A pulsed laser device

Abstract

This invention discloses a pulsed laser device. The pulsed laser device includes a seed source, a pre-amplification unit, a main amplification unit, an acousto-optic modulation unit, and a frequency conversion unit. The seed source outputs a seed pulse beam to be amplified; the pre-amplification unit amplifies the pulse into a first-stage amplified beam; the main amplification unit further amplifies the pulse; the acousto-optic modulation unit controls the repetition frequency of the pulse; and the frequency conversion unit converts the frequency of the output pulse using frequency doubling or sum-frequency effects. The technical solution of this invention employs a step-by-step amplification method of pre-amplification and main amplification to amplify the seed pulse beam. Furthermore, the main amplification unit flexibly shapes the incident beam, coordinating with the shaping of the pump light to achieve optimal matching between the two, thereby improving energy extraction efficiency and beam quality, and achieving the dual effects of high power and high beam quality.

Description

Technical Field

[0001] This invention relates to the field of optical technology, and more particularly to a pulsed laser device. Background Technology

[0002] Pulsed lasers, with their extremely high peak power and narrow pulse width, have been widely used in fields such as precision micromachining of materials, semiconductor industry, solar photovoltaic, and scientific research.

[0003] High-power pulsed lasers typically employ a seed source to output a seed pulse, which is then amplified using an optical amplifier. For example, the currently popular picosecond laser technology uses a seed source with traveling-wave single-pass or multi-pass solid-state amplification to achieve high single-pulse energy and frequency-controllable picosecond laser pulse output. However, traveling-wave amplification results in low energy efficiency and is prone to nonlinear effects, making it unsuitable for generating higher power and higher beam quality pulses. Summary of the Invention

[0004] This invention provides a pulsed laser device that amplifies a seed pulse beam using a step-by-step amplification method of pre-amplification and main amplification. The main amplification unit flexibly shapes the incident beam, and in conjunction with the shaping of the pump light, the two are optimally matched, thereby improving energy extraction efficiency and beam quality, achieving the dual effects of high power and high beam quality.

[0005] This invention provides a pulsed laser device, including a seed source, a pre-amplification unit, a main amplification unit, an acousto-optic modulation unit, and a frequency conversion unit;

[0006] The seed source is used to output a seed pulse beam to be amplified;

[0007] The pre-amplification unit is used to receive the seed pulse beam and amplify it into a first-level amplified beam;

[0008] The main amplification unit includes at least one stage of optical amplifier. The optical amplifier includes a shaping lens, a first laser crystal, a reflector, a first pump lens group, and a first pump source. The shaping lens is used to expand the divergence angle of the first-stage amplified beam by 1 to 2 times before transmitting it to the first laser crystal. The first pump lens group is used to converge the pump light output from the first pump source to the first laser crystal. The reflector is used to reflect and output the beam amplified by the first laser crystal.

[0009] The acousto-optic modulation unit is used to control the repetition frequency of the pulse;

[0010] The frequency conversion unit is used to convert the frequency of the output pulse using frequency doubling or sum-frequency effects.

[0011] Optionally, the pre-amplification unit includes a second pump source, a second laser crystal, and a beam modulation unit, wherein the beam modulation unit includes multiple reflecting surfaces;

[0012] The seed pulse beam is incident on the beam modulation unit, and changes its transmission direction when reflected by the reflective surface, passing through the second laser crystal four times;

[0013] The second pump source is used to emit pump light to the second laser crystal, and the second laser crystal absorbs the pump light to achieve four-pass amplification of the seed pulse beam.

[0014] Optionally, when the seed pulse beam passes through the second laser crystal, the beam paths of at least two passes through the second laser crystal overlap.

[0015] Optionally, the beam paths passing through the second laser crystal four times overlap;

[0016] The beam modulation unit includes an isolator, a polarizing beam splitter, a Faraday rotator, a half-wave plate, and a first reflecting surface arranged coaxially along a first direction. The beam modulation unit also includes a second reflecting surface arranged coaxially with the polarizing beam splitter along a second direction, wherein the first direction intersects the second direction.

[0017] A seed pulse beam with a first polarization direction is incident on the first end of the isolator, exits through the second end of the isolator, and is transmitted to the polarizing beam splitter. After being transmitted through the Faraday rotator and the half-wave plate, it passes through the second laser crystal for the first time, is reflected by the first reflecting surface, passes through the second laser crystal for the second time, and is transmitted through the half-wave plate and the Faraday rotator again, and is converted into a beam with a second polarization direction.

[0018] The beam of light in the second polarization direction is incident on the polarizing beam splitter and reflected. After being reflected by the second reflecting surface, it is incident on the polarizing beam splitter and reflected again. After being transmitted through the Faraday rotator and the half-wave plate, it passes through the second laser crystal for the third time. After being reflected by the first reflecting surface, it passes through the second laser crystal for the fourth time. After being transmitted through the half-wave plate and the Faraday rotator again, it is converted into a beam of light in the first polarization direction.

[0019] The beam of light in the first polarization direction is transmitted through the polarizing beam splitter to the second end of the isolator and output from the third end of the isolator.

[0020] Optionally, the beam paths of the first and second passes through the second laser crystal coincide, and the beam paths of the third and fourth passes through the second laser crystal coincide.

