A high beam quality laser with adjustable repetition rate

Abstract

The present application relates to a kind of high beam quality laser of adjustable repetition frequency, comprising: seed source, output 20-100MHz repetition frequency picosecond signal laser;Pulse selector is connected seed source and is configured as: response to target repetition frequency value set by user, when repetition frequency>50kHz, carry out normal pulse selection, when repetition frequency≤50kHz, enable Burst Mode editing function, generate the pulse train envelope containing 2-10 sub-pulses;Three-stage laser amplifier in series, pulse is amplified, each stage contains pump source, focusing lens and laser crystal;Thermal lens cooperative control unit is used to improve the thermal lens effect of laser crystal, including: pump spot adjusting module, response the target repetition frequency value, automatically adjust the distance of each stage focusing lens to laser crystal and pump current;Pulse energy editing module, under Burst Mode, dynamically modulate the sub-pulse energy in pulse train and make it show increasing distribution;Uniform temperature field module, including the TEC array and temperature sensor array arranged around laser crystal, according to target repetition frequency value, automatically match laser crystal temperature field set value and maintain laser crystal temperature field uniform, the high beam quality laser of adjustable repetition frequency provided by the present application supports adjustable repetition frequency, and after repetition frequency is adjusted in a large range, thermal lens effect in laser crystal, thermal equilibrium is stable, laser can stably output excellent beam quality laser beam.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of laser, in particular, to a high beam quality laser with adjustable repetition frequency. BACKGROUND

[0002] Most of the traditional high-energy picosecond lasers have fixed repetition frequency, and even if the repetition frequency is adjustable, it can only be adjusted in a small range, and the beam quality and optical power cannot be well balanced. However, in actual application, there will be scenes that need to switch the repetition frequency, such as glass cutting. In glass cutting, different thickness of glass will be involved. When thick glass needs to be cut, high energy (single pulse greater than 1 MJ or more) is required. However, high energy often requires low repetition frequency to achieve, which will result in slow processing speed. However, when cutting thin glass, high energy is not required. If low repetition frequency and high energy are continued to be used, the processing speed will be very slow. At this time, higher repetition frequency and lower single pulse energy are used to achieve the purpose.

[0003] However, if the adjustable high-energy laser on the market is changed to low frequency, the beam quality will deteriorate, resulting in poor processing effect. If it is changed to high frequency, the beam quality is good, but the average power and single pulse energy are not enough, which leads to the inability to cut through thicker materials. In fact, low frequency and high frequency are different when matching thermal lens. When the frequency is high, the laser crystal is easy to absorb pump heat, and the lens is not obvious. The pump spot focused on the laser crystal can be very small, so the amplification efficiency will be higher. On the contrary, when the frequency is low, the thermal lens is obvious, and the single pulse energy is large. The pump spot focused on the laser crystal is large, otherwise the laser crystal will be damaged. Therefore, many traditional laser manufacturers can only adjust the light according to customer needs and repetition frequency. The laser cannot be changed arbitrarily after leaving the factory, which greatly limits the application scenarios of the laser. If the repetition frequency is directly changed, the thermal lens in the laser changes dramatically, resulting in poor output beam quality and greatly reduced amplification efficiency.

[0004] If the change of thermal lens caused by the change of repetition frequency can be solved, high beam quality output and high amplification efficiency can be maintained. SUMMARY

[0005] Therefore, in view of the above problems, the present application provides a high beam quality laser with adjustable repetition frequency, which supports adjustable repetition frequency. After a large range of repetition frequency adjustment, the thermal lens effect and thermal balance in the laser crystal are stable, and the laser can stably output laser beams with excellent beam quality.

[0006] To achieve the above object, the application provides a high-brightness laser with adjustable repetition frequency and high beam quality, comprising: a seed source, which outputs picosecond signal laser with a repetition frequency of 20-100 MHz; a pulse selector, which is connected to the seed source and is configured to: in response to a target repetition frequency value set by a user, perform normal pulse selection when the repetition frequency is greater than 50 kHz, and enable a Burst Mode editing function when the repetition frequency is less than or equal to 50 kHz, to generate a pulse train envelope containing 2-10 sub-pulses; a three-stage serial laser amplifier, which performs power amplification on the pulses, each stage containing a pump source, a focusing lens and a laser crystal connected by an optical path; and a thermal lens cooperative control unit, which is used to improve the thermal lens effect of the laser crystal and comprises: a pump spot adjustment module, which automatically adjusts the distance from each stage of focusing lens to the laser crystal and the pump current in response to the target repetition frequency value; a pulse energy editing module, which dynamically modulates the sub-pulse energy in the pulse train under the Burst Mode so that the sub-pulse energy is in an increasing distribution; and a uniform temperature field module, which comprises a TEC array and a temperature sensor array arranged around the laser crystal, and automatically matches the temperature field setting value of the laser crystal and maintains the uniform temperature field of the laser crystal according to the target repetition frequency value.

