阅读说明：本技术 一种可调谐长波中红外超快激光光源装置 (Tunable long-wave mid-infrared ultrafast laser light source device ) 是由 田文龙 韩康 朱江峰 张大成 魏志义 于 2021-07-16 设计创作，主要内容包括：本发明属于长波中红外超快激光技术领域,公开了一种可调谐长波中红外超快激光光源装置,设置有：用于产生光参量振荡器模块所需的泵浦光,并对其输出功率进行调节的泵浦源模块；用于发生频率变换,使泵浦光和生成的信号光周期性的同时通过非线性晶体产生并输出5～10μm波段的闲频光的光参量振荡器模块。本发明采用YbLaser直接泵浦基于LISe晶体的飞秒光参量振荡器获取5～10μm的中红外超快激光,避免了由于缺乏高效长波泵浦源,基于OPO组合技术获取中红外超快激光系统的难度和复杂度高,对晶体的透过率要求较高和转换效率低的问题。同时解决组合结构系统复杂、搭建难度高、对晶体透过率要求高和转换效率低的问题。(The invention belongs to the technical field of long-wave mid-infrared ultrafast laser, and discloses a tunable long-wave mid-infrared ultrafast laser light source device, which is provided with: the pump source module is used for generating pump light required by the optical parametric oscillator module and adjusting the output power of the pump light; and the optical parametric oscillator module is used for generating frequency conversion, so that the pump light and the generated signal light are periodic and simultaneously generate and output idler frequency light with a wave band of 5-10 mu m through the nonlinear crystal. According to the invention, a YbLaser direct pumping LISe crystal-based femtosecond optical parametric oscillator is adopted to obtain the intermediate infrared ultrafast laser with the thickness of 5-10 microns, so that the problems of high difficulty and complexity, high requirement on the transmittance of the crystal and low conversion efficiency of an intermediate infrared ultrafast laser system obtained based on an OPO combination technology due to the lack of a high-efficiency long-wavelength pumping source are solved. Meanwhile, the problems of complex combined structure system, high building difficulty, high requirement on the transmittance of crystals and low conversion efficiency are solved.)

1. A tunable long-wave mid-infrared ultrafast laser light source device is characterized in that the tunable long-wave mid-infrared ultrafast laser light source device is provided with:

the pump source module is used for generating pump light required by the optical parametric oscillator module and adjusting the output power of the pump light;

and the optical parametric oscillator module is used for generating frequency conversion, so that the pump light and the generated signal light are periodic and simultaneously generate and output idler frequency light with a wave band of 5-10 mu m through the nonlinear crystal.

2. The tunable longwave mid-infrared ultrafast laser source apparatus of claim 1, wherein the pump source module comprises: an all-solid-state Yb femtosecond laser source YbLaser, a first half-wave plate HWP1, a broadband high-power polarization beam splitter PBS, and a second half-wave plate HWP 2.

3. The tunable long-wave mid-infrared ultrafast laser source device according to claim 2, wherein the right end of the all-solid-state Yb femtosecond laser source YbLaser is provided with a first half-wave plate HWP1, the right end of the first half-wave plate HWP1 is provided with a broadband high-power polarization beam splitter PBS, and the right end of the broadband high-power polarization beam splitter PBS is provided with a second half-wave plate HWP 2.

4. The tunable longwave mid-infrared ultrafast laser source device of claim 1, wherein said optical parametric oscillator module comprises: a ring cavity structure and a linear cavity structure.

5. The tunable long wave mid-infrared ultrafast laser source device of claim 4, wherein said ring cavity structure comprises: a focusing mirror L, a concave mirror CM, a LISe crystal, a silver-plated concave mirror SM, a ZnSe plane mirror ZM, a Ge window GW and an output coupling mirror OC.

6. The tunable long-wave mid-infrared ultrafast laser source device according to claim 4, wherein the ring cavity structure receives a pump light, the pump light is emitted into the LISe crystal through the focusing mirror L and the concave mirror CM in sequence to perform nonlinear frequency conversion to generate a signal light and an idler light, and then the signal light and the idler light are reflected to the ZnSe plane mirror ZM by the silver-plated concave mirror SM.

