High energy mid-infrared femtosecond laser and mid-infrared femtosecond laser generation method

Abstract

The present invention discloses a high-energy mid-infrared femtosecond laser and a mid-infrared femtosecond laser generation method thereof, wherein the laser comprises a mid-infrared picosecond pulse laser optical path, a mid-infrared laser amplifier and a pulse compressor which are sequentially arranged; wherein the mid-infrared laser amplifier adopts a multi-stroke slat amplification structure. The present invention adopts a multi-stroke slat structure to amplify the mid-infrared ultrashort pulse laser, which has many advantages such as good mode matching, good cooling effect, small thermal effect, high gain, etc., and can obtain a mid-infrared ultrashort pulse laser output with high energy, high efficiency and high beam quality.

Description

Technical Field

[0001] The present invention relates to the field of ultrafast laser technology, and in particular to a high-energy mid-infrared femtosecond laser and a method for generating the mid-infrared femtosecond laser. Background Art

[0002] Mid-infrared femtosecond lasers are widely used in thermal imaging, environmental monitoring, mid-infrared guidance, optoelectronic countermeasures, etc. In particular, mid-infrared femtosecond lasers with high pulse energy have unique advantages in applications such as strong field physics, attosecond science, high-order harmonic generation, and frequency comb precision measurement.

[0003] At present, mid-infrared femtosecond lasers are mainly produced by parametric down-conversion of femtosecond lasers in the visible light band or near-infrared band, including optical parametric oscillation (OPO) and optical parametric amplification (OPA). The use of OPO to produce mid-infrared femtosecond lasers requires the use of synchronous pumping technology, so the adjustment accuracy of the resonant cavity is extremely high, resulting in poor resistance of the laser system to environmental interference; in addition, limited by the optical length of the resonant cavity, the repetition frequency of the mid-infrared femtosecond lasers produced by OPO is usually in the hundreds of megahertz range, so the energy of a single pulse is often very low (only tens of nJ), which is difficult to meet the needs of practical applications. OPA is currently the mainstream method for generating high-energy mid-infrared femtosecond lasers. The single pulse energy it generates can reach the mJ level. However, OPA usually uses multi-stage amplification, and each stage of amplification must strictly ensure that the pump light and the idler light are synchronized in time and overlap in space. Therefore, it is difficult to adjust, the system is complex and the cost is high. In addition, during the OPA process, an inverse conversion effect is likely to occur between the pump light and the idler light, thereby destroying the time domain waveform and coherence of the idler light. Therefore, it is usually necessary to suppress the conversion efficiency of the OPA at a low level. In 2019, Reference 1 [E. Migal, A. Pushkin, B. Bravy et al., 3.5-mJ 150-fs Fe: ZnSe hybrid mid-IR femtosecond laser at 4.4μm for driving extreme nonlinear optics, Optics Letters 44 (10), 2550-2553 (2019)] used OPA to generate low-energy mid-infrared femtosecond lasers, and then used bulk Fe: ZnSe crystal chirped pulse amplification (CPA) to a mid-infrared femtosecond laser, and finally achieved 3.5mJ of 4.4-micron mid-infrared femtosecond laser output. Although this scheme achieves higher-energy mid-infrared femtosecond laser output, it still uses a three-level OPA system, so there are still problems such as difficult adjustment, complex system, high cost, and low conversion efficiency; in addition, it is difficult to further improve the pulse energy of the mid-infrared femtosecond laser due to the limitation of the gain capability and heat dissipation capability of the bulk Fe: ZnSe crystal.Reference 2 [LJHe, K.Liu, Y.Bo et al., 30.5-μJ, 10-kHz, picosecond optical parametric oscillator pumped synchronously and intracavity by a regenerative amplifier, Optics Letters 43(3), 539-542(2018)] proposed using regenerative amplification OPO technology to convert a high repetition rate (76MHz), low energy (22.4nJ) 1 micron picosecond laser into a low repetition rate (10kHz), high energy (30.5μJ) 1.5 micron picosecond laser. This solution only requires the optical length of the OPO cavity to be consistent with the optical length of the regenerative amplifier cavity, thereby reducing the requirements for the adjustment accuracy of the resonant cavity. In principle, this technology can generate higher energy mid-infrared picosecond pulse lasers, but it is limited by the damage threshold of nonlinear optical crystals and does not consider dispersion compensation, so it is difficult to generate high energy (mJ level) mid-infrared femtosecond pulse lasers.

