A mid-infrared narrow linewidth pulsed laser

Abstract

This invention relates to the field of laser technology, and more particularly to a mid-infrared narrow-linewidth pulsed laser, comprising: a first total reflection mirror, a gain medium, an acousto-optic modulator, an F-P etalon, a second total reflection mirror, and a third total reflection mirror; the gain medium is located on a first side of the acousto-optic modulator, and the first total reflection mirror is located on the side of the gain medium away from the acousto-optic modulator; the F-P etalon is located on a second side of the acousto-optic modulator, and the second total reflection mirror is located on the side of the F-P etalon away from the acousto-optic modulator; the third total reflection mirror is located on a third side of the acousto-optic modulator; in each cycle, the acousto-optic modulator sequentially enters a Raman-Nice diffraction state, a Bragg diffraction state, and a non-diffraction state, so that the mid-infrared narrow-linewidth pulsed laser sequentially performs linewidth narrowing operation, gain amplification operation, and cavity emptying output operation, thereby outputting a narrow-linewidth amplified pulsed laser. This invention is at least advantageous for achieving narrow-linewidth, high-power single-longitudinal-mode laser output.

Description

Technical Field

[0001] This invention belongs to the field of laser technology, and particularly relates to a mid-infrared narrow-linewidth pulsed laser. Background Technology

[0002] Mid-infrared 2μm lasers, due to their output wavelength falling within an important atmospheric transmission window and the safe range for the human eye, have broad application prospects in fields such as lidar, environmental remote sensing, medical surgery, and optoelectronic countermeasures. For coherent lidar systems, the core requirement is that the laser can achieve high-power, stable pulse output in a single longitudinal mode. 2μm solid-state lasers operating in a single longitudinal mode not only inherit the good coherence and directionality of traditional lasers, but also significantly improve the system's detection accuracy and resolution due to their extremely narrow spectral linewidth and ultra-long coherence length. Since the advent of lasers, researchers have found that most lasers oscillate in multiple longitudinal modes during operation. Numerous experimental and theoretical studies have shown that multi-longitudinal-mode lasers have inherent drawbacks such as poor monochromaticity and short coherence lengths leading to fluctuating output energy. The beat frequency effect between multiple longitudinal modes generates irregular energy spikes in the time domain, not only reducing the signal-to-noise ratio but also potentially causing irreversible damage to optical components in high-peak-power applications. Therefore, developing high-performance single-longitudinal-mode laser technology to obtain high-quality laser beams with narrow linewidth, smooth time-domain waveforms, and long coherence lengths has become a key technical problem that urgently needs to be solved in this field.

[0003] To obtain lasers operating in a single longitudinal mode, many single-longitudinal-mode selection techniques have been developed, mainly including the torsional cavity method, the FP etalon method, and the pre-laser Q-switching method. Among them, the torsional cavity method and the FP etalon method can effectively suppress side modes and achieve single-longitudinal-mode laser output by introducing specific frequency selection mechanisms. However, these two methods usually have high insertion loss, which limits the output efficiency of the laser. Under high-power pump conditions, their stability is poor and they still need to be combined with other mode selection techniques. The pre-laser Q-switching method controls the dynamic process of resonant cavity loss, first generating a broadband "pre-laser" pulse as a seed in a low Q-value state, and then amplifying the seed light through rapid Q-switching. This method has the advantages of relatively simple system and easy realization of high repetition rate pulse output, but its core drawback is its limited frequency selection capability. Under high pump power injection, it is very easy to excite multiple longitudinal modes, resulting in low single-longitudinal-mode success rate and poor output stability, making it difficult to meet the stringent requirements of high-end applications for laser source quality. Summary of the Invention

[0004] In view of this, the present invention aims to provide a mid-infrared narrow linewidth pulsed laser, which is at least advantageous for achieving narrow linewidth, high-power single longitudinal mode laser output.

[0005] To achieve the above objectives, the technical solution created by this invention is implemented as follows: This invention provides a mid-infrared narrow-linewidth pulsed laser, comprising: a first total reflection mirror, a gain medium, an acousto-optic modulator, a FP etalon, a second total reflection mirror, and a third total reflection mirror; the gain medium is located on the first side of the acousto-optic modulator, and the first total reflection mirror is located on the side of the gain medium away from the acousto-optic modulator; the FP etalon is located on the second side of the acousto-optic modulator, and the second total reflection mirror is located on the side of the FP etalon away from the acousto-optic modulator; the third total reflection mirror is located on the third side of the acousto-optic modulator; in each cycle, the acousto-optic modulator sequentially enters a Raman-Nice diffraction state, a Bragg diffraction state, and a non-diffraction state, so that the mid-infrared narrow-linewidth pulsed laser sequentially performs linewidth narrowing operation, gain amplification operation, and cavity emptying output operation, thereby outputting a narrow-linewidth amplified pulsed laser.

