A dual-pulse difference frequency mid-infrared laser generator with automatic overlap in time and space domains

Abstract

The present invention belongs to the field of infrared laser technology and discloses a dual-pulse difference frequency mid-infrared laser generating device with automatic overlap in time and space, comprising: a synchronous pump optical parametric oscillator, a dual-wavelength wave plate, and a difference frequency generator; the synchronous pump optical parametric oscillator is designed to output signal pulses and idler pulses that automatically overlap in time and space from the same output port; the signal pulse serves as the pump pulse of the difference frequency generator, and the idler pulse serves as the seed pulse of the difference frequency generator; the dual-wavelength wave plate is used to simultaneously adjust the polarization state of the signal pulse and the idler pulse to meet the polarization condition of phase matching in the difference frequency generation process in the difference frequency generator; the difference frequency generator generates mid-infrared laser based on the difference frequency of the pump pulse and the seed pulse. The present invention can automatically achieve temporal and spatial overlap of the pump and seed pulses in the difference frequency process, without the need for complex pulse delay adjustment and spatial alignment optical path, effectively reducing system complexity and cost, and facilitating the miniaturization and practicality of the device.

Description

Technical Field

[0001] The present invention belongs to the field of infrared laser technology, and more specifically, relates to a dual-pulse difference-frequency mid-infrared laser generating device with automatic overlap in time and space domains. Background Art

[0002] The mid-infrared band (2-20 μm) corresponds to the spectroscopic fingerprint region of molecules and holds significant research value. Absorption spectroscopy measurements in the mid-infrared band enable precise identification and quantitative detection of molecular components, providing a crucial foundational tool for applications such as nanoscale chemical analysis, environmental measurement, disease diagnosis, biohazard detection, and industrial process control.

[0003] Nonlinear frequency conversion is a "classic" technical route for generating mid-infrared lasers. Using a second-order nonlinear crystal as the gain medium, mid-infrared lasers can be generated through an optical parametric oscillator (OPO), an optical difference frequency generator (DFG), or an optical parametric amplifier (OPA). Comparing the three technical solutions, OPA is mainly used to generate high-energy femtosecond pulses, and the repetition rate of the pulses it generates is relatively low, usually below 1MHz; OPO is limited by the crystal material and coating, and the wavelength range of the long-wave infrared laser it generates is limited; in comparison, DFG has a greater advantage in generating high-repetition-rate long-wavelength (5-20μm) mid-infrared lasers.

[0004] In traditional dual-pulse DFG systems, the seed pulse is typically obtained by frequency conversion of the pump pulse. The process of generating the seed pulse requires frequency conversion through nonlinear media such as optical fibers, resulting in a certain time delay difference between the seed pulse and the pump pulse. For ultrashort optical pulses, this time delay requires a precise mechanical time delay compensation device to ensure that the two pulses overlap in the time domain. This increases the system's construction and maintenance costs, increases the system's complexity, and reduces its stability. Furthermore, because the pump and seed pulses in traditional dual-pulse DFG systems do not overlap in space, a beam combining system is required to achieve alignment and spatial overlap of the two beams, further increasing the system's complexity. Summary of the Invention

[0005] In response to the above defects or improvement needs of the prior art, the present invention provides a dual-pulse difference-frequency mid-infrared laser generating device with automatic overlap in time and space domains, the purpose of which is to reduce the complexity of the dual-pulse difference-frequency mid-infrared laser generating device and improve the stability of the system.

[0006] To achieve the above objectives, according to a first aspect of the present invention, a dual-pulse difference-frequency mid-infrared laser generator with automatic spatial and temporal overlap is provided, comprising: a synchronously pumped optical parametric oscillator, a dual-wavelength wave plate, and a difference-frequency generator; wherein the synchronously pumped optical parametric oscillator comprises a nonlinear crystal, a laser reflector assembly, a laser output coupling mirror, and a precision displacement platform; and the nonlinear crystal is a quasi-phase-matched or a type-I phase-matched crystal;

[0007] The pump pulse is focused on the nonlinear crystal to generate a signal pulse and an idler pulse; the laser reflection mirror group and the laser output coupling mirror constitute a laser resonant cavity for positive feedback of the signal pulse; the laser output coupling mirror is used to fully transmit the idler pulse and partially reflect and partially transmit the signal pulse, the reflected signal pulse returns to the laser resonant cavity to oscillate again, and the transmitted signal pulse and the idler pulse are simultaneously output from the laser output coupling mirror; the precision displacement platform is used to adjust the cavity length of the laser resonant cavity to achieve time synchronization of the signal pulse, idler pulse and pump pulse;

[0008] The signal pulse and idler pulse output simultaneously from the laser output coupling mirror are adjusted by the dual-wavelength wave plate to have polarization states perpendicular to each other, and then input into the difference frequency generator for difference frequency generation to generate mid-infrared laser; wherein the signal pulse and idler pulse correspond to the pump pulse and seed pulse in the difference frequency process.

