A device and method for generating mid-infrared laser based on period phase matching crystal

Abstract

The application discloses a device and method for generating mid-infrared laser based on period phase matching crystal, which comprises a pulse pumping source, a resonant cavity, a pumping input mirror, a nonlinear crystal, a dispersion management element, a third-order nonlinear effect unit and a filter. The resonant cavity comprises a first curved mirror, a second curved mirror, a cavity mirror and an output coupling mirror arranged in an X-shaped structure. The pulse pumping source outputs pumping light which generates signal light and idler light after passing through the nonlinear crystal. The idler light is widened to a required bandwidth by the third-order nonlinear effect unit and oscillation is established in the resonant cavity. The cavity length of the resonant cavity is matched with the repetition frequency of the pumping source, so that the idler light, the adjacent period pumping light and the signal light are coincided in time and space, the gain of the idler light is greater than the loss, and the required broadband mid-infrared laser output is formed. The device can directly generate super wideband idler light without wavelength tuning, has a lower overall cost and has a higher popularization value.

Description

Technical Field

[0001] This invention belongs to the field of broadband optical radiation control technology, and more specifically, relates to a device and method for generating mid-infrared laser based on a periodic phase-matched crystal. Background Technology

[0002] Mid-infrared lasers with wavelengths in the 3-5 μm range are located within the atmospheric window and coincide with the absorption peaks of numerous atoms and molecules, thus holding broad and significant application prospects in spectroscopy, medicine, communications, remote sensing, environmental monitoring, and infrared countermeasures. Optical parametric oscillators (OPOs), as an important means of generating mid-infrared coherent radiation, have always been a focus of research institutions both domestically and internationally. To generate mid-infrared lasers that cover the atmospheric window (wavelengths in the 3-5 μm range), wavelength-tunable OPOs are generally used. However, wavelength tuning is complex, and the instantaneous bandwidth is limited, restricting measurement accuracy and speed.

[0003] Patent CN106405974B discloses a device and method for generating ultra-wideband optical radiation, which generates continuous idler light by resonating multiple narrowband signal lights through a time delay component. However, its time delay component is complex, the experiment is difficult, and the bandwidth is limited by the resonant wavelength of the signal light. Patent CN110471234B discloses a device and method for generating broadband optical radiation based on a chirped nonlinear crystal, which generates an instantaneous bandwidth of 3μm-5μm by designing a quasi-phase-matched crystal with a chirped period. However, the chirped crystal is complex to manufacture and designed, and its cost is high, which is not conducive to its production and use.

[0004] Therefore, the following technical problems exist in the current mid-infrared light source based on optical parametric oscillators: (1) the bandwidth is limited by the resonant wavelength of the signal light; (2) the chirped nonlinear crystal is used, which is complex to process and expensive; (3) the resonant cavity uses multiple dielectric mirrors, which increases the dispersion. Although dispersion functional elements are used to compensate for the dispersion, the residual dispersion still affects the bandwidth. Summary of the Invention

[0005] In view of the above-mentioned defects or improvement needs of the prior art, the present invention provides a device for generating mid-infrared laser based on periodic phase-matching crystal to solve such problems.

[0006] To achieve the above objectives, the present invention provides a device for generating mid-infrared laser based on a periodic phase-matched crystal, comprising: a pulsed pump source, which is an ultrashort pulse laser; a resonant cavity, the cavity length of which is matched with the repetition rate of the pump source, including a first curved mirror and a second curved mirror disposed at the bottom, a cavity mirror and an output coupling mirror respectively disposed above the first curved mirror and the second curved mirror, the four being arranged in an X-shape; a first reflected optical path is formed between the first curved mirror and the second curved mirror, a second reflected optical path is formed between the second curved mirror and the cavity mirror, and a third reflected optical path is formed between the first curved mirror and the output coupling mirror; a nonlinear crystal disposed in the first reflected optical path, which, through being disposed in the resonant cavity, forms an optical parametric oscillator with the pulsed pump source; and a pump source is sequentially disposed in the third reflected optical path. The system comprises a pump input mirror and a third-order nonlinear effect unit. The pump input mirror reflects the pump light output from the pulsed pump source onto a first curved mirror. The pump light then passes through a nonlinear crystal along the first reflection path to generate signal light and idler light. The third-order nonlinear effect unit broadens the spectrum of the idler light to the required bandwidth. The idler light, acting as an oscillating light, establishes oscillation within the resonant cavity, coinciding with the adjacent periodic pump light and signal light in time and space, ensuring that the gain of the idler light exceeds its loss, thus forming the desired broadband mid-infrared laser output. A dispersion management element located in the second reflection path compensates for dispersion within the resonant cavity, reducing the total dispersion within the cavity. A filter located at the output end of the output coupling mirror filters the pump light and signal light, ensuring high transmittance for the broadband mid-infrared laser.

