Digitally tunable off-axis pumped laser system

Abstract

The application belongs to the technical field of ultrafast optics and light field regulation, and provides a digital adjustable off-axis pumping laser system, which comprises a digital off-axis pumping module with sequentially connected pumping source, collimating lens, spatial light modulator and first focusing lens, astigmatic resonant cavity with sequentially connected input coupling mirror, gain medium, concave mirror and output coupling mirror, and mode conversion module with sequentially connected plane mirror, dove prism, second focusing lens and cylindrical lens pair. The application realizes order of magnitude improvement in the regulation accuracy of off-axis pumping by integrating the spatial light modulator to digitally modulate the pumping light in the off-axis pumping laser system. Meanwhile, through programmable control of the spatial light modulator, combined with efficient excitation of two-dimensional high-order Hermite-Gaussian mode by the astigmatic resonant cavity and the astigmatic transformation function of the mode conversion module, high-order structured light beams covering the entire Hermite-Laguerre-Gaussian mode space can be conveniently generated.

Description

Technical Field

[0001] This application belongs to the field of ultrafast optics and light field manipulation technology, specifically, it relates to a digitally tunable off-axis pumped laser system. Background Technology

[0002] High-order structured beams, due to their unique amplitude, phase, and polarization distributions, have shown great application potential in cutting-edge fields such as optical communication, optical micromanipulation, high-resolution imaging, and laser precision machining. Among the many structured beams, the Hermit-Gaussian (HG) mode, the Laguerre-Gaussian (LG) mode, and the Hermit-Laguerre-Gaussian (HLG) mode, as its more general form, provide the foundation for constructing and manipulating complex optical fields.

[0003] Currently, the main technical approaches for generating such high-order mode beams are the external cavity conversion method and the direct intracavity generation method. The external cavity conversion method typically uses spatial light modulators, special phase plates, and other diffraction elements to modulate the fundamental Gaussian beam. This method suffers from problems such as complex optical paths, high alignment accuracy requirements, limited conversion efficiency, and low damage threshold of optical elements, making it difficult to meet the application requirements of high power and high beam quality. In contrast, directly generating high-order modes within the laser resonator is considered a more efficient approach. Common techniques involve precisely designing asymmetric astigmatic resonators to disrupt intracavity symmetry and directly output HG mode beams. However, these methods usually have fixed structures; once the design is complete, the output mode type and order are difficult to adjust, lacking flexibility and tunability.

[0004] Off-axis pumping is another effective technique for exciting higher-order mode beams within a cavity. By adjusting the relative position of the pump spot and the cavity's fundamental mode, it allows for effective selection of the output mode. However, traditional off-axis pumping techniques heavily rely on precise manual mechanical translation or tilting of optical components such as mirrors and lenses. This adjustment method is not only cumbersome and time-consuming, but also suffers from poor repeatability and instability, and cannot achieve rapid, dynamic mode switching, thus limiting its development in applications requiring digital control. Consequently, the field currently lacks a laser system that can combine programmable digital pump control with efficient and stable direct generation of higher-order mode beams, failing to meet the application requirements for dynamic and precise control of higher-order structure beams. Summary of the Invention

[0005] To address the limitations of existing high-order mode structured beam laser systems, which are either constrained by low power and low efficiency due to external cavity conversion or by the limited range of modes generated within the cavity and the inconvenience of adjustment, this application provides a digitally tunable off-axis pumped laser system.

[0006] In one embodiment, a digitally tunable off-axis pumped laser system includes a digital off-axis pumping module, an astigmatic resonator, and a mode conversion module.

[0007] The digital off-axis pumping module includes a pump source, a collimating lens, a spatial light modulator, and a first focusing lens connected in sequence.

[0008] The image resonant cavity includes an input coupling mirror, a gain medium, a concave reflector, and an output coupling mirror connected in sequence, and the input end of the input coupling mirror is connected to the output end of the first focusing lens;

[0009] The mode conversion module includes a plane mirror, a Dowell prism, a second focusing lens, and a pair of cylindrical lenses connected in sequence, and the input end of the plane mirror is connected to the output end of the output coupling mirror.