7. The tunable long-wave mid-infrared ultrafast laser source device as claimed in claim 6, wherein the idler and pump light are transmitted from the ZnSe plane mirror ZM and the signal light is reflected to the output coupling mirror OC, and the light transmitted from the ZnSe plane mirror ZM is filtered from the pump light by the Ge window GW to complete the output of the idler light; the output coupling mirror OC outputs a certain amount of signal light and reflects the rest signal light to the first concave mirror M1 to continue oscillating in the cavity;

in addition, the output coupling mirror OC can control the nonlinear process in the LISe crystal by translating and adjusting the cavity length back and forth so as to realize the tuning of the output light wavelength.

8. The tunable long wave mid-infrared ultrafast laser source device of claim 4, wherein said line cavity structure comprises: a focusing mirror L1, a focusing mirror L2, a concave mirror CM, a LISe crystal, a ZnSe concave mirror ZCM, a plane mirror M, Ge window GW and an output coupling mirror OC;

the linear cavity structure receives pump light, the pump light is emitted into the LISe crystal through the focusing mirror L and the concave mirror CM in sequence to perform nonlinear frequency conversion to generate signal light and idler frequency light, the signal light and the idler frequency light are emitted to the surface of the ZnSe concave mirror ZCM, the idler frequency light and the pump light are transmitted from the ZnSe concave mirror ZCM, and the signal light is reflected to the output coupling mirror OC;

the light transmitted from the ZnSe concave mirror ZCM is filtered by a Ge window GW to filter pump light so as to complete the output of idler frequency light; the output coupling mirror OC outputs a certain amount of signal light and reflects the residual signal light to the ZnSe concave mirror ZCM, the ZnSe concave mirror ZCM passes through the LISe crystal again, the ZnSe concave mirror ZCM is transmitted to the surface of the concave mirror CM and then reflected to the surface of the plane mirror M, and finally the ZnSe concave mirror ZCM is reflected back to the concave mirror CM by the concave mirror CM and continues to oscillate in the cavity;

in addition, the output coupling mirror OC can control the nonlinear process in the LISe crystal by translating and adjusting the cavity length back and forth so as to realize the tuning of the output light wavelength.

9. A method of controlling a tunable long wave mid-infrared ultrafast laser source apparatus as claimed in any one of claims 1 to 8, wherein said method of controlling comprises: pumping light output from the pumping source module is sequentially emitted into the LISe crystal through the first focusing mirror and the concave mirror to perform nonlinear frequency conversion to generate signal light and idle frequency light, and then the signal light and the idle frequency light are reflected to the ZnSe plane mirror by the silver-plated concave mirror; the idler frequency light and the pump light are transmitted from the ZnSe plane mirror, and the signal light is reflected to the output coupling mirror; the light transmitted from the ZnSe plane mirror is filtered by the Ge window to filter the pump light so as to complete the output of idler frequency light; the output coupling mirror outputs a certain amount of signal light and reflects the rest signal light to the first concave mirror to continue oscillation in the cavity, and in addition, the output coupling mirror can control a nonlinear process in the LISe crystal by adjusting the cavity length through forward and backward translation to realize tuning of the output light wavelength.

Technical Field

The invention belongs to the technical field of long-wave intermediate infrared ultrafast lasers, and particularly relates to a tunable long-wave intermediate infrared ultrafast laser source device.

Background

At present, the intermediate infrared ultrafast laser has the advantages of both the intermediate infrared band and the ultrafast laser, has important application in a plurality of fields such as scientific research, medical treatment, industry, military and the like, and becomes a research hotspot of people. Wherein, the long-wave mid-infrared laser with the wavelength of 5-10 μm is one of important laser wave bands. The band is an important atmospheric window due to less water vapor absorption and low electromagnetic scattering absorption, so the band becomes a guide band of a novel infrared guide weapon. And the band covers the absorption spectrum line of the fundamental frequency characteristic fingerprint of various molecules, wherein the absorption intensity of benzene pollutants such as benzene, toluene, ethylbenzene and the like in the band is even higher by one order of magnitude than that in the band of 3-5 mu m, so that the detection sensitivity is greatly improved, and the method is widely applied to various detection and analysis. These all indicate significant and strong expectations for wide military and civilian applications in the fields of directional infrared antagonism, remote sensing, spectral analysis and aerospace, etc.

