A partitioned laminar gas stimulated Raman scattering frequency conversion device

Abstract

This invention belongs to the field of Raman laser technology and relates to a stimulated Raman scattering frequency conversion device for partitioned laminar gas. It includes a sealed gas circulation pipe shell, airflow stratification baffles, a first optical window, and a second optical window. The upper end of the sealed gas circulation pipe shell is an airflow inlet, and the lower end is an airflow outlet. The first and second optical windows are respectively arranged parallel to each other on the left and right sides of the sealed gas circulation pipe shell. A set of airflow stratification baffles is arranged inside the sealed gas circulation pipe shell, dividing the interior of the sealed gas circulation pipe shell into multiple parallel and relatively independent small pipes. This invention maintains a good laminar flow state in the light-transmitting section of the Raman medium circulation pipe, ensuring effective heat dissipation while reducing optical path deflection and distortion of the pump laser and Raman laser caused by airflow inhomogeneity or turbulence. This stimulated Raman frequency conversion device can be used for Raman frequency conversion of high-power or high-repetition-rate lasers.

Description

Technical Field

[0001] This invention belongs to the field of Raman laser technology, and more specifically, relates to a partitioned laminar gas stimulated Raman scattering frequency conversion device, which utilizes a gas Raman medium flowing laminarly in a closed Raman device to stably generate Raman laser at a high repetition frequency. Background Technology

[0002] Stimulated Raman scattering (SRS) is a common laser frequency conversion method. Its advantages lie in its simple device design, convenient debugging, and the variety of selectable SRS media. Different Raman media produce different spectral shifts in the pump laser; for example, solids can produce shifts of tens of wavenumbers, while gaseous Raman media can produce shifts of thousands of wavenumbers. Therefore, Raman frequency conversion offers a wide range of conversions and a rich variety of variable wavelengths. Currently, commonly used Raman media include crystals (e.g., diamond, SrWO4), liquids (e.g., H2O, CS2, C6H6), and gases (e.g., H2, CH4). Among these, gaseous Raman media produce large SRS frequency shifts and have low damage thresholds, making them suitable for wavelength conversion in high-power lasers, and thus have found wide application in various fields.

[0003] In Raman frequency conversion devices using a gas medium, the thermal effect generated at the laser focusing position can diffuse with the movement of gas molecules, thus maintaining the stability of the Raman frequency conversion device within a certain repetition frequency range. However, when the heat generated during stimulated Raman conversion is excessive or the laser repetition frequency is high, the heat generated at the laser focusing position may not diffuse away in time, leading to adverse consequences such as decreased Raman conversion efficiency, beam drift, or thermal distortion. These issues include non-uniform gas density within the Raman cell due to thermal effects (e.g., thermal lensing effect) or localized turbulence caused by disordered gas molecule flow due to temperature variations. This limits the operation of stimulated Raman scattering frequency conversion devices to lower repetition frequencies or makes them unsuitable for Raman frequency conversion with higher power lasers.

[0004] To address this issue, existing technologies employ a method of heat dissipation through the flow of the Raman medium. However, considering the influence of the flowing medium on beam propagation, a laminar flow field is required to reduce or even eliminate the deterioration of beam quality caused by the fluid (such as optical distortion and jitter). Gas-stimulated Raman converters typically use Raman tubes, and the laser beam generally propagates along the axial direction of the Raman tube. When the airflow also flows axially, there is a long interaction zone between the laser and the flow field, which can easily lead to beam distortion due to non-uniform flow field. In contrast, the crossflow mode, where the laser beam and the airflow direction intersect, effectively reduces the impact of such effects due to the shorter interaction zone between the laser beam and the flow field. However, the crossflow mode generally has a larger cavity volume, and to meet the laminar flow condition, the airflow velocity needs to be significantly reduced, thus reducing the heat transfer capacity. Summary of the Invention

[0005] To address the aforementioned technical problems, this invention proposes a stimulated Raman scattering frequency conversion device based on a partitioned cross-flow gas circulating Raman cell. By setting up airflow stratification baffles and optical windows, the portion of the Raman medium through which the laser passes maintains a good laminar flow state, generating little or no turbulence. This ensures effective heat dissipation while allowing the pump laser and Raman laser to pass through the laminar gas region, reducing optical path deflection and distortion caused by airflow inhomogeneity or turbulence. This enables the stimulated Raman frequency conversion device to be used for Raman frequency conversion of high-power, high-repetition-rate lasers. This invention improves the frequency conversion effect and stability of Raman frequency conversion devices in the field of high-power lasers, expanding the application range of stimulated Raman scattering frequency conversion technology.