[0007] In one specific embodiment, the focusing lens is connected with a servo motor moving device, and in the pump spot adjustment module, the repetition frequency is pre-set into 5 intervals: 20-50 kHz, 50-100 kHz, 100-300 kHz, 300-500 kHz and 500-2000 kHz, each interval corresponds to a pre-stored pump current value and a distance from the focusing lens to the laser crystal, in response to the repetition frequency value, the pump current is switched to the pre-set current value, and the servo motor drives the focusing lens to move a pre-set distance, each repetition frequency interval corresponds to a stored temperature field setting value, in response to the repetition frequency value, the TEC array is switched to the pre-set current value, so that the temperature field of the laser crystal reaches the pre-set value.

[0008] In one specific embodiment, the pump source outputs pump laser with a wavelength of 888 nm, the pump current varies in a range of 6-10 A, and the moving distance of the focusing lens is ±10 mm.

[0009] In one specific embodiment, the pulse selector is a fiber AOM, and the pulse energy editing module is realized by the fiber AOM, under the Burst Mode, the fiber AOM receives the original pulse train of the seed source, modulates the sub-pulse energy based on an RF driving voltage synchronized with the timing of the seed source, applies an RF driving voltage Vi to the i-th sub-pulse in the sub-pulse, which satisfies V1

[0010] In one of the specific embodiments, the uniform temperature field module further comprises a red copper heat sink surrounding the laser crystal for rapid heat dissipation of the laser crystal.

[0011] In one of the specific embodiments, the laser crystal is gradiently doped along the direction of incident pump light, 0-5mm region: doping concentration 0%; 5-10mm region: doping concentration 0.1%; 10-11mm region: doping concentration 0.2%; 11-30mm region: doping concentration 0.3%.

[0012] In one of the specific embodiments, the laser crystal is a Nd:YVO4 crystal or a Nd:YAG crystal.

[0013] In one of the specific embodiments, the output power of the seed source is 50-100mW, M2<1.1, and pulse width <10pS.

[0014] In one of the specific embodiments, a power feedback module is further included, connected to the output end of the third-stage laser amplifier, for real-time monitoring of the output power by a power detector and feedback adjustment of the pump current and / or the position of the focusing lens.

[0015] In one of the specific embodiments, when the power detector detects that the output power deviates from the predetermined value: the first-stage pump current is preferentially fine-tuned ±0.2A, if the requirement is not met, the second-stage pump current is adjusted ±0.5A, the third-stage pump current is adjusted ±1A, and if the requirement is still not met, the position of the third-stage focusing lens is adjusted ±2mm.

[0016] Compared with the prior art, the present application has the following beneficial effects:

[0017] The present application provides a high-beam-quality MOPA structure laser with adjustable repetition frequency, which comprises a seed source, a pulse selector and a three-stage laser amplifier, the pulse selector automatically switches the working mode according to the target repetition frequency: when the repetition frequency is greater than 50kHz, the conventional frequency reduction is used, and when the repetition frequency is less than or equal to 50kHz, the Burst Mode is used to generate a pulse train containing 2-10 sub-pulses, thereby avoiding damage to the laser crystal during low repetition frequency amplification, and a thermal lens cooperative control unit is innovatively used, which comprises three modules: (1) a pump light spot adjustment module for dynamically optimizing the pump focal length and current according to the repetition frequency; (2) a pulse energy editing module under the Burst Mode for making the sub-pulse energy incrementally distributed to compensate for gain saturation; and (3) a high-precision uniform temperature field module for realizing a circumferential temperature difference of the laser crystal of ±0.05℃ and an axial temperature difference of ≤0.1℃, thereby significantly suppressing thermal lens effect and thermal-induced birefringence and other thermal effects, the system supports a wide range of repetition frequency adjustment of 20Hz-100MHz, and through multi-dimensional thermal management, high-quality and stable output of the light beam in the entire frequency band is ensured. BRIEF DESCRIPTION OF DRAWINGS

[0018] Figure 1Figure 1 is a structural schematic diagram of a laser with adjustable repetition frequency and high beam quality according to an embodiment of the present application.