[0021] The beam modulation unit includes a first polarizing beam splitter, a Faraday rotator, a half-wave plate, and a first reflecting surface arranged coaxially along a first direction. The beam modulation unit also includes a first reflecting mirror and a second reflecting mirror, which are located on the same side of the first polarizing beam splitter and on the two sides adjacent to the Faraday rotator.

[0022] A seed pulse beam with a first polarization direction is incident from a first position onto the first polarizing beam splitter and transmitted. After being transmitted through the Faraday rotator and the half-wave plate, it passes through the second laser crystal for the first time. After being reflected by the first reflecting surface, it passes through the second laser crystal for the second time. After being transmitted through the half-wave plate and the Faraday rotator again, it is converted into a beam with a second polarization direction.

[0023] The beam of the second polarization direction is incident on the first polarizing beam splitter and reflected. After being reflected by the first mirror and the second mirror in sequence, it is incident on the first polarizing beam splitter and reflected again. After being transmitted through the Faraday rotator and the half-wave plate, it passes through the second laser crystal for the third time. After being reflected by the first reflective surface, it passes through the second laser crystal for the fourth time. After being transmitted through the half-wave plate and the Faraday rotator again, it is converted into a beam of the first polarization direction.

[0024] The beam of light in the first polarization direction is transmitted through the first polarizing beam splitter and output from the second position.

[0025] Optionally, a second polarizing beam splitter may also be included, located between the half-wave plate and the laser crystal, and passing through the beam path of the laser crystal for the first and second times.

[0026] Optionally, the beam paths of the third and fourth passes through the second laser crystal overlap;

[0027] The beam modulation unit includes a polarizing beam splitter, a first half-wave plate, a Faraday rotator, a second half-wave plate, a converging lens, and a first reflecting surface, all arranged coaxially along a first direction. The extension length of the first half-wave plate is greater than the extension length of the second half-wave plate. The beam modulation unit also includes a third reflecting mirror and a fourth reflecting mirror, which are located on the same side of the polarizing beam splitter and on adjacent sides of the first half-wave plate.

[0028] A seed pulse beam with a first polarization direction is incident from a first position onto the polarizing beam splitter and transmitted. After passing through the first half-wave plate and the Faraday rotator, it is incident onto the converging lens. After being converged by the converging lens, it is obliquely incident at a first incident angle and passes through the second laser crystal for the first time. After being reflected by the first reflecting surface, it passes through the second laser crystal for the second time. After being transmitted through the converging lens, the Faraday rotator, and the first half-wave plate again, it is converted into a beam with a second polarization direction.

[0029] The beam of light in the second polarization direction is incident on the polarizing beam splitter and reflected. After being reflected by the third and fourth reflecting mirrors in sequence, it is incident on the polarizing beam splitter and reflected again. After being transmitted through the Faraday rotator, the second half-wave plate and the converging lens, it passes through the second laser crystal for the third time. After being reflected by the first reflecting surface, it passes through the second laser crystal for the fourth time. After being transmitted through the converging lens, the second half-wave plate and the Faraday rotator again, it is converted into a beam of light in the first polarization direction.

[0030] The beam of light in the first polarization direction is transmitted through the polarizing beam splitter and output from the second position.

[0031] Optionally, the beam paths of the third and fourth passes through the second laser crystal overlap;

[0032] The beam modulation unit includes a fifth mirror, a sixth mirror, an isolator, and a first reflecting surface;

[0033] The seed pulse beam is obliquely incident at the second incident angle, passes through the second laser crystal for the first time, is reflected by the first reflecting surface, passes through the second laser crystal for the second time, is reflected by the fifth and sixth reflecting mirrors in sequence, and then enters the isolator from the first end, exits from the second end, passes through the second laser crystal for the third time, is reflected by the first reflecting surface, passes through the second laser crystal for the fourth time, and then enters the isolator from the second end and exits from the third end.

[0034] Optionally, the beam paths passing through the second laser crystal four times do not overlap;

[0035] The beam modulation unit includes a polarizing beam splitter, a third half-wave plate, a Faraday rotator, a fourth half-wave plate, a converging lens, and a first reflecting surface, all arranged coaxially along a first direction. The extension length of the third half-wave plate is greater than that of the fourth half-wave plate. The beam modulation unit also includes a seventh reflecting mirror and an eighth reflecting mirror, which are located on the same side of the polarizing beam splitter and on adjacent sides of the third half-wave plate.

[0036] A seed pulse beam with a first polarization direction is incident from a first position onto the polarizing beam splitter and transmitted. After being transmitted through the third half-wave plate and the Faraday rotator, it is incident onto the converging lens. After being converged by the converging lens, it is obliquely incident at a third incident angle and passes through the second laser crystal for the first time. After being reflected by the first reflecting surface, it passes through the second laser crystal for the second time. After being transmitted through the converging lens, the Faraday rotator, and the third half-wave plate again, it is converted into a beam with a second polarization direction.

[0037] The beam with the second polarization direction is incident on the polarizing beam splitter and reflected. After being reflected in sequence by the seventh and eighth reflecting mirrors, it is incident on the polarizing beam splitter again and reflected. After being transmitted through the Faraday rotator, the fourth half-wave plate, and the converging lens, it is obliquely incident at the fourth incident angle and passes through the second laser crystal for the third time. After being reflected by the first reflecting surface, it passes through the second laser crystal for the fourth time. After being transmitted through the converging lens, the fourth half-wave plate, and the Faraday rotator again, it is converted into a beam with the first polarization direction, wherein the fourth incident angle is smaller than the third incident angle.