[0009] Furthermore, the laser reflector group includes a dielectric reflector and a metal reflector;

[0010] The pump pulse is focused on the nonlinear crystal through the dielectric reflector, and the generated signal pulse and idler pulse are reflected to the laser output coupling mirror through the metal reflector. The signal pulse reflected by the laser output coupling mirror is again partially reflected by the metal reflector into the laser resonant cavity for oscillation.

[0011] Furthermore, the laser resonant cavity is an X-type resonant cavity composed of a dielectric reflector M1, a metal reflector M2, a dielectric reflector M3 and the laser output coupling mirror;

[0012] Alternatively, the laser resonant cavity is a V-shaped resonant cavity structure consisting of a dielectric reflector M1, a metal reflector M2 and the laser output coupling mirror;

[0013] The nonlinear crystal is arranged between the dielectric reflector M1 and the metal reflector M2.

[0014] Furthermore, the nonlinear crystal is arranged at the beam waist of the corresponding Gaussian pulse in the laser resonant cavity.

[0015] Furthermore, the difference frequency generator includes a beam focusing element, a difference frequency crystal and a beam collimating element;

[0016] The beam focusing element is used to focus the pump pulse and seed pulse in the difference frequency process; the difference frequency crystal is used to provide gain for the difference frequency process to generate mid-infrared laser; the beam collimating element is used to collimate the generated mid-infrared laser to obtain collimated mid-infrared laser.

[0017] Furthermore, the synchronous pump optical parametric oscillator further includes: an ultrashort pulse pump source and a pump focusing lens; the ultrashort pulse pump source is used to generate pump pulses; and the pump focusing lens is used to focus the pump pulses on the nonlinear crystal.

[0018] Furthermore, it also includes a half-wave plate and / or an optical isolator arranged between the ultrashort pulse pump source and the pump focusing lens; wherein the half-wave plate is used to adjust the polarization state of the pump pulse generated by the ultrashort pulse pump source to be consistent with the polarization state required by the nonlinear crystal; the optical isolator is used to isolate the pump pulse returning from the laser resonant cavity.

[0019] According to another aspect of the present invention, a method for generating mid-infrared laser using the dual-pulse difference-frequency mid-infrared laser generating device described in any one of the first aspects is provided.

[0020] Furthermore, the method further includes: simultaneously changing the phase matching condition of the nonlinear crystal and the cavity length of the laser resonant cavity to achieve wavelength tunability of the signal pulse and the idler pulse;

[0021] By changing the phase matching condition of the difference frequency crystal, the phase matching of the wavelength-tunable signal pulse and the idler pulse is achieved, so as to realize the wavelength-tunable mid-infrared laser output.

[0022] Furthermore, the phase matching condition of the nonlinear crystal is: the pump pulse wave vector is equal to the sum of the signal pulse wave vector and the idler pulse wave vector;

[0023] The phase matching condition of the difference frequency crystal is: the mid-infrared pulse wave vector generated by the difference frequency is equal to the difference between the pump pulse wave vector and the seed pulse wave vector in the difference frequency process.

[0024] In general, the above technical solutions conceived by the present invention can achieve the following beneficial effects:

[0025] (1) The dual-pulse difference frequency mid-infrared laser generating device with automatic time-space overlap in the present invention realizes the time synchronization of the signal pulse, idler pulse and ultrashort pulse pump source through the designed synchronous pump optical parametric oscillator; uses quasi-phase matching or a type of phase-matched nonlinear crystal to ensure that the output signal pulse and idler pulse have the same polarization state, thereby avoiding the spatial walk-off of the pulses due to the birefringence effect and ensuring the spatial overlap of the dual pulses. Therefore, the signal pulse and idler pulse output simultaneously from the same laser output coupling mirror automatically overlap in both the time domain and the space domain. Afterwards, the polarization state is adjusted by a dual-wavelength wave plate so that the dual pulses meet the polarization conditions of phase matching in the difference frequency generation process. In this way, the signal pulse is used as the pump pulse in the difference frequency process, and the idler pulse is used as the seed pulse in the difference frequency process, and the difference frequency can generate mid-infrared laser. Compared with the traditional DFG system, there is no need to use a complex beam delay adjustment device or a complex dual-beam combining device, which reduces the system complexity and device cost and improves the robustness of the system.