The main means for generating the intermediate infrared ultrafast laser at the present stage include the direct generation of the ultrafast laser and the indirect generation of the nonlinear frequency conversion. The ultrafast laser for directly generating the intermediate infrared band ultrafast laser is mainly an all-solid-state ultrafast laser, and as for the all-solid-state ultrafast laser, a gain medium, a mode locking device and a pumping source are three important factors for obtaining the ultrafast laser with wide wavelength range and narrow pulse width. All-solid-state ultrafast lasers have been able to generate ultrashort pulsed lasers with wavelengths covering the visible, near-infrared, and even part of the mid-infrared band, with pulse widths ranging from hundreds of picoseconds to several femtoseconds. However, the wavelength range and pulse width of the mid-infrared ultrafast laser directly obtained from the all-solid-state ultrafast laser are limited by the absorption emission spectrum range of the laser gain medium, the working wavelength and bandwidth of the mode-locked device, the radiation wavelength and efficiency of the pump source, and other factors.

For the nonlinear frequency conversion method, the oxide-based nonlinear crystal is mostly used for the frequency conversion below 5 μm, because the spectral coverage range exceeding 5 μm is greatly influenced by multi-phonon absorption, so that the oxide-based nonlinear crystal cannot realize the frequency conversion of the band. As the research on nonlinear crystal materials makes a major breakthrough, people have more choices along with the continuous generation of a plurality of high-quality oxygen-free crystals. The nonlinear Optical Frequency transformation commonly used at present mainly includes Optical Parametric Generation (OPG), Optical Parametric Oscillator (OPO), Optical Parametric Amplifier (OPA), Difference Frequency Generation (DFG), and the like. Among them, OPG and OPA generally require high energy of pump laser, usually require an amplifier as a pump source, and have high requirement on the damage threshold of the crystal material, thereby limiting the selectivity of nonlinear materials; the required pump energy of the OPO is lower than the former two, and the ultrafast laser can be directly used as a pump source. And because the requirement of the OPO on the pumping source is reduced, visible and near-infrared ultrafast lasers with the single pulse energy in the nano-focus level, such as a titanium sapphire ultrafast laser, a Yb all-solid-state ultrafast laser, a Yb fiber ultrafast laser, an Er fiber ultrafast laser and the like, can be used as the pumping source of the OPO, and the intermediate infrared ultrafast laser is further developed. Although the OPO technology further expands the wave band of the intermediate infrared ultrafast laser, the output wave band of the mature laser with high power and high beam quality is basically concentrated on about 1 μm, so that a high-efficiency long-wave pumping source is lacked, the wavelength of the intermediate infrared ultrafast laser is far from reaching the light transmission range of the nonlinear crystal, and a large excavation space is provided. In order to solve the problem, a combination method is generally adopted, such as an optical parametric oscillation difference frequency (OPO + DFG) and an optical parametric oscillation amplification difference frequency (OPO + OPA + DFG), and is a cascade optical parametric oscillator (OPO + OPO), so that the output of the 5-10 μm mid-infrared femtosecond laser is obtained. The first OPO outputs signal light pump light with the diameter of more than 1 mu m to pump a second frequency conversion device to obtain long-wave mid-infrared laser. But each pass through a single stage of frequency conversion means reduces the conversion efficiency. The LISe crystal has a wide transparency range (0.45-13.7 mu m), a large nonlinear coefficient (d33 is 16pm/V), and a large thermal conductivity of 5W/(m.K). LISe can be directly pumped by a commercial 1-micron laser to generate mid-infrared laser light due to the small near-infrared two-photon absorption. A wider bandgap and higher thermal conductivity will result in a higher damage threshold, which is important for high power laser output. In addition, the LISe crystal has lower melting temperature and lower vapor pressure, is beneficial to the growth of large-size high-quality crystals, and has great potential in the field of long-wave mid-infrared parametric oscillators directly pumped by 1 mu m. At present, the LISe crystal is applied to a nanosecond optical parametric oscillator to realize pulse output of more than 5 microns, but no relevant report exists in the field of a femtosecond optical parametric oscillator directly pumped by a 1-micron light source. However, in the prior art, the combined structure system is complex, the building difficulty is high, the requirement on the crystal transmittance is high, and the conversion efficiency is low.