[0007] Furthermore, the path of the frequency light reflected back and forth in the resonant cavity is as follows: it shines on the second curved mirror along the first reflected light path, and after reflection, it shines perpendicularly on the cavity mirror along the second reflected light path. After reflection by the cavity mirror, it shines on the second curved mirror along the second reflected light path. After reflection, it shines on the first curved mirror along the first reflected light path. After reflection, it passes through the pump input mirror along the third reflected light path and enters the third-order nonlinear crystal. After achieving spectral broadening, it shines perpendicularly on the output coupling mirror. After reflection by the output coupling mirror, it shines on the first curved mirror along the third reflected light path. After the spectrally broadened idler light is reflected by the first curved mirror and enters the nonlinear crystal along the first reflected light path, the idler light completes one oscillation cycle in the resonant cavity.

[0008] Furthermore, the third-order nonlinear effect unit provides additional self-phase modulation for the oscillating light, including a third-order nonlinear effect crystal and a focusing module; the oscillating light adjusts the focusing distance through the focusing module, changes the size of the spot focused on the crystal, thereby changing the self-phase modulation intensity, and thus achieving different degrees of spectral broadening of the oscillating light.

[0009] Furthermore, the nonlinear refractive index of the third-order nonlinear effect crystal is higher than that of the nonlinear refractive index of the nonlinear crystal in the optical parametric oscillator.

[0010] Furthermore, the first and second curved mirrors are curved mirrors with a silver plating layer on their surfaces to reflect light.

[0011] Furthermore, the cavity mirror is a plane mirror with a silver-plated layer on its surface, which can reflect light.

[0012] Furthermore, the pump input mirror is a dielectric mirror with a first coating layer on its surface, which can highly reflect the pump light and highly transmit the signal light and idler light; the output coupling mirror is a dielectric mirror with a second coating layer on its surface, which can highly transmit the signal light and highly reflect the idler light.

[0013] Furthermore, the dispersion management element employs any one of the dispersion compensation devices, such as a silicon wafer, a grating, or a prism.

[0014] Furthermore, the filter is made of germanium with high transmittance in the mid-infrared band.

[0015] According to another aspect of the present invention, a method for generating mid-infrared laser based on a periodic phase-matched crystal is also provided, comprising the following steps:

[0016] S100: Based on the broadband light to be generated, determine the appropriate pulse pump source and nonlinear crystal; adjust the third-order nonlinear effect unit according to the calculated idler light bandwidth generated by the nonlinear crystal, so that the focusing module adjusts the focusing distance, changes the spot size of the idler light focused on the crystal, thereby performing self-phase modulation, and broadening the spectrum of the idler light to the required bandwidth.

[0017] S200: Determine the cavity length of the resonant cavity based on the repetition frequency of the pulse pump source, and select appropriate values ​​according to the cavity stabilization calculation formula to determine the placement positions of the first curved mirror, the second curved mirror, the cavity mirror, and the output coupling mirror, as well as the radii of curvature of the first and second curved mirrors; after adjusting the position and angle of the resonant cavity components, determine the placement angle and position of the pulse pump source, the pump input mirror, the third-order nonlinear effect unit, and the filter;

[0018] S300: A dispersion management element is placed in the second reflected light path formed between the second curved mirror and the cavity mirror to compensate for intracavity dispersion;

[0019] S400: The pump light output from the pulse pump source is reflected sequentially by the pump input mirror and the first curved mirror before entering the nonlinear crystal to generate signal light and idler light. The signal light is filtered out by the output coupling mirror, leaving the idler light as the oscillation light to establish oscillation. The idler light is then spectrally broadened by a third-order nonlinear effect unit. The spectrally broadened idler light coincides with the adjacent periodic pump light and signal light in time and space, so that the gain of the idler light is greater than the loss, forming the desired broadband mid-infrared laser output.