[0026] (2) Preferably, the nonlinear crystal is arranged at the beam waist of the corresponding Gaussian pulse in the laser resonant cavity to increase the peak power of the pump pulse and the signal pulse, thereby improving the efficiency of the nonlinear conversion process.

[0027] In summary, the dual-pulse difference-frequency mid-infrared laser generating device with automatic overlap in the time and space domain of the present invention avoids the introduction of complex time delay adjustment and spatial beam alignment structures in the DFG system, and can significantly reduce the complexity of the DFG system while improving its performance stability. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 This is a dual-pulse difference-frequency mid-infrared laser generating device with automatic overlap in time and space domains in an embodiment of the present invention.

[0029] Figure 2 This is a spectrum tuning diagram of a signal pulse output by a synchronous pump optical parametric oscillator obtained by numerical simulation based on the parameters in the embodiment of the present invention.

[0030] Figure 3 This is a spectrum tuning diagram of the idler pulse output by the synchronous pump optical parametric oscillator obtained by numerical simulation based on the parameters in the embodiment of the present invention.

[0031] Figure 4 This is a relationship diagram between the phase matching angle of the difference frequency crystal and the central wavelength of the optical parametric oscillator signal pulse in the difference frequency generation process obtained by numerical simulation based on the parameters in the embodiment of the present invention.

[0032] Figure 5This is a diagram showing the change of the idler center wavelength in the difference frequency generation process with the synchronous pump optical parametric oscillator signal pulse and the idler center wavelength obtained by numerical simulation based on the parameters in the embodiment of the present invention.

[0033] Figure 6 This is a mid-infrared spectrum tuning diagram of the difference frequency generation process obtained through numerical simulation based on the parameters in the embodiment of the present invention. DETAILED DESCRIPTION

[0034] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only intended to illustrate the present invention and are not intended to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below may be combined with each other as long as they do not conflict with each other.

[0035] like Figure 1 As shown, an embodiment of the present invention provides a dual-pulse difference frequency mid-infrared laser generating device with automatic overlap in time and space domains, comprising: a synchronous pump optical parametric oscillator, a dual-wavelength wave plate and a difference frequency generator;

[0036] The synchronously pumped optical parametric oscillator is designed to output signal pulses and idler pulses that automatically overlap in time and space from the same output port. The signal pulse serves as the pump pulse for the difference frequency generator, and the idler pulse serves as the seed pulse for the difference frequency generator. A dual-wavelength wave plate is used to simultaneously adjust the polarization states of the signal pulse and idler pulse to meet the polarization conditions for phase matching in the difference frequency generation process in the difference frequency generator. The difference frequency generator uses the pump pulse and seed pulse to generate mid-infrared laser light.

[0037] Specifically, the synchronous pump optical parametric oscillator includes an ultrashort pulse pump source, a pump focusing lens, a nonlinear crystal, a laser reflection mirror group, a laser output coupling mirror and a precision displacement platform.

[0038] An ultrashort pulse pump source is used to generate pump pulses.

[0039] The pump focusing lens is used to focus the pump pulse onto the nonlinear crystal so that the nonlinear crystal generates a signal pulse and an idler pulse.

[0040] A nonlinear crystal is disposed within a resonant cavity formed by a laser reflector assembly and a laser output coupling mirror. The nonlinear crystal is a quasi-phase-matched or first-class phase-matched crystal, ensuring that the output signal pulse and idler pulse have the same polarization state, thereby avoiding spatial walk-off and ensuring spatial overlap of the dual pulses. The resonant cavity formed by the laser reflector assembly can be an "X"-shaped resonant cavity, a "V"-shaped resonant cavity, or other types. Preferably, the nonlinear crystal is disposed within the resonant cavity at the beam waist of the corresponding Gaussian pulse to increase the peak power of the pump pulse and signal pulse, thereby improving the efficiency of the nonlinear conversion process.

