Femtosecond deep ultraviolet laser

Abstract

The utility model provides a femtosecond deep ultraviolet laser, and relates to the technical field of laser. The device comprises a pumping source, a pumping laser focus lens and a PPKTP crystal which are sequentially arranged at intervals along a light path, wherein the PPKTP crystal is arranged in a resonant cavity; the pumping laser focus lens is used for focusing the pumping light generated by the pumping source into the PPKTP crystal; the PPKTP crystal is used for generating second harmonics through a nonlinear process, and the resonant cavity is used for reflecting the generated second harmonics to the PPKTP crystal. According to the high-order quasi-phase matching OPO based on the PPKTP crystal, the wavelength of the generated pulse is shortened to green and blue from near infrared and finally shortened to deep ultraviolet (DUV) through multi-stage cascading of the frequency mixing process in the high-order quasi-phase matching OPO based on the PPKTP crystal, and the efficiency and the stability of deep ultraviolet pulse generation are improved.

Description

Technical Field

[0001] The utility model relates to the field of laser technology, in particular to a femtosecond deep ultraviolet laser. Background Art

[0002] A laser is a device that generates light (light amplification by stimulated emission of radiation) and is widely used in scientific research, biomedicine, materials processing, and other fields. However, due to the influence of the laser medium, the output wavelength of existing lasers is limited to a small wavelength band, which restricts their application in certain areas. Therefore, expanding the wavelength range of laser output has become a hot research topic in the industry. Currently, existing methods for expanding laser output suffer from poor efficiency and stability, and are in urgent need of improvement. Utility Model Content

[0003] In light of this, and addressing the shortcomings of existing methods for extending laser output, the present invention achieves deep-ultraviolet laser output through a femtosecond pulse-pumped optical parametric oscillator (OPO) using multi-step cascade frequency conversion. By employing a multi-stage cascade of frequency mixing processes within a quasi-phase-matched OPO based on a PPKTP crystal, the generated pulse wavelength is shortened from the near-infrared to the green, blue, and ultimately the deep ultraviolet (DUV). Furthermore, cavity length detuning allows for broadband tunability of the generated DUV pulses.

[0004] The utility model provides a femtosecond deep ultraviolet laser, comprising: a pump source, a pump laser focusing mirror, and a PPKTP crystal which are sequentially arranged at intervals along an optical path, wherein the PPKTP crystal is arranged in a resonant cavity;

[0005] The pump laser focusing mirror is used to focus the pump light generated by the pump source into the PPKTP crystal;

[0006] The PPKTP crystal is used to generate signal light with a wavelength between 1060nm and 1400nm, the resonant cavity is used to reflect light with a wavelength between 1060nm and 1400nm and a wavelength between 427nm and 477nm to the PPKTP crystal, and the PPKTP crystal is also used to perform multi-level quasi-phase matching mixing on the light reflected by the resonant cavity and the pump light to generate deep ultraviolet pulses.

[0007] According to a femtosecond deep ultraviolet laser of the present utility model, the resonant cavity includes a first reflecting mirror group and a second reflecting mirror group;

[0008] The first reflector group is used to reflect light reflected from the PPKTP crystal back to the PPKTP crystal;

[0009] The second reflector group is used to reflect light transmitted from the PPKTP crystal back to the PPKTP crystal.

[0010] According to a femtosecond deep ultraviolet laser of the present invention, the first reflector group includes a first curved reflector and at least one first plane reflector;

[0011] The first curved reflector is arranged on the optical path and located between the PPKTP crystal and the pump laser focusing mirror, and is used to deflect the light reflected by the PPKTP crystal and then inject it into at least one first-level flat reflector;

[0012] The at least one first plane reflector is used to allow the incident deflected signal light to return to the PPKTP crystal along the original path through the first curved reflector.

