308nm all-solid-state ultraviolet laser based on stimulated raman scattering

Abstract

The application discloses a 308nm all-solid-state ultraviolet laser based on stimulated Raman scattering and belongs to the technical field of lasers. The 308nm all-solid-state ultraviolet laser based on stimulated Raman scattering comprises a pump source system for generating 1123nm pump laser; a Raman laser generating system for generating 1232nm Stokes light through stimulated Raman scattering; a wavelength conversion system for converting into 616nm visible light through second harmonic generation; and an ultraviolet laser generating system for converting into 308nm ultraviolet laser through second harmonic generation. The 308nm all-solid-state ultraviolet laser based on stimulated Raman scattering adopts a phosphorus-doped optical fiber as a Raman gain medium, utilizes the large Raman shift characteristic of the phosphorus-doped optical fiber, realizes single-stage stimulated Raman scattering wavelength conversion, simplifies the system structure and improves the conversion efficiency; through two-stage nonlinear frequency conversion, low-repetition-frequency, high-single-pulse-energy ns-level 308nm ultraviolet pulse laser output is obtained, so that the requirement of application fields such as clinical treatment can be met.

Description

Technical Field

[0001] This application belongs to the field of laser technology, and specifically relates to a 308nm all-solid-state ultraviolet laser based on stimulated Raman scattering. Background Technology

[0002] Ultraviolet (UV) lasers play a crucial role in biomedical instruments, semiconductor testing, integrated circuit manufacturing, and disease diagnosis and treatment. Particularly in bioanalysis and clinical treatment, UV light's strong penetrating power and scattering characteristics allow it to penetrate deep into biological tissues and interact with tissue components, thereby enabling disease diagnosis and treatment. For example, 308nm UV lasers can treat skin diseases by inhibiting sebaceous gland secretion, killing Propionibacterium acnes, and promoting skin cell regeneration. Furthermore, 308nm UV laser ablation is playing an increasingly important role in the clinical treatment of cardiovascular diseases such as coronary atherosclerosis and arterial embolism. Therefore, obtaining a highly efficient, stable, and easy-to-maintain 308nm UV laser is of significant research and application value.

[0003] Currently, the main methods for obtaining 308nm ultraviolet lasers include the following: First, excimer lasers, which use xenon chloride gas as the working medium and release high-energy ultraviolet lasers under electrical or optical excitation. However, they suffer from drawbacks such as large size, unstable power, long preheating time before use, complex maintenance, and high operating costs. Second, all-solid-state lasers based on fiber laser pumps, which use single-frequency 1030nm and 1535nm seed light, amplified through multiple stages, and then obtain 308nm laser output through frequency doubling and summing. Although they achieve an all-solid-state structure, their single-pulse energy is limited by the nonlinear effects in the fiber, and can only be maintained at tens of μJ, making it difficult to achieve high-energy nanosecond pulse outputs of tens of mJ or more. Third, semiconductor lasers based on AlGaN materials, whose output wavelength can be extended to 308nm, but currently the output power is only about 10 milliwatts, which is insufficient to meet the needs of clinical treatment.

[0004] Therefore, overcoming the shortcomings of the existing technologies, such as large size, complex maintenance, low single-pulse energy, or insufficient output power, is an urgent problem to be solved in this technical field. Summary of the Invention

[0005] To address the aforementioned problems, this application provides a 308nm all-solid-state ultraviolet laser based on stimulated Raman scattering, comprising: Pump source system for generating 1123nm pump laser; The Raman laser generation system includes a high-reflectivity fiber Bragg grating, a Raman gain fiber, and an output coupling fiber Bragg grating. The 1123nm pump laser output from the pump source system is injected into the Raman gain fiber through the high-reflectivity fiber Bragg grating, and 1232nm Stokes light is generated through stimulated Raman scattering, and then output through the output coupling fiber Bragg grating. A wavelength conversion system includes a first nonlinear medium for receiving 1232nm Stokes light and converting it into 616nm visible light through second harmonic generation. An ultraviolet laser generation system includes a second nonlinear medium for receiving 616nm visible light and converting it into 308nm ultraviolet laser light through second harmonic generation.

[0006] Furthermore, the Raman gain fiber is a phosphorus-doped fiber.

