A device for generating blue laser light with high conversion efficiency under negative pressure

Abstract

The application belongs to the technical field of laser frequency conversion, and particularly relates to a device for generating blue laser with high conversion efficiency under negative pressure. The device comprises, in sequence along the laser transmission direction, a laser pumping unit, a Raman frequency conversion unit, a gas pressure regulation unit and a light splitting detection unit. The laser pumping unit is used for outputting laser. The output laser propagates through a free space optical path and then enters the Raman frequency conversion unit. The Raman frequency conversion unit generates multi-wavelength laser pulses through the stimulated Raman scattering process under negative pressure and outputs the multi-wavelength laser pulses. The gas pressure regulation unit is used for controlling the negative pressure condition of the Raman frequency conversion unit. The light splitting detection unit is used for separating the blue laser with selectable wavelength from the multi-wavelength laser pulses output by the Raman frequency conversion unit. The application greatly improves the energy conversion efficiency of anti-Stokes light by regulating the gas pressure, optimizing the focusing parameters and the pumping energy, and can realize the output of blue pulse laser with high conversion efficiency.

Description

Technical Field

[0001] This invention belongs to the field of laser frequency conversion technology, and specifically relates to a device for generating high-conversion-efficiency blue laser under negative pressure conditions. Background Technology

[0002] Due to the extremely low absorption loss of seawater in the blue light band, blue lasers have wide applications in marine surveying, underwater secure communication, and underwater guidance. Furthermore, pulsed blue lasers also play important roles in many fields such as spectroscopy, laser display, information storage, materials processing, and biomedical detection. The main methods for obtaining blue light include: semiconductor lasers using II-VI or III-V group compounds as wide-bandgap PN or PIN junctions; rare gas lasers such as argon or krypton ions; high-repetition-rate XeF excimer lasers; frequency up-conversion of red and infrared wavelengths using nonlinear techniques; and frequency conversion through stimulated Raman scattering (SRS). Due to the poor frequency stability and beam quality of blue light generated by semiconductors, problems such as wavelength drift, large divergence angle, and uneven beam spot exist. Argon ion lasers can output a series of lasers with different wavelengths in the blue-green light band (454-528nm) through electrode discharge, and the working wavelength can be selected by rotating the cavity prism. However, this device is large in size, short in life, and has low conversion efficiency. XeF2 vapor generates XeF(CA) laser radiation in the band of 450-520nm with a center wavelength of 480nm under photodissociation. Its pulse energy is high and the pulse width is in the range of hundreds of nanoseconds to microseconds. However, the overall conversion efficiency is extremely low (only 0.1%).

[0003] Currently, the most common method for generating blue lasers is nonlinear frequency upconversion, which mainly includes frequency doubling and sum-frequency generation. Frequency doubling includes intracavity frequency doubling, external cavity frequency doubling, and self-frequency doubling. Sum-frequency generation methods include pumping the two emission cross-sections of a single laser crystal to generate a dual-wavelength laser sum-frequency, or pumping two laser crystals separately. These methods typically use Nd:N ... 3+ Doped crystals such as LuVO4, YAG, GdVO4, and YVO4 are used as gain media to generate laser light by suppressing strong spectral lines (1.06 μm, 1.32 μm bands, etc.) and selecting weak spectral lines (around 950 nm band). This necessitates consideration of complex spectral line gain competition. To output a suitable wavelength, such devices also place high demands on the coating process of optical components. Furthermore, stringent phase matching and intracavity mode matching, precise control of electrical parameters, polarization, and temperature, and poor scaling amplification result in very limited pulse energy and peak power for this type of blue light output. Another upconversion approach to obtain blue-band laser light is to pump doped Yb using red or infrared lasers such as GaAlAs and InGaAlP. 3+ As a sensitizing ion, Er 3+ Ho3+ Tm 3+ Fluorides, halides, or complex oxides with rare-earth ions as activating ions utilize mechanisms such as excited-state absorption, energy transfer, or rare-earth ion energy level transitions induced by photon avalanches. For example, Tm is pumped using a red laser. 3＋ LiYF4 can output 30mW of 483nm blue laser light with a conversion efficiency of 8%. This method is not constrained by phase matching and has low requirements for the wavelength stability, polarization, and beam quality of the pump light, but it involves complex optical material fabrication processes. Frequency conversion and tuning of the laser can also be achieved using effects such as third-order mixing of alkali metal atomic vapors, stimulated Raman scattering, or coherent anti-Stokes Raman scattering, thereby generating blue light output. However, such blue lasers have a high threshold (above 10kW / cm²) and an output power only in the hundreds of microwatts range, which is still some distance from practical applications.

[0004] Stimulated Raman scattering (SRS) of gases has received considerable attention since its first report in 1963, and has been widely applied in wavelength conversion, ultrashort pulse generation, coherent anti-Stokes Raman spectroscopy, and frequency comb generation. Among these applications, the generation of anti-Stokes light can extend the output wavelength to shorter wavelengths. Therefore, SRS has become an effective means of obtaining blue laser output. This process places strict requirements on the temporal and spatial overlap and phase matching between the pump light and the first-order Stokes light, as well as the anti-Stokes light of each order. Therefore, focusing parameters and gas pressure significantly affect the energy conversion efficiency of anti-Stokes blue light. In 2016, a team led by Gu Bo at the National University of Defense Technology used a 1064nm laser to pump a hollow fiber filled with high-pressure hydrogen gas, simultaneously obtaining red, green, and blue laser outputs at 737.6nm, 564.2nm, and 457.1nm through cascaded SRS, corresponding to the first, second, and third-order vibrational anti-Stokes light of hydrogen gas, respectively. They proposed that the higher the gas pressure, the higher the conversion efficiency from pump light to Stokes light and anti-Stokes light. However, the transmission loss and nonlinear effects of optical fibers limit their conversion efficiency and output power; at an air pressure of 3.5 MPa, a pump power of 42.6 mW corresponds to only tens of microwatts of output. Therefore, how to achieve a simple working structure, high conversion efficiency, and stable and reliable blue light pulse output is an urgent problem to be solved. Summary of the Invention

