Herriot type multi-pass cell anti-stokes raman high peak power blue laser

Abstract

The application belongs to the field of Raman laser, and particularly relates to a Herriot type multi-pass cell anti-Stokes Raman high peak power blue laser, which comprises a pumping laser, a plano-convex lens A, a Raman cell, a plano-convex lens B and a 45-degree angle dichroic mirror, the pumping laser is a Nd:YAG pulse solid laser, a 532nm pulse laser is used to pump a mixed gas of H2 and inert gas in the Raman cell, three times of focusing are carried out in the Raman cell, and finally a first order anti-Stokes Raman blue laser is output, the conversion efficiency of the first order anti-Stokes Raman blue laser can reach 10-15%, the pulse energy can be more than 50mJ, and the peak power reaches 10MW level. The application has the advantages of simple Raman laser structure, convenient and fast installation and adjustment, and provides a blue laser for generating high peak power blue laser with high cost performance, especially for the blue laser which is difficult to generate by a conventional method.

Description

Technical Field

[0001] This invention belongs to the field of Raman lasers, specifically a Herriot-type multi-pass cell anti-Stokes Raman high peak power blue laser. Background Technology

[0002] Lasers, due to their inherent advantages such as high coherence and monochromaticity, are widely used in numerous fields including industry, national defense, and medicine. However, existing lasers cannot meet the diverse wavelength requirements of various industries, thus necessitating the development of laser wavelength conversion. Stimulated Raman scattering of gas possesses characteristics such as a high damage threshold, large Raman frequency shift, and high conversion efficiency. Furthermore, it can achieve longer wavelength laser outputs than pump lasers using Stokes Raman lasers and shorter wavelength laser outputs than pump lasers using anti-Stokes Raman lasers. Therefore, Raman lasers are an important frequency conversion method.

[0003] Blue lasers possess characteristics such as low attenuation coefficient, short wavelength, and small spot area, making them widely used in underwater communication and detection, high-density information storage, and laser medicine. However, compared to other wavelengths (such as green light), the performance of blue lasers still lags significantly behind the requirements of scientific research and market applications; this gap is particularly pronounced in pulse energy and peak power. Therefore, to meet the demands of these fields, there is an urgent need to develop a high-peak-power, cost-effective Raman blue laser, which holds great promise for future development. Summary of the Invention

[0004] To meet the demand for blue lasers in many fields, the present invention aims to provide a Herriot-type multi-pass cell anti-Stokes Raman high peak power blue laser.

[0005] The objective of this invention is achieved through the following technical solution:

[0006] This invention includes a pump laser and a plano-convex lens A, a Raman cell, a plano-convex lens B, and a 45° dichroic mirror arranged sequentially in the direction of the pump laser output. The Raman cell has a window A at one end near the plano-convex lens A and a window B at the other end near the plano-convex lens B. Concave reflectors for transmitting and focusing the laser are located at both ends of the Raman cell along its length. The Raman cell is filled with a Raman gas medium, which is a mixture of H2 and an inert gas. The pump laser emitted by the pump laser enters the Raman cell through window A at one end of the Raman cell via the plano-convex lens A. The plano-convex lens A focuses the pump laser to a central point within the Raman cell space, and then it continues to propagate, passing through the concave reflectors within the Raman cell. After reflection by the mirror, the pump laser is output from window B at the other end of the Raman cell. The pump laser is refracted and transmitted multiple times within the Raman cell to extend the interaction length between the pump laser and the Raman gas medium, achieving a transmission distance of three times the length of the Raman cell. The pump laser is focused three times within the Raman cell, with each focal point located at the spatial center along the length of the Raman cell, and none of the focal points coincide in space. During laser transmission, the pump laser output from the pump laser interacts with the Raman gas medium within the Raman cell, generating a first-order Stokes Raman laser and a first-order anti-Stokes Raman laser. The laser emitted from the Raman cell is collimated by the plano-convex lens B and finally split by the 45° dichroic mirror to output a 436 nm blue laser.

[0007] Wherein: There are two concave mirrors in the Raman cell, namely concave mirror A and concave mirror B. Concave mirror B is located at one end of the Raman cell near window A, and concave mirror A is located at the other end of the Raman cell near window B. The pump laser injected from window A first irradiates concave mirror A, and is reflected by concave mirror A to concave mirror B, and then reflected by concave mirror B before being output from window B.

