A method and device for difference frequency generation of mid-infrared femtosecond laser

Abstract

The present invention provides a method and device for difference frequency generation of mid-infrared femtosecond laser, which belongs to the field of ultrafast laser technology. The method and device for difference frequency generation of mid-infrared femtosecond laser are based on passive synchronization of Yb fiber and Er fiber femtosecond laser, and include the steps of: using a Yb fiber oscillator and an Er fiber oscillator to share a single-mode fiber to achieve synchronization of femtosecond pulse sequences after mode locking of the Yb fiber oscillator and the Er fiber oscillator; and injecting the pulses into a PPLN crystal for difference frequency generation after amplification and merging to generate mid-infrared femtosecond laser. The method and device for difference frequency generation of mid-infrared femtosecond laser provided by the present invention have the advantages of high efficiency and high power output, and the stability and reliability are improved, and the advantages of achieving high average power femtosecond mid-infrared laser are achieved, and the method and device have important application value and scientific significance.

Description

Technical Field

[0001] The invention relates to the technical field of ultrafast lasers, and in particular to a method and a device for generating mid-infrared femtosecond lasers by difference frequency. Background Art

[0002] Mid-infrared lasers with a wavelength range of 3 to 5 μm have strong penetration into fog and smoke due to their location in the atmospheric window, and have important applications in communications, environmental detection, ranging, laser radar, and target interference. Femtosecond lasers in this band have high peak power, which is more conducive to transmission in the atmosphere and interaction with matter, such as filamentation in the atmosphere and generation of high-order harmonics, so the development of femtosecond laser pulses in the mid-infrared band has important scientific value and application prospects.

[0003] Currently, there are only a few laser materials such as Er-doped YAG crystals, fluoride crystals, and chemical materials that can directly generate lasers in this band. Since the optical properties of these materials are not ideal and the output power is limited, the laser devices for this band are mostly parametric oscillators and parametric amplifiers pumped by conventional lasers. However, since near-infrared lasers are required as pump light sources, the complex structure, low output power, and difficult operation of parametric lasers limit their application. Summary of the invention

[0004] An object of the present invention is to provide a method for difference frequency generating mid-infrared femtosecond laser in view of the above-mentioned defects existing in the prior art, so as to propose a new method for generating mid-infrared femtosecond laser and solve the shortcomings of the current mid-infrared laser such as low output power, complex structure and difficult operation.

[0005] An object of the present invention is to provide a device for difference frequency generation of mid-infrared femtosecond lasers in view of the above-mentioned defects in the prior art, so as to generate different wavelength lasers of mid-infrared femtosecond lasers based on passive synchronization of Yb fiber and Er fiber femtosecond laser difference frequency.

[0006] In particular, the present invention provides a method for difference frequency generation of mid-infrared femtosecond laser, based on passive synchronization of Yb fiber and Er fiber femtosecond laser difference frequency generation of mid-infrared femtosecond laser, comprising the following steps:

[0007] A Yb fiber oscillator and an Er fiber oscillator share a single-mode optical fiber to achieve synchronization of femtosecond pulse sequences of the Yb fiber oscillator and the Er fiber oscillator after mode locking;

[0008] After amplification and merging, they are injected into the PPLN crystal for frequency difference to generate mid-infrared femtosecond laser.

[0009] Optionally, the method further comprises the steps of:

[0010] The mid-infrared femtosecond laser generated by the difference frequency is injected into the ZEBLAN optical fiber for further amplification.

[0011] Optionally, the method further comprises the steps of:

[0012] The mid-infrared femtosecond laser generated by the difference frequency is compressed through a calcium fluoride glass block.