[0006] To achieve the above objectives, the technical solution of the present invention is as follows:

[0007] This invention provides a zoned crossflow gas stimulated Raman scattering frequency conversion device, the device comprising a sealed gas circulation pipeline shell, an airflow stratification baffle, a first optical window, and a second optical window; the upper end of the sealed gas circulation pipeline shell is an airflow inlet, and the lower end is an airflow outlet; the first optical window and the second optical window are respectively arranged parallel to each other on the left and right sides of the sealed gas circulation pipeline shell, and a set of airflow stratification baffles is arranged inside the sealed gas circulation pipeline shell; the airflow stratification baffles divide the sealed gas circulation pipeline shell into multiple parallel and relatively independent sets of small pipelines; the portion of the airflow stratification baffle parallel to the first optical window and the second optical window is a transparent optical window.

[0008] Both the first and second optical windows are planar optical windows coated with pump laser and Raman laser antireflection coatings.

[0009] The thickness of the airflow stratification baffle is <3mm, which divides the pipeline into multiple small pipelines. The inner walls of each group of small pipelines are smooth and free of burrs or protrusions to maintain a uniform internal gas flow field.

[0010] Another aspect of the present invention provides a method of using the above-described stimulated Raman scattering frequency conversion device, comprising the following steps:

[0011] (1) Gas is filled into the stimulated Raman scattering frequency converter, and the gas is controlled to flow from top to bottom. After passing through the airflow stratification baffle, the gas enters each small pipe, so that the gas flow in the small pipe is laminar, and then it is output from each small pipe.

[0012] (2) The angle between the center line of the pump laser beam and the normals of the first and second optical windows is α, where α is the Brewster angle; the Raman laser generated by the pump laser in the high-pressure Raman medium is transmitted coaxially with the pump laser.

[0013] The airflow velocity v in the small pipe is related to the width d of the small pipe, and the Reynolds number Re = ρvd / μ < 3000. Further preferred, the Reynolds number of the airflow in the small pipe is Re = ρvd / μ < 2500, where ρ is the gas density and μ is the gas viscosity.

[0014] The pump laser is p-polarized light.

[0015] In step (1), the airflow is driven by an axial flow fan and an air pump to flow in the pipeline.

[0016] The beneficial effects of this invention are as follows:

[0017] This invention utilizes a layered baffle with optical windows to divide a sealed gas circulation pipeline into multiple small gas circulation pipelines, ensuring that the light-transmitting section in the Raman medium circulation pipeline maintains a good laminar flow state. The linearly polarized pump laser beam passes through each optical window at Brewster's angle, reducing interface loss. While ensuring effective heat dissipation, it also reduces optical path deflection and distortion of the pump laser and Raman laser caused by uneven airflow or turbulence, enabling this stimulated Raman frequency conversion device to be used for Raman frequency conversion of high-power or high repetition frequency lasers.

[0018] This invention reduces the impact of thermal effects on stimulated Raman conversion efficiency while also ensuring the uniformity of the flow field, thereby minimizing beam quality degradation caused by flow field inhomogeneity and improving stimulated Raman conversion efficiency and beam quality.

[0019] This invention improves the frequency conversion effect and stability of Raman frequency conversion devices in the field of high-power lasers, and expands the application scope of stimulated Raman scattering frequency conversion technology. Attached Figure Description

[0020] Appendix Figure 1 This is a schematic diagram of the structure of a flow gas stimulated Raman scattering frequency conversion device according to the present invention;

[0021] Among them: 1. Sealed gas circulation pipeline shell, 2. Airflow stratification baffle, 3-1. First optical window, 3-2. Second optical window. Detailed Implementation

[0022] To make the objectives, technical solutions, and advantages of this invention clearer, the following description is provided in conjunction with the appendix. Figure 1 The invention will be further described in detail below with reference to embodiments. To address the problems of optical distortion or reduced conversion efficiency during high-repetition-rate stimulated Raman scattering, this invention designs a circulating gas stimulated Raman scattering frequency converter that utilizes a circulating airflow for heat dissipation. Through appropriate design, the light-transmitting section in the pipeline maintains a good laminar flow state, ensuring effective heat dissipation while reducing optical path deflection and distortion of the pump laser and Raman laser caused by uneven or turbulent airflow. Several embodiments are briefly described below:

[0023] A frequency conversion device for stimulated Raman scattering of cross-flow gas in partitioned sections, such as Figure 1 As shown, the system includes a sealed gas circulation pipeline housing 1, an airflow stratification baffle 2, a first optical window 3-1, and a second optical window 3-2. The upper end of the sealed gas circulation pipeline housing 1 is an airflow inlet, and the lower end is an airflow outlet. The first optical window 3-1 and the second optical window 3-2 are respectively arranged parallel to each other on the left and right sides of the sealed gas circulation pipeline housing 1. A set of airflow stratification baffles 2 is installed inside the sealed gas circulation pipeline housing 1. The airflow stratification baffles 2 divide the sealed gas circulation pipeline housing 1 into multiple parallel and relatively independent small pipelines. The part of the airflow stratification baffles 2 parallel to the first optical window 3-1 and the second optical window 3-2 is a transparent optical window.

