certain amount of polarization angle relative to the first light beam to attenuate the first energy of the first light beam to generate the first light beam attenuated to a level not exceeding a defined first energy level; comprising a second pair of Pockels cells and a second polarizer disposed between the first pair of wave plates and the first polarizer, and an optical filter; It also includes a beam detector coupled to the first polarizer, the second polarizer, and one or a combination of the beam delivery devices arranged after the multi-stage amplifier, and the beam detector is used to monitor one or a combination of the beam pulse width, beam diameter and energy level.

2. The apparatus of claim 1 , wherein the second pair of Pockels cells and the second polarizer are configured to perform nanosecond duration switching on the attenuated first light beam from the first polarizer by allowing or preventing the attenuated first light beam from leaving the Pockels cell, wherein: The exit beam is the modified first beam having the modified pulse width PW2 and the second temporal distribution.

3. The device as claimed in claim 2, wherein: The Pockels cell includes a crystalline material including one of barium borate or potassium dideuterium phosphate.

4. The device as claimed in claim 3, wherein: In the case where the Pockels cell includes the crystal material containing the potassium dideuterium phosphate, the Pockels cell is further configured to perform pulse slicing on the leading edge of the first light beam or the attenuated first light beam to output the modified pulse width PW2 of less than 12 nanoseconds and the modified first light beam having a modified time distribution.

5. The device according to claim 3, wherein: The first light beam output from the diode pumped solid state laser oscillator has a first diameter and a wing, and the filter comprises: a beam expander configured to expand a diameter of the modified first beam to be larger than the first diameter; and An apodizer is configured to receive the expanded modified first beam from the beam expander to remove the wing portion to output the second beam having the second spatial distribution without the wing portion.

6. The device according to claim 1, wherein: The multi-stage amplifier further comprises: a third stage amplifier configured to amplify and modify the fourth light beam to output a fifth light beam having a fifth energy and a fifth time distribution; and A fourth stage amplifier is configured to amplify and modify the fifth light beam to output a sixth light beam or an output light beam having a sixth energy and a sixth time distribution.

7. The device of claim 1, wherein: An exit beam from the multi-stage amplifier to a beam delivery device has a near-field value and a measurement value, and the beam delivery device includes a vacuum relay imaging module (VRIM), which is configured to maintain the near-field value and the measurement value of the exit beam and deliver the exit beam to a target component.

8. The device of claim 1, wherein: The beam detector generates an error signal during the monitoring process and sends it back to the controller as a feedback signal, wherein if the magnitude of the error signal exceeds a defined error range, the feedback signal causes the controller to perform one or a combination of the following: configuring a current source to output a correction current to tune the diode-pumped solid-state laser oscillator to offset the pulse width error signal until the pulse width PW1 remains within the defined tolerance according to the current setting selection; configuring the first pair of wave plates and the first polarizer to rotate a certain amount of a correction polarization angle relative to the first light beam to increase or decrease attenuation of the first energy of the first light beam to remain within a defined first energy level; configuring the Pockels cell to switch on or off, or adjusting the modified pulse width PW2 to an amount that remains within the defined tolerance; and The multi-stage amplifier is configured to adjust one or a combination of the beam energy amplification and the beam profile modification to remain within a defined output energy level and a defined beam profile.

9. The apparatus as claimed in claim 1, further comprising a first isolator disposed between the diode-pumped solid-state laser oscillator and the wave plate, and a second isolator disposed between the multi-stage amplifier and the beam delivery device, wherein: The first isolator and the second isolator prevent the light beam from being reflected in opposite directions.

