Laser amplifier and method for avoiding thermal depolarization of side pump

Abstract

The invention discloses a laser amplifier and a method for avoiding thermal depolarization of a side pump. According to an exemplary embodiment, a laser amplifier comprises: a vector polarization conversion device for converting linearly polarized light into light in a single vector polarization state; and a side pump module for amplifying the light incident on the side pump module. According to the technical scheme provided by the invention, only one vector polarization component exists in the module through the polarization conversion device, and thermal depolarization does not occur in single radial or angular vector polarization under cylindrical symmetric anisotropic refractive index distribution, so that thermal depolarization does not occur no matter whether a light beam passes through a crystal rod for one time or multiple times, and therefore, the reliability of the module is improved. Therefore, the influence of the thermal depolarization effect of the side pump module on the polarization state of the light beam is reduced, and the amplification quality of the high-energy picosecond laser and the stability of an amplification system are improved.

Description

Technical Field

[0001] This application relates to the field of laser technology, and more specifically, various exemplary embodiments relate to laser amplifiers and methods for avoiding side-pumped thermal depolarization. Background Technology

[0002] Picosecond pulsed lasers, as an advanced laser technology combining high peak power and a simple structure, have demonstrated irreplaceable application value in many key fields such as modern industrial production, cutting-edge scientific research, and national defense security due to their unique performance advantages. They have become a research hotspot and a core direction for industrialization in the field of laser technology. Compared with traditional nanosecond lasers, picosecond pulsed lasers compress the pulse width to the picosecond level. While maintaining high average power, the peak power can easily break through the megawatt level or even higher. This characteristic enables cold working effects in material processing, where laser energy is instantly deposited on the material surface, avoiding processing defects such as edge melting and cracks caused by thermal diffusion, significantly improving processing accuracy and product yield.

[0003] However, current picosecond pulsed lasers generate picosecond pulse energy directly from the oscillator using mode-locking technology. This pulse energy is typically only in the nanojoule range, far from meeting the demands of high-energy, high-power laser output in industrial processing, scientific research, and military defense. Therefore, laser amplification technology is necessary to increase the pulse energy to realize the practical application of picosecond lasers. The core of the laser amplification process lies in the selection of the gain medium and the optimization of the pumping method, which directly determines the energy, power, beam quality, and system stability of the amplified laser.

[0004] Among various gain media, neodymium-doped yttrium aluminum garnet (Nd:YAG) crystals exhibit superior optical properties. Nd:YAG crystals possess a wide absorption bandwidth, high fluorescence quantum efficiency, and good thermal and mechanical stability, enabling them to maintain stable laser output even at high pump power, making them an ideal gain medium for high-energy, high-power laser systems. Regarding the choice of pumping method, side-pumping offers significant advantages over end-pumping: side-pumping allows for large-area coupling between the pump light and the gain medium, enabling the injection of higher pump power and thus providing sufficient energy input for efficient pulse amplification; simultaneously, side-pumping facilitates the use of large-area water-cooling structures, rapidly dissipating the heat generated by the gain medium during pumping and laser amplification.

[0005] Based on the above advantages, side-pumping of Nd:YAG crystals has become the mainstream solution for gain medium pumping in high-energy picosecond lasers. This approach, through optimization of key technologies such as pump source layout, heat dissipation structure design, and optical coupling efficiency, enables efficient injection and rapid heat dissipation of high pump power, providing a reliable technical guarantee for the efficient and stable amplification of picosecond pulses and promoting the industrialization and widespread application of high-energy, high-power picosecond laser technology. Summary of the Invention

[0006] The subject matter of the independent claims is provided according to several aspects. Further aspects are defined in the dependent claims. Embodiments that do not fall within the scope of the claims should be interpreted as examples that aid in understanding this disclosure.

[0007] According to a first aspect of this disclosure, a laser amplifier is provided, which may include: a vector polarization conversion device for converting linearly polarized light into light with a single vector polarization state; and a side pump module for amplifying light incident into the side pump module.

[0008] According to a second aspect of this disclosure, a laser amplification method is provided, comprising: converting linearly polarized light into light with a single vector polarization state; and amplifying the light with the single vector polarization state using a side-pumping module. Attached Figure Description

[0009] Figure 1 A schematic diagram of a laser amplifier according to an exemplary embodiment of the present disclosure is shown;

[0010] Figure 2 A schematic diagram of a laser amplifier according to another exemplary embodiment of the present disclosure is shown;

[0011] Figure 3 A schematic diagram of a laser amplifier according to another exemplary embodiment of the present disclosure is shown;

[0012] Figure 4 A schematic diagram of a laser amplifier according to another exemplary embodiment of the present disclosure is shown;

[0013] Figure 5 A flowchart illustrating an exemplary method according to an exemplary embodiment of the present disclosure is shown.

[0014] The same or substantially the same elements, operations, and steps shown in the various figures may be indicated by the same reference numerals. For clarity, not every element, operation, or step is shown in every figure. Detailed Implementation

[0015] Exemplary embodiments of the present application will now be described in more detail with reference to the accompanying drawings. It should be understood that this disclosure should not be construed as limiting to the exemplary embodiments described herein, but rather that it can be implemented in various other forms, provided only for a more thorough and complete understanding of the present application. It should also be understood that the accompanying drawings are given by way of example only and are not intended to limit the precise form of the embodiments or to limit the scope of protection of the present application.

[0016] The following embodiments are exemplary. Although the specification refers to "a," "an," or "some" embodiments in various places, this does not necessarily mean that each reference refers to the same embodiment, or that a specific feature applies only to a single embodiment. Individual features of different embodiments may also be combined to provide other embodiments. Moreover, when specific features, structures, or characteristics are described in conjunction with embodiments, whether explicitly described or not, such features, structures, or characteristics will be applied to other embodiments to the extent that those skilled in the art possess the knowledge to do so. It should be understood that although terms such as "first" and "second" may be used to describe various elements, these elements should not be limited by these terms. These terms are merely used to distinguish one element from another.

[0017] In this disclosure, the terms "at least one of A or B", "at least one of A and B", and "A and / or B" mean [A], [B], or [A and B]. In this disclosure, "A, B, and / or C" means [A], [B], [C], [A and B], [A and C], [B and C], or [A, B, and C].

