Polarization tunable extreme ultraviolet pulse laser generating device

Abstract

The invention provides a polarization-tunable extreme ultraviolet pulse laser generating device, and the device comprises a fiber laser which is used for generating fundamental frequency laser; the light beam direction stabilizing system is used for stabilizing the output direction of the fundamental frequency laser; the frequency conversion module is used for performing frequency tripling operation on the fundamental frequency laser to obtain frequency tripled linear polarization laser and first residual laser; the dichroic mirror is used for separating the triple-frequency linear polarization laser and the residual laser; the first light beam collector is used for collecting first residual laser; the frequency tripling reflector is used for reflecting the frequency tripling linear polarization laser to the polarization tuning module; the polarization tuning module is used for performing polarization tuning on the triple-frequency linear polarization laser; the inert gas frequency conversion module is used for performing frequency tripling operation on the tuned frequency tripling linear polarization laser to obtain extreme ultraviolet laser and second residual laser; and the focusing-monochromatic-detection module is used for separating the extreme ultraviolet laser and the second residual laser.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of laser, in particular to the technical field of ultraviolet laser acquisition, more particularly to an extreme ultraviolet pulse laser generating device. BACKGROUND

[0002] With the characteristics of short wavelength and high photon energy, ultraviolet laser shows important application prospects in many fields. In the industrial field, ultraviolet laser can be used for high-precision manufacturing and intelligent detection, such as using ultraviolet laser for photoetching in the semiconductor manufacturing process, and using ultraviolet laser for product element composition and defect analysis in the industrial safety detection process. In the scientific research field, ultraviolet laser is widely used in the frontier directions such as ultrafast spectroscopy, material excitation, material synthesis and physical property regulation. At present, the acquisition methods of ultraviolet laser mainly include two kinds: one is that the ultraviolet laser is directly generated by an excimer laser; the other is that the ultraviolet laser is indirectly obtained by multi-stage nonlinear frequency conversion of the fundamental light. Among them, according to the principle of nonlinear frequency conversion and the different system settings, different frequency lasers with central wavelength from ultraviolet to extreme ultraviolet can be obtained. Using nonlinear crystals such as barium borate (BBO) and potassium fluoro borate beryllium (KBBF), ultraviolet laser with a photon energy of about 8eV and adjustable polarization can be obtained. Among them, by using nonlinear crystal frequency conversion combined with gas high harmonic generation, extreme ultraviolet laser with higher photon energy and shorter wavelength can be obtained, but the extreme ultraviolet light often only has linear polarization and the polarization direction is not adjustable. Especially in the research of angle-resolved photoelectron spectroscopy technology for the characterization of material electronic state, researchers want to use ultraviolet laser with higher photon energy to increase the momentum space range of material observation, and also need to retain the polarization adjustable characteristics of the laser for the study of the orbital, spin and other characteristics of the electrons in the material. Therefore, although the extreme ultraviolet laser generation technology combining nonlinear crystal frequency conversion and inert gas four-wave mixing principle has been developed, this method can only obtain extreme ultraviolet laser with higher photon energy than single nonlinear crystal frequency conversion, and the wavelength is still limited by the transmission efficiency of lithium fluoride (LiF) and magnesium fluoride (MgF2) crystals. However, since this method is more efficient than the high harmonic generation method, and does not require a complex light splitting system, it is very suitable as a light source for ultra-high vacuum spectroscopy characterization means such as angle-resolved photoelectron spectroscopy system, therefore, it is of great significance to study a better polarization adjustable extreme ultraviolet light source scheme. At present, there is a femtosecond 11eV extreme ultraviolet light source obtained by nonlinear frequency conversion, but it has limitations such as poor energy resolution, low light flux, and non-adjustable linear polarization, which limits its application in the study of material complex electronic state, orbital and spin characteristics. Therefore, there is an urgent need for a new extreme ultraviolet light source generation scheme that can solve the problems of poor energy resolution, low light flux, and non-adjustable linear polarization, so as to improve the application of extreme ultraviolet light in various industries. It should be noted that the background technology is only used to introduce the related information of the present application, in order to help understand the technical scheme of the present application, but it does not mean that the related information must be prior art. In the absence of evidence that the related information has been disclosed before the filing date of the present application, the related information should not be regarded as prior art. SUMMARY

[0003] Therefore, the present application aims to overcome the defects of the prior art, and provide a new polarization tunable extreme ultraviolet pulse laser generating device.

[0004] The object of the present application is achieved by the following technical solutions:

[0005] The present application provides a polarization tunable extreme ultraviolet pulse laser generating device, which comprises a fiber laser, a beam direction stabilizing system, a frequency conversion module, a dichroic mirror, a first beam collector, a third harmonic reflection mirror, a polarization tuning module, an inert gas frequency conversion module, a focusing-monochromatic-detection module, wherein: the fiber laser is used to generate fundamental frequency laser; the beam direction stabilizing system is used to stabilize the output direction of the fundamental frequency laser; the frequency conversion module is used to perform a third harmonic operation on the fundamental frequency laser to obtain third harmonic linearly polarized laser and first residual laser; the dichroic mirror is used to separate the third harmonic linearly polarized laser and the residual laser, and the third harmonic linearly polarized laser is injected into the reflection mirror, and the first residual laser is injected into the first beam collector; the first beam collector is used to collect the first residual laser; the third harmonic reflection mirror is used to reflect the third harmonic linearly polarized laser injected by the dichroic mirror to the polarization tuning module; the polarization tuning module is used to perform polarization tuning on the third harmonic linearly polarized laser; the inert gas frequency conversion module is used to perform a third harmonic operation on the tuned third harmonic linearly polarized laser to obtain extreme ultraviolet laser and second residual laser; and the focusing-monochromatic-detection module is used to separate the extreme ultraviolet laser and the second residual laser, and detect the optical power and optical flux of the extreme ultraviolet laser.

[0006] Preferably, the fiber laser is an ytterbium-doped fiber laser, which is used to generate fundamental frequency laser with a wavelength of 1030 nm.