[0013] The present invention also provides a device for generating mid-infrared femtosecond laser by difference frequency, comprising a Yb fiber femtosecond oscillator, an Er fiber femtosecond oscillator, a single-mode optical fiber, a translation stage, a Yb fiber amplifier, an Er fiber amplifier, a first compressor, a second compressor, a laser beam combining lens group, a PPLN crystal, a ZEBLAN (i.e., a nonlinear fiber laser using ZEBLAN material (Zr, Ba, La, Al, Nd) as a laser medium) fiber amplifier, and a glass block compressor, which are placed in sequence;

[0014] The Yb fiber femtosecond oscillator is used to generate a femtosecond pulse sequence with a central wavelength of 1030 nm;

[0015] The Er fiber femtosecond oscillator is used to generate a femtosecond pulse sequence with a central wavelength of 1560nm;

[0016] The Yb fiber amplifier is used to amplify the pulse sequence output by the Yb fiber femtosecond oscillator;

[0017] The Er fiber amplifier is used to amplify the pulse sequence output by the Er fiber femtosecond oscillator;

[0018] The first compressor is used to compress the laser amplified by the Yb fiber amplifier to a femtosecond pulse width, that is, to obtain a 1030nm femtosecond laser;

[0019] The second compressor is used to compress the laser amplified by the Er fiber amplifier to a femtosecond pulse width, that is, to obtain a 1560nm femtosecond laser;

[0020] The laser beam combining lens group is used to combine the 1030nm femtosecond laser and the 1560nm femtosecond laser;

[0021] The PPLN crystal is used to generate ultrashort pulse laser at a difference frequency when the 1030nm femtosecond laser and the 1560nm femtosecond laser are combined and beam-formed and then pass through the PPLN crystal;

[0022] The ZEBLAN optical fiber amplifier is used to amplify the ultrashort pulse laser;

[0023] The glass block compressor is used to compress the ultrashort pulse laser to achieve mid-infrared laser output with a pulse width of the order of 100 fs.

[0024] Optionally, the laser beam combining lens group includes a first 1560nm reflector, a second 1560nm reflector, a first 1030nm reflector, a first 1560nm anti-reflection mirror and a 1030nm high reflector;

[0025] The first 1560nm reflector and the second 1560nm reflector are used to reflect the 1560nm femtosecond laser to the next stage;

[0026] The first 1030nm reflector is used to reflect the 1030nm femtosecond laser to the next stage;

[0027] The first 1560nm anti-reflection and 1030nm high reflective mirror is used to allow the 1560nm femtosecond laser to pass through the lens, while the 1030nm femtosecond laser is totally reflected from the front surface of the lens to combine two femtosecond laser beams with central wavelengths of 1030nm and 1560nm.

[0028] Optionally, the Yb fiber femtosecond oscillator adopts NPE mode locking to achieve picosecond pulse sequence output with a repetition frequency of 40 MHz, and the central wavelength is 1030 nm; the Er fiber femtosecond oscillator adopts NPE mode locking to achieve picosecond pulse sequence output with a repetition frequency of 40 MHz, and the central wavelength is 1560 nm.

[0029] Optionally, the Yb fiber oscillator and the Er fiber oscillator share a section of single-mode optical fiber, and the mode-locked laser pulses of the two oscillators pass through the single-mode optical fiber at the same time;

[0030] The cavity length of the Yb fiber oscillator is fixed, and one end of the Er fiber oscillator is mounted on the translation stage. The cavity length of the Er fiber oscillator is changed by adjusting the translation stage to achieve synchronization of the mode-locked pulse sequences output by the Yb fiber oscillator and the Er fiber oscillator.

[0031] Optionally, the surfaces of the first 1560nm reflector and the second 1560nm reflector are coated with a 1560nm broadband high-reflection film; the surface of the first 1030nm reflector is coated with a 1030nm broadband high-reflection film; the surfaces of the first 1560nm anti-reflection and 1030nm high-reflection mirror are coated with a 1030nm broadband high-reflection film and a 1560 broadband high-transmittance film.

[0032] Optionally, the ZEBLAN optical fiber is an Er-doped ZEBLAN-based optical fiber;

[0033] The glass block compressor is two wedge-angle glass blocks made of calcium fluoride. Both end surfaces of the glass block compressor are coated with anti-reflection films. One of the wedge-angle glass blocks is installed on the translation stage.

[0034] Optionally, the PPLN crystal has a diameter of 10×1 mm, a length of 3 mm, and a polarization interval period of 29.52 nm.

[0035] The present invention provides a method for difference frequency generation of mid-infrared femtosecond lasers, and provides a synchronization scheme for lasers with different wavelengths based on passively synchronizing Yb fiber and Er fiber femtosecond laser difference frequency generation of mid-infrared femtosecond lasers. After passive synchronization is achieved by using a Yb fiber oscillator and an Er fiber oscillator through a common single-mode optical fiber, a mid-infrared band high-power femtosecond laser with a wavelength of 3.1 μm is generated by difference frequency in a PPLN crystal.