[0018] The side-pumping method based on Nd:YAG crystals uses a side-pumping module crystal rod as its core component. During laser amplification, the crystal rod heats up as a whole but dissipates heat only from its sides. Under uniform pumping conditions at all angles, the crystal rod develops an anisotropic refractive index distribution that is symmetrical about its central axis. When linearly polarized laser light passes through the crystal rod, this cylindrically symmetric anisotropic refractive index distribution alters the wavefront and polarization state of the beam, causing the laser to converge after leaving the module crystal rod. This phenomenon is called thermal lensing. Simultaneously, the polarization state of the laser changes after passing through the side-pumping module, and the degree of change depends on the laser's position within the beam spot. This phenomenon is called thermal depolarization. For dual-pass laser amplifiers that use polarization beam splitters to distinguish between the injected and exiting lasers, thermal depolarization can cause the linear polarization state of the amplified laser to change from the linear polarization state that should be transmitted through the polarization beam splitter to the linear polarization state that will be reflected by the polarization beam splitter. This causes the amplified laser to return to the previous stage, resulting in power loss and device damage.

[0019] The reason for thermal depolarization is that when the radial and angular vector polarization components decomposed from linearly polarized light propagate in the crystal rod, the refractive index of the crystal rod is different for these two vector polarization components. This results in the two polarization components acquiring two different centrosymmetric phase distributions from the crystal rod. The phases experienced by these two polarization components are unequal, and the consequence of resynthesis is that the polarization state deviates from the linear polarization state at the time of injection, leading to thermal depolarization.

[0020] Existing thermal depolarization compensation schemes involve passing the beam through the crystal rod a second time with the same polarization state, angle, and position as the first pass. This causes the radially polarized component of the incident light to be given the phase experienced by the angularly polarized light during the second pass, while the angularly polarized component is conversely given the phase of the radially polarized light. In this way, the two sets of polarization components within the beam have equal phase under ideal conditions, and after recombining, they will not deviate from the linear polarization state, thus compensating for thermal depolarization.

[0021] The drawback of this scheme is that, due to the different focal lengths of the thermal lenses for different polarization components, the two sets of polarization components of the beam converge differently after passing through the crystal rod. This makes it impossible to collimate them simultaneously using a single isotropic optical system. Consequently, the two sets of polarization components of the beam can never enter the crystal rod a second time at completely identical angles and positions, and the two phases cannot be fully compensated. The beam is always affected by the combined effects of thermal lensing and thermal depolarization during propagation, which cannot be simultaneously avoided.

[0022] To address the aforementioned technical problems, this disclosure proposes a laser amplifier structure that employs a side-pumping module while avoiding thermal depolarization. This structure ensures that the linearly polarized light incident on the beam remains linearly polarized after amplification by the side-pumping module, thus circumventing the aforementioned defects. The device uses a polarization conversion device to ensure that only one vector polarization component exists within the module at a time. Since a single radial or angular vector polarization does not undergo thermal depolarization under a cylindrically symmetric anisotropic refractive index distribution, thermal depolarization does not occur regardless of whether the beam passes through the crystal rod once or multiple times. This reduces the impact of the thermal depolarization effect of the side-pumping module on the beam polarization state, thereby improving the amplification quality and stability of the high-energy picosecond laser amplification system.

[0023] Figure 1A schematic diagram of a laser amplifier 100 according to an exemplary embodiment of the present disclosure is shown. The laser amplifier 100 can be a vector-polarized double-pass amplifier, enabling highly stable continuous operation. The laser amplifier 100 may include: a picosecond laser 110, a polarizing flat beam splitter 120, a vector polarization conversion device 130, a side-pumping module 140, an image transfer system 150, a beam rotator 160, and a zero-degree mirror 170. The picosecond laser 110 can be a picosecond laser with a repetition rate of 1 kHz, a single pulse energy of 0.44 mJ, a pulse width of approximately 60 ps, ​​and a center wavelength of 1064 nm. This wavelength is in the near-infrared band, possessing good atmospheric transmission characteristics and material absorption efficiency. The spot diameter can be 5.5 mm, and its output spot meets Gaussian distribution characteristics, providing a high-quality seed light source for subsequent amplification processes.

[0024] The polarizing flat beam splitter 120 can be made of fused silica, a material with advantages such as low dispersion, high transmittance, high mechanical strength, and good thermal stability, which can meet the stringent requirements of high-power laser transmission scenarios. In some embodiments, the polarizing flat beam splitter 120 can be coated on both sides, wherein the coating can be applied to the S1 side (i.e., Figure 1 A polarizing film can be deposited on the upper left plane of the polarizing flat beam splitter 120 in the middle, so that a polarizing film can be deposited on S2 (i.e. Figure 1 The lower right plane of the polarizing flat beam splitter 120 is coated with an anti-reflection film, which can effectively reduce interface reflection loss. In some embodiments, the S1 plane of the polarizing flat beam splitter 120 can satisfy an extinction ratio greater than 1000:1 at a wavelength of 1064nm, ensuring the accuracy of polarization selection and avoiding stray polarized light interference, while the S2 plane can have a transmittance of >99% at a wavelength of 1064nm, minimizing transmission energy loss.

[0025] The vector polarization conversion device 130 can be a spatially anisotropic linear polarization state rotation element. Based on the phase modulation of the polarization state of light, it can achieve the reversibility of linearly polarized light and vector polarized light through a spatially gradually changing optical anisotropic structure. It can convert horizontal or vertical linearly polarized light into radial or angular vector polarized light, and vice versa. This conversion process has almost no energy loss. In some embodiments, the vector polarization conversion device 130 can be a first-order vortex waveplate (or a first-order vortex waveplate), such as a first-order vortex waveplate of liquid crystal polymer. When the 0° fast axis of the first-order vortex waveplate is in the horizontal direction, it can convert P-polarized light (i.e., horizontally polarized light) into radially vector polarized light and S-polarized light (i.e., vertically polarized light) into angularly vector polarized light. It can also convert in reverse, that is, convert radially vector polarized light into P-polarized light and angularly vector polarized light into S-polarized light. The polarization direction of the converted vector polarized light is axially symmetric and the polarization state remains stable when propagating in a cylindrically symmetric medium. In some embodiments, the vector polarization converter 130 can be coated with 1064nm antireflection films on both surfaces to further reduce surface reflection loss. The vector polarization converter 130 can have a transmittance of >99% at 1064nm, ensuring efficient transmission of light energy. In some embodiments, the vector polarization converter 130 can be a spatially graded waveplate formed by etching microstructures on glass. By precisely designing the spatial distribution of the microstructures, precise control of the polarization state can be achieved.

[0026] The side-pumping module 140 can be an Nd:YAG side-pumping module, where the Nd:YAG crystal can serve as the gain medium for a high-power laser amplifier. The Nd:YAG side-pumping module can use a cylindrical crystal rod, with 1064nm anti-reflection coatings at both ends to prevent optical oscillation interference caused by end-face reflection. The side-pumping module 140 can be pumped from the side, which allows for large-area contact between the pump light and the gain medium, improving pump uniformity and reducing thermal gradient generation. In some embodiments, the pump light wavelength of the side pump module 140 can be 808 nm, the transmittance of the antireflection film can be greater than 99.5%, the diameter of the crystal rod of the side pump module can be 7 mm, the doping concentration of the crystal rod can be 0.6%, the pump mode can be quasi-continuous pumping, pulse pumping or continuous pumping, the pump light pulse width can be 125 μs, the repetition frequency can be 1 kHz, which can be the same as the seed light to achieve timing synchronization between the pump and the seed light, and the pump light power can be about 950 W to provide sufficient pump energy to achieve efficient amplification of the seed light.

