An equal-interval three-wavelength laser simultaneous irradiation generating device and method

Abstract

This invention provides a device and method for generating simultaneously emitted three wavelengths of laser light with equal spacing, relating to the field of laser technology. The device includes a pump source, a half-wave plate, an optical isolator, a focusing lens, an input mirror, a Raman crystal, an output mirror, a nonlinear crystal, and a dichroic mirror arranged sequentially along the optical path. The pump light, after its polarization direction is adjusted by the half-wave plate and the optical isolator, is focused onto the Raman crystal. Stimulated Raman scattering generates first and second Stokes beams, which are then converted to sum-frequency light by the sum-frequency effect of the nonlinear crystal. Finally, the dichroic mirror outputs three equally spaced wavelengths of laser light. This invention separates the Raman conversion and sum-frequency processes through an external cavity structure, achieving for the first time the simultaneous emission of three equally spaced wavelengths of laser light, offering advantages such as high output energy, equal wavelength spacing, and simultaneous emission of three wavelengths.

Description

Technical Field

[0001] This invention relates to the field of laser technology, and in particular to a device and method for generating simultaneous radiation of three equally spaced wavelength lasers. Background Technology

[0002] High-energy, multi-wavelength visible light laser sources have wide applications in biomedical diagnosis and treatment, laser display systems, multispectral analysis, and retinal photocoagulation. However, the generation of visible light lasers has always been a challenge in the laser field due to the lack of available rare-earth ion-doped laser crystals. Currently, the traditional approach utilizes nonlinear optical frequency doubling, typically employing a mature 1064nm near-infrared laser frequency-doubled to 532nm green light using an LBO crystal. However, this method can only generate a single wavelength of laser light, specifically in the green band, failing to capture other visible light wavelengths such as yellow, orange, and red. To expand the visible light laser band, Raman / mixing technology has been developed in recent years. This involves using a 1064nm laser to pump a Raman crystal to generate first- or even second-order Raman light, and then further achieving visible light laser output through nonlinear mixing processes such as frequency doubling and sum-frequency generation. Currently, one approach is to utilize Raman crystals with single-frequency shifting peaks, such as Ba(NO3)2, YVO4, and diamond, to generate first-order Raman light. By matching different temperatures using LBO (Light Booster), frequency doubling of the 1064nm laser, frequency doubling of the first-order Raman light, or a combination of both can be achieved. Another method utilizes multi-frequency shifting crystals, such as KGW crystals. In practical applications, rotating the Raman crystal is required to match different frequency shifting peaks (768 cm⁻¹). -1 and 901 cm -1 The wavelength can be switched and matched with different frequency doubling crystal temperatures. However, existing multi-wavelength visible lasers can only achieve selective output of a single wavelength, and cannot achieve true simultaneous radiation of multiple wavelengths. In addition, the output wavelength spacing and intensity of these lasers are uneven, which cannot meet the application requirements of simultaneous radiation of multiple wavelengths with equal spacing. Summary of the Invention

[0003] To address the technical problem in the background art that it is impossible to achieve simultaneous radiation output of multi-wavelength lasers with equal spacing, the present invention provides a device and method for generating simultaneous radiation of three-wavelength lasers with equal spacing.

[0004] The first aspect of the present invention provides a device for generating simultaneous radiation of three equally spaced wavelength lasers, comprising: Pump source, used to output pump light; The components arranged sequentially along the optical path are: first half-wave plate, optical isolator, second half-wave plate, focusing lens L1, input mirror, Raman crystal, output mirror, focusing lens L2, nonlinear crystal, and dichroic mirror. The pump light is polarized by the first half-wave plate, the optical isolator and the second half-wave plate, and then focused by the focusing lens L1 onto the Raman crystal. The Raman crystal is used to generate the first Stokes light and the second Stokes light through stimulated Raman scattering. After the first and second Stokes beams are output through the output mirror, they are focused onto the nonlinear crystal by the focusing lens L2. The nonlinear crystal is used to generate sum-frequency light through the sum-frequency effect. The dichroic mirror is used to output simultaneously radiated equidistant first-wavelength laser, second-wavelength laser, and third-wavelength laser.

[0005] Furthermore, the Raman crystal includes potassium yttrium tungstate crystal and potassium gadolinium tungstate crystal.

