A sub-pulse energy programmable high power picosecond pulse train laser and method

Abstract

The application discloses a high-power picosecond pulse train laser with programmable sub-pulse energy and a method, relates to the technical field of lasers, and comprises a mode-locked fiber laser, an acousto-optic modulator and a solid amplification chain arranged in sequence along an optical transmission path; the mode-locked fiber laser generates a mode-locked picosecond pulse sequence; the acousto-optic modulator performs pulse selection and pulse train grouping on the mode-locked picosecond pulse sequence, pre-programmed shaping is performed on the sub-pulse energy in the pulse train according to a set intensity distribution, and a pre-shaped pulse train is generated; the solid amplification chain comprises at least one solid amplifier, the solid amplifier comprises a dichroic mirror, a laser gain crystal, a coupling optical assembly and an LD pumping source; the dichroic mirror is used for focusing the pre-shaped pulse train amplified by the last stage and the LD pumping light transmitted through the coupling optical assembly into the laser gain crystal. Independent programmable control of the energy of each sub-pulse in the pulse train is realized, and the energy distribution of each sub-pulse in the pulse sequence can be flexibly adjusted.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of lasers, in particular to a high-power picosecond pulse train laser with programmable sub-pulse energy and a method. BACKGROUND

[0002] Traditional single-pulse laser processing methods have low processing efficiency, rough cutting seam edges, and large heat-affected zones, which seriously reduce the processing precision and quality of materials. Pulse train mode laser can more accurately control the material removal amount and heat input of the processing area by adjusting the number of sub-pulses, pulse interval, and energy distribution in the pulse cluster, thereby optimizing the cutting seam width and cutting depth and other processing effects. Under the same total pulse energy, pulse train mode distributes energy to multiple sub-pulses, reducing the peak power of each sub-pulse, which not only reduces the nonlinear effects and damage risk in optical components, but also improves the stability and reliability of the system. Compared with single-pulse output of the same energy, the heat effect of pulse train mode is smaller, the material removal process is more controllable, and the processing effect is better. However, in the prior art, the sub-pulse energy of the pulse train laser is difficult to accurately and flexibly control, which limits the further optimization of the processing technology.

[0003] At present, common time-domain shaping methods of ultra-short laser pulses include using a beam splitter to divide the incident pulse into two beams, adjusting the transmission path of the laser pulse through a pair of mirrors, or adjusting the optical path by changing the refractive index of the transmission medium. These methods all change the optical path of the ultra-short laser pulse to produce a certain delay.

[0004] The prior art discloses a system which is arranged in sequence along the light path direction, including a laser seed source, a pulse beam splitter, a laser amplifier and a beam combiner. The laser seed source is used to generate an initial pulse optical signal. The pulse beam splitter receives the pulse optical signal of the laser seed source and distributes power in a certain proportion while controlling the time delay of the pulse optical signal. The laser amplifier receives the pulse optical signal output by the pulse beam splitter and amplifies the low-power pulse optical signal. The beam combiner combines the pulse optical signal output by the laser amplifier into the same optical fiber to form a pulse train mode laser pulse output. However, this method has low controllability of sub-pulses, complex operation, low accuracy, and is difficult to efficiently shape the time domain of ultra-short pulses. SUMMARY

[0005] In order to solve the above problems, the application provides a high-power picosecond pulse train laser with programmable seed pulse energy and a method, the seed pulse is pre-shaped by an acousto-optic modulator to compensate for the influence of dynamic nonlinear effects such as gain saturation in a solid-state amplifier, the energy of each sub-pulse in the pulse train is independently programmable and controllable, the energy distribution of each sub-pulse in the pulse sequence can be flexibly adjusted, high average power and high-energy picosecond pulse train output is realized, and diversified laser processing application scenarios and requirements are met.

[0006] In order to achieve the above purpose, the application adopts the following technical solutions:

[0007] In the first aspect, the application provides a high-power picosecond pulse train laser with programmable seed pulse energy, comprising: a mode-locked fiber laser, an acousto-optic modulator and a solid-state amplifier chain arranged in sequence along an optical transmission path.

[0008] The mode-locked fiber laser is used to generate a mode-locked picosecond pulse sequence.

[0009] The acousto-optic modulator is used to select and group the pulse train, and pre-program the energy of the sub-pulse in the pulse train according to the set intensity distribution to generate a pre-shaped pulse train.

[0010] The solid-state amplifier chain includes at least one solid-state amplifier, and the solid-state amplifier includes a dichroic mirror, a laser gain crystal, a coupling optical assembly and an LD pump source; the dichroic mirror is used to focus the pre-shaped pulse train amplified by the previous stage and the LD pump light transmitted through the coupling optical assembly into the laser gain crystal.

[0011] As an optional implementation, the mode-locked fiber laser includes a first 976 nm laser diode, a first polarization-maintaining wavelength division multiplexer, a first polarization-maintaining single-mode ytterbium-doped fiber, a polarization-maintaining passive fiber, a non-reciprocal phase shifter, a polarization-maintaining fiber coupler, a fiber Bragg grating and a first polarization-maintaining optical isolator.

[0012] The first 976 nm laser diode is connected to the first polarization-maintaining wavelength division multiplexer, two output ends of the first polarization-maintaining wavelength division multiplexer are respectively connected to the input ends of the first polarization-maintaining single-mode ytterbium-doped fiber and the polarization-maintaining passive fiber, and two input ends of the polarization-maintaining fiber coupler are respectively connected to the output ends of the first polarization-maintaining single-mode ytterbium-doped fiber and the polarization-maintaining passive fiber; the first output end of the polarization-maintaining fiber coupler is connected to the fiber Bragg grating to form a high-reflection end of a resonant cavity, and the second output end is used as an output end of the mode-locked pulse, and the mode-locked picosecond pulse sequence is output through the first polarization-maintaining optical isolator; wherein the polarization-maintaining passive fiber is connected to the non-reciprocal phase shifter to introduce a fixed non-reciprocal phase shift of π / 2.

[0013] As an alternative embodiment, at least one optical fiber pre-amplifier is arranged before the acousto-optic modulator, which comprises a second polarization maintaining wavelength division multiplexer, a second 976 nm laser diode, a second polarization maintaining single-mode ytterbium-doped fiber and a second polarization maintaining optical isolator; the inputted upper-level mode-locked picosecond pulse sequence and the pump light outputted by the second 976 nm laser diode enter the second polarization maintaining single-mode ytterbium-doped fiber through the second polarization maintaining wavelength division multiplexer for amplification, and then the seed pulse sequence amplified by the optical fiber is outputted through the second polarization maintaining optical isolator.

[0014] As an alternative embodiment, the acousto-optic modulator is used for pulse selection according to the received driving signal to realize the adjustment of the pulse train repetition frequency in the range of 20 kHz to 200 kHz; and the selected pulse sequence is grouped into pulse trains, and the sub-pulse energy in each pulse train is independently pre-programmed and shaped according to the modulation of the amplitude of the driving signal.

[0015] As an alternative embodiment, at least one optical fiber post-amplifier is arranged after the acousto-optic modulator, which comprises a fourth polarization maintaining wavelength division multiplexer, a fourth 976 nm laser diode, a fourth polarization maintaining single-mode ytterbium-doped fiber, a fourth polarization maintaining optical isolator and an optical fiber collimator; the pre-shaped pulse train and the pump light outputted by the fourth 976 nm laser diode enter the fourth polarization maintaining single-mode ytterbium-doped fiber, the fourth polarization maintaining optical isolator and the optical fiber collimator in sequence through the fourth polarization maintaining wavelength division multiplexer, and then the pre-shaped pulse train amplified by the optical fiber is outputted.

[0016] As an alternative embodiment, the solid-state amplification chain comprises a cascaded solid-state pre-amplifier and at least one solid-state main amplifier.

[0017] The solid-state pre-amplifier comprises an isolating optical assembly, a first plano-convex lens, a first laser gain crystal, a 0° dichroic mirror, a first biconvex lens, a second biconvex lens and a first LD pump source.