[0007] Preferably, the beam direction stabilizing system comprises a first electrically controlled mirror, a first mirror, a second mirror, a second electrically controlled mirror, a first wave plate, a beam splitting cube, a first plano-convex lens, a third mirror, a second plano-convex lens, a fourth mirror, a filter, a spot position analyzer, a fifth mirror, a second wave plate, wherein: the first electrically controlled mirror is arranged in the laser emission direction of the fiber laser, and is used to reflect the fundamental frequency laser generated by the fiber laser to the first mirror, and the first electrically controlled mirror is provided with a step motor and a piezoelectric ceramic for adjusting the propagation direction of the fundamental frequency laser when the beam propagation is unstable as fed back by the spot position analyzer; the first mirror is used to reflect the incident fundamental frequency laser to the second mirror; the second mirror is used to reflect the incident fundamental frequency laser to the second electrically controlled mirror; the second electrically controlled mirror is used to reflect the incident fundamental frequency laser to the first The wave plate is configured with a step motor and a piezoelectric ceramic for adjusting the propagation direction of the fundamental laser when the spot position analyzer feedbacks the unstable propagation of the light beam; the first The wave plate is used to separate the sampling reference light from the fundamental laser for judging the stability of the light beam; the beam splitting cube is used to split the sampling reference light separated by the first The wave plate into the first plano-convex lens and the fundamental laser into the fifth mirror; the first plano-convex lens is used to perform the first beam shrinking on the sampling reference light and then reflect it into the third mirror; the third mirror is used to reflect the sampling reference light after the first beam shrinking to the second plano-convex lens; the second plano-convex lens is used to perform the second beam shrinking on the sampling reference light and then reflect it into the fourth mirror; the fourth mirror is used to reflect the sampling reference light after the second beam shrinking to the filter; the filter is used to attenuate the power of the sampling reference light to meet the requirement of the spot analysis; the spot position analyzer is used to analyze the spot of the sampling reference light after the filter processing to judge the stability of the light beam propagation, and feedback the first and second electrically controlled mirrors when the light beam propagation is unstable; the fifth mirror is used to reflect the fundamental laser to the second Wave plate; the second Wave plate is used to adjust the polarization direction of the fundamental laser and then reflect it into the frequency conversion module.

[0008] Preferably, the frequency conversion module comprises a third plano-convex lens, a first BBO crystal, a second BBO crystal, and a fourth plano-convex lens, wherein: the third plano-convex lens and the fourth plano-convex lens are used to form a first focusing lens group for adjusting the intersection of the fundamental laser to be located at the middle position of the first BBO crystal and the second BBO crystal; the first BBO crystal is used to generate a second harmonic light with a center wavelength of 515 nm based on the fundamental laser, and the second harmonic light and the first remaining fundamental laser are jointly reflected into the second BBO crystal; the second BBO crystal is used to generate a third harmonic linearly polarized laser with a center wavelength of 343 nm based on the reflected second harmonic light and the first remaining fundamental laser, and the third harmonic linearly polarized laser, the remaining second harmonic light, and the second remaining fundamental laser are jointly reflected into the dichroic mirror.

[0009] Preferably, the dichroic mirror is used to separate the third harmonic linearly polarized laser, the remaining second harmonic light, and the second remaining fundamental laser, and reflect the third harmonic linearly polarized laser into the mirror, and reflect the remaining second harmonic light and the second remaining fundamental laser into the first beam collector as the first remaining laser.

[0010] Preferably, the third harmonic mirror is a first 343 nm mirror.

[0011] Preferably, the polarization tuning module comprises a first 343 nm Wave plate, a 343 nm Wave plate, second 343nm Wave plate, wherein: first 343nm Wave plate is used to adjust the linearly polarized light of three times frequency to s-type or P-type linear polarization according to application requirement; 343nm Wave plate is used to adjust the linearly polarized light of three times frequency to s-type or P-type linear polarization according to application requirement; 343nm Wave plate is used to adjust the linearly polarized light of three times frequency to s-type or P-type linear polarization according to application requirement; 343nm

[0012] Preferably, the inert gas frequency conversion module comprises a fifth plano-convex lens, an inert gas generating pool and a LiF lens window, wherein: the inert gas generating pool is used to provide an inert gas cavity and a charge-discharge circuit for three times frequency operation of linearly polarized light to obtain extreme ultraviolet laser with a wavelength of 114nm, and the extreme ultraviolet laser and the remaining linearly polarized light of three times frequency are jointly injected into the focusing-monochromatic-detection module; the fifth plano-convex lens and the LiF lens window jointly constitute a second focusing lens group for focusing the extreme ultraviolet laser.

[0013] Preferably, the focusing-monochromatic-detection module comprises a LiF three-prism, an extreme ultraviolet reflector, an extreme ultraviolet laser detection screen, a second 343nm reflector, a second light beam collector, a vacuum gauge and a molecular pump, and the LiF three-prism, the extreme ultraviolet reflector, the extreme ultraviolet laser detection screen, the second 343nm reflector and the second light beam collector are arranged in an ultrahigh vacuum cavity, wherein: the LiF three-prism is used to separate the extreme ultraviolet laser and the remaining linearly polarized light of three times frequency, and the extreme ultraviolet laser is injected into the extreme ultraviolet reflector, and the remaining linearly polarized light of three times frequency is injected into the second 343nm reflector as second remaining laser; the extreme ultraviolet reflector is used to reflect the injected extreme ultraviolet laser to the extreme ultraviolet laser detection screen; the extreme ultraviolet laser detection screen is used to develop the extreme ultraviolet laser for observing the extreme ultraviolet laser beam profile; the second 343nm reflector is used to reflect the injected remaining linearly polarized light to the second light beam collector; the second light beam collector is used to collect the injected second remaining laser; the vacuum gauge is used to detect the vacuum state; and the molecular pump is used to maintain the vacuum state in the ultrahigh vacuum cavity and can adjust the vacuum when the vacuum state is unstable.