[0038] The beam of light in the first polarization direction is transmitted through the polarizing beam splitter and output from the second position.

[0039] Optionally, the reflecting surface may be the reflecting surface of a device in the beam modulation unit and / or the reflecting surface of a mirror.

[0040] Optionally, the pre-amplification unit further includes a second pump lens group located between the second pump source and the second laser crystal, the second pump lens group being used to focus the pump light onto the second laser crystal.

[0041] Optionally, the pump light is incident on the second laser crystal from one end and / or at least one sidewall.

[0042] The technical solution of this invention includes a seed source, a pre-amplification unit, a main amplification unit, an acousto-optic modulation unit, and a frequency conversion unit. The main amplification unit includes at least one stage of optical amplifier, which includes a shaping lens, a first laser crystal, a mirror, a first pump lens group, and a first pump source. A seed pulse beam to be amplified is output through the seed source. The seed pulse beam is received by the pre-amplification unit and amplified into a first-stage amplified beam. The divergence angle of the first-stage amplified beam is expanded by 1 to 2 times through the shaping lens and then transmitted to the first laser crystal to avoid self-focusing due to excessive light intensity and to avoid nonlinear effects. The pump light output from the first pump source is focused onto the first laser crystal through the first pump lens group, and the beam amplified by the first laser crystal is reflected and output through the mirror. The repetition frequency of the pulse is controlled by the acousto-optic modulation unit. The frequency conversion unit uses frequency doubling or sum-frequency effects to convert the frequency of the output pulse, thereby improving energy extraction efficiency and beam quality, and achieving the dual effects of high power and high beam quality.

[0043] It should be understood that the description in this section is not intended to identify key or essential features of the embodiments of the present invention, nor is it intended to limit the scope of the invention. Other features of the invention will become readily apparent from the following description. Attached Figure Description

[0044] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0045] Figure 1 This invention provides a schematic diagram of the structure of a pulsed laser device according to an embodiment of the invention;

[0046] Figure 2 This is a schematic diagram of the structure of a pre-amplification unit provided in an embodiment of the present invention;

[0047] Figure 3 This is a schematic diagram of another pre-amplification unit provided in an embodiment of the present invention;

[0048] Figure 4 and Figure 5 These are schematic diagrams of another pre-amplification unit provided in the embodiments of the invention;

[0049] Figure 6 This is a schematic diagram of another pre-amplification unit provided in an embodiment of the present invention;

[0050] Figure 7 This is a schematic diagram of another pre-amplification unit provided in an embodiment of the present invention;

[0051] Figure 8 This is a schematic diagram of another pre-amplification unit provided in an embodiment of the present invention;

[0052] Figure 9 This is a schematic diagram of another pre-amplification unit provided in an embodiment of the present invention;

[0053] Figure 10 This is a schematic diagram of another pre-amplification unit provided in an embodiment of the present invention. Detailed Implementation

[0054] To enable those skilled in the art to better understand the present invention, the technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of the present invention.

[0055] It should be noted that the terms "first," "second," etc., in the specification, claims, and accompanying drawings of this invention are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such data can be interchanged where appropriate so that the embodiments of the invention described herein can be implemented in orders other than those illustrated or described herein. Furthermore, the terms "comprising" and "having," and any variations thereof, are intended to cover a non-exclusive inclusion; for example, a process, method, system, product, or apparatus that comprises 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.

[0056] Figure 1 This is a schematic diagram of a pulsed laser device provided in an embodiment of the present invention. (Reference) Figure 1 The pulsed laser device provided in this embodiment can be a picosecond pulsed laser device, including a seed source 1, a pre-amplification unit 2, a main amplification unit 3, an acousto-optic modulation unit 4, and a frequency conversion unit 5; the seed source 1 is used to output a seed pulse beam to be amplified; the pre-amplification unit 2 is used to receive the seed pulse beam and amplify it into a first-stage amplified beam; the main amplification unit 3 includes at least one stage optical amplifier 300 (… Figure 1Taking only the first stage as an example, the optical amplifier 300 includes a shaping lens 301, a first laser crystal 302, a reflector 303, a first pump lens group 304, and a first pump source 305. The shaping lens 301 is used to expand the divergence angle of the first-stage amplified beam by 1 to 2 times before transmitting it to the first laser crystal 302. The first pump lens group 304 is used to converge the pump light output from the first pump source 305 to the first laser crystal 302. The reflector 303 is used to reflect and output the beam amplified by the first laser crystal 302. The acousto-optic modulation unit 4 is used to control the repetition frequency of the pulse. The frequency conversion unit 5 is used to convert the frequency of the output pulse using frequency doubling or sum-frequency effects.

[0057] The seed pulse beam emitted from seed source 1 can be generated by a mode-locked resonant cavity, which is the source of all subsequent light. Typically, it generates a very weak pulsed laser, appearing as a pulse train with a repetition frequency of tens of megahertz on the detector. Since such a high repetition frequency is not required in practical applications, the pulse train needs to be down-clocked to meet the actual operating frequency. Furthermore, because the energy of each generated pulse is relatively small (typically in the nJ range), pulse energy amplification is necessary. This includes the amplification section within seed source 1 and subsequent solid-state pre-amplification (provided by pre-amplification unit 1) and main amplification section (provided by main amplification unit 3). In specific implementation, seed source 1 can use a semiconductor saturable absorber mirror (SEASAM) mode-locking method to achieve a laser pulse with a single pulse energy of 20 nJ and a repetition frequency adjustable from 0 to 20 MHz.