[0019] Figure 2 Figure 2 is a structural schematic diagram of a laser with adjustable repetition frequency and high beam quality according to another embodiment of the present application.

[0020] Figure 3 Figure 3 is a structural schematic diagram of a uniform temperature field module according to an embodiment of the present application.

[0021] Figure 4 Figure 4 is an output form schematic diagram when the number of sub-pulses in the pulse train envelope is 2-5 according to an embodiment of the present application. Figure 5 Figure 5 is a shape of an unedited seed pulse train and a shape of an amplified pulse train thereof according to an embodiment of the present application.

[0022] Figure 6 Figure 6 is a shape of an edited seed pulse train and a shape of an amplified pulse train thereof according to an embodiment of the present application. DETAILED DESCRIPTION

[0023] In order to make the above objectives, features and advantages of the present application more apparent, specific embodiments of the present application will be described in detail below with reference to the accompanying drawings. In the following description, numerous specific details are set forth in order to provide a thorough understanding of the present application. However, the present application can be practiced in a number of different ways beyond the specific embodiments described and it is therefore contemplated to cover all such modifications as fall within the scope of the application. It is to be understood that other embodiments can be utilized and structural or procedural changes can be made without departing from the scope of the present application.

[0024] As shown in FIG. 1, the present embodiment provides a laser with adjustable repetition frequency and high beam quality, which adopts a MOPA structure and includes a seed source 10, a pulse selector 20, a pulse amplifier 30, a pulse compressor 40, and a beam combiner 50. Figures 1-3 The pulse selector 20 is connected to the seed source 10 and is configured to: in response to a target repetition frequency value set by a user, perform normal pulse selection when the repetition frequency is > 50 kHz, and enable a Burst Mode editing function when the repetition frequency is ≤ 50 kHz to generate a pulse train envelope containing 2-10 sub-pulses; for example, the user sets the target repetition frequency to 60 kHz, and normal pulse selection is performed to directly reduce the frequency output; if the normal frequency selection mode is still used when the repetition frequency is lower than 50 kHz, the risk of damaging the laser crystal will be increased, and therefore the Burst Mode editing and modulation function is used, as shown in FIG. 2. Figure 4As shown, the output form when the number of sub-pulses in the pulse train envelope is 2 to 5 is listed, which is characterized in that a plurality of sub-pulses with a time interval of tens of nanoseconds form a cluster, and the time interval of adjacent pulses in the pulse train envelope is determined by the repetition frequency of the seed source, for example, the repetition frequency of the seed source is 20 MHz, then the pulse interval inside the pulse train is 1 / 20 MHz = 50 ns, 50 kHz is selected, 4burst, and the actual repetition frequency is still 50 kHz. The high-brightness laser with adjustable repetition frequency provided in the embodiment further includes a three-stage cascade laser amplifier 30 for power amplification of the pulse, each stage containing a pump source 301, a focusing lens 302 and a laser crystal 303 connected by an optical path; a thermal lens cooperative control unit for improving the thermal lens effect of the laser crystal, including: a pump spot adjusting module 401, which automatically adjusts the distance from the focusing lens 302 to the laser crystal 303 and the pump current in response to the target repetition frequency value; a pulse energy editing module 402, which dynamically modulates the sub-pulse energy in the pulse train under Burst Mode to show an increasing distribution, compensates for the gain saturation effect in the amplification process, and makes the output laser energy more uniform; a uniform temperature field module 403, including a TEC array 4031 and a temperature sensor array 4032 arranged around the laser crystal 303, which automatically matches the laser crystal temperature field setting value according to the target repetition frequency value and maintains the uniformity of the laser crystal 303 temperature field, the temperature control accuracy of the TEC in the uniform temperature field module is ±0.05℃, the circumferential temperature control accuracy of the laser crystal 303 is ±0.05℃, and the axial temperature difference is ≤0.1℃, so that the temperature field around the laser crystal 303 is uniform, thereby reducing thermal lens effect, thermal birefringence effect and thermal distortion effect, and improving the beam quality. The high-brightness laser with adjustable repetition frequency provided in the embodiment supports adjustable repetition frequency, and after a wide range of repetition frequency adjustment, the thermal lens effect in the laser crystal 303 is stable, the thermal equilibrium is stable, and the laser can stably output a laser beam with excellent beam quality.