[0041] The laser reflector group includes a dielectric reflector and a metal reflector; wherein the dielectric reflector is used to fully transmit the pump pulse generated by the ultrashort pulse pump source and fully reflect the signal pulse oscillating in the resonant cavity, and the metal reflector is used to fully reflect the signal pulse and the idler pulse; specifically, the pump pulse generated by the ultrashort pulse pump source passes through the pump focusing lens and the dielectric reflector in sequence and is incident on the nonlinear crystal, the nonlinear crystal generates a signal pulse and an idler pulse, the signal pulse and the idler pulse are fully reflected by the metal reflector to the laser output coupling mirror, the laser output coupling mirror is a dielectric reflector, which fully reflects the idler pulse Transmission: Part of the signal pulse is transmitted, while another part is reflected, achieving simultaneous output of the idler pulse and a portion of the signal pulse through the laser output coupling mirror. This results in a dual pulse output from the same output port, serving as the pump pulse and seed pulse for the difference frequency generator. The remaining signal pulse, reflected by the laser output coupling mirror, returns to the resonant cavity, is reflected by the metal reflector to the dielectric reflector, and oscillates between the dielectric and metal reflectors until it encounters the next pump pulse generated by the ultrashort pulse pump source. This process is repeated, resulting in the next dual pulse output from the same output port. During this process, the precision displacement stage adjusts the cavity length of the resonant cavity to achieve time synchronization between the signal pulse, idler pulse, and the ultrashort pulse pump source. This means that the time it takes for the signal pulse reflected back to complete a round trip within the laser cavity matches the repetition frequency of the pump pulses generated by the ultrashort pulse pump source. The laser reflector is typically mounted on a precision displacement stage and moved back and forth to adjust the cavity length.

[0042] The dual-wavelength wave plate is used to adjust the polarization states of the signal pulse and idler pulse simultaneously output from the laser output coupling mirror to be perpendicular to each other. Preferably, the dual-wavelength wave plate introduces a relative phase delay of an odd multiple of half a wavelength to the pump and seed pulses, which originally have the same polarization state. This ensures that the two pulses have orthogonal polarization directions, meeting the polarization requirements for phase matching during difference frequency generation.

[0043] The difference frequency generator performs difference frequency on the signal pulse and idler pulse whose polarization states are adjusted by the dual-wavelength wave plate to generate mid-infrared laser; wherein the signal pulse serves as the pump pulse in the difference frequency process, and the idler pulse serves as the seed pulse in the difference frequency process.

[0044] Preferably, the difference frequency generator includes a beam focusing element, a difference frequency crystal and a beam collimating element; the beam focusing element is used to focus the signal pulse serving as the pump pulse and the idler pulse serving as the seed pulse to a light spot; the difference frequency crystal is used to provide gain for the difference frequency process of generating the mid-infrared laser, wherein the difference frequency crystal satisfies the phase matching conditions for the pump pulse and the seed pulse to realize the difference frequency process; the beam collimating element is used to collimate the generated mid-infrared laser to obtain the collimated mid-infrared laser.

[0045] Preferably, for synchronously pumped optical parametric oscillators, wavelength tuning of the signal and idler pulses can be achieved by simultaneously changing the phase matching conditions of the nonlinear crystal and the resonant cavity length. For difference frequency generators, phase matching of the wavelength-tunable signal and idler pulse can be achieved by changing the phase matching conditions of the difference frequency crystal, thereby achieving wavelength-tunable mid-infrared laser output.

[0046] In the embodiment of the present invention, the phase matching condition of the nonlinear crystal is: the pump pulse wave vector k generated by the ultrashort pulse pump source is pump1 Equal to the signal pulse wave vector k signal and idler pulse wave vector k idler The sum is:

[0047] k pump1 =k signal +k idler ,Right now,

[0048] Where n is the refractive index, ω is the optical pulse angular frequency, and c is the speed of light. The subscripts pump1, signal, and idler correspond to the pump pulse, signal pulse, and idler pulse generated by the ultrashort pulse pump source, respectively.