[0006] Furthermore, the single-pulse linewidth of narrow-linewidth amplified pulsed lasers is in the range of 30MHz to 100MHz.

[0007] Furthermore, the first and second total internal reflection mirrors serve as the two ends of the linewidth-narrowing resonant cavity, while the first and third total internal reflection mirrors serve as the two ends of the gain-amplifying resonant cavity. Within each cycle, stimulated emission of the gain medium generates broadband spontaneous emission light. The acousto-optic modulator first enters the Raman-Nice diffraction state. The broadband spontaneous emission light, after passing through the acousto-optic modulator, forms multi-order diffraction light. Specific order diffracted light within the multi-order diffracted light resonates within the linewidth-narrowing resonant cavity. The FP etalon performs mode selection and linewidth narrowing on the specific order diffracted light, thereby forming seed light. (Mid-infrared...) A narrow-linewidth pulsed laser achieves linewidth narrowing operation. Subsequently, when the acousto-optic modulator enters the Bragg diffraction state, the seed light passes through the acousto-optic modulator to form Bragg diffraction, generating first-order diffracted light. The first-order diffracted light resonates in the gain amplification resonant cavity to achieve gain amplification, forming a narrow-linewidth amplified pulsed laser. The mid-infrared narrow-linewidth pulsed laser achieves gain amplification operation. After the energy in the gain amplification resonant cavity reaches saturation, the acousto-optic modulator enters a non-diffraction state, and the narrow-linewidth amplified pulsed laser is directly output from the fourth side of the acousto-optic modulator. The mid-infrared narrow-linewidth pulsed laser achieves cavity emptying output operation.

[0008] Furthermore, a specific order of diffraction light in multi-order diffraction light is second-order diffraction light.

[0009] Furthermore, the mid-infrared narrow linewidth pulsed laser also includes a side-pump module, which is arranged in a ring around the outside of the gain medium and is used to pump the gain medium.

[0010] Furthermore, the side pump module includes N side pump units, which are arranged circumferentially along the gain medium, where N is an odd number.

[0011] Furthermore, the mid-infrared narrow-linewidth pulsed laser also includes an acousto-optic frequency driver, which is connected to an acousto-optic modulator. The acousto-optic frequency driver is used to send low-frequency radio frequency signals to the acousto-optic modulator to induce the acousto-optic modulator into a Raman-Nice diffraction state. The acousto-optic frequency driver is also used to send high-frequency radio frequency signals to the acousto-optic modulator to induce the acousto-optic modulator into a Bragg diffraction state. Finally, the acousto-optic frequency driver stops sending radio frequency signals to the acousto-optic modulator to induce the acousto-optic modulator into a non-diffraction state.

[0012] Furthermore, the frequency of low-frequency radio frequency signals is in the range of 1MHz to 10MHz; the frequency of high-frequency radio frequency signals is in the range of 100MHz to 130MHz.

[0013] Furthermore, the output center wavelength of the mid-infrared narrow-linewidth pulsed laser is in the range of 1.8μm to 2.2μm.

[0014] Furthermore, when the acousto-optic modulator is in Raman-Nice diffraction state, the diffraction angle of the second-order diffracted light formed by the acousto-optic modulator diffraction is... satisfy: When the acousto-optic modulator is in Bragg diffraction mode, the diffraction angle of the first-order diffracted light along the diffraction path of the acousto-optic modulator. satisfy: ;in, Represents the angle of incident light. Represents wavelength, Represents the wavelength of sound waves. It represents the refractive index of the acousto-optic medium.