[0005] To address the aforementioned problems, the present invention aims to provide a device for generating high-conversion-efficiency blue laser under negative pressure conditions, so as to obtain blue pulsed laser that meets the needs of practical applications, solve the key problem of phase matching between pump light and first-order Stokes light and anti-Stokes light of various orders, explore the pressure selectivity of anti-Stokes light of various orders, and improve the conversion efficiency of blue light.

[0006] The objective of this invention is achieved through the following technical solution: This invention provides a device for generating high-conversion-efficiency blue laser under negative pressure conditions, comprising a laser pumping unit, a Raman frequency conversion unit, a gas pressure control unit, and a beam splitting and detection unit arranged sequentially along the laser transmission direction; wherein, The laser pump unit is used to output laser light, which propagates through a free space optical path and then enters the Raman frequency conversion unit. The Raman frequency conversion unit generates and outputs multi-wavelength laser pulses through stimulated Raman scattering under negative pressure conditions. The air pressure control unit is used to control the negative pressure conditions of the Raman frequency converter unit; The spectrophotometer is used to separate blue laser with selectable wavelength from the multi-wavelength laser pulses output by the Raman frequency conversion unit.

[0007] The laser pumping unit includes a pump laser, a half-wave plate, a polarizing beam splitter, a laser beam collector, and a plane mirror assembly for forming a free-space optical path. The pump laser, half-wave plate, and polarizing beam splitter are arranged sequentially along the laser transmission direction. A laser beam collector is provided on one side of the polarizing beam splitter. The combination of the half-wave plate and the polarizing beam splitter enables continuous adjustment of the laser energy entering the Raman conversion unit. The plane mirror assembly is positioned on the laser transmission path to ensure the effective propagation length of the optical path.

[0008] The planar reflector group includes a first planar reflector, a second planar reflector, a third planar reflector, a fourth planar reflector, and a fifth planar reflector. The first planar reflector is disposed between the pump laser and the half-wave plate to reflect the laser output from the pump laser onto the half-wave plate. The second, third, fourth, and fifth planar reflectors are arranged sequentially behind the polarizing beam splitter along the laser transmission direction.

[0009] The Raman frequency conversion unit includes a focusing lens, a first Perinbroca prism, a Raman cell, and a collimating lens arranged sequentially along the laser transmission direction. The Raman cell is a hollow, sealed cavity with a laser incident window and a laser exit window at each end. The interior of the hollow, sealed cavity is filled with Raman-active gas. After the incident pulsed laser is focused by the focusing lens, it passes through the first Perinbroca prism and enters the Raman cell. In the Raman cell, it undergoes stimulated Raman scattering to generate multi-wavelength laser pulses, including Stokes light, anti-Stokes light, and residual pump light. The output multi-wavelength laser pulses are collimated by the collimating lens and then enter the beam splitting and detection unit.

[0010] The laser incident window of the Raman cell is a quartz window; the laser exit window of the Raman cell is a calcium fluoride window.

[0011] The air pressure control unit includes a pressurizing device, a depressurizing device, an air pressure detection device, and a monitoring and control device. The pressurizing device, the depressurizing device, and the air pressure detection device are all connected to the Raman cell. The air pressure detection device is used to detect the air pressure in the Raman cell. The pressurizing device and the depressurizing device are controlled by the monitoring and control device. When the actual gas pressure in the Raman cell measured by the gas pressure detection device is lower than the ideal negative pressure condition, the monitoring and control device starts the pressurization device to fill the Raman cell with Raman active gas; when the actual gas pressure in the Raman cell measured by the gas pressure detection device is higher than the ideal negative pressure condition, the monitoring and control device starts the depressurization device to extract part of the Raman active gas from the Raman cell.

[0012] The pressurization device includes a high-pressure gas cylinder, a pressure reducing valve, a first gas guide pipe, and a first adapter. The high-pressure gas cylinder is filled with Raman active gas. One end of the first gas guide pipe is connected to the high-pressure gas cylinder, and the other end is connected to the Raman cell through the first adapter. The pressure reducing valve is installed on the first gas guide pipe.

[0013] The pressure reducing valve includes a valve body, an inlet connector, an inlet pressure display gauge, an outlet pressure display gauge, a pressure regulating rod, a pressure relief valve, and an outlet connector. The inlet connector and the outlet connector are located at both ends of the valve body. The inlet pressure display gauge is located at the inlet end of the valve body, and the outlet pressure display gauge, the pressure regulating rod, and the pressure relief valve are located at the outlet end of the valve body. The reading on the inlet pressure display gauge is the pressure of the gas stored in the high-pressure gas cylinder, and the pressure shown on the outlet pressure display gauge is controlled by the pressure regulating rod.

[0014] The pressure reducing device includes a vacuum pump, a second gas guide pipe, and a second adapter, wherein one end of the second gas guide pipe is connected to the vacuum pump, and the other end is connected to the Raman cell via the second adapter.