[0007] Furthermore, the phosphorus pentoxide doping concentration in the Raman gain fiber is 1~50 mol%, the refractive index difference between the cladding and the core of the Raman gain fiber is 0.005~0.050, the length is 1~1000 m, and the loss at 1232 nm is 0.1~10 dB / km.

[0008] Furthermore, the high-reflectivity fiber Bragg grating has a reflectivity of over 90% for 1232nm laser; the output-coupled fiber Bragg grating has a transmittance of 5% to 50% for 1232nm laser.

[0009] Furthermore, the pump source system includes an infrared pulsed laser and a focusing coupling module, wherein the infrared pulsed laser is used to generate an 1123nm pump laser. The focusing coupling module is located between the infrared pulsed laser and the Raman laser generation system. The focusing coupling module is used to couple the 1123nm pump laser into the Raman laser generation system.

[0010] Furthermore, the infrared pulsed laser uses an Nd:YAG laser or an Nd:LuYAG laser, with a repetition frequency of 1~100 Hz, a single pulse energy of 1~10000 mJ, and a pulse width of 1~500 ns.

[0011] Furthermore, the wavelength conversion system also includes an isolator, a λ / 2 waveplate, and a first focusing lens. The isolator is disposed between the Raman laser generation system and the first nonlinear medium to prevent the subsequent reflected light from returning to the Raman laser generation system. A λ / 2 waveplate is placed between the isolator and the first nonlinear medium to adjust the polarization direction of the 1123nm pump laser to match the phase matching condition of the first nonlinear medium. The first focusing lens is positioned between the λ / 2 waveplate and the first nonlinear medium.

[0012] Furthermore, the wavelength conversion system also includes a collimating lens and a first reflecting mirror. The collimating lens is disposed between the first nonlinear medium and the second nonlinear medium and is used to collimate the 616nm visible light output from the first nonlinear medium. The first reflector is disposed between the first nonlinear medium and the second nonlinear medium, and is used to guide 616nm visible light to the second nonlinear medium.

[0013] Furthermore, the ultraviolet laser generation system also includes a second reflecting mirror and a second focusing lens. The second reflecting mirror is disposed between the wavelength conversion system and the second nonlinear medium and is used to guide 616nm visible light to the second nonlinear medium. The second focusing lens is disposed between the second reflecting mirror and the second nonlinear medium, and is used to focus 616nm visible light into the second nonlinear medium.

[0014] Furthermore, the ultraviolet laser generation system also includes a filter for receiving 308nm ultraviolet laser light, the filter having a transmittance of more than 95% for 308nm ultraviolet laser light and a reflectance of more than 90% for 616nm visible light.

[0015] Furthermore, the first nonlinear medium is a lithium triborate crystal, a barium metaborate crystal, a potassium titanate phosphate crystal, a periodically polarized lithium niobate crystal, a periodically polarized potassium titanate phosphate crystal, or a periodically polarized lithium tantalate crystal. The second nonlinear medium is barium metaborate crystal, lithium cesium hexaborate crystal, or potassium fluoroborate-beryllium crystal.

[0016] Compared with the prior art, this application has the following advantages: This invention proposes a 308nm all-solid-state ultraviolet laser based on stimulated Raman scattering. Employing an all-solid-state structure, it overcomes the drawbacks of traditional excimer lasers, such as large size, long preheating time, complex maintenance, and high operating costs. Furthermore, by using phosphorus-doped fiber as the Raman gain medium and leveraging its large Raman frequency shift characteristics, single-stage stimulated Raman scattering wavelength conversion is achieved, simplifying the system structure and improving conversion efficiency. Through two-stage nonlinear frequency conversion, a low-repetition-rate, high-single-pulse-energy ns-level 308nm ultraviolet pulsed laser output is obtained to meet the needs of clinical treatment and other applications.

[0017] Other features and advantages of this application will be set forth in the following description and will be apparent in part from the description or may be learned by practicing the application. The objectives and other advantages of this application may be realized and obtained by means of the structures pointed out in the description and the accompanying drawings. Attached Figure Description

[0018] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0019] Figure 1 A schematic diagram of the structure of a 308nm all-solid-state ultraviolet laser based on stimulated Raman scattering in an embodiment of the present invention is shown; Figure 2 The Raman gain spectrum of the Raman gain fiber in an embodiment of the present invention is shown.