[0013] According to a femtosecond deep ultraviolet laser of the present invention, the second reflector group includes a second curved reflector and at least one second flat reflector;

[0014] The second curved reflector is arranged on the optical path and is symmetrical with the first curved reflector relative to the PPKTP crystal, and is used to deflect the signal light transmitted by the PPKTP crystal and then inject it into at least one second flat reflector;

[0015] The at least one second plane reflector is used to allow the incident deflected signal light to return to the PPKTP crystal along the original path through the second curved reflector.

[0016] According to a femtosecond deep ultraviolet laser of the present invention, the first plane reflector is multi-stage, and the distance of the first plane reflector of the last stage is adjustable relative to the first plane reflector of the previous stage.

[0017] According to a femtosecond deep ultraviolet laser of the present invention, the second plane reflector is multi-stage, and the distance between the second plane reflector of the last stage and the second plane reflector of the previous stage is adjustable.

[0018] According to the femtosecond deep ultraviolet laser of the present invention, the deep ultraviolet pulse is emitted through the second curved reflector.

[0019] According to a femtosecond deep ultraviolet laser of the utility model, the pump light pulse width generated by the pump source is 130fs, the repetition frequency is 76MHz, the central wavelength is about 787nm, and the maximum average power is about 1W; the pump laser focusing mirror is a convex lens with a focal length of 10cm, and the crystal size of the PPKTP crystal is 5×2×1mm.

[0020] According to a femtosecond deep ultraviolet laser of the utility model, the first curved reflector and the second curved reflector are both coated with a first optical film, the first optical film has a transmittance of more than 80% for the pump light, and a reflectance of more than 99.8% for signal light with a wavelength between 1060nm and 1400nm and light with a wavelength between 427nm and 477nm;

[0021] Each of the first plane reflectors and each of the second plane reflectors is coated with a second optical film, the second optical film has a transmittance of more than 90% for the pump light and a reflectivity of more than 99.8% for signal light with a wavelength between 1060nm and 1400nm and light with a wavelength between 427nm and 477nm.

[0022] According to a femtosecond deep ultraviolet laser of the present invention, the multi-stage quasi-phase matching mixing effect of the PPKTP crystal includes:

[0023] The signal light with wavelength between 1060nm and 1400nm interacts with each other through the frequency doubling effect to generate green light pulses with a peak wavelength of about 531nm;

[0024] The signal light with a wavelength between 1060nm and 1400nm and the pump light generate blue light pulses with a peak wavelength of about 453nm through the sum frequency effect;

[0025] The deep ultraviolet pulse is generated by using the sum frequency effect of the green light pulse and the blue light pulse of the wavelength.

[0026] The utility model discloses a femtosecond deep ultraviolet laser, which uses a femtosecond pulse-pumped optical parametric oscillator (OPO) with multi-step cascade frequency conversion to achieve deep ultraviolet laser output. Through the multi-stage cascade of the mixing process in the quasi-phase matching OPO based on the PPKTP crystal, the wavelength of the generated light pulse is shortened from near-infrared to green, blue, and finally to deep ultraviolet (DUV), significantly improving the efficiency and stability of deep ultraviolet pulse generation. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] In order to more clearly illustrate the technical solutions in the present invention or the prior art, a brief introduction will be given below to the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0028] Figure 1 This is one of the optical path schematic diagrams of the femtosecond deep ultraviolet laser provided by the utility model.

[0029] Figure 2 This is the second optical path schematic diagram of the femtosecond deep ultraviolet laser provided by the utility model.

[0030] Figure 3 It is a schematic diagram of the reflection spectrum of the resonant cavity mirror (curved reflector and flat reflector) provided by the utility model.

[0031] Figure 4 This is an energy level diagram of the frequency up-conversion process achieved through multi-stage cascading provided by the present invention.

[0032] Figure 5 This is a schematic diagram of the output spectrum of signal light under different cavity lengths provided by the present invention.

[0033] Figure 6 It is a schematic diagram of the cavity length tuning curve provided by the utility model.