[0015] The beam splitting detection unit includes a second Perinbroca prism, a third Perinbroca prism, a beam splitter, a beam expander, and an energy meter arranged sequentially along the laser transmission direction. The second and third Perinbroca prisms are used to separate the wavelengths of the laser beam. The beam splitter can move left and right in the direction perpendicular to the beam propagation to filter out each order of anti-Stokes light, thereby achieving adjustable output blue light wavelength. After the output blue laser is expanded by the beam expander, the output light energy is recorded by the energy meter.

[0016] The advantages and positive effects of this invention are as follows: 1. This invention utilizes the stimulated Raman scattering effect of Raman-active gases in a Raman cell to generate anti-Stokes light for blue light output. Its principle is simple, its structure is straightforward, and its cost is low. Compared to diode-based blue light, it offers significant advantages in frequency stability and beam uniformity, and avoids the technical difficulties of phase matching and cavity mode matching in nonlinear frequency up-conversion blue light output. Furthermore, it has low requirements for controlling electrical parameters, polarization, and temperature. Moreover, it eliminates the need to consider the complex energy level transition structures of various rare-earth activated ions and the gain competition between emission cross-sections.

[0017] 2. This invention solves the key problem of phase matching between pump light and first-order Stokes light, as well as between anti-Stokes light and various orders, by exploring the pressure selectivity of anti-Stokes light within a negative pressure range, thus greatly improving the conversion efficiency of blue light. By controlling the gas pressure and optimizing the focusing parameters and pump energy, the energy conversion efficiency of anti-Stokes light is greatly improved. It can achieve blue pulsed laser output with pulse widths of several nanoseconds to tens of nanoseconds, single-pulse energies of tens to hundreds of millijoules, peak power of tens of megawatts, and energy conversion efficiency exceeding 10%.

[0018] 3. This invention can obtain blue pulsed lasers of different wavelengths by selecting pump lasers with different emission wavelengths and gas gain media with different Raman frequency shifts to change the frequency of the output anti-Stokes light.

[0019] 4. The pressure control unit of the present invention has high monitoring sensitivity and adjustment flexibility. It monitors the pressure in the Raman cell in real time through a high-sensitivity electronic pressure gauge. By linking the pressurization device and the depressurization device, it can achieve fine control of the Raman active gas pressure in the negative pressure range, which is convenient for finding the optimal negative pressure conditions corresponding to each pumping condition and gain medium. Attached Figure Description

[0020] To more clearly illustrate the technical solutions in the embodiments of the present invention 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 the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0021] Figure 1 This is a schematic diagram of the structure of a high-conversion-efficiency blue laser generating device under negative pressure conditions according to the present invention; Figure 2 This is a schematic diagram of the pressure reducing valve in the pressure regulating unit booster device of the present invention; Figure 3 This is a schematic diagram of the vacuum pump in the pressure reducing device of the air pressure regulating unit of the present invention; Figure 4The graph shows the variation of the anti-Stokes blue laser energy conversion efficiency with air pressure obtained by controlling the air pressure through the air pressure regulation unit under different pump energies using the device of the present invention. In the diagram: 1 is the laser pumping unit, 101 is the pump laser, 102 is the first plane mirror, 103 is the half-wave plate, 104 is the polarizing beam splitter, 105 is the laser beam collector, 106 is the second plane mirror, 107 is the third plane mirror, 108 is the fourth plane mirror, 109 is the fifth plane mirror; 2 is the Raman frequency conversion unit, 201 is the focusing lens, 202 is the first Perinbroka prism, 203 is the Raman cell, 204 is the collimating lens; 3 is the gas pressure control unit, 31 is the pressurization device, 311 is the high-pressure gas cylinder, 312 is the pressure reducing valve, 312-1 is the gas inlet connector, 312-2 is the gas inlet pressure display gauge, 312-3 is the gas outlet pressure display gauge, 312-4 is the pressure adjusting rod, 31... 2-5 is a pressure relief valve, 312-6 is an air outlet connector, 313 is the first air guide pipe, 314 is the first adapter, 32 is a pressure reducing device, 321 is a vacuum pump, 321-1 is the pump cylinder body, 321-2 is the working fluid, 321-3 is the pump impeller, 321-4 is the air intake port, 321-5 is the air intake pipe, 321-6 is the air exhaust port, 321-7 is the air exhaust pipe, 322 is the second air guide pipe, 323 is the second adapter, 33 is a pressure detection device, 331 is an electronic pressure gauge, 332 is the second adapter, 34 is a monitoring and control device, 4 is a spectrophotometer, 401 is the second Perinbroca prism, 402 is the third Perinbroca prism, 403 is a spectrophotometer aperture, 404 is a beam expander, and 405 is an energy meter. Detailed Implementation

[0022] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be described in detail below with reference to the accompanying drawings and specific embodiments.

[0023] like Figure 1 As shown, this invention provides a device for generating high-conversion-efficiency blue laser under negative pressure conditions, comprising a laser pumping unit 1, a Raman frequency conversion unit 2, a gas pressure control unit 3, and a beam splitting and detection unit 4 arranged sequentially along the laser transmission direction; wherein, the laser pumping unit 1 is used to output laser light, and the output laser light propagates through a free space optical path and then enters the Raman frequency conversion unit 2; the Raman frequency conversion unit 2 generates multi-wavelength laser pulses through stimulated Raman scattering under negative pressure conditions and outputs them to the beam splitting and detection unit 4; the gas pressure control unit 3 is used to control the negative pressure conditions of the Raman frequency conversion unit 2; the beam splitting and detection unit 4 is used to separate wavelength-selectable blue laser light from the multi-wavelength laser pulses output by the Raman frequency conversion unit 2.