[0014] Preferably, the extreme ultraviolet laser detection screen comprises a fluorescent screen, an extreme ultraviolet photodiode and a detection bottle shell, wherein: the fluorescent screen is provided with a slit for the extreme ultraviolet laser to be injected into the dark chamber of the screen; and the extreme ultraviolet photodiode is used to measure the current of the extreme ultraviolet laser to calculate the optical power and the luminous flux.

[0015] Compared with the prior art, the application has the advantages that: the application utilizes several low-cost, miniaturized polarization optical elements in combination, and obtains photon energy 10.8 eV extreme ultraviolet pulse laser with the same polarization characteristics and adjustable polarization generated based on four-wave mixing of inert gas by adjusting the driving light polarization characteristics. Due to the narrow bandwidth of the fundamental light spectrum and the high-efficiency monochromatization and dispersion compensation realized in the whole generation process, the generated extreme ultraviolet pulse laser has outstanding energy resolution in practical applications, for example, as a light source of angle-resolved photoelectron spectroscopy. In addition, the 10.8 eV extreme ultraviolet light has greater photon energy than the ultraviolet light generated by frequency conversion of a single nonlinear crystal, so such an extreme ultraviolet laser light source has both a wide range of momentum space coverage and the application requirement of adjustable polarization in the application of angle-resolved photoelectron spectroscopy. BRIEF DESCRIPTION OF DRAWINGS

[0016] The embodiments of the application will be further described below with reference to the drawings, in which:

[0017] Figure 1 A schematic diagram of a polarization-tunable extreme ultraviolet laser pulse generation device system according to an embodiment of the application;

[0018] Figure 2 A schematic diagram of an optical path of a polarization-tunable extreme ultraviolet laser pulse generation device according to an embodiment of the application;

[0019] Figure 3 A schematic diagram of a generation cell and a vacuum cavity model in a polarization-tunable extreme ultraviolet laser pulse generation device according to an embodiment of the application;

[0020] Figure 4 A schematic diagram of a structure model of a detection fluorescent screen of a polarization-tunable extreme ultraviolet laser pulse generation device according to an embodiment of the application.

[0021] Figure 5 A schematic diagram of test results of different polarized extreme ultraviolet lasers generated by a polarization-tunable extreme ultraviolet laser pulse generation device according to an embodiment of the application. DETAILED DESCRIPTION

[0022] In order to make the objects, technical solutions and advantages of the application clearer, the application will be further described in detail below with reference to the drawings and specific embodiments. It should be understood that the specific embodiments described herein are only used to explain the application and not used to limit the application.

[0023] As described in the background art, the existing scheme has the limitations of poor energy resolution, low light flux, and unadjustable polarization of the generated extreme ultraviolet light source, therefore, the present application proposes a polarization tunable extreme ultraviolet pulse laser generation scheme to obtain an extreme ultraviolet light source with greater photon energy than the ultraviolet light generated by frequency conversion of a single nonlinear crystal.

[0024] In summary, in the present application, a high-power, high-repetition-rate ytterbium-doped fiber laser is used to generate fundamental frequency laser, and a beam direction stabilizing system, a mirror, a beam splitting cube, a lens group, a BBO crystal, a convex lens, an extreme ultraviolet mirror, an electrically controlled mirror holder, a two-dimensional electrically controlled displacement stage and a controller, a fluorescent screen, an extreme ultraviolet photodiode, a picoammeter, an ultrahigh vacuum cavity, an ultrahigh vacuum window flange, an ultrahigh vacuum electrode flange, an ultrahigh vacuum magnetic rod, a vacuum gauge, a molecular pump, a mechanical pump, a stainless steel charging and discharging circuit, Ar gas, Xe gas, etc. are configured to construct a polarization tunable extreme ultraviolet pulse laser generation device. Figure 1As shown, functionally, the polarization-tunable extreme ultraviolet pulsed laser generator of the present invention includes: a laser generation module 101 (including a fiber laser and a beam direction stabilization system), a frequency conversion module 102, a dichroic mirror, a beam collector (to distinguish it from other light-speed collectors, the beam collector here is referred to as the first beam collector), a third-harmonic reflector, a polarization tuning module 103, an inert gas frequency conversion module 104, and a focusing-monochromatic-detection module 105, wherein: the fiber laser is used to generate a fundamental frequency laser; the beam direction stabilization system is used to stabilize the output direction of the fundamental frequency laser; and the frequency conversion module is used to perform a third-harmonic operation on the fundamental frequency laser to obtain a linearly polarized laser. The system consists of a light source and a first residual laser beam. The dichroic mirror separates the linearly polarized laser from the first residual laser beam, directing the linearly polarized laser into a reflecting mirror and the first residual laser beam into a first beam collector. The first beam collector collects the first residual laser beam. The reflecting mirror reflects the linearly polarized laser beam from the dichroic mirror to a polarization tuning module. The polarization tuning module tunes the linearly polarized laser beam. The inert gas frequency conversion module performs a third-harmonic operation on the tuned linearly polarized laser beam to obtain an extreme ultraviolet (EUV) laser and a second residual laser beam. The focusing-monochromatic-detection module separates the EUV laser from the residual linearly polarized laser and detects the optical power and flux of the EUV laser. In simple terms, the 1030nm fundamental frequency laser generation module is suitable for generating a 1030nm fundamental frequency laser; the nonlinear optical crystal frequency conversion module is suitable for tripling the 1030nm fundamental frequency light to obtain a 343nm laser; the polarization tuning module is suitable for adjusting the polarization characteristics of the 343nm laser, which is ultimately equivalent to adjusting the polarization characteristics of a 10.8eV extreme ultraviolet pulse laser; the inert gas frequency conversion module is suitable for further tripling the 343nm laser to obtain a 114nm (i.e., photon energy 10.8eV) extreme ultraviolet pulse laser; and the 10.8eV focusing-monochromatic-detection module is suitable for characterizing and detecting the final 10.8eV extreme ultraviolet laser in terms of focusing, monochromaticity, beam profile, and optical power.

[0025] To better understand the present invention, the various parts of the device of the present invention will be described in detail below.