[0006] Furthermore, the nonlinear crystal includes lithium triborate crystal and barium β-metabort crystal.

[0007] Furthermore, the first wavelength laser is a frequency-doubled light of the first Stokes light, the third wavelength laser is a frequency-doubled light of the second Stokes light, and the second wavelength laser is a sum-frequency light of the first Stokes light and the pump light.

[0008] Furthermore, the wavelength range of the pump light is 1030~1080nm.

[0009] Furthermore, the dichroic mirror has a transmittance of not less than 95% in the visible light band and a transmittance of 50% in the infrared band.

[0010] Furthermore, the ratio of the transmittance of the output mirror at the first Stokes wavelength to the transmittance at the second Stokes wavelength is 1:4 to 1:3.

[0011] Furthermore, the wavelength range of the first Stokes light is 1136~1198nm, and the wavelength range of the second Stokes light is 1266~1342nm.

[0012] Furthermore, the wavelength range of the first wavelength laser is 568~599nm, the wavelength range of the second wavelength laser is 600~635nm, and the wavelength range of the third wavelength laser is 633~671nm.

[0013] A second aspect of the present invention provides a method for generating simultaneous radiation of three equally spaced wavelength lasers based on the device described in the first aspect, comprising: S1. Start the pump source and output pump light; S2. Adjust the polarization direction of the pump light by using the first half-wave plate, the optical isolator, and the second half-wave plate to align it along the Ng axis or Nm axis of the Raman crystal. S3. The pump light is focused onto the Raman crystal by the focusing lens L1 to excite stimulated Raman scattering effect and generate the first Stokes light and the second Stokes light. S4. After the first Stokes beam and the second Stokes beam are output through the output mirror, they are focused onto the nonlinear crystal through the focusing lens L2, and sum-frequency light is generated through the sum-frequency effect. S5. The first, second, and third wavelength lasers are simultaneously emitted through a dichroic mirror.

[0014] Compared with existing technologies, the present invention provides a device and method for generating three wavelengths of laser light simultaneously with equal spacing, which has the following advantages: The pump light is focused onto a Raman crystal after its polarization direction is adjusted sequentially by passing it through a half-wave plate and an optical isolator. Stimulated Raman scattering generates a first Stokes beam and a second Stokes beam, which are then converted to a sum-frequency beam by the sum-frequency effect of a nonlinear crystal. Finally, the three wavelengths of laser light are output through a dichroic mirror. Through the aforementioned external cavity structure design, the Raman conversion and sum-frequency processes are separated, allowing stimulated Raman scattering and the frequency doubling / sum-frequency process to proceed synchronously and efficiently. By setting the ratio of the transmittance of the output mirror at the first Stokes beam wavelength to the transmittance at the second Stokes beam wavelength to 1:4 to 1:3, the output light intensity of the first and second Stokes beams is balanced, thus achieving simultaneous radiation output of three wavelengths of laser light with equal spacing for the first time. Attached Figure Description

[0015] The accompanying drawings, which form part of this disclosure, are used to provide a further understanding of this disclosure. The illustrative embodiments of this disclosure and their descriptions are used to explain this disclosure and do not constitute an undue limitation of this disclosure. The spacing or dimensions between parts are exaggerated to show the position of each part, and the schematic diagrams are for illustrative purposes only.

[0016] Figure 1 This is a schematic diagram of a device for generating three equally spaced wavelength lasers that radiate simultaneously, according to Embodiment 1 of the present invention.

[0017] Figure 2 This is a schematic diagram of the optical axis of a Raman crystal (taking potassium yttrium tungstate as an example) provided in Embodiment 1 of the present invention.

[0018] Figure 3 The three-dimensional distribution diagram of the effective nonlinear coefficients of the three-wavelength output of the nonlinear crystal (taking lithium triborate crystal as an example) provided in Embodiment 1 of the present invention.

[0019] Figure 4 This is an equidistant three-wavelength laser spectrum with pump polarization aligned with the Nm axis at the highest output power, provided in Embodiment 2 of the present invention.

