A polarization-tunable extreme ultraviolet pulsed laser generator

Abstract

This invention provides a polarization-tunable extreme ultraviolet pulsed laser generator, comprising: a fiber laser for generating a fundamental frequency laser; a beam direction stabilization system for stabilizing the output direction of the fundamental frequency laser; a frequency conversion module for performing a third-harmonic operation on the fundamental frequency laser to obtain a third-harmonic linearly polarized laser and a first residual laser; a dichroic mirror for separating the third-harmonic linearly polarized laser and the residual laser; a first beam collector for collecting the first residual laser; a third-harmonic reflector for reflecting the third-harmonic linearly polarized laser to the polarization tuning module; the polarization tuning module for polarization tuning the third-harmonic linearly polarized laser; an inert gas frequency conversion module for performing a third-harmonic operation on the tuned third-harmonic linearly polarized laser to obtain an extreme ultraviolet laser and a second residual laser; and a focusing-monochrome-detection module for separating the extreme ultraviolet laser and the second residual laser.

Description

Technical Field

[0001] This invention relates to the field of laser technology, specifically to ultraviolet laser acquisition technology, and more specifically to an extreme ultraviolet pulsed laser generator. Background Technology

[0002] Ultraviolet (UV) lasers, with their short wavelength and high photon energy, have shown significant application prospects in multiple fields. In industry, UV lasers can be used for high-precision manufacturing and intelligent inspection, such as photolithography in semiconductor manufacturing and elemental composition and defect analysis in industrial safety inspection. In scientific research, UV lasers have wide applications in cutting-edge areas such as ultrafast spectroscopy, matter excitation, material synthesis, and property control. Currently, there are two main methods for obtaining UV lasers: 1. Direct generation of UV lasers using excimer lasers; 2. Indirect generation of UV lasers from fundamental frequency light through multi-stage nonlinear frequency conversion. In the second method, depending on the nonlinear frequency conversion principle and system settings, lasers with different frequencies from ultraviolet to extreme ultraviolet can be obtained. Using nonlinear crystals such as barium metaborate (BBO) and potassium beryllium fluoroborate (KBBF), UV lasers with photon energies up to approximately 8 eV and tunable polarization can be obtained. One approach is to utilize nonlinear crystal frequency doubling combined with gas high-harmonic generation to obtain extreme ultraviolet (EUV) lasers with higher photon energy and shorter wavelengths. However, this EUV light often exhibits only linear polarization, and the polarization direction is not adjustable. Particularly in angle-resolved photoelectron spectroscopy (ARPS) for characterizing the electronic states of matter, researchers aim to use higher photon-energy UV lasers to expand the momentum space range for material observation, while simultaneously retaining the tunable polarization characteristics of the laser to study the orbital and spin properties of electrons within the material. Therefore, although EUV laser generation techniques combining nonlinear crystal frequency conversion and inert gas four-wave mixing have been developed, this method can only produce EUV lasers with higher photon energy compared to those obtained using a single nonlinear crystal frequency conversion; the wavelength remains limited by the limiting transmission efficiency of crystals such as lithium fluoride (LiF) and magnesium fluoride (MgF2). However, since this method is more efficient than higher harmonic generation methods and does not require a complex spectroscopic system, it is very suitable as a light source for ultra-high vacuum spectroscopic characterization methods such as angle-resolved photoelectron spectroscopy systems. Therefore, researching better polarization-tunable extreme ultraviolet (EUV) light source schemes is of great significance. Currently, there are femtosecond 11 eV EUV EUV light sources obtained by nonlinear frequency conversion, but they have limitations such as poor energy resolution, low luminous flux, and non-tunable polarization, which restrict their application in studying complex electronic states, orbitals, and spin properties of materials. Therefore, there is an urgent need for a new EUV light source generation scheme that can solve the problems of poor energy resolution, low luminous flux, and non-tunable low linear polarization, thereby improving the application of EUV light in various industries. It should be noted that the background information is only used to introduce relevant information of the present invention to help understand the technical solution of the present invention, but does not mean that the relevant information is necessarily prior art. In the absence of evidence that the relevant information was disclosed before the filing date of this invention, the relevant information should not be regarded as prior art. Summary of the Invention

[0003] Therefore, the purpose of this invention is to overcome the defects of the prior art and provide a new polarization-tunable extreme ultraviolet pulsed laser generator.