[0026] According to one embodiment of the present invention, such as Figure 2 As shown, the fiber laser 201 in the device of this invention is a ytterbium-doped fiber laser, used to generate a fundamental frequency laser with a wavelength of 1030nm. This invention employs a self-built high-power, high-repetition-rate ytterbium-doped fiber laser to output 1030nm near-infrared light as the fundamental frequency light. The laser output parameters are: center wavelength 1030nm, pulse width 350fs, repetition rate 1MHz, maximum average output power 55W, and linearly polarized output.

[0027] The fundamental laser beam emitted by the laser in the present application first passes through a beam direction stabilizing system to ensure that the subsequent spatial light path will not be deflected due to the shift of the laser output spot position, and to ensure the stability of the entire frequency conversion light path. The beam direction stabilizing system is mainly composed of a mirror frame controlled by two electric motors and a beam propagation path detector. The detector monitors the position and pitch change of the output spot along the propagation direction to confirm the degree of shift relative to the stable output position, and then the electrically controlled mirror frame including a coarse adjustment motor and a fine adjustment piezoelectric ceramic precisely controls the actual output direction of the laser. According to an embodiment of the present application, still referring to Figure 2 The beam direction stabilizing system in the present application scheme includes a first electrically controlled mirror 202, a first mirror 203, a second mirror 204, a second electrically controlled mirror 205, a first wave plate 206, a beam splitting cube 207, a first plano-convex lens 208, a third mirror 209, a second plano-convex lens 210, a fourth mirror 211, a filter 212, a spot position analyzer 213, a fifth mirror 214, a second wave plate 215, wherein: the first electrically controlled mirror 202 is arranged in the direction of the fiber laser output, used to reflect the fundamental frequency laser generated by the fiber laser to the first mirror, and the first electrically controlled mirror 202 is configured with a step motor and a piezoelectric ceramic to adjust the propagation direction of the fundamental frequency laser when the beam propagation is unstable as feedback by the spot position analyzer. Since the use method and configuration means of the step motor and the piezoelectric ceramic are known to those skilled in the art, they are not specifically described in the present application, only the function is simply described; the first mirror 203 is used to reflect the incident fundamental frequency laser to the second mirror; the second mirror 204 is used to reflect the incident fundamental frequency laser to the second electrically controlled mirror; the second electrically controlled mirror 205 is used to reflect the incident fundamental frequency laser to the first wave plate, and the second electrically controlled mirror is configured with a step motor and a piezoelectric ceramic to adjust the propagation direction of the fundamental frequency laser when the beam propagation is unstable as feedback by the spot position analyzer. Since the use method and configuration means of the step motor and the piezoelectric ceramic are known to those skilled in the art, they are not specifically described in the present application, only the function is simply described; the first wave plate 206 is used to separate the sampling reference light from the fundamental frequency laser for beam stability judgment; the beam splitting cube 207 is used to split the first The sample reference light separated by the wave plate is incident to the first plano-convex lens 208, and the fundamental frequency laser is incident to the fifth mirror 214; the first plano-convex lens 208 is used for performing first beam shrinking on the sample reference light and then the sample reference light is incident to the third mirror 209; the third mirror 209 is used for reflecting the sample reference light after the first beam shrinking to the second plano-convex lens 210; the second plano-convex lens 210 is used for performing second beam shrinking on the incident sample reference light and then the sample reference light is incident to the fourth mirror 211; the fourth mirror 211 is used for reflecting the sample reference light after the second beam shrinking to the filter 212; the filter 212 is used for attenuating the power of the incident sample reference light to adapt to the requirement of the spot analysis; the spot position analyzer 213 is used for judging the stability of the light beam propagation of the sample reference light after the filter processing, and feeding back the first electrically-controlled mirror 202 and the second electrically-controlled mirror 205 when the light beam propagation is unstable; the fifth mirror 214 is used for reflecting the fundamental frequency laser to the second wave plate 215; the second The wave plate 215 is used for adjusting the polarization direction of the fundamental frequency laser and then the fundamental frequency laser is incident to the frequency conversion module. In brief, the linearly polarized fundamental frequency laser with the center wavelength of 1030 nm, the repetition frequency of 1 MHz and the pulse width of 350 fs is emitted from the ytterbium-doped fiber laser 201, and the light beam is stabilized by the light beam direction stabilization system composed of the electrically-controlled mirrors 202 to 213. The first mirror 203, the second mirror 204, the third mirror 209 and the fourth mirror 211 are used for changing the propagation direction of the laser; the first electrically-controlled mirror 202 and the second electrically-controlled mirror 205 receive the feedback from the spot position analyzer 213 and then correct the propagation direction of the light beam by the stepping motor and the piezoelectric ceramic installed thereon; the first plano-convex lens 208 and the second plano-convex lens 210 constitute a lens group to shrink the sample reference light; the filter 212 attenuates the power of the sample reference light to adapt to the requirement of the spot position analyzer 213 for the size and power intensity of the sample reference light spot. The wave plate 206 and the beam splitter cube 207 are used for separating the sample reference light from the main light path for judging the stability of the light beam propagation; the first plano-convex lens 208 and the second plano-convex lens 210 constitute a lens group to shrink the sample reference light; and the filter 212 attenuates the power of the sample reference light to adapt to the requirement of the spot position analyzer 213 for the size and power intensity of the sample reference light spot.

[0028] In the present application, the 1030 nm fundamental frequency light is incident to the optical crystal group composed of two BBO crystals arranged close to each other to perform preliminary three times frequency conversion, and then the light is incident to the nonlinear optical crystal frequency conversion module to perform final frequency conversion. Figure 1 It can be seen that the nonlinear optical crystal frequency conversion module comprises a lens group composed of two plano-convex lenses and two BBO crystals.