[0020] In the figure, pump source system 1, infrared pulsed laser 11, and focusing coupling module 12 are shown. Raman laser generation system 2, reflective fiber Bragg grating 21, Raman gain fiber 22, output coupling fiber Bragg grating 23; Wavelength conversion system 3 includes isolator 31, λ / 2 waveplate 32, first focusing lens 33, first nonlinear medium 34, collimating lens 35, and first reflecting mirror 36; 4. Ultraviolet laser generating system, 41. Second reflecting mirror, 42. Second focusing lens, 43. Second nonlinear medium, 44. Filter. Detailed Implementation

[0021] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0022] This invention provides a 308nm all-solid-state ultraviolet laser based on stimulated Raman scattering. Figure 1 The diagram shows a schematic of the structure of a 308nm all-solid-state ultraviolet laser based on stimulated Raman scattering in an embodiment of the present invention, specifically including: a pump source system 1, a Raman laser generation system 2, a wavelength conversion system 3, and an ultraviolet laser generation system 4.

[0023] The pump source system 1 includes an infrared pulsed laser 11, which outputs an infrared pulsed laser with a wavelength of 1123 nm. Exemplarily, the infrared pulsed laser 11 is an Nd:YAG laser or an Nd:LuYAG laser, with an output laser repetition rate of 1~100 Hz, a single pulse energy of 1~10000 mJ, and a pulse width of 1~500 ns, thereby achieving the provision of high-energy, low-repetition-rate pump laser.

[0024] Correspondingly, the Raman laser generation system 2 includes a high-reflectivity fiber Bragg grating 21, a Raman gain fiber 22, and an output coupling fiber Bragg grating 23; High-reflectivity fiber Bragg grating 21 and output-coupled fiber Bragg grating 23 are respectively disposed at both ends of Raman gain fiber 22, together forming a Raman resonant cavity; Reference Figure 1 The high-reflectivity fiber Bragg grating 21 is located between the Raman gain fiber 22 and the pump source system (i.e., on the left side of the Raman gain fiber 22), and the output coupling fiber Bragg grating 23 is located between the Raman gain fiber 22 and the wavelength conversion system (i.e., on the right side of the Raman gain fiber 22).

[0025] The 1123nm infrared pulsed laser output from the pump source system is injected into the Raman gain fiber 22 via a high-reflectivity fiber Bragg grating 21. Within the Raman resonant cavity, the pump laser interacts with the Raman gain fiber 22, generating stimulated Raman scattering, thereby exciting Stokes light with a wavelength of 1232nm. The Stokes light oscillates back and forth within the Raman resonant cavity and is continuously amplified, ultimately outputting a stable 1232nm pulsed laser via the output coupling fiber Bragg grating 23.

[0026] It should be noted that the Raman gain fiber 22 is a phosphorus-doped fiber. Phosphorus-doped fiber has a large Raman frequency shift range and a high Raman gain coefficient. It can directly shift the pump laser from 1123nm to 1232nm through Stokes scattering, avoiding the use of multi-stage Raman scattering schemes, thus simplifying the system structure and improving conversion efficiency.

[0027] Correspondingly, the wavelength conversion system 3 includes a first nonlinear medium 34, which receives 1232nm Stokes light from the Raman laser generation system 2 and converts the 1232nm infrared laser into visible light with a wavelength of 616nm through a second harmonic generation process. The first nonlinear medium 34 is made of lithium triborate crystal, barium metaborate crystal, potassium titanate phosphate crystal, periodically polarized lithium niobate crystal, periodically polarized potassium titanate phosphate crystal, or periodically polarized lithium tantalate crystal.

[0028] The ultraviolet laser generation system 4 includes a second nonlinear medium 43, which receives 616nm visible light from the wavelength conversion system 3 and converts the 616nm visible light into 308nm ultraviolet laser light through a second harmonic generation process. The second nonlinear medium 43 is made of barium metaborate crystal, lithium cesium hexaborate crystal, or potassium fluoroborate-beryllium crystal.