[0015] Compared with the prior art, the present invention can achieve the following beneficial effects: In order to improve the output performance of single-longitudinal-mode pulsed lasers and simplify their structure, the present invention provides a mid-infrared narrow-linewidth pulsed laser. By acousto-optic modulation of the diffraction state of the acousto-optic modulator, the entire process of linewidth narrowing operation, gain amplification operation and cavity emptying output operation is realized with a relatively simple laser structure, thereby outputting a narrow-linewidth amplified pulsed laser. This is beneficial to further compress the pulse width while reducing the structural complexity of the single-longitudinal-mode pulsed laser, and realize stable and efficient output of narrow-linewidth, high-power single-longitudinal-mode laser. Attached Figure Description

[0016] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments and descriptions of the invention are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings: Figure 1 A schematic diagram of the structure of the mid-infrared narrow-linewidth pulsed laser described in the embodiment of the present invention; Figure 2A schematic diagram of the acousto-optic modulation process of the mid-infrared narrow-linewidth pulsed laser described in the embodiments of the present invention; Figure 3 A schematic diagram of the side pump module and gain medium as described in the embodiment of the present invention; Figure 4 This is a schematic diagram of the optical path of the mid-infrared narrow-linewidth pulsed laser performing linewidth narrowing operation according to an embodiment of the present invention; Figure 5 This is a schematic diagram of the optical path when the mid-infrared narrow-linewidth pulsed laser performs gain amplification operation according to an embodiment of the present invention; Figure 6 This is a schematic diagram of the optical path during cavity emptying output operation of the mid-infrared narrow-linewidth pulsed laser described in the embodiments of the present invention; Figure 7 A comparison diagram of the spectral linewidth of the mid-infrared narrow-linewidth pulsed laser described in the embodiments of the present invention and that of a conventional single-mode laser.

[0017] Explanation of reference numerals in the attached figures: 1. First total reflection mirror; 2. Side pump module; 3. Gain medium; 4. Acousto-optic modulator; 6. FP etalon; 5. Second total reflection mirror; 7. Third total reflection mirror; 21. Side pump unit. Detailed Implementation

[0018] 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 specific embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and do not constitute a limitation thereof.

[0019] It should be noted that, unless otherwise specified, the embodiments and features described in the present invention can be combined with each other.

[0020] In the description of this invention, it should be understood that the terms "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," and "counterclockwise," etc., indicating orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, are only for the convenience of describing this 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, and therefore should not be construed as a limitation on this invention. Furthermore, the terms "first," "second," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, features defined with "first," "second," etc., may explicitly or implicitly include one or more of that feature. In the description of this invention, unless otherwise stated, "a plurality of" means two or more.

[0021] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art will understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0022] The invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0023] refer to Figures 1 to 6 This invention provides a mid-infrared narrow-linewidth pulsed laser, comprising: a first total reflection mirror 1, a gain medium 3, an acousto-optic modulator 4, a FP etalon 6, a second total reflection mirror 5, and a third total reflection mirror 7; the gain medium 3 is located on the first side of the acousto-optic modulator 4, and the first total reflection mirror 1 is located on the side of the gain medium 3 away from the acousto-optic modulator 4; the FP etalon 6 is located on the second side of the acousto-optic modulator 4, and the second total reflection mirror 5 is located on the side of the FP etalon 6 away from the acousto-optic modulator 4; the third total reflection mirror 7 is located on the third side of the acousto-optic modulator 4; in each cycle, the acousto-optic modulator 4 sequentially enters a Raman-Nice diffraction state, a Bragg diffraction state, and a non-diffraction state, so that the mid-infrared narrow-linewidth pulsed laser sequentially performs linewidth narrowing operation, gain amplification operation, and cavity emptying output operation, thereby outputting a narrow-linewidth amplified pulsed laser.

[0024] In some embodiments, the gain medium 3 can be a Tm:YAP laser crystal.

[0025] It should be noted that the acousto-optic interaction in the acousto-optic modulator 4 is mainly divided into two types: Raman-Nice diffraction and Bragg diffraction. This invention achieves linewidth narrowing, gain amplification, and cavity emptying output operations by controlling the diffraction type of the acousto-optic modulator 4.

[0026] Furthermore, the single-pulse linewidth of narrow-linewidth amplified pulsed lasers is in the range of 30MHz to 100MHz, which can also be expressed as being in the range of 0.378pm to 1.26pm.