[0029] According to one embodiment of the present application, still referring to Figure 2As shown, the frequency conversion module in the scheme of the present application comprises a third plano-convex lens 216, a first BBO crystal 217, a second BBO crystal 218, and a fourth plano-convex lens 219, wherein: the third plano-convex lens 216 and the fourth plano-convex lens 219 are used to constitute a first focusing lens group, and are used to adjust the intersection point of the fundamental laser to be located at the middle position of the first BBO crystal 217 and the second BBO crystal 218; the first BBO crystal 218 is used to generate second-harmonic light with a center wavelength of 515 nm based on the fundamental laser, and the second-harmonic light and the first residual fundamental laser are jointly injected into the second BBO crystal; and the second BBO crystal 218 is used to generate third-harmonic linearly polarized laser with a center wavelength of 343 nm based on the injected second-harmonic light and the first residual fundamental laser, and the third-harmonic linearly polarized laser, the residual second-harmonic light, and the second residual fundamental laser are jointly injected into a dichroic mirror. It can be seen that, in the present application, two BBO crystals are used to achieve different frequency conversion purposes. The 1030 nm fundamental light is first doubled to generate linearly polarized second-harmonic green light with a center wavelength of 515 nm through the first BBO crystal, and then the 515 nm second-harmonic light and the residual 1030 nm fundamental light in the original propagation direction are co-linearly injected into the next second BBO crystal to further obtain linearly polarized laser with a center wavelength of 343 nm which is three times the frequency of the original fundamental light through nonlinear sum frequency. In addition, there are also 1030 nm fundamental light and 515 nm green light generated by the first BBO crystal in the same propagation direction. The three kinds of co-linearly propagated laser are then separated by the dichroic mirror 220, and finally the 343 nm linearly polarized laser is left for subsequent frequency conversion. The BBO crystal group is provided with a convex lens before and after the group to constitute a lens group, and the focal point is located between the two BBO crystals, so as to improve the frequency conversion efficiency of the entire third-harmonic generation process. It should be noted that the lens group in the frequency conversion module in the present application is suitable for focusing the 1030 nm fundamental light to improve the power density of the light beam passing through the BBO crystal, thereby improving the frequency conversion efficiency. The nonlinear optical crystal has a nonlinear optical effect, and the 1030 nm fundamental light is incident to the optical crystal group composed of two closely arranged BBO crystals to achieve preliminary overall third-harmonic generation effect, wherein the 1030 nm fundamental light is first doubled to generate linearly polarized second-harmonic green light with a center wavelength of 515 nm through the first BBO crystal, and the 515 nm second-harmonic light and the residual 1030 nm fundamental light in the original propagation direction are co-linearly injected into the next second BBO crystal to further obtain linearly polarized laser with a center wavelength of 343 nm which is three times the frequency of the original fundamental light through nonlinear sum frequency, and in addition, there are also 1030 nm fundamental light and 515 nm green light generated by the first BBO crystal in the same propagation direction. The three kinds of co-linearly propagated laser are then separated by the dichroic mirror, and finally the 343 nm linearly polarized laser is left for subsequent frequency conversion.The conversion rate of the first frequency doubling to obtain 515 nm green light is about 35% of the maximum 1030 nm fundamental frequency light, and the conversion rate of the second frequency doubling to finally obtain 343 nm laser light is about 10% of the maximum 1030 nm fundamental frequency light.

[0030] Still referring to Figure 2 It can be seen that the triple-frequency linearly polarized laser, the remaining second-frequency light, and the second remaining fundamental frequency laser after the frequency conversion module are jointly injected into the dichroic mirror 220, the dichroic mirror 220 is used for separating the triple-frequency linearly polarized laser, the remaining second-frequency light, and the second remaining fundamental frequency laser, and the triple-frequency linearly polarized laser is injected into the triple-frequency reflecting mirror, wherein the triple-frequency reflecting mirror is the first 343 nm reflecting mirror 222, and the remaining second-frequency light and the second remaining fundamental frequency laser are injected into the first beam collector 221 as the first remaining laser.

[0031] From Figure 1 It can be seen that the polarization tuning module 103 includes a wave plate, a wave plate, and a wave plate. Since the 343 nm laser is subjected to the frequency doubling process by the four-wave mixing effect of the inert gas in the generation cell, the spatial distribution of the transmitted inert gas is uniform, there is no phase matching condition of the polarization influence of the nonlinear crystal, and the optical device after the generation of 10.8 eV does not have selectivity to the polarization direction of the laser. The polarization characteristics of the 10.8 eV extreme ultraviolet light remain the same as the precursor 343 nm laser and remain unchanged in the subsequent propagation process. By adjusting the angle between the axis of the wave plate 1 and the incident linearly polarized 343 nm laser perpendicular to the laser propagation direction, the s-type or p-type linear polarization of the 10.8 eV output can be adjusted; on the basis of the foregoing optical path, the wave plate 2 and wave plate are inserted, and the angle between the axes of the respective wave plates perpendicular to the laser propagation direction is adjusted, so that the left-handed or right-handed circular polarization of the 10.8 eV output can be adjusted. According to an embodiment of the present application, still referring to Figure 2 , the polarization tuning module includes a first 343 nm wave plate 223, a 343 nm wave plate 224, and a second 343 nm wave plate 225, wherein: the first 343 nm wave plate is used to adjust the triple-frequency linearly polarized light to be s-type or p-type linear polarization according to application requirements; the 343 nm wave plate is used to adjust the triple-frequency linearly polarized laser to be left-handed or right-handed circular polarization according to application requirements; and the second 343 nm wave plate is used to adjust the polarization direction of the triple-frequency linearly polarized or circularly polarized laser according to application requirements.