[0004] The objective of this invention is achieved through the following technical solution:

[0005] This invention provides a polarization-tunable extreme ultraviolet pulsed laser generator, comprising: a fiber laser, a beam stabilization system, a frequency conversion module, a dichroic mirror, a first beam collector, a third-harmonic reflector, a polarization tuning module, an inert gas frequency conversion module, and a focusing-monochromatic-detection module, wherein: the fiber laser is used to generate a fundamental frequency laser; the beam stabilization 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 a third-harmonic linearly polarized laser and a first residual laser; the dichroic mirror is used to separate the third-harmonic linearly polarized laser and the residual laser. The process involves directing a third-harmonic linearly polarized laser into a reflector, and then directing the first residual laser into a first beam collector. The first beam collector collects the first residual laser. The third-harmonic reflector reflects the third-harmonic linearly polarized laser incident through the dichroic mirror to a polarization tuning module. The polarization tuning module performs polarization tuning on the third-harmonic linearly polarized laser. The inert gas frequency conversion module performs a third-harmonic operation on the tuned third-harmonic linearly polarized laser to obtain extreme ultraviolet (EUV) laser and the second residual laser. The focusing-monochromatic-detection module separates the EUV laser and the second residual laser and detects the optical power and luminous flux of the EUV laser.

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

[0007] Preferably, the beam direction stabilization system includes a first electrically controlled reflector, a second reflector, a third electrically controlled reflector, and a fourth reflector. Waveplate, beam splitter cube, first plano-convex lens, third mirror, second plano-convex lens, fourth mirror, filter, spot position analyzer, fifth mirror, second A waveplate, wherein: a first electrically controlled reflector is disposed in the laser emission direction of the fiber laser, used to reflect the fundamental frequency laser generated by the fiber laser back to the first reflector; the first electrically controlled reflector is equipped with a stepper motor and piezoelectric ceramic to adjust the propagation direction of the fundamental frequency laser when the beam propagation is unstable according to the feedback from the beam position analyzer; the first reflector is used to reflect the incident fundamental frequency laser back to a second reflector; the second reflector is used to reflect the incident fundamental frequency laser back to the second electrically controlled reflector; the second electrically controlled reflector is used to reflect the incident fundamental frequency laser back to the first reflector. Waveplate, the second electrically controlled reflector is equipped with a stepper motor and piezoelectric ceramic to adjust the propagation direction of the fundamental frequency laser when the beam propagation is unstable according to the feedback from the beam position analyzer; first Waveplates are used to separate the sampling reference light from the fundamental frequency laser for beam stability assessment; beam splitters are used to separate the first... Waveplate-separated sampling reference light is incident on a first plano-convex lens, and fundamental frequency laser light is incident on a fifth reflecting mirror. The first plano-convex lens performs a first beam-shrinking process on the sampling reference light before it is incident on a third reflecting mirror. The third reflecting mirror reflects the first-beam-shrinking sampling reference light to a second plano-convex lens. The second plano-convex lens performs a second beam-shrinking process on the incident sampling reference light before it is incident on a fourth reflecting mirror. The fourth reflecting mirror reflects the second-processed sampling reference light to a filter. The filter attenuates the power of the incident sampling reference light to meet the requirements of beam spot analysis. A beam spot position analyzer performs beam spot analysis on the filtered sampling reference light to determine the beam propagation stability and provides feedback to the first and second electrically controlled reflecting mirrors when the beam propagation is unstable. The fifth reflecting mirror reflects the fundamental frequency laser light to the second... Wave plate; second Waveplates are used to adjust the polarization direction of the fundamental frequency laser and direct it into the frequency conversion module.