Through the above analysis, the problems and defects of the prior art are as follows: in the prior art, a combined structure system is complex, high in building difficulty, high in requirement on crystal transmittance and low in conversion efficiency.

The difficulty in solving the above problems and defects is:

to solve the above problem, directly generating 5-10 μm femtosecond pulses using a single frequency variation is the best choice. And the most part of the converter supports the mid-infrared nonlinear crystal supporting the frequency conversion and only supports laser pumping with the central wavelength more than or equal to 1.55 mu m or even more than or equal to 2 mu m due to the limitation of multiphoton absorption. Because the quality and power density of output light beams are inseparable, and the current watt femtosecond light source with high light beam quality is mainly concentrated near 1 μm, the power and the light beam quality of output light can be greatly limited.

The significance of solving the problems and the defects is as follows:

1. the simplified device is beneficial to reducing the volume of the device and saving a large number of devices, and the cost is reduced while the miniaturization is realized;

2. the construction difficulty is reduced, so that the production efficiency can be improved, the defective rate is reduced, and the commercialization is facilitated;

3. the conversion efficiency is improved, and the 1 mu m high-quality light source pump is used, so that the output light power and the light beam quality are improved.

Disclosure of Invention

Aiming at the problems in the prior art, the invention provides a tunable long-wave mid-infrared ultrafast laser light source device. The invention directly uses a YbLaser pump to output 5-10 mu m wavelength ultrashort pulses based on the LISe crystal femtosecond optical parametric oscillator, is a 5-10 mu m intermediate infrared femtosecond optical parametric oscillator, and solves the problems of complex combined structure system, high construction difficulty, high requirement on crystal transmittance and low conversion efficiency to a certain extent.

The invention is realized in this way, a tunable long wave mid-infrared ultrafast laser light source device, the tunable long wave mid-infrared ultrafast laser light source device is provided with:

the pump source module is used for generating pump light required by the optical parametric oscillator module and adjusting the output power of the pump light;

and the optical parametric oscillator module is used for generating frequency conversion, so that the pump light and the generated signal light are periodic and simultaneously generate and output idler frequency light with a wave band of 5-10 mu m through the nonlinear crystal.

Further, the pump source module includes: an all-solid-state Yb femtosecond laser source YbLaser, a first half-wave plate HWP1, a broadband high-power polarization beam splitter PBS, and a second half-wave plate HWP 2.

Further, the right end of the all-solid-state Yb femtosecond laser source YbLaser is provided with a first half-wave plate HWP1, the right end of the first half-wave plate HWP1 is provided with a broadband high-power polarization beam splitter PBS, and the right end of the broadband high-power polarization beam splitter PBS is provided with a second half-wave plate HWP 2.

Further, the optical parametric oscillator module includes: a ring cavity structure and a linear cavity structure.

Further, the ring cavity structure includes: a focusing mirror L, a concave mirror CM, a LISe crystal, a silver-plated concave mirror SM, a ZnSe plane mirror ZM, a Ge window GW and an output coupling mirror OC.

Further, the ring cavity structure receives pump light, the pump light is emitted into the LISe crystal through the focusing mirror L and the concave mirror CM in sequence to perform nonlinear frequency conversion to generate signal light and idle frequency light, and the signal light and the idle frequency light are reflected to the ZnSe plane mirror ZM by the silver-plated concave mirror SM.

Further, the idler light and the pump light are transmitted from the ZnSe plane mirror ZM, the signal light is reflected to the output coupling mirror OC, and the light transmitted from the ZnSe plane mirror ZM is filtered by the Ge window GW to filter the pump light, so that the output of the idler light is completed; the output coupling mirror OC outputs a certain amount of signal light and reflects the rest signal light to the first concave mirror M1 to continue oscillating in the cavity;

in addition, the output coupling mirror OC can control the nonlinear process in the LISe crystal by translating and adjusting the cavity length back and forth so as to realize the tuning of the output light wavelength.

Further, the linear cavity structure comprises: a focusing mirror L1, a focusing mirror L2, a concave mirror CM, a LISe crystal, a ZnSe concave mirror ZCM, a plane mirror M, Ge window GW and an output coupling mirror OC.