[0018] The pre-shaped pulse train enters the first laser gain crystal in sequence through the isolating optical assembly and the first plano-convex lens for one-time amplification;

[0019] The pump light emitted by the first LD pump source enters the first laser gain crystal after passing through the 0° dichroic mirror through the coupling optical assembly composed of the second biconvex lens and the first biconvex lens in sequence;

[0020] The pre-shaped pulse train after one-time amplification is reflected to the first laser gain crystal through the 0° dichroic mirror for two-time amplification;

[0021] The pre-shaped pulse train after two-time amplification is outputted in sequence through the first plano-convex lens and the isolating optical assembly and enters the next-level solid-state main amplifier.

[0022] As an alternative implementation, the isolation optical assembly comprises a first spatial isolator, a first 1064 nm half-wave plate, a second spatial isolator and a second 1064 nm half-wave plate connected in sequence.

[0023] As an alternative implementation, each stage of the solid main amplifier comprises a 45° dichroic mirror, a coupling optical assembly composed of a lenticular lens, a second laser gain crystal, a second LD pump source and a plano-concave lens; the pulse train input from the previous stage and the LD pump light transmitted through the coupling optical assembly are focused into the second laser gain crystal through the dichroic mirror, and the pulse train amplified by the second laser gain crystal enters the next stage of the solid main amplifier through the plano-concave lens.

[0024] As an alternative implementation, the first stage of the solid main amplifier is further provided with a second plano-convex lens before the 45° dichroic mirror, and the other stages of the solid main amplifier are provided with a 45° mirror before the 45° dichroic mirror.

[0025] The last stage of the solid main amplifier is provided with a third plano-convex lens before the plano-concave lens and a pinhole aperture after the plano-concave lens.

[0026] In the last stage of the solid main amplifier, the amplified pulse train is expanded and shaped through the third plano-convex lens and the plano-concave lens in sequence, and finally output as a multi-stage amplified high-power picosecond pulse train through the pinhole aperture.

[0027] In a second aspect, the application provides a working method of a high-power picosecond pulse train laser with programmable sub-pulse energy, comprising:

[0028] Generating a mode-locked picosecond pulse sequence through a mode-locked fiber laser;

[0029] Performing pulse selection and pulse train grouping on the mode-locked picosecond pulse sequence through an acousto-optic modulator, and pre-programming and shaping the sub-pulse energy in the pulse train according to a set intensity distribution to generate a pre-shaped pulse train;

[0030] Performing multi-stage amplification on the pre-shaped pulse train through at least one stage of solid amplifiers to output a multi-stage amplified high-power picosecond pulse train; wherein the solid amplifiers comprise a dichroic mirror, a laser gain crystal, a coupling optical assembly and an LD pump source, and the dichroic mirror is used to focus the pre-shaped pulse train amplified by the previous stage and the LD pump light transmitted through the coupling optical assembly into the laser gain crystal.

[0031] Compared with the prior art, the application has the following beneficial effects:

[0032] The application realizes pulse train output with consistent energy and high sub-pulse energy fidelity by the synergistic effect of seed pulse pre-shaping and gain saturation effect of solid amplification chain, and the sub-pulse energy of the pulse train is programmable, the relative intensity and energy of each pulse in the pulse sequence can be flexibly regulated, and the application has high configurability and can meet diversified laser processing application scenarios and requirements.

[0033] The application places a programmable acousto-optic modulator in a low-power seed light path, independently pre-programmed shaping of pulse train grouping and relative energy of sub-pulses, and combines a fiber-solid hybrid amplification architecture, while realizing high average power and high pulse train energy output, effectively suppressing the disturbance of gain saturation and other nonlinear effects in the solid amplifier to the sub-pulse energy distribution in the pulse envelope. Compared with the problem that the energy of each sub-pulse in the pulse train is uncontrollable or poor consistency in the prior art, the application can accurately and flexibly independently regulate the relative energy distribution of each sub-pulse in the pulse train, significantly improving the controllability of heat input and material removal accuracy in the laser processing process. In addition, the introduction of the fiber amplification chain effectively improves the signal-to-noise ratio of the seed signal, suppresses the ASE (Amplified Spontaneous Emission) effect in the subsequent solid amplification, and guarantees the beam quality and system stability under high energy output. It can meet the high flexibility requirements of pulse energy distribution in various laser processing scenarios such as precision micro-machining, brittle material cutting, and surface texturing.

[0034] The application can realize an average output power of more than 100 W and a pulse train energy of more than 5 mJ at a pulse train repetition frequency of 20 kHz, and support high-precision, programmable independent regulation of the relative energy of each sub-pulse in the pulse train, effectively overcoming the sub-pulse energy distortion problem caused by gain saturation effect in the existing pulse train laser, and the performance is significantly better than that of the traditional scheme. BRIEF DESCRIPTION OF DRAWINGS

[0035] In order to more clearly illustrate the technical solutions in the embodiments of the application or the prior art, the following will briefly introduce the drawings needed to be used in the embodiments or prior art description. Obviously, the drawings in the following description are only embodiments of the application, and other drawings can be obtained by those skilled in the art without creative labor on the basis of the provided drawings.

[0036] Figure 1 A structure schematic view of a sub-pulse energy programmable high-power picosecond pulse train laser provided for Embodiment 1 of the application;

[0037] Figure 2 A mode-locked picosecond pulse sequence output by a mode-locked fiber laser provided for Embodiment 1 of the application;

[0038] Figure 3 Pulse train waveform diagram without pre-shaping by acousto-optic modulator for embodiment 1 of the present application;

[0039] Figure 4 Driving signal of acousto-optic modulator and corresponding seed pulse synchronization electrical signal waveform diagram for embodiment 1 of the present application;

[0040] Figure 5 Seed pulse intensity distribution diagram after pre-shaping by acousto-optic modulator for embodiment 1 of the present application;

[0041] Figure 6 Final output pulse train waveform diagram after pre-shaping and amplification by acousto-optic modulator for embodiment 1 of the present application;

[0042] Figure 7 Uniformly distributed sub-pulse energy distribution waveform diagram output after programmed control for embodiment 1 of the present application;

[0043] Figure 8 Stepped-increasing sub-pulse energy distribution waveform diagram output after programmed control for embodiment 1 of the present application;

[0044] Figure 9 Stepped-decreasing sub-pulse energy distribution waveform diagram output after programmed control for embodiment 1 of the present application;

[0045] Figure 10 Center-enhanced sub-pulse energy distribution waveform diagram output after programmed control for embodiment 1 of the present application;

[0046] Figure 11 Edge-enhanced sub-pulse energy distribution waveform diagram output after programmed control for embodiment 1 of the present application;

[0047] Figure 12 Pulse output sequence diagram at 20 kHz repetition frequency for embodiment 1 of the present application;

[0048] Figure 13 Pulse output sequence diagram at 50 kHz repetition frequency for embodiment 1 of the present application;

[0049] Figure 14 Pulse output sequence diagram at 100 kHz repetition frequency for embodiment 1 of the present application;

[0050] Figure 15 Pulse output sequence diagram at 200 kHz repetition frequency for embodiment 1 of the present application;

[0051] Figure 16 Output power evolution curve diagram of each stage of solid-state amplifier for embodiment 1 of the present application;

[0052] Figure 17 Intensity autocorrelation trace of the output laser after multi-stage amplification provided for the embodiment 1 of the present application;

[0053] Figure 18 Spectrum characteristic diagram of the output laser provided for the embodiment 1 of the present application;

[0054] Figure 19 Measurement result of the beam quality factor and far field spot distribution diagram of the output beam provided for the embodiment 1 of the present application;