[0008] Preferably, the frequency conversion module includes a third plano-convex lens, a first BBO crystal, a second BBO crystal, and a fourth plano-convex lens, wherein: the third and fourth plano-convex lenses 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 and second BBO crystals; the first BBO crystal is used to generate second-harmonic light with a center wavelength of 515nm based on the fundamental frequency laser, and the second-harmonic light and the first remaining fundamental frequency laser are jointly incident on the second BBO crystal; the second BBO crystal is used to generate third-harmonic linearly polarized laser with a center wavelength of 343nm based on the incident second-harmonic light and the first remaining fundamental frequency laser, and the third-harmonic linearly polarized laser, the remaining second-harmonic light, and the second remaining fundamental frequency laser are jointly incident on 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 frequency laser, and to direct the third-harmonic linearly polarized laser into the reflector, while the remaining second-harmonic light and the second remaining fundamental frequency laser are directed into the first beam collector as the first remaining laser.

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

[0011] Preferably, the polarization tuning module includes a first 343nm... Wave plate, 343nm Wave plate, second 343nm Waveplate, wherein: first 343nm Waveplates are used to adjust the third harmonic linearly polarized light to S-type or P-type linear polarization according to application requirements; 343nm Waveplates are used to adjust the polarization of linearly third-harmonic lasers to left-handed or right-handed circular polarization, depending on application requirements; the second 343nm Waveplates are used to adjust the polarization direction of third-harmonic linearly or circularly polarized lasers according to application requirements.

[0012] Preferably, the inert gas frequency conversion module includes a fifth plano-convex lens, an inert gas generation cell, and a LiF lens window, wherein: the inert gas generation cell is used to provide an inert gas cavity and a gas filling and discharging circuit for performing a third harmonic operation on linearly polarized light to obtain extreme ultraviolet laser with a wavelength of 114nm; the extreme ultraviolet laser and the remaining third harmonic linearly polarized light are jointly incident on the focusing-monochrome-detection module; the fifth plano-convex lens and the LiF lens window together constitute a second focusing lens group for focusing the extreme ultraviolet laser.

[0013] Preferably, the focusing-monochromatic-detection module includes a LiF prism, an extreme ultraviolet (EUV) mirror, an EUV laser detection screen, a second 343nm mirror, a second beam collector, a vacuum gauge, and a molecular pump. The LiF prism, EUV mirror, EUV laser detection screen, second 343nm mirror, and second beam collector are configured in an ultra-high vacuum cavity. The LiF prism separates the EUV laser from the remaining third-harmonic linearly polarized light and directs the EUV laser into the EUV mirror. The remaining third-harmonic linearly polarized light is used as the second residual beam. The laser beam is incident on a second 343nm reflector; an extreme ultraviolet (EUV) reflector is used to reflect the incident EUV laser beam onto an EUV laser detection screen; the EUV laser detection screen is used to develop the EUV laser beam to observe its profile; the second 343nm reflector is used to reflect the incident residual linearly polarized light to a second beam collector; the second beam collector is used to collect the incident residual laser beam; a vacuum gauge is used to detect the vacuum state; a molecular pump is used to maintain the vacuum state in the ultra-high vacuum chamber and can adjust the evacuation when the vacuum state is unstable.

[0014] Preferably, the extreme ultraviolet laser detection screen includes: a fluorescent screen, an extreme ultraviolet photodiode, and a detection bottle shell, wherein: the fluorescent screen is provided with a slit to allow the extreme ultraviolet laser to enter the dark chamber inside the screen; the extreme ultraviolet photodiode is used to measure the extreme ultraviolet laser current to calculate the optical power and luminous flux.

[0015] Compared with existing technologies, the advantages of this invention are as follows: This invention utilizes a combination of several low-cost, miniaturized polarization optical elements to obtain an extreme ultraviolet (EUV) pulsed laser with the same polarization characteristics and tunable polarization, generated based on four-wave mixing of inert gas, by adjusting the polarization characteristics of the driving light. Due to the narrow bandwidth of the fundamental frequency spectrum and the efficient monochromaticity and dispersion compensation achieved throughout the generation process, the generated EUV pulsed laser exhibits outstanding energy resolution in practical applications, such as as a light source for angle-resolved photoelectron spectroscopy. Furthermore, since 10.8 eV EUV light has a greater photon energy than ultraviolet light generated by frequency conversion of a single nonlinear crystal, this EUV laser source provides both a wide momentum space coverage and retains the application requirement of polarization tunability in angle-resolved photoelectron spectroscopy applications. Attached Figure Description