[0029] In the specific operation, the 1123nm pump laser output from the pump source system is coupled to a Raman resonant cavity, with a high-reflectivity fiber Bragg grating 21 and an output coupling fiber Bragg grating 23 at both ends of the Raman gain fiber 22. Using stimulated Raman scattering (SRS), the 1123nm pump laser oscillates and amplifies multiple times within the resonant cavity through the SRS effect, generating Stokes light, and outputting a 1232nm pulsed laser from the output coupling fiber Bragg grating 23. The 1232nm pulsed laser output from the Raman laser generation system 2 enters the first nonlinear medium 34, where it is converted into visible light with a wavelength of 616nm through a second harmonic generation (SHG) process. Subsequently, it is introduced into the second nonlinear medium 43, where it is again converted into a low-repetition-rate (1-100 Hz), nanosecond-level 308nm ultraviolet pulsed laser through a second harmonic generation process.

[0030] This invention proposes a 308nm all-solid-state ultraviolet laser based on stimulated Raman scattering (SRS). Employing an all-solid-state structure, it overcomes the drawbacks of traditional excimer lasers, such as large size, long preheating time, complex maintenance, and high operating costs. Furthermore, by using phosphorus-doped fiber as the Raman gain medium and leveraging its large Raman frequency shift characteristics, single-stage stimulated Raman scattering wavelength conversion is achieved, simplifying the system structure and improving conversion efficiency. Through two stages of nonlinear frequency conversion, a low-repetition-rate, high-single-pulse-energy ns-level 308nm ultraviolet pulsed laser output is obtained to meet the needs of clinical treatment and other applications.

[0031] In this embodiment, the Raman gain fiber 22 is a phosphorus-doped fiber.

[0032] refer to Figure 2 Raman gain fiber 22 at 1326.5 There is a Raman gain peak at a certain point. Based on this spectral characteristic, when a pump light with a wavelength of 1123 nm is injected into the Raman gain fiber 22, the large frequency shift characteristic corresponding to the Raman gain peak can be utilized to shift the pump light frequency to 1232 nm through a single stimulated Raman scattering (SRS) process, without the need for a multi-stage Raman scattering scheme, thus simplifying the system structure.

[0033] The phosphorus doping concentration in the Raman gain fiber 22 needs to be balanced between Raman gain effect and fiber fabrication process. For example, the phosphorus pentoxide doping concentration in the Raman gain fiber 22 is 1~50 mol%; the refractive index difference between the cladding and core of the Raman gain fiber 22 is 0.005~0.050, the length is 1~1000 m, and the loss at 1232 nm is 0.1~10 dB / km. By setting these parameters, the fiber's waveguide characteristics and stimulated Raman scattering efficiency are ensured.

[0034] In addition, the pump source system includes an infrared pulsed laser 11 and a focusing coupling module 12. The infrared pulsed laser 11 is used to generate an 1123nm pump laser. The focusing coupling module 12 is located between the infrared pulsed laser 11 and the Raman laser generation system 2. The focusing coupling module 12 is used to shape and output the 1123nm pump laser, and then couple the 1123nm pump laser into the core of the Raman gain fiber 22 of the Raman laser generation system 2 to ensure sufficient pump power density to excite stimulated Raman scattering.

[0035] Among them, the infrared pulsed laser 11 is either an Nd:YAG laser or an Nd:LuYAG laser. Both lasers can stably output pulsed laser light with a wavelength of 1123nm, corresponding to repetition frequencies of 1~100 Hz, single pulse energies of 1~10000mJ, and pulse widths of 1~500ns. The parameter range covers a variety of application scenarios from low to high energy, demonstrating good versatility; moreover, the single pulse energy of up to 10000 mJ overcomes the technical challenge of AlGaN semiconductor lasers currently having an output power of only about 10 milliwatts.

[0036] The focusing coupling module 12 employs one or more combinations of spherical lenses and / or aspherical lenses and / or volume Bragg gratings.

[0037] In addition, the wavelength conversion system 3 also includes an isolator 31, a λ / 2 waveplate 32, and a first focusing lens 33. The isolator 31 is disposed between the Raman laser generation system 2 and the first nonlinear medium 34 to prevent the reflected light from returning to the Raman laser generation system 2, thereby avoiding damage to the Raman gain fiber 22, the high-reflectivity fiber Bragg grating 21, and the output coupling fiber Bragg grating 23 in the Raman resonant cavity, and ensuring the stability of the Raman laser generation system 2.