[0055] 1, a first 976 nm laser diode; 2, a first polarization maintaining wavelength division multiplexer; 3, a first polarization maintaining single-mode ytterbium-doped fiber; 4, a polarization maintaining passive fiber; 5, a non-reciprocal phase shifter; 6, a polarization maintaining fiber coupler; 7, a fiber Bragg grating; 8, a first polarization maintaining optical isolator; 9, a second polarization maintaining wavelength division multiplexer; 10, a second 976 nm laser diode; 11, a second polarization maintaining single-mode ytterbium-doped fiber; 12, a second polarization maintaining optical isolator; 13, a third polarization maintaining wavelength division multiplexer; 14, a third 976 nm laser diode; 15, a third polarization maintaining single-mode ytterbium-doped fiber; 16, a third polarization maintaining optical isolator; 17, an acousto-optic modulator; 18, an acousto-optic modulator control board; 19, a fourth polarization maintaining wavelength division multiplexer; 20, a fourth 976 nm laser diode; 21, a fourth polarization maintaining single-mode ytterbium-doped fiber; 22, a fourth polarization maintaining optical isolator; 23, a fiber collimator; 24, a first spatial isolator; 25, a first 1064 nm half-wave plate; 26, a second spatial isolator; 27, a second 1064 nm half-wave plate; 28, a first plano-convex lens; 29, a first laser gain crystal; 30, a 0° dichroic mirror; 31, a first lenticular lens; 32, a second lenticular lens; 33, a first LD pump source; 34, a second plano-convex lens; 35, a first 45° dichroic mirror; 36, a third lenticular lens; 37, a fourth lenticular lens; 38, a second LD pump source; 39, a second laser gain crystal; 40, a first plano-concave lens; 41, a first 45° mirror; 42, a second 45° dichroic mirror; 43, a fifth lenticular lens; 44, a sixth lenticular lens; 45, a third LD pump source; 46, a third laser gain crystal; 47, a second plano-concave lens; 48, a second 45° mirror; 49, a third 45° dichroic mirror; 50, a seventh lenticular lens; 51, an eighth lenticular lens; 52, a fourth LD pump source; 53, a fourth laser gain crystal; 54, a third plano-concave lens; 55, a third 45° mirror; 56, a fourth 45° dichroic mirror; 57, a ninth lenticular lens; 58, a tenth lenticular lens; 59, a fifth LD pump source; 60, a fifth laser gain crystal; 61, a third plano-convex lens; 62, a fourth plano-concave lens; 63, a pinhole diaphragm. DETAILED DESCRIPTION

[0056] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0057] It should be noted that the following detailed descriptions are exemplary and intended to provide further illustration of the invention. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0058] It should be noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the scope of exemplary embodiments according to the invention. As used herein, unless the context clearly indicates otherwise, the singular form is intended to include the plural form as well. Furthermore, it should be understood that the terms “comprising” and “including”, and any variations thereof, are intended to cover non-exclusive inclusion, for example, a process, method, system, product, or apparatus that includes a series of steps or units is not necessarily limited to those steps or units explicitly listed, but may include other steps or units not explicitly listed or inherent to such processes, methods, products, or apparatus.

[0059] Where there is no conflict, the embodiments and features in the embodiments of the present invention can be combined with each other.

[0060] Example 1

[0061] like Figure 1 As shown, this embodiment provides a high-power picosecond pulse train laser with programmable sub-pulse energy, comprising: a mode-locked fiber laser, an acousto-optic modulator, and a solid-state amplifier chain arranged sequentially along the optical transmission path;

[0062] Mode-locked fiber lasers are used to generate mode-locked picosecond pulse sequences;

[0063] The acousto-optic modulator is used to select pulses and group pulse trains in mode-locked picosecond pulse sequences, pre-program and shape the energy of sub-pulses within the pulse train according to a set intensity distribution, and generate a pre-shaped pulse train.

[0064] The solid-state amplification chain includes at least one solid-state amplifier, which includes a dichroic mirror, a laser gain crystal, a coupling optical component, and an LD pump source. The dichroic mirror is used to focus the pre-shaped pulse train amplified by the previous stage and the LD pump light transmitted through the coupling optical component onto the laser gain crystal.

[0065] In this embodiment, a mode-locked fiber laser is used to generate stable mode-locked laser pulses and output a mode-locked picosecond pulse sequence with a specific wavelength, repetition frequency, and pulse width as a seed pulse.

[0066] The mode-locked fiber laser comprises a first 976 nm laser diode 1, a first polarization-maintaining wavelength division multiplexer 2, a first polarization-maintaining single-mode ytterbium-doped fiber 3, a polarization-maintaining passive fiber 4, a non-reciprocal phase shifter 5, a polarization-maintaining fiber coupler 6, a fiber Bragg grating 7, and a first polarization-maintaining optical isolator 8.

[0067] Specifically,

[0068] The first 976 nm laser diode 1 is used for outputting a laser beam, and the output end thereof is connected to the input end of the first polarization-maintaining wavelength division multiplexer 2.

[0069] The first output end of the first polarization-maintaining wavelength division multiplexer 2 is connected to the first polarization-maintaining single-mode ytterbium-doped fiber 3, and the second output end is connected to the polarization-maintaining passive fiber 4, which is used for splitting the laser beam into two paths and transmitting them through the first polarization-maintaining single-mode ytterbium-doped fiber 3 and the polarization-maintaining passive fiber 4 respectively.

[0070] The first polarization-maintaining single-mode ytterbium-doped fiber 3 is used as a gain fiber, and has a core diameter of 6 μm, a numerical aperture of 0.11, and an absorption coefficient of 250 dB / m at a wavelength of 976 nm; the first polarization-maintaining single-mode ytterbium-doped fiber 3 is pumped by the first 976 nm laser diode 1 through the first polarization-maintaining wavelength division multiplexer 2, and is configured to have an appropriate length to provide sufficient intracavity gain.

[0071] The polarization-maintaining passive fiber 4 is connected to the non-reciprocal phase shifter 5, and the polarization-maintaining passive fiber 4 adopts a polarization-maintaining single-mode fiber with a zero dispersion wavelength of about 980 nm, has a stable birefringence axis and a low transmission loss (less than 0.1 dB / m), and is used for accurately regulating the optical path length in the resonant cavity and the polarization evolution path, so as to maintain the polarization stability in the cavity and provide the required phase reference condition for the non-reciprocal phase mode-locking mechanism.

[0072] The non-reciprocal phase shifter 5 is used for introducing a fixed non-reciprocal phase shift of π / 2, constructing an asymmetric optical path, breaking the phase symmetry of the round-trip light in the cavity, thereby realizing the self-starting mode-locking function, effectively suppressing the continuous light oscillation, and improving the pulse stability.

[0073] The two input ends of the polarization-maintaining fiber coupler 6 are connected to the first polarization-maintaining single-mode ytterbium-doped fiber 3 and the polarization-maintaining passive fiber 4 respectively, the first output end is connected to the fiber Bragg grating 7 with a center wavelength of 1064 nm and a reflectivity of 99%, and the polarization-maintaining fiber coupler 6 constitutes a high-reflection end of the resonant cavity;

[0074] The second output end is used as an output port of the mode-locked pulse, and the output mode-locked picosecond pulse sequence enters a fiber preamplifier through the first polarization-maintaining optical isolator 8;

[0075] The final output is a mode-locked picosecond pulse train with a center wavelength of 1064 nm, a repetition rate of 20 MHz, and a pulse width of 10 ps, providing a high-quality seed source for subsequent pulse train editing and high-power amplification.

[0076] As an alternative embodiment, the polarization maintaining fiber coupler 6 has high polarization maintaining capability and precise splitting ratio, which is used to directionally couple the in-cavity forward and backward propagating light, on one hand, to form the output coupling port of the resonant cavity, and on the other hand, to feedback part of the light to the gain medium to maintain oscillation, ensuring efficient extraction and stable output of the mode-locked pulse.

[0077] As an alternative embodiment, the fiber Bragg grating 7 has high reflectivity (≥99%) and narrow band wavelength selectivity (center wavelength 1064 nm), which is used as a high reflectivity mirror of the resonant cavity, can effectively reflect the signal light and suppress the spontaneous emission of non-target wavelengths, and improve the spectral purity and output stability of the laser.

[0078] In this embodiment, at least one fiber amplifier is arranged before or after the acousto-optic modulator 17 to improve the seed pulse power and suppress amplified spontaneous emission.