[0020] In summary, compared with the prior art, the above-described technical solutions conceived by this invention can achieve the following beneficial effects:

[0021] 1. The present invention provides a device for generating mid-infrared laser based on a periodic phase-matched crystal. By using a low-frequency idler light as the oscillation light in the resonant cavity, the bandwidth of the idler light is no longer limited by the bandwidth of the signal light. Furthermore, a third-order nonlinear effect is introduced, which can directly generate ultra-wideband idler light without wavelength tuning. Its overall cost is low and it has high promotional value.

[0022] 2. The present invention provides a device for generating mid-infrared laser based on a periodic phase-matched crystal. By performing multiple reflections on the beam within the resonant cavity, the large dispersion generated by the beam passing through multiple dielectric mirrors is avoided, effectively reducing the number of dielectric mirrors and lowering the dispersion. When managing dispersion, only four types of dispersion need to be considered: material dispersion of the nonlinear crystal, material dispersion of the third-order nonlinear crystal, material dispersion of the pump input mirror, and reflection dispersion of the output coupling mirror. The first curved mirror, the second curved mirror, and the cavity mirror have silver-plated layers on their surfaces, and the metallic dispersion generated by their reflection is very small and negligible. Finally, by using a dispersion management unit to compensate for the intracavity dispersion, the total intracavity dispersion can be made close to zero. Attached Figure Description

[0023] Figure 1 This is a schematic diagram of a device for generating mid-infrared laser based on a periodic phase-matching crystal, according to an embodiment of the present invention.

[0024] Figure 2 This is a spectrum of the oscillating idler light in an embodiment of the present invention;

[0025] Figure 3 This is a schematic diagram of the process steps of a method for generating mid-infrared laser based on a periodic phase-matching crystal in an embodiment of the present invention.

[0026] In all the accompanying drawings, the same reference numerals denote the same technical features, specifically: 1-pulse pump source, 2-pump input mirror, 3-first curved mirror, 4-second curved mirror, 5-cavity mirror, 6-output coupling mirror, 7-nonlinear crystal, 8-dispersion management element, 9-third-order nonlinear effect unit, 10-filter. Detailed Implementation

[0027] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. Furthermore, the technical features involved in the various embodiments of this invention described below can be combined with each other as long as they do not conflict with each other.

[0028] like Figure 1-2 As shown, this invention discloses a device for generating mid-infrared laser based on a periodic phase-matched crystal, comprising a pulse pump source 1, a resonant cavity, a pump input mirror 2, a nonlinear crystal 7, a dispersion management element 8, a third-order nonlinear effect unit 9, and a filter 10. The resonant cavity includes a first curved mirror 3 and a second curved mirror 4 symmetrically arranged, an output coupling mirror 6 forming a reflection optical path with the first curved mirror 3, and a cavity mirror 5 forming a reflection optical path with the second curved mirror 4. The nonlinear crystal 7 is disposed between the first curved mirror 3 and the second curved mirror 4, converting the pump light into signal light and idler light; the pump input mirror 2 and the third-order nonlinear effect unit 9 are sequentially disposed in the reflection optical path formed by the first curved mirror 3 and the output coupling mirror 6. When the device of this invention is in operation, the pulse pump source 1 outputs pump light, which is reflected by the pump input mirror 2 onto the first curved mirror 3. After entering the nonlinear crystal 7, it generates signal light and idler light. The idler light has a lower frequency, and its bandwidth is not limited by the bandwidth of the pump light and signal light. It can be selected as the oscillating light to establish resonance by reflecting back and forth in the resonant cavity. When the idler light passes through the third-order nonlinear effect unit 9, the self-phase modulation intensity can be adjusted to achieve spectral broadening. When the spectrally broadened idler light oscillates, it coincides with the pump light input in the adjacent period in the resonant cavity, making the gain greater than the loss, forming a broadband mid-infrared laser output from the output coupling mirror 6. The device of this invention does not require wavelength tuning and other operations, has lower cost, and the idler light bandwidth is no longer limited by the signal light bandwidth. The resonant cavity adopts a method of reducing dielectric mirrors, which gives it better dispersion management function and is beneficial for generating ultrashort pulses.

