Device and method for generating frequency comb laser with wide spectral range by using single-wavelength laser

Abstract

The present invention discloses a device and method for generating a frequency comb laser with a wide spectral range from a single-wavelength laser. By undergoing multiple stimulated Raman scatterings in different gas media, the number of output wavelengths is increased to achieve a frequency comb laser with a wide spectral range. In the present invention, a laser with a wavelength of 1064 nm is used as the pump source. Through its combination with the gas stimulated Raman technology, the output of dozens of frequency comb laser lines can ultimately be obtained, and the wavelength coverage ranges from visible light to mid-infrared. To a certain extent, the present invention not only realizes the expansion of the laser wavelength but also realizes the simultaneous output of multi-wavelength lasers. The device of the present invention has a simple design, convenient debugging, and can achieve frequency conversion of high-power lasers. The wavelength conversion span is relatively large, and the variable wavelengths are rich.

Description

Technical Field

[0001] The present invention belongs to the field of laser Raman frequency conversion, and particularly relates to a method for effectively generating frequency comb lasers with a wide spectral range from a single-wavelength laser. Technical Background

[0002] Due to the characteristics of monochromaticity, directivity, and high intensity, lasers have now been applied in many fields. However, the existing output laser wavelengths are limited and cannot fully meet the usage requirements. Therefore, in order to expand the application range of lasers, laser wavelength expansion is an important research direction. Stimulated Raman scattering is a common method for laser wavelength expansion, and there are also various types of Raman media. Crystals (such as diamond, SrWO4), liquids (such as CS2, C6H6), and gases (such as H2, CH4) can all be used as Raman media for frequency conversion research. Compared with other solid media, gas media have their unique advantages. When a crystal is used as a Raman medium, if the pump energy is increased, it may damage the crystal medium and thus affect the experimental results. This problem will not occur if a gas is used as the Raman medium. This is also an important reason for the present invention to use a gas medium.

[0003] As one of the most significant inventions in the field of laser science, optical frequency combs have played a huge role in fields such as precision spectroscopy, laser physics, and metrology. At the same time, due to the unique spectral characteristics of optical frequency combs, they have better application prospects in frequency standard conversion, high-precision measurement, etc. Therefore, optical frequency combs will continuously pursue high-performance optical frequency combs with broadbandwidth, high flatness, and independently tunable central wavelength and spectral line spacing in their generation technology to meet the needs of different application fields.

[0004] Based on the principle of gas-stimulated Raman scattering, the present invention expands a single-wavelength pump light into dozens of frequency comb laser spectral lines through multiple wavelength frequency shifts, thereby realizing the output of frequency comb lasers with a wide spectral range. Summary of the Invention

[0005] The practicality of the present invention is achieved by using a 1064nm laser to pump a mixed gas Raman cell, and finally obtaining a frequency comb spectrum with wavelengths ranging from visible light to mid-infrared. The process is as follows: The pump light generated by a 1064nm wavelength laser is injected into the Raman cell through a focusing lens, and after two reflections by two coated mirrors in the cell, the generated Stokes light and the remaining un-converted pump light are output from the other end of the Raman cell.

[0006] The technical solution of the present invention is as follows:

[0007] On the one hand, the present invention provides a gas-stimulated Raman frequency comb output device, which includes a 1064 nm wavelength laser, a plano-convex lens, and a Raman cell arranged in sequence along the direction of the laser optical axis; a first mirror and a second mirror are built in at both ends of the Raman cell; the gas medium in the Raman cell is a mixture of methane and hydrogen.

[0008] Preferably, the ratio of methane to hydrogen is 1:1 to 3:1; the pressure of the gas medium is 0.5 to 6 Mpa.

[0009] Preferably, the Raman cell is a sealed metal cylinder, which can withstand high pressure and has good airtightness. Flanges are installed at both ends of the metal cylinder, and a coated window plate is installed on each flange.

[0010] The pump light enters from the window plate at one end of the Raman cell. When the pump laser passes through the gas Raman cell, Raman light is generated through stimulated Raman action. Two reflectors or two prisms can be built in at both ends of the cell as needed to increase the action length and form a multi-pass Raman cell. The generated Raman light and the remaining pump light come out from the window plate at the other end.