[0004] Therefore, the industry urgently needs to develop a mid-infrared femtosecond laser with a simple structure that can produce high energy, high efficiency, and high beam quality. Summary of the invention

[0005] The purpose of the present invention is to overcome the deficiencies of the above prior art and to provide a high-energy mid-infrared femtosecond laser and a mid-infrared femtosecond laser generation method thereof which can produce high efficiency and high beam quality.

[0006] The purpose of the present invention is achieved through the following technical solutions:

[0007] A high-energy mid-infrared femtosecond laser comprises a mid-infrared picosecond pulse laser optical path, a mid-infrared laser amplifier and a pulse compressor which are arranged in sequence; wherein the mid-infrared laser amplifier adopts a multi-stroke slab amplification structure.

[0008] Preferably, the mid-infrared laser amplifier comprises a first reflector, a first cavity mirror, a mid-infrared laser gain medium, a second cavity mirror, a second reflector and a mid-infrared laser pump source. The first cavity mirror and the second cavity mirror are arranged up and down to form an amplifying cavity. The mid-infrared laser gain medium is arranged in the amplifying cavity. The first reflector and the second reflector are respectively arranged obliquely at the two ends of the mid-infrared laser gain medium, serving as the input end and the output end of the mid-infrared laser amplifier respectively. The mid-infrared laser pump source is arranged above the first cavity mirror or below the second cavity mirror, and the angle of the first cavity mirror and the second cavity mirror is adjustable.

[0009] Preferably, the mid-infrared picosecond pulse laser optical path includes a 2-micron femtosecond laser oscillator, an optical isolator, a pulse stretcher, a 2-micron laser amplifier and a regenerative amplifier synchronously pumped optical parametric oscillator, a first dichroic mirror, and a second dichroic mirror; the 2-micron femtosecond laser oscillator, the optical isolator, the pulse stretcher, the 2-micron laser amplifier, the regenerative amplifier synchronously pumped optical parametric oscillator and the first dichroic mirror are arranged on the same optical axis; the pulse compressor, the mid-infrared laser amplifier and the second dichroic mirror are arranged on the same optical axis in sequence, and the first dichroic mirror and the second dichroic mirror are both tilted, with opposite tilt directions, and are located on the same vertical optical axis.

[0010] Preferably, the 2-micron femtosecond laser oscillator is a 2-micron all-solid-state femtosecond mode-locked laser or a 2-micron fiber femtosecond mode-locked laser; the 2-micron laser amplifier is one of a rod-shaped amplification structure, a slab amplification structure and a disk amplification structure.

[0011] Preferably, the mid-infrared laser gain medium is Fe 2+ The doped II-VI group ternary laser crystal material comprises a mid-infrared laser gain medium which is one of Fe:ZnS, Fe:ZnSe, Fe:ZnMnSe, Fe:ZnMgSe, Fe:CdMnTe, Fe:CdTe and Fe:CdHgTe.

[0012] Preferably, the first surfaces of the first dichroic mirror and the second dichroic mirror are coated with a high-transmittance film for 2-micron laser and a high-reflection film for mid-infrared laser; the second surfaces of the first dichroic mirror and the second dichroic mirror are coated with a high-transmittance film for 2-micron laser; the first surfaces of the first reflector and the second reflector are coated with a high-reflection film for mid-infrared laser; the first surfaces of the first cavity mirror and the second cavity mirror are coated with an anti-reflection film for pump light and a high-reflection film for mid-infrared laser, and the second surfaces of the first cavity mirror and the second cavity mirror are coated with an anti-reflection film for pump light.

[0013] Preferably, the mid-infrared laser pump source is a high-energy 2.7-3.0 micron band nanosecond pulse laser.

[0014] Preferably, the number of mid-infrared laser pump sources is 2, and the two mid-infrared laser pump sources are respectively arranged above the first cavity mirror and below the second cavity mirror.