[0034] Figure 7 This is a schematic diagram of the dual-signal pulse output spectrum under different cavity lengths provided by the present invention.

[0035] Figure 8 This is a schematic diagram of the pulse output spectrum of the pump light and signal light provided by the utility model through sum frequency generation.

[0036] Figure 9 This is a schematic diagram of deep ultraviolet pulse output spectra under different cavity lengths provided by the present invention.

[0037] Figure 10 It is a schematic diagram of the normalized cavity length tuning curve of the deep ultraviolet pulse output spectrum provided by the utility model.

[0038] Figure 11 It is a function diagram of the central wavelength, peak intensity and cavity tuning length provided by the utility model.

[0039] Description of reference numerals;

[0040] 100: pump source;

[0041] 200: pump laser focusing mirror;

[0042] 300:PPKTP crystal;

[0043] 400: resonant cavity;

[0044] 410: first reflector group; 411: first curved reflector; 412: first plane reflector; 420: second reflector group; 421: second curved reflector; 422: second plane reflector. DETAILED DESCRIPTION

[0045] To make the purpose, technical solutions, and advantages of the present invention more clear, the following will be combined with the accompanying drawings to clearly and completely describe the technical solutions of the present invention. Obviously, the embodiments described are only some of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0046] It should be noted that all expressions using "first" and "second" in the embodiments of the present invention are for the purpose of distinguishing two non-identical entities or non-identical parameters with the same name. It can be seen that "first" and "second" are only for the convenience of expression and should not be understood as limitations on the embodiments of the present invention. Subsequent embodiments will not explain this one by one.

[0047] In order to facilitate understanding, the present invention is briefly described from the perspective of its implementation principle:

[0048] Optical parametric oscillator (OPO) is one of the main technical means to expand the laser spectrum and obtain tunable laser through nonlinear frequency conversion technology. OPO can be tuned within a broadband range, producing a wide range of continuously adjustable wavelength output from ultraviolet to far-infrared lasers, overcoming the output wavelength limitations of solid-state and gas lasers. At the same time, OPO has the advantages of simple structure, reliable operation, high conversion efficiency, and high repetition rate.

[0049] The synchronous pump optical parametric oscillator involved in the utility model is an effective method for generating tunable ultrashort laser pulses in infrared and visible light. OPO can obtain high tunability by adopting a variety of methods, such as changing the wavelength of the pump light, changing the phase matching angle, or changing the temperature of the nonlinear crystal. In addition, the use of periodically poled nonlinear crystals in the quasi-phase matching process not only greatly improves the conversion efficiency of the nonlinear optical process in the OPO, but also provides the OPO with more and more flexible tuning methods. Therefore, the quasi-phase matching OPO in the near-infrared range usually generates stronger visible light pulses by generating the second harmonic of the signal pulse and the sum frequency between the signal pulse and the pump pulse. These visible light pulses can be tuned by tuning the near-infrared signal pulse. In addition, the high efficiency of the quasi-phase matching process allows them to be further cascaded, and the high-order quasi-phase matching cascade process greatly enhances the tunability of the OPO with multiple nonlinear processes.

[0050] The following combination Figures 1 to 11 The utility model describes a femtosecond deep ultraviolet laser.

[0051] Figure 1 This is one of the optical path diagrams of the femtosecond deep ultraviolet laser provided by this utility model. Please refer to Figure 1As shown, this embodiment provides a femtosecond deep ultraviolet laser, which includes a pump source 100, a pump laser focusing mirror 200, and a PPKTP crystal 300, which are sequentially arranged along the optical path. The PPKTP crystal 300 is arranged in a resonant cavity 400;

[0052] The pump laser focusing mirror 200 is used to focus the pump light generated by the pump source 100 into the PPKTP crystal 300; the laser pulse output by the pump source 100 serves as the pump beam of the OPO, and its polarization direction is horizontally parallel to the plane of the optical platform, which is consistent with the z-axis direction of the PPKTP crystal 300 and the periodic polarization direction of the crystal;