[0024] Both the first optical window 3-1 and the second optical window 3-2 are planar optical windows coated with pump laser and Raman laser antireflection coatings.

[0025] The thickness of the airflow stratification baffle 2 is <3mm, which divides the pipeline into multiple small pipelines. The inner walls of each group of small pipelines are smooth without burrs or protrusions to maintain a uniform internal gas flow field.

[0026] Example 1: Stimulated Raman Scattering Frequency Conversion Device Based on Flowing CO2 Gas:

[0027] The specific method is as follows: CO2 gas with a pressure of 10 atm is introduced into the partitioned cross-flow gas stimulated Raman scattering frequency converter. The fan is controlled to drive the high-pressure CO2 gas to flow from top to bottom. After passing through the airflow stratification baffle area, the airflow enters each small pipe and is then output from each small pipe. It returns to the airflow drive section through the high-pressure hose. The gas flow rate is controlled by controlling the fan speed to adapt to different heat dissipation requirements.

[0028] An electro-optically Q-switched Nd:YAG pulsed laser is used as the pump laser source, with an output wavelength of 1064 nm, a pulse width of 10 ns, a single pulse energy of 1 J, and an adjustable operating repetition frequency up to 20 Hz. The 1064 nm pulsed laser is input into the stimulated Raman scattering frequency converter through the first optical window 3-1, and then sequentially passes through the first optical window 3-1, the optical window of the airflow stratification baffle 2, and the second optical window 3-2 before being output. The angle between the centerline of the pump laser beam and the normals of the first optical window 3-1 and the second optical window 3-2 is α, where α is 57 degrees.

[0029] When the fan is not operating, the high-pressure CO2 gas inside the stimulated Raman scattering (SRS) frequency converter does not flow. At a laser repetition frequency of 1 Hz, the SRS operates stably, with no decrease in laser Raman conversion efficiency over time, and the output Raman laser beam exhibits no jitter or distortion. At a laser repetition frequency of 2 Hz, the SRS operates stably, with no decrease in laser Raman conversion efficiency over time, but the output Raman laser beam shows slight jitter and distortion. At a laser repetition frequency of 4 Hz, the laser Raman conversion efficiency decreases over time, the output Raman laser beam exhibits significant jitter, and the stimulated Raman laser spot also shows significant distortion. When the laser repetition frequency increases further, the stimulated Raman laser severely degrades or even becomes inoperable within seconds.

[0030] When the fan starts working, the airflow in each small pipe is always in a flowing state, which can promptly remove the heat generated by the stimulated Raman effect. Therefore, the repetition frequency of the stimulated Raman scattering device can be significantly improved for stable operation. For example, when the wind speed is 5 m / s and the laser repetition frequency is 5 Hz, the laser Raman conversion efficiency does not decrease with time, and the output Raman laser beam has no jitter or deformation. When the laser repetition frequency is 10 Hz, the laser Raman conversion efficiency does not decrease with time, but the output Raman laser beam shows slight jitter and deformation. When the wind speed is 12 m / s and the laser repetition frequency is 10 Hz, the laser Raman conversion efficiency does not decrease with time, and the output Raman laser beam has no jitter or deformation. When the laser repetition frequency is 20 Hz, the laser Raman conversion efficiency does not decrease with time, but the output Raman laser beam shows slight jitter and deformation.

[0031] Example 2, Stimulated Raman Scattering Frequency Conversion Device Based on Flowing N2 Gas:

[0032] The specific method is as follows: N2 gas with a pressure of 30 atm is filled into the partitioned cross-flow gas stimulated Raman scattering frequency converter. The fan is controlled to drive the high-pressure N2 gas to flow from top to bottom. After passing through the baffle area, the gas flow enters each small pipe and then exits from each small pipe through the high-pressure hose and returns to the gas flow drive section. The gas flow rate is controlled by controlling the speed of the fan to adapt to different heat dissipation requirements.