[0036] The present invention provides a method for difference frequency generation of mid-infrared femtosecond laser, which is based on the technical solution of passively synchronizing Yb fiber and Er fiber femtosecond laser difference frequency generation of mid-infrared femtosecond laser, and can output femtosecond laser with a central wavelength of 3.1μm. The femtosecond laser light source has important applications in the fields of atmospheric transmission, optical communication, pollution detection, etc.

[0037] The method for difference frequency generating mid-infrared femtosecond laser provided by the present invention has the advantages of high efficiency and high power output, and the stability and reliability are improved. It has the advantage of realizing high average power femtosecond mid-infrared laser and has important application value and scientific significance.

[0038] Based on the following detailed description of specific embodiments of the present invention in conjunction with the accompanying drawings, those skilled in the art will become more aware of the above and other objects, advantages and features of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Hereinafter, some specific embodiments of the present invention will be described in detail in an exemplary and non-limiting manner with reference to the accompanying drawings. The same reference numerals in the accompanying drawings indicate the same or similar components or parts. It should be understood by those skilled in the art that these drawings are not necessarily drawn to scale. In the accompanying drawings:

[0040] Figure 1 It is a schematic structural diagram of a device for generating mid-infrared femtosecond laser by difference frequency according to the present invention;

[0041] Figure 2 Based on Figure 1 Schematic diagram of laser generated by Er fiber oscillator shown;

[0042] Figure 3 Based on Figure 1 The schematic diagram shown is that the pulse sequence repetition frequency of the Yb fiber oscillator and the Er fiber oscillator mode-locked output is the same to achieve synchronization of the output pulses of the two oscillators;

[0043] Figure 4 Based on Figure 1Schematic diagram of ultrashort pulse laser generated by difference frequency as shown;

[0044] Figure 5 Based on Figure 1 Schematic diagram of amplification performed by the ZEBLAN fiber amplifier shown. DETAILED DESCRIPTION

[0045] The invention is further described below through the accompanying drawings and implementation methods. However, the protection of the invention is not limited to the following examples, but should include all the contents in the claims.

[0046] The inventor of the present invention found in research that the difference frequency process is the opposite of the parametric process, which is the process of absorbing two photons at the same time and merging them into one photon. Infrared laser can be generated through the difference frequency process. In addition, since the light is transmitted in the optical fiber, the fiber laser avoids the disturbance caused by external airflow and temperature drift. Moreover, Yb fiber laser and Er fiber laser are very mature and can achieve high average power output.

[0047] Based on this, the inventors synchronized and locked the two lasers through a passive synchronization method, and then performed difference frequency to produce a mid-infrared femtosecond laser with a central wavelength of 3.1μm. Compared with conventional solutions, it has high efficiency and improved stability and reliability because it does not require the spectrum broadening process of highly nonlinear optical fibers. It has the advantage of achieving high average power femtosecond mid-infrared lasers and has important application value and scientific significance.

[0048] Figure 1 Schematic diagram of the structure of a device for difference frequency generation of mid-infrared femtosecond laser according to the present invention. Figure 1 As shown, the present invention provides a method for generating mid-infrared femtosecond laser by difference frequency, which is based on passive synchronization of Yb fiber and Er fiber femtosecond laser difference frequency to generate mid-infrared femtosecond laser. Generally, it can include the following steps:

[0049] A Yb fiber oscillator and an Er fiber oscillator share a single-mode optical fiber to achieve synchronization of femtosecond pulse sequences of the Yb fiber oscillator and the Er fiber oscillator after mode locking;

[0050] After amplification and merging, they are injected into the PPLN crystal for frequency difference to generate mid-infrared femtosecond laser.

[0051] Specifically, the method may further include the step of injecting the mid-infrared femtosecond laser generated by the difference frequency into the ZEBLAN optical fiber for further amplification.

[0052] Specifically, the method may further include the step of compressing the mid-infrared femtosecond laser generated by the difference frequency through a calcium fluoride material glass block.