[0038] For example, isolator 31 is a terbium gallium garnet isolator, which has a damage threshold of more than 20 J / cm² for 1123nm laser and a transmittance of more than 90%, and can withstand high-energy pulsed laser without being damaged.

[0039] A λ / 2 waveplate 32 is also disposed between the isolator 31 and the first nonlinear medium 34. The λ / 2 waveplate 32 is used to adjust the polarization direction of the 1123nm pump laser to match the phase matching condition of the first nonlinear medium 34. It should be noted that since the frequency doubling efficiency of most nonlinear crystals is extremely sensitive to the polarization direction of the incident light, adjusting the polarization direction to the optimal matching angle by using a λ / 2 waveplate improves the conversion efficiency of the second harmonic.

[0040] A first focusing lens 33 is also disposed between the λ / 2 waveplate 32 and the first nonlinear medium 34. The first focusing lens 33 is used to focus 1232nm Stokes light into the first nonlinear medium 34, thereby increasing the optical power density and improving the frequency doubling efficiency.

[0041] In addition, the wavelength conversion system 3 also includes a collimating lens 35 and a first reflecting mirror 36. The collimating lens 35 is disposed between the first nonlinear medium 34 and the second nonlinear medium 43. The collimating lens 35 is used to collimate the divergent 616nm visible light output from the first nonlinear medium 34 into a parallel beam, which facilitates the processing and transmission of subsequent optical elements.

[0042] Correspondingly, the first reflector 36 is disposed between the first nonlinear medium 34 and the second nonlinear medium 43. The first reflector 36 is used to guide 616nm visible light to the optical path where the second nonlinear medium 43 is located. At the same time, it uses its high transmittance of 1232nm infrared light and high reflectance of 616nm visible light to filter out residual 1232nm infrared light in the beam, thus playing a preliminary purification role.

[0043] In this embodiment, the first nonlinear medium 34 is a lithium triborate crystal, a barium metaborate crystal, a potassium titanate phosphate crystal, a periodically polarized lithium niobate crystal, a periodically polarized potassium titanate phosphate crystal, or a periodically polarized lithium tantalate crystal; and the length of the first nonlinear medium 34 is 2~20 mm.

[0044] The second nonlinear medium 43 is made of barium metaborate crystal, lithium cesium hexaborate crystal, or potassium fluoroborate beryllium crystal, and the length of the second nonlinear medium 43 is the same as that of the first nonlinear medium 34, which is 2~20 mm.

[0045] In this embodiment, the ultraviolet laser generating system 4 further includes a second reflecting mirror 41 and a second focusing lens 42; The second reflector 41 is disposed between the wavelength conversion system 3 and the second nonlinear medium 43. It is used to guide 616nm visible light to the optical path where the second nonlinear medium 43 is located, and further filter out the residual 1232nm infrared light, thereby improving the purity of the beam entering the second nonlinear medium 43. It also corresponds to the first reflector 36, thereby reducing the overall size of the laser and improving its integration.

[0046] The second focusing lens 42 is disposed between the second reflecting mirror 41 and the second nonlinear medium 43. The second focusing lens 42 is used to focus 616nm visible light into the interior of the second nonlinear medium 43 to increase the optical power density, thereby improving the second harmonic conversion efficiency from 616nm to 308nm.

[0047] It should be added that both the first reflector 36 and the second reflector 41 can be made of quartz glass film or ordinary glass film to achieve the effect of providing high reflection while filtering out interfering light.

[0048] In this embodiment, the ultraviolet laser generating system 4 further includes a filter 44 for receiving 308nm ultraviolet laser light. The filter 44 has a transmittance of more than 95% for 308nm ultraviolet laser light, a reflectance of more than 90% for 616nm visible light, and a reflectance of more than 95% for 1232nm infrared light. Through this film system design, the filter 44 can efficiently transmit the target 308nm ultraviolet laser light, while reflecting or absorbing the residual 616nm visible light and 1232nm infrared light, thereby improving the spectral purity of the final output laser and meeting the needs of high-requirement applications such as clinical treatment.