[0049] The phase matching condition of the difference frequency crystal is: the difference frequency generates the mid-infrared pulse wave vector k MIR Equal to the pump pulse wave vector k in the difference frequency process pump2 Subtract the seed pulse wave vector k seed ,Right now:

[0050] k MIR =k pump2 -k seed ,Right now,

[0051] Where n is the refractive index, ω is the optical pulse angular frequency, and c is the speed of light. The subscripts MIR, pump2, and seed correspond to the infrared pulse, pump pulse, and seed pulse in the difference frequency process, respectively.

[0052] Preferably, the dual-wavelength wave plate has a certain working bandwidth, which can introduce a relative phase delay of an odd multiple of half a wavelength into the dual pulses within the wavelength tuning range of the pump and signal pulses, so that the two pulses have orthogonal polarization directions to meet the phase matching conditions in the process of generating pulse difference frequencies with different central wavelengths.

[0053] Preferably, along the optical path, the laser reflectors between the nonlinear crystal and the laser output coupling mirror are all metal reflectors to prevent the signal pulse and idler pulse from leaking from other ports.

[0054] Preferably, the system further includes a half-wave plate and / or an optical isolator disposed between the ultrashort pulse pump source and the pump focusing lens. The half-wave plate is used to adjust the polarization state of the pump pulses generated by the ultrashort pulse pump source to align with the polarization state required by the nonlinear crystal. The optical isolator is used to isolate pump pulses that may return from the laser resonant cavity to prevent damage to the ultrashort pulse pump source.

[0055] The dual-pulse difference-frequency mid-infrared laser generator with automatic spatial and temporal overlap in the present invention achieves temporal synchronization of the signal pulse, idler pulse, and ultrashort pulse pump source through a designed synchronous pump optical parametric oscillator. Quasi-phase matching or a type of phase-matched nonlinear crystal is used to ensure that the output signal pulse and idler pulse have the same polarization state, thereby avoiding spatial walk-off of the pulses due to birefringence and ensuring spatial overlap of the dual pulses. Therefore, the signal pulse and idler pulse simultaneously output from the same laser output coupling mirror automatically overlap in both the temporal and spatial domains. Subsequently, the polarization state is adjusted using a dual-wavelength waveplate to ensure that the dual pulses meet the polarization conditions for phase matching during the difference-frequency generation process. In this way, the signal pulse serves as the pump pulse in the difference-frequency generation process, and the idler pulse serves as the seed pulse in the difference-frequency generation process, and mid-infrared laser light is generated by difference-frequency generation. Compared to traditional DFG systems, there is no need for complex beam delay adjustment devices or complex dual-beam combining devices, reducing system complexity and device cost while improving system robustness.

[0056] The device of the present invention is further described below by taking an "X"-shaped resonant cavity structure formed by a laser reflecting mirror group in a synchronous pump optical parametric oscillator as an example.

[0057] The laser reflector assembly includes laser reflectors M1, M2, and M3. Together, M1, M2, M3, and the laser output coupling mirror form an "X"-shaped laser resonant cavity for positive feedback of the signal pulse. M1 is a dielectric plano-concave laser reflector with a curvature radius of 100 mm. Its surface is coated with a dielectric film that provides high transmittance for the pump pulses generated by the ultrashort pulse pump source and high reflectivity for the signal pulses. M2 is a metal plano-concave laser reflector with a curvature radius of 100 mm. Its surface is coated with a broadband reflective metal silver film that achieves high reflectivity for both signal and idler pulses. M3 is a dielectric planar laser reflector with the same coating as M1. It is mounted on a precision displacement platform and is used to adjust the cavity length of the optical parametric oscillator to meet the requirements of synchronous pumping at different wavelengths. The laser output coupling mirror is a dielectric planar mirror coated with a dielectric film that provides 40% transmittance for signal pulses and full transmittance for idler pulses. The nonlinear crystal providing gain within the resonant cavity is a 3mm long, fan-out periodically poled lithium niobate (PPLN) crystal with a polarization period gradient from 31.41 to 31.90μm. Its quasi-phase-matched gain bandwidth covers the 1700-2000nm signal wavelength range. The ultrashort pulse pump source is an yttrium-doped fiber master oscillator-amplifier system based on nonlinear polarization rotation mode locking. The system outputs a pump pulse train with a central wavelength of 1050nm, a temporal pulse width of 300fs, a maximum average power of 8W, a pulse repetition frequency of 80MHz, and horizontal polarization. A 1050nm central wavelength half-wave plate and an optical isolator are installed behind the pump source to adjust the average power of the pump source and provide isolation protection.