[0020] The components are: 1. Pump source; 2. First half-wave plate; 3. Optical isolator; 4. Second half-wave plate; 5. Focusing lens L1; 6. Input mirror; 7. Raman crystal (e.g., potassium yttrium tungstate crystal or potassium gadolinium tungstate crystal); 8. Output mirror; 9. Focusing lens L2; ​​10. Nonlinear crystal (e.g., lithium triborate crystal or barium β-metabolic acid crystal); 11. Dichroic mirror. Detailed Implementation

[0021] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments.

[0022] It should be noted that the following detailed descriptions are exemplary and intended to provide further illustration of the invention. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0023] It should be noted that the terminology used herein is for the purpose of describing specific embodiments only and is not intended to limit the exemplary embodiments of the present invention. As used herein, unless the context clearly indicates otherwise, the singular form is intended to include the plural form as well. Furthermore, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof. The use of the words "upper," "lower," "left," and "right" in this invention only indicates alignment with the upper, lower, left, and right directions of the drawings themselves and does not limit the structure. They are merely for the convenience of describing the invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limiting the invention.

[0024] Terminology Explanation: 1. Raman Laser: This is a laser based on stimulated Raman scattering. It generates frequency-shifted light through the interaction of photons with the vibrations of molecules in the medium. The frequency shift is the same as the Raman frequency shift peak. First-order Raman light, second-order Raman light, and other multi-order Raman light can be generated by using multiple Raman frequencies.

[0025] 2. Frequency doubling: Laser frequency doubling refers to the process of converting fundamental frequency light (frequency ω) into frequency-doubled light (frequency 2ω) using a nonlinear crystal under the influence of a strong laser. For example: 1064 nm infrared light → 532 nm green light.

[0026] 3. Sum-frequency: This refers to the interaction of two laser beams of different frequencies in a nonlinear crystal, producing a new laser beam with a frequency equal to the sum of the two frequencies. Frequency doubling is a special case of sum-frequency. This process requires phase matching, which means using the birefringence of the crystal to compensate for dispersion effects and synchronize the wave velocities of the two beams. Generally, this requires cutting the crystal at a specific angle and achieving precise phase matching through temperature control.

[0027] 4. Frequency mixing: A nonlinear process that simultaneously has frequency harmonics and sum frequencies.

[0028] Example 1 This embodiment provides a device for generating three wavelengths of laser light simultaneously at equal intervals, the specific structure of which is as follows: Figure 1 As shown, the components arranged sequentially along the optical path are: pump source (1), first half-wave plate (2), optical isolator (3), second half-wave plate (4), focusing lens L1 (5), input mirror (6), Raman crystal (7, specifically potassium yttrium tungstate crystal in this embodiment), output mirror (8), focusing lens L2 (9), nonlinear crystal (10, specifically lithium triborate crystal in this embodiment) and dichroic mirror (11). The pump source (1) is a flash-pumped Nd:YAG laser that generates a linearly polarized laser output of over 73.6 mJ at a repetition frequency of 1 Hz, used to output a pump beam of 1064 nm. An optical isolator (3) is used to prevent back-transmitted light from entering the pump source. The pump power can be adjusted by rotating the first half-wave plate (2) placed in front of the optical isolator. The second half-wave plate (4) is used to adjust the pump polarization direction so that it is aligned with the Ng axis or Nm axis of the potassium yttrium tungstate crystal (7). The pump beam is focused onto the center of the potassium yttrium tungstate crystal (7) through the focusing lens L1 (5), with a spot size of 1.67 mm.

[0029] The Raman medium was an undoped, uncoated potassium yttrium tungstate crystal (7) with dimensions of 5 × 5 × 45 mm. 3 It possesses moderate Raman gain (3.6 cm / GW@1064 nm) and thermal conductivity (3.3 W / m / K). The optical axes Np, Nm, and Ng of the potassium yttrium tungstate crystal are as follows: Figure 2 As shown. The crystal is cut along the Np axis, and the pump light propagates along the Np axis, thus reaching a length of 765 cm⁻¹. -1 and 905cm -1 Phonon mode provides high gain. When the second half-wave plate (4) adjusts the pump polarization direction to be aligned along the Ng axis, it excites 765 cm⁻¹ -1 Phonon mode; when the pump polarization direction is aligned along the Nm axis, 905 cm⁻¹ is excited. -1Phonon mode. The crystal is encased in indium foil and mounted in a copper heat sink, cooled to 20°C by circulating water. This setup allows for the selective generation of Stokes light with different frequency shifts, laying the foundation for the subsequent formation of three equally spaced wavelengths.