[0053] like Figure 1 As shown, the present invention also provides a device for difference frequency generation of mid-infrared femtosecond laser, which generally includes a Yb fiber femtosecond oscillator 1, an Er fiber femtosecond oscillator 2, a single-mode optical fiber 3, a translation stage 4, a Yb fiber amplifier 5, an Er fiber amplifier 6, a first compressor 7, a second compressor 8, a laser beam combining lens group (9, 10, 11, 12), a PPLN crystal 13, a ZEBLAN fiber amplifier 14, and a glass block compressor 15 which are placed in sequence.

[0054] Specifically, the Yb fiber femtosecond oscillator 1 is used to generate a femtosecond pulse sequence with a central wavelength of 1030nm. The Er fiber femtosecond oscillator 2 is used to generate a femtosecond pulse sequence with a central wavelength of 1560nm. The Yb fiber amplifier 5 is used to amplify the pulse sequence output by the Yb fiber femtosecond oscillator 1. The Er fiber amplifier 6 is used to amplify the pulse sequence output by the Er fiber femtosecond oscillator 2. The first compressor 7 is used to compress the laser amplified by the Yb fiber amplifier 1 to a femtosecond pulse width, that is, to obtain a 1030nm femtosecond laser. The second compressor 8 is used to compress the laser amplified by the Er fiber amplifier 2 to a femtosecond pulse width, that is, to obtain a 1560nm femtosecond laser. The laser beam combining lens group (9, 10, 11, 12) is used to combine the 1030nm femtosecond laser and the 1560nm femtosecond laser. The PPLN crystal 13 is used to generate ultrashort pulse lasers at a difference frequency when the 1030nm femtosecond laser and the 1560nm femtosecond laser are combined and beamed. The ZEBLAN fiber amplifier 14 is used to amplify the ultrashort pulse lasers. The glass block compressor 15 is used to compress the ultrashort pulse lasers to achieve a mid-infrared laser output with a pulse width of the order of 100fs.

[0055] Specifically, the laser beam combining lens group (9, 10, 11, 12) includes a first 1560nm reflector 9, a second 1560nm reflector 10, a first 1030nm reflector 11, and a first 1560nm anti-reflection and 1030nm high reflector 12. The first 1560nm reflector 9 and the second 1560nm reflector 10 are used to reflect the 1560nm femtosecond laser to the next stage. The first 1030nm reflector 11 is used to reflect the 1030nm femtosecond laser to the next stage. The first 1560nm anti-reflection and 1030nm high reflector 12 is used to allow the 1560nm femtosecond laser to pass through the lens, and the 1030nm femtosecond laser is totally reflected from the front surface of the lens to combine two femtosecond lasers with central wavelengths of 1030nm and 1560nm.

[0056] The Yb fiber femtosecond oscillator 1 uses NPE mode locking to achieve the output of a picosecond pulse sequence with a repetition frequency of 40 MHz, and its central wavelength is 1030 nm. The Er fiber femtosecond oscillator 2 uses NPE mode locking to achieve the output of a picosecond pulse sequence with a repetition frequency of 40 MHz, and its central wavelength is 1560 nm. The Yb fiber oscillator 1 and the Er fiber oscillator 2 share a section of single-mode fiber 3, and the mode-locked laser pulses of the two oscillators pass through the single-mode fiber 3 at the same time. The cavity length of the Yb fiber oscillator 1 is fixed, and one end of the Er fiber oscillator 2 is installed on the translation stage 4. The cavity length of the Er fiber oscillator 2 is changed by adjusting the translation stage 4 to achieve synchronization of the mode-locked pulse sequences output by the Yb fiber oscillator 1 and the Er fiber oscillator 2.

[0057] Optionally, the surfaces of the first 1560nm reflector 9 and the second 1560nm reflector 10 are coated with a 1560nm broadband high reflection film. The surface of the first 1030nm reflector 11 is coated with a 1030nm broadband high reflection film. The surfaces of the first 1560nm anti-reflection and 1030nm high reflector 12 are coated with a 1030nm broadband high reflection film and a 1560 broadband high transmittance film.

[0058] The ZEBLAN optical fiber is an optical fiber based on Er-doped ZEBLAN. The glass block compressor 15 is two wedge-angle glass blocks made of calcium fluoride. Both end surfaces of the glass block compressor 15 are coated with anti-reflection films, and one of the wedge-angle glass blocks is installed on the translation stage 4.