[0015] A method for generating an infrared femtosecond laser based on the above-mentioned high-energy mid-infrared femtosecond laser comprises: a mid-infrared picosecond pulse laser optical path generates a mid-infrared picosecond pulse laser, the mid-infrared picosecond pulse laser is input into a mid-infrared laser amplifier to generate a mid-infrared picosecond pulse laser with energy E1 (high energy), and finally a mid-infrared femtosecond pulse laser with energy E2 (high energy) is output through a pulse compressor, where E1>E2>0, wherein the step of inputting the mid-infrared picosecond pulse laser into the mid-infrared laser amplifier to generate a high-energy mid-infrared picosecond pulse laser comprises: the mid-infrared picosecond pulse laser passes through a first reflector and then reflects to a first cavity mirror, passes through a mid-infrared laser gain medium for the first time after being reflected by the first cavity mirror and incident to a second cavity mirror, passes through a mid-infrared laser gain medium for the second time after being reflected by the second cavity mirror and incident to the first cavity mirror, passes through a mid-infrared laser gain medium for the third time after being reflected by the first cavity mirror and incident to the second cavity mirror, and repeats this process until the mid-infrared picosecond pulse laser passes through the second cavity mirror for the last time and then reflects and is output through the second reflector, thereby realizing that the mid-infrared pulse laser passes through the mid-infrared laser gain medium for multiple times to achieve high-gain amplification.

[0016] Preferably, the mid-infrared picosecond pulse laser optical path generates the mid-infrared picosecond pulse laser, including: a 2-micron femtosecond laser oscillator outputs a 2-micron femtosecond pulse laser, the 2-micron femtosecond pulse laser is converted into a 2-micron picosecond pulse laser after passing through an optical isolator and a pulse stretcher in turn, the 2-micron picosecond pulse laser is injected into a 2-micron laser amplifier for laser pulsation, and the 2-micron picosecond pulse laser is injected into a 2-micron laser amplifier for amplification; the amplified 2-micron picosecond pulse laser passes through a regenerative amplifier synchronously pumped optical parametric oscillator, the regenerative amplifier synchronously pumped optical parametric oscillator outputs a mid-infrared picosecond pulse laser, and the mid-infrared picosecond pulse laser is reflected by a first dichroic mirror and a second dichroic mirror in turn and then incident on the mid-infrared laser amplifier.

[0017] Preferably, the number of times the mid-infrared picosecond pulse laser passes through the mid-infrared laser gain medium is controlled by adjusting the angles of the first cavity mirror and the second cavity mirror.

[0018] Preferably, the amplified high repetition rate, low energy 2 micron picosecond pulse laser is synchronously pumped by a regenerative amplifier to generate a low repetition rate, high energy mid-infrared picosecond pulse laser. The present invention has the following advantages over the prior art:

[0019] 1. The multi-stroke slat structure is used to amplify the mid-infrared ultrashort pulse laser, which has many advantages such as good mode matching, good cooling effect, small thermal effect, and high gain. The mid-infrared picosecond pulse laser passes through the first reflector and is reflected to the first cavity mirror. After being reflected by the first cavity mirror, it passes through the mid-infrared laser gain medium for the first time and is incident on the second cavity mirror. After being reflected by the second cavity mirror, it passes through the mid-infrared laser gain medium for the second time and is incident on the first cavity mirror. After being reflected by the first cavity mirror, it passes through the mid-infrared laser gain medium for the third time and is incident on the second cavity mirror. This is repeated until the mid-infrared picosecond pulse laser is reflected by the second cavity mirror for the last time and is output through the second reflector. High-energy, high-efficiency, and high-beam-quality mid-infrared ultrashort pulse laser output can be obtained.

[0020] 2. The regenerative amplification OPO technology is used to generate mid-infrared ultrashort pulse lasers, which can convert high-repetition-rate, low-energy 2-micron ultrashort pulse lasers into low-repetition-rate, high-energy mid-infrared ultrashort pulse lasers, and reduce the adjustment difficulty, complexity and cost of the mid-infrared ultrashort pulse laser generation system.

[0021] 3. From a series of Fe 2+ Mid-infrared laser gain media are preferably used in doped II-VI group ternary laser crystal materials to facilitate obtaining high-energy and high-efficiency mid-infrared ultrashort pulse laser output. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0023] Figure 1 Schematic diagram of the optical path structure of Example 1.