[0079] As an alternative embodiment, at least one fiber pre-amplifier is arranged before the acousto-optic modulator 17, and at least one fiber post-amplifier is arranged after the acousto-optic modulator 17.

[0080] Further, two-stage fiber pre-amplifiers are arranged before the acousto-optic modulator 17, and one-stage fiber post-amplifier is arranged after the acousto-optic modulator 17.

[0081] The fiber amplifier is described as follows.

[0082] In this embodiment, the fiber pre-amplifier is used to modulate the output power and pulse energy of the mode-locked fiber laser to improve to a set intermediate power level while maintaining the spectral characteristics of the seed pulse.

[0083] The fiber pre-amplifier includes a first-stage single-mode ytterbium-doped fiber pre-amplifier and a second-stage single-mode ytterbium-doped fiber pre-amplifier.

[0084] The first-stage single-mode ytterbium-doped fiber pre-amplifier includes a second polarization division multiplexer 9, a second 976 nm laser diode 10, a second polarization maintaining single-mode ytterbium-doped fiber 11, and a second polarization maintaining optical isolator 12.

[0085] The second-stage single-mode ytterbium-doped fiber pre-amplifier includes a third polarization division multiplexer 13, a third 976 nm laser diode 14, a third polarization maintaining single-mode ytterbium-doped fiber 15, and a third polarization maintaining optical isolator 16.

[0086] Wherein:

[0087] The first input end of the second polarization maintaining wavelength division multiplexer 9 is connected to the output end of the first polarization maintaining optical isolator 8 of the mode-locked fiber laser, and the second input end is connected to the output end of the second 976 nm laser diode 10; the output end of the second polarization maintaining wavelength division multiplexer 9 is connected to the input end of the second polarization maintaining single-mode ytterbium-doped fiber 11, and the output end of the second polarization maintaining single-mode ytterbium-doped fiber 11 is connected to the input end of the second polarization maintaining optical isolator 12.

[0088] The first input end of the third polarization maintaining wavelength division multiplexer 13 is connected to the output end of the second polarization maintaining optical isolator 12, and the second input end is connected to the output end of the third 976 nm laser diode 14; the output end of the third polarization maintaining wavelength division multiplexer 13 is connected to the input end of the third polarization maintaining single-mode ytterbium-doped fiber 15, the output end of the third polarization maintaining single-mode ytterbium-doped fiber 15 is connected to the input end of the third polarization maintaining optical isolator 16, and the output end of the third polarization maintaining optical isolator 16 is connected to the acousto-optic modulator 17.

[0089] Specifically:

[0090] The mode-locked picosecond pulse sequence output by the mode-locked fiber laser enters the second polarization maintaining single-mode ytterbium-doped fiber 11 through the second polarization maintaining wavelength division multiplexer 9 for amplification; the pump light output by the second 976 nm laser diode 10 enters the second polarization maintaining single-mode ytterbium-doped fiber 11 through the second polarization maintaining wavelength division multiplexer 9 for amplification; the signal light amplified by the second polarization maintaining single-mode ytterbium-doped fiber 11 is then filtered and isolated by the second polarization maintaining optical isolator 12, thereby realizing higher-power narrow-band output.

[0091] The first-stage single-mode ytterbium-doped fiber preamplifier outputs a first-stage fiber-amplified seed pulse sequence, and the mode-locked picosecond pulse sequence amplified by the first-stage single-mode ytterbium-doped fiber preamplifier enters the third polarization maintaining single-mode ytterbium-doped fiber 15 through the third polarization maintaining wavelength division multiplexer 13 for amplification; the pump light output by the third 976 nm laser diode 14 enters the third polarization maintaining single-mode ytterbium-doped fiber 15 through the third polarization maintaining wavelength division multiplexer 13 for amplification; the signal light amplified by the third polarization maintaining single-mode ytterbium-doped fiber 15 is then filtered and isolated by the third polarization maintaining optical isolator 16, thereby realizing higher-power narrow-band output.

[0092] Finally, the second-stage single-mode ytterbium-doped fiber preamplifier outputs a second-stage fiber-amplified seed pulse sequence.

[0093] In this embodiment, the second-stage fiber-amplified seed pulse sequence enters the acousto-optic modulator 17, the acousto-optic modulator 17 performs pulse selection and pulse string grouping on the seed pulse sequence, and independently pre-programmed shaping on the sub-pulse energy in each pulse string, to generate a pre-shaped pulse string with sub-pulse energy according to a set intensity distribution.

[0094] Specifically:

[0095] The acousto-optic modulator 17 is connected with an acousto-optic modulator control board 18, the acousto-optic modulator control board 18 has high-precision analog / digital hybrid output capability and programmable waveform generation function, generates a driving signal for driving the acousto-optic modulator 17, and controls the time-domain waveform of the seed pulse sequence by adjusting the amplitude of the driving signal, so as to realize pulse pre-shaping of stepped, linear or arbitrarily set intensity distribution.

[0096] The acousto-optic modulator 17 receives the driving signal, selects the seed pulse sequence according to the driving signal to selectively pick up the required pulse sequence to realize the adjustment of the pulse train repetition frequency in the range of 20 kHz to 200 kHz, and groups the selected pulse sequence, independently pre-programmed shaping of the sub-pulse energy in each pulse train according to the modulation of the amplitude of the driving signal to generate a pre-shaped pulse train with sub-pulse energy according to the set intensity distribution, such as discrete stepped sub-pulse energy with stepwise increasing intensity distribution.

[0097] As an alternative embodiment, the acousto-optic modulator 17 has high diffraction efficiency, fast switching response (rise / fall time ≤ 50 ns) and wide radio frequency bandwidth, which is used for high-speed gating and amplitude modulation of the input pulse sequence, realizes continuous adjustment of the pulse train repetition frequency in the range of 20 kHz to 200 kHz, and supports programmable control of the intensity of each sub-pulse in the pulse train.

[0098] As shown in Figure 2 is a mode-locked picosecond pulse sequence with a repetition frequency of 20 MHz and a pulse width of 10 ps output by a mode-locked fiber laser.

[0099] As shown in Figure 3 , the mode-locked picosecond pulse sequence is not pre-shaped by the acousto-optic modulator, but directly amplified by multiple-stage solid-state amplifiers. Due to the gain saturation effect of the solid-state amplifier, the first few sub-pulses in the pulse train preferentially extract the amplifier gain, resulting in higher amplitude and energy than the subsequent sub-pulses, and the energy distribution in the pulse train is uneven, thus presenting a non-uniform waveform with high front and low back due to gain saturation.

[0100] As shown in Figure 4 is the driving signal waveform of the acousto-optic modulator and its corresponding seed pulse synchronization electrical signal waveform; the driving signal has an increasing amplitude distribution from front to back, which is used to offset the uneven sub-pulse energy in the pulse train caused by the gain saturation effect in the solid-state amplifier through feedforward compensation, so as to realize accurate control of the output pulse train waveform.

[0101] As shown in Figure 5 , the intensity distribution of the seed pulse after pre-shaping by the acousto-optic modulator presents a stepwise increasing pattern with low front and high back, which is Figure 4The driving signal waveforms shown are matched, laying a foundation for subsequent gain saturation compensation.

[0102] In the embodiment, the fiber post-amplifier is used to preliminarily amplify the pre-shaped pulse train, improve the output power and pulse energy of the seed pulse, improve the signal-to-noise ratio of the seed pulse, and suppress the ASE effect in the subsequent solid-state amplification.

[0103] The fiber post-amplifier comprises a fourth polarization-maintaining wavelength division multiplexer 19, a fourth 976 nm laser diode 20, a fourth polarization-maintaining single-mode ytterbium-doped fiber 21, a fourth polarization-maintaining optical isolator 22, and a fiber collimator 23.