10. A method for controlling a pulsed laser beam, the method comprising: generating from a diode-pumped solid-state laser oscillator and outputting a pulsed laser beam having predefined beam characteristics corresponding to a current setting selection of a controller; In response to the current setting selection, the controller controls a current source output current to tune the diode-pumped solid-state laser oscillator to generate a first optical beam having a pulse width PW1 within a defined tolerance, a first energy, a first spatial distribution, and a first temporal distribution; Modifying the received modified first light beam having the modified pulse width PW2 and the second temporal distribution by a filter to output a second light beam having a second energy, a second spatial distribution, and a second temporal distribution; as well as Amplifying the energy of the light beam and modifying the light beam distribution by a multi-stage amplifier to output an outgoing light beam, wherein the multi-stage amplifier amplifies the energy of the light beam and modifies the light beam distribution comprises: amplifying and modifying the second light beam by a first stage amplifier to output a third light beam having a third energy and a third time distribution; and amplifying and modifying the third light beam by a second stage amplifier to output a fourth light beam having a fourth energy and a fourth time distribution, wherein the fourth light beam substantially maintains the pulse width PW1 or the modified pulse width PW2 within the defined tolerance; The method further includes attenuating the first energy of the first light beam by a first pair of wave plates and a first polarizer, wherein the first pair of wave plates and the first polarizer are disposed at an output end of the diode-pumped solid-state laser oscillator, and the first pair of wave plates and the first polarizer are configured to rotate a certain amount of polarization angle relative to the first light beam to attenuate the first energy of the first light beam to generate the attenuated first light beam that does not exceed a defined first energy level; Also comprising switching the attenuated first light beam through a second pair of Pockels cells and a second polarizer for a duration of each nanosecond; It also includes using a beam detector to monitor one or more combinations of the following: beam pulse width, beam diameter, and energy level, wherein the beam detector is coupled to one or a combination of the first polarizer, the second polarizer, and a beam delivery device disposed after the multi-stage amplifier, and the beam delivery device is used to deliver the output beam from the multi-stage amplifier to a target component.

11. The method of claim 10, wherein the second pair of Pockels cells and the second polarizer are disposed between the first pair of wave plates and the first polarizer, and further comprising a filter, wherein the second polarizer is configured to perform nanosecond duration switching on the attenuated first light beam by allowing or preventing the attenuated first light beam from leaving the Pockels cell, wherein the exit light beam is the modified first light beam having the modified pulse width PW2 and the second time distribution.

12. The method of claim 11, wherein: The Pockels cell includes a crystalline material including one of barium borate or potassium dideuterium phosphate.

13. The method of claim 12, wherein: In the case where the Pockels cell includes the crystalline material containing the potassium deuterium phosphate, the Pockels cell is further configured to perform pulse slicing on the leading edge of the first light beam or the attenuated first light beam to output the modified pulse width PW2 of less than 12 nanoseconds and the modified first light beam having a modified time distribution.

14. The method of claim 11, wherein: The first light beam output from the diode pumped solid state laser oscillator has a first diameter and a wing, and wherein the filter comprises: a beam expander configured to expand a diameter of the modified first beam to be larger than the first diameter; and An apodizer is configured to receive the expanded modified first beam from the beam expander to remove the wing portion to output the second beam having the second spatial distribution without the wing portion.

15. The method of claim 10, wherein: The multi-stage amplifier further comprises: a third stage amplifier configured to amplify and modify the fourth light beam to output a fifth light beam having a fifth energy and a fifth time distribution; and A fourth-stage amplifier is configured to amplify and modify the fifth light beam to output a sixth light beam or the output light beam having a sixth energy and a sixth time distribution.

16. The method of claim 10, wherein: The outgoing beam from the multi-stage amplifier to the beam delivery device has a near-field value and a measurement value, and the beam delivery device includes a vacuum relay imaging module (VRIM), which is configured to maintain the near-field value and the measurement value of the outgoing beam and deliver the outgoing beam to a target component.

17. The method of claim 10, further comprising using the beam detector to generate an error signal during monitoring, which is sent back to the controller as a feedback signal, wherein: If the magnitude of the error signal exceeds a defined error range, the feedback signal causes the controller to perform one or a combination of the following: configuring a current source to output a correction current to tune the diode-pumped solid-state laser oscillator to offset the pulse width error signal until the pulse width PW1 remains within the defined tolerance according to the current setting selection; configuring the first pair of wave plates and the first polarizer to rotate the first light beam by a correction polarization angle to increase or decrease attenuation of the first energy of the first light beam to remain within a defined first energy level; configuring the Pockels cell to switch on or off, or to adjust the modified pulse width PW2 to an amount that remains within the defined tolerance; And, configuring the multi-stage amplifier to adjust one or a combination of the beam energy amplification and the beam profile modification to remain within a defined output energy level and a defined beam profile.

18. The method of claim 10, further comprising a first isolator disposed between the diode-pumped solid-state laser oscillator and the wave plate, and a second isolator disposed between the multi-stage amplifier and the beam delivery device, wherein: The first isolator and the second isolator prevent the light beam from being reflected in opposite directions.

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