[0016] The embodiments of the present invention will be further described below with reference to the accompanying drawings, wherein:

[0017] Figure 1 This is a schematic diagram of a polarization-tunable extreme ultraviolet laser pulse generator system according to an embodiment of the present invention;

[0018] Figure 2 This is a schematic diagram of the optical path of a polarization-tunable extreme ultraviolet laser pulse generator according to an embodiment of the present invention;

[0019] Figure 3 This is a schematic diagram of the generation cell and vacuum cavity model in the polarization-tunable extreme ultraviolet laser pulse generator according to an embodiment of the present invention;

[0020] Figure 4 This is a schematic diagram of the structural model of the detection fluorescent screen of a polarimetric tunable extreme ultraviolet laser pulse generator according to an embodiment of the present invention.

[0021] Figure 5 This is a schematic diagram showing the test results of extreme ultraviolet lasers with different polarizations generated by a polarization-tunable extreme ultraviolet laser pulse generator according to an embodiment of the present invention. Detailed Implementation

[0022] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are merely illustrative and are not intended to limit the invention.

[0023] As described in the background section, existing extreme ultraviolet (EUV) light sources have limitations such as poor energy resolution, low luminous flux, and untunable polarization. Therefore, this invention proposes a polarization-tunable EUV pulsed laser generation scheme to obtain an EUV light source with greater photon energy than the UV light generated by frequency conversion of a single nonlinear crystal.