[0010] The digital off-axis pumping module digitally controls the pump light through a spatial light modulator; the astigmatic resonator converts the modulated pump light into a two-dimensional high-order Hermitian-Gaussian mode laser; and the mode conversion module performs astigmatic transformation on the two-dimensional high-order Hermitian-Gaussian mode laser to output a Hermitian-Laguerre-Gaussian mode laser.

[0011] In one scheme, the first focusing lens focuses the fundamental Gaussian beam onto the input coupling mirror;

[0012] The fundamental Gaussian beam is then amplified by a gain medium, causing the focused fundamental Gaussian beam to shift laterally. This shift makes the pump region of the fundamental Gaussian beam match the spatial distribution of the two-dimensional higher-order Hermit-Gaussian mode.

[0013] After gaining, the output beam is directed to the concave mirror, which then reflects the beam through a 20° angle to the output coupling mirror. After a round trip, the beam outputs a two-dimensional high-order Hermit-Gaussian mode laser.

[0014] In one design, the radius of curvature of the concave mirror is 200 mm;

[0015] The distance between the gain medium and the concave mirror is 130mm, and the distance between the concave mirror and the output coupling mirror is 170mm.

[0016] In one scheme, the focused spot radius of the digital off-axis pump module is greater than 100μm and less than 135μm, thereby ensuring the energy absorption efficiency in the gain medium and supporting the generation of tunable higher-order modes.

[0017] In one scheme, the pump source outputs a fundamental mode Gaussian beam, which is collimated by a collimating lens, then reflected and modulated by a spatial light modulator to output the fundamental mode Gaussian beam, and finally focused at a first focusing lens.

[0018] The focal length of the collimating lens does not exceed 30mm, and the focal length of the first focusing lens does not exceed 50mm.

[0019] In one scheme, the focal length of the collimating lens is 25mm and the focal length of the first focusing lens is 50mm, resulting in a pump light focused spot with a radius of 120μm.

[0020] In one scheme, the gain medium is an Nd:YVO4 crystal cut on the a-plane with a cross-section of 5mm × 5mm and a length of 8mm, and a doping concentration of 0.5-at.%.

[0021] In one scheme, the second focusing lens acts as a relay lens to perform waist matching on the cylindrical lens pair;

[0022] The focal length of the second focusing lens is 100mm.

[0023] In one design, the output coupler is a planar output coupler with a reflectivity of 95%.

[0024] In one scheme, the pump source is an 808nm multimode fiber pump source with a numerical aperture of 0.22.

[0025] The beneficial effects of this application are:

[0026] This application integrates a spatial light modulator into an off-axis pumped laser system to digitally modulate the pump light, replacing the traditional method of mechanically adjusting mirrors and lenses. This fundamentally eliminates adjustment errors caused by mechanically moving parts, resulting in an order-of-magnitude improvement in the control precision of off-axis pumping. Furthermore, digital control eliminates the need for manual operation, and the adjustment response speed is far faster than the time-consuming traditional mechanical adjustment, significantly improving the efficiency of mode switching and parameter optimization. Simultaneously, through the programmable control of the spatial light modulator, combined with the efficient excitation of two-dimensional high-order Hermitian-Gaussian modes by an astigmatic resonator, and the astigmatic transformation function of the mode conversion module, high-order structured beams covering the entire Hermitian-Laguerre-Gaussian mode space can be easily generated. Attached Figure Description

[0027] To more clearly illustrate the technical solutions in the embodiments of this application, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0028] Figure 1 This is a schematic diagram of a digitally adjustable off-axis pumped laser system according to one embodiment of this application;

[0029] Labels for each item in the figure:

[0030] 1. Digital off-axis pump module; 101. Pump source; 102. Collimating lens; 103. Spatial light modulator; 104. First focusing lens;

[0031] 2. Astigmatic resonant cavity; 201. Input coupling mirror; 202. Gain medium; 203. Concave reflector; 204. Output coupling mirror;

[0032] 3. Mode conversion module; 301. Plane mirror; 302. Dowell prism; 303. Second focusing lens; 304. Cylindrical lens pair. Detailed Implementation

[0033] The specific embodiments of this application will be further described in detail below with reference to the accompanying drawings and examples. The following examples are used to illustrate this application, but are not intended to limit the scope of this application. Similarly, the following examples are only some embodiments of this application, not all embodiments. All other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0034] In the description of this application, it should be understood that the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", "clockwise", "counterclockwise", "axial", "radial", "circumferential", etc., indicating the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of this application.