[0027] Furthermore, the first total reflection mirror 1 and the second total reflection mirror 5 serve as the two ends of the linewidth narrowing resonant cavity, and the first total reflection mirror 1 and the third total reflection mirror 7 serve as the two ends of the gain amplification resonant cavity. In each cycle, the gain medium 3 generates broadband spontaneous emission light through stimulated emission. The acousto-optic modulator 4 first enters the Raman-Nice diffraction state. The broadband spontaneous emission light passes through the acousto-optic modulator 4 to form Raman-Nice diffraction, generating multi-order diffraction light. Specific order diffraction lights in the multi-order diffraction light resonate within the linewidth narrowing resonant cavity. The FP etalon 6 performs mode selection and linewidth narrowing on the specific order diffraction light, thereby forming seed light. The mid-infrared narrow-linewidth pulsed laser achieves linewidth narrowing operation, that is, realizes the cultivation of seed light with a single longitudinal mode and narrow linewidth. However, the seed light in this invention is a self-injected seed light; subsequently, when the acousto-optic modulator 4 enters the Bragg diffraction state, the seed light passes through the acousto-optic modulator 4 to form Bragg diffraction and generate first-order diffracted light. The first-order diffracted light resonates in the gain amplification resonant cavity to achieve gain amplification and form a narrow-linewidth amplified pulse laser. The mid-infrared narrow-linewidth pulse laser achieves gain amplification operation, that is, achieves efficient energy amplification. After the energy in the gain amplification resonant cavity reaches saturation, the acousto-optic modulator 4 enters a non-diffraction state, and the narrow-linewidth amplified pulse laser is directly output from the fourth side of the acousto-optic modulator 4. That is, the energy stored in the gain amplification resonant cavity is efficiently output in the form of a narrow-linewidth pulse at once, and the mid-infrared narrow-linewidth pulse laser achieves cavity emptying output operation.

[0028] Furthermore, a specific order of diffraction light in multi-order diffraction light is second-order diffraction light.

[0029] In this process, the FP etalon 6 needs to be placed in the second-order diffraction path. The FP etalon 6 has frequency selectivity, meaning that only extremely narrow-band longitudinal modes matching the transmission peak of the FP etalon 6 are allowed to pass through with low loss, while other side modes are suppressed, achieving further linewidth compression. The energy of the first-order diffracted light generated by Bragg diffraction is highly concentrated; therefore, the first-order diffracted beam can be used to achieve efficient seed light amplification.

[0030] It should be noted that the mid-infrared narrow linewidth pulsed laser provided by the present invention requires multiple cycles of linewidth narrowing operation, gain amplification operation, and cavity emptying output operation to perform pulsed energy injection and energy storage on the gain medium 3, that is, intermittently injecting energy into the gain medium 3, which is beneficial to achieve high peak power output and to alleviate thermal effects.

[0031] The reason for choosing second-order diffraction light for linewidth narrowing is that, under Raman-Nice diffraction conditions, second-order diffraction light can provide a low-power, low-gain, and controllable-loss pre-laser oscillation channel, making it more suitable for use with FP etalon 6 to complete seed photoculture.

[0032] For linewidth narrowing operations, the remaining light that does not pass through the FP etalon 6 or is in other diffraction orders is lost. Therefore, it is possible to perform spectrally specific selection and optimization of a single longitudinal mode seed, thereby achieving effective linewidth compression.

[0033] For gain amplification operation, the light energy is highly concentrated in the first-order diffraction path. The first-order diffraction path and the cavity mirror form a low-loss master oscillation cavity, namely the gain amplification resonant cavity. The high-quality narrow-linewidth seed light that has completed the longitudinal mode selection after the linewidth narrowing operation is then injected into the gain amplification resonant cavity. Due to the sudden drop in cavity loss, the seed light obtains extremely high cyclic amplification gain in the gain medium 3, rapidly extracts the number of inverted particles stored in the cavity, and the pulse energy is efficiently amplified.

[0034] For cavity emptying output operation, the acousto-optic modulator 4 will only enter the diffraction-free state and achieve cavity emptying output when the energy accumulation in the gain amplification resonant cavity reaches saturation. It should be noted that the energy accumulation in the gain amplification resonant cavity is considered to have reached saturation when the seed light undergoes multiple round trips of amplification within the cavity, causing the light intensity increase to stabilize and the energy stored in the gain medium 3 to reach its maximum. When the acousto-optic modulator 4 enters the diffraction-free state, all high-energy laser light within the cavity can no longer be confined and will be released entirely out of the cavity along the output direction, forming a high peak power, narrow linewidth output pulse.

[0035] Furthermore, the mid-infrared narrow linewidth pulsed laser also includes a side-pump module 2, which is arranged around the outside of the gain medium 3 and is used to pump the gain medium 3.

[0036] Furthermore, the side pump module 2 includes N side pump units 21, which are uniformly arranged along the circumference of the gain medium 3. N is an odd number. The use of an odd number of side pump units 21 uniformly arranged along the circumference of the gain medium 3 is to prevent collinear damage of the side pump units. In some examples, the side pump unit 21 is an LD (Laser Diode) target strip.