[0024] This invention utilizes the stimulated Raman scattering effect of Raman active gas in Raman frequency conversion unit 2 to generate anti-Stokes light for blue light output. Its principle is simple, its structure is straightforward, and its cost is low. Compared to diode-based blue light, it offers significant advantages in frequency stability and beam uniformity, and avoids the technical difficulties of phase matching and cavity mode matching in nonlinear frequency up-conversion blue light output. Furthermore, it has low requirements for controlling electrical parameters, polarization, and temperature. Moreover, it eliminates the need to consider the complex energy level transition structures of various rare-earth activated ions and the gain competition between emission cross-sections.

[0025] like Figure 1 As shown, in an embodiment of the present invention, the laser pumping unit 1 includes a pump laser 101, a half-wave plate 103, a polarizing beam splitter 104, a laser beam collector 105, and a plane mirror group for forming a free-space optical path. The pump laser 101, the half-wave plate 103, and the polarizing beam splitter 104 are arranged sequentially along the laser transmission direction. The laser beam collector 105 is provided on one side of the polarizing beam splitter 104. The combination of the half-wave plate 103 and the polarizing beam splitter 104 can realize the continuous adjustment of the laser energy entering the Raman cell 203 of the Raman frequency conversion unit 2. The plane mirror group is set on the laser transmission path to ensure the effective propagation length of the optical path while reducing the spatial volume of the device.

[0026] In this embodiment, the plane mirror group includes a first plane mirror 102, a second plane mirror 106, a third plane mirror 107, a fourth plane mirror 108, and a fifth plane mirror 109. The first plane mirror 102 is disposed between the pump laser 101 and the half-wave plate 103, and is used to reflect the laser output from the pump laser 101 onto the half-wave plate 103. The second plane mirror 106, the third plane mirror 107, the fourth plane mirror 108, and the fifth plane mirror 109 are arranged sequentially along the laser transmission direction behind the polarizing beam splitter 104. Specifically, the number and placement of the plane mirrors can be adjusted according to the actual required optical path length.

[0027] like Figure 1As shown in the embodiment of the present invention, the Raman frequency conversion unit 2 includes a focusing lens 201, a first Perinbroca prism 202, a Raman cell 203, and a collimating lens 204 arranged sequentially along the laser transmission direction. The Raman cell 203 is a hollow sealed cavity with a laser incident window and a laser exit window respectively at both ends. The interior of the hollow sealed cavity is filled with Raman-active gas. After the incident pulsed laser is focused by the focusing lens 201, it passes through the first Perinbroca prism 202 and enters the Raman cell 203. In the Raman cell 203, a stimulated Raman scattering process is performed to generate multi-wavelength laser pulses including Stokes light, anti-Stokes light, and residual pump light. The output multi-wavelength laser pulses are collimated by the collimating lens 204 and then enter the beam splitting detection unit 4.

[0028] Specifically, the laser incident window of Raman cell 203 is a quartz window; the laser exit window of Raman cell 203 is a calcium fluoride window. The distance from focusing lens 201 to the laser incident window of Raman cell 203 is determined by the focal length of focusing lens 201 and the actual length of Raman cell 203. The focal length of focusing lens 201 is variable, and can be selected as 1.0m, 1.5m, and 2.0m. The distance from collimating lens 204 to the laser exit window of Raman cell 203 is determined by the focal length of collimating lens 204 and the actual length of Raman cell 203. The focal length of collimating lens 204 is variable, and can be selected as 0.4m, 0.5m, and 1m.

[0029] like Figure 1 As shown in the embodiment of the present invention, the pressure control unit 3 includes a pressurizing device 31, a depressurizing device 32, a pressure detection device 33, and a monitoring and control device 34. The pressurizing device 31, the depressurizing device 32, and the pressure detection device 33 are all connected to the Raman cell 203. The pressure detection device 33 is used to detect the pressure inside the Raman cell 203. The pressurizing device 31 and the depressurizing device 32 are controlled by the monitoring and control device 34. During operation, when the actual pressure inside the Raman cell 203 measured by the pressure detection device 33 is lower than the ideal negative pressure condition, the monitoring and control device 34 activates the pressurizing device 31 to fill the Raman cell 203 with Raman active gas. When the actual pressure inside the Raman cell 203 measured by the pressure detection device 33 is higher than the ideal negative pressure condition, the monitoring and control device 34 activates the depressurizing device 32 to extract part of the Raman active gas from the Raman cell 203.

[0030] In an embodiment of the present invention, the pressurization device 31 includes a high-pressure gas storage cylinder 311, a pressure reducing valve 312, a first gas guide pipe 313, and a first adapter 314. The high-pressure gas storage cylinder 311 is filled with Raman active gas. One end of the first gas guide pipe 313 is connected to the high-pressure gas storage cylinder 311, and the other end is connected to the Raman cell 203 through the first adapter 314. The pressure reducing valve 312 is disposed on the first gas guide pipe 313.