[0058] The pre-amplification unit 2 performs first-stage amplification of the seed pulse beam, and the main amplification unit 3 provides at least one stage of main amplification. The main amplification section is characterized in two ways: firstly, the signal light entering the main amplification unit 3 is modulated into a divergent signal light by the shaping lens 301, with the beam waist generally located near the main amplifier entrance, and the distance between them being close to the Rayleigh length of the incident signal light. In this case, the signal light entering the first laser crystal 302 first undergoes beam shaping to adapt to the solid angle spatial distribution of the pump light within the first laser crystal 302, thereby improving the beam quality to satisfy M... 2The dual benefits include a factor of less than 1.2 and a 10% improvement in energy extraction efficiency. On the other hand, the divergent signal light, under the thermal lensing effect of the first laser crystal 302, ultimately outputs light with a divergence angle close to parallel light, effectively expanding the beam. This avoids nonlinear effects and facilitates higher power amplification in the subsequent main amplification stage. In specific implementation, to avoid nonlinear effects and facilitate higher power amplification in the subsequent main amplification stage, the size and trend of the light spot entering the first laser crystal 302 are controlled to prevent self-focusing due to excessive light intensity. Before entering the first laser crystal 302, the divergence angle of the signal light is expanded by 1 to 2 times, mainly by setting the shaping lens 301 as a negative lens. Typically, the focal length of the negative lens is selectable between -100mm and -300mm. The pump spot size of the first laser crystal 302 is controlled between 1mm and 2mm, and the pump power is adjusted within the range of 60W to 100W.

[0059] The acousto-optic modulation unit 4 may include an acousto-optic modulator (AOM). The AOM primarily uses an ultrasonic field to form a Bragg volume grating within itself, performing Bragg diffraction on the incident signal light. This splits the incident light into two beams at a specific angle, the angle of which is related to the radio frequency (RF) frequency used by the AOM, and the energy ratio of the two beams is related to the intensity of the ultrasonic field. This attenuates the energy of the optical pulse. Furthermore, when synchronized with the pulse sequence, controlling the on / off state of the AOM can further control the pulse repetition frequency. In specific implementations, the RF frequency range of the AOM can be 24MHz to 120MHz.

[0060] Frequency conversion unit 5 can convert the laser frequency through the nonlinear effect of lithium triborate (LBO) crystal. In specific implementations, LBO crystal can be used for frequency doubling or summing, for example, 1064nm wavelength infrared light can be converted into 532nm or 355nm light through frequency doubling or summing.

[0061] The technical solution of this invention involves: outputting a seed pulse beam to be amplified from a seed source; receiving the seed pulse beam through a pre-amplification unit and amplifying it into a first-stage amplified beam; expanding the divergence angle of the first-stage amplified beam by 1 to 2 times through a shaping lens before transmitting it to a first laser crystal to avoid self-focusing due to excessive light intensity and to avoid nonlinear effects; focusing the pump light output from the first pump source to the first laser crystal through a first pump lens group, reflecting it through a mirror, and outputting the amplified beam from the first laser crystal; controlling the repetition frequency of the pulse through an acousto-optic modulation unit; and converting the frequency of the output pulse using a frequency conversion unit with frequency doubling or sum-frequency effects, thereby improving energy extraction efficiency and beam quality, achieving the dual effects of high power and high beam quality.

[0062] Optionally, the pre-amplification unit includes a second pump source, a second laser crystal, and a beam modulation unit. The beam modulation unit includes multiple reflecting surfaces. The seed pulse beam is incident on the beam modulation unit, and its transmission direction changes when reflected by the reflecting surfaces. It passes through the second laser crystal four times. The second pump source is used to emit pump light to the second laser crystal, and the second laser crystal absorbs the pump light to achieve four-pass amplification of the seed pulse beam.

[0063] In this embodiment, the technical solution provides pump light to the second laser crystal through a second pump source. The seed pulse beam changes its transmission direction upon reflection from the reflective surface of the beam modulation unit, achieving four-stage amplification of the seed pulse beam by passing through the laser crystal four times. This pre-amplification unit structure suppresses self-oscillation while achieving high-gain amplification of seed light of different energies, ensuring high efficiency for subsequent power amplification.

[0064] Optionally, when the seed pulse beam passes through the second laser crystal, the beam paths passing through the second laser crystal at least twice overlap.

[0065] For example, Figure 2 This is a schematic diagram of a pre-amplification unit provided in an embodiment of the present invention. (Reference) Figure 2 The pre-amplification unit provided in this embodiment includes a second pump source 10, a second laser crystal 20, and a beam modulation unit 30. The beam modulation unit 30 includes an isolator 31, a polarizing beam splitter 32, a Faraday rotator 33, a half-wave plate 34, and a first reflecting surface 35 arranged along the first direction x and coaxially. The beam modulation unit 30 also includes a second reflecting surface 36 arranged along the second direction y and coaxially with the polarizing beam splitter 32. The first direction x and the second direction y intersect.