[0024] In summary, this invention employs a high-power, high-repetition-rate ytterbium-doped fiber laser to generate fundamental frequency laser light, and configures a beam stabilization system, a reflector, a beam-splitting cubic crystal, a lens group, a BBO crystal, a convex lens, an extreme ultraviolet (EUV) reflector, an electrically controlled mirror frame, a two-dimensional electrically controlled displacement stage and controller, a fluorescent screen, an EUV photodiode, a picoampere meter, an ultra-high vacuum cavity, an ultra-high vacuum window flange, an ultra-high vacuum electrode flange, an ultra-high vacuum magnetic rod, a vacuum gauge, a molecular pump, a mechanical pump, a stainless steel charging / discharging circuit, Ar gas, Xe gas, etc., to construct a polarization-tunable EUV pulsed laser generator. 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] In this invention, the fundamental frequency laser beam emitted by the laser first passes through a beam direction stabilization system to ensure that the subsequent spatial optical path will not be deflected due to the shift in the position of the laser output spot, thus ensuring the stability of the entire frequency conversion optical path. The beam direction stabilization system mainly consists of a reflector frame controlled by two electrically controlled motors and a beam propagation path detector. The detector monitors the position and pitch changes of the output spot along the propagation direction to confirm the offset relative to the stable output position. Then, the electrically controlled reflector frame, which includes a coarse-adjustment motor and a fine-adjustment piezoelectric ceramic, precisely controls the actual output direction of the laser. According to one embodiment of the invention, reference is still made to... Figure 2 As shown, the beam direction stabilization system in this invention includes a first electrically controlled reflector 202, a first reflector 203, a second reflector 204, a second electrically controlled reflector 205, and a first... Waveplate 206, beam splitter 207, first plano-convex lens 208, third mirror 209, second plano-convex lens 210, fourth mirror 211, filter 212, spot position analyzer 213, fifth mirror 214, second Waveplate 215, wherein: a first electrically controlled reflector 202 is disposed in the laser emission direction of the fiber laser, used to reflect the fundamental frequency laser generated by the fiber laser to the first reflector; the first electrically controlled reflector 202 is configured with a stepper motor and piezoelectric ceramic to adjust the propagation direction of the fundamental frequency laser when the beam propagation is unstable according to the feedback from the beam position analyzer; since the usage and configuration of the stepper motor and piezoelectric ceramic are known to those skilled in the art, they will not be specifically described in this invention, only their functions will be briefly described; a first reflector 203 is used to reflect the incident fundamental frequency laser to a second reflector; a second reflector 204 is used to reflect the incident fundamental frequency laser to a second electrically controlled reflector; a second electrically controlled reflector 205 is used to reflect the incident fundamental frequency laser to the first reflector. The waveplate, the second electrically controlled reflector is equipped with a stepper motor and piezoelectric ceramic to adjust the propagation direction of the fundamental frequency laser when the beam propagation is unstable according to the feedback from the beam position analyzer. Since the usage and configuration of the stepper motor and piezoelectric ceramic are known to those skilled in the art, they will not be described in detail here, only their functions will be briefly described; First Waveplate 206 is used to separate the sampling reference light from the fundamental frequency laser for beam stability assessment; beam splitter 207 is used to separate the first... The waveplate-separated sampling reference light is incident on the first plano-convex lens 208, and the fundamental frequency laser is incident on the fifth reflecting mirror 214; the first plano-convex lens 208 is used to perform a first beam-shrinking process on the sampling reference light before it is incident on the third reflecting mirror 209; the third reflecting mirror 209 is used to reflect the sampling reference light after the first beam-shrinking process to the second plano-convex lens 210; the second plano-convex lens 210 is used to perform a second beam-shrinking process on the incident sampling reference light before it is incident on the fourth reflecting mirror 211; the fourth reflecting mirror 211 is used to reflect the sampling reference light after the second processing to the filter 212; the filter 212 is used to attenuate the power of the incident sampling reference light to meet the requirements of beam spot analysis; the beam spot position analyzer 213 is used to perform optical disc sharing on the sampling reference light after the filter processing to determine the beam propagation stability, and to provide feedback to the first electrically controlled reflecting mirror 202 and the second electrically controlled reflecting mirror 205 when the beam propagation is unstable; the fifth reflecting mirror 214 is used to reflect the fundamental frequency laser to the second waveplate 215; the second Waveplate 215 is used to adjust the polarization direction of the fundamental frequency laser and direct it into the frequency conversion module. In simple terms, a linearly polarized fundamental frequency laser with a center wavelength of 1030 nm, a repetition frequency of 1 MHz, and a pulse width of 350 fs is emitted from a ytterbium-doped fiber laser 201. The beam is stabilized by a beam direction stabilization system consisting of a series of optical components, including an electrically controlled mirror 202 and a beam position analyzer 213. The first mirror 203, second mirror 204, third mirror 209, and fourth mirror 211 are used to change the propagation direction of the laser. The first electrically controlled mirror 202 and the second electrically controlled mirror 205 receive feedback from the beam position analyzer 213 and, through stepper motors and piezoelectric ceramics mounted on them, correct the beam propagation direction. Waveplate 206 and beam splitter 207 are used to separate the sampling reference light from the main optical path for beam propagation stability judgment; first plano-convex lens 208 and second plano-convex lens 210 form a lens group to shrink the sampling reference light, and filter 212 attenuates the power of the sampling reference light to meet the requirements of the spot size and power intensity of the sampling reference light of the spot position analyzer 213.

[0028] In this invention, the 1030nm fundamental frequency light passes through a beam direction stabilization system, and then the 1030nm fundamental frequency light is incident on an optical crystal group composed of two closely arranged BBO crystals for preliminary third harmonic harmonicization. Figure 1 As can be seen, the nonlinear optical crystal frequency conversion module includes a lens group consisting of two plano-convex lenses and two BBO crystals.