Further, the linear cavity structure receives pump light, the pump light is emitted into the LISe crystal through the focusing mirror L and the concave mirror CM in sequence to perform nonlinear frequency conversion to generate signal light and idler frequency light, the signal light and the idler frequency light are emitted to the surface of the ZnSe concave mirror ZCM, the idler frequency light and the pump light are transmitted from the ZnSe concave mirror ZCM, and the signal light is reflected to the output coupling mirror OC.

Further, the light transmitted from the ZnSe concave mirror ZCM is filtered by a Ge window GW to filter pump light so as to complete the output of idler frequency light; the output coupling mirror OC outputs a certain amount of signal light and reflects the residual signal light to the ZnSe concave mirror ZCM, the ZnSe concave mirror ZCM passes through the LISe crystal again, the ZnSe concave mirror ZCM is transmitted to the surface of the concave mirror CM and then reflected to the surface of the plane mirror M, and finally the ZnSe concave mirror ZCM is reflected back to the concave mirror CM by the concave mirror CM and continues to oscillate in the cavity;

in addition, the output coupling mirror OC can control the nonlinear process in the LISe crystal by translating and adjusting the cavity length back and forth so as to realize the tuning of the output light wavelength.

Another object of the present invention is to provide a control method of the tunable long-wave mid-infrared ultrafast laser source device, the control method comprising: pumping light output from the pumping source module is sequentially emitted into the LISe crystal through the first focusing mirror and the concave mirror to perform nonlinear frequency conversion to generate signal light and idle frequency light, and then the signal light and the idle frequency light are reflected to the ZnSe plane mirror by the silver-plated concave mirror; the idler frequency light and the pump light are transmitted from the ZnSe plane mirror, and the signal light is reflected to the output coupling mirror; the light transmitted from the ZnSe plane mirror is filtered by the Ge window to filter the pump light so as to complete the output of idler frequency light; the output coupling mirror outputs a certain amount of signal light and reflects the rest signal light to the first concave mirror to continue oscillation in the cavity, and in addition, the output coupling mirror can control a nonlinear process in the LISe crystal by adjusting the cavity length through forward and backward translation to realize tuning of the output light wavelength.

Another object of the present invention is to provide a directional infrared countermeasure, remote sensing or spectroscopic analysis method using the tunable long-wave mid-infrared ultrafast laser source apparatus.

By combining all the technical schemes, the invention has the advantages and positive effects that: according to the invention, a YbLaser direct pumping LISe crystal-based femtosecond optical parametric oscillator is adopted to obtain the intermediate infrared ultrafast laser with the thickness of 5-10 microns, so that the problems of high difficulty and complexity, high requirement on the transmittance of the crystal and low conversion efficiency of an intermediate infrared ultrafast laser system obtained based on an OPO combination technology due to the lack of a high-efficiency long-wavelength pumping source are solved. According to the invention, the YbLaser is adopted to directly pump the LISe crystal-based optical parametric oscillator to obtain the intermediate infrared ultrafast laser with the wavelength of 5-10 microns, so that the problem that the quantum cascade laser is limited in the range of picoseconds due to the limitation of the active mode locking technology to obtain the laser pulse width is avoided. According to the invention, the YbLaser is adopted to directly pump the LISe crystal-based optical parametric oscillator to obtain the intermediate infrared ultrafast laser with the wavelength of 5-10 μm, so that the problem that the wavelength range and the pulse width of the intermediate infrared ultrafast laser directly obtained from the all-solid-state ultrafast laser are limited by factors such as the absorption emission spectrum range of a laser gain medium, the working wavelength and bandwidth of a mode locking device, the radiation wavelength and efficiency of a pumping source and the like is solved. The wavelength range of the intermediate infrared ultrafast laser which can be generated by the invention can reach 5-10 mu m, the pulse width can reach hundreds of femtoseconds, the system has simpler structure and is easy to adjust, and the conversion efficiency is higher than that of an OPO combined system and a cascade OPO.

Drawings

Fig. 1 is a schematic structural diagram of a tunable long-wave mid-infrared ultrafast laser source device based on a ring cavity structure according to an embodiment of the present invention.