[0031] like Figure 2As shown, in an embodiment of the present invention, the pressure reducing valve 312 includes a valve body, an inlet connector 312-1, an inlet pressure display gauge 312-2, an outlet pressure display gauge 312-3, a pressure regulating rod 312-4, a pressure relief valve 312-5, and an outlet connector 312-6. The inlet connector 312-1 and the outlet connector 312-6 are located at both ends of the valve body. The inlet connector 312-1 is connected to a high-pressure gas cylinder 311 containing high-purity carbon dioxide. The outlet connector 312-6 is connected to the Raman cell 203 through a first gas guide pipe 313 and a first adapter 314. An inlet pressure display gauge 312-2 is located at the inlet end of the valve body, while an outlet pressure display gauge 312-3, a pressure regulating rod 312-4, and a pressure relief valve 312-5 are located at the outlet end of the valve body. The inlet pressure display gauge 312-2 shows the pressure of the gas stored in the high-pressure gas cylinder 311, and the pressure shown in the outlet pressure display gauge 312-3 is controlled by the pressure regulating rod 312-4. During the experiment, when the monitoring and control device 34 receives a pressure reading from the electronic pressure gauge 331 indicating that the pressure in the Raman cell 203 is lower than the set pressure, it issues a command to rotate the pressure regulating rod 312-4 to activate the pressure reducing valve 312. At this time, the high-pressure gas in the high-pressure gas cylinder 311 is throttled and reduced in pressure, then adjusted to the required experimental pressure value before finally entering the Raman cell 203. The pressure relief valve 312-5 is a device to protect the pressure reducing valve and ensure its safe use. It is also a signal device for when the pressure reducing valve malfunctions. If the outlet pressure rises on its own and exceeds a certain safe value for some reason, the pressure relief valve 312-5 will automatically open to release the pressure.

[0032] like Figure 1 As shown, in an embodiment of the present invention, the pressure reducing device 32 includes a vacuum pump 321, a second air guide pipe 322 and a second adapter 323, wherein one end of the second air guide pipe 322 is connected to the vacuum pump 321, and the other end is connected to the Raman cell 203 through the second adapter 323.

[0033] like Figure 3As shown, in an embodiment of the present invention, the vacuum pump 321 is a liquid ring pump. The working liquid 321-2 within the cylinder fully condenses the vapor generated during the operation of the vacuum pump to ensure the vacuum level. Specifically, the vacuum pump 321 includes a pump cylinder body 321-1, a working liquid 321-2, a pump impeller 321-3, a suction port 321-4, a suction pipe 321-5, an exhaust port 321-6, and an exhaust pipe 321-7. The pump impeller 321-3 is eccentrically mounted within the pump cylinder body 321-1. When the pump impeller 321-3 rotates, it pumps the working liquid 321-2 to a certain height under the action of centrifugal force. When the pump impeller 321-3 rotates 180°, the cavity is connected to the suction port 321-4. When the internal gas pressure is lower than the pressure in the Raman cell, the gas in the Raman cell is drawn into the pump cylinder 321-1 of the vacuum pump 321 through the second gas guide pipe 322, the second adapter 323 and the suction pipe 321-5. When the pump impeller 321-3 continues to rotate, the cavity is connected to the exhaust port 321-6, and the gas is continuously compressed. When the pressure is greater than the exhaust pressure, the gas is discharged from the pump through the exhaust pipe 321-7.

[0034] In an embodiment of the present invention, the pressure detection device 33 includes an electronic pressure gauge 331 and a third adapter 332. The electronic pressure gauge 331 is connected to the Raman cell 203 via the third adapter 332. When the actual pressure in the Raman cell 203 measured by the electronic pressure gauge 331 is lower than the ideal negative pressure condition, the monitoring and control device 34 activates the pressurization device 31, which injects Raman active gas into the Raman cell 203 through the pressure reducing valve 312. When the actual pressure in the Raman cell 203 measured by the electronic pressure gauge 331 is higher than the ideal negative pressure condition, the monitoring and control device 34 activates the pressure reducing device 32, which extracts a portion of the Raman active gas from the Raman cell 203 through the vacuum pump 321.

[0035] In this embodiment, the pressure control unit 3 has high monitoring sensitivity and adjustment flexibility. A high-sensitivity electronic barometer 331 monitors the pressure within the Raman cell 203 in real time. By linking the pressurization device 31 with the depressurization device 32, precise control of the Raman active gas pressure within the negative pressure range can be achieved, facilitating the search for the optimal negative pressure conditions corresponding to each pumping condition and gain medium. Specifically, the pressure control unit 3 needs to precisely control the negative pressure conditions between 0.4 atm and 0.9 atm.

[0036] like Figure 1As shown, in an embodiment of the present invention, the beam-splitting detection unit 4 includes a second Perinbroca prism 401, a third Perinbroca prism 402, a beam-splitting aperture 403, a beam expander 404, and an energy meter 405 arranged sequentially along the laser transmission direction. The second Perinbroca prism 401 and the third Perinbroca prism 402 are used to separate the wavelengths of the laser beam. The beam-splitting aperture 403 can move left and right in a direction perpendicular to the beam propagation direction to filter out anti-Stokes light of each order, so as to realize that the output blue light wavelength is adjustable between 430-495 nm. After the output blue laser is expanded by the beam expander 404, the output light energy is recorded by the energy meter 405.

[0037] Specifically, one or more Raman gain gas media, such as CO2 and ethane, are filled into the Raman cell 203. Further, inert gases such as helium, neon, and argon can be added to the Raman cell 203 as buffer gases to change the partial pressure of the Raman active gas. The pump laser 101 can be a solid-state laser such as a yttrium aluminum garnet (YAG) laser, a ruby ​​laser, or a neodymium glass laser to generate pulsed laser light; the pump light can be ultraviolet, visible, or infrared light; preferably, the present invention uses a frequency-doubled output 532nm pulsed light pump from an Nd:YAG laser, or a frequency-doubled output 515nm pulsed light pump from a Yb:YAG laser. As an optical isolation device, the Perin Broca prism works by deflecting light of a specific wavelength and incident angle by 90° to effectively prevent back-flowing laser light from damaging the laser. Preferably, this solution uses a Perin Broca prism of model Union Optic PPB0122 with Brewster angle designed for 500-600nm.