[0049] To better illustrate the practical implementation of the 308nm all-solid-state ultraviolet laser based on stimulated Raman scattering proposed in this application, specific examples of the parameters of each component are provided below: Example 1; In the pump source system, the infrared pulsed laser 11 is an Nd:YAG laser with an adjustable repetition rate of 1~10 Hz, a single pulse energy of 100 mJ, and a pulse width of 60 ns. The focusing coupling module 12 uses two spherical lenses coated with 1123nm antireflection films, with a transmittance T greater than 99%.

[0050] In the Raman laser generation system 20, the high-reflectivity fiber Bragg grating 21 has a reflectivity of 99.5% at 1232 nm, and the output coupling fiber Bragg grating 23 has a transmittance T of 10% at 1232 nm. The Raman gain fiber 22 is a phosphorus-doped fiber with a phosphorus pentoxide doping concentration of 10 mol%, a cladding-core refractive index difference of 0.010, a length of 100 m, and a loss of 0.5 dB / km at 1232 nm.

[0051] In the wavelength conversion system 3, the isolator 31 uses terbium gallium garnet crystal with a damage threshold of 30 J / cm² and a transmittance of 99% at 1123 nm. The λ / 2 waveplate 32 uses mica material with a damage threshold of 20 J / cm² at 1123 nm. The first focusing lens 33 is a quartz spherical lens with a focal length of 20 mm. The first nonlinear medium 34 is lithium triborate (LiB3O5, LBO) crystal with dimensions of 3×3×15 mm³. The collimating lens 35 is a quartz spherical lens with a focal length of 10 mm. The first reflecting mirror 36 has a reflectance of 99% at 616 nm and a transmittance of 98% at 1232 nm.

[0052] In the ultraviolet laser generation system 4, the second reflecting mirror 41 has a reflectivity of 99% for 616 nm and a transmittance of 98% for 1232 nm. The second focusing lens 42 is a quartz spherical lens with a focal length of 10 mm. The second nonlinear medium 43 is made of barium metaborate (β-BaB₂O₄, BBO) crystal with dimensions of 4×4×8 mm³. The filter 44 has a transmittance of 99% for 308 nm and a reflectivity of 98% for both 616 nm and 1232 nm.

[0053] The first reflector 36 and the second reflector 41 are arranged correspondingly, and both have an incident angle of 45º.

[0054] Under the above parameter conditions, this embodiment achieves stable 308nm ultraviolet pulsed laser output.

[0055] Example 2: This embodiment is basically the same as embodiment 1, except that the type and parameters of the infrared pulse laser 11, the structure of the focusing coupling module 12, and the parameters of the Raman gain fiber 22 have been adjusted.

[0056] The infrared pulsed laser 11 is an Nd:LuYAG laser with an adjustable repetition rate of 1~100 Hz, a single pulse energy of 80 mJ, and a pulse width of 50 ns. The focusing coupling module 12 uses two aspherical lenses, both coated with a 1123 nm high transmittance (HT) film, which has a transmittance of 99% for 1123 nm laser light.

[0057] The doping concentration of Raman gain fiber 22 was adjusted to 15 mol%, the refractive index difference between the cladding and the core was 0.020, the length was 10 m, and the loss at 1232 nm was 0.6 dB / km.

[0058] Example 3: This embodiment is basically the same as embodiment 1, except that the repetition frequency of the infrared pulse laser 11 and the parameters of the Raman gain fiber 22 have been adjusted.

[0059] The infrared pulsed laser 11 is an Nd:LuYAG laser with an adjustable repetition frequency of 10 Hz, a single pulse energy of 100 mJ, and a pulse width of 60 ns.

[0060] The Raman gain fiber 22 has a phosphorus pentoxide doping concentration of 20 mol%, a cladding-core refractive index difference of 0.015, a length of 100 m, and a loss of 0.8 dB / km at 1232 nm.

[0061] Example 4: This embodiment is basically the same as Embodiment 1, except that the parameters of the infrared pulse laser 11 and the Raman gain fiber 22 have been adjusted, and the material of the first nonlinear medium 34 has been changed.

[0062] The infrared pulsed laser 11 is an Nd:LuYAG laser with an adjustable repetition rate of 1~100 Hz, a single pulse energy of 100 mJ, and a pulse width of 60 ns. The focusing coupling module 12 uses two aspherical lenses.

[0063] The doping concentration of Raman gain fiber 22 was adjusted to 20 mol%, the refractive index difference between the cladding and the core was 0.015, the length was 100 m, and the loss at 1232 nm was 0.8 dB / km.