[0058] Specifically, the optical path of the signal and idler pulses within the "X"-shaped laser resonator, formed by M1, M2, M3, and the laser output coupling mirror, is as follows: After being generated within the nonlinear crystal, the signal and idler pulses are totally reflected by M2 to the laser output coupling mirror. The idler pulse is then fully transmitted and output, while the signal pulse is partially transmitted. The remaining signal pulse is reflected by the output coupling mirror to M2, then from M2 to M1, then from M1 to M3, and finally from M3 back to M1, repeating this cycle within the cavity.

[0059] It should be noted that in other embodiments, a "V"-shaped resonant cavity comprising M1, M2, and a laser output coupling mirror for positive feedback of the signal pulse may also be employed, wherein M1 is a planar dielectric reflector, M2 is a plano-concave metal reflector, and the laser output coupling mirror is a planar dielectric reflector. A nonlinear crystal is placed between M1 and M2, as close as possible to the side of plane mirror M1. The pump pulses generated by the ultrashort pulse pump source are focused by pump focusing lens L1, fully transmitted through M1, and converged on the nonlinear crystal to generate signal pulses and idler pulses. The signal pulses and idler pulses are reflected through M2 to the laser output coupling mirror. The idler pulse is fully transmitted and output. A portion of the signal pulse is transmitted and output, while the remaining portion is reflected to M2, and then reflected back to M1 through M2, completing this cycle, oscillating back and forth between M1, M2, and the output coupling mirror.

[0060] To make it easier for those skilled in the art to understand the characteristics of the signal pulse and idler pulse output by the optical parametric oscillator in the embodiment of the present invention, the three-wave coupling equation is numerically solved by the distributed Fourier algorithm to respectively provide tunable spectra of the signal pulse and idler pulse output by the optical parametric oscillator, as shown in FIG. Figure 2 、 3 As shown in FIG. 1 , it can be seen that the wavelength tuning range of the signal pulse covers 1700-2000 nm, and the corresponding wavelength tuning range of the idler pulse is 2746-2210 nm.

[0061] Since the optical parametric oscillator in the embodiment of the present invention operates in a quasi-phase matching mode of e=e+e type polarization, the generated signal pulses and idler pulses do not experience spatial walk-off caused by the birefringence effect in the crystal. The two pulses highly overlap in space, and their polarization states remain consistent with the pump light, both being horizontally polarized.

[0062] The signal and idler pulses output by the optical parametric oscillator then pass through a broadband dual-wavelength waveplate in an embodiment of the present invention. This waveplate provides a flat λ phase shift for signal pulses with a central wavelength of 1700-2000 nm, and a flat 1 / 2λ phase shift for idler pulses with a central wavelength of 2746-2210 nm. As a result, the polarization state of the signal pulse remains unchanged after passing through this waveplate, while the polarization state of the idler pulse changes to vertical polarization after passing through this waveplate.

[0063] The signal with orthogonal polarization state and the idler pulse are focused onto the difference frequency crystal through the plano-convex lens L2 (focal length 50mm). In the embodiment of the present invention, the difference frequency crystal is a 2mm long GaSe crystal fixed on a precision 6-axis adjustment frame. Under different signal and idler wavelength conditions, the relationship between the phase matching angle corresponding to the crystal that satisfies Type I (o=eo) phase matching and the central wavelength of the infrared laser generated by the difference frequency and the change of the central wavelength of the signal and idler pulse is as follows: Figure 4 、 5 shown. Figure 6 The spectrum of the mid-infrared laser obtained by simulation during the difference frequency generation process is given. It can be seen that in the embodiment of the present invention, tunable mid-infrared laser output is achieved without using a beam delay adjustment device and a dual-beam combining device.

[0064] It will be easily understood by those skilled in the art 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 in the scope of protection of the present invention.