[0032] After the second 343 nm The tripled linearly polarized light after the wave plate 225 is injected into the inert gas frequency conversion module, according to an embodiment of the present application, the inert gas frequency conversion module includes a fifth plano-convex lens, an inert gas generation pool, a LiF lens window, wherein: the inert gas generation pool is used to provide an inert gas cavity and a charging and discharging circuit for the triple frequency operation of the linearly polarized light to obtain an extreme ultraviolet laser with a wavelength of 114 nm, and the extreme ultraviolet laser and the remaining tripled linearly polarized light are jointly injected into a focusing-monochromatic-detection module; the fourth plano-convex lens and the LiF lens window jointly constitute a second focusing lens group for focusing the extreme ultraviolet laser. From Figure 1 As can be seen, the inert gas frequency conversion module 104 includes a stainless steel inert gas cavity and a charging and discharging circuit, a lens group. Among them, still referring to Figure 2 , the 343 nm laser is injected into the Xe-filled stainless steel 10.8 eV extreme ultraviolet light generation pool 227 through the fifth plano-convex lens 226 and the vacuum flange window with 343 nm antireflection lens, and focused in the generation pool. In the generation pool 227, the 343 nm laser ionizes Xe gas with a certain pressure, and a four-wave mixing nonlinear effect occurs, which further triple-frequencies the 343 nm wavelength light to obtain an extreme ultraviolet laser with a photon energy of 10.8 eV and a wavelength of 114 nm. In order to reduce the consumption rate of Xe gas, Ar gas can also be additionally charged in the generation pool to increase the partial pressure in the cavity. The 114 nm laser generated at this time is equivalent to nine times the frequency of the initial 1030 nm fundamental frequency light. The 114 nm laser passes through the customized LiF lens window 228 into the square ultrahigh vacuum cavity connected with the generation pool. The LiF lens window 228 and the plano-convex lens before the vacuum flange window constitute a lens group, which can adjust the focusing position of the finally generated 10.8 eV extreme ultraviolet light.

[0033] 10.8 eV extreme ultraviolet laser will be strongly absorbed by oxygen in the air in the atmospheric environment, affecting its subsequent application. Therefore, after the generation of 10.8 eV laser, the subsequent 10.8 eV laser parameter measurement and final use are in the ultrahigh vacuum environment maintained by the 316 stainless steel cavity and the vacuum pump system. Still referring to Figure 2The focusing-monochromatic-detecting module comprises a LiF triangular prism 229, an extreme ultraviolet reflecting mirror 230, an extreme ultraviolet laser detecting screen 231, a second 343 nm reflecting mirror 232, a second light beam collector 233, a vacuum gauge 234, and a molecular pump 235. The LiF triangular prism, the extreme ultraviolet reflecting mirror, the extreme ultraviolet laser detecting screen, the second 343 nm reflecting mirror, and the second light beam collector are arranged in the ultra-high vacuum cavity. The LiF triangular prism is used to separate the extreme ultraviolet laser and the remaining three times frequency linearly polarized light, and the extreme ultraviolet laser is shot into the extreme ultraviolet reflecting mirror, and the remaining three times frequency linearly polarized light is shot into the second 343 nm reflecting mirror as second remaining laser; the extreme ultraviolet reflecting mirror is used to reflect the shot-in extreme ultraviolet laser to the extreme ultraviolet laser detecting screen; the extreme ultraviolet laser detecting screen is used to detect the extreme ultraviolet laser to observe the extreme ultraviolet laser beam profile; the second 343 nm reflecting mirror is used to reflect the shot-in remaining linearly polarized light to the second light beam collector; the second light beam collector is used to collect the shot-in second remaining laser; the vacuum gauge is used to detect the vacuum state; and the molecular pump is used to maintain the vacuum state in the ultra-high vacuum cavity and can adjust the vacuum when the vacuum state is unstable. The 10.8 eV laser is incident on the LiF triangular prism 229 in the vacuum cavity, and the difference in refractive index of the 114 nm and the driving 343 nm light is used to separate the 114 nm and the 343 nm light in the spatial propagation path, that is, to monochromatize the 10.8 eV extreme ultraviolet light. The 10.8 eV laser is reflected by the extreme ultraviolet reflecting mirror to change the propagation direction. The extreme ultraviolet reflecting mirror is fixed on a two-axis electrically controlled vacuum compatible reflecting mirror frame on a two-dimensional vacuum electrically controlled displacement table, and the front, back, left and right positions of the displacement table and the deflection and pitch of the reflecting mirror frame are controlled by an external controller to adjust the final exit direction of the 10.8 eV laser. An aluminum extreme ultraviolet laser detecting screen can be inserted into the ultra-high vacuum magnetic rod in the 10.8 eV laser exit direction in the ultra-high vacuum square cavity. The outside of the screen is coated with fluorescent powder to develop the 10.8 eV extreme ultraviolet laser to observe the beam profile; a slit with a width of 1 mm and a length of 10 mm is processed in the central vertical optical platform direction of the screen to allow the laser to enter the dark room inside the screen. An extreme ultraviolet photodiode is placed in the dark room to measure the 10.8 eV incident light current to convert the 10.8 eV light power and light flux. The entire ultra-high vacuum square cavity has the functions of 10.8 eV focusing and monochromaticity and parameter measurement.

[0034] Figure 3 A pool generating model of a vacuum cavity is shown according to an embodiment of the present application, as shown in Figure 3 Figure 3 ​The main body is a cubic 316 stainless steel ultra-high vacuum chamber with main body dimensions of 400mm×360mm×280mm. The chamber body is connected to a molecular pump 301 via an ultra-high vacuum flange for evacuating and maintaining the vacuum environment inside the chamber; the generation cell 302 is used to triple the frequency of the 343 nm driving light to obtain a 10.8 eV extreme ultraviolet pulse laser; the vacuum gauge 303 is used to detect the vacuum level inside the chamber.

[0035] Figure 4 A structural model diagram of a detection fluorescent screen according to an embodiment of the present invention is shown, as follows: Figure 4 As shown, it is the detection fluorescent screen designed by this invention for measuring the laser parameters of a 10.8 eV extreme ultraviolet pulsed laser, corresponding to... Figure 2 The extreme ultraviolet (EUV) laser detection screen 231 consists of a slit fluorescent screen 401, an EUV photodiode 402, and an aluminum detection screen housing 403. The slit fluorescent screen is coated with phosphor to develop 10.8 eV EUV laser light and observe the beam profile. A 1 mm wide and 10 mm long slit is machined in the center of the screen, perpendicular to the optical platform, to allow the laser to enter the dark chamber inside the screen. The EUV photodiode is placed inside the dark chamber to measure the 10.8 eV incident photocurrent and then convert it into 10.8 eV optical power and luminous flux. The EUV photodiode is encapsulated by the aluminum detection screen housing 403.