[0104] The first input end of the fourth polarization-maintaining wavelength division multiplexer 19 is connected to the output end of the acousto-optic modulator 17, and the second input end is connected to the output end of the fourth 976 nm laser diode 20; the output end of the fourth polarization-maintaining wavelength division multiplexer 19 is connected to the input end of the fourth polarization-maintaining single-mode ytterbium-doped fiber 21, the output end of the fourth polarization-maintaining single-mode ytterbium-doped fiber 21 is connected to the input end of the fourth polarization-maintaining optical isolator 22, and the output end of the fourth polarization-maintaining optical isolator 22 is connected to the input end of the fiber collimator 23.

[0105] Specifically:

[0106] The pre-shaped pulse train programmed and controlled by the acousto-optic modulator 17 enters the fourth polarization-maintaining single-mode ytterbium-doped fiber 21 through the fourth polarization-maintaining wavelength division multiplexer 19;

[0107] The pump light output by the fourth 976 nm laser diode 20 enters the fourth polarization-maintaining single-mode ytterbium-doped fiber 21 through the fourth polarization-maintaining wavelength division multiplexer 19;

[0108] The signal light amplified by the fourth polarization-maintaining single-mode ytterbium-doped fiber 21 is isolated and filtered by the fourth polarization-maintaining optical isolator 22 to realize higher-power narrowband output;

[0109] The signal light output by the fourth polarization-maintaining optical isolator 22 is collimated into parallel light by the fiber collimator 23, and finally the pre-shaped pulse train amplified by the fiber with programmable control of sub-pulse energy is output.

[0110] The embodiment adopts fiber amplification technology to realize efficient and narrow spectrum pulse amplification through optimization of fiber length and narrow-band filtering technology. The optimization of fiber length comprehensively considers the suppression of nonlinear effects (such as self-phase modulation, stimulated Raman scattering, etc.) and the maximization of small signal gain, and the typical length range of the gain fiber is determined through experimental test. The narrow-band filter adopts a fiber Bragg grating with a center wavelength consistent with the output wavelength of the mode-locked fiber laser and a 3dB bandwidth less than 0.5 nm, which is arranged between adjacent fiber amplification stages to selectively transmit signal light and effectively suppress broadband amplified spontaneous emission noise. By multi-stage fiber amplification of the mode-locked fiber laser with low output power, the signal light power is improved, and the problems of low efficiency and easy generation of spontaneous radiation light amplification caused by direct solid amplification, which deteriorate the signal-to-noise ratio, are avoided.

[0111] As an optional implementation, the fiber collimator 23 has high coupling efficiency, low wavefront distortion and excellent polarization maintaining performance, and is used to convert the divergent laser beam output by the fiber into a parallel free-space light beam, which can realize low-loss and high-stability butt joint between the fiber and the free-space optical path, and provide a high-quality input light beam for subsequent free-space modulation or amplification.

[0112] As an optional implementation, the first polarization maintaining wavelength division multiplexer 2, the second polarization maintaining wavelength division multiplexer 9, the third polarization maintaining wavelength division multiplexer 13 and the fourth polarization maintaining wavelength division multiplexer 19 all adopt high-extinction-ratio polarization maintaining structures, have excellent wavelength selectivity and low insertion loss (typical value <0.3 dB), and can efficiently realize beam combining or beam splitting of 976 nm pump light and 1064 nm signal light, ensure effective injection of pump energy, and reduce stray interference in the signal light path.

[0113] As an optional implementation, the first 976 nm laser diode 1, the second 976 nm laser diode 10, the third 976 nm laser diode 14 and the fourth 976 nm laser diode 20 all output light spectrum with a center wavelength stable at 976 nm, have high output power and narrow linewidth characteristics, and provide sufficient and stable pump sources for each stage of the ytterbium-doped fiber amplification section.

[0114] As an optional implementation, the first polarization maintaining single-mode ytterbium-doped fiber 3, the second polarization maintaining single-mode ytterbium-doped fiber 11, the third polarization maintaining single-mode ytterbium-doped fiber 15 and the fourth polarization maintaining single-mode ytterbium-doped fiber 21 all adopt high-doping-concentration design, have high small-signal gain coefficient and excellent polarization maintaining capability (extinction ratio greater than 20 dB), effectively maintain the linear polarization state of the output light beam while amplifying the 1064 nm signal light, and guarantee the polarization matching requirements of the subsequent free-space modulation and amplification modules.

[0115] As an alternative implementation, the first polarization-maintaining isolator 8, the second polarization-maintaining isolator 12, the third polarization-maintaining isolator 16, and the fourth polarization-maintaining isolator 22 have high transmittance and high wavelength selectivity, which can achieve isolation, prevent interference from reverse light, filter out stray light, and improve the purity of signal light.

[0116] This embodiment employs the figure-9 cavity fiber mode-locking technology, which introduces the synergistic effect of non-reciprocal phase-shifting units and polarization-sensitive components into a fully polarization-maintaining fiber resonant cavity to construct a ring equivalent cavity structure with asymmetric round-trip phase response.

[0117] Specifically, a non-reciprocal phase shifter 5 is used to introduce... A fixed non-reciprocal phase shift of π / 2, combined with the intrinsic birefringence of polarization-maintaining fiber, creates a difference in the polarization state evolution of forward and reverse propagating light, thus forming an equivalent nonlinear polarization rotation mechanism. This mechanism generates intensity-dependent non-reciprocal loss within the cavity, satisfying the conditions for self-starting mode-locking, and enabling stable picosecond pulse output without the need for an additional saturable absorber. This structure offers advantages such as all-fiber operation, full polarization maintenance, high environmental stability, and strong self-starting capability, making it suitable for constructing high-reliability industrial-grade ultrafast laser seed sources.

[0118] In this embodiment, a solid-state amplifier chain is used to amplify the power of the pre-shaped pulse train, increase the output power and pulse energy, and utilize the characteristic that the gain medium is not yet saturated in the early stage of pulse train propagation (i.e., gain saturation effect) to enable the earlier pulses to obtain higher gain, thereby compensating for the non-uniform intensity distribution in the pre-shaped pulse train (such as a preset decreasing step-like intensity distribution), thereby outputting a high-power picosecond pulse train with consistent or on-demand distribution of sub-pulse energy, achieving consistent energy output of each sub-pulse within the pulse train.

[0119] In this embodiment, the solid-state amplifier chain includes a cascaded solid-state preamplifier and at least one solid-state main amplifier, used to further amplify the energy of the sub-pulse train to a high-energy output level.

[0120] The solid-state preamplifier is a dual-pass amplification structure. It uses a mirror to make the signal light pass through the same laser gain crystal twice, which is used to amplify low-power signal light to achieve higher gain.

[0121] The solid-state preamplifier includes a first spatial isolator 24, a first 1064 nm half-wave plate 25, a second spatial isolator 26, a second 1064 nm half-wave plate 27, a first plano-convex lens 28, a first laser gain crystal 29, a 0° dichroic mirror 30, a first biconvex lens 31, a second biconvex lens 32, and a first LD pump source 33.

[0122] Specifically:

[0123] The input end of the first spatial isolator 24 is connected to the output end of the fiber collimator 23 of the fiber post-amplifier. The fiber-amplified pre-shaped pulse train output by the fiber collimator 23 passes through the first spatial isolator 24, the first 1064 nm half-wave plate 25, the second spatial isolator 26, the second 1064 nm half-wave plate 27 in sequence, and then is focused by the first plano-convex lens 28 to be incident into the first laser gain crystal 29.

[0124] When the fiber-amplified pre-shaped pulse train passes through the first laser gain crystal 29 for the first time, part of the stored energy is extracted to realize the first amplification.

[0125] Subsequently, the amplified pre-shaped pulse train is reflected by the 0° dichroic mirror 30 and passes through the first laser gain crystal 29 again to further extract energy and realize the second amplification.

[0126] The pump light emitted by the first LD pump source 33 passes through the coupling optical assembly composed of the second lenticular lens 32 and the first lenticular lens 31 in sequence, is focused after passing through the 0° dichroic mirror 30, and is also incident into the first laser gain crystal 29. The purpose is to excite the first laser gain crystal 29 by pump light to realize population inversion, so as to provide initial optical gain for the incident pulse. This process is a necessary condition for realizing laser amplification: only when the gain medium is in a population inversion state, the incident signal light can obtain energy amplification through stimulated radiation after passing through the gain medium.