[0038] Example 1

[0039] The pump source is a Nimma600 Nd:YAG Q-switched pulsed laser with an output spot diameter of 6 mm, a wavelength of 532 nm, a maximum output energy of 350 mJ, and a pulse width of 10 ns. The laser is horizontally linearly polarized. The pump light passes sequentially through a first plane mirror 102, a half-wave plate 103, a polarizing beam splitter 104, a second plane mirror 106, a third plane mirror 107, a fourth plane mirror 108, and a fifth plane mirror 109. After being focused by a 1000 mm focal length focusing lens 201, it passes through a first Perinbrocca prism 202 and enters a 1.8 m long Raman cell 203. When the angle of the half-wave plate 103 is 208°, the maximum total energy of the emitted pump light is approximately 300 mJ. The laser incident window and laser exit window of the Raman cell 203 are uncoated (transmittance is 93.5%), and the interior of the Raman cell 203 is filled with high-purity CO2 gas with a purity of 99.999%. The pressure control unit 3 monitors and adjusts the pressure of the gain gas in the Raman cell 203, controlling it to be within a negative pressure range of 0.55-0.85 atm. When the actual pressure inside the Raman cell 203 measured by the electronic pressure gauge 331 is lower than the ideal negative pressure condition, the monitoring and control device 34 activates the pressure regulating rod 312-4 to fill the Raman cell 204 with Raman active gas; when the actual pressure inside the Raman cell 203 measured by the electronic pressure gauge 331 is higher than the ideal negative pressure condition, the monitoring and control device 34 activates the vacuum pump 321 to extract a portion of the Raman active gas from the Raman cell 203. At the central focal point of the Raman cell 203, CO2 light generated by stimulated Raman scattering (SERS) produces a series of beams: a 436nm third-order anti-Stokes beam, a 464nm second-order anti-Stokes beam, a 495nm first-order anti-Stokes beam, a 532nm residual pump beam, a 574nm first-order Stokes beam, a 624nm second-order Stokes beam, a 683nm third-order Stokes beam, and a 755nm fourth-order Stokes beam. These beams exit through the laser exit window of the Raman cell 203 and are collimated into parallel light by a 1000mm collimating lens 204. The parallel light undergoes wavelength separation by passing through a second Perimbrocca prism 401 and a third Perimbrocca prism 402, and then a beam splitter 403 separates the light into a 495nm blue laser pulse. By moving the beam splitter 403 left and right in a direction perpendicular to the optical path, blue light output at both 436nm and 464nm wavelengths can be achieved. The output blue laser beam is expanded by a 500 mm focal length beam expander lens 404, and the output light energy is recorded by an energy meter 405 (Gentec-EO QE50LP-H-MB-D0).

[0040] Example 2

[0041] The pump source is a passively Q-switched, high-repetition-rate, single-longitudinal-mode micro Yb:YAG laser, model STA-01SH-Yb:YAG-2, with a working wavelength of 1030nm. Its second-harmonic output light at 515nm is used as the pump light, with a maximum average output power of 125mJ, a pulse width of 800ps, and a maximum repetition rate of 25kHz. The laser is horizontally linearly polarized. The pump light passes sequentially through a first plane mirror 102, a half-wave plate 103, a polarizing beam splitter 104, a second plane mirror 106, a third plane mirror 107, a fourth plane mirror 108, and a fifth plane mirror 109. After being focused by a 2000mm focal length focusing lens 201, it passes through a first Perinbrocca prism 202 and enters a 2.3m long Raman cell 203. When the angle of the half-wave plate 103 is 163°, the maximum total energy of the emitted pump light is approximately 108mJ. The Raman cell 203 has a quartz window for laser incidence, coated with a 515nm high-transmittance film (transmittance greater than 96%), and a calcium fluoride window for laser emission, with a transmittance greater than 95% for visible light. The Raman cell 203 is filled with 99.999% pure CO2 gas. The pressure control unit 3 monitors and regulates the pressure of the gain gas in the Raman cell 203, controlling it within a negative pressure range of 0.6 atm to 0.95 atm. When the actual pressure inside the Raman cell 203, as measured by the electronic pressure gauge 331, is lower than the ideal negative pressure condition, the monitoring and control device 34 activates the pressure regulating rod 312-4 to introduce Raman active gas into the Raman cell 203; when the actual pressure inside the Raman cell 203, as measured by the electronic pressure gauge 331, is higher than the ideal negative pressure condition, the monitoring and control device 34 activates the vacuum pump 321 to extract a portion of the Raman active gas from the Raman cell 203. At the central focal point of Raman cell 203, CO2 emitted by stimulated Raman scattering (SERS) produces a 424.1 nm third-order anti-Stokes beam, a 450.6 nm second-order anti-Stokes beam, a 480 nm first-order anti-Stokes beam, a 515 nm residual pump beam, a 554.6 nm first-order Stokes beam, a 601 nm second-order Stokes beam, and a 656 nm third-order Stokes beam. These beams exit through the laser exit window of Raman cell 203 and are collimated into parallel light by a 600 mm focal length collimating lens 204. The parallel light then passes through a second Perimbrocca prism 401 and a third Perimbrocca prism 402, and is separated into a 480 nm blue laser pulse by a beam splitter 403. The output blue laser beam is then expanded by a 500 mm focal length beam expander lens 404 and its energy is recorded by an energy meter 405 (Gentec-EO QE50LP-H-MB-D0).