[0011] Preferably, the first mirror and the second mirror are both selected from one of a concave perforated mirror and an isosceles right prism: the concave perforated mirror is coated with a high-reflection film for the pump light wavelength and the generated Raman light wavelength, and the inclined surface of the isosceles right prism is coated with an anti-reflection film for the pump light wavelength and the generated Raman light wavelength.

[0012] On the other hand, the present invention provides a method for generating a frequency comb laser with a wide spectral range using the above device. The method is as follows: the pump light generated by a 1064 nm wavelength laser is injected into the Raman cell through a plano-convex lens. The gas medium serves as a stimulated Raman gain medium, and the laser pumps the gas medium to generate a stimulated Raman effect, thereby realizing a frequency comb. After two reflections by the first mirror and the second mirror in the Raman cell, the generated Stokes light and the remaining un-converted pump light are output from the other end of the Raman cell, and finally a frequency comb spectrum with wavelengths from visible light to mid-infrared is obtained.

[0013] Preferably, when the first mirror and the second mirror are concave perforated mirrors, the concave perforated mirrors are coated with a high-reflection film for the pump light wavelength and the generated Raman light wavelength. The pump laser first hits the coated mirror two, and the reflected light is adjusted to hit the coated mirror one by adjusting the lens, and then after another reflection, the light is output from one end of the Raman cell. The optical path is changed by changing the number of reflections of the two coated mirrors.

[0014] Preferably, when the first endoscope and the second endoscope are isosceles right prisms, an antireflection film with the pump light wavelength and the generated Raman light wavelength is coated on the inclined surface of the isosceles right prism. The pump light is perpendicularly incident on the inclined surface of the right prism, changes its direction after two reflections in the prism, and propagates along the direction completely opposite to the incident light. Adjust the angle of the second endoscope so that the output light hits the inclined surface of the right prism of the first endoscope, and then adjust the angle of the first endoscope so that the laser whose direction is changed after passing through the first endoscope is output from the output window of the Raman cell.

[0015] The advantages of the present invention are as follows:

[0016] (1) The present invention provides an effective method for generating frequency comb lasers with a wide spectral range from a single-wavelength laser. Using the existing single-wavelength laser as a pump source, dozens of frequency comb laser spectra are output through stimulated Raman scattering in multiple different gas media, providing a practical and effective new method for obtaining frequency comb lasers with a wide spectral range in the field of laser frequency conversion.

[0017] (2) The multi-pass Raman cell provided by the present invention can reduce the stimulated Raman threshold and broaden the scope of Raman frequency conversion technology.

[0018] (3) The Raman cell provided by the present invention can select the length, air pressure, and optical path length according to the situation, and the intensity of the laser frequency comb can be regulated by changing these parameters.

[0019] (4) Gas is not easily affected by the thermal effect during the Raman process compared to solids, and using gas as the Raman medium can withstand higher pump energies. Description of the Drawings

[0020] Figure 1 It is a schematic diagram of a device for generating frequency comb by stimulated Raman scattering of gas;

[0021] In the figure: 1. 1064nm laser; 2. plano-convex lens; 3. Raman cell; 4. first endoscope; 5. second endoscope; among them, 2, 3, 4, and 5 form a single-wavelength laser frequency conversion device. Detailed Embodiments

[0022] Embodiment 1

[0023] The technical solution of the wide-spectrum range frequency comb laser of the present invention is as follows: The laser generated by the 1064nm laser passes through a lens with f = 500mm and a window piece coated with an antireflection film at the 1064nm wavelength in sequence, and then enters the gas cell. The focus of the lens is located at the center of the Raman cell, and the length of the Raman cell is about 1m. The first mirror and the second mirror are respectively placed at both ends of the Raman cell. The first mirror and the second mirror are concave perforated reflecting mirrors with R = 500mm. The diameter of the hole is larger than the beam diameter of the pump light, and the concave surfaces of the two mirrors are coated with the same wide-band high-reflection film, and the range covers all wavelengths of the output frequency comb. The pump laser passes through the hole on the first mirror and first hits the second mirror. By adjusting the angle of the second mirror, the returned laser hits the first mirror, and then by adjusting the angle of the first mirror, the laser is output through the hole on the second mirror. The Raman cell is filled with a mixed gas of methane and hydrogen with a ratio of 1:1 and a gas pressure of 2MPa. Due to the stimulated Raman effect of the pump light in the gas medium, the output laser contains at least wavelengths such as 2802nm, 1542nm, 812nm, 657nm, 551nm, 475nm, 1908nm, 738nm, 564nm, 457nm, and 384nm, thereby realizing the output of the wide-spectrum range frequency comb laser.