[0059] More specifically, the Yb fiber oscillator 1 is an ultrashort pulse laser with an output central wavelength of 1030 nm, a repetition frequency of 40 MHz, an average power of 20 mW, and a pulse width of 5 picoseconds.

[0060] Er fiber oscillator 2 is an ultrashort pulse laser with an output central wavelength of 1560nm, a repetition frequency of 40MHz, an average power of 15mW, and a pulse width of 2 picoseconds.

[0061] The single-mode optical fiber 3 is a single-mode optical fiber with a core diameter of 5 μm and a length of 100 mm. The single-mode optical fiber 3 is a medium through which the mode-locked laser pulses in the Yb fiber oscillator and the Er fiber oscillator pass together.

[0062] The translation stage 4 has a size of 40×40 mm, a moving range of 12 mm, and an accuracy of less than 1 μm.

[0063] The Yb fiber amplifier 5 is a Yb-doped fiber with a core diameter of 10 / 125 μm and a length of 5 meters. It uses a pump source with a central wavelength of 976 nm and a power of 10 W.

[0064] The Er fiber amplifier 6 has a core diameter of 10 / 125 μm, is Er-doped fiber, has a length of 5 meters, and uses a pump source with a central wavelength of 976 nm and a power of 15 W.

[0065] The first compressor 7 is a transmission grating with a size of 50 mm (length) × 30 mm (width) × 1 mm (thickness), a grating line density of 1400 lines / mm, a wide anti-reflection film from 1000 to 1100 nm, and a first-order diffraction efficiency greater than 90%.

[0066] The second compressor 8 is a transmission grating with dimensions of 50 mm (length) × 30 mm (width) × 1 mm (thickness), a grating line density of 1400 lines / mm, a wide anti-reflection film from 1500 to 1600 nm, and a first-order diffraction efficiency greater than 90%.

[0067] The first 1560nm laser reflector 9 and the first 1560nm laser reflector 10 have a size of 25mm×6mm, and are coated with a dielectric film with high reflection to 1500nm~1600nm. The first 1030nm laser reflector 11 has a size of 25mm×6mm, and is coated with a dielectric film with high reflection to 1000nm~1100nm. The first 1030nm anti-reflection and 1550nm reflector 12 has a size of 25mm×6mm, and is coated with a dielectric film with high transmittance to 1000nm~1100nm and high reflection to 1500~1600nm.

[0068] The PPLN crystal 13 has an aperture of 10×1 mm, a length of 3 mm, a polarization interval period of 29.52 nm, and is coated with 1030 nm, 1560 nm and 3.1 μm antireflection films on both end faces.

[0069] The ZEBLAN fiber amplifier 14 has a core diameter of 30 / 250 μm, is Er-doped, and is 5 meters long. It uses a pump light with a power of 50 W and a central wavelength of 976 nm.

[0070] The glass block compressor 15 has a diameter of 10×10 mm and a length of 15 mm. The material is CaF2 and the two end surfaces are plated with 3 μm of transparency enhancement. One of the wedge-angle glasses is installed on a manual translation stage to accurately change the amount of glass block insertion.

[0071] Optionally, the first 1560nm laser reflecting mirror 9 and the first 1560nm laser reflecting mirror 10, the first 1030nm laser reflecting mirror 11 and the first 1030nm anti-reflection and 1550nm reflecting mirror 12 are all arranged at an angle of 45°.

[0072] Optionally, the translation stage 4 is a high-precision manual translation stage, which is used to install the Er fiber port on the manual translation stage and accurately translate the port position, thereby accurately changing the cavity length and the laser repetition frequency.