[0066] The second pump source 10 can be a semiconductor laser diode (LD), for example, an LD with an output wavelength of 880nm, 888nm, or 914nm and a power of 120W. It can be output via optical fiber with a fiber core diameter of 200μm and a numerical aperture NA = 0.22. The second laser crystal 20 can be 0.3% doped Nd:YVO4 or 1% doped Nd:YAG. The isolator 31 is a unidirectional transmission device used to ensure unidirectional transmission of the beam. It only allows light to propagate from the input port (first end) to the output port (second end). Light propagating from the output port (second end) to the input port (first end) is blocked and output from the side (third end). The polarizing beam splitter 32 transmits light with one polarization direction (e.g., horizontally polarized light) and reflects light with another polarization direction (e.g., vertically polarized light). For example, it can be a PBS polarizing beam splitter made of 25.4mm × 25.4mm × 25.4mm UVFS material with an aperture greater than 80% and a wavelength of 1064nm. The Faraday rotator 33 has an optical rotation function, used to rotate the polarization direction of the transmitted beam by 45°. The half-wave plate 34 is used to perform an axially symmetric transformation of the light's polarization direction along the waveplate's optical axis. In practice, the positions of the Faraday rotator 33 and the half-wave plate 34 can be interchanged. Figure 2 The first reflecting surface 35 and the second reflecting surface 36 shown are merely schematic representations of the reflecting surfaces in the mirror. In specific implementations, the reflecting surface may optionally be the reflecting surface of a device in the beam modulation unit and / or the reflecting surface of the mirror. For example, in other embodiments, the right side surface of the second laser crystal 20 can be set as the first reflecting surface, and the lower surface of the polarizing beam splitter 32 can be set as the second reflecting surface. That is, at least one of the first reflecting surface and the second reflecting surface can be the reflecting surface of a separately set mirror, or it can be the surface of a device at the corresponding position as the reflecting surface. In the following embodiments, the reflecting surface is the reflecting surface of a separately set mirror as an example for illustration.

[0067] Figure 2 A schematic diagram of light transmission is also shown; please refer to [link / reference]. Figure 2 The beam paths of the four passes through the second laser crystal 20 coincide; the seed pulse beam with the first polarization direction (e.g., horizontal polarization direction) is incident on the first end a of the isolator 31, exits through the second end b of the isolator 31 and is incident on the polarizing beam splitter 32 for transmission, after being transmitted through the Faraday rotator 33 and the half-wave plate 34, it passes through the second laser crystal 20 for the first time, is reflected by the first reflecting surface 35 and passes through the second laser crystal 20 for the second time, and is transmitted through the half-wave plate 34 and the Faraday rotator 33 again and is converted into a beam with the second polarization direction (e.g., vertical polarization direction).

[0068] The beam with the second polarization direction is incident on the polarizing beam splitter 32 and reflected. After being reflected by the second reflecting surface 36, it is incident on the polarizing beam splitter 32 and reflected again. After being transmitted through the Faraday rotator 33 and the half-wave plate 34, it passes through the second laser crystal 20 for the third time. After being reflected by the first reflecting surface 35, it passes through the second laser crystal 20 for the fourth time. After being transmitted through the half-wave plate 34 and the Faraday rotator 33 again, it is converted into a beam with the first polarization direction.

[0069] The beam in the first polarization direction is transmitted through the polarizing beam splitter 32 to the second end b of the isolator 31 and output from the third end c of the isolator 31.

[0070] The pre-amplification unit provided in this embodiment has most of its components located on the same optical axis, and the beam paths passing through the second laser crystal 20 four times overlap, resulting in a compact structure that helps to reduce the size of the pre-amplification unit.

[0071] Figure 3 This is a schematic diagram of another pre-amplification unit provided in an embodiment of the present invention. (See reference) Figure 3 The beam modulation unit 30 includes a first polarizing beam splitter 32, a Faraday rotator 33, a half-wave plate 34, and a first reflecting surface 35 arranged along the first direction x-axis. The beam modulation unit 30 also includes a first reflecting mirror 361 and a second reflecting mirror 362. The first reflecting mirror 361 and the second reflecting mirror 362 are located on the same side of the first polarizing beam splitter 32 and are located on the two sides adjacent to the Faraday rotator 33 of the first polarizing beam splitter 32.

[0072] Figure 3 A schematic diagram of light transmission is also shown; please refer to [link / reference]. Figure 3 The beam paths of the first and second passes through the second laser crystal 20 coincide, and the beam paths of the third and fourth passes through the second laser crystal 20 coincide as well. The seed pulse beam with the first polarization direction is incident from the first position d to the first polarizing beam splitter 32 and is transmitted. After passing through the Faraday rotator 33 and the half-wave plate 34, it passes through the second laser crystal 20 for the first time. After being reflected by the first reflecting surface 35, it passes through the second laser crystal 20 for the second time. After passing through the half-wave plate 34 and the Faraday rotator 33 again, it is converted into a beam with the second polarization direction.

[0073] The beam with the second polarization direction is incident on the first polarizing beam splitter 32 and reflected. After being reflected by the first reflecting mirror 361 and the second reflecting mirror 362 in sequence, it is incident on the first polarizing beam splitter 32 and reflected again. After being transmitted through the Faraday rotator 33 and the half-wave plate 34, it passes through the second laser crystal 20 for the third time. After being reflected by the first reflecting surface 35, it passes through the second laser crystal 20 for the fourth time. After being transmitted through the half-wave plate 34 and the Faraday rotator 33 again, it is converted into a beam with the first polarization direction.