[0024] Example 2

[0025] The technical solution of the wide-spectrum range frequency comb laser of the present invention is as follows: The laser generated by the 1064nm laser enters the gas cell through the incident window of the Raman cell coated with an antireflection film at the 1064nm wavelength. The length of the Raman cell is about 2m. The first mirror and the second mirror are respectively placed at both ends of the Raman cell. The first mirror and the second mirror are two isosceles right-angled prisms made of calcium fluoride material with wide-band antireflection films coated on their inclined surfaces, and the coating range covers all wavelengths of the output frequency comb. The pump light is perpendicularly incident on the inclined surface of the right-angled prism, changes its direction after two reflections in the prism, and propagates along the direction completely opposite to the incident light. By adjusting the angle of the second mirror, the output light hits the inclined surface of the first right-angled prism mirror, and then by adjusting the angle of the first mirror, the laser whose direction has changed after passing through the first mirror is output from the exit window of the Raman cell. The Raman cell is filled with a mixed gas of methane and hydrogen with a ratio of 2:1 and a gas pressure of 1MPa. Due to the stimulated Raman effect of the pump light in the gas medium, the output laser contains at least wavelengths such as 2802nm, 1542nm, 812nm, 657nm, 551nm, 475nm, 1908nm, 738nm, 564nm, 457nm, and 384nm, thereby realizing the output of the wide-spectrum range frequency comb laser.

Claims

1. A gas-stimulated Raman frequency comb output device, characterized in that The device includes a 1064nm wavelength laser, a plano-convex lens and a Raman cell arranged in sequence along the direction of the laser optical axis; two end faces of the Raman cell are internally provided with a first mirror and a second mirror; the gas medium in the Raman cell is a mixture of methane and hydrogen; The ratio of methane to hydrogen is 1:1 to 3:1; the pressure of the gas medium is 0.5 to 6 Mpa.

2. The gas-stimulated Raman frequency comb output device according to claim 1, characterized in that, The Raman cell is a sealed metal cylinder, and flanges are installed at both ends of the metal cylinder, and a coated window plate is installed on each flange.

3. The gas-stimulated Raman frequency comb output device according to claim 1, characterized in that The first mirror and the second mirror are both selected from a concave perforated mirror and an isosceles right prism: the concave perforated mirror is coated with a high-reflection film for the pump light wavelength and the generated Raman light wavelength, and the inclined surface of the isosceles right prism is coated with an antireflection film for the pump light wavelength and the generated Raman light wavelength.

4. A method for generating a frequency comb laser with a wide spectral range using the device according to any one of claims 1 to 3, characterized in that, The method is as follows: the pump light generated by the 1064nm wavelength laser is injected into the Raman cell through the plano-convex lens. The gas medium serves as the stimulated Raman gain medium, and the laser pumps the gas medium to generate the stimulated Raman effect, thereby realizing a frequency comb. After two reflections by the first mirror and the second mirror in the Raman cell, the generated Stokes light and the remaining un-converted pump light are output from the other end of the Raman cell, and finally a frequency comb spectrum with wavelengths from visible light to mid-infrared is obtained.

5. The method according to claim 4, characterized in that, When the first mirror and the second mirror are concave perforated mirrors, the concave perforated mirrors are coated with a high-reflection film for the pump light wavelength and the generated Raman light wavelength. The pump laser first hits the coated mirror two, and the reflected light is made to hit the coated mirror one by adjusting the lens, and then after another reflection, the light is output from one end of the Raman cell, and the optical path is changed by changing the number of reflections of the two coated mirrors.

6. The method according to claim 4, characterized in that, When the first mirror and the second mirror are isosceles right prisms, the inclined surfaces of the isosceles right prisms are coated with an antireflection film for the pump light wavelength and the generated Raman light wavelength. The pump light is perpendicularly incident on the inclined surface of the right prism, and the direction is changed after two reflections in the prism and propagates along a direction completely opposite to the incident light. The angle of the second mirror is adjusted so that the output light hits the inclined surface of the first right prism, and then the angle of the first mirror is adjusted so that the laser whose direction is changed after passing through the first mirror is output from the exit window of the Raman cell.

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