[0029] like Figure 1As shown, the device described in this embodiment of the invention includes a pulse pump source 1, a pump input mirror 2, a first curved mirror 3, a second curved mirror 4, a cavity mirror 5, an output coupling mirror 6, a nonlinear crystal 7, a dispersion management element 8, a third-order nonlinear effect unit 9, and a filter 10. The pulse pump source 1 is an ultrashort pulse laser, which, together with the nonlinear crystal 7 located inside the resonant cavity, forms an optical parametric oscillator. Its output pump light, after passing through the nonlinear crystal 7, generates a higher-frequency signal light and a lower-frequency idler light. The first curved mirror 3 and the second curved mirror 4 are curved mirrors with a silver-plated layer on their surfaces to reflect light. The cavity mirror 5 is a plane mirror with a silver-plated layer on its surface to reflect light. The pump input mirror 2 is a dielectric mirror with a first coating layer on its surface, providing high reflectivity for the pump light and high transmittance for the signal and idler light. The output coupling mirror 6 is a dielectric mirror with a second coating layer on its surface, providing high transmittance for the signal light and high reflectivity for the idler light. The third-order nonlinear effect unit 9 provides additional self-phase modulation for the oscillating light, including a third-order nonlinear effect crystal and a focusing module. The oscillating light adjusts its focusing distance through the focusing module, changing the size of the spot focused on the crystal to alter the self-phase modulation intensity, thereby achieving different degrees of spectral broadening of the oscillating light. It should be noted that the nonlinear refractive index of the third-order nonlinear effect crystal must be higher than the nonlinear refractive index of the second-order nonlinear crystal (i.e., nonlinear crystal 7) in the optical parametric oscillator to provide third-order nonlinearity.

[0030] In this embodiment of the invention, the pulse pump source 1, together with the nonlinear crystal 2 disposed inside the resonant cavity, constitutes an optical parametric oscillator. The pump light, after passing through the nonlinear crystal 7, generates a higher-frequency signal light and a lower-frequency idler light. The frequency relationship among the idler light, signal light, and pump light is: ωi = ωp - ωs. The lower-frequency light is called the idler light ωi, and the higher-frequency light is called the signal light ωs. When the signal light resonates within the cavity, the bandwidth of the generated idler light is limited by the bandwidths of the pump light and the signal light. Therefore, this invention proposes using the low-frequency idler light as the oscillating light, and by introducing a third-order nonlinear effect, broadening the spectrum of the oscillating light to directly generate broadband mid-infrared laser light, whose bandwidth is not limited by the bandwidths of the pump light and the signal light.

[0031] In this embodiment of the invention, to achieve near-zero dispersion within the resonant cavity, the beam within the resonant cavity undergoes multiple reflections while introducing the dispersion management element 8. This avoids significant dispersion caused by the beam passing through multiple dielectric mirrors, effectively reducing the number of times the beam passes through the dielectric mirrors and lowering the dispersion. The resonant cavity includes a first curved mirror 3, a second curved mirror 4, a cavity mirror 5, and an output coupling mirror 6, forming multiple reflected light paths. Idle light oscillates by reflecting back and forth along these paths. The first curved mirror 3, the second curved mirror 4, the cavity mirror 5, and the output coupling mirror 6 are arranged in an X-shape, with the first curved mirror 3 and the second curved mirror 4 located at the bottom, and the cavity mirror 5 and the output coupling mirror 6 respectively located above the first curved mirror 3 and the second curved mirror 4. The nonlinear crystal 7 is disposed in the first reflected light path formed between the first curved mirror 3 and the second curved mirror 4; the dispersion management element 8 is disposed in the second reflected light path formed between the second curved mirror 4 and the cavity mirror 5; the pump input mirror 2 and the third-order nonlinear effect unit 9 are sequentially disposed in the third reflected light path formed by the first curved mirror 3 and the output coupling mirror 6. The pump input mirror 2 and the pump light output from the pulse pump source 1 have a certain tilt angle. After the pump light shines on the pump input mirror 2, it is reflected along the third reflected light path to the first curved mirror 3. After being reflected by the first curved mirror 3, it enters the nonlinear crystal 7 to generate idler light and signal light.