[0027] In addition to the crystal rod, the side pump module 140 may also include other auxiliary components to achieve pump light injection, energy amplification, and stable system operation. In some implementations, the side-pumping module may include: a semiconductor laser diode array pump source, which serves as the source of pump light emission and can be arranged in an array to achieve high-power pump light output; an optical coupling system, which may consist of coupling lenses, mirrors, light guides, etc., and its function is to focus, collimate, and deflect the divergent pump light emitted by the pump source, and finally uniformly couple it to the side of the crystal rod, ensuring that the pump light can cover the entire side area of ​​the crystal rod, improving the absorption efficiency of the pump light and reducing the energy loss of the pump light; a cooling system, since a large amount of pump light energy is converted into heat energy during the pumping process, if the heat cannot be dissipated in time, it will seriously affect the laser beam quality. Therefore, a cooling system can be used to remove the heat generated by the crystal rod and pump source during operation, avoiding the accumulation of excessive heat and the generation of thermal stress, which could damage the crystal rod; and structural support and packaging components, which may include a module housing, a crystal rod holder, a pump source mounting bracket, seals, dust covers, etc., to isolate external dust and moisture, prevent the crystal rod from deforming due to mechanical stress, protect internal optical components, and extend the module's service life. The side-pumping module emits pump light of a specific wavelength through a semiconductor laser diode array pump source. After being focused and deflected by an optical coupling system, the pump light is uniformly irradiated onto the side of the crystal rod. Activated ions in the crystal rod absorb the pump light energy and transition from the ground state to a higher-energy excited state. Due to the short lifetime of the higher-energy excited state, the activated ions quickly transition to a metastable state through a non-radiative relaxation process. Through continuous pumping, the number of activated ions in the metastable state is greater than the number of activated ions in the second metastable state. At this point, under the stimulation of photons generated by spontaneous emission (or external incident photons), the activated ions in the metastable state will transition to the second metastable state, and then return to the ground state through a non-radiative transition, releasing photons with the same frequency, phase, and propagation direction as the stimulating photons. Simultaneously, the cooling system removes the heat generated by the crystal rod and pump source in real time, suppressing thermal distortion and thermal lensing effects, and ensuring the stability of the laser beam quality.

[0028] The image transmission system 150 allows the incident laser to maintain a collimated state as it leaves the system, achieving distortion-free beam transmission and maintaining the stability of the spot size and wavefront phase. The image transmission system 150 can consist of two plano-convex lenses 152 and 156 with a focal length of 150mm and a central vacuum tube 154. The plano-convex lenses can be made of BK7 glass. The first convex lens 152 can be configured with its convex surface facing the side pump module 140 to reduce spherical aberration during beam incidence. The distance between the first convex lens 152 and the center of the side pump module can be approximately 19cm to achieve efficient beam focusing. The second convex lens 156 can be configured with its flat surface facing the side pump module 140. The distance between the two convex lenses can be set slightly shorter than twice the lens focal length, for example, less than 30cm. The specific distance can be fine-tuned according to actual beam quality requirements to achieve optimal collimation. The vacuum tube 154 between the two lenses can be used to prevent laser ionization at the focal point. The vacuum environment can effectively prevent beam distortion caused by plasma generated by air ionization. The gas pressure inside the vacuum tube 154 can be less than 0.1 mbar. A small hole for biaxial adjustment can be installed at the laser focal point in the vacuum tube 154 to block stray light. In some embodiments, the small hole for biaxial adjustment in the vacuum tube 154 can be a ceramic hole with a diameter of 1.5 mm. Ceramic material has the characteristics of high temperature resistance and high laser damage threshold, which can prevent it from being burned by stray light.

[0029] The optical rotator 160 can be a 45° optical rotator, its function being to achieve controllable rotation of the polarization state, providing support for the polarization state cycle of dual-pass amplification. In some embodiments, the optical rotator 160 can be a Faraday rotator, where the rotation direction is independent of the light propagation direction and is determined only by the direction of the magnetic field. Both sides of the optical rotator 160 can be coated with a 1064nm antireflection film, achieving a transmittance greater than 99% and a polarization rotation angle deviation of less than 1°, ensuring the accuracy of polarization state conversion.

[0030] The zero-degree reflector 170 allows the light beam to return along its original path, achieving a closed-loop optical path for dual-pass amplification and ensuring the collimation of the reflected beam. In some embodiments, the zero-degree reflector 170 can be coated with a 1064nm high-reflectivity film, which has a reflectivity of not less than 95% for the incident light wavelength. In other embodiments, the zero-degree reflector 170 can have a reflectivity of 99% for the incident light wavelength, with a reflection loss ≤1%, which can meet the requirements of high-power laser reflection.

[0031] The following describes the working principle of the amplifier. For clarity and not limitation, the laser beam emitted by the picosecond laser may be referred to as seed light. During the use of amplifier 100, the picosecond laser 110 first emits vertically polarized (S-polarized) seed light. This seed light is incident at a 45° angle onto the S1 plane of the polarizing beam splitter 120. Due to the polarization selectivity of the S1 plane, the S-polarized light is efficiently reflected, while any potential P-polarized stray light is transmitted and removed. The reflected S-polarized light is then converted into angularly vector-polarized light by a vector polarization converter 130 with its fast axis at the horizontal direction (0°). The converted angularly vector-polarized light is amplified for the first time by the side-pump module 140, maintaining its angularly vector polarization state. It then enters the image transfer system 150. The amplified seed light is converged by the first convex lens 152 in the image transfer system 150, and the resulting focal point passes through a dual-axis adjustable aperture within the vacuum tube 154. Simultaneously, stray light reflected from the lenses and other transmissive optical elements is blocked by the aperture. When the seed light leaves the image transfer system 150, it remains collimated. After passing through the optical rotator 160, its polarization state is rotated by 45°, and then it is reflected by the 0° mirror 170. The reflected beam returns to the polarizing plate beam splitter 120 along the same path. During this time, it passes through the optical rotator 160 a second time, and its polarization state is rotated by another 45°, for a cumulative rotation of 90°, changing from angular vector polarized light to radial vector polarized light. Then, it passes through the image transfer system 150 a second time, and is filtered for stray light through the aperture to maintain the purity of the beam. Subsequently, it is amplified a second time by the side pump module 140, further increasing the single-pulse energy and maintaining the radial vector polarization state. Then, it passes through the vector polarization conversion device 130 a second time, and the radial vector polarized light is converted into P-polarized light. Finally, the P-polarized light is incident on the polarizing plate beam splitter 120 at an incident angle of 45°. Due to the high transmittance of the polarizing plate beam splitter 120 for P-polarized light, the P-polarized light is transmitted away, thus completing the dual-pass laser amplification process. In some embodiments, the vector polarization conversion device 130 can be rotated 90 degrees, so that its 0° fast axis direction changes from parallel to the optical platform to perpendicular to the optical platform. This placement state allows the S-polarization of the seed light to be converted into radial vector polarization, and the angular vector polarization to be converted into P-polarization. The polarization state change sequence of the seed light changes from the previous S-polarization-angular vector polarization-radial vector polarization-P-polarization to S-polarization-radial vector polarization-angular vector polarization-P-polarization. The amplification efficiency and beam quality are basically the same under the two configurations, and those skilled in the art can flexibly choose according to the actual optical path requirements.