[0053] The PPKTP crystal 300 is used to generate signal light with a wavelength between 1060nm and 1400nm, the resonant cavity 400 is used to reflect light with a wavelength between 1060nm and 1400nm and a wavelength between 427nm and 477nm to the PPKTP crystal 300, and the PPKTP crystal 300 is also used to perform multi-stage quasi-phase matching mixing on the light reflected by the resonant cavity (400) and the pump light to generate deep ultraviolet pulses.

[0054] In this embodiment, the resonant cavity 400 includes a curved reflector and a plane reflector. The curved reflector transmits the linearly polarized pump laser into the nonlinear crystal, and then reflects it back into the nonlinear crystal through the plane reflector. The signal light forms an optical parametric oscillation between the curved reflector and the plane reflector and repeatedly passes through the nonlinear crystal. Idle light is generated along with the signal light. At the same time, multiple nonlinear processes occur in the resonant cavity, and deep ultraviolet femtosecond pulses are generated through multi-stage cascades.

[0055] The femtosecond deep ultraviolet laser of this embodiment uses a femtosecond pulse-pumped optical parametric oscillator (OPO) that uses multi-step cascade frequency conversion to achieve deep ultraviolet laser output. Through a multi-stage cascade of the mixing process in a quasi-phase-matched OPO based on a PPKTP crystal, the wavelength of the generated light pulses is shortened from near-infrared to green, blue, and ultimately to deep ultraviolet (DUV), significantly improving the efficiency and stability of deep ultraviolet pulse generation.

[0056] For some possible implementations, please continue to refer to Figure 1 As shown, the resonant cavity 400 includes a first reflector group 410 and a second reflector group 420;

[0057] The first reflector group 410 is used to reflect the light reflected from the PPKTP crystal 300 back to the PPKTP crystal 300;

[0058] The second reflector assembly 420 is configured to reflect light transmitted from the PPKTP crystal 300 back to the PPKTP crystal 300 .

[0059] It should be noted that, since the first reflector group 410 and the second reflector group 420 are composed of multiple lenses, Figure 1 The reference numerals of the first reflector assembly 410 and the second reflector assembly 420 are indicated by dotted brackets. The dotted brackets and the reference numerals of other components do not exist and are only used to assist in identifying the locations of the components.

[0060] For some possible implementations, please continue to refer to Figure 1 As shown, the first reflector group 410 includes a first curved reflector 411 and at least one first flat reflector 412;

[0061] The first curved reflector 411 is disposed on the optical path and located between the PPKTP crystal 300 and the pump laser focusing mirror 200, and is used to deflect the light reflected by the PPKTP crystal 300 and then inject it into at least one first-level flat reflector 412;

[0062] The at least one first plane reflector 412 is configured to allow the incident deflected signal light to return to the PPKTP crystal 300 along the original path through the first curved reflector 411 .

[0063] For some possible implementations, please continue to refer to Figure 1 As shown, the second reflector group 420 includes a second curved reflector 421 and at least one second flat reflector 422;

[0064] The second curved reflector 421 is arranged on the optical path and is symmetrical to the first curved reflector 411 relative to the PPKTP crystal 300, and is used to deflect the signal light transmitted by the PPKTP crystal 300 and then inject it into at least one second flat reflector 422;

[0065] The at least one second plane reflector 422 is configured to allow the incident deflected signal light to return to the PPKTP crystal 300 along the original path through the second curved reflector 421 .

[0066] It should be noted that, please combine Figure 2 As shown, in order to make the first plane reflector 412 and the second plane reflector 422 reflect the signal light back to the PPKTP crystal 300, in a specific implementation process, the first plane reflector 412 and the second plane reflector 422 located at the last stage can be set to be perpendicular to the signal light in a multi-stage sequentially spaced manner, thereby realizing the return of the signal light along the original path.