[0035] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this application, "multiple" means at least two, such as two, three, etc., unless otherwise explicitly specified.

[0036] In this application, unless otherwise expressly specified and limited, the terms "installation," "connection," "linking," and "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection, an electrical connection, or a connection that allows communication between components; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components, unless otherwise expressly limited. Those skilled in the art can understand the specific meaning of the above terms in this application based on the specific circumstances.

[0037] In this application, the terms "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., refer to a specific feature, structure, material, or characteristic described in connection with that embodiment or example, which is included in at least one embodiment or example of this application. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0038] To address the limitations of existing high-order mode structured beam laser systems, which are either constrained by low power and efficiency due to external cavity conversion, or by the limited range of modes generated within the cavity and the inconvenience of adjustment, this application provides a digitally tunable off-axis pumped laser system, with specific embodiments as follows:

[0039] In one embodiment, please refer to Figure 1 A digitally tunable off-axis pumped laser system includes a digital off-axis pumping module 1, an astigmatic resonator 2, and a mode conversion module 3.

[0040] In this embodiment, the digital off-axis pumping module 1 includes a pump source 101, a collimating lens 102, a spatial light modulator 103, and a first focusing lens 104 connected in sequence. The pump light is then digitally controlled by the spatial light modulator 103. The pump source 101 outputs a fundamental Gaussian beam; the collimating lens 102 collimates the beam, precisely controlling the size of the focused spot after focusing by the first focusing lens 104, providing a favorable foundation for subsequent off-axis accuracy and pump light beam quality; the first focusing lens 104 is used to converge parallel light into a high-power-density focal point. In other words, the digital off-axis pumping module 1 is based on off-axis pumping. The spatial light modulator 103 can digitally and precisely control the off-axis amount. The output fundamental Gaussian beam is diverged into parallel Gaussian light by the collimating lens 102, and then reflected by the spatial light modulator 103 to the first focusing lens 104 for focused output.

[0041] The spatial light modulator 103 is an optical device capable of spatially distributing and modulating the amplitude, phase, polarization, or intensity of light waves. It controls the characteristics of light pixel-by-pixel, converting the input light field into a preset distribution pattern. In use, the operator receives digital commands via a computer or control module. Each optical pixel synchronously adjusts its physical state according to the commands. When the incident light beam passes through these pixels, it is modulated into the preset shape, ultimately outputting the target light beam. This covers the core requirements of laser applications, such as phase modulation, amplitude modulation, and mode conversion. For example, if the system power is less than 100W, a reflective liquid crystal spatial light modulator 103 can be selected; if the system power is greater than 100W, a microelectromechanical system (MEMS) spatial light modulator 103 can be selected.

[0042] In this embodiment, the astigmatic resonant cavity 2 includes an input coupling mirror 201, a gain medium 202, a concave reflector 203, and an output coupling mirror 204 connected in sequence. The input end of the input coupling mirror 201 is connected to the output end of the first focusing lens 104. The astigmatic resonant cavity 2 can convert the modulated pump light into a two-dimensional higher-order Hermitian-Gaussian mode laser. Since resonant cavities often have cylindrical symmetry, even if the pump light deviates from the axis of the resonant cavity in both directions, the system will operate in a tilted one-dimensional Hermitian-Gaussian mode and cannot excite a two-dimensional Hermitian-Gaussian mode. Therefore, by constructing a resonant cavity using the input coupling mirror 201, the concave reflector 203, and the output coupling mirror 204, the different effective focal lengths of the concave reflector 203 in the meridional and sagittal planes can be utilized to introduce astigmatism, which limits the symmetry and intrinsic modes of the resonant cavity, thereby disrupting the cylindrical symmetry of the resonant cavity and generating a higher-order two-dimensional Hermitian-Gaussian mode.