Fig. 2 is a schematic structural diagram of a tunable long-wave mid-infrared ultrafast laser source device based on a linear cavity structure provided in an embodiment of the present invention.

In the figure: 1. an all-solid-state Yb femtosecond laser source; 2. a first half wave plate; 3. a broadband high power polarizing beam splitter; 4. a second half-wave plate; 5. a first focusing mirror; 6. a second focusing mirror; 7. a concave mirror; 8. a ZnSe plane mirror; 9. a ZnSe concave mirror; 10. a LISe crystal; 11. a silver-plated concave mirror; 12. a plane mirror; 13. a Ge window; 14. an output coupling mirror.

Fig. 3 is a schematic diagram of the correspondence between the transmittance and the wavelength of the LISe crystal according to the embodiment of the invention.

Fig. 4 is a diagram illustrating a relationship between a phase matching angle of a crystal and each wavelength of light according to an embodiment of the present invention.

Fig. 5 is a schematic diagram of a correspondence relationship between a phase matching angle and an effective nonlinear coefficient according to an embodiment of the present invention.

Fig. 6 is a schematic diagram of a correspondence relationship between a phase matching angle and a gain factor according to an embodiment of the present invention.

Fig. 7 is a spectrum diagram obtained by simulation according to an embodiment of the present invention.

Detailed Description

In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is further described in detail with reference to the following embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

Aiming at the problems in the prior art, the invention provides a tunable long-wave mid-infrared ultrafast laser light source device, and the invention is described in detail below with reference to the accompanying drawings.

Those skilled in the art can also implement the tunable long-wave mid-infrared ultrafast laser source device provided by the present invention by adopting other steps, and the tunable long-wave mid-infrared ultrafast laser source device provided by the present invention in fig. 1 is only one specific embodiment.

As shown in fig. 1-2, a tunable long-wave mid-infrared ultrafast laser source apparatus provided by the embodiment of the present invention includes:

and the pump source module is used for generating pump light (about 1 mu m) required by the optical parametric oscillator module and adjusting the output power of the pump light (by rotating the second half-wave plate 4).

And the optical parametric oscillator module is used for generating frequency conversion, so that the pump light and the generated signal light are generated and output idler frequency light with a wave band of 5-10 mu m through the nonlinear crystal while being periodic.

The pump source module includes: the device comprises an all-solid Yb femtosecond laser source 1, a first half-wave plate 2, a broadband high-power polarization beam splitter 3 and a second half-wave plate 4.

The right end of the all-solid Yb femtosecond laser source 1 is provided with a first half-wave plate 2, the right end of the first half-wave plate 2 is provided with a broadband high-power polarization beam splitter 3, and the right end of the broadband high-power polarization beam splitter 3 is provided with a second half-wave plate 4.

The all-solid Yb femtosecond laser source 1 is used for generating pump light with the central wavelength of 1030nm, the pulse width of 100fs and the maximum output power of 6W; the first half wave plate 2 is used for forming a power regulating system; the broadband high-power polarization beam splitter 3 is used for forming a power regulation system, and the second half-wave plate 4 is used for forming the power regulation system.

The optical parametric oscillator module includes: a ring cavity structure and a linear cavity structure.

The optical parametric oscillator module of the ring cavity structure includes: the device comprises a first focusing mirror 5, a concave mirror 7, a LISe crystal 10, a silver-plated concave mirror 11, a ZnSe plane mirror 8, a Ge window 13 and an output coupling mirror 14;

the first focusing lens 5 is used for focusing the pump light onto the LISe crystal 10, and the focused pump intensity is more than or equal to 50MW/cm²The peak intensity on the axis, the concave mirror 7 is plated with the film which transmits the wave band of the pump light and reflects the wave band of the signal light, the silver-plated concave mirror 11 reflects the light of each wave band in the cavity, the ZnSe plane mirror 8 is plated with the film which reflects the wave band of the signal light and has the transmittance of about 70 percent to the idle frequency wave band, the Ge window 13 reflects the wave band of the pump light, the output coupling mirror 14 is plated with the film which partially transmits the wave band of the signal light, the transmittance is 1.5 percent, and the output coupling mirror is arranged on a precision translation table which can move back and forth.