[0030] The length of the flat resonant cavity is 60 mm. The input mirror (6) is a plane mirror coated with a high-reflectivity film (reflectivity >99.5%) at 1150–1350 nm and anti-reflection films (reflectivity <1%) at 1064 nm and 1480 nm. The output mirror (8) is a plane mirror with a transmittance of 25% at 1178 nm, a transmittance of 80% at 1313 nm, and a high-reflectivity film coated at 1064 nm. The transmittance ratio of 1178 nm to 1313 nm is 1:4 to 1:3. This transmittance ratio is set to balance the output light intensity of the first Stokes beam (1178 nm) and the second Stokes beam (1313 nm), which is beneficial for the efficient operation of the subsequent mixing process.

[0031] The lithium triborate crystal (10) has dimensions of 4 × 4 × 15 mm³, is cut along the direction of θ=90° and φ=3.8°, and is placed on a TEC temperature control seat. Its two optical end faces are polished but not coated. Raman light is focused onto the lithium triborate crystal (10) through a focusing lens L2 (9), and sum-frequency light is generated through the sum-frequency effect. The crystal angle and temperature control design optimize the phase matching conditions to ensure that the sum-frequency process is carried out efficiently.

[0032] The dichroic mirror (11) is composed of four optical lenses, with a transmittance of not less than 95% in the 532–700 nm band and a transmittance of 50% in the 1150–1350 nm band. The dichroic mirror is used to filter out residual Raman light and output three wavelength lasers of 589 nm, 624 nm and 659 nm.

[0033] In this embodiment, the pump source, Raman light, and multi-wavelength visible light energy were also measured using a pyroelectric laser energy detector (QE65LP-H-MB-QED, gentec-eo). The time pulse profile was recorded using a fast InGaAs photodetector (DET10N2, THORLABS) and monitored on a digital oscilloscope (DHO4804, RIGOL).

[0034] To explain the feasibility of three-wavelength visible light output in principle, a three-dimensional simulation was performed under a class of phase-matching conditions to investigate the relationship between the nonlinear coefficients of three nonlinear processes and the cutting angles ɵ and φ. Figure 3As shown, it can be seen that the nonlinear coefficient does not decrease much in the region near the point of perfect phase matching. Therefore, the LBO mixing process does not require perfect phase matching. These three nonlinear optical processes can achieve high-efficiency mixing and conversion simultaneously based on LBO crystals at the same temperature.

[0035] Example 2 This embodiment provides a method for generating simultaneous radiation of three equally spaced wavelength lasers based on the device described in Embodiment 1, including: S1. Start the pump source (1) and output 1064 nm pump light.

[0036] S2. The polarization direction of the pump light is adjusted by the first half-wave plate (2), the optical isolator (3), and the second half-wave plate (4) to align it along the Ng axis or Nm axis of the Raman crystal (7, specifically a potassium yttrium tungstate crystal in this embodiment). The purpose of this step is to select the excitation 765 cm⁻¹. - ¹ or 905 cm - ¹Ponton mode, thereby controlling the wavelengths of the first and second Stokes lights.

[0037] S3. The pump light is focused by the focusing lens L1 (5) onto the Raman crystal (7, specifically potassium yttrium tungstate crystal in this embodiment), which excites stimulated Raman scattering and generates the first Stokes light (1178 nm) and the second Stokes light (1313 nm).

[0038] S4. After the first Stokes beam and the second Stokes beam are output through the output mirror (8), they are focused by the focusing lens L2 (9) onto the nonlinear crystal (10, specifically a lithium triborate crystal in this embodiment). The sum frequency effect generates sum frequency light (624 nm), while the first Stokes beam generates 589 nm laser by frequency doubling, and the second Stokes beam generates 659 nm laser by frequency doubling.

[0039] S5. The dichroic mirror (11) outputs three equally spaced three-wavelength lasers with wavelengths of 589 nm, 624 nm and 659 nm, respectively, which are simultaneously radiated.