[0008] The concave mirrors A and B are simultaneously coated with a film system that highly reflects the pump laser wavelength, the first-order Stokes Raman laser wavelength, and the first-order anti-Stokes Raman laser wavelength while highly transmitting the second-order Stokes Raman laser wavelength. The second-order Stokes Raman laser transmitted through the concave mirrors A and B is absorbed by the inner wall of the Raman cell. The concave mirrors A and B have the same radius of curvature, which is equal to 0.43 to 0.46 times the length of the Raman cell.

[0009] The inert gas is He or Ar. The Raman cell is first filled with H2, and the pressure of H2 is adjusted within the range of 0.5 to 1.5 atmospheres so that the Raman laser does not output second-order Stokes Raman laser. Then He or Ar is filled in, and the pressure of He or Ar is adjusted within the range of 0.5 to 2.5 atmospheres until the output blue light pulse energy reaches its maximum.

[0010] The plano-convex lens A is coated with a film system that has high transmission of pump laser wavelength, and the focal length f of the plano-convex lens A is equal to 0.53 to 0.55 times the length of the Raman cell.

[0011] Window A is coated with a film system that has high transmission of pump laser wavelength, while window B is coated with a film system that has high transmission of pump laser wavelength, first-order Stokes Raman laser wavelength and first-order anti-Stokes Raman laser wavelength.

[0012] The plano-convex lens A is a long focal length lens with its focal point located at 1 / 2 of the spatial position along the length of the Raman cell; the plano-convex lens B is a long focal length lens coated with a multi-wavelength high-transmittance film, which shapes the diverging laser beam into a parallel laser beam; the plano-convex lens B is simultaneously coated with a film system that has high transmittance for the pump laser wavelength, the first-order Stokes Raman laser wavelength, and the first-order anti-Stokes Raman laser wavelength.

[0013] The 45° angle dichroic mirror is coated with a film system that simultaneously reflects the pump laser wavelength and the first-order Stokes Raman laser wavelength with high reflectivity, while simultaneously transmitting the first-order anti-Stokes Raman laser wavelength with high transmittance.

[0014] The Raman cell adopts a Herriot-type multi-pass cell structure, the length of the Raman cell is in the range of 1.5 to 3m, and the wall thickness of the cell meets the pressure bearing conditions of the Raman gas medium.

[0015] The advantages and positive effects of this invention are as follows:

[0016] This invention is a device for laser wavelength conversion by generating anti-Stokes Raman laser through stimulated Raman scattering of gas, and provides a blue laser that generates high peak power blue laser at a high cost-performance ratio. The invention has a compact structure, is easy and quick to install and debug, and is relatively inexpensive. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of the overall structure of the present invention;

[0018] Wherein: 1 is the pump laser, 2 is the plano-convex lens A, 3 is the Raman cell, 4-1 is the window A, 4-2 is the concave mirror A, 4-3 is the concave mirror B, 4-4 is the window B, 5 is the plano-convex lens B, and 6 is the 45° angle dichroic mirror. Detailed Implementation

[0019] The invention will now be described in further detail with reference to the accompanying drawings.

[0020] This invention relates to a blue laser device that utilizes stimulated Raman scattering (SRS) of a gas to achieve laser frequency conversion. Through SRS, a first-order Stokes Raman laser and a first-order anti-Stokes Raman laser are generated within a Raman cell 3. After collimation by a plano-convex lens B5 and beam splitting by a 45° angle dichroic mirror 6, a blue laser with a wavelength of 436 nanometers is finally output. A key feature of this invention is the use of a Herriot-type multi-pass cell structure. To improve the conversion efficiency of the 436-nanometer blue laser, three focusing operations are performed within the Raman cell 3. By adjusting the pressure conditions of the Raman gas medium within the Raman cell 3, the conversion efficiency of the output blue laser reaches 10–15%, with a pulse energy greater than 50 mJ and a peak power on the order of 10 MW. The specific structure is as follows:

[0021] like Figure 1 As shown, the present invention includes a pump laser 1, a plano-convex lens A2, a Raman cell 3, a plano-convex lens B5, and a 45° angle dichroic mirror 6. The plano-convex lens A2, the Raman cell 3, the plano-convex lens B5, and the 45° angle dichroic mirror 6 are arranged sequentially in the direction of the output laser of the pump laser 1. The Raman cell 3 has a window A4-1 at one end near the plano-convex lens A2 and a window B4-4 at the other end near the plano-convex lens B5. Both ends of the Raman cell 3 in the length direction are provided with concave reflectors that serve to transmit and focus the laser. The Raman cell 3 is filled with a Raman gas medium.