[0029] According to one embodiment of the present invention, still referring to Figure 2As shown, the frequency conversion module of the present invention includes a third plano-convex lens 216, a first BBO crystal 217, a second BBO crystal 218, and a fourth plano-convex lens 219. The third plano-convex lens 216 and the fourth plano-convex lens 219 form a first focusing lens group, used to adjust the intersection point of the fundamental frequency laser to be located between the first BBO crystal 217 and the second BBO crystal 218. The first BBO crystal 218 generates a second-harmonic light with a center wavelength of 515nm based on the fundamental frequency laser; the second-harmonic light and the first remaining fundamental frequency laser are incident together on the second BBO crystal. The second BBO crystal 218 generates a third-harmonic linearly polarized laser with a center wavelength of 343nm based on the incident second-harmonic light and the first remaining fundamental frequency laser; the third-harmonic linearly polarized laser, the remaining second-harmonic light, and the second remaining fundamental frequency laser are incident together on the dichroic mirror. It can be seen that in this invention, the two BBO crystals use different chamfers to achieve different frequency conversion purposes. The 1030nm fundamental frequency light first undergoes frequency doubling through the first BBO crystal to generate frequency-doubled green light with a linearly polarized center wavelength of 515nm. Then, the 515nm frequency-doubled light and the remaining 1030nm fundamental frequency light in the original propagation direction are collinearly incident on the next adjacent second BBO crystal. Through nonlinear sum-frequency analysis, a linearly polarized laser with a center wavelength of 343nm, three times the frequency of the initial fundamental frequency light, is obtained. Additionally, the remaining 1030nm fundamental frequency light and the 515nm green light generated by the first frequency doubling in the same propagation direction are also present. These three collinearly propagating lasers are then separated by a dichroic mirror 220, ultimately leaving the 343nm linearly polarized laser for subsequent frequency conversion. A convex lens group is formed at the front and rear of the BBO crystal group, with the focal point positioned between the two BBO crystals to improve the frequency doubling efficiency of the entire frequency doubling process. It should be noted that the lens group in the frequency conversion module of this invention is suitable for focusing the 1030nm fundamental frequency light to increase the power density of the beam passing through the BBO crystal, thereby improving the frequency conversion efficiency. Nonlinear optical crystals exhibit nonlinear optical effects. When 1030 nm fundamental frequency light is incident on an optical crystal group consisting of two closely arranged BBO crystals, a preliminary overall third-harmonic effect is achieved. The 1030 nm fundamental frequency light is first frequency-doubled by the first BBO crystal to generate a linearly polarized green light with a center wavelength of 515 nm. The 515 nm second-harmonic light and the remaining 1030 nm fundamental frequency light in the original propagation direction are incident collinearly on the next adjacent second BBO crystal. Through nonlinear sum-frequency generation, a linearly polarized laser with a center wavelength of 343 nm, which is three times the frequency of the initial fundamental frequency light, is obtained. In addition, the remaining 1030 nm fundamental frequency light and the 515 nm green light generated by the first frequency-doubled light by the first BBO crystal are also present in the same propagation direction. The three different components of the collinear propagating laser are then separated by a dichroic mirror, leaving the 343 nm linearly polarized laser for subsequent frequency conversion.The conversion rate of the first step, frequency doubling, to obtain 515nm green light is approximately 35% higher than that of the 1030nm fundamental frequency light. The second step, frequency summing, to obtain 343nm laser light, has a conversion rate of approximately 10% higher than that of the 1030nm fundamental frequency light.

[0030] Still for reference Figure 2 As can be seen, the third-harmonic linearly polarized laser, the remaining second-harmonic light, and the second remaining fundamental frequency laser after passing through the frequency conversion module are all incident on the dichroic mirror 220. The dichroic mirror 220 is used to separate the third-harmonic linearly polarized laser, the remaining second-harmonic light, and the second remaining fundamental frequency laser, and to incident the third-harmonic linearly polarized laser into the third-harmonic reflector. The third-harmonic reflector is the first 343nm reflector 222, and the remaining second-harmonic light and the second remaining fundamental frequency laser are incident on 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 wave plate, waveplate and Waveplate. Because the 343nm laser undergoes a four-wave mixing process within the inert gas in the generation cell, the spatial distribution of the transmitted inert gas is uniform, eliminating the phase-matching condition caused by the polarization influence of nonlinear crystals. Furthermore, the optical devices passing through the 10.8eV generated laser do not exhibit selectivity regarding the laser's polarization direction; therefore, the polarization characteristics of the 10.8eV extreme ultraviolet light remain identical to those of the preceding 343nm laser and remain unchanged during subsequent propagation. By adjusting... The angle between the waveplate's first axis and the incident ray-polarized 343nm laser, perpendicular to the laser propagation direction, can be adjusted to output s-type or p-type linear polarization at 10.8 eV; further, an insertion can be made into the aforementioned optical path. Waveplate 2 and By adjusting the waveplates and the angles between their axes perpendicular to the laser propagation direction, the 10.8 eV output can be adjusted to either left-hand or right-hand circular polarization. According to one embodiment of the invention, still referring to... Figure 2 The polarization tuning module includes a first 343nm... Waveplate 223, 343nm Waveplate 224, second 343nm Waveplate 225, wherein: first 343nm Waveplates are used to adjust the third harmonic linearly polarized light to S-type or P-type linear polarization according to application requirements; 343nm Waveplates are used to adjust the frequency of third-harmonic linearly polarized laser light to left-hand or right-hand circular polarization, depending on the application requirements; the second 343nm Waveplates are used to adjust the polarization direction of third-harmonic linearly or circularly polarized lasers according to application requirements.