[0025] In one of the specific embodiments, the focusing lens 302 is connected with a servo motor as the moving device of the focusing lens 302, the repetition frequency is preset to 5 intervals in the pump spot adjusting module 401: 20-50 kHz, 50-100 kHz, 100-300 kHz, 300-500 kHz, 500-2000 kHz, each interval corresponds to the pre-stored pump current value, the distance from the focusing lens 302 to the laser crystal 303, in response to the repetition frequency value, the pump current is switched to the preset current value, the pump spot adjusting module 401 controls the servo motor to drive the forward and backward movement of the focusing lens 302 at each level by a preset distance, and the low frequency moves towards the laser crystal 303 to expand the spot to 3 mm, preventing the laser crystal from being damaged, and the high frequency moves away from the laser crystal to reduce the spot to 0.5 mm. The pump source 301 outputs pump laser with a wavelength of 888 nm, the laser crystal 303 absorbs the pump laser in this wavelength band more uniformly, which is beneficial to reduce the transverse thermal distortion, the change range of the pump current is 6-10 A, and the moving distance of the focusing lens 302 is ±10 mm. The regular change of the spot size on the laser crystal 303 is realized by the accurate forward and backward movement of the focusing lens 302 by ±10 mm through the servo motor, the spot change range is generally 0.5-3 mm, and then the pump current is matched according to different repetition frequencies, the current range is generally 6-10 A, to suppress the thermal lens effect. Further, each repetition frequency interval corresponds to a preset temperature field setting value, the uniform temperature field module 403 controls the TEC array to switch to the preset current value according to the target repetition frequency value of the user, so that the temperature field of the laser crystal 303 reaches the preset value, the temperature of the crystal is adjusted in real time to be in an appropriate range, the thermal lens effect in the laser crystal 303 is improved, the laser crystal 303 is in thermal equilibrium and stable, and the laser with excellent beam quality is ensured to be stably output.

[0026] In one embodiment, the pulse selector is a fiber AOM, the pulse energy editing module 402 is implemented by the fiber AOM, in Burst Mode, the fiber AOM receives the original pulse train of the seed source 10, and the sub-pulse energy modulation is implemented based on the RF drive voltage synchronized with the seed source timing, the RF drive voltage Vi applied to the i-th sub-pulse in the sub-pulse satisfies V1 < V2 <... < Vn (1 ≤ i ≤ n), the RF drive voltage is linearly related to the sub-pulse energy, the first sub-pulse energy is adjusted to the lowest, and the subsequent sub-pulse energy is gradually increased, so that the edited pulse train energy is in an increasing distribution. Due to the influence of gain saturation and recovery time of the pulse train in the amplification process, the gain of the laser crystal (such as Ti: sapphire crystal, Nd: YAG, Nd: YVO4, etc.) is directly related to the upper energy level particle density of the laser crystal. When the first sub-pulse passes, the laser crystal is in a fully inverted state (high particle density), and the energy absorbed and amplified is the most. When the first pulse absorbs a large number of upper energy level particles, the gain of the laser crystal temporarily decreases (i.e. gain saturation), and the available particles encountered by the subsequent pulse decrease, resulting in a decrease in the energy absorbed. Moreover, the gain recovery time depends on the energy level lifetime of the medium (such as the upper energy level lifetime of Ti: sapphire is about 3.2us, and the upper energy level lifetime of Nd: YVO4 is about 90us). If the pulse train interval (such as 12.5ns@80MHz) is much shorter than the recovery time, the gain cannot be fully recovered, resulting in a decrease in the energy absorbed by the subsequent pulse, and thus the amplified pulse train presents a phenomenon from high to low, as shown in Figure 5 The present application aims at this technical defect, and the first sub-pulse energy is the lowest and the last sub-pulse energy is the highest through pulse editing, so that the pulses are more fully and uniformly absorbed under the action of the laser crystal, the high and low of the amplified pulses are consistent, the amplification efficiency is greatly improved, the thermal effect is reduced, and the beam quality is improved, and the edited seed pulse and the amplified pulse are as shown in Figure 6