[0067] In some possible implementations, please combine Figure 2As shown, the first plane reflector 412 is multi-stage, and the distance of the first plane reflector 412 of the last stage is adjustable relative to the first plane reflector 412 of the previous stage.

[0068] In some possible implementations, please combine Figure 2 As shown, the second plane reflector 422 is multi-stage, and the distance between the second plane reflector 422 of the last stage and the second plane reflector 422 of the previous stage is adjustable.

[0069] In some possible implementations, the deep ultraviolet pulse is emitted through the second curved reflector 421 .

[0070] In some possible implementations, the pump light pulse width generated by the pump source 100 is 130 fs, the repetition frequency is 76 MHz, the central wavelength is approximately 787 nm, and the maximum average power is approximately 1 W; the pump laser focusing mirror 200 is a convex lens with a focal length of 10 cm, and the crystal size of the PPKTP crystal 300 is 5×2×1 mm.

[0071] In some possible implementations, the first curved reflector 411 and the second curved reflector 421 are both coated with a first optical film, wherein the first optical film has a transmittance of more than 80% for the pump light and a reflectance of more than 99.8% for signal light with a wavelength between 1060 nm and 1400 nm and light with a wavelength between 427 nm and 477 nm.

[0072] Each of the first plane reflectors 412 and the second plane reflectors 422 is coated with a second optical film, which has a transmittance of more than 90% for the pump light and a reflectivity of more than 99.8% for signal light with a wavelength between 1060nm and 1400nm and light with a wavelength between 427nm and 477nm.

[0073] In some possible implementations, the multi-stage quasi-phase-matched mixing effect of the PPKTP crystal 300 includes:

[0074] The signal light with wavelength between 1060nm and 1400nm interacts with each other through the frequency doubling effect to generate green light pulses with a peak wavelength of about 531nm;

[0075] The signal light with a wavelength between 1060nm and 1400nm and the pump light generate blue light pulses with a peak wavelength of about 453nm through the sum frequency effect;

[0076] The deep ultraviolet pulse is generated by using the sum frequency effect of the green light pulse and the blue light pulse of the wavelength.

[0077] In another embodiment, in order to facilitate understanding of the solution of the utility model, it may be useful to Figure 2 The resonant cavity composed of eight plane mirrors and two curved mirrors shown in the figure is used as an example to illustrate the scheme of the present invention in detail. This embodiment provides another femtosecond deep ultraviolet laser, which specifically includes a pump light source pump source 100, a pump laser focusing mirror 200, a first curved mirror 411 as an input mirror, a PPKTP crystal 300, a second curved mirror 421 as an output mirror, and eight plane mirrors arranged in sequence along the optical path, wherein four plane mirrors serve as first plane mirrors 412 corresponding to the first curved mirror 411, and the other four plane mirrors serve as second plane mirrors 422 corresponding to the second curved mirror 421, and the PPKTP crystal 300 is located between the first curved mirror 411 and the second curved mirror 421. The above eight plane mirrors, two curved mirrors and the PPKTP crystal 300 together constitute a resonant cavity 400 for optical parametric oscillation.

[0078] The pump light with a central wavelength of 787 nm generated by the pump source 100 passes through the pump laser focusing mirror 200 and then enters the PPKTP crystal 300 through the first curved reflector 411, pumping the PPKTP crystal 300 to generate signal light and idler light to form optical parametric oscillation in the resonant cavity;

[0079] Furthermore, the pump laser focusing lens 200 is a convex lens with a focal length of 10 cm, which is used to focus the pump laser output by the pump source 100 into the resonant cavity.

[0080] Furthermore, the resonant cavity 400 is divided into two curved reflectors and eight plane reflectors. The resonant cavity is composed of plane reflectors and curved reflectors. The two curved reflectors are respectively arranged on both sides of the light transmission direction of the PPKTP crystal 300. The signal light oscillates in the resonant cavity and is output outside the cavity through the curved reflector 421.