[0127] Finally, the twice-amplified pre-shaped pulse train passes through the first plano-convex lens 28 and the second 1064 nm half-wave plate 27, and is finally output through the side output port of the second spatial isolator 26 to enter the multi-stage solid main amplifier.

[0128] As an optional implementation, the first spatial isolator 24 and the second spatial isolator 26 both have high isolation degree (> 30 dB) and low insertion loss (< 0.2 dB), which can effectively block the reverse propagation light and prevent it from interfering with the upstream optical components and the seed source, thereby improving the system operation stability.

[0129] As an optional implementation, the first 1064 nm half-wave plate 25 and the second 1064 nm half-wave plate 27 are made of a high-damage-threshold substrate and coated with a wide-spectrum anti-reflection film, and have excellent transmittance (> 99.5%) and extremely low polarization-dependent loss, which are used to accurately control the polarization direction of the 1064 nm laser to match the polarization-sensitive components of the subsequent amplification module.

[0130] In the embodiment, the multi-stage solid main amplifier is used to further increase the output power of the solid pre-amplifier to a high power level; based on the physical relationship between the pump power density and the ASE threshold in the solid amplifier (ASE starting condition: gain x length > loss), high pump density will cause local gain to be too high, accelerating ASE accumulation. Therefore, under the premise of maintaining sufficient total pump energy to provide the required small signal gain, the pump power per unit area (i.e. pump density) is reduced by increasing the pump spot area or reducing the pump power, thereby increasing the threshold of ASE, suppressing the adverse effects of ASE, further improving the signal-to-noise ratio of the output laser pulse, and ultimately realizing high-power picosecond pulse train laser output.

[0131] Specifically, the multi-stage solid main amplifier includes a first-stage solid main amplifier, a second-stage solid main amplifier, a third-stage solid main amplifier, and a fourth-stage solid main amplifier.

[0132] Among them:

[0133] The first-stage solid main amplifier includes a second plano-convex lens 34, a first 45° dichroic mirror 35, a third double convex lens 36, a fourth double convex lens 37, a second LD pump source 38, a second laser gain crystal 39, and a first plano-concave lens 40.

[0134] The second-stage solid main amplifier includes a first 45° mirror 41, a second 45° dichroic mirror 42, a fifth double convex lens 43, a sixth double convex lens 44, a third LD pump source 45, a third laser gain crystal 46, and a second plano-concave lens 47.

[0135] The third-stage solid main amplifier includes a second 45° mirror 48, a third 45° dichroic mirror 49, a seventh double convex lens 50, an eighth double convex lens 51, a fourth LD pump source 52, a fourth laser gain crystal 53, and a third plano-concave lens 54.

[0136] The fourth-stage solid main amplifier includes a third 45° mirror 55, a fourth 45° dichroic mirror 56, a ninth double convex lens 57, a tenth double convex lens 58, a fifth LD pump source 59, a fifth laser gain crystal 60, a third plano-convex lens 61, a fourth plano-concave lens 62, and a small aperture diaphragm 63.

[0137] Specifically:

[0138] (1) The laser pulse train amplified by the solid pre-amplifier passes through the second plano-convex lens 34 and the first 45° dichroic mirror 35 in turn and is focused into the second laser gain crystal 39;

[0139] Meanwhile the pump light emitted by the second LD pump source 38 is focused into the second laser gain crystal 39 through the coupling optical assembly composed of the fourth lenticular lens 37 and the third lenticular lens 36 in turn and also through the first 45° dichroic mirror 35;

[0140] The laser pulse train amplified by the second laser gain crystal 39 enters into the second stage solid main amplifier through the first plano-concave lens 40.

[0141] (2) The laser pulse train amplified by the first stage solid main amplifier enters into the third laser gain crystal 46 through the first 45° reflecting mirror 41 and the second 45° dichroic mirror 42;

[0142] Meanwhile the pump light emitted by the third LD pump source 45 is focused into the third laser gain crystal 46 through the coupling optical assembly composed of the sixth lenticular lens 44 and the fifth lenticular lens 43 in turn and also through the second 45° dichroic mirror 42;

[0143] The laser pulse train amplified by the third laser gain crystal 46 enters into the third stage solid main amplifier through the second plano-concave lens 47.

[0144] (3) The laser pulse train amplified by the second stage solid main amplifier enters into the fourth laser gain crystal 53 through the second 45° reflecting mirror 48 and the third 45° dichroic mirror 49;

[0145] Meanwhile the pump light emitted by the fourth LD pump source 52 is focused into the fourth laser gain crystal 53 through the coupling optical assembly composed of the eighth lenticular lens 51 and the seventh lenticular lens 50 in turn and also through the third 45° dichroic mirror 49;

[0146] The laser pulse train amplified by the fourth laser gain crystal 53 enters into the fourth stage solid main amplifier through the third plano-concave lens 54.

[0147] (4) The laser pulse train amplified by the third stage solid main amplifier enters into the fifth laser gain crystal 60 through the third 45° reflecting mirror 55 and the fourth 45° dichroic mirror 56;

[0148] Meanwhile the pump light emitted by the fifth LD pump source 59 is focused into the fifth laser gain crystal 60 through the coupling optical assembly composed of the tenth lenticular lens 58 and the ninth lenticular lens 57 in turn and also through the fourth 45° dichroic mirror 56;

[0149] The laser pulse train amplified by the fifth laser gain crystal 60 is shaped and expanded through the telescope system composed of the third plano-concave lens 61 and the fourth plano-concave lens 62 in turn, and finally the multi-stage amplified high-power picosecond pulse train is outputted through the pinhole diaphragm 63.

[0150] As an alternative embodiment, the first laser gain crystal 29, the second laser gain crystal 39, the third laser gain crystal 46, the fourth laser gain crystal 53 and the fifth laser gain crystal 60 are made of Nd³ + The ion doping concentration, single-end YVO4 bonding and low thermal lens effect of Nd:YVO4 material have high small signal gain coefficient and excellent thermal management performance, which can efficiently amplify 1064 nm picosecond pulse train laser. The two end faces are coated with double-wavelength antireflection film (HT@1064 nm and HT@878 nm) with high transmittance to pump light and signal light.

[0151] As an alternative embodiment, the surfaces of the first plano-convex lens 28 and the second plano-convex lens 34 are coated with 1064 nm high transmittance (HT) antireflection film, designed for 0° incidence condition, mainly used for collimating or focusing 1064 nm signal light, and its low aberration characteristics ensure high fidelity transmission of beam wavefront quality.

[0152] As an alternative embodiment, the first plano-convex lens 28 and the second plano-convex lens 34 are coated with 1064 nm high transmittance (HT) antireflection film, designed for 0° incidence condition, mainly used for collimating or focusing 1064 nm signal light, and its low aberration characteristics ensure high fidelity transmission of beam wavefront quality.

[0153] As an alternative embodiment, the 0° dichroic mirror 30 works under 0° incidence condition, and its film system is designed to realize high transmittance (T>99%) of 878 nm pump light and high reflectance (R>99.8%) of 1064 nm signal light, effectively completing the combination and separation of pump light and laser, and reducing energy loss.

[0154] As an alternative embodiment, the ten lenticular lenses (i.e. first to tenth lenticular lenses) for pump light path are coated with 878 nm high transmittance film, suitable for 0° incidence, mainly used for beam waist control, focusing and mode shaping of 878 nm pump light, ensuring good matching with gain medium mode field, while maintaining low wavefront distortion.

[0155] As an alternative embodiment, the first LD pump source 33, the second LD pump source 38, the third LD pump source 45, the fourth LD pump source 52 and the fifth LD pump source 59 output center wavelength of 878 nm, with 200 μm core diameter, numerical aperture NA = 0.22, and output power up to 120 W. Each pump source couples the pump light to the corresponding laser gain crystal through the lenticular lens group, realizing high brightness pumping.