[0073] The following is a specific embodiment in combination with actual use:

[0074] Yb fiber oscillator 1 generates laser pulses with a pulse width of 5 picoseconds, a central wavelength of 1030nm, and a repetition frequency of 40MHz. Figure 2 As shown in the figure, the Er fiber oscillator generates a laser with a pulse width of 2 picoseconds, a central wavelength of 1560nm, and a repetition frequency of approximately 40MHz. Figure 3 As shown in the figure, the lasers of the two oscillators pass through a single-mode optical fiber 3 together. By precisely adjusting the position of the translation stage 4, the repetition frequency of the pulse sequence output by the Yb fiber oscillator 1 and the Er fiber oscillator 2 is made the same, thus achieving precise synchronization of the output pulses of the two oscillators, with a synchronization accuracy of less than 1fs. Figure 4 As shown; the laser pulse output from the Yb fiber oscillator 1 enters the Yb fiber amplifier 5 for further amplification, and is compressed to 100fs by the 1030nm compressor 7; the laser pulse output from the Er fiber oscillator 2 enters the Er fiber amplifier 6 for further amplification; and is compressed to about 100fs by the 1560nm compressor 8; the femtosecond laser output from the 1560nm compressor 8 is reflected by the first 45°1560nm laser reflector 9 and the second 45°1560nm laser reflector 10, and the femtosecond laser output from the 1030nm compressor 7 is reflected by the first 45°1030nm laser reflector 11, and the above two wavelength lasers are combined together by the first 45°1030 high reflection and 1560nm high transmission laser reflectors 12, and injected into the PPLN crystal 13 to realize the difference frequency generation of 3.1μm wavelength laser. As shown Figure 5 and then further amplified by the ZEBLAN fiber amplifier 14, and finally compressed by the glass block compressor 15 to output a mid-infrared laser output with a pulse width of less than 200fs and a power greater than 10W.

[0075] The present invention provides a method and device for difference frequency generation of mid-infrared femtosecond lasers, aiming to provide a synchronization solution for lasers of different wavelengths based on passive synchronization of Yb fiber and Er fiber femtosecond laser difference frequency generation of mid-infrared femtosecond lasers.

[0076] The present invention provides a method and device for difference frequency generation of mid-infrared femtosecond laser, aiming to provide an optical parametric amplifier for generating mid-infrared femtosecond laser by difference frequency generation of passively synchronized Yb fiber and Er fiber femtosecond laser.

[0077] The present invention provides a method and device for difference frequency generation of mid-infrared femtosecond laser, aiming to provide an ultrafast spectroscopy based on passive synchronization of Yb fiber and Er fiber femtosecond laser difference frequency generation of mid-infrared femtosecond laser.

[0078] The present invention provides a method and device for difference frequency generation of mid-infrared femtosecond laser, which is based on the technical solution of passively synchronizing Yb fiber and Er fiber femtosecond laser difference frequency generation of mid-infrared femtosecond laser. After passive synchronization is achieved by Yb fiber oscillator and Er fiber oscillator through a common single-mode optical fiber, a mid-infrared band high-power femtosecond laser with a wavelength of 3.1 μm is generated by difference frequency in a PPLN crystal.

[0079] The present invention provides a method and device for difference frequency generation of mid-infrared femtosecond lasers, and provides a synchronization scheme for lasers of different wavelengths based on passive synchronization of Yb fiber and Er fiber femtosecond laser difference frequency generation of mid-infrared femtosecond lasers. After passive synchronization is achieved by using a Yb fiber oscillator and an Er fiber oscillator through a common single-mode optical fiber, a mid-infrared band high-power femtosecond laser with a wavelength of 3.1 μm is generated by difference frequency in a PPLN crystal.

[0080] The present invention provides a method for difference frequency generation of mid-infrared femtosecond laser, which is based on the technical solution of passively synchronizing Yb fiber and Er fiber femtosecond laser difference frequency generation of mid-infrared femtosecond laser, and can output femtosecond laser with a central wavelength of 3.1μm. The femtosecond laser light source has important applications in the fields of atmospheric transmission, optical communication, pollution detection, etc.

[0081] The method for difference frequency generating mid-infrared femtosecond laser provided by the present invention has the advantages of high efficiency and high power output, and the stability and reliability are improved. It has the advantage of realizing high average power femtosecond mid-infrared laser and has important application value and scientific significance.

[0082] At this point, those skilled in the art should recognize that, although the exemplary embodiments of the present invention have been shown and described in detail herein, many other variations or modifications that conform to the principles of the present invention can still be directly determined or derived based on the content disclosed in the present invention without departing from the spirit and scope of the present invention. Therefore, the scope of the present invention should be understood and identified as covering all these other variations or modifications.