[0081] Furthermore, both the first curved reflector 411 and the second curved reflector 421 are coated with a first optical thin film, which has a high transmittance of over 80% for pump light and a high reflectance of over 99.8% for signal light in the range of 1060nm to 1400nm, and a high reflectance of over 98% for light in the range of 427nm to 477nm. Both the first flat reflector 412 and the second flat reflector 422 are coated with a second optical thin film, which has a high transmittance of over 90% for pump light and a high reflectance of over 99% for signal light in the range of 1060nm to 1400nm, and a high reflectance of over 98% for light in the range of 427nm to 477nm.

[0082] Furthermore, the generated signal light passes through the PPKTP crystal and undergoes a frequency doubling effect, interacting with each other to produce a green light pulse with a peak wavelength of approximately 531nm.

[0083] Furthermore, the generated signal light also generates a sum frequency effect with the pump light through the PPKTP crystal to produce a blue light pulse with a peak wavelength of approximately 453nm;

[0084] Furthermore, the generated green and blue pulses undergo a sum-frequency effect through the PPKTP crystal, ultimately producing deep-ultraviolet pulses. These blue pulses then oscillate within the resonant cavity, significantly improving the efficiency of deep-ultraviolet pulse generation. Furthermore, by adjusting the position of the final plane mirror in the resonant cavity, the cavity length is tuned, achieving tuning of all output light pulses. Furthermore, cavity length detuning also enables broadband tunability of the generated deep-ultraviolet pulses.

[0085] It should be noted that the wavelength and tuning range of the deep ultraviolet femtosecond pulses output by the femtosecond pulse-pumped optical parametric oscillator are related to the pump wavelength, polarization period, operating temperature and the optical film coated on the cavity mirror.

[0086] Please combine Figures 3 to 11 As shown, compared with the existing extended laser output scheme, the beneficial effects of the present invention are as follows: It provides a femtosecond pulse pumped optical parametric oscillator that uses multi-step cascade frequency conversion to achieve deep ultraviolet laser output. Through the frequency doubling process of the near-infrared signal pulse in the resonant cavity and the sum frequency process between the pump pulse and the near-infrared signal pulse, femtosecond pulses are generated in the green and blue light bands respectively. Then, the deep ultraviolet pulse is generated by the sum frequency process between the blue and green light pulses, thereby achieving further cascade. Using a cavity mirror designed with high reflection in both infrared (1000-1600nm) and blue light (427-477nm) wavelengths, the near-infrared signal pulse and the two-photon fluorescence pulse are simultaneously oscillated in the resonant cavity. Through a multi-stage cascade approach and a unique design of the cavity mirror, the generated deep ultraviolet pulses can be broadband tuned. At the same time, by using pump wavelength tuning, crystal polarization period tuning and temperature tuning, the generation of deep ultraviolet pulses can also be optimized in terms of efficiency and tuning range. This is of great significance for the design and realization of new broadband tunable ultrafast lasers.

[0087] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the various embodiments of the present invention.

Claims

1. A femtosecond deep ultraviolet laser, characterized in that: include: A pump source (100), a pump laser focusing mirror (200), and a PPKTP crystal (300) are sequentially arranged at intervals along the optical path, wherein the PPKTP crystal (300) is arranged in a resonant cavity (400); The pump laser focusing mirror (200) is used to focus the pump light generated by the pump source (100) into the PPKTP crystal (300); The PPKTP crystal (300) is used to generate signal light with a wavelength between 1060 nm and 1400 nm, the resonant cavity (400) is used to reflect light with a wavelength between 1060 nm and 1400 nm and a wavelength between 427 nm and 477 nm to the PPKTP crystal (300), and the PPKTP crystal (300) is further used to perform multi-stage quasi-phase matching mixing on the light reflected by the resonant cavity (400) and the pump light to generate deep ultraviolet pulses.