[0064] The first nonlinear medium 34 is a BBO crystal with a size of 3×3×10 mm³. The front and back surfaces of the crystal are coated with antireflective films of 1232 nm and 616 nm, respectively. Its transmittance at 1232 nm is 99%, and its transmittance at 616 nm is 98%.

[0065] Example 4: Increasing the doping concentration of the Raman gain fiber 22 and replacing the material of the first nonlinear medium 34, while maintaining a high conversion efficiency, further broadens the applicable range of the pump source repetition frequency and improves the system flexibility.

[0066] Furthermore, based on Example 1, when the first nonlinear medium 34 adopts a periodically polarized lithium niobate (PPLN) crystal with a crystal size of 2×1×5 mm³, and antireflection films of 1232nm and 616nm are deposited on the front and back surfaces of the crystal, the transmittance T for 1232nm is 99%, the transmittance T for 616nm is 98%, and the polarization period is 7μm.

[0067] When the first nonlinear medium 34 adopts a periodically polarized lithium tantalate (PPSLT) crystal with a crystal size of 10×1×20mm³, the front and back surfaces of the crystal are coated with antireflection films of 1232nm and 616nm, the transmittance T for 1232nm is 99%, the transmittance T for 616nm is 98%, and the polarization period is 8μm.

[0068] When the first nonlinear medium 34 adopts a periodically polarized KTP (PPKTP) crystal with a crystal size of 5×1×10 mm³, the front and back surfaces of the crystal are coated with antireflection films of 1232nm and 616nm, the transmittance T for 1232nm is 99%, the transmittance T for 616nm is 98%, and the polarization period is 9μm.

[0069] Correspondingly, based on Example 1, when the second nonlinear medium 43 is a cesium lithium borate crystal (CsLiB6O10, CLBO) with a crystal size of 5×5×20 mm³, and antireflection films of 308nm and 616nm are deposited on the front and back surfaces of the crystal, the transmittance T for 308nm is 99% and the transmittance T for 616nm is 98%.

[0070] Alternatively, the second nonlinear medium 43 may be a KBBF crystal with a thickness of 2 mm, and the front and back surfaces of the crystal may be coated with antireflective films of 308 nm and 616 nm, respectively. The transmittance T for 308 nm is 99%, and the transmittance T for 616 nm is 98%.

[0071] In the description of this invention, 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 indicated technical features. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more features. In the description of this invention, "a plurality of" means two or more, unless otherwise explicitly specified. Furthermore, the terms "installed," "connected," and "linked" should be interpreted broadly; for example, they may refer to a fixed connection, a detachable connection, or an integral connection; they may refer to a mechanical connection, an electrical connection, or a connection that allows for communication; they may refer to a direct connection or an indirect connection through an intermediate medium. Those skilled in the art can understand the specific meaning of these terms in this invention according to the specific circumstances.

[0072] It should be understood that all terms used to indicate orientation or positional relationship are based on the orientation or positional relationship shown in the accompanying drawings and are only for the convenience of describing the present invention and simplifying the description, and are not intended to 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 should not be construed as a limitation of the present invention.

[0073] Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of this application.

Claims

1. A 308nm all-solid-state ultraviolet laser based on stimulated Raman scattering, characterized in that, include: Pump source system (1) is used to generate 1123nm pump laser; The Raman laser generation system (2) includes a high-reflectivity fiber Bragg grating (21), a Raman gain fiber (22), and an output coupling fiber Bragg grating (23). The 1123nm pump laser output from the pump source system (1) is injected into the Raman gain fiber (22) through the high-reflectivity fiber Bragg grating (21), and a 1232nm Stokes light is generated through stimulated Raman scattering, and then output through the output coupling fiber Bragg grating (23). The wavelength conversion system (3) includes a first nonlinear medium (34) for receiving the 1232nm Stokes light and converting it into 616nm visible light through second harmonic generation; The ultraviolet laser generation system (4) includes a second nonlinear medium (43) for receiving the 616nm visible light and generating and converting it into 308nm ultraviolet laser light through second harmonic generation.

2. The 308nm all-solid-state ultraviolet laser based on stimulated Raman scattering according to claim 1, characterized in that, The Raman gain fiber (22) is a phosphorus-doped fiber.