[0032] The path of the idler light reflected back and forth in the resonant cavity is as follows: it shines on the second curved mirror 4 along the first reflection path, and after reflection, it shines perpendicularly on the cavity mirror 5 along the second reflection path. After being reflected by the silver plating layer on the surface of the cavity mirror 5, it shines on the second curved mirror 4 along the second reflection path. After being reflected, it shines on the first curved mirror 3 along the first reflection path. After being reflected, it passes through the pump input mirror 2 and enters the nonlinear effect unit 9 along the third reflection path. After achieving spectral broadening, it shines perpendicularly on the output coupling mirror 6. After being reflected by the output coupling mirror 6, it shines on the first curved mirror 3 along the third reflection path. The spectrally broadened idler light is reflected by the first curved mirror 3 and enters the nonlinear crystal 7 along the first reflection path, thus completing one oscillation cycle of the idler light in the resonant cavity.

[0033] In this embodiment of the invention, the cavity length of the resonant cavity is matched with the repetition rate of the pump source, that is, the period of the idler light oscillating back and forth in the cavity is equal to the period of the adjacent pump light entering the oscillator. During the process of the idler light establishing oscillation in the resonant cavity, the pump light, signal light, and idler light coincide in time and space, making the gain of the idler light greater than its loss, thus forming a broadband mid-infrared laser output. When the broadband mid-infrared laser is output through the output coupling mirror 6, part of the pump light and signal light are also simultaneously output through the output coupling mirror 6. To avoid interference from the pump light and signal light to the broadband mid-infrared laser, the output end of the output coupling mirror 6 is also provided with a filter 10 to filter the pump light and signal light. The filter 10 is made of germanium, which has a wide infrared transmission band and can transmit the broadband mid-infrared laser while filtering the pump light and signal light.

[0034] In this embodiment of the invention, by placing a dispersion management element 8 inside the resonant cavity, which can be a silicon wafer, grating, or prism pair, the total dispersion inside the cavity is brought close to zero. When using a silicon wafer to compensate for the dispersion inside the cavity, it should be placed at Brewster's angle to reduce cavity losses. In the dispersion management of the device of the present invention, only four types of dispersion need to be considered: the material dispersion of the nonlinear crystal 7, the material dispersion of the third-order nonlinear crystal, the material dispersion of the pump input mirror 2, and the reflection dispersion of the output coupling mirror 6. Among them, the first curved mirror 3, the second curved mirror 4, and the cavity mirror 5 have a silver-plated layer on their mirror surfaces, and the metallic dispersion generated by their reflection is very small and negligible.

[0035] Taking numerical simulation as an example, the center wavelength of the pump light output from pulse pump source 1 is 1064 nm, the average power is 5 W, and the pulse width is 100 fs. The nonlinear crystal 7 is a uniformly periodically polarized lithium niobate crystal with a polarization period of 29.48 μm, generating idler light with a center wavelength of 3700 nm. The third-order nonlinear crystal is a zinc selenide crystal; the idler light, after passing through the focusing module, has a focused spot diameter of 15 μm on the third-order nonlinear crystal. The dispersion compensation element is a 10 mm long silicon wafer. Simulation results are as follows: Figure 2 As shown, the instantaneous bandwidth of the generated oscillating light is 3-5μm, directly covering an atmospheric window without the need for wavelength tuning or other operations, breaking the limitation of conventional idler light bandwidth on the bandwidth of signal light and pump light.