2. The femtosecond deep ultraviolet laser according to claim 1, wherein The resonant cavity (400) comprises a first reflecting mirror group (410) and a second reflecting mirror group (420); The first reflector group (410) is used to reflect light reflected from the PPKTP crystal (300) back to the PPKTP crystal (300); The second reflector group (420) is used to reflect light transmitted from the PPKTP crystal (300) back to the PPKTP crystal (300).

3. The femtosecond deep ultraviolet laser according to claim 2, characterized in that The first reflector group (410) includes a first curved reflector (411) and at least one first plane reflector (412); The first curved reflector (411) is arranged on the optical path and located between the PPKTP crystal (300) and the pump laser focusing mirror (200), and is used to deflect the light reflected by the PPKTP crystal (300) and then inject it into at least one first-level plane reflector (412); At least one first plane reflector (412) is used to return the incident deflected signal light to the PPKTP crystal (300) along the original path through the first curved reflector (411).

4. The femtosecond deep ultraviolet laser according to claim 3, characterized in that The second reflector group (420) includes a second curved reflector (421) and at least one second plane reflector (422); The second curved reflector (421) is arranged on the optical path and is symmetrically arranged with the first curved reflector (411) relative to the PPKTP crystal (300), and is used to deflect the signal light transmitted by the PPKTP crystal (300) and then inject it into at least one first-level second plane reflector (422); At least one second plane reflector (422) is used to allow the incident deflected signal light to return to the PPKTP crystal (300) along the original path via the second curved reflector (421).

5. The femtosecond deep ultraviolet laser according to claim 3, characterized in that: The first plane reflector (412) is multi-stage, and the distance of the first plane reflector (412) of the last stage is adjustable relative to the first plane reflector (412) of the previous stage.

6. The femtosecond deep ultraviolet laser according to claim 4, characterized in that: The second plane reflector (422) is multi-stage, and the distance between the second plane reflector (422) of the last stage and the second plane reflector (422) of the previous stage is adjustable.

7. The femtosecond deep ultraviolet laser according to claim 4, characterized in that: The deep ultraviolet pulse is emitted through the second curved reflector (421).

8. The femtosecond deep ultraviolet laser according to claim 2, characterized in that: The pump source (100) is a pulsed laser, generating a pump light pulse with a width of 130 fs, a repetition frequency of 76 MHz, a central wavelength of approximately 787 nm, and a maximum average power of approximately 1 W; the pump laser focusing lens (200) is a convex lens with a focal length of 10 cm; and the PPKTP crystal (300) has a crystal size of 5×2×1 mm.

9. The femtosecond deep ultraviolet laser according to claim 4, characterized in that: The first curved reflector (411) and the second curved reflector (421) are both coated with a first optical film, wherein the first optical film has a transmittance of more than 80% for the pump light and a reflectance of more than 99.8% for signal light with a wavelength between 1060 nm and 1400 nm and light with a wavelength between 427 nm and 477 nm; Each of the first plane reflectors (412) and each of the second plane reflectors (422) is coated with a second optical film, wherein the second optical film has a transmittance of more than 90% for the pump light and a reflectance of more than 99.8% for signal light with a wavelength between 1060nm and 1400nm and light with a wavelength between 427nm and 477nm.

10. The femtosecond deep ultraviolet laser according to claim 1, characterized in that: The multi-stage quasi-phase matching mixing effect of the PPKTP crystal (300) includes: The signal light with wavelength between 1060nm and 1400nm interacts with each other through the frequency doubling effect to generate green light pulses with a peak wavelength of about 531nm; The signal light with a wavelength between 1060nm and 1400nm and the pump light generate blue light pulses with a peak wavelength of about 453nm through the sum frequency effect; The deep ultraviolet pulse is generated by using the sum frequency effect of the green light pulse and the blue light pulse of the wavelength.

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