[0042] Example 3

[0043] The pump source is an Nd:YAG laser (Quantel Brilliant Class-4) with an output spot diameter of 6 mm and a wavelength of 1064 nm. Utilizing its frequency-doubled 532 nm laser, the maximum output energy is 360 mJ, with a pulse width of 6 ns. The laser is vertically linearly polarized. The pump light sequentially passes through a first plane mirror 102, a half-wave plate 103, a polarizing beam splitter 104, a second plane mirror 106, a third plane mirror 107, a fourth plane mirror 108, and a fifth plane mirror 109. After being focused by a 1500 mm focal length focusing lens 201, it passes through a first Perinbrocca prism 202 and enters a 2.3 m long Raman cell 203. When the angle of the half-wave plate 103 is 28°, the maximum total energy of the emitted pump light is approximately 350 mJ. The Raman cell 203 has a quartz window for laser incidence, coated with a 532nm high-transmittance film (transmittance greater than 96.5%), and a calcium fluoride window for laser emission, with a transmittance of over 97% for visible light. The Raman cell 203 is filled with ethane gas. The pressure control unit 3 monitors and adjusts the pressure of the gain gas in the Raman cell 203, controlling it within a negative pressure range of 0.7 atm to 0.85 atm. When the actual pressure inside the Raman cell 203, as measured by the electronic pressure gauge 331, is lower than the ideal negative pressure condition, the monitoring and control device 34 activates the pressure regulating rod 312-4 to introduce Raman active gas into the Raman cell 203; when the actual pressure inside the Raman cell 203, as measured by the electronic pressure gauge 331, is higher than the ideal negative pressure condition, the monitoring and control device 34 activates the vacuum pump 321 to extract a portion of the Raman active gas from the Raman cell 203. At the central focal point of Raman cell 302, ethane's 460nm first-order anti-Stokes light, 515nm residual pump light, 631nm first-order Stokes light, and 776nm second-order Stokes light, generated by stimulated Raman scattering, are emitted from the laser exit window of Raman cell 203 and collimated into parallel light by collimating lens 204 with a focal length of 600mm. The parallel light undergoes wavelength separation by second Perinbrocca prism 401 and third Perinbrocca prism 402, and then a beam splitter 403 separates a blue laser pulse with a wavelength of 480nm. The output blue laser is expanded by beam expander lens 404 with a focal length of 500mm, and the output light energy is recorded by energy meter 405 (Gentec-EO QE50LP-H-MB-D0).

[0044] like Figure 4 As shown in the embodiments of the present invention, under different pump energies, the air pressure is controlled by the air pressure regulation unit 3, and the obtained curves of the anti-Stokes blue laser energy conversion efficiency versus air pressure are sufficient to prove that the scheme proposed in this invention can achieve high conversion efficiency blue light output under negative pressure conditions.

[0045] This invention provides a device for generating high-conversion-efficiency blue laser under negative pressure conditions. The laser output from the laser pump unit propagates through a free space and then enters the Raman frequency conversion unit. At the focal point of the Raman cell, it undergoes stimulated Raman scattering to generate multi-wavelength laser pulses, including Stokes light, anti-Stokes light, and residual pump light. The wavelength-selectable blue laser can be separated from the output light pulses by a beam splitting detection unit. The specific negative pressure conditions are controlled by a gas pressure control unit by increasing or decreasing the amount of gain gas in the Raman cell.

[0046] This invention employs a free-space system, effectively circumventing the limitations of optical fiber on output power. Under negative pressure conditions, it utilizes stimulated Raman scattering of anti-Stokes light to generate a high-conversion-efficiency blue laser. By adjusting the gas pressure and optimizing the focusing parameters and pump energy, the energy conversion efficiency of the anti-Stokes light is greatly improved. This enables the output of blue pulsed lasers with pulse widths ranging from several nanoseconds to tens of nanoseconds, single-pulse energies ranging from tens of millijoules to hundreds of millijoules, peak power of tens of megawatts, and energy conversion efficiency exceeding 10%.

[0047] The above description is merely an embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, extensions, etc., made within the spirit and principles of the present invention are included within the scope of protection of the present invention.