[0040] Figure 4 The spectrum of an equally spaced three-wavelength laser with its pump polarization aligned to the Nm axis is shown at maximum output power. The wavelengths of the first and second Stokes beams and the sum-frequency pulse are 589 nm, 659 nm, and 624 nm, respectively. The calculated frequency shift between adjacent Stokes beam stages is 907.8 cm⁻¹. - ¹ and 903.4 cm -¹, which is close to the theoretical reference value. In this embodiment, when the three wavelengths of laser light radiate simultaneously, the maximum output energy is 6.4 mJ, the pulse width is 19.5 ns, the normalized intensities of the three wavelengths are 0.38, 0.43 and 0.44, respectively, and the adjacent wavelengths are spaced 35 nm apart, showing an equal distribution.

[0041] In the description of this specification, the terms "connection", "installation", "fixing", "setting", etc. are interpreted broadly. For example, "connection" can be a fixed connection or an indirect connection through an intermediate component without affecting the relationship between components and the technical effect. It can also be an integral connection or a partial connection. In such cases, those skilled in the art can understand the specific meaning of the above terms in this invention or invention according to the specific circumstances.

[0042] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A device for simultaneously radiating three wavelengths of laser light at equal intervals, characterized in that, include: Pump source (1) is used to output pump light; The following components are arranged sequentially along the optical path: first half-wave plate (2), optical isolator (3), second half-wave plate (4), focusing lens L1 (5), input mirror (6), Raman crystal (7), output mirror (8), focusing lens L2 (9), nonlinear crystal (10), and dichroic mirror (11). The pump light is polarized by the first half-wave plate (2), the optical isolator (3), and the second half-wave plate (4), and then focused by the focusing lens L1 (5) onto the Raman crystal (7). The Raman crystal (7) is used to generate the first Stokes light and the second Stokes light through stimulated Raman scattering. After the first Stokes beam and the second Stokes beam are output through the output mirror (8), they are focused by the focusing lens L2 (9) onto the nonlinear crystal (10), which is used to generate sum-frequency light through the sum-frequency effect; The dichroic mirror (11) is used to output simultaneously radiated equidistant first-wavelength laser, second-wavelength laser and third-wavelength laser.

2. The apparatus according to claim 1, characterized in that, The Raman crystal (7) includes potassium yttrium tungstate crystal and potassium gadolinium tungstate crystal.

3. The apparatus according to claim 1, characterized in that, The nonlinear crystal (10) includes lithium triborate crystal and barium β-metabort crystal.

4. The apparatus according to claim 1, characterized in that, The first wavelength laser is a frequency-doubled light of the first Stokes light, the third wavelength laser is a frequency-doubled light of the second Stokes light, and the second wavelength laser is a sum-frequency light of the first Stokes light and the pump light.

5. The apparatus according to claim 1, characterized in that, The wavelength range of the pump light is 1030~1080nm.

6. The apparatus according to claim 1, characterized in that, The dichroic mirror (11) has a transmittance of not less than 95% in the visible light band and a transmittance of 50% in the infrared band.

7. The apparatus according to claim 1, characterized in that, The ratio of the transmittance of the output mirror (8) at the first Stokes wavelength to the transmittance at the second Stokes wavelength is 1:

4.

8. The apparatus according to claim 1, characterized in that, The wavelength range of the first Stokes light is 1136~1198nm, and the wavelength range of the second Stokes light is 1266~1342nm.

9. The apparatus according to claim 1, characterized in that, The first wavelength laser has a wavelength range of 568~599nm, the second wavelength laser has a wavelength range of 600~635nm, and the third wavelength laser has a wavelength range of 633~671nm.

10. A method for generating simultaneous radiation of three equally spaced wavelength lasers based on the device according to any one of claims 1 to 9, characterized in that, Includes the following steps: S1. Start pump source (1) and output pump light; S2. Adjust the polarization direction of the pump light by using the first half-wave plate (2), the optical isolator (3), and the second half-wave plate (4) to align it along the Ng axis or Nm axis of the Raman crystal (7). S3. The pump light is focused by the focusing lens L1 (5) onto the Raman crystal (7) to excite stimulated Raman scattering and generate the first Stokes light and the second Stokes light. S4. After the first Stokes beam and the second Stokes beam are output through the output mirror (8), they are focused onto the nonlinear crystal (10) through the focusing lens L2 (9) to generate sum-frequency light through the sum-frequency effect; S5. The first wavelength laser, the second wavelength laser, and the third wavelength laser are simultaneously radiated through the dichroic mirror (11).

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