[0027] ​In one embodiment, the uniform temperature field module 403 further comprises a copper heat sink (not shown in the figure) surrounding the laser crystal 303 for rapid heat dissipation. In a conventional structure, the laser crystal 303 is surrounded by indium foil and packaged with a nickel-coated crystal holder. This conventional heat dissipation and temperature control scheme can only ensure that the laser crystal does not burst due to excessive temperature, but the heat generation and temperature field around the laser crystal 303 are different, which causes a gradient distribution of the temperature field in the laser crystal 303, and further causes a gradient distribution of the refractive index of the laser crystal 303, forming severe thermal lens effect, thermal birefringence effect, and thermal distortion effect, and there is no feedback adjustment mechanism. In this embodiment, based on the TEC array 4031 and the temperature sensor array 4032 surrounding the laser crystal 303, the laser crystal 303 is surrounded by copper for all-around rapid heat dissipation, and the temperature control precision and effect, and speed are greatly improved. The temperature control precision can reach 0.05℃, and the temperature field around the crystal holder can be kept consistent. As the pump power increases, the heat generation of the laser crystal 303 will continue to increase, and the use of TEC array temperature control can quickly respond, so that the temperature of the laser crystal 303 is rapidly controllable, and can be feedback adjusted according to the real-time heat and environment, so that the temperature control of the laser crystal 303 is more stable. In this way, the pump light and the signal light can be fully absorbed in the laser crystal 303, and the heat generated by each section of the laser crystal 303 is uniform, and the severe change of thermal lens caused by large frequency change can be quickly improved, and high-quality laser beams can be ensured.

[0028] In one embodiment, the laser crystal 303 is gradiently doped along the direction of the incident pump light, with a doping concentration of 0% in the 0-5mm region, a doping concentration of 0.1% in the 5-10mm region, a doping concentration of 0.2% in the 10-11mm region, and a doping concentration of 0.3% in the 11-30mm region. This makes the heat uniformly distributed in the axial direction, reduces the thermal gradient, improves the thermal lens effect of the laser crystal 303, and ensures the output of high-beam-quality laser beams.

[0029] In one embodiment, the laser crystal 303 is a Nd:YVO4 crystal or a Nd:YAG crystal.

[0030] In one embodiment, the output power of the seed source 10 is 50-100mW, M2<1.1, and the pulse width is <10pS.

[0031] In one of the specific embodiments, a high-brightness laser with adjustable repetition frequency is provided, further comprising a power feedback module connected to the output end of the third-stage laser amplifier, which monitors the output power in real time through the power detector 50 and feeds back to the pump spot adjustment module 401, which adjusts the pump current and / or the position of the focusing lens 302 according to the feedback power value, so that the output power finally reaches the preset target accurately. The output end of the power detector 50 is also connected with an acousto-optic Q 60 for realizing accurate pulse output and rapid control. In one of the specific embodiments, when the power detector 50 detects that the output power deviates from the predetermined value: the pump spot adjustment module 401 preferentially fine-tunes the first-stage pump current ±0.2A, if it does not meet the standard, adjusts the second-stage pump current ±0.5A, the third-stage pump current ±1A in turn, and still does not meet the standard, adjusts the position of the third-stage focusing lens ±2mm, and when the power is low, the servo motor controls the focusing lens to move away from the laser crystal, otherwise it moves in the opposite direction.

[0032] It should be noted that, for those skilled in the art, it is obvious that the present application is not limited to the details of the above-mentioned exemplary embodiments, and the present application can be implemented in other specific forms without departing from the spirit or essential characteristics of the present application. Therefore, from any point of view, the embodiments should be regarded as exemplary and non-limiting, and the scope of the present application is defined by the appended claims rather than the above description, and therefore all changes falling within the meaning and scope of the equivalent elements of the claims are intended to be included in the present application, and any reference signs in the claims should not be regarded as limiting the claims involved.

[0033] In the present application, specific examples are applied to illustrate the principles and implementation modes of the present application, and the above embodiment descriptions are only used to help understand the method of the present application and its core idea; at the same time, for those skilled in the art, according to the idea of the present application, there will be changes in specific implementation modes and application scope. In conclusion, the content of the present description should not be understood as a limitation of the present application.