The pump light output from the pump source module is emitted into the LISe crystal 10 through the first focusing mirror 5 and the concave mirror 7 in sequence to perform nonlinear frequency conversion to generate signal light and idle frequency light, and then the signal light and the idle frequency light are reflected to the ZnSe plane mirror 8 by the silver-plated concave mirror 11. The idler and pump light are transmitted from the ZnSe plane mirror 8 and the signal light is reflected to the output coupling mirror 14. The light transmitted from the ZnSe mirror 8 is filtered by the Ge window 13 to remove the pump light, thereby completing the output of idler light. The output coupling mirror 14 outputs a certain amount of signal light and reflects the rest signal light to the first concave mirror 7 to continue oscillation in the cavity, and in addition, the output coupling mirror 14 can realize tuning of output light wavelength by controlling a nonlinear process in the LISe crystal 10 by adjusting the cavity length through back and forth translation.

The optical parametric oscillator module of the line cavity structure comprises: a first focusing mirror 5, a second focusing mirror 6, a concave mirror 7, a LISe crystal 10, a ZnSe concave mirror 9, a plane mirror 12, a Ge window 13 and an output coupling mirror 14;

the first focusing lens 5 is used for focusing the pump light onto the LISe crystal 10, and the focused pump intensity is more than or equal to 50MW/cm²The ZnSe concave mirror 9 is coated with a film reflecting the signal light wave band and has a transmittance of about 70% to the idle frequency light wave band, the plane mirror 12 is coated with a film reflecting the signal light, the Ge window 13 reflects the pump light wave band, the output coupling mirror 14 is coated with a film partially transmitting the signal light wave band and is arranged on a precision translation stage capable of moving back and forth;

the pump light output from the pump source module is emitted into the LISe crystal through the focusing mirror L and the concave mirror CM in sequence to perform nonlinear frequency conversion to generate signal light and idler light, and then is emitted to the surface of the ZnSe concave mirror ZCM, the idler light and the pump light are transmitted from the ZnSe concave mirror ZCM, and the signal light is reflected to the output coupling mirror OC. The light transmitted from the ZnSe concave mirror ZCM is filtered by the Ge window GW to filter the pump light, and the output of the idler frequency light is finished. The output coupling mirror OC outputs a certain amount of signal light and reflects the residual signal light to the ZnSe concave mirror ZCM, the ZnSe concave mirror ZCM passes through the LISe crystal again, the ZnSe concave mirror ZCM is transmitted to the surface of the concave mirror CM and then reflected to the surface of the plane mirror M, and finally the ZnSe concave mirror ZCM is reflected back to the concave mirror CM by the concave mirror M and continues to oscillate in the cavity. In addition, the output coupling mirror OC can control the nonlinear process in the LISe crystal by translating and adjusting the cavity length back and forth so as to realize the tuning of the output light wavelength.

The LISe crystal has two blocks, and is used for outputting femtosecond pulses with the pulse diameters of 5-7 microns and 7-10 microns respectively. The phase matching angles of the LISe crystal are 45.8 degrees and 36.5 degrees, the thickness of the LISe crystal is 1mm, and the surface of the crystal is also plated with a film which is transparent to pump light, signal light and idler frequency light wave bands. The OPO uses II-type phase matching (e → o + e), the signal light is o light, the wavelength range is 1148-1297 nm, the conversion efficiency is-30%, and the output power is-1.8W; the idler frequency light is e light, the wavelength range is 5-10 mu m, the conversion efficiency is 8 percent, and the output power is 467 mW.

The technical scheme of the invention is described in detail in combination with simulation experiments.

As shown in FIG. 3, the transmittance of a 1cm LISe crystal in a 0.45-13.7 μm band exceeds 95% according to the corresponding relationship between the LISe crystal transmittance and the wavelength.

As shown in FIG. 4, the LISe crystal provided by the present invention has a corresponding relationship between the phase matching angle and each optical wavelength, and when the wavelength of the pump light is 1030nm, the LISe crystal supports frequency conversion with an idler frequency of 5-10 μm, and the phase matching angle is 33-52 degrees.

As shown in FIG. 5, the corresponding relationship between the phase matching angle and the effective nonlinear coefficient provided by the invention is that the LISe crystal has an effective nonlinear coefficient more than 9pm/V within the range of 33-52 degrees.