[0032] Through the laser amplifier 100 of this exemplary embodiment, a seed light with a single pulse energy of 0.44 mJ can obtain a single pulse energy output of about 3 mJ after dual-pass amplification, with an energy amplification factor of about 6.8 times. Furthermore, this disclosure converts linearly polarized light into single vector polarized light through a vector polarization conversion device 130. Since a single radial or angular vector polarization will not undergo thermal depolarization under a cylindrically symmetric anisotropic refractive index distribution, the influence of thermal depolarization effect of the side-pump module is reduced. Compared with a conventional linearly polarized dual-pass amplifier, the amplification efficiency and beam quality stability are significantly improved.

[0033] Figure 2 A schematic diagram of a laser amplifier 200 according to another exemplary embodiment of the present disclosure is shown. Compared to laser amplifier 100, the polarization state of the seed light output from the picosecond laser in laser amplifier 200 changes from S-polarization to P-polarization. Since the polarizing plate beam splitter allows the P-polarized seed light to pass through, in laser amplifier 200, the seed light enters from the side of the polarizing plate beam splitter coated with an antireflection film (i.e., the S2 side). After being amplified twice by laser amplifier 200, the laser light is converted to S-polarization and reflected by the side of the polarizing plate beam splitter coated with a polarizing film (i.e., the S1 side). This configuration provides another flexible option for the incident direction of the seed light, adapting to different system integration requirements. Other than this, the arrangement and parameters of the components are the same as... Figure 1 The laser amplifier 100 is consistent with that in the above, specifically:

[0034] Laser amplifier 200 can still be a vector polarized double-pass amplifier, and may include: a picosecond laser 210, a polarizing flat beam splitter 220, a vector polarization conversion device 230, a side-pumping module 240, an image transfer system 250, a beam rotator 260, and a zero-degree mirror 270. The picosecond laser 210 can be a picosecond laser with a repetition rate of 1 kHz, a single pulse energy of 0.44 mJ, a pulse width of approximately 60 ps, ​​and a center wavelength of 1064 nm. Its spot diameter can be 5.5 mm, and its output spot also satisfies Gaussian distribution characteristics, maintaining consistency with the seed light parameters of amplifier 100 to ensure compatibility and stability during the amplification process.

[0035] The polarizing flat beam splitter 220 can be made of fused silica, making it suitable for high-power laser transmission environments. In some embodiments, the polarizing flat beam splitter 220 can be coated on both sides, and the coating process can be completely consistent with that of the polarizing flat beam splitter 120 in the amplifier 100. Specifically, a polarizing film can be coated on the S1 surface with an incident angle of 45°, and an anti-reflection film can be coated on the S2 surface. In some embodiments, the S1 surface of the polarizing flat beam splitter 220 can achieve an extinction ratio greater than 1000:1 at a wavelength of 1064 nm, effectively filtering stray polarized light, while the S2 surface can achieve a transmittance of >99% at a wavelength of 1064 nm, ensuring efficient transmission of seed light.

[0036] The vector polarization converter 230 can be a spatially anisotropic linear polarization state rotation element. Its working principle is the same as that of the vector polarization converter 130 in the amplifier 100. It achieves reversibility based on the phase modulation of the polarization state of light, and can convert horizontal or vertical linearly polarized light into radial or angular vector polarized light, and vice versa. In some embodiments, the vector polarization converter 230 can be a first-order vortex waveplate, such as a first-order vortex waveplate of liquid crystal polymer. When the 0° fast axis of the first-order vortex waveplate is in the horizontal direction, it can convert P-polarized light into radial vector polarized light and S-polarized light into angular vector polarized light. It can also convert in reverse, that is, convert radial vector polarized light into P-polarized light and angular vector polarized light into S-polarized light. The polarization state of the converted vector polarized light remains stable when it propagates in a cylindrically symmetric medium, without depolarization. In some embodiments, the vector polarization converter 230 can be coated with 1064nm antireflection films on both surfaces to further reduce surface reflection loss. The vector polarization converter 230 can have a transmittance of >99% at 1064nm, ensuring efficient transmission of light energy. In some embodiments, the vector polarization converter 230 can be a spatially gradient waveplate formed by etching microstructures on glass, achieving controllable conversion of polarization states through precise microstructure design.

[0037] The side-pump module 240 can be an Nd:YAG side-pump module, completely identical to the side-pump module 140 in amplifier 100. It uses an Nd:YAG cylindrical crystal rod as the gain medium, and both ends of the crystal rod can be coated with a 1064nm antireflection film, with a transmittance greater than 99.5%, avoiding end-face reflection interference. The side-pump module 240 can be pumped from the side, improving pump uniformity and reducing thermal gradient. In some embodiments, the pump light wavelength of the side-pump module 240 can be 808nm, the antireflection film transmittance can be greater than 99.5%, the crystal rod diameter can be 7mm, the doping concentration can be 0.6%, the pump mode can be quasi-continuous pumping, pulsed pumping, or continuous pumping, the pump light pulse width can be 125μs, the repetition frequency can be 1kHz (synchronized with the seed light repetition frequency), and the pump light power can be approximately 950W, providing sufficient amplification energy. In addition to the crystal rod, the side pump module 240 may also include the same semiconductor laser diode array pump source, optical coupling system, cooling system and structural support and packaging components as the side pump module 140. The structure, parameters and working principle of each component are completely consistent to ensure the stability and consistency of amplification performance.