[0037] Furthermore, the mid-infrared narrow-linewidth pulsed laser also includes an acousto-optic frequency driver (not shown), which is connected to the acousto-optic modulator 4. The acousto-optic frequency driver is used to send radio frequency signals to the acousto-optic modulator 4 to control the diffraction state of the acousto-optic modulator 4. Specifically, the acousto-optic frequency driver sends low-frequency radio frequency signals to the acousto-optic modulator 4 to make the acousto-optic modulator 4 enter the Raman-Nice diffraction state; the acousto-optic frequency driver sends high-frequency radio frequency signals to the acousto-optic modulator 4 to make the acousto-optic modulator 4 enter the Bragg diffraction state; the acousto-optic frequency driver stops sending radio frequency signals to the acousto-optic modulator 4 to make the acousto-optic modulator 4 enter the non-diffraction state.

[0038] In other words, the acousto-optic frequency driver can generate and switch radio frequency signals of different frequencies to precisely control the diffraction type of the acousto-optic modulator 4. Specifically, the radio frequency signal output by the acousto-optic frequency driver acts on the acousto-optic modulator 4 and is converted into ultrasonic waves. When the ultrasonic waves pass through the acousto-optic medium of the acousto-optic modulator 4, they cause local compression and elongation of the medium, resulting in elastic strain. This strain changes periodically with time and space, causing the medium to exhibit alternating periods of density and rarefaction, like a phase grating. When light passes through this medium disturbed by ultrasonic waves, diffraction occurs.

[0039] Furthermore, the frequency of low-frequency radio frequency signals is in the range of 1MHz to 10MHz; the frequency of high-frequency radio frequency signals is in the range of 100MHz to 130MHz.

[0040] Furthermore, the mid-infrared narrow-linewidth pulsed laser is a 2μm band narrow-linewidth pulsed laser, and the output center wavelength of the mid-infrared narrow-linewidth pulsed laser is in the range of 1.8μm to 2.2μm.

[0041] For the Bragg diffraction of the acousto-optic modulator 4, the following formula exists: For the Raman-Nass diffraction of the acousto-optic modulator 4, the following formula exists: ,in, The wavelength of the sound wave. The refractive index of the acousto-optic medium, The angle of incidence light, For the first First-order diffraction angle, For wavelength, This refers to the diffraction order.

[0042] Therefore, when the acousto-optic modulator 4 is in Raman-Nice diffraction state, the diffraction angle of the second-order diffracted light formed by the acousto-optic modulator 4 can be obtained. satisfy: When the acousto-optic modulator 4 is in Bragg diffraction state, the diffraction angle of the first-order diffracted light in the diffraction path of the acousto-optic modulator 4 is... satisfy: ;in, Represents the angle of incident light. Represents wavelength, Represents the wavelength of sound waves. It represents the refractive index of the acousto-optic medium.

[0043] Figure 7 This invention provides a comparison diagram of the spectral linewidth of a mid-infrared narrow-linewidth pulsed laser and that of a conventional single-mode laser. The dashed line represents the output spectrum of the conventional single-mode laser, which exhibits a wider spectral linewidth, while the solid line represents the output spectrum of this invention, which shows a significantly narrower spectral linewidth. Thus, it can be seen that the mid-infrared narrow-linewidth pulsed laser provided by this invention can achieve a single-pulse spectral linewidth in the range of 30MHz to 100MHz, realizing the output of a narrower linewidth pulsed laser.

[0044] It should be understood that the various forms of processes shown above can be used to reorder, add, or delete steps. For example, the steps described in this invention disclosure can be executed in parallel, sequentially, or in different orders, as long as the desired result of the technical solution disclosed in this invention can be achieved, and this is not limited herein.

[0045] The specific embodiments described above do not constitute a limitation on the scope of protection of this invention. Those skilled in the art should understand that various modifications, combinations, sub-combinations, and substitutions can be made according to design requirements and other factors. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of this invention should be included within the scope of protection of this invention.

Claims

1. A mid-infrared narrow-linewidth pulsed laser, characterized in that, include: First total reflection mirror, gain medium, acousto-optic modulator, FP etalon, second total reflection mirror, and third total reflection mirror; The gain medium is located on the first side of the acousto-optic modulator, and the first total reflection mirror is located on the side of the gain medium away from the acousto-optic modulator. The FP etalon is located on the second side of the acousto-optic modulator, and the second total reflection mirror is located on the side of the FP etalon away from the acousto-optic modulator; The third total reflection mirror is located on the third side of the acousto-optic modulator; Within each cycle, the acousto-optic modulator sequentially enters a Raman-Nice diffraction state, a Bragg diffraction state, and a non-diffraction state, so that the mid-infrared narrow-linewidth pulsed laser sequentially performs linewidth narrowing operation, gain amplification operation, and cavity emptying output operation, thereby outputting narrow-linewidth amplified pulsed laser.