[0036] like Figure 3 As shown, this embodiment of the invention also provides a method for generating mid-infrared laser based on a periodic phase-matched crystal, comprising the following steps:

[0037] S100: Based on the broadband light to be generated, determine the appropriate pulse pump source and nonlinear crystal; adjust the third-order nonlinear effect unit according to the calculated idler light bandwidth generated by the nonlinear crystal, so that the focusing module adjusts the focusing distance, changes the spot size of the idler light focused on the crystal, thereby performing self-phase modulation, and broadening the spectrum of the idler light to the required bandwidth.

[0038] S200: Determine the cavity length of the resonant cavity based on the repetition frequency of the pulse pump source, and select appropriate values ​​according to the cavity stabilization calculation formula to determine the placement positions of the first curved mirror 3, the second curved mirror 4, the cavity mirror 5, and the output coupling mirror 6, as well as the radii of curvature of the first curved mirror 3 and the second curved mirror 4; after adjusting the position and angle of the resonant cavity components, determine the placement angle and position of the pulse pump source 1, the pump input mirror 2, the third-order nonlinear effect unit 9, and the filter 10;

[0039] S300: A dispersion management element 8 is placed in the second reflected light path formed between the second curved mirror 4 and the cavity mirror 5 to compensate for intracavity dispersion;

[0040] S400: The pump light output from the pulse pump source 1 is reflected sequentially by the pump input mirror 2 and the first curved mirror 3 before entering the nonlinear crystal 7 to generate signal light and idler light. The signal light is filtered out by the output coupling mirror 6, leaving the idler light as the oscillation light to establish oscillation. The idler light is then spectrally broadened by the third-order nonlinear effect unit 9. The spectrally broadened idler light coincides with the adjacent periodic pump light and signal light in time and space, so that the gain of the idler light is greater than the loss, forming the desired broadband mid-infrared laser output.

[0041] Those skilled in the art will readily understand that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A device for generating mid-infrared laser based on a periodic phase-matched crystal, characterized in that, include: The pulse pump source (1) is an ultrashort pulse laser; The resonant cavity, whose cavity length matches the repetition frequency of the pump source, includes a first curved mirror (3) and a second curved mirror (4) located at the bottom, a cavity mirror (5) and an output coupling mirror (6) located above the first curved mirror (3) and the second curved mirror (4) respectively, and the four are arranged in an X-shaped structure; a first reflected light path is formed between the first curved mirror (3) and the second curved mirror (4), a second reflected light path is formed between the second curved mirror (4) and the cavity mirror (5), and a third reflected light path is formed between the first curved mirror (3) and the output coupling mirror (6); The nonlinear crystal (7) located in the first reflected optical path forms an optical parametric oscillator with the pulse pump source (1) located in the resonant cavity; A pump input mirror (2) and a third-order nonlinear effect unit (9) are sequentially arranged in the third reflection optical path. The pump input mirror (2) reflects the pump light output from the pulse pump source (1) onto the first curved mirror (3). The pump light then passes through the nonlinear crystal (7) along the first reflection optical path to generate signal light and idler light. The third-order nonlinear effect unit (9) broadens the spectrum of the idler light to the required bandwidth. The idler light, as an oscillating light, establishes oscillation in the resonant cavity. It coincides with the adjacent periodic pump light and signal light in time and space, so that the gain of the idler light is greater than the loss, forming the required broadband mid-infrared laser output. The dispersion management element (8) located in the second reflected optical path compensates for the dispersion in the resonant cavity and reduces the total dispersion in the cavity; The filter (10) located at the output end of the output coupling mirror (6) filters the pump light and signal light, and provides high transmittance for broadband mid-infrared laser.

2. The device for generating mid-infrared laser based on a periodic phase-matched crystal according to claim 1, characterized in that, The path by which the idler light establishes oscillation in the resonant cavity is as follows: it is irradiated on the second curved mirror (4) along the first reflected light path, and after reflection, it is irradiated perpendicularly on the cavity mirror (5) along the second reflected light path. After reflection by the cavity mirror (5), it is irradiated on the second curved mirror (4) along the second reflected light path. After reflection, it is irradiated on the first curved mirror (3) along the first reflected light path. After reflection, it passes through the pump input mirror (2) and enters the nonlinear effect unit (9) along the third reflected light path. After achieving spectral broadening, it is irradiated perpendicularly on the output coupling mirror (6). After reflection by the output coupling mirror (6), it is irradiated on the first curved mirror (3) along the third reflected light path. After the spectrally broadened idler light is reflected by the first curved mirror (3) and enters the nonlinear crystal (7) along the first reflected light path, the idler light completes one oscillation cycle in the resonant cavity.