[0043] The first focusing lens 104 focuses the fundamental mode Gaussian beam onto the gain medium 202 via the input coupling mirror 201. The pump spot after focusing is laterally shifted within the gain medium 202. This shift allows the pump region to achieve the best match with the spatial distribution of a specific two-dimensional higher-order Hermit-Gaussian mode, resulting in mode-selective gain. The gained beam is output to the concave mirror 203, and then reflected by the concave mirror 203 to the output coupling mirror 204, ultimately causing the two-dimensional higher-order Hermit-Gaussian mode laser to be output from the output coupling mirror 204.

[0044] In this embodiment, the mode conversion module 3 includes a plane mirror 301, a Dowell prism 302, a second focusing lens 303, and a cylindrical lens pair 304 connected in sequence. The input end of the plane mirror 301 is connected to the output end of the output coupling mirror 204. The mode conversion module 3 is used to perform astigmatism transformation on the two-dimensional higher-order Hermitian-Gaussian mode laser to output a Hermitian-Laguerre-Gaussian mode laser. After the two-dimensional higher-order Hermitian-Gaussian mode laser is output from the output coupling mirror 204 to the plane mirror 301, it is reflected by the plane mirror 301 to the Dowell prism 302. The Dowell prism 302 acts as a λ / 2 astigmatism delayer to generate a π phase delay for the laser. The beam is then output from the Dowell prism 302 to the second focusing lens 303 so that the beam waist matches the cylindrical lens pair 304. The cylindrical lens pair 304 acts as a λ / 4 astigmatism delayer to generate a π / 2 phase delay for the laser. Finally, the arbitrary Hermitian-Laguerre-Gaussian mode beam is output through the cylindrical lens pair 304.

[0045] In this system, the Dowell prism 302 acts as a λ / 2 astigmatic delayer. Its core function is to rotate the spatial orientation of the Hermit-Gaussian mode field, that is, to change its azimuth angle on the SU(2) mode sphere. Specifically, when the Dowell prism is rotated around the optical axis, the input mode distribution will undergo a rotation transformation with an angle twice that of the prism rotation angle.

[0046] In addition, the cylindrical lens pair 304 consists of two cylindrical lenses with mutually perpendicular refractive directions, serving as a λ / 4 delay in the astigmatic mode conversion system. During the conversion process, the Hermitian-Gaussian mode input to the Dowell prism 302 is first rotated in the coordinate system through the Dowell prism 302 to adjust the azimuth angle of the mode; subsequently, the beam enters the cylindrical lens pair 304, which introduces astigmatic delay to control the elliptic parameters of the mode. Through the coordinated arrangement and parameter adjustment of the Dowell prism 302 and the cylindrical lens pair 304, astigmatic mode conversion can be achieved, mapping the Hermitian-Gaussian mode onto any Hermitian-Laguerre-Gaussian mode beam on the SU(2) mode sphere, thereby covering the entire spatial spectrum. This process is based on the SU(2) group structure principle, rather than a simple focusing force balance, ensuring high modal purity and tunability.

[0047] Specifically, when digital control of the pump light is required, MATLAB and Python are used on a computer. The software or dedicated control module inputs parameters such as the target off-axis amount, spot size, and mode order; the control software converts the target mode parameters into pixel-level instructions that the spatial light modulator 103 can recognize. After receiving the instructions, each pixel adjusts its own state according to the preset electro-optic / electro-mechanical response mechanism to form a spatial modulation distribution that matches the target mode; after the pump light is modulated by the spatial light modulator 103, its spatial distribution is etched into the beam; the modulated pump light is focused by the first focusing lens 104 onto the off-axis region of the gain medium 202, so that the population inversion density of this region is higher than that of the central region, and preferentially excites the higher-order mode that matches the pump distribution; the astigmatic resonator 2 amplifies the excited two-dimensional higher-order Hermitian-Gaussian mode; then the mode conversion module 3 performs a unitary transformation on the two-dimensional higher-order Hermitian-Gaussian mode, converting the input Hermitian-Gaussian mode into an arbitrary Hermitian-Laguerre-Gaussian mode beam on its corresponding SU(2) mode sphere, and finally outputs a stable target beam.