[0156] As an alternative embodiment, the reflective surfaces of the first 45° mirror 41, the second 45° mirror 48 and the third 45° mirror 55 are coated with a 1064 nm high reflection (HR) film, and work at a 45° incidence angle, with a reflectivity of over 99.8%, for guiding the 1064 nm laser to propagate in the free-space optical path, while maintaining low absorption and scattering loss.

[0157] As an alternative embodiment, the first 45° dichroic mirror 35, the second 45° dichroic mirror 42, the third 45° dichroic mirror 49 and the fourth 45° dichroic mirror 56 realize high transmission of the 878 nm pump light and high reflection of the 1064 nm signal light under 45° incidence conditions, and the film layer performance ensures efficient multiplexing of the pump and signal light paths in a compact space, improving system integration.

[0158] In this embodiment, each laser gain crystal is firmly welded in a high-thermal-conductivity red copper heat sink through an indium foil thermal interface material. The heat sink is internally integrated with a micro-channel water cooling structure, which, in combination with a constant-temperature circulating cooling system, can quickly remove the waste heat generated by the crystal under high average power operation, effectively suppressing thermal lensing and thermal-induced birefringence effects, and ensuring output beam quality and long-term operation reliability.

[0159] In addition, by optimizing the spatial overlap (i.e. fill factor) of the pump spot and the laser cavity fundamental mode, and combining with in-cavity pinhole spatial filtering, high-order transverse mode oscillation is effectively suppressed. Specifically, by adjusting the focal length or position of the pump focusing lens, the waist size and position of the pump beam in the laser gain crystal are matched with the fundamental mode; then the M 2 factor and far-field pattern of the output beam are monitored using a beam quality analyzer, and the pump parameters are fine-tuned until the M 2 <1.3 and the output energy is stable, indicating that the high-order modes have been effectively suppressed and the energy extraction efficiency is high. On this basis, a pinhole aperture slightly larger than the fundamental mode diameter is set in the optical path to further filter out residual high-order transverse modes. This design maintains high extraction efficiency while significantly improving beam quality, achieving near-diffraction-limited output, thereby greatly improving the energy density and process consistency of the laser in focused machining.

[0160] In this embodiment, the mode-locked fiber laser, the fiber preamplifier, the acousto-optic modulator, the fiber post-amplifier, the solid preamplifier and the multi-stage solid main amplifier are connected in sequence along the optical transmission path to form a complete seed source-modulation-amplification link.

[0161] The mode-locked fiber laser is used to generate stable picosecond mode-locked pulses with a repetition frequency of 20 MHz and a pulse width of about 10 ps, and the fiber preamplifier is used to increase the seed pulse power to the milliwatt level, providing a high-quality input signal for subsequent high-speed modulation and high-gain amplification.

[0162] The acousto-optic modulator 17 is used to perform high-speed gating operation on the input mode-locked pulse sequence, realizing pulse selection, repetition frequency division and pulse train grouping functions. A programmable radio frequency drive signal can be generated through the acousto-optic modulator control board 18 connected thereto, which can independently regulate the diffraction efficiency of each sub-pulse in the pulse train. This allows the energy of each sub-pulse to be flexibly and accurately adjusted, thereby realizing customized shaping of the sub-pulse energy distribution in the time domain.

[0163] In the present embodiment, the working process of the above-mentioned sub-pulse energy programmable high-power picosecond pulse train laser is as follows:

[0164] Firstly, the mode-locked picosecond pulse sequence output by the mode-locked fiber laser is energy-boosted by the fiber pre-amplifier for the weak signal light.

[0165] Then, pulse selection and grouping are performed by the acousto-optic modulator, and the amplitude of the radio frequency drive signal driving the acousto-optic modulator is generated and adjusted in real time by the acousto-optic modulator control board. The acousto-optic modulator control board has high-precision analog / digital hybrid output and programmable waveform generation functions, and can accurately control the time-domain waveform of the seed pulse sequence, realizing pulse pre-shaping with stepped, linear or arbitrary preset intensity distribution.

[0166] Subsequently, the modulated pre-shaped pulse train is further amplified by the fiber post-amplifier, and the average power reaches about 2.5 mW (corresponding to a 20 kHz pulse train repetition frequency and 5 sub-pulses per train), thereby improving the signal light power level entering the solid amplification chain, improving the signal-to-noise ratio of the amplified spontaneous emission, and effectively suppressing the accumulation of ASE.

[0167] Finally, the laser pulse train sequentially passes through the solid pre-amplifier, the first to fourth solid main amplifiers for multi-stage power boosting. The typical output powers are about 12 W, 30 W, 50 W and 75 W, respectively, and finally exceed 100 W; under the working conditions of 20 kHz repetition frequency and 5 sub-pulses per pulse train, the corresponding pulse train energy is greater than 5 mJ.

[0168] Figure 6 The pulse train waveform of the final output after the acousto-optic modulator pre-shaping and multi-stage solid amplification is shown. Through the synergistic compensation of the modulation signal and the amplifier gain saturation effect, each sub-pulse realizes energy consistency, and the output is a high-fidelity equal-amplitude pulse train laser, verifying the effectiveness of the distortion compensation.

[0169] Figures 7-11Various seed pulse energy distribution waveforms after programmed regulation are respectively shown, including uniform distribution, stepwise increasing type, stepwise decreasing type, center enhancement type (high in the middle and low on both sides) and edge enhancement type (low in the middle and high on both sides). Through the programmed regulation of the acousto-optic modulator to the seed light, diversified sub-pulse energy output in the pulse train is realized, meeting different application requirements.

[0170] Figures 12-15 The pulse output sequence under the repetition frequency of 20 kHz, 50 kHz, 100 kHz and 200 kHz is respectively shown. The results show that the repetition frequency can be continuously adjusted in the range of 20 kHz to 200 kHz to adapt to the needs of different processing scenarios for pulse timing.

[0171] Figure 16 The output power evolution curve of each solid-state amplifier is shown, reflecting the power gain of each amplification stage from the seed source to the final output. Under the condition of 20 kHz repetition frequency and each pulse train containing 5 sub-pulses (burst = 5), the average output power is more than 100 W, and the pulse train energy is greater than 5 mJ, which is suitable for high energy density deep processing and cutting applications, providing efficient and strong processing effect.

[0172] Figure 17 The intensity autocorrelation trace of the output laser after multi-stage amplification is shown, and the full width at half maximum (FWHM) is 11.3 ps.

[0173] Figure 18 The spectral properties of the output laser are shown, with a center wavelength of 1064.4575 nm and a spectral width (FWHM) of 0.1518 nm, indicating that the laser has excellent spectral purity and narrow linewidth output capability.

[0174] Figure 19 The beam quality and far-field spot distribution of the output beam are shown. The results show that the beam quality factors in the horizontal and vertical directions are = 1.110, = 1.094, and the beam quality is close to the diffraction limit; the far-field spot is distributed in a Gaussian type, the profile is symmetrical and the energy is concentrated.

[0175] The sub-pulse energy programmable high-power picosecond burst laser proposed in the embodiment has a burst mode output function. Under the condition of a 20 kHz repetition frequency and each burst containing 5 sub-pulses (burst=5), the average output power exceeds 100 W, and the single burst energy is greater than 5 mJ. The laser realizes precise programming control of the energy of each sub-pulse through an acousto-optic modulator, thereby supporting personalized setting of the pulse energy distribution and adapting to various complex processing requirements. This flexibility not only improves the material removal efficiency, but also optimizes the processing quality according to different application scenarios, such as achieving fine cutting, deep engraving and other diversified process effects.

[0176] Although the specific embodiments of the present application are described above in combination with the drawings, they are not a limitation on the scope of protection of the present application. Those skilled in the art should understand that various modifications or changes made by those skilled in the art on the basis of the technical solutions of the present application without creative labor are still within the scope of protection of the present application.