[0022] Pump laser 1 is a pulsed laser. The pump laser emitted by pump laser 1 enters Raman cell 3 through window A4-1 at one end of Raman cell 3 via plano-convex lens A2. The plano-convex lens A2 focuses the pump laser to a central point within Raman cell 3, and then it continues to propagate. After being reflected by a concave mirror within Raman cell 3, it is output through window B4-4 at the other end of Raman cell 3. The pump laser refracts and propagates multiple times within Raman cell 3 to extend the interaction length between the pump laser and the Raman gas medium, achieving a transmission distance three times the length of the Raman cell. The laser is focused three times within the Raman cell 3, with each focal point located at the spatial center along the length of the Raman cell 3, and none of the focal points coincide in space. During laser transmission, the pump laser output from the pump laser 1 interacts with the Raman gas medium within the Raman cell 3, consuming the energy of the pump laser and generating a first-order Stokes Raman laser and a first-order anti-Stokes Raman laser. The first-order anti-Stokes Raman laser emitted from the Raman cell 3 is collimated by the plano-convex lens B5 and finally split by the 45° angle dichroic mirror 6 to output a 436 nm blue laser.

[0023] The plano-convex lens A2 is a long focal length lens with a focal length f equal to 0.53 to 0.55 times the length of the Raman cell 3. The plano-convex lens A2 plays the role of focusing the laser beam, with the focal point located at the spatial center of the Raman cell 3. The plano-convex lens A2 is coated with a film system that has high transmission (T > 99.5%) of the pump laser wavelength.

[0024] Raman cell 3 is a closed hollow cavity. Coated windows A4-1 and B4-4 are installed at both ends of Raman cell 3. Raman cell 3 can withstand Raman gas media up to 1 MPa. It is filled with a mixture of H2 and inert gas (volume ratio 1:1). The inert gas can be He or Ar. By changing the pressure of the gas medium inside Raman cell 3, the conversion efficiency of the first-order anti-Stokes Raman laser can be optimized. At the same time, concave mirrors A4-2 and B4-3 are installed inside Raman cell 3. The concave mirrors play the role of laser transmission and focusing, extending the interaction distance between the pump laser and the Raman gas medium, and increasing the conversion efficiency of Raman laser near the focal point.

[0025] The laser-injected window A4-1 at one end of the Raman cell 3 is coated with a film system that has high transmission (T>99.5%) of the pump laser wavelength, while the laser-out window B4-4 is coated with a film system that has high transmission (T>99.5%) of the pump laser wavelength, the first-order Stokes Raman laser wavelength, and the first-order anti-Stokes Raman laser wavelength.

[0026] Concave mirror B4-3 is located inside Raman cell 3 near window A4-1, and concave mirror A4-2 is located inside Raman cell 3 near window B4-4. Pump laser entering through window A4-1 first irradiates concave mirror A4-2, and is reflected by concave mirror A4-2 to concave mirror B4-3, and then reflected by concave mirror B4-3 before being output through window B4-4. Concave mirrors A4-2 and B4-3 are simultaneously coated with a film system that exhibits high reflectivity (R > 99.5%) for the pump laser wavelength, the first-order Stokes Raman laser wavelength, and the first-order anti-Stokes Raman laser wavelength, while simultaneously exhibiting high transmittance (T > 99.5%) for the second-order Stokes Raman laser wavelength. The second-order Stokes Raman laser light transmitted through concave mirrors A4-2 and B4-3 is absorbed by the inner wall of Raman cell 3. Furthermore, the concave mirrors A4-2 and B4-3 have the same radius of curvature, both equal to 0.43 to 0.46 times the length of Raman cell 3.

[0027] The plano-convex lens B5 is a high-transmission (T>99.5%) film system that simultaneously coats the pump laser wavelength, the first-order Stokes Raman laser wavelength, and the first-order anti-Stokes Raman laser wavelength; the plano-convex lens B5 is a long focal lens coated with multi-wavelength high-transmission film, which shapes non-parallel lasers into parallel lasers.

[0028] The 45° angle dichroic mirror 6 is coated with a film system that simultaneously provides high reflectivity (R > 99.5%) for the pump laser wavelength and the first-order Stokes Raman laser wavelength, and high transmittance (T > 99.5%) for the first-order anti-Stokes Raman laser wavelength. The 45° angle dichroic mirror 6 should be positioned such that the incident light and the reflected light form a 90-degree angle. The 45° angle dichroic mirror 6 serves to separate the first-order anti-Stokes Raman laser from the pump laser and the first-order Stokes Raman laser, ultimately separating a 436-nanometer blue laser beam.