3. The 308nm all-solid-state ultraviolet laser based on stimulated Raman scattering according to claim 2, characterized in that, The phosphorus pentoxide doping concentration in the Raman gain fiber (22) is 1~50 mol%, the refractive index difference between the cladding and the core of the Raman gain fiber (22) is 0.005~0.050, the length is 1~1000 m, and the loss at 1232 nm is 0.1~10 dB / km.

4. The 308nm all-solid-state ultraviolet laser based on stimulated Raman scattering according to claim 1, characterized in that, The high-reflectivity fiber Bragg grating (21) has a reflectivity of more than 90% for 1232nm laser; the output-coupled fiber Bragg grating (23) has a transmittance of 5%~50% for 1232nm laser.

5. The 308nm all-solid-state ultraviolet laser based on stimulated Raman scattering according to claim 1, characterized in that, The pump source system (1) includes an infrared pulsed laser (11) and a focusing coupling module (12), wherein the infrared pulsed laser (11) is used to generate 1123nm pump laser; The focusing coupling module (12) is located between the infrared pulse laser (11) and the Raman laser generation system (2). The focusing coupling module (12) is used to couple the 1123nm pump laser into the Raman laser generation system (2).

6. The 308nm all-solid-state ultraviolet laser based on stimulated Raman scattering according to claim 5, characterized in that, The infrared pulsed laser (21) is an Nd:YAG laser or an Nd:LuYAG laser, with a repetition frequency of 1~100 Hz, a single pulse energy of 1~10000 mJ, and a pulse width of 1~500 ns.

7. The 308nm all-solid-state ultraviolet laser based on stimulated Raman scattering according to claim 1, characterized in that, The wavelength conversion system (3) further includes an isolator (31), a λ / 2 waveplate (32) and a first focusing lens (33). The isolator (31) is disposed between the Raman laser generation system (2) and the first nonlinear medium (34) to prevent the subsequent reflected light from returning to the Raman laser generation system (2). The λ / 2 waveplate (32) is disposed between the isolator (31) and the first nonlinear medium (34) to adjust the polarization direction of the 1123nm pump laser to be compatible with the phase matching condition of the first nonlinear medium (34); The first focusing lens (33) is disposed between the λ / 2 waveplate (32) and the first nonlinear medium (34).

8. The 308nm all-solid-state ultraviolet laser based on stimulated Raman scattering according to claim 7, characterized in that, The wavelength conversion system (3) further includes a collimating lens (35) and a first reflecting mirror (36). The collimating lens (35) is disposed between the first nonlinear medium (34) and the second nonlinear medium (43) for collimating the 616nm visible light output from the first nonlinear medium (34). The first reflector (36) is disposed between the first nonlinear medium (34) and the second nonlinear medium (43) to guide 616nm visible light to the second nonlinear medium (43).

9. The 308nm all-solid-state ultraviolet laser based on stimulated Raman scattering according to claim 1, characterized in that, The ultraviolet laser generating system (4) further includes a second reflector (41) and a second focusing lens (42). The second reflector (41) is disposed between the wavelength conversion system (3) and the second nonlinear medium (43) for guiding 616nm visible light to the second nonlinear medium (43). The second focusing lens (42) is disposed between the second reflecting mirror (41) and the second nonlinear medium (43) to focus 616nm visible light into the second nonlinear medium (43).

10. The 308nm all-solid-state ultraviolet laser based on stimulated Raman scattering according to claim 9, characterized in that, The ultraviolet laser generating system (4) further includes a filter (44) for receiving 308nm ultraviolet laser light. The filter (44) has a transmittance of more than 95% for 308nm ultraviolet laser light and a reflectance of more than 90% for 616nm visible light.

11. The 308nm all-solid-state ultraviolet laser based on stimulated Raman scattering according to any one of claims 1-10, characterized in that, The first nonlinear medium (34) is a lithium triborate crystal, a barium metaborate crystal, a potassium titanate phosphate crystal, a periodically polarized lithium niobate crystal, a periodically polarized potassium titanate phosphate crystal, or a periodically polarized lithium tantalate crystal. The second nonlinear medium (43) is a barium metaborate crystal, a lithium cesium hexaborate crystal, or a potassium fluoroborate crystal.

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