Claims

1. A laser with adjustable repetition rate and high beam quality, characterized in that: include: Seed source, outputting picosecond laser signal with a repetition frequency of 20kHz-2000kHz; The pulse selector, connected to the seed source, is configured to: respond to the user-defined target repetition frequency value, perform normal pulse selection when the repetition frequency is >50kHz, and enable the Burst Mode editing function when the repetition frequency is ≤50kHz to generate a pulse train envelope containing 2-10 sub-pulses; A three-stage cascaded laser amplifier amplifies the power of the pulses. Each stage contains a pump source, a focusing lens, and a laser crystal, which are connected by optical paths. A thermal lensing co-control unit, used to improve the thermal lensing effect of laser crystals, includes: The pump spot adjustment module, in response to the target repetition rate value, automatically adjusts the distance from each focusing lens to the laser crystal and the pump current. The pulse energy editing module dynamically modulates the sub-pulse energy within the pulse train in Burst Mode to make it increase in distribution. The uniform temperature field module includes a TEC array and a temperature sensor array set around the laser crystal. It automatically matches the laser crystal temperature field setpoint and maintains the uniformity of the laser crystal temperature field based on the target repetition rate value.

2. The laser with adjustable repetition rate and high beam quality according to claim 1, characterized in that: The focusing lens is connected to a servo motor. In the pump spot adjustment module, the repetition frequency is preset to 5 intervals: 20-50kHz, 50-100kHz, 100-300kHz, 300-500kHz, and 500-2000kHz. Each interval corresponds to a pre-stored pump current value and the distance from the focusing lens to the laser crystal. In response to the repetition frequency value, the pump current is controlled to switch to the preset current value, and the servo motor drives each stage of the focusing lens to move back and forth a preset distance. Each repetition frequency interval corresponds to a stored temperature field setting value. In response to the repetition frequency value, the TEC array is controlled to switch to the preset current value so that the temperature field of the laser crystal reaches the preset value.

3. A laser with adjustable repetition rate and high beam quality according to claim 2, characterized in that: The pump source outputs a pump laser with a wavelength of 888nm, a pump current ranging from 6 to 10A, and a focusing lens with a moving distance of ±10mm.

4. A laser with adjustable repetition rate and high beam quality according to claim 1, characterized in that: The pulse selector is an optical fiber AOM, and the pulse energy editing module is implemented through the optical fiber AOM. In Burst Mode, the optical fiber AOM receives the original pulse train from the seed source and modulates the sub-pulse energy based on the RF driving voltage synchronized with the seed source timing. The RF driving voltage Vi applied to the i-th sub-pulse satisfies V1<V2<…<Vn (1≤i≤n). The RF driving voltage is linearly related to the sub-pulse energy. The energy of the first sub-pulse is adjusted to the lowest level, and the energy of subsequent sub-pulses is increased successively, so that the energy of the edited pulse train is distributed in an increasing manner.

5. A laser with adjustable repetition rate and high beam quality according to claim 1, characterized in that: The uniform temperature field module also includes a copper heat sink surrounding the laser crystal for rapid heat dissipation of the laser crystal.

6. A laser with adjustable repetition rate and high beam quality according to claim 1, characterized in that: The laser crystal is doped with a gradient concentration along the incident direction of the pump light: 0-5mm region: 0% doping concentration; 5-10mm region: 0.1% doping concentration; 10-11mm region: 0.2% doping concentration; 11-30mm region: 0.3% doping concentration.

7. A laser with adjustable repetition rate and high beam quality according to claim 6, characterized in that: The laser crystal is an Nd:YVO4 crystal or an Nd:YAG crystal.

8. A laser with adjustable repetition rate and high beam quality according to claim 1, characterized in that: The output power of the seed source is 50-100mW, M2 < 1.1, and pulse width < 10pS.

9. A laser with adjustable repetition rate and high beam quality according to claim 1, characterized in that: It also includes a power feedback module, which is connected to the output of the third-stage laser amplifier. The power detector monitors the output power in real time and provides feedback to adjust the pump current and / or the position of the focusing lens.

10. A laser with adjustable repetition rate and high beam quality according to claim 9, characterized in that: When the power detector detects that the output power of xx deviates from the predetermined value: Prioritize fine-tuning the first-stage pump current by ±0.2A. If the target is not met, adjust the second-stage pump current by ±0.5A and the third-stage pump current by ±1A in sequence. If the condition is still not met, adjust the position of the third-stage focusing lens by ±2mm.

Images