[0024] Figure 2 Schematic diagram of the optical path structure of Example 2. DETAILED DESCRIPTION

[0025] The specific implementation of the present invention is further described in detail below in conjunction with the accompanying drawings and examples. The following examples are used to illustrate the present invention, but are not intended to limit the scope of the present invention.

[0026] Example 1

[0027] Figure 1 This is a schematic diagram of the optical path of a high-energy mid-infrared femtosecond laser of the present invention, see Figure 1A high-energy mid-infrared femtosecond laser comprises a 2-micron femtosecond mode-locked laser 1, an optical isolator 2, a pulse stretcher 3, a 2-micron laser amplifier 4, a regenerative amplifier synchronously pumped optical parametric oscillator 5, a mid-infrared laser amplifier 8 and a pulse compressor 15; the 2-micron femtosecond pulse laser output by the 2-micron femtosecond laser oscillator 1 is converted into a 2-micron picosecond pulse laser after passing through the optical isolator 2 and the pulse stretcher 3 in sequence, and then injected into the 2-micron laser amplifier 4; the amplified 2-micron picosecond pulse laser first passes through the regenerative amplifier synchronously pumped optical parametric oscillator 5 to generate a mid-infrared picosecond pulse laser, and the mid-infrared picosecond pulse laser passes through a first dichroic mirror 6 and a second dichroic mirror 7 in sequence, and is injected into the mid-infrared laser amplifier 8 to generate a high-energy mid-infrared picosecond pulse laser, and finally outputs a high-energy mid-infrared femtosecond pulse laser through the pulse compressor 15.

[0028] Specifically, the 2-micron femtosecond mode-locked laser 1 is a 2-micron all-solid-state femtosecond mode-locked laser, which is used to generate a 2-micron femtosecond mode-locked laser with a repetition frequency of 100 MHz, a pulse width of less than 100 fs, and an average power of 100 mW; the optical isolator 2 is composed of a Faraday rotator and a polarizer, which is used to prevent the return pulse laser from interfering with the 2-micron femtosecond mode-locked laser 1; the pulse stretcher 3 is a gold-plated grating, which is used to widen the pulse width of the 2-micron femtosecond seed laser to the order of 100 ps; the 2-micron laser amplifier 4 adopts a rod-shaped amplification structure, which is used to amplify the 2-micron picosecond pulse laser, and the average power after amplification is 10 W; the regenerative amplifier synchronous pump optical parametric oscillator 5 is used to convert the high-repetition-rate (100 MHz) and low-energy (100 nJ) 2-micron picosecond pulse laser into a low-repetition-rate (100 MHz) 2-micron picosecond pulse laser. The invention relates to a mid-infrared picosecond pulse laser with a high frequency (10Hz) and high energy (hundreds of μJ), a wavelength tuning range of 3-5 microns, and a pulse width of the order of 100ps; the first dichroic mirror 6 and the second dichroic mirror 7 are coated with a high-transmittance film for 2-micron laser and a high-reflection film for 3-5-micron laser, and are used to reflect the mid-infrared picosecond pulse laser and transmit the 2-micron picosecond pulse laser; the mid-infrared laser amplifier 8 adopts a multi-stroke slat amplification structure, and is used to amplify the mid-infrared picosecond pulse laser, and the energy of the amplified single pulse is 50mJ; the pulse compressor 15 is a gold-plated grating, and is used to compress the pulse width of the amplified mid-infrared picosecond pulse laser to 100fs, and the single pulse energy of the compressed mid-infrared femtosecond pulse laser is 40mJ, the repetition frequency is 10Hz, and the wavelength tuning range is 3.9-4.8 microns.

[0029] The mid-infrared laser amplifier 8 includes a first reflector 9, a first cavity mirror 10, a mid-infrared laser gain medium 11, a second cavity mirror 12, a second reflector 13 and a mid-infrared laser pump source 14; the first reflector 9 and the second reflector 13 are coated with a high reflection film for 3-5 micron laser; the first cavity mirror 10 and the second cavity mirror 12 are coated with an anti-reflection film for 2.8 micron laser and a high reflection film for 3-5 micron laser; the mid-infrared laser gain medium 11 is a Fe:ZnSe crystal, which is arranged in a strip shape with length ≥ width > height, with the length × width plane of the gain medium 11 as a horizontal plane, and a cooling device is arranged on the plane; the mid-infrared laser pump source 14 adopts an actively Q-switched Cr:Er:YSGG laser with a central wavelength of 2.8 microns, a repetition frequency of 10 Hz, a single pulse energy of 200 mJ, and a pulse width of 50 ns.