[0048] Therefore, this application integrates a spatial light modulator 103 into the off-axis pumped laser system to digitally modulate the pump light, replacing the traditional method of mechanically adjusting the reflector and lens. This fundamentally eliminates the adjustment errors caused by mechanically moving parts, resulting in an order-of-magnitude improvement in the control precision of off-axis pumping. Furthermore, digital control eliminates the need for manual operation, and the adjustment response speed is much faster than the time-consuming traditional mechanical adjustment, significantly improving the efficiency of mode switching and parameter optimization. Moreover, by eliminating mechanically moving parts, adjustment deviations caused by mechanical wear, vibration, and temperature drift are avoided, significantly improving the long-term stability of the system. The digital modulation commands can be accurately reproduced, ensuring the consistency of the output mode under different times and operating conditions.

[0049] Meanwhile, this application, through the programmable control of the spatial light modulator 103, combined with the efficient excitation of two-dimensional high-order Hermitian-Gaussian modes by the astigmatic resonator 2 and the astigmatic transformation function of the mode conversion module 3, can conveniently generate high-order structured beams covering the entire Hermitian-Laguerre-Gaussian mode space. Compared with traditional fixed intracavity structures or external cavity conversion methods, this system can dynamically switch mode types and orders by modifying digital modulation instructions, greatly expanding the flexibility of mode control and meeting the needs of diverse application scenarios for different high-order modes. That is, this application adopts a technical path combining direct intracavity excitation and mode conversion, avoiding the energy loss and beam quality degradation problems caused by multi-optical-path coupling in external cavity conversion methods. The precise modulation of the pump light by the spatial light modulator 103 can ensure its efficient matching with the resonator, improve energy conversion efficiency, and the final output high-order structured beam has high beam quality, which can meet the application requirements of high-power, high-quality high-order beams.

[0050] In one embodiment, based on the aforementioned embodiment, the first focusing lens 104 focuses the fundamental mode Gaussian beam onto the input coupling mirror 201; then the fundamental mode Gaussian beam is amplified by the gain medium 202, and the beam is output to the concave reflector 203 after amplification by the gain medium 202. The radius of curvature of the concave reflector 203 is 200 mm, and the distance between the input coupling mirror 201 and the concave reflector 203 is 130 mm. The concave reflector 203 outputs the beam to the output coupling mirror 204 at a distance of 170 mm through a reflection angle of 20°. After the beam goes round trip, a two-dimensional high-order Hermit-Gaussian mode laser is output.

[0051] In this embodiment, the layout logic of the resonant cavity structure, consisting of the input coupling mirror 201, the concave reflector 203, and the output coupling mirror 204, is based on obtaining the π-order astigmatic transformation. The π-order astigmatic transformation refers to introducing optical elements within the cavity to accumulate a π-order astigmatic phase delay in the beam along two orthogonal directions, thereby breaking the rotational symmetry of intracavity diffraction. The gain positions of some one-dimensional 45° Hermitian-Gaussian modes are the same as those of some two-dimensional Hermitian-Gaussian modes. However, the energy distribution of the one-dimensional Hermitian-Gaussian modes distributed along the 45° direction is more concentrated, resulting in higher overlap efficiency with the pump light, making it easier to obtain gain and preferentially oscillate, thus suppressing the two-dimensional Hermitian-Gaussian modes. By introducing π astigmatic transformation, the phase of the one-dimensional Hermit-Gaussian mode in the 45° direction is reversed when it propagates in the resonant cavity, causing its energy distribution in the gain medium 202 to shift from the overlapping region of the pump light, resulting in a decrease in gain. The two-dimensional Hermit-Gaussian mode has axial similarity, which means that its spatial wave function can be accurately "self-reproduced" when the mode passes through the gain medium in each oscillation cycle, similar to the transmission of a linear polarization state along the birefringence axis. Therefore, the pump overlap integral of the target mode remains consistent in each cycle, the net modal gain is stable, it is not easily affected by competing modes, and the gain can be stably obtained and output in the resonant cavity.