[0036] To verify the extreme ultraviolet laser generated by this invention, the extreme ultraviolet laser generated by the scheme of this invention was used as the probe light for angle-resolved electron spectroscopy. Wherein, Figure 5 A schematic diagram of the test results of extreme ultraviolet lasers with different polarizations generated according to an embodiment of the present invention is shown. The specific test method used in this invention is as follows: Extreme ultraviolet lasers with different polarizations generated by this invention are used as probe light for an angle-resolved photoelectron spectrometer. These probe light beams are used to characterize the surface electronic states of a gold single crystal sample (Au(111) sample). Due to the different responses of the gold single crystal sample to probe light with different polarizations, the spectral intensity distribution at different positions in the final analyzer-collected surface electronic state test band diagram of the gold single crystal sample shows significant differences. The surface electronic state test results of the gold single crystal sample verify that this invention generates extreme ultraviolet lasers with different polarizations through tuning. Figure 5 The p-type linear polarization test result 501 indicates that the present invention currently outputs p-type linearly polarized extreme ultraviolet pulsed laser. Figure 5 The S-type linear polarization test result 502 indicates that the present invention currently outputs S-type linear polarized extreme ultraviolet pulsed laser. Figure 5 The test result 503 indicates that the current output of this invention is a left-handed circularly polarized extreme ultraviolet pulsed laser. Figure 5The middle right circular polarization test result 504 indicates that the present output right circular polarized ultraviolet pulse laser of the application.

[0037] Due to the inert gas four-wave mixing effect in the generation pool during the frequency doubling process of the 343 nm laser, the spatial distribution of the transmitted inert gas is uniform, there is no phase matching condition affected by the incident laser polarization direction of the nonlinear crystal, and the optical device after the generation of 10.8 eV has no selectivity for the polarization direction of the laser. Therefore, the inventors found through research that the polarization characteristics of the 10.8 eV ultraviolet laser generated by this process only depend on the polarization characteristics of the incident 343 nm driving laser, and the polarization characteristics of the 10.8 eV ultraviolet laser can be maintained in the subsequent system. By introducing a polarization tuning optical element group before the 343 nm light incident lens, the polarization characteristics of the 10.8 eV ultraviolet light at the user end can be adjusted by adjusting the polarization characteristics of the 343 nm driving light.

[0038] Compared with the prior art, the application uses a combination of several low-cost and miniaturized polarization optical elements to obtain a 10.8 eV ultraviolet pulse laser with the same polarization characteristics and adjustable polarization based on inert gas four-wave mixing generation by adjusting the polarization characteristics of the driving light. Due to the narrow bandwidth of the fundamental light spectrum and the high efficiency of monochromatization and dispersion compensation achieved throughout the generation process, the generated ultraviolet pulse laser has outstanding energy resolution in practical applications, such as as a light source for angle-resolved photoelectron spectroscopy. In addition, the 10.8 eV ultraviolet light has a larger photon energy than the ultraviolet light generated by frequency conversion of a single nonlinear crystal, so such an ultraviolet laser source not only has a wide range of momentum space coverage in the application of angle-resolved photoelectron spectroscopy, but also meets the application requirements of adjustable polarization.

[0039] The above specific embodiments further illustrate the purpose, technical solutions and beneficial effects of the application. It should be understood that the above are only specific embodiments of the application and are not intended to limit the application. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the application should be included in the protection scope of the application.

Claims

1. A polarization-tunable extreme-ultraviolet pulse laser generating apparatus, characterized by comprising: a first laser device; a second laser device; a polarization conversion device; and a polarization control device. The device comprises a fiber laser, a beam direction stabilizing system, a frequency conversion module, a dichroic mirror, a first beam collector, a third harmonic reflection mirror, a polarization tuning module, an inert gas frequency conversion module, a focusing-monochromatic-detection module, wherein: The fiber laser is used to generate fundamental frequency laser; The beam direction stabilizing system is used to stabilize the output direction of the fundamental frequency laser; The frequency conversion module is used to perform a third harmonic operation on the fundamental frequency laser to obtain third harmonic linearly polarized laser and first residual laser; The dichroic mirror is used to separate the third harmonic linearly polarized laser and the residual laser, and the third harmonic linearly polarized laser is shot into the reflection mirror, and the first residual laser is shot into the first beam collector; The first beam collector is used to collect the first residual laser; The third harmonic reflection mirror is used to reflect the third harmonic linearly polarized laser shot by the dichroic mirror to the polarization tuning module; The polarization tuning module is used to perform polarization tuning on the third harmonic linearly polarized laser; The inert gas frequency conversion module is used to perform a third harmonic operation on the tuned third harmonic linearly polarized laser to obtain extreme ultraviolet laser and second residual laser; The focusing-monochromatic-detection module is used to separate the extreme ultraviolet laser and the second residual laser, and detect the optical power and optical flux of the extreme ultraviolet laser.

2. The extreme ultraviolet pulse laser generating apparatus according to claim 1, wherein The fiber laser is an ytterbium-doped fiber laser, which is used to generate fundamental frequency laser with a wavelength of 1030 nm.