[0030] Specifically, the mid-infrared picosecond pulse laser from the regenerative amplifier synchronously pumped optical parametric oscillator 5 is incident on the first cavity mirror 10 after passing through the first reflector 9, and then passes through the mid-infrared laser gain medium 11 for the first time, passes through the second cavity mirror 12, and then passes through the mid-infrared laser gain medium 11 for the second time, passes through the first cavity mirror 10 again, and then passes through the mid-infrared laser gain medium 11 for the third time, and then passes through the second cavity mirror 12, ..., by adjusting the angles of the first cavity mirror 10 and the second cavity mirror 12, the number of times the mid-infrared picosecond pulse laser passes through the mid-infrared laser gain medium 11 can be controlled. After the mid-infrared picosecond pulse laser passes through the second cavity mirror 12 for the last time, it is output through the second reflector 13, thereby achieving high-gain amplification by passing through the mid-infrared laser gain medium 11 for multiple times.

[0031] The pulse compressor 15 includes a grating, a chirped mirror, a prism pair, a GTI mirror and a photonic crystal fiber, and is used to compress the pulse width of the high-energy mid-infrared picosecond laser to the sub-hundredth femtosecond level.

[0032] Example 2

[0033] The difference between Example 2 and Example 1 is that the mid-infrared laser amplifier 8 adopts a mid-infrared laser pump source 14 and a mid-infrared laser pump source 15 for double-end pumping, and the mid-infrared laser pump source 14 and the mid-infrared laser pump source 15 are respectively arranged below the second cavity mirror 12 and above the first cavity mirror 10, thereby increasing the pump light power and reducing the thermal effect of the laser crystal, thereby achieving a mid-infrared femtosecond laser output with higher energy and better beam quality.

[0034] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present invention can be modified or replaced by equivalents without departing from the spirit and scope of the technical solutions of the present invention, which should all be included in the scope of the claims of the present invention.

Claims

1. A high energy mid-infrared femtosecond laser, characterized in that: It includes a mid-infrared picosecond pulse laser optical path, a mid-infrared laser amplifier and a pulse compressor which are arranged in sequence; Among them, the mid-infrared laser amplifier adopts a multi-stroke slab amplification structure; The mid-infrared picosecond pulse laser optical path includes a 2-micron femtosecond laser oscillator, an optical isolator, a pulse stretcher, a 2-micron laser amplifier and a regenerative amplifier synchronously pumped optical parametric oscillator, a first dichroic mirror, and a second dichroic mirror; A 2-micron femtosecond laser oscillator, an optical isolator, a pulse stretcher, a 2-micron laser amplifier, a regenerative amplifier synchronously pumped optical parametric oscillator and a first dichroic mirror are arranged on the same optical axis; a pulse compressor, a mid-infrared laser amplifier and a second dichroic mirror are arranged on the same optical axis in sequence, and the first dichroic mirror and the second dichroic mirror are both tilted, with opposite tilt directions, and are located on the same vertical optical axis; The mid-infrared picosecond pulse laser optical path generates a mid-infrared picosecond pulse laser, the mid-infrared picosecond pulse laser is input into a mid-infrared laser amplifier to generate a mid-infrared picosecond pulse laser with energy E1, and finally the pulse compressor outputs a mid-infrared femtosecond pulse laser with energy E2, where E1>E2.

2. The high energy mid-infrared femtosecond laser according to claim 1, characterized in that: The mid-infrared laser amplifier comprises a first reflector, a first cavity mirror, a mid-infrared laser gain medium, a second cavity mirror, a second reflector and a mid-infrared laser pump source. The first cavity mirror and the second cavity mirror are arranged up and down to form an amplifying cavity. The mid-infrared laser gain medium is arranged in the amplifying cavity. The first reflector and the second reflector are respectively arranged at an angle at two ends of the mid-infrared laser gain medium, serving as an input end and an output end of the mid-infrared laser amplifier, respectively. The mid-infrared laser pump source is arranged above the first cavity mirror or below the second cavity mirror, and the angle between the first cavity mirror and the second cavity mirror is adjustable.