As shown in FIG. 6, the corresponding relationship between the phase matching angle and the gain coefficient provided by the invention is that the gain coefficient of the LISe crystal is more than 0.000125W within the range of 33-52 DEG^-0.5. Wherein, the length of the LISe crystal: 1 cm; principal plane of the LISe crystal: an XY plane; the phase matching type: type II phase matching (e + o → e); phase matching angle: 45.8 ° or 36.5 °; pump light parameters: the center wavelength is 1030nm, the pulse width is 100fs, and the output power is more than or equal to 6W.

The invention has the advantages that the whole system structure is simple, the adjustment is easy, and the conversion rate is higher than that of an OPO combined system and a cascaded OPO, so that the 5-10 mu m mid-infrared femtosecond laser, namely an optical parametric oscillator directly pumped by YbLaser and based on the LISe crystal, is obtained.

The working principle of the invention is as follows: firstly, a pump source module is operated, pump light is output by using an all-solid Yb femtosecond laser source YbLaser, a power regulator consisting of a first half-wave plate HWP1, a broadband high-power polarization beam splitter PBS and a second half-wave plate HWP2 is used for regulation, the average output power of the pump light can be properly regulated according to a theoretical oscillation starting threshold value of a resonant cavity in an optical parametric oscillator module and a damage threshold value of a LISe crystal, and then the pump light is focused by a focusing mirror L and then is emitted into the LISe crystal through a concave mirror CM to perform nonlinear frequency conversion to generate 5-10 mu m of frequency idle light and corresponding signal light. When the ring cavity structure is used, the pump light, the idler frequency light and the signal light are emitted to the silver-plated concave mirror SM together and are totally reflected to the ZnSe plane mirror ZM, the pump light and the idler frequency light are emitted out of the resonant cavity through the mirror, the pump light is filtered by the Ge window GW to complete the output of the idler frequency light of 5-10 mu m, and the signal light is reflected to the output coupling mirror OC by the ZnSe plane mirror ZM. The signal light incident on the OC surface of the output coupling mirror projects a part of the signal light as output signal light, and the other part of the signal light is reflected to the CM surface of the concave mirror and then reflected again to enter the LISe crystal to participate in nonlinear frequency conversion. When the linear cavity structure is used, pump light, idler frequency light and signal light are emitted to the ZnSe concave mirror together, the pump light and the idler frequency light are emitted out of the resonant cavity through the mirror, the pump light is filtered by the Ge window GW to complete the output of the idler frequency light of 5-10 μm, and the signal light is reflected to the output coupling mirror OC by the ZnSe concave mirror ZCM. The signal light incident on the surface of the output coupling mirror OC projects a part of the signal light as output signal light, and the other part of the signal light is reflected back to the surface of the ZnSe concave mirror ZCM, is reflected again into the LISe crystal to undergo nonlinear frequency conversion, is incident on the concave mirror CM, and is reflected to the plane mirror M. Finally, the light is reflected by the plane mirror M back to the concave mirror CM to complete a cycle.

In addition, the spectrum obtained by simulation is shown in fig. 7. The phase matching used for the simulation was 1208nm (e) +7000nm (o) 1030nm (e), the single pulse energy was 80nJ, the spot diameter was 80 μm, the effective nonlinear coefficient was 9.97pm/V, and the pulse tended to stabilize after 1087 round trips within the oscillator.

In the description of the present invention, "a plurality" means two or more unless otherwise specified; the terms "upper", "lower", "left", "right", "inner", "outer", "front", "rear", "head", "tail", and the like, indicate orientations or positional relationships based on the orientations or positional relationships shown in the drawings, are only for convenience in describing and simplifying the description, and do not indicate or imply that the device or element referred to must have a particular orientation, be constructed in a particular orientation, and be operated, and thus, should not be construed as limiting the invention. Furthermore, the terms "first," "second," "third," and the like are used for descriptive purposes only and are not to be construed as indicating or implying relative importance.

The above description is only for the purpose of illustrating the present invention and the appended claims are not to be construed as limiting the scope of the invention, which is intended to cover all modifications, equivalents and improvements that are within the spirit and scope of the invention as defined by the appended claims.