[0038] The image transfer system 250 maintains collimation when the incident laser leaves the system, and its structural parameters are completely identical to those of the image transfer system 150 of the amplifier 100. The image transfer system 250 can consist of two plano-convex lenses 252 and 256 and a vacuum tube 254 in the middle. The plano-convex lenses can be made of BK7 glass. The first convex lens 252 can be configured with its convex surface facing the side pump module 240, and its distance from the center of the side pump module can be approximately 19 cm. The second convex lens 256 can be configured with its flat surface facing the side pump module 240. The distance between the two convex lenses can be set slightly shorter than twice the lens focal length, for example, less than 30 cm, and can be fine-tuned according to beam quality. The vacuum 254 between the two lenses is used to prevent laser ionization at the focal point. The gas pressure inside the vacuum tube 254 can be less than 0.1 mbar. A small, dual-axis adjustable aperture can be installed at the laser focal point in the vacuum tube 254 to block stray light. In some implementations, the biaxial adjustment orifice within the vacuum tube 254 can be a ceramic orifice with a diameter of 1.5 mm, which is resistant to high temperatures and has a high laser damage threshold.

[0039] The rotator 260 can be a 45° rotator, with parameters consistent with the rotator 160 of the amplifier 100. Its core function is to achieve controllable rotation of the polarization state. In some embodiments, the rotator 260 can be a Faraday rotator, with 1064nm antireflection coatings on both sides, achieving a transmittance greater than 99% and a polarization rotation angle deviation of less than 1°.

[0040] The zero-degree reflector 270 can return the beam along its original path, exhibiting the same performance as the zero-degree reflector 170 of the amplifier 100. In some embodiments, the zero-degree reflector 270 can be coated with a 1064nm high-reflectivity film, which can reflect at least 95% of the incident light wavelength. In other embodiments, the reflectivity can be 99%, with a reflection loss ≤1%, to meet high-power reflection requirements.

[0041] During the use of amplifier 200, picosecond laser 210 first emits horizontally polarized (P-polarized) seed light. Then, the seed light enters from the S2 surface of polarizing beam splitter 220 at a 45° incident angle. Due to the anti-reflection coating characteristics of the S2 surface and the polarization selectivity of the S1 surface, the P-polarized light is efficiently transmitted and reaches vector polarization converter 230, whose fast axis is horizontal. After passing through vector polarization converter 230, the seed light is converted into radially vector polarized light. The converted radially vector polarized light is amplified for the first time by side-pump module 240, still maintaining its radially vector polarization state, and then enters image transfer system 250. The seed light is converged by the first convex lens 252 in image transfer system 250, and the resulting focal point passes through a biaxially adjustable aperture in vacuum tube 254. Simultaneously, stray light reflected from the surfaces of lenses and other transmissive optical elements is blocked by the aperture. When the seed light leaves the image transfer system 250, it remains collimated. After passing through the optical rotator 260, its polarization state is rotated by 45°, and then it is reflected by the 0° mirror 270. The reflected beam returns to the polarizing flat beam splitter 220 along the same path. During this time, it passes through the optical rotator 260 a second time, and its polarization state is rotated by another 45°, for a cumulative rotation of 90°, changing from radial vector polarized light to angular vector polarized light. Then, it passes through the image transfer system 250 a second time to filter stray light, and then passes through the side pump module 240 for a second amplification, still maintaining the angular vector polarization state. Next, it passes through the vector polarization conversion device 230 a second time, converting the angular vector polarized light into S-polarized light. Finally, the S-polarized light is incident on the S1 surface of the polarizing flat beam splitter 220, is efficiently reflected, and then output, thus completing the dual-pass laser amplification process. In some implementations, the vector polarization conversion device 230 can be rotated 90 degrees, so that its 0° fast axis direction changes from parallel to the optical platform to perpendicular to the optical platform. In this placement state, the polarization state change sequence of the seed light changes from the previous P-polarization-radial vector polarization-angular vector polarization-S-polarization to P-polarization-angular vector polarization-radial vector polarization-S-polarization. The energy amplification factor, beam quality and stability of the two configurations are basically the same, which can adapt to different polarization state control requirements.

[0042] Figure 3 A schematic diagram of a laser amplifier 300 according to another exemplary embodiment of the present disclosure is shown. Compared to laser amplifier 100, laser amplifier 300 is a single-pass amplifier. The seed light only passes through the side-pumping module once, and the laser amplified by the side-pumping module does not return to the system. Therefore, the system does not need to use a rotator and a 0-degree reflector, and the polarizing flat beam splitter can be replaced with a common reflector, thereby reducing the complexity and cost of the system and simplifying the optical path debugging process. In addition, the amplified single vector polarized light also needs to be converted into linearly polarized light output, so a device for converting vector polarized light into linearly polarized light needs to be added. Apart from this, the arrangement and parameters of other components are the same as those of the laser amplifier 100. Figure 1 The laser amplifier 100 is consistent with that in the above, specifically:

[0043] The laser amplifier 300 can be a vector-polarized single-pass amplifier, and may include: a picosecond laser 310, a mirror 320, a vector polarization converter 330, a side-pumping module 340, an image transfer system 350, and a linear polarization converter 360. The picosecond laser 310 can be a picosecond laser with a repetition rate of 1 kHz, a single pulse energy of 0.44 mJ, a pulse width of approximately 60 ps, ​​and a center wavelength of 1064 nm. The spot diameter can be 5.5 mm, and its output spot also satisfies Gaussian distribution characteristics, providing high-quality seed light for single-pass amplification.

[0044] As a core component for changing the direction of beam propagation, the reflector 320 has a high-reflectivity film deposited on its front surface (the beam incident surface, i.e., the aforementioned S1 surface). This high-reflectivity film can be a multilayer dielectric film designed for a specific polarization state. In some embodiments, the reflectivity of the reflector 320 for S-polarized light can be greater than 99% to achieve polarization-selective reflection, reduce interference from non-target polarization beams, and ensure the collimation of the reflected beam. In some embodiments, to adapt to different optical path layout requirements, the incident angle of the laser beam incident on the reflector 320 can deviate from the conventional 45°, as long as it is ensured that the beam can be completely incident on the effective reflection area of ​​the reflector 320 without being blocked by other components. For example, the incident angle can be designed to be 30°, 40°, 50°, etc. In this case, the reflection angle of the beam is equal to the incident angle, which can be flexibly adjusted according to the actual optical path space, facilitating optical path calibration.

[0045] The vector polarization converter 330 can be a spatially anisotropic linear polarization rotation element. Its structure, parameters, and working principle are completely consistent with the vector polarization converter 130 of the amplifier 100. Based on phase modulation, it achieves reversible polarization conversion, capable of converting horizontally or vertically linearly polarized light into radially or angularly vector-polarized light, and vice versa. In some embodiments, the vector polarization converter 330 can be a first-order vortex waveplate, such as a first-order vortex waveplate of a liquid crystal polymer. When the 0° fast axis of the first-order vortex waveplate is in the horizontal direction, it can convert P-polarized light into radially vector-polarized light and S-polarized light into angularly vector-polarized light. It can also convert in reverse, that is, convert radially vector-polarized light into P-polarized light and angularly vector-polarized light into S-polarized light. In some embodiments, the vector polarization conversion device 330 can be coated with a 1064nm antireflection film on both surfaces, with a transmittance of >99% at 1064nm. Alternatively, it can be a spatially gradient waveplate formed by etching microstructures on glass, achieving controllable conversion of polarization state through precise microstructure design.