Claims

1. A dual-pulse difference frequency mid-infrared laser generating device with automatic overlap in time and space domains, characterized in that: include: A synchronously pumped optical parametric oscillator, a dual-wavelength wave plate, and a difference frequency generator; wherein the synchronously pumped optical parametric oscillator comprises a nonlinear crystal, a laser reflector assembly, a laser output coupling mirror, and a precision displacement platform; and the nonlinear crystal is a quasi-phase matching or a type I phase matching crystal; The pump pulse is focused on the nonlinear crystal to generate a signal pulse and an idler pulse; the laser reflection mirror group and the laser output coupling mirror constitute a laser resonant cavity for positive feedback of the signal pulse; the laser output coupling mirror is used to fully transmit the idler pulse and partially reflect and partially transmit the signal pulse, the reflected signal pulse returns to the laser resonant cavity to oscillate again, and the transmitted signal pulse and the idler pulse are simultaneously output from the laser output coupling mirror; the precision displacement platform is used to adjust the cavity length of the laser resonant cavity to achieve time synchronization of the signal pulse, idler pulse and pump pulse; The signal pulse and idler pulse output simultaneously from the laser output coupling mirror are adjusted by the dual-wavelength wave plate to have polarization states perpendicular to each other, and then input into the difference frequency generator for difference frequency generation to generate mid-infrared laser; wherein the signal pulse and idler pulse correspond to the pump pulse and seed pulse in the difference frequency process.

2. The double-pulse difference frequency mid-infrared laser generating device according to claim 1, characterized in that: The laser reflector group includes a dielectric reflector and a metal reflector; The pump pulse is focused on the nonlinear crystal through the dielectric reflector, and the generated signal pulse and idler pulse are reflected to the laser output coupling mirror through the metal reflector. The signal pulse reflected by the laser output coupling mirror is reflected again by the metal reflector into the laser resonant cavity for oscillation.

3. The double-pulse difference frequency mid-infrared laser generating device according to claim 2, characterized in that: The laser resonant cavity is an X-shaped resonant cavity composed of a dielectric reflector M1, a metal reflector M2, a dielectric reflector M3 and the laser output coupling mirror; Alternatively, the laser resonant cavity is a V-shaped resonant cavity structure consisting of a dielectric reflector M1, a metal reflector M2 and the laser output coupling mirror; The nonlinear crystal is arranged between the dielectric reflector M1 and the metal reflector M2.

4. The double-pulse difference frequency mid-infrared laser generating device according to any one of claims 1 to 3, characterized in that: The nonlinear crystal is arranged at the beam waist of the corresponding Gaussian pulse in the laser resonant cavity.

5. The double-pulse difference frequency mid-infrared laser generating device according to claim 4, characterized in that: The difference frequency generator includes a beam focusing element, a difference frequency crystal and a beam collimating element; The beam focusing element is used to focus the pump pulse and seed pulse in the difference frequency process; the difference frequency crystal is used to provide gain for the difference frequency process to generate mid-infrared laser; the beam collimating element is used to collimate the generated mid-infrared laser to obtain collimated mid-infrared laser.

6. The double-pulse difference frequency mid-infrared laser generating device according to claim 1, characterized in that: The synchronous pump optical parametric oscillator further includes: an ultrashort pulse pump source and a pump focusing lens; the ultrashort pulse pump source is used to generate pump pulses; the pump focusing lens is used to focus the pump pulses on the nonlinear crystal.

7. The double-pulse difference frequency mid-infrared laser generating device according to claim 6, characterized in that: The system further includes a half-wave plate and / or an optical isolator arranged between the ultrashort pulse pump source and the pump focusing lens; wherein the half-wave plate is used to adjust the polarization state of the pump pulse generated by the ultrashort pulse pump source to be consistent with the polarization state required by the nonlinear crystal; and the optical isolator is used to isolate the pump pulse returning from the laser resonant cavity.

8. A method for generating mid-infrared laser using the double-pulse difference frequency mid-infrared laser generating device according to any one of claims 1 to 7.

9. The method according to claim 8, characterized in that Also includes: By simultaneously changing the phase matching condition of the nonlinear crystal and the cavity length of the laser resonant cavity, the wavelength of the signal pulse and the idler pulse can be tuned; By changing the phase matching condition of the difference frequency crystal, the phase matching of the wavelength-tunable signal pulse and the idler pulse is achieved, so as to realize the wavelength-tunable mid-infrared laser output.

10. The method according to claim 9, characterized in that The phase matching condition of the nonlinear crystal is: the pump pulse wave vector is equal to the sum of the signal pulse wave vector and the idler pulse wave vector; The phase matching condition of the difference frequency crystal is: the mid-infrared pulse wave vector generated by the difference frequency is equal to the difference between the pump pulse wave vector and the seed pulse wave vector in the difference frequency process.

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