[0074] The beam of light in the first polarization direction is transmitted through the first polarizing beam splitter 32 and output from the second position e.

[0075] The pre-amplification unit provided in this embodiment is configured such that the beam paths of the first and second passes through the second laser crystal 20 coincide, and the beam paths of the third and fourth passes through the second laser crystal 20 coincide. This allows for an increase in the position of the seed pulse beam passing through the laser crystal 20 while maintaining a compact pre-amplification unit structure, which is beneficial for improving amplification efficiency.

[0076] Figure 4 and Figure 5 These are schematic diagrams of another pre-amplification unit provided in the embodiments of the present invention, for reference. Figure 4 and Figure 5 ,exist Figure 3 Based on the embodiment shown, the pre-amplification unit further includes a second polarizing beam splitter 38 located between the half-wave plate 34 and the laser crystal 20, and passing through the beam path of the laser crystal 20 for the first and second times. The second polarizing beam splitter 38 can prevent light from returning and damaging the optical path, thereby improving the performance of the optical amplifier.

[0077] Figure 6 This is a schematic diagram of another pre-amplification unit provided in an embodiment of the present invention. (See reference) Figure 6 The beam modulation unit 30 includes a polarizing beam splitter 32, a first half-wave plate 341, a Faraday rotator 33, a second half-wave plate 342, a converging lens 37, and a first reflecting surface 35 arranged along the first direction x, all coaxially. The extension length of the first half-wave plate 341 is greater than the extension length of the second half-wave plate 342. The extension directions of the first half-wave plate 341 and the second half-wave plate 342 are perpendicular to the first direction x. The beam modulation unit 30 also includes a third reflecting mirror 363 and a fourth reflecting mirror 364. The third reflecting mirror 363 and the fourth reflecting mirror 364 are located on the same side of the polarizing beam splitter 32 and are located on the adjacent sides of the first half-wave plate 341.

[0078] Figure 6 A schematic diagram of light transmission is also shown; please refer to [link / reference]. Figure 6The beam paths of the third and fourth passes through the second laser crystal 20 coincide; the seed pulse beam with the first polarization direction is incident from the first position d to the polarizing beam splitter 32 and transmitted. After passing through the first half-wave plate 341 and the Faraday rotator 33, it is incident to the converging lens 37. After being converged by the converging lens 37, it is obliquely incident at the first incident angle α and passes through the second laser crystal 20 for the first time. After being reflected by the first reflecting surface 35, it passes through the second laser crystal 20 for the second time. After passing through the converging lens 37, the Faraday rotator 33 and the first half-wave plate 341 again, it is converted into a beam with the second polarization direction.

[0079] The beam with the second polarization direction is incident on the polarizing beam splitter 32 and reflected. After being reflected in sequence by the third mirror 363 and the fourth mirror 364, it is incident on the polarizing beam splitter 32 and reflected again. After being transmitted through the Faraday rotator 33, the second half-wave plate 342 and the converging lens 37, it passes through the second laser crystal 20 for the third time (perpendicularly incident). After being reflected by the first reflecting surface 35, it passes through the second laser crystal 20 for the fourth time. After being transmitted through the converging lens 37, the second half-wave plate 342 and the Faraday rotator 33 again, it is converted into a beam with the first polarization direction.

[0080] The beam of light in the first polarization direction is transmitted through the polarizing beam splitter 32 and output from the second position e.

[0081] Figure 7 This is a schematic diagram of another pre-amplification unit provided in an embodiment of the present invention, with reference to... Figure 7 ,and Figure 6 The difference is that an isolator 31 is added in this embodiment to change the emission direction of the emitted light; other structures are the same as... Figure 6 The embodiments are the same as those in the example.

[0082] and Figure 6 Similar to the structure shown, in another embodiment, the beam paths passing through the second laser crystal for the third and fourth times can be designed to not overlap, that is, the beam paths passing through the second laser crystal for the fourth time do not overlap. Figure 8 This is a schematic diagram of another pre-amplification unit provided in an embodiment of the present invention. (See reference) Figure 8 The beam modulation unit 30 includes a polarizing beam splitter 32, a third half-wave plate 343, a Faraday rotator 33, a fourth half-wave plate 344, a converging lens 37, and a first reflecting surface 35 arranged along the first direction x-axis. The extension length of the third half-wave plate 343 is greater than the extension length of the fourth half-wave plate 344. The beam modulation unit 30 also includes a seventh reflecting mirror 367 and an eighth reflecting mirror 368. The seventh reflecting mirror 367 and the eighth reflecting mirror 368 are located on the same side of the polarizing beam splitter 32 and are located on the adjacent sides of the third half-wave plate 343.

[0083] Figure 8 A schematic diagram of light transmission is also shown; please refer to [link / reference]. Figure 8 The seed pulse beam with the first polarization direction is incident from the first position d to the polarizing beam splitter 32 and transmitted. After being transmitted through the third half-wave plate 343 and the Faraday rotator 33, it is incident to the converging lens 37. After being converged by the converging lens 37, it is obliquely incident at the third incident angle γ and passes through the second laser crystal 20 for the first time. After being reflected by the first reflecting surface 35, it passes through the second laser crystal 20 for the second time. After being transmitted through the converging lens 37, the Faraday rotator 33 and the third half-wave plate 343 again, it is converted into a beam with the second polarization direction.