[0046] The side-pump module 340 can be an Nd:YAG side-pump module, with structural parameters completely identical to those of the side-pump module 140 of the amplifier 100. The Nd:YAG side-pump module can use a cylindrical crystal rod, with 1064nm antireflection coatings (transmittance >99.5%) deposited at both ends. The pumping method of the side-pump module 340 can be side-pumping. In some embodiments, the pump light wavelength of the side-pump module 340 can be 808nm, the crystal rod diameter can be 7mm, the doping concentration can be 0.6%, the pumping mode can be quasi-continuous pumping, pulsed pumping, or continuous pumping, the pump light pulse width can be 125μs, the repetition frequency can be 1kHz (synchronized with the seed light), and the pump light power can be approximately 950W. In addition to the crystal rod, the side-pump module 340 may also include the same semiconductor laser diode array pump source, optical coupling system, cooling system, and structural support and packaging components as the side-pump module 140, with the structure, parameters, and working principle of each component being completely identical.

[0047] The image transfer system 350 maintains collimation when the incident laser leaves the image transfer system 350, and is completely identical to the image transfer system 150 of the amplifier 100. The image transfer system 350 can be composed of two plano-convex lenses 352 and 356 with a focal length of 150 mm and a vacuum tube 354 in the middle. The plano-convex lenses can be made of BK7 glass. The first convex lens 352 can be configured with its convex surface facing the side pump module 340, and its distance from the center of the side pump module can be about 19 cm. The second convex lens 356 can be configured with its flat surface facing the side pump module 340. The distance between the two convex lenses can be set slightly shorter than twice the focal length of the lenses (e.g., shorter than 30 cm). The gas pressure inside the vacuum tube 354 between the two lenses can be <0.1 mbar. A biaxial adjustment aperture can be installed at the laser focal point. In some embodiments, the aperture can be a ceramic aperture with a diameter of 1.5 mm.

[0048] The linear polarization converter 360 can be a device with the same parameters as the vector polarization converter 330, forming a closed loop for polarization state conversion. The vector polarization converter 330 is used to convert S-polarized light into angular vector polarized light, while the linear polarization converter 360 is used to convert angular vector polarized light into S-polarized light. Similarly, the linear polarization converter 360 can also be a spatially anisotropic linear polarization state rotation element, capable of converting horizontal or vertical linearly polarized light into radial or angular vector polarized light, and vice versa. In some embodiments, the linear polarization converter 360 can also be a first-order liquid crystal polymer vortex waveplate. When the 0° fast axis of the first-order vortex waveplate is in the horizontal direction, it can convert P-polarized light into radial vector polarized light and S-polarized light into angular vector polarized light, or vice versa, that is, converting radial vector polarized light into P-polarized light and angular vector polarized light into S-polarized light. In some embodiments, the linear polarization converter 360 can also have a 1064nm antireflection coating deposited on both surfaces, with coating parameters completely consistent with those of the vector polarization converter 330. The linear polarization converter 360 can also achieve a transmittance of >99% at 1064nm, reducing energy loss. In some embodiments, the linear polarization converter 360 can also be a spatially graded waveplate formed by etching microstructures on glass, perfectly matching the microstructure design of the vector polarization converter 330. This precise microstructure design enables controllable polarization state conversion, ensuring the symmetry and high efficiency of polarization state conversion.

[0049] During the operation of amplifier 300, a vertically polarized (S-polarized) seed light with a polarization purity ≥99.5% and a spot diameter of 5.5 mm is first emitted by picosecond laser 310. Next, the seed light is incident on the S1 surface of reflector 320 at a set incident angle (e.g., 45°). Due to the high reflectivity of reflector 320 for S-polarized light, the seed light is efficiently reflected and its propagation direction is changed, while the collimation accuracy of the reflected beam remains unchanged. The reflected S-polarized light is then converted into angularly vector-polarized light by vector polarization converter 330, whose fast axis is horizontally positioned at 0°. The converted angularly vector-polarized light enters the side-pump module 340 and is amplified under stimulated emission from the Nd:YAG crystal rod, maintaining its angularly vector polarization state throughout the process. The amplified angularly vector-polarized light then enters the image transfer system 350, where it is focused by the first convex lens 352 and precisely passes through a biaxial adjustment aperture within the vacuum tube 354. Simultaneously, stray light (mainly parasitic light generated by multi-beam interference) from transmissive optical elements such as the lens surface and crystal rod end face is efficiently blocked by the aperture, ensuring beam purity. The seed light remains collimated as it leaves the image transfer system 350 and then passes through the linear polarization converter 360, where it is efficiently converted into S-polarized light, ultimately emitting amplified laser beam, thus completing the single-pass laser amplification process. In some embodiments, the vector polarization converter 330 and the linear polarization converter 360 can be rotated synchronously by 90 degrees, so that their 0° fast axis direction changes from parallel to the optical platform to perpendicular to the optical platform. This placement state allows the P-polarization state of the seed light to be converted into angular vector polarization, and the radial vector polarization to S-polarization. The polarization state change sequence of the seed light changes from the previous S-polarization-angular vector polarization-S-polarization to S-polarization-radial vector polarization-S-polarization. The amplification efficiency, beam quality and energy stability are basically the same under the two configurations. Those skilled in the art can flexibly choose according to the polarization state requirements in the actual application scenario.

[0050] Compared to dual-pass amplifiers, the single-pass architecture of Amplifier 300 offers significant cost advantages and structural simplification: by eliminating the rotator and zero-degree mirror, and simplifying the optical path adjustment process, it is more suitable for applications with strict limitations on equipment size and cost, and relatively mild output energy requirements. Furthermore, the single-pass architecture avoids the optical path interference risks caused by beam back-and-forth transmission, further improving operational stability.

[0051] Figure 4A schematic diagram of a laser amplifier 400 according to yet another exemplary embodiment of the present disclosure is shown. Compared to laser amplifier 300, laser amplifier 400 eliminates the reflector used to reflect the seed light, further reducing the complexity and cost of the system, while also reducing energy loss from a single beam reflection, making it more suitable for scenarios with extremely high requirements for device miniaturization and integration. The arrangement and parameters of the other components are consistent with those of laser amplifier 300 in the figure, specifically:

[0052] The laser amplifier 400 can be a vector-polarized single-pass amplifier, and may include: a picosecond laser 410, a vector polarization conversion device 420, a side-pumping module 430, an image transfer system 440, and a linear polarization conversion device 450. The picosecond laser 410 can be a picosecond laser with a repetition rate of 1 kHz, a single pulse energy of 0.44 mJ, a pulse width of approximately 60 ps, ​​and a center wavelength of 1064 nm. The spot diameter can be 5.5 mm, and its output spot also satisfies Gaussian distribution characteristics, ensuring that the seed light can be efficiently incident on subsequent devices.