3. The device for generating mid-infrared laser based on a periodic phase-matched crystal according to claim 1, characterized in that, The third-order nonlinear effect unit (9) provides additional self-phase modulation for the oscillating light, including a third-order nonlinear effect crystal and a focusing module; the oscillating light adjusts the focusing distance through the focusing module, changes the size of the spot focused on the crystal, and thus changes the self-phase modulation intensity, thereby achieving different degrees of spectral broadening of the oscillating light.

4. The device for generating mid-infrared laser based on a periodic phase-matched crystal according to claim 3, characterized in that, The nonlinear refractive index of the third-order nonlinear effect crystal is higher than that of the nonlinear crystal (7) in the optical parametric oscillator.

5. A device for generating mid-infrared laser based on a periodic phase-matched crystal according to any one of claims 1-4, characterized in that, The first curved mirror (3) and the second curved mirror (4) are curved mirrors with a silver plating layer on the mirror surface to reflect light.

6. A device for generating mid-infrared laser based on a periodic phase-matched crystal according to any one of claims 1-4, characterized in that, The cavity mirror (5) is a plane mirror with a silver-plated layer on its surface, which can reflect light.

7. A device for generating mid-infrared laser based on a periodic phase-matched crystal according to any one of claims 1-4, characterized in that, The pump input mirror (2) is a dielectric mirror with a first coating layer on its surface, which can reflect the pump light highly and transmit the signal light and idler light highly. The output coupling mirror (6) is a dielectric mirror with a second coating layer on its surface, which can transmit signal light at high speed and reflect idler light at high speed.

8. A device for generating mid-infrared laser based on a periodic phase-matched crystal according to any one of claims 1-4, characterized in that, The dispersion management element (8) is any one of a dispersion compensation device, such as a silicon wafer, a grating, or a prism.

9. A device for generating mid-infrared laser based on a periodic phase-matched crystal according to any one of claims 1-4, characterized in that, The filter (10) is made of germanium with high transmittance in the mid-infrared band.

10. A method for generating mid-infrared laser based on a periodic phase-matched crystal, characterized in that, Includes the following steps: S100: Based on the broadband light to be generated, determine the appropriate pulse pump source and second-order nonlinear crystal; adjust the third-order nonlinear effect unit based on the calculated idler light bandwidth generated by the nonlinear crystal, including the selection of third-order nonlinear crystal materials and optimization of the focusing module, so that the focusing module adjusts the focusing distance, changes the spot size of the idler light focused on the crystal, thereby performing self-phase modulation, and broadening the spectrum of the idler light to the required bandwidth; S200: Determine the cavity length of the resonant cavity based on the repetition frequency of the pulse pump source, and select appropriate values ​​according to the cavity stabilization calculation formula to determine the placement positions of the first curved mirror (3), the second curved mirror (4), the cavity mirror (5), and the output coupling mirror (6), as well as the curvature radii of the first curved mirror (3) and the second curved mirror (4); After completing the position and angle adjustment of the resonant cavity constituent elements, determine the placement angle and position of the pulse pump source (1), the pump input mirror (2), the third-order nonlinear effect unit (9), and the filter (10); S300: A dispersion management element (8) is placed in the second reflected light path formed between the second curved mirror (4) and the cavity mirror (5) to compensate for intracavity dispersion; S400: The pump light output from the pulse pump source (1) is reflected sequentially by the pump input mirror (2) and the first curved mirror (3) and then enters the nonlinear crystal (7) to generate signal light and idler light. The signal light is filtered out by the output coupling mirror (6), leaving the idler light as the oscillation light to establish oscillation. The idler light is then spectrally broadened by the third-order nonlinear effect unit (9). The spectrally broadened idler light coincides with the adjacent periodic pump light and signal light in time and space, so that the gain of the idler light is greater than the loss, forming the required broadband mid-infrared laser output.

Images