[0052] Furthermore, the focused spot radius of the digital off-axis pump module 1 is greater than 100μm and less than 135μm.

[0053] In this embodiment, the radius of the laser fundamental mode is approximately 135 μm after calculation using the ABCD matrix of the astigmatic resonator 2 structure. To optimize the energy absorption efficiency within the gain medium 202 and support the generation of tunable higher-order modes, the pump spot size is limited based on the size of the laser fundamental mode, ensuring good overlap with the intensity peak of the target higher-order mode at the off-axis position. Simultaneously, the pump spot size must match the absorption region of the gain medium 202. If the pump spot is too large, the gain distribution tends to be uniform, and the Gaussian light of the fundamental mode can still obtain sufficient gain, making it difficult to form effective mode selection; if it is too small, the gain region may be too limited, leading to a reduction in output power.

[0054] In one embodiment, the pump source 101 outputs a fundamental Gaussian beam, which is collimated by a collimating lens 102, then reflected and modulated by a spatial light modulator 103, and finally focused at a first focusing lens 104. The collimating lens 102 has a focal length not exceeding 30 mm, and the first focusing lens 104 has a focal length not exceeding 50 mm.

[0055] Preferably, the focal length of the collimating lens 102 is set to 25mm, and the focal length of the first focusing lens 104 is set to 50mm. Using these parameter values ​​for the focal lengths of the collimating lens 102 and the first focusing lens 104, the pump light can be focused onto the crystal with a spot radius of 120μm, meeting the energy absorption efficiency requirements within the gain medium 202, and supporting selective excitation of specific higher-order modes.

[0056] Furthermore, the gain medium 202 is an Nd:YVO4 crystal cut from the a-plane, with a cross-section of 5mm×5mm, a length of 8mm, and a doping concentration of 0.5-at.%.

[0057] In this embodiment, Nd:YVO4, or neodymium-doped yttrium vanadate, is a mature laser gain medium 202. The doped Nd³⁺ ions have a strong absorption peak in the 808nm band, resulting in high energy conversion efficiency. The crystal is cut along the a-axis, giving its output laser a natural linear polarization characteristic. Since Hermite-Gaussian modes are mostly linearly polarized, the a-plane cutting can reduce mode loss caused by polarization mismatch. The 5mm×5mm cross-section provides sufficient pump light absorption area, and the 8mm length ratio balances gain length and thermal management. The 0.5-at.% atomic percentage represents low to medium doping, ensuring sufficient absorption of the 808nm pump light while avoiding fluorescence quenching caused by high concentration.

[0058] In one embodiment, the second focusing lens 303 acts as a relay lens to perform waist matching with the cylindrical lens pair 304. The focal length of the second focusing lens 303 can be 100mm. The 100mm focal length of the second focusing lens 303 can focus the beam emitted from the Dove prism 302 to a suitable beam waist, while ensuring that the beam propagation direction in the cylindrical lens pair 304 is parallel to the optical axis, reducing astigmatic distortion deviations.

[0059] In one embodiment, the output coupling mirror 204 is a planar output coupling mirror with a reflectivity of 95%, meaning that only 5% of the optical energy is output from the cavity, with 95% of the energy being reflected back into the cavity to continue participating in oscillation. The high reflectivity of 95% causes the optical field inside the cavity to be amplified multiple times through the gain medium 202, ensuring that the energy of the higher-order Hermitian-Gaussian modes is high enough to overcome mode loss. At the same time, the planar characteristics avoid wavefront distortion, ensuring the beam quality of the output Hermitian-Gaussian mode.

[0060] In one embodiment, the pump source 101 is an 808nm multimode fiber pump source 101 with a numerical aperture of 0.22. The multimode fiber allows the pump light to be transmitted in multiple modes, resulting in an output beam with low coherence and a wide spatial distribution, making it easier for the spatial light modulator 103 to digitally shape it. The 808nm wavelength precisely matches the absorption peak of Nd³⁺ ions in the Nd:YVO₄ crystal, maximizing the conversion of pump light energy into crystal gain and reducing energy waste. The numerical aperture of 0.22 corresponds to a half-divergence angle of approximately 12.7°, which is considered moderate divergence, avoiding both excessive concentration of the pump light due to small divergence angles and excessive beam divergence due to large divergence angles.