3. The high energy mid-infrared femtosecond laser according to claim 1, characterized in that: The 2 micron femtosecond laser oscillator is a 2 micron all-solid-state femtosecond mode-locked laser or a 2 micron fiber femtosecond mode-locked laser; The 2-micron laser amplifier is one of a rod-shaped amplification structure, a slat-shaped amplification structure and a disk-shaped amplification structure.

4. The high energy mid-infrared femtosecond laser according to claim 2, characterized in that: The mid-infrared laser gain medium is Fe 2+ The doped II-VI group ternary laser crystal material, the mid-infrared laser gain medium is one of Fe:ZnS, Fe:ZnSe, Fe:ZnMnSe, Fe:ZnMgSe, Fe:CdMnTe, Fe:CdTe and Fe:CdHgTe.

5. The high energy mid-infrared femtosecond laser according to claim 2, characterized in that: The first surfaces of the first dichroic mirror and the second dichroic mirror are both coated with a high-transmittance film for 2-micron lasers and a high-reflection film for mid-infrared lasers; the second surfaces of the first dichroic mirror and the second dichroic mirror are both coated with a high-transmittance film for 2-micron lasers; The first surfaces of the first reflector and the second reflector are both coated with a high reflection film for mid-infrared laser; The first surfaces of the first cavity mirror and the second cavity mirror are coated with an anti-reflection film for pump light and a high-reflection film for mid-infrared laser, and the second surfaces of the first cavity mirror and the second cavity mirror are coated with an anti-reflection film for pump light.

6. The high energy mid-infrared femtosecond laser according to claim 2, characterized in that: The mid-infrared laser pump source is a high-energy 2.7-3.0 micron band nanosecond pulse laser; The number of mid-infrared laser pump sources is 2, and the two mid-infrared laser pump sources are respectively arranged above the first cavity mirror and below the second cavity mirror.

7. An infrared femtosecond laser generation method based on the high-energy mid-infrared femtosecond laser according to any one of claims 1 to 6, characterized in that: include: The mid-infrared picosecond pulse laser optical path generates a mid-infrared picosecond pulse laser, which is input into a mid-infrared laser amplifier to generate a mid-infrared picosecond pulse laser with energy E1, and finally a pulse compressor outputs a mid-infrared femtosecond pulse laser with energy E2, where E1>E2, wherein, The step of inputting a mid-infrared picosecond pulse laser into a mid-infrared laser amplifier to generate a mid-infrared picosecond pulse laser with energy E1 includes: the mid-infrared picosecond pulse laser passes through a first reflector and then reflects to a first cavity mirror, passes through a mid-infrared laser gain medium for the first time after being reflected by the first cavity mirror and is incident on a second cavity mirror, passes through a mid-infrared laser gain medium for the second time after being reflected by the second cavity mirror and is incident on the first cavity mirror, passes through a mid-infrared laser gain medium for the third time after being reflected by the first cavity mirror and is incident on the second cavity mirror, and repeats this process until the mid-infrared picosecond pulse laser is reflected by the second cavity mirror for the last time and then outputted through the second reflector, thereby realizing that the mid-infrared pulse laser passes through the mid-infrared laser gain medium multiple times to achieve high-gain amplification.

8. The infrared femtosecond laser generating method according to claim 7, characterized in that: Mid-infrared picosecond pulse laser optical path to generate mid-infrared picosecond pulse laser includes: The 2-micron femtosecond laser oscillator outputs a 2-micron femtosecond pulse laser, which is converted into a 2-micron picosecond pulse laser after passing through an optical isolator and a pulse stretcher in turn, and the 2-micron picosecond pulse laser is injected into a 2-micron laser amplifier for amplification; the amplified 2-micron picosecond pulse laser passes through a regenerative amplifier to synchronously pump an optical parametric oscillator, and the regenerative amplifier synchronously pumps an optical parametric oscillator to output a mid-infrared picosecond pulse laser, which is reflected by a first dichroic mirror and a second dichroic mirror in turn and then incident on a mid-infrared laser amplifier.

9. The infrared femtosecond laser generating method according to claim 7, characterized in that: The number of times that the mid-infrared picosecond pulse laser passes through the mid-infrared laser gain medium is controlled by adjusting the angles of the first cavity mirror and the second cavity mirror.

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