[0084] The beam with the second polarization direction is incident on the polarizing beam splitter 32 and reflected. After being reflected by the seventh mirror 367 and the eighth mirror 368 in sequence, it is incident on the polarizing beam splitter 32 and reflected again. After being transmitted through the Faraday rotator 33, the fourth half-wave plate 344 and the converging lens 37, it is obliquely incident at the fourth incident angle δ for the third time and passes through the second laser crystal 20. After being reflected by the first reflecting surface 35, it passes through the second laser crystal 20 for the fourth time. After being transmitted through the converging lens 37, the fourth half-wave plate 344 and the Faraday rotator 33 again, it is converted into a beam with the first polarization direction. The fourth incident angle δ is smaller than the third incident angle γ.

[0085] The beam of light in the first polarization direction is transmitted through the polarizing beam splitter 32 and output from the second position e.

[0086] In specific implementations, a reflector can be set on the left side of the polarizing beam splitter 32 to change the beam transmission direction, or an isolator can be set. The specific implementation can be designed according to the actual situation, and the embodiments of the present invention are not limited.

[0087] Figure 9 This is a schematic diagram of another pre-amplification unit provided in an embodiment of the present invention. (See reference) Figure 9 The beam modulation unit includes a fifth reflector 365, a sixth reflector 366, an isolator 31, and a first reflector 35; wherein the beam paths of the third and fourth beams passing through the second laser crystal 20 overlap.

[0088] The seed pulse beam is obliquely incident at the second incident angle β, passes through the second laser crystal 20 for the first time, is reflected by the first reflecting surface 35, passes through the second laser crystal 20 for the second time, and is then reflected by the fifth reflecting mirror 365 and the sixth reflecting mirror 366 in sequence. It then enters from the first end a of the isolator 31, exits from the second end b, passes through the second laser crystal 20 for the third time (perpendicular incident), is reflected by the first reflecting surface 35, passes through the second laser crystal 20 for the fourth time, and then enters from the second end b of the isolator 31 and exits from the third end c.

[0089] In a specific implementation, the seed pulse beam is obliquely incident on the second laser crystal 20 at the second incident angle β. The beam transmission path can be changed by reflecting the beam using a mirror. This embodiment of the invention does not limit the scope of the invention.

[0090] Figure 10 This is a schematic diagram of another pre-amplification unit provided in an embodiment of the present invention. (See reference) Figure 10 Optionally, the pre-amplification unit also includes a second pump lens group 40 located between the second pump source 10 and the second laser crystal 20, the second pump lens group 40 being used to focus the pump light onto the second laser crystal 20.

[0091] The second pump lens group 40 may include at least one lens with light-converging function. By setting the second pump lens group 40, the efficiency of pump light coupling to the second laser crystal 20 can be improved. In specific implementations, the relative positional relationship between the second pump source 10 and the second laser crystal 20 can be designed according to actual conditions. Optionally, the pump light may be incident on the second laser crystal 20 from one end and / or at least one sidewall. For example, refer to... Figures 2-9 The pump light can be incident from one end of the second laser crystal 20, or it can be as follows: Figure 10 As shown, the pump light is incident from one sidewall of the second laser crystal 20. In other embodiments, two or more second pump sources 10 may be provided, but this embodiment of the present invention does not limit this.

[0092] The specific embodiments described above do not constitute a limitation on the scope of protection of this invention. Those skilled in the art should understand that various modifications, combinations, sub-combinations, and substitutions can be made according to design requirements and other factors. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of this invention should be included within the scope of protection of this invention.

Claims

1. A pulsed laser device, characterized in that, It includes a seed source, a pre-amplification unit, a main amplification unit, an acousto-optic modulation unit, and a frequency conversion unit; The seed source is used to output a seed pulse beam to be amplified; The pre-amplification unit is used to receive the seed pulse beam and amplify it into a first-level amplified beam; The main amplification unit includes at least one stage of optical amplifier. The optical amplifier includes a shaping lens, a first laser crystal, a reflector, a first pump lens group, and a first pump source. The shaping lens is used to expand the divergence angle of the first-stage amplified beam by 1 to 2 times before transmitting it to the first laser crystal. The first pump lens group is used to converge the pump light output from the first pump source to the first laser crystal. The reflector is used to reflect and output the beam amplified by the first laser crystal. The acousto-optic modulation unit is used to control the repetition frequency of the pulse; The frequency conversion unit is used to convert the frequency of the output pulse using frequency doubling or sum-frequency effects; The pre-amplification unit includes a second pump source, a second laser crystal, and a beam modulation unit, wherein the beam modulation unit includes multiple reflective surfaces; The seed pulse beam is incident on the beam modulation unit, and changes its transmission direction when reflected by the reflective surface, passing through the second laser crystal four times; when the seed pulse beam passes through the second laser crystal, the beam paths of the second laser crystal overlap at least twice; The beam paths of the third and fourth passes through the second laser crystal overlap. The beam modulation unit includes a polarizing beam splitter, a first half-wave plate, a Faraday rotator, a second half-wave plate, a converging lens, and a first reflecting surface, all arranged coaxially along a first direction. The extension length of the first half-wave plate is greater than the extension length of the second half-wave plate. The beam modulation unit also includes a third reflecting mirror and a fourth reflecting mirror, which are located on the same side of the polarizing beam splitter and on adjacent sides of the first half-wave plate. A seed pulse beam with a first polarization direction is incident from a first position onto the polarizing beam splitter and transmitted. After passing through the first half-wave plate and the Faraday rotator, it is incident onto the converging lens. After being converged by the converging lens, it is obliquely incident at a first incident angle and passes through the second laser crystal for the first time. After being reflected by the first reflecting surface, it passes through the second laser crystal for the second time. After being transmitted through the converging lens, the Faraday rotator, and the first half-wave plate again, it is converted into a beam with a second polarization direction. The beam of light in the second polarization direction is incident on the polarizing beam splitter and reflected. After being reflected by the third and fourth reflecting mirrors in sequence, it is incident on the polarizing beam splitter and reflected again. After being transmitted through the Faraday rotator, the second half-wave plate and the converging lens, it passes through the second laser crystal for the third time. After being reflected by the first reflecting surface, it passes through the second laser crystal for the fourth time. After being transmitted through the converging lens, the second half-wave plate and the Faraday rotator again, it is converted into a beam of light in the first polarization direction. The beam of light in the first polarization direction is transmitted through the polarizing beam splitter and output from the second position.