3. The extreme ultraviolet pulse laser generating apparatus according to claim 2, wherein The light beam direction stabilizing system comprises a first electrically controlled mirror, a first mirror, a second mirror, a second electrically controlled mirror, a first wave plate, a beam splitting cube, a first plano-convex lens, a third mirror, a second plano-convex lens, a fourth mirror, a filter, a spot position analyzer, a fifth mirror, a second wave plate, wherein: The first electrically controlled mirror is arranged in the laser emission direction of the fiber laser, and is used to reflect the fundamental frequency laser generated by the fiber laser to the first mirror. The first electrically controlled mirror is provided with a stepping motor and a piezoelectric ceramic to adjust the propagation direction of the fundamental frequency laser when the beam propagation is unstable under the feedback of the spot position analyzer; The first mirror is used to reflect the incident fundamental frequency laser to the second mirror; The second mirror is used to reflect the incident fundamental frequency laser to the second electrically controlled mirror; A second electrically controlled mirror is used to reflect the incident fundamental laser to the first wave plate, the second electrically controlled mirror is configured with a stepper motor and a piezoelectric ceramic for adjusting the propagation direction of the fundamental laser when the spot position analyzer feedback beam propagation is unstable; First A wave plate is used to separate the sampling reference light from the fundamental laser for beam stability judgment; The beam splitter cube is used for splitting the first The sampling reference light separated by the wave plate is injected into the first plano-convex lens, and the fundamental laser is injected into the fifth mirror. The first plano-convex lens is used to perform first beam shrinking on the sampling reference light and then shoot it into the third mirror; The third mirror is used to reflect the sampling reference light after the first beam shrinking to the second plano-convex lens; The second plano-convex lens is used to perform second beam shrinking on the incident sampling reference light and then shoot it into the fourth mirror; The fourth mirror is used to reflect the sampling reference light after the second beam shrinking to the filter; The filter is used to attenuate the power of the incident sampling reference light to meet the requirements of spot analysis; The spot position analyzer is used to judge the beam propagation stability of the sampling reference light after the filter processing, and feedback the first electrically controlled mirror and the second electrically controlled mirror when the beam propagation is unstable; The fifth mirror is used for reflecting the fundamental frequency laser to the second Wave plate; Second A wave plate is used to adjust the polarization direction of the fundamental laser and inject into the frequency conversion module.

4. The extreme ultraviolet pulse laser generating apparatus according to claim 3, wherein The frequency conversion module comprises a third plano-convex lens, a first BBO crystal, a second BBO crystal, and a fourth plano-convex lens, wherein: The third plano-convex lens and the fourth plano-convex lens are used to form a first focusing lens group to adjust the intersection of the fundamental frequency laser to be located at the middle position of the first BBO crystal and the second BBO crystal; The first BBO crystal is used to generate second harmonic light with a center wavelength of 515 nm based on the fundamental frequency laser, and the second harmonic light and the first residual fundamental frequency laser are jointly shot into the second BBO crystal; The second BBO crystal is used for generating linearly polarized laser of third harmonic with central wavelength of 343 nm based on the injected second harmonic light and the first residual fundamental laser, and the linearly polarized laser of third harmonic, the residual second harmonic light and the second residual fundamental laser are injected into the dichroic mirror.

5. The extreme ultraviolet pulse laser generating apparatus according to claim 4, wherein The dichroic mirror is used for separating the linearly polarized laser of third harmonic, the residual second harmonic light and the second residual fundamental laser, and injecting the linearly polarized laser of third harmonic into the mirror, and injecting the residual second harmonic light and the second residual fundamental laser into the first beam collector as the first residual laser.

6. The extreme ultraviolet pulse laser generating apparatus according to claim 5, wherein The third harmonic mirror is the first 343 nm mirror.

7. The extreme ultraviolet pulse laser generating apparatus according to claim 6, wherein The polarization tuning module comprises a first 343nm waveplate, 343nm waveplate, a second 343nm waveplate, wherein: First 343 nm The wave plate is used to adjust the linearly polarized light of the third harmonic to be s-type or P-type linear polarization according to the application requirements. 343 nm Waveplates are used to adjust the polarization of the tripled linear laser light to be left or right circularly polarized, depending on the application requirements. Second 343 nm The wave plate is used to adjust the polarization direction of the triple-frequency linearly or circularly polarized laser according to the application requirements.

8. The extreme ultraviolet pulse laser generating apparatus according to claim 7, wherein The inert gas frequency conversion module comprises a fifth plano-convex lens, an inert gas generating cell and a LiF lens window sheet, wherein: The inert gas generating cell is used for providing an inert gas cavity and a charge and discharge circuit for performing a third harmonic operation on linearly polarized light to obtain extreme ultraviolet laser with wavelength of 114 nm, and the extreme ultraviolet laser and the residual linearly polarized light of third harmonic are injected into the focusing-monochromatic-detection module; The fifth plano-convex lens and the LiF lens window sheet jointly constitute a second focusing lens group for focusing the extreme ultraviolet laser.

9. The extreme ultraviolet pulse laser generating apparatus according to claim 8, wherein The focusing-monochromatic-detection module comprises a LiF three-prism, an extreme ultraviolet mirror, an extreme ultraviolet laser detection screen, a second 343 nm mirror, a second beam collector and a vacuum gauge, and the LiF three-prism, the extreme ultraviolet mirror, the extreme ultraviolet laser detection screen and the second 343 nm mirror are arranged in an ultrahigh vacuum cavity, wherein: The LiF three-prism is used for separating the extreme ultraviolet laser and the residual linearly polarized light of third harmonic, and injecting the extreme ultraviolet laser into the extreme ultraviolet mirror, and injecting the residual linearly polarized light of third harmonic into the second 343 nm mirror as the second residual laser; The extreme ultraviolet mirror is used for reflecting the injected extreme ultraviolet laser to the extreme ultraviolet laser detection screen; The extreme ultraviolet laser detection screen is used for developing the extreme ultraviolet laser to observe the beam profile of the extreme ultraviolet laser; The second 343 nm mirror is used for reflecting the injected residual linearly polarized light to the second beam collector; The second beam collector is used for collecting the second residual laser; The vacuum gauge is used for detecting the vacuum state; The molecular pump is used for maintaining the vacuum state in the ultrahigh vacuum cavity, and can adjust the vacuum when the vacuum state is unstable.

10. The extreme ultraviolet pulse laser generating apparatus according to claim 9, wherein The extreme ultraviolet laser detection screen comprises a fluorescent screen, an extreme ultraviolet photodiode and a detection bottle shell, wherein: The fluorescent screen is provided with a slit for the extreme ultraviolet laser to enter the dark chamber in the screen; The extreme ultraviolet photodiode is used for measuring the current of the extreme ultraviolet laser to calculate the optical power and the luminous flux.

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