[0053] The vector polarization converter 420 can be a spatially anisotropic linear polarization state rotation element. Its structure, parameters, and working principle are completely consistent with the vector polarization converter 330 of the amplifier 300. Based on the phase modulation of the polarization state of light, it achieves reversibility, capable of converting horizontally or vertically linearly polarized light into radially or angularly vector-polarized light, and vice versa. In some embodiments, the vector polarization converter 420 can be a first-order vortex waveplate, such as a first-order vortex waveplate of a liquid crystal polymer. When the 0° fast axis of the first-order vortex waveplate is in the horizontal direction, it can convert P-polarized light into radially vector-polarized light and S-polarized light into angularly vector-polarized light, or vice versa, that is, converting radially vector-polarized light into P-polarized light and angularly vector-polarized light into S-polarized light. In some embodiments, the vector polarization converter 420 can be coated with a 1064nm antireflection film on both surfaces, achieving a transmittance of >99% at 1064nm, ensuring efficient light energy transmission. In some implementations, the vector polarization conversion device 420 can be a spatially gradient waveplate formed by etching microstructures on glass, achieving controllable conversion of polarization states through precise microstructure design.

[0054] The side-pump module 430 can be an Nd:YAG side-pump module, with structural parameters completely identical to those of the side-pump module 340 of the amplifier 300, ensuring consistency and compatibility in amplification performance. The Nd:YAG side-pump module can use a cylindrical crystal rod, with both ends coated with a 1064nm anti-reflection film, achieving a transmittance greater than 99.5% to prevent optical oscillation interference caused by end-face reflection. The side-pump module 430 can be pumped from the side, enabling large-area contact between the pump light and the gain medium, improving pump uniformity and reducing thermal gradient generation. In some embodiments, the pump light wavelength of the side-pump module 430 can be 808 nm, matching the optimal absorption peak of Nd³⁺ ions, and the transmittance of the antireflection film can be greater than 99.5%. The crystal rod diameter of the side-pump module can be 7 mm, the doping concentration can be 0.6%, the pumping mode can be quasi-continuous pumping, pulsed pumping, or continuous pumping, the pump light pulse width can be 125 μs, and the repetition frequency can be 1 kHz, which is the same as the seed light, to achieve timing synchronization between the pump and the seed light. The pump light power can be approximately 950 W to provide sufficient amplification energy for the seed light. In addition to the crystal rod, the side-pump module 430 may also include the same semiconductor laser diode array pump source, optical coupling system, cooling system, and structural support and packaging components as the side-pump module 140, with the structure, parameters, and working principle of each component being completely identical.

[0055] The image transfer system 440 maintains collimation when the incident laser leaves the system, and its structural parameters are completely consistent with those of the image transfer system 350 of the amplifier 300. The image transfer system 440 can consist of two plano-convex lenses 442 and 446 and a vacuum tube 444 in the middle. The plano-convex lenses can be made of BK7 glass. The first convex lens 442 can be configured with its convex surface facing the side pump module 430, and its distance from the center of the side pump module can be approximately 19 cm to achieve efficient beam focusing. The second convex lens 446 can be configured with its flat surface facing the side pump module 430. The distance between the two convex lenses can be set slightly shorter than twice the lens focal length, for example, less than 30 cm. The specific distance can be fine-tuned according to the actual beam quality requirements. The vacuum tube 444 between the two lenses is used to prevent ionization of the laser at the focal point. The gas pressure inside the vacuum tube 444 can be less than 0.1 mbar. A small, dual-axis adjustable aperture can be installed at the laser focal point in the vacuum tube 444 to block stray light. In some implementations, the biaxial adjustment orifice inside the vacuum tube 444 can be a ceramic orifice with a diameter of 1.5 mm. The ceramic material is resistant to high temperatures and has a high laser damage threshold, which can prevent it from being burned by stray light.

[0056] The linear polarization converter 450 can be a device with the same parameters as the vector polarization converter 420, forming a closed loop for polarization state conversion. The vector polarization converter 420 converts S-polarized light into angular vector polarized light, while the linear polarization converter 450 converts angular vector polarized light into S-polarized light, ensuring complete restoration of the polarization state. Similarly, the linear polarization converter 450 can also be a spatially anisotropic linear polarization state rotation element, capable of converting horizontal or vertical linearly polarized light into radial or angular vector polarized light, and vice versa. In some embodiments, the linear polarization converter 450 can also be a first-order liquid crystal polymer vortex waveplate. When the 0° fast axis of the first-order vortex waveplate is in the horizontal direction, it can convert P-polarized light into radial vector polarized light and S-polarized light into angular vector polarized light, or vice versa, that is, converting radial vector polarized light into P-polarized light and angular vector polarized light into S-polarized light. In some embodiments, the linear polarization converter 450 may also have a 1064 nm antireflection coating deposited on both surfaces, with a transmittance of >99% at 1064 nm. In some embodiments, the linear polarization converter 450 may also be a spatially graded waveplate formed by etching microstructures on glass, perfectly matching the microstructure design of the vector polarization converter 420.

[0057] During the use of amplifier 400, a vertically polarized (S-polarized) seed light with a polarization purity ≥99.5% and a spot diameter of 5.5 mm is first emitted by picosecond laser 410. Next, the seed light is directly incident on a vector polarization converter 420 with its fast axis in the horizontal direction (without requiring a mirror to change direction). After passing through the converter, it is converted into angularly vector-polarized light. This process reduces energy loss from a single reflection, further improving the light energy utilization rate. The converted angularly vector-polarized light enters the side-pump module 430 for amplification, maintaining its angularly vector polarization state during this process. It then enters the image transfer system 440, where the seed light is focused by the first convex lens 442. The resulting focal point passes through a dual-axis adjustment aperture within the vacuum tube 444. Simultaneously, stray light from components such as lenses and crystal rod end faces is efficiently blocked by the aperture. When the seed light leaves the image transfer system 440, it remains collimated and then passes through the linear polarization converter 450, where it is converted from angularly vector polarized light to S-polarized light. Finally, the amplified laser light is emitted outward, thus completing the single-pass laser amplification process. In some embodiments, the vector polarization converter 420 and the linear polarization converter 450 can be rotated synchronously by 90 degrees, so that their 0° fast axis direction changes from parallel to the optical platform to perpendicular to the optical platform. This placement allows the P-polarization state of the seed light to be converted to angular vector polarization, while the radial vector polarization is converted to S-polarization. The polarization state change sequence of the seed light changes from the previous S-polarization-angular vector polarization-S-polarization to S-polarization-radial vector polarization-S-polarization. The amplification performance of the two configurations is basically the same, and those skilled in the art can flexibly adjust them according to the actual polarization state requirements.