2. The mid-infrared narrow-linewidth pulsed laser according to claim 1, characterized in that, The single-pulse linewidth of the narrow-linewidth amplified pulse laser is in the range of 30MHz to 100MHz.

3. The mid-infrared narrow-linewidth pulsed laser according to claim 1, characterized in that, The first total reflection mirror and the second total reflection mirror serve as the two ends of the linewidth-shortened resonant cavity, and the first total reflection mirror and the third total reflection mirror serve as the two ends of the gain-amplified resonant cavity. Within each cycle, the gain medium generates broadband spontaneous emission light through stimulated emission. The acousto-optic modulator first enters the Raman-Nice diffraction state. The broadband spontaneous emission light passes through the acousto-optic modulator to form Raman-Nice diffraction, generating multi-order diffraction light. Specific order diffraction light in the multi-order diffraction light resonates in the linewidth-narrowing resonant cavity. The FP etalon performs mode selection and linewidth narrowing on the specific order diffraction light to form seed light. The mid-infrared narrow-linewidth pulsed laser performs linewidth narrowing operation. Subsequently, when the acousto-optic modulator enters the Bragg diffraction state, the seed light passes through the acousto-optic modulator to form Bragg diffraction and generate first-order diffracted light. The first-order diffracted light resonates in the gain amplification resonant cavity to achieve gain amplification and form a narrow-linewidth amplified pulsed laser. The mid-infrared narrow-linewidth pulsed laser achieves the gain amplification operation. After the energy in the gain amplification resonant cavity reaches saturation, the acousto-optic modulator enters a diffraction-free state, and the narrow-linewidth amplified pulsed laser is directly output from the fourth side of the acousto-optic modulator. The mid-infrared narrow-linewidth pulsed laser achieves cavity emptying output operation.

4. The mid-infrared narrow-linewidth pulsed laser according to claim 3, characterized in that, The specific order of diffraction light in the multi-level diffraction light is second-order diffraction light.

5. The mid-infrared narrow-linewidth pulsed laser according to claim 1, characterized in that, The mid-infrared narrow-linewidth pulsed laser further includes a side-pumping module, which is arranged around the outside of the gain medium and is used to pump the gain medium.

6. The mid-infrared narrow-linewidth pulsed laser according to claim 5, characterized in that, The side pumping module includes N side pumping units, which are arranged circumferentially along the gain medium, where N is an odd number.

7. The mid-infrared narrow-linewidth pulsed laser according to claim 1, characterized in that, The mid-infrared narrow-linewidth pulsed laser also includes an acousto-optic frequency driver, which is connected to the acousto-optic modulator. The acousto-optic frequency driver is used to send a low-frequency radio frequency signal to the acousto-optic modulator so that the acousto-optic modulator enters the Raman-Nice diffraction state; The acousto-optic frequency driver is used to send a high-frequency radio frequency signal to the acousto-optic modulator so that the acousto-optic modulator enters the Bragg diffraction state. The acousto-optic frequency driver stops sending radio frequency signals to the acousto-optic modulator, so that the acousto-optic modulator enters a diffraction-free state.

8. The mid-infrared narrow-linewidth pulsed laser according to claim 7, characterized in that, The low-frequency radio frequency signal has a frequency range of 1MHz to 10MHz; the high-frequency radio frequency signal has a frequency range of 100MHz to 130MHz.

9. The mid-infrared narrow-linewidth pulsed laser according to claim 1, characterized in that, The output center wavelength of the mid-infrared narrow-linewidth pulsed laser is in the range of 1.8μm to 2.2μm.

10. The mid-infrared narrow-linewidth pulsed laser according to claim 4, characterized in that, When the acousto-optic modulator is in Raman-Nice diffraction state, the diffraction angle of the second-order diffracted light generated by the acousto-optic modulator is... satisfy: ; When the acousto-optic modulator is in Bragg diffraction mode, the diffraction angle of the first-order diffracted light in the diffraction path of the acousto-optic modulator is... satisfy: ; in, Represents the angle of incident light. Represents wavelength, Represents the wavelength of sound waves. It represents the refractive index of the acousto-optic medium.

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