[0033] An electro-optically Q-switched Nd:YAG pulsed laser is used as the pump laser source, with an output wavelength of 1064 nm, a pulse width of 10 ns, a single pulse energy of 1 J, and an adjustable laser repetition frequency up to 20 Hz. The 1064 nm pulsed laser is input into the stimulated Raman scattering frequency converter through the first optical window 3-1, and then sequentially passes through the first optical window 3-1, the airflow stratification baffle 2, and the second optical window 3-2 before being output. The angle between the centerline of the pump laser beam and the normals of the first optical window 3-1 and the second optical window 3-2 is α, where α is 56 degrees. All optical windows used are JGS1 quartz.

[0034] When the fan is not operating, the high-pressure N2 gas inside the stimulated Raman scattering (SRS) frequency converter does not flow. At a laser repetition frequency of 1 Hz, the SRS operates stably, with no decrease in laser Raman conversion efficiency over time, and the output Raman laser beam exhibits no jitter or distortion. At a laser repetition frequency of 2 Hz, the SRS operates stably, with no decrease in laser Raman conversion efficiency over time, but the output Raman laser beam shows slight jitter and distortion. At a laser repetition frequency of 5 Hz, the laser Raman conversion efficiency decreases over time, the output Raman laser beam exhibits significant jitter, and the stimulated Raman laser spot also shows significant distortion. When the laser repetition frequency increases further, the stimulated Raman laser severely degrades or even becomes inoperable within seconds.

[0035] When the fan starts working, the airflow in each small pipe is always in a flowing state, which can promptly remove the heat generated by the stimulated Raman effect. Therefore, the repetition frequency of the stimulated Raman scattering device can be significantly improved for stable operation. For example, when the wind speed is 6 m / s and the laser repetition frequency is 5 Hz, the laser Raman conversion efficiency does not decrease with time, and the output Raman laser beam has no jitter or deformation. When the laser repetition frequency is 10 Hz, the laser Raman conversion efficiency does not decrease with time, but the output Raman laser beam shows slight jitter and deformation. When the wind speed is 12 m / s and the laser repetition frequency is 10 Hz, the laser Raman conversion efficiency does not decrease with time, and the output Raman laser beam has no jitter or deformation. When the laser repetition frequency is 30 Hz, the laser Raman conversion efficiency does not decrease with time, but the output Raman laser beam shows slight jitter and deformation.

Claims

1. A frequency conversion device for stimulated Raman scattering of cross-flow gas in a partitioned configuration, characterized in that, The system includes a sealed gas circulation pipeline housing (1), an airflow stratification baffle (2), a first optical window (3-1), and a second optical window (3-2). The upper end of the sealed gas circulation pipeline housing (1) is the airflow inlet, and the lower end is the airflow outlet. The first optical window (3-1) and the second optical window (3-2) are arranged parallel to each other on the left and right sides of the sealed gas circulation pipeline housing (1). A set of airflow stratification baffles (2) is arranged inside the sealed gas circulation pipeline housing (1). The airflow stratification baffles (2) divide the sealed gas circulation pipeline housing (1) into multiple parallel and relatively independent small pipelines. The part of the airflow stratification baffles (2) that is parallel to the first optical window (3-1) and the second optical window (3-2) is a transparent optical window, so that the light transmission section in the Raman medium circulation pipeline remains in a laminar flow state, and the linearly polarized pump laser beam passes through each optical window at Brewster angle.

2. The stimulated Raman scattering frequency conversion device according to claim 1, characterized in that, The first optical window (3-1) and the second optical window (3-2) are both planar optical windows coated with pump laser and Raman laser antireflection coatings.

3. The stimulated Raman scattering frequency conversion device according to claim 1, characterized in that, The thickness of the airflow stratification baffle (2) is <3mm.

4. A method of using the stimulated Raman scattering frequency conversion device according to any one of claims 1-3, characterized in that, Includes the following steps: (1) Gas is filled into the stimulated Raman scattering frequency converter and the gas is controlled to flow from top to bottom. After passing through the airflow stratification baffle (2), the gas flows into each small pipe, so that the gas flow in the small pipe is laminar and then outputs from each small pipe. (2) The angle between the center line of the pump laser beam and the normals of the first and second optical windows is α, where α is the Brewster angle; the Raman laser generated by the pump laser in the high-pressure Raman medium is transmitted coaxially with the pump laser.

5. The method of use according to claim 4, characterized in that, The airflow velocity v in the small pipe is related to the pipe width d, and the Reynolds number Re = ρvd / µ < 3000, where ρ is the gas density and µ is the gas viscosity.

6. The method of use according to claim 5, characterized in that, The Reynolds number Re = ρvd / µ < 2500 for the airflow in the small pipe, where ρ is the gas density and µ is the gas viscosity.

7. The method of use according to claim 4, characterized in that, The pump laser is p-polarized light.

8. The method of use according to claim 4, characterized in that, In step (1), the airflow is driven to flow in the pipeline by an axial flow fan or an air pump.

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