Claims

1. A device for generating mid-infrared femtosecond laser by difference frequency, characterized in that: It includes a Yb fiber femtosecond oscillator, an Er fiber femtosecond oscillator, a single-mode optical fiber, a translation stage, a Yb fiber amplifier, an Er fiber amplifier, a first compressor, a second compressor, a laser beam combining lens group, a PPLN crystal, a ZEBLAN fiber amplifier, and a glass block compressor, which are placed in sequence; The Yb fiber femtosecond oscillator is used to generate a femtosecond pulse sequence with a central wavelength of 1030 nm; The Er fiber femtosecond oscillator is used to generate a femtosecond pulse sequence with a central wavelength of 1560nm; The Yb fiber amplifier is used to amplify the pulse sequence output by the Yb fiber femtosecond oscillator; The Er fiber amplifier is used to amplify the pulse sequence output by the Er fiber femtosecond oscillator; The first compressor is used to compress the laser amplified by the Yb fiber amplifier to a femtosecond pulse width, that is, to obtain a 1030nm femtosecond laser; The second compressor is used to compress the laser amplified by the Er fiber amplifier to a femtosecond pulse width, that is, to obtain a 1560nm femtosecond laser; The laser beam combining lens group is used to combine the 1030nm femtosecond laser and the 1560nm femtosecond laser; The PPLN crystal is used to generate ultrashort pulse laser at a difference frequency when the 1030nm femtosecond laser and the 1560nm femtosecond laser are combined and beam-formed and then pass through the PPLN crystal; The ZEBLAN optical fiber amplifier is used to amplify the ultrashort pulse laser; The glass block compressor is used to compress the ultrashort pulse laser to achieve mid-infrared laser output with a pulse width of the order of 100 fs; The laser beam combining lens group includes a first 1560nm reflector, a second 1560nm reflector, a first 1030nm reflector, a first 1560nm anti-reflection mirror and a 1030nm high reflector; The first 1560nm reflector and the second 1560nm reflector are used to reflect the 1560nm femtosecond laser to the next stage; The first 1030nm reflector is used to reflect the 1030nm femtosecond laser to the next stage; The first 1560nm anti-reflection and 1030nm high reflective mirror is used to allow the 1560nm femtosecond laser to pass through the lens, while the 1030nm femtosecond laser is totally reflected from the front surface of the lens, so as to combine two femtosecond laser beams with central wavelengths of 1030nm and 1560nm; The Yb fiber femtosecond oscillator and the Er fiber femtosecond oscillator share a section of single-mode fiber, and the mode-locked laser pulses of the two oscillators pass through the single-mode fiber at the same time; The cavity length of the Yb fiber femtosecond oscillator is fixed, and one end of the Er fiber femtosecond oscillator is mounted on the translation stage, and the cavity length of the Er fiber femtosecond oscillator is changed by adjusting the translation stage to achieve synchronization of the mode-locked pulse sequences output by the Yb fiber femtosecond oscillator and the Er fiber femtosecond oscillator; The glass block compressor is two wedge-angle glass blocks made of calcium fluoride. Both end surfaces of the glass block compressor are coated with anti-reflection films. One of the wedge-angle glass blocks is installed on the translation stage.

2. The device according to claim 1, characterized in that The Yb fiber femtosecond oscillator uses NPE mode locking to achieve picosecond pulse sequence output with a repetition frequency of 40 MHz, and its central wavelength is 1030 nm; the Er fiber femtosecond oscillator uses NPE mode locking to achieve picosecond pulse sequence output with a repetition frequency of 40 MHz, and its central wavelength is 1560 nm.

3. The device according to claim 1, characterized in that The surfaces of the first 1560nm reflector and the second 1560nm reflector are coated with a 1560nm broadband high-reflection film; the surface of the first 1030nm reflector is coated with a 1030nm broadband high-reflection film; the surfaces of the first 1560nm anti-reflection and 1030nm high-reflection mirror are coated with a 1030nm broadband high-reflection film and a 1560 broadband high-transmittance film.

4. The device according to claim 1, characterized in that The ZEBLAN optical fiber is an Er-doped ZEBLAN-based optical fiber.

5. The device according to claim 1, characterized in that The PPLN crystal has a diameter of 10×1 mm, a length of 3 mm, and a polarization interval period of 29.52 nm.

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