Claims

1. A sub-pulse energy programmable high power picosecond pulse train laser, characterized in that, The application relates to a high-power picosecond pulse laser device. The device comprises a mode-locked fiber laser, an acousto-optic modulator and a solid-state amplification chain arranged in sequence along an optical transmission path. The mode-locked fiber laser is used for generating a mode-locked picosecond pulse sequence. The acousto-optic modulator is used for pulse selection and pulse train grouping of the mode-locked picosecond pulse sequence, pre-programmed shaping of the sub-pulse energy in the pulse train according to a set intensity distribution, and generation of a pre-shaped pulse train. The acousto-optic modulator is used for pulse selection according to a received driving signal to realize adjustment of a pulse train repetition frequency in a range of 20 kHz to 200 kHz, pulse train grouping of the selected pulse sequence, and independent pre-programmed shaping of the sub-pulse energy in each pulse train according to modulation of the amplitude of the driving signal. The solid-state amplification chain comprises at least one solid-state pre-amplifier and at least one solid-state main amplifier.

2. A sub-pulse energy programmable high power picosecond pulse train laser as claimed in claim 1, wherein, The solid-state pre-amplifier comprises an isolating optical assembly, a first plano-convex lens, a first laser gain crystal, a 0-degree dichroic mirror, a first biconvex lens, a second biconvex lens and a first LD pump source. The first 976 nm laser diode is connected with the first polarization maintaining wavelength division multiplexer, two output ends of the first polarization maintaining wavelength division multiplexer are connected with input ends of the first polarization maintaining single-mode ytterbium-doped fiber and the polarization maintaining passive optical fiber respectively, two input ends of the polarization maintaining fiber coupler are connected with output ends of the first polarization maintaining single-mode ytterbium-doped fiber and the polarization maintaining passive optical fiber respectively; the first output end of the polarization maintaining fiber coupler is connected with the fiber Bragg grating, and the second output end is used as an output end of the mode-locked pulse, and the mode-locked picosecond pulse sequence is output through the first polarization maintaining optical isolator; wherein the polarization maintaining passive optical fiber is connected with the non-reciprocal phase shifter, and is used for introducing a fixed non-reciprocal phase shift of π / 2.

3. A sub-pulse energy programmable high power picosecond pulse train laser as claimed in claim 1, wherein, The pre-shaped pulse train is incident into the first laser gain crystal through the isolating optical assembly and the first plano-convex lens for one-time amplification.

4. A sub-pulse energy programmable high power picosecond pulse train laser as claimed in claim 1, wherein, The pump light emitted by the first LD pump source is incident into the first laser gain crystal through a coupling optical assembly composed of the second biconvex lens and the first biconvex lens and a 0-degree dichroic mirror.

5. A sub-pulse energy programmable high power picosecond pulse train laser as claimed in claim 1, wherein, The pre-shaped pulse train after one-time amplification is reflected to the first laser gain crystal through the 0-degree dichroic mirror for two-time amplification. The pre-shaped pulse train after two-time amplification is output through the first plano-convex lens and the isolating optical assembly and enters the next solid-state main amplifier. The mode-locked fiber laser comprises a first 976 nm laser diode, a first polarization-maintaining wavelength division multiplexer, a first polarization-maintaining single-mode ytterbium-doped optical fiber, a polarization-maintaining passive optical fiber, a non-reciprocal phase shifter, a polarization-maintaining fiber coupler, a fiber Bragg grating and a first polarization-maintaining optical isolator. At least one fiber pre-amplifier is arranged before the acousto-optic modulator and comprises a second polarization-maintaining wavelength division multiplexer, a second 976 nm laser diode, a second polarization-maintaining single-mode ytterbium-doped optical fiber and a second polarization-maintaining optical isolator. The mode-locked picosecond pulse sequence input from the previous stage and the pump light output by the second 976 nm laser diode are incident into the second polarization-maintaining single-mode ytterbium-doped optical fiber through the second polarization-maintaining wavelength division multiplexer for amplification, and then the seed pulse sequence amplified by the optical fiber is output through the second polarization-maintaining optical isolator. At least one fiber post-amplifier is arranged after the acousto-optic modulator and comprises a fourth polarization-maintaining wavelength division multiplexer, a fourth 976 nm laser diode, a fourth polarization-maintaining single-mode ytterbium-doped optical fiber, a fourth polarization-maintaining optical isolator and a fiber collimator. The pre-shaped pulse train and the pump light output by the fourth 976 nm laser diode are sequentially passed through the fourth polarization-maintaining wavelength division multiplexer, the fourth polarization-maintaining single-mode ytterbium-doped optical fiber, the fourth polarization-maintaining optical isolator and the fiber collimator, and then the pre-shaped pulse train amplified by the optical fiber is output. The solid-state amplification chain comprises a cascaded solid-state pre-amplifier and at least one solid-state main amplifier. The solid-state pre-amplifier comprises an isolating optical assembly, a first plano-convex lens, a first laser gain crystal, a 0-degree dichroic mirror, a first biconvex lens, a second biconvex lens and a first LD pump source. The pre-shaped pulse train is incident into the first laser gain crystal through the isolating optical assembly and the first plano-convex lens for one-time amplification. The pump light emitted by the first LD pump source is incident into the first laser gain crystal through a coupling optical assembly composed of the second biconvex lens and the first biconvex lens and a 0-degree dichroic mirror. The pre-shaped pulse train after one-time amplification is reflected to the first laser gain crystal through the 0-degree dichroic mirror for two-time amplification. The pre-shaped pulse train after two-time amplification is output through the first plano-convex lens and the isolating optical assembly and enters the next solid-state main amplifier.

6. A sub-pulse energy programmable high power picosecond pulse train laser as claimed in claim 5, wherein, The isolation optical assembly comprises a first spatial isolator, a first 1064 nm half-wave plate, a second spatial isolator and a second 1064 nm half-wave plate connected in sequence.

7. A sub-pulse energy programmable high power picosecond pulse train laser as claimed in claim 5, wherein, Each solid main amplifier comprises a 45° dichroic mirror, a coupling optical assembly composed of a double convex lens, a second laser gain crystal, a second LD pump source and a plano-concave lens; the pulse train input from the previous stage and the LD pump light transmitted through the coupling optical assembly are focused into the second laser gain crystal through the dichroic mirror, and the pulse train amplified by the second laser gain crystal enters the next stage solid main amplifier through the plano-concave lens.

8. A sub-pulse energy programmable high power picosecond pulse train laser as claimed in claim 7, wherein, The first stage solid main amplifier is further provided with a second plano-convex lens before the 45° dichroic mirror, and the other stage solid main amplifier is provided with a 45° mirror before the 45° dichroic mirror; The last stage solid main amplifier is provided with a third plano-convex lens before the plano-concave lens and a pinhole diaphragm after the plano-concave lens; In the last stage solid main amplifier, the amplified pulse train is expanded and shaped through the third plano-convex lens and the plano-concave lens in sequence, and finally output as a multi-stage amplified high-power picosecond pulse train through the pinhole diaphragm.

9. A method for operating a high-power picosecond pulse train laser with programmable sub-pulse energy, characterized in that, It comprises: generating a mode-locked picosecond pulse sequence by a mode-locked fiber laser; performing pulse selection and pulse train grouping on the mode-locked picosecond pulse sequence by an acousto-optic modulator, and pre-programming shaping the sub-pulse energy in the pulse train according to a set intensity distribution to generate a pre-shaped pulse train; the acousto-optic modulator is used for pulse selection according to the received driving signal to realize the adjustment of the pulse train repetition frequency in the range of 20 kHz to 200 kHz; and pulse train grouping is performed on the selected pulse sequence, and the sub-pulse energy in each pulse train is independently pre-programmed shaped according to the modulation of the amplitude of the driving signal; performing multi-stage amplification on the pre-shaped pulse train by at least one solid amplifier to output a multi-stage amplified high-power picosecond pulse train; wherein the solid amplifier comprises a dichroic mirror, a laser gain crystal, a coupling optical assembly and an LD pump source, and the dichroic mirror is used for focusing the pre-shaped pulse train amplified by the previous stage and the LD pump light transmitted through the coupling optical assembly into the laser gain crystal.

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