2. The pulsed laser device according to claim 1, characterized in that, The reflecting surface is the reflecting surface of a device in the beam modulation unit and / or the reflecting surface of a mirror.

3. The pulsed laser device according to claim 1, characterized in that, The pre-amplification unit further includes a second pump lens group located between the second pump source and the second laser crystal, the second pump lens group being used to focus the pump light onto the second laser crystal.

4. The pulsed laser device according to claim 1, characterized in that, The pump light is incident on the second laser crystal from one end and / or at least one sidewall.

5. A pulsed laser device, characterized in that, It includes a seed source, a pre-amplification unit, a main amplification unit, an acousto-optic modulation unit, and a frequency conversion unit; The seed source is used to output a seed pulse beam to be amplified; The pre-amplification unit is used to receive the seed pulse beam and amplify it into a first-level amplified beam; The main amplification unit includes at least one stage of optical amplifier. The optical amplifier includes a shaping lens, a first laser crystal, a reflector, a first pump lens group, and a first pump source. The shaping lens is used to expand the divergence angle of the first-stage amplified beam by 1 to 2 times before transmitting it to the first laser crystal. The first pump lens group is used to converge the pump light output from the first pump source to the first laser crystal. The reflector is used to reflect and output the beam amplified by the first laser crystal. The acousto-optic modulation unit is used to control the repetition frequency of the pulse; The frequency conversion unit is used to convert the frequency of the output pulse using frequency doubling or sum-frequency effects; The pre-amplification unit includes a second pump source, a second laser crystal, and a beam modulation unit, wherein the beam modulation unit includes multiple reflective surfaces; The seed pulse beam is incident on the beam modulation unit, and changes its transmission direction when reflected by the reflective surface, passing through the second laser crystal four times; The beam paths passing through the second laser crystal four times do not overlap; The beam modulation unit includes a polarizing beam splitter, a third half-wave plate, a Faraday rotator, a fourth half-wave plate, a converging lens, and a first reflecting surface, all arranged coaxially along a first direction. The extension length of the third half-wave plate is greater than that of the fourth half-wave plate. The beam modulation unit also includes a seventh reflecting mirror and an eighth reflecting mirror, which are located on the same side of the polarizing beam splitter and on adjacent sides of the third half-wave plate. A seed pulse beam with a first polarization direction is incident from a first position onto the polarizing beam splitter and transmitted. After being transmitted through the third half-wave plate and the Faraday rotator, it is incident onto the converging lens. After being converged by the converging lens, it is obliquely incident at a third incident angle and passes through the second laser crystal for the first time. After being reflected by the first reflecting surface, it passes through the second laser crystal for the second time. After being transmitted through the converging lens, the Faraday rotator, and the third half-wave plate again, it is converted into a beam with a second polarization direction. The beam with the second polarization direction is incident on the polarizing beam splitter and reflected. After being reflected in sequence by the seventh and eighth reflecting mirrors, it is incident on the polarizing beam splitter again and reflected. After being transmitted through the Faraday rotator, the fourth half-wave plate, and the converging lens, it is obliquely incident at the fourth incident angle and passes through the second laser crystal for the third time. After being reflected by the first reflecting surface, it passes through the second laser crystal for the fourth time. After being transmitted through the converging lens, the fourth half-wave plate, and the Faraday rotator again, it is converted into a beam with the first polarization direction, wherein the fourth incident angle is smaller than the third incident angle. The beam of light in the first polarization direction is transmitted through the polarizing beam splitter and output from the second position.

6. The pulsed laser device according to claim 5, characterized in that, The reflecting surface is the reflecting surface of a device in the beam modulation unit and / or the reflecting surface of a mirror.

7. The pulsed laser device according to claim 5, characterized in that, The pre-amplification unit further includes a second pump lens group located between the second pump source and the second laser crystal, the second pump lens group being used to focus the pump light onto the second laser crystal.

8. The pulsed laser device according to claim 5, characterized in that, The pump light is incident on the second laser crystal from one end and / or at least one sidewall.

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