Claims

1. A device for generating high-conversion-efficiency blue laser under negative pressure conditions, characterized in that, It includes a laser pumping unit (1), a Raman frequency conversion unit (2), a gas pressure control unit (3), and a beam-splitting detection unit (4) arranged sequentially along the laser transmission direction; among which, The laser pumping unit (1) is used to output laser light. The output laser light propagates through a free space optical path and then enters the Raman frequency conversion unit (2). Raman frequency conversion unit (2) generates and outputs multi-wavelength laser pulses through stimulated Raman scattering under negative pressure conditions; The air pressure regulation unit (3) is used to control the negative pressure condition of the Raman frequency converter unit (2); The spectrophotometer (4) is used to separate a wavelength-selectable blue laser from the multi-wavelength laser pulses output by the Raman frequency conversion unit (2); The Raman frequency conversion unit (2) includes a focusing lens (201), a first Perinbroca prism (202), a Raman cell (203), and a collimating lens (204) arranged sequentially along the laser transmission direction. The Raman cell (203) is a hollow sealed chamber with a laser incident window and a laser exit window at both ends. The interior of the hollow sealed chamber is filled with Raman active gas. After the incident pulse laser is focused by the focusing lens (201), it passes through the first Perinbroca prism (202) and enters the Raman cell (203). In the Raman cell (203), a stimulated Raman scattering process is performed to generate multi-wavelength laser pulses including Stokes light, anti-Stokes light, and residual pump light. The multi-wavelength laser pulses are collimated by the collimating lens (204) and then enter the beam splitting detection unit (4). The beam splitting detection unit (4) includes a second Perinbroca prism (401), a third Perinbroca prism (402), a beam splitter (403), a beam expander (404), and an energy meter (405) arranged sequentially along the laser transmission direction. The second Perinbroca prism (401) and the third Perinbroca prism (402) are used to separate the wavelengths of the laser beam. The beam splitter (403) can move left and right in the direction perpendicular to the beam propagation to filter out anti-Stokes light of each order, thereby achieving adjustable output blue light wavelength. After the output blue laser is expanded by the beam expander (404), the output light energy is recorded by the energy meter (405).

2. The device for generating high-conversion-efficiency blue laser under negative pressure conditions according to claim 1, characterized in that, The laser pumping unit (1) includes a pump laser (101), a half-wave plate (103), a polarizing beam splitter (104), a laser beam collector (105), and a plane mirror group for forming a free-space optical path. The pump laser (101), half-wave plate (103), and polarizing beam splitter (104) are arranged sequentially along the laser transmission direction. A laser beam collector (105) is provided on one side of the polarizing beam splitter (104). The combination of the half-wave plate (103) and the polarizing beam splitter (104) realizes the continuous adjustment of the laser energy entering the Raman frequency conversion unit (2). The plane mirror group is set on the laser transmission path to ensure the effective propagation length of the optical path.

3. The device for generating high-conversion-efficiency blue laser under negative pressure conditions according to claim 2, characterized in that, The planar reflector group includes a first planar reflector (102), a second planar reflector (106), a third planar reflector (107), a fourth planar reflector (108), and a fifth planar reflector (109). The first planar reflector (102) is disposed between the pump laser (101) and the half-wave plate (103) to reflect the laser output from the pump laser (101) onto the half-wave plate (103). The second planar reflector (106), the third planar reflector (107), the fourth planar reflector (108), and the fifth planar reflector (109) are arranged sequentially along the laser transmission direction on the rear side of the polarizing beam splitter (104).

4. The device for generating high-conversion-efficiency blue laser under negative pressure conditions according to claim 1, characterized in that, The laser incident window of the Raman cell (203) is a quartz window; the laser exit window of the Raman cell (203) is a calcium fluoride window.

5. The device for generating high-conversion-efficiency blue laser under negative pressure conditions according to claim 1, characterized in that, The pressure control unit (3) includes a pressurizing device (31), a depressurizing device (32), a pressure detection device (33), and a monitoring and control device (34). The pressurizing device (31), the depressurizing device (32), and the pressure detection device (33) are all connected to the Raman cell (203). The pressure detection device (33) is used to detect the pressure in the Raman cell (203). The pressurizing device (31) and the depressurizing device (32) are controlled by the monitoring and control device (34). When the actual gas pressure in the Raman cell (203) measured by the gas pressure detection device (33) is lower than the ideal negative pressure condition, the monitoring and control device (34) starts the pressurization device (31) to fill the Raman cell (203) with Raman active gas; when the actual gas pressure in the Raman cell (203) measured by the gas pressure detection device (33) is higher than the ideal negative pressure condition, the monitoring and control device (34) starts the depressurization device (32) to extract part of the Raman active gas from the Raman cell (203).

6. The apparatus for generating high-conversion-efficiency blue laser under negative pressure conditions according to claim 5, characterized in that, The pressurization device (31) includes a high-pressure gas cylinder (311), a pressure reducing valve (312), a first gas guide pipe (313), and a first adapter (314). The high-pressure gas cylinder (311) is filled with Raman active gas. One end of the first gas guide pipe (313) is connected to the high-pressure gas cylinder (311), and the other end is connected to the Raman cell (203) through the first adapter (314). The pressure reducing valve (312) is installed on the first gas guide pipe (313).

7. The apparatus for generating high-conversion-efficiency blue laser under negative pressure conditions according to claim 6, characterized in that, The pressure reducing valve (312) includes a valve body, an inlet connector (312-1), an inlet pressure display gauge (312-2), an outlet pressure display gauge (312-3), a pressure regulating rod (312-4), a pressure relief valve (312-5), and an outlet connector (312-6). The inlet connector (312-1) and the outlet connector (312-6) are located at both ends of the valve body. The inlet pressure display gauge (312-2) is located at the inlet end of the valve body. The outlet pressure display gauge (312-3), the pressure regulating rod (312-4), and the pressure relief valve (312-5) are located at the outlet end of the valve body. The reading of the inlet pressure display (312-2) is the pressure of the gas stored in the high-pressure gas cylinder (311), and the pressure shown by the outlet pressure display (312-3) is controlled by the pressure regulating rod (312-4).

8. The apparatus for generating high-conversion-efficiency blue laser under negative pressure conditions according to claim 5, characterized in that, The pressure reducing device (32) includes a vacuum pump (321), a second air guide pipe (322) and a second adapter (323), wherein one end of the second air guide pipe (322) is connected to the vacuum pump (321) and the other end is connected to the Raman cell (203) through the second adapter (323).

Images