[0029] Example

[0030] In this embodiment, the pump source is an Nd:YAG pulsed solid-state laser, and the pump laser is a frequency-doubled 532 nm laser with a pulse width of 5–50 nanoseconds.

[0031] The Nd:YAG pulsed solid-state laser outputs a pump laser with a wavelength of 532 nm. This laser first passes through a plano-convex lens A2 coated with a 532 nm high-transmittance film, then enters the Raman cell 3 through a window A4-1 also coated with a 532 nm high-transmittance film. The plano-convex lens A2 acts as a focusing element, focusing the 532 nm pump laser to half the length of the Raman cell 3. The laser then passes sequentially through concave mirrors A4-2 and B4-3 for reflection, through window B4-4 for transmission, and collimated by plano-convex lens B5. After being split by a 45° angle dichroic mirror 6, the laser finally outputs a first-order anti-Stokes Raman blue laser with a wavelength of 436 nm. This Raman blue laser has a conversion efficiency of 10–15%, a pulse energy exceeding 50 mJ, and a peak power on the order of 10 MW. In addition, during the transmission of the pump laser inside the Raman cell 3, it interacts with the Raman gas medium and generates a first-order Stokes Raman laser with a wavelength of 683 nm. The lasers with wavelengths of 532 nm and 683 nm are reflected and output through the 45° angle dichroic mirror 6.

[0032] A plano-convex lens A2 is placed at the front end of the laser incident window A4-1 on the Raman cell 3, with a focal length of 1000 mm. Its focal point falls on a point in the center of the space inside the Raman cell 3. The plano-convex lens A2 is coated with a 532 nm high-transmittance film (T > 99.5%).

[0033] Raman cell 3 is made of 304 stainless steel, with a hollow chamber structure, a length of 1800 mm, an outer diameter of 100 mm, and an inner diameter of 80 mm. Windows A4-1 and B4-4 at both ends are fixed by flanges, ensuring good sealing. Concave reflectors A4-2 and B4-3 are installed inside, with the radius of curvature of the concave surfaces being -800 mm. Before the experiment, Raman cell 3 is filled with a mixture of H2 and He or a mixture of H2 and Ar (here, a mixture of H2 and Ar is chosen) at a set pressure. The pressure of H2 is 0.05–0.15 MPa, and the pressure of Ar is 0.05–0.25 MPa. The addition of the inert gas Ar helps to adjust the dispersion and suppress the generation of second-order Stokes Raman laser with a wavelength of 954 nm.

[0034] The window A4-1 at the laser incident end of the Raman cell is coated with a 532 nm high-transmittance film (T > 99.5%), and the window B4-4 at the laser exit end is coated with 532 nm, 683 nm, and 436 nm high-transmittance films (T > 99.5%).

[0035] The surfaces of concave mirrors A4-2 and B4-3 in Raman cell 3 are coated with high reflectivity films of 532 nm, 683 nm, and 436 nm (R > 99.5%) and a high transmittance film of 954 nm (T > 99.5%), respectively. The transmitted 954 nm laser light is absorbed by the inner wall of Raman cell 3.

[0036] The surface of the plano-convex lens B5 is coated with a high-transmittance film of 532 nm, 683 nm, and 436 nm (T > 99.5%). The plano-convex lens B5 is a long focal length lens with a focal length of 1000 mm.

[0037] The 45° dichroic mirror is coated with 532 nm and 683 nm high reflectivity films (R > 99.5%) and 436 nm high transmittance films (T > 99.5%).

Claims

1. A Herriot-type multi-pass cell anti-Stokes Raman high peak power blue laser, characterized by: The system includes a pump laser (1) and a plano-convex lens A (2), a Raman cell (3), a plano-convex lens B (5), and a 45° dichroic mirror (6) arranged sequentially in the direction of the output laser from the pump laser (1). The Raman cell (3) has a window A (4-1) at one end near the plano-convex lens A (2) and a window B (4-4) at the other end near the plano-convex lens B (5). Concave reflectors for transmitting and focusing the laser are located at both ends of the Raman cell (3) along its length. The Raman cell (3) is filled with a Raman gas medium, which is a mixture of H2 and an inert gas. The pump laser emitted by the pump laser (1) enters the Raman cell (3) through the window A (4-1) at one end of the Raman cell (3) via the plano-convex lens A (2). The plano-convex lens A (2) focuses the pump laser to the center point within the Raman cell (3) and then continues to transmit the laser. The pump laser, after being reflected by the concave mirror in the Raman cell (3), is output through window B (4-4) at the other end of the Raman cell (3). The pump laser is refracted and transmitted multiple times in the Raman cell (3) to extend the interaction length between the pump laser and the Raman gas medium. The transmission distance reaches three times the length of the Raman cell body. The pump laser is focused three times in the Raman cell (3). The three focal points are located at the spatial center position along the length of the Raman cell (3), and each focal point does not coincide in space. During the laser transmission process, the pump laser output by the pump laser (1) interacts with the Raman gas medium in the Raman cell (3) to generate a first-order Stokes Raman laser and a first-order anti-Stokes Raman laser. The laser emitted from the Raman cell (3) is collimated by the plano-convex lens B (5) and finally split by the 45° angle dichroic mirror (6) to output a 436-nanometer blue laser.