[0058] Figure 5 A flowchart illustrating an exemplary method 500 according to an exemplary embodiment of the present disclosure is shown. The exemplary method 500 may use, for example... Figures 1-4 Performed by any of the laser amplifiers 100, 200, 300 or 400 shown.

[0059] See Figure 5 The exemplary method 500 may include: operation 510, converting linearly polarized light into light with a single vector polarization state; operation 520, amplifying the light with the single vector polarization state using a side pump module.

[0060] In some embodiments, the method may further include: reflecting light of a single vector polarization state amplified by the side-pumping module, and rotating the light of the single vector polarization state into light of different vector polarization states before it is reflected back to the side-pumping module; and amplifying the light of the different vector polarization states using the side-pumping module.

[0061] In some implementations, the method may further include converting light amplified by the side-pump module into linearly polarized light.

[0062] In the methods of this disclosure, although the operations are described in a specific order, this should not be construed as requiring such operations to be performed in the specific order or sequence shown, or requiring all of the shown operations to be performed to obtain the desired result. In some cases, multitasking and parallel processing can be advantageous. Similarly, although several specific implementation details are included in the foregoing discussion, these details should not be construed as limiting the scope of this disclosure, but rather as descriptions of features specific to particular embodiments. Certain features described in the context of a single embodiment may also be implemented in combination in a single embodiment. Conversely, various features described in the context of a single embodiment may also be implemented individually or in any suitable sub-combination in multiple embodiments.

[0063] The basic principles of this disclosure have been described above in conjunction with embodiments. However, it should be noted that the advantages, benefits, and effects mentioned in this disclosure are merely examples and not limitations, and should not be considered as essential features of each embodiment of this disclosure. Furthermore, the specific details disclosed above are for illustrative and facilitative purposes only, and are not limitations. These details do not limit the scope of this disclosure to the necessity of employing the aforementioned specific details for implementation.

[0064] The block diagrams of devices, apparatuses, devices, and systems disclosed herein are merely illustrative examples and are not intended to require or imply that they must be connected, arranged, or configured in the manner shown in the block diagrams. As those skilled in the art will recognize, these devices, apparatuses, devices, and systems can be connected, arranged, and configured in any manner. Words such as “comprising,” “including,” “having,” etc., are open-ended terms meaning “including but not limited to,” and are used interchangeably with them. The terms “or” and “and” as used herein refer to the terms “and / or,” and are used interchangeably with them unless the context clearly indicates otherwise. The term “such as” as used herein refers to the phrase “such as but not limited to,” and is used interchangeably with it.

[0065] Furthermore, in the apparatus, devices, and methods disclosed herein, the components or steps can be disassembled and / or recombined. Such disassembly and / or recombination should be considered equivalent solutions to this disclosure.

[0066] The above description of the disclosed aspects is provided to enable any person skilled in the art to make or use this disclosure. Various modifications to these aspects will be readily apparent to those skilled in the art, and the general principles defined herein may be applied to other aspects without departing from the scope of this disclosure. Therefore, this disclosure is not intended to be limited to the aspects shown herein, but rather to be carried out within the widest scope consistent with the principles and novel features disclosed herein.

[0067] The above description has been given for illustrative and descriptive purposes and is not intended to limit the embodiments of this disclosure to the forms disclosed herein. Although numerous exemplary aspects and embodiments have been discussed above, those skilled in the art will recognize certain variations, modifications, alterations, additions, and sub-combinations thereof.

[0068] Although the subject matter has been described in language specific to structural features and / or method actions, it should be understood that the subject matter defined in the appended claims is not limited to the specific features or actions described above. Rather, the specific features and actions described above are disclosed as examples of implementing the claims.

Claims

1. A laser amplifier, comprising: Vector polarization conversion devices are used to convert linearly polarized light into light with a single vector polarization state. as well as Side pump module, used to amplify the light entering the side pump module.

2. The laser amplifier as described in claim 1, wherein, The vector polarization conversion device is a first-order vortex waveplate; The vector polarization conversion device is coated with anti-reflection films on both sides; The light with a single vector polarization state includes radially vector polarized light or angularly vector polarized light.

3. The laser amplifier as described in claim 1, wherein, The side pump module includes a cylindrical crystal; The two ends of the cylindrical crystal are coated with antireflective films; The side pump module performs side pumping using a quasi-continuous mode, a pulse mode, or a continuous mode.

4. The laser amplifier as described in claim 1, further comprising: An image transfer system is used to collimate the light incident upon it. The image transmission system includes two convex lenses; The two surfaces of the convex lens are coated with anti-reflective coatings.

5. The laser amplifier as described in any one of claims 1-4, further comprising: A polarizing flat beam splitter is used to reflect light in the first linearly polarized state and allow light in the second linearly polarized state to pass through; Optical rotators are used to rotate the polarization angle of light. A zero-degree reflector is used to reflect light along its incident path.

6. The laser amplifier as described in claim 5, wherein, The polarizing flat beam splitter is made of fused silica; One side of the polarizing flat beam splitter is coated with a polarizing film, and the other side is coated with an anti-reflection film. Both sides of the optical rotator are coated with anti-reflective films; The zero-degree mirror is coated with a high-reflectivity film; The light in the first linearly polarized state is vertically polarized, and the light in the second linearly polarized state is horizontally polarized.

7. The laser amplifier as described in any one of claims 1-4, further comprising: A reflector is used to reflect light to the vector polarization conversion device; as well as Linear polarization conversion devices are used to convert light with a single vector polarization state into linearly polarized light.

8. The laser amplifier as claimed in claim 7, wherein, The linear polarization conversion device is a first-order vortex wave plate; The linear polarization conversion device is coated with antireflective films on both sides; The light with a single vector polarization state includes radially vector polarized light or angularly vector polarized light.

9. A laser amplification method, comprising: Convert linearly polarized light into light with a single vector polarization state; The light of the single vector polarization state is amplified using a side pump module.

10. The laser amplification method as described in claim 9, further comprising: The light amplified by the side pump module is reflected, and the light of the single vector polarization state is rotated into light of different vector polarization states before being reflected to the side pump module; The side pump module is used to amplify the light with different vector polarization states.

11. The laser amplification method as described in claim 9, further comprising: The light, which is amplified by the side pump module, is converted into linearly polarized light.

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