[0061] The above are merely optional embodiments of this application and are not intended to limit this application. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A digitally adjustable off-axis pumped laser system, characterized in that, Includes a digital off-axis pump module, an astigmatic resonator, and a mode conversion module; The digital off-axis pumping module includes a pump source, a collimating lens, a spatial light modulator, and a first focusing lens connected in sequence. The astigmatic resonant cavity includes an input coupling mirror, a gain medium, a concave reflector, and an output coupling mirror connected in sequence, and the input end of the input coupling mirror is connected to the output end of the first focusing lens; The mode conversion module includes a plane mirror, a Dowell prism, a second focusing lens, and a pair of cylindrical lenses connected in sequence, and the input end of the plane mirror is connected to the output end of the output coupling mirror. The digital off-axis pumping module controls the off-axis amount of the pump light digitally through the spatial light modulator; the astigmatic resonator converts the modulated pump light into a two-dimensional high-order Hermitian-Gaussian mode laser; the mode conversion module performs astigmatic transformation on the two-dimensional high-order Hermitian-Gaussian mode laser and outputs a Hermitian-Laguerre-Gaussian mode laser. The focal spot radius of the focused light by the digital off-axis pumping module is greater than 100μm and less than 135μm; the focal length of the collimating lens is no more than 30mm, the focal length of the first focusing lens is no more than 50mm, and the focal length of the second focusing lens is 100mm. When the spatial light modulator is in use, the operator inputs digital commands for the target off-axis amount, spot size, and mode order through a computer or control module. Each optical pixel in the spatial light modulator synchronously adjusts its physical state according to the commands to form a spatial modulation distribution that matches the target mode. Phase modulation is used to digitally shift the pump light in the gain medium, and amplitude modulation is used to excite a high-order two-dimensional Hermit-Gaussian mode.

2. The digitally adjustable off-axis pumped laser system according to claim 1, characterized in that, The first focusing lens focuses the fundamental Gaussian beam onto the input coupling mirror; The fundamental Gaussian beam is then amplified by the gain medium, causing a lateral shift in the focused fundamental Gaussian beam. This shift makes the pump region of the fundamental Gaussian beam match the spatial distribution of the two-dimensional higher-order Hermit-Gaussian mode. After gaining, the output beam is directed to the concave mirror, and the concave mirror outputs the beam to the output coupling mirror after a 20° reflection angle; after a round trip of the beam cycle, a two-dimensional high-order Hermit-Gaussian mode laser is output.

3. The digitally adjustable off-axis pumped laser system according to claim 2, characterized in that, The radius of curvature of the concave mirror is 200 mm; The distance between the gain medium and the concave mirror is 130 mm, and the distance between the concave mirror and the output coupling mirror is 170 mm.

4. The digitally adjustable off-axis pumped laser system according to claim 3, characterized in that, The pump source outputs a fundamental Gaussian beam, which is collimated by the collimating lens, then reflected and modulated by the spatial light modulator, and finally focused at the first focusing lens.

5. The digitally adjustable off-axis pumped laser system according to claim 4, characterized in that, The collimating lens has a focal length of 25mm, and the first focusing lens has a focal length of 50mm.

6. The digitally tunable off-axis pumped laser system according to claim 4 or 5, characterized in that, The gain medium is an Nd:YVO4 crystal cut on the a-plane, with a cross-section of 5mm × 5mm and a length of 8mm, and a doping concentration of 0.5-at.%.

7. The digitally adjustable off-axis pumped laser system according to claim 6, characterized in that, The second focusing lens acts as a relay lens to perform waist matching on the cylindrical lens pair.

8. The digitally adjustable off-axis pumped laser system according to claim 7, characterized in that, The output coupling mirror is a planar output coupling mirror with a reflectivity of 95%.

9. The digitally adjustable off-axis pumped laser system according to claim 8, characterized in that, The pump source is an 808nm multimode fiber pump source with a numerical aperture of 0.22.

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