2. The Herriot-type multi-pass cell anti-Stokes Raman high-peak-power blue laser according to claim 1, characterized in that: The Raman cell (3) contains two concave mirrors, namely concave mirror A (4-2) and concave mirror B (4-3). Concave mirror B (4-3) is located at one end of the Raman cell (3) near window A (4-1), and concave mirror A (4-2) is located at the other end of the Raman cell (3) near window B (4-4). The pump laser injected through window A (4-2) first irradiates concave mirror A (4-2), and is reflected by concave mirror A (4-2) onto concave mirror B (4-3), and then reflected by concave mirror B (4-3) and output through window B (4-4).

3. The Herriot-type multi-pass cell anti-Stokes Raman high-peak-power blue laser according to claim 2, characterized in that: The concave mirrors A (4-2) and B (4-3) are coated with a film system that has high reflectivity for pump laser wavelength, first-order Stokes Raman laser wavelength, and first-order anti-Stokes Raman laser wavelength, while having high transmittance for second-order Stokes Raman laser wavelength. The second-order Stokes Raman laser transmitted through the concave mirrors A (4-2) and B (4-3) is absorbed by the inner wall of the Raman cell (3). The concave mirrors A (4-2) and B (4-3) have the same radius of curvature, which is equal to 0.43 to 0.46 times the length of the Raman cell (3).

4. The Herriot-type multi-pass cell anti-Stokes Raman high-peak-power blue laser of claim 1, wherein: The inert gas is He or Ar. The Raman cell (3) is first filled with H2, and the pressure of H2 is adjusted in the range of 0.5 to 1.5 atmospheres so that the Raman laser does not output second-order Stokes Raman laser. Then He or Ar is filled in, and the pressure of He or Ar is adjusted in the range of 0.5 to 2.5 atmospheres until the output blue light pulse energy reaches the maximum.

5. The Herriot-type multi-pass cell anti-Stokes Raman high-peak-power blue laser of claim 1, wherein: The plano-convex lens A(2) is coated with a film system that has high transmission of pump laser wavelength, and the focal length f of the plano-convex lens A(2) is equal to 0.53 to 0.55 times the length of the Raman cell (3).

6. The Herriot-type multi-pass cell anti-Stokes Raman high-peak-power blue laser according to claim 1, characterized in that: Window A (4-1) is coated with a film system that has high transmission of pump laser wavelength, and window B (4-4) is coated with a film system that has high transmission of pump laser wavelength, first-order Stokes Raman laser wavelength and first-order anti-Stokes Raman laser wavelength.

7. The Herriot-type multi-pass cell anti-Stokes Raman high peak power blue laser according to claim 1, characterized in that: The plano-convex lens A (2) is a long focal length lens with its focal point located at 1 / 2 of the spatial position along the length of the Raman cell (3); the plano-convex lens B (5) is a long focal length lens coated with a multi-wavelength high-transmittance film, which shapes the diverging laser beam into a parallel laser beam; the plano-convex lens B (5) is coated with a film system that has high transmittance for the pump laser wavelength, the first-order Stokes Raman laser wavelength and the first-order anti-Stokes Raman laser wavelength.

8. The Herriot-type multi-pass cell anti-Stokes Raman high-peak-power blue laser according to claim 1, characterized in that: The 45° angle dichroic mirror (6) is coated with a film system that has high reflectivity for both the pump laser wavelength and the first-order Stokes Raman laser wavelength, while having high transmittance for the first-order anti-Stokes Raman laser wavelength.

9. The Herriot-type multi-pass cell anti-Stokes Raman high-peak-power blue laser of claim 1, wherein: The Raman cell (3) adopts a Herriot type multi-pass cell structure. The length of the Raman cell (3) is in the range of 1.5 to 3m, and the wall thickness of the cell meets the pressure bearing conditions of the Raman gas medium.

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