[0032] After the second 343nm The third-harmonic linearly polarized light following waveplate 225 is incident on the frequency conversion module. According to one embodiment of the invention, the inert gas frequency conversion module includes a fifth plano-convex lens, an inert gas generation cell, and a LiF lens window. The inert gas generation cell provides an inert gas cavity and a filling / discharging circuit for third-harmonic operation of the linearly polarized light to obtain extreme ultraviolet (EUV) laser light with a wavelength of 114 nm. The EUV laser light and the remaining third-harmonic linearly polarized light are incident together on the focusing-monochromatic-detection module. The fourth plano-convex lens and the LiF lens window together constitute a second focusing lens group for focusing the EUV laser light. Figure 1 As can be seen, the inert gas frequency conversion module 104 includes a stainless steel inert gas chamber and a filling / discharging circuit, as well as a lens assembly. (The reference is still incomplete.) Figure 2 A 343nm laser beam passes through a fifth plano-convex lens 226 and enters a stainless steel 10.8eV extreme ultraviolet (EUV) light generation cell 227 filled with Xe gas through a vacuum flange window equipped with a 343nm intensifying lens. The laser beam is focused within the cell. In the cell 227, the 343nm laser ionizes Xe gas at a certain pressure, resulting in a four-wave mixing nonlinear effect. This further triharmles the 343nm wavelength light to obtain a photon energy of 10.8eV, corresponding to an EUV laser with a wavelength of 114nm. To reduce the Xe gas consumption rate, Ar gas can be added to the cell to increase the partial pressure within the cavity. The resulting 114nm laser is equivalent to nine times the frequency of the initial 1030nm fundamental frequency light. The 114nm laser beam then passes through a custom-designed LiF lens window 228 and enters a square ultra-high vacuum cavity connected to the generation cell. The LiF lens window 228 and the plano-convex lens in front of the vacuum flange window form a lens group that allows adjustment of the focusing position of the final 10.8eV EUV laser beam.

[0033] 10.8 eV extreme ultraviolet lasers are strongly absorbed by oxygen in the atmosphere, affecting their subsequent applications. Therefore, after the 10.8 eV laser is generated, all subsequent parameter measurements and final applications are conducted within an ultra-high vacuum environment maintained by a 316 stainless steel chamber and a vacuum pump system. (Still referencing...) Figure 2The focusing-monochromatic-detection module includes a LiF prism 229, an extreme ultraviolet (EUV) mirror 230, an EUV laser detection screen 231, a second 343nm mirror 232, a second beam collector 233, a vacuum gauge 234, and a molecular pump 235. The LiF prism, EUV mirror, EUV laser detection screen, second 343nm mirror, and second beam collector are configured in an ultra-high vacuum cavity. The LiF prism separates the EUV laser from the remaining third-harmonic linearly polarized light and directs the EUV laser into the EUV mirror, while the remaining third-harmonic linearly polarized light... The second residual laser beam is incident on a second 343nm reflector. An extreme ultraviolet (EUV) reflector reflects the incident EUV laser beam onto an EUV laser detection screen. The EUV laser detection screen is used to detect and develop the EUV laser beam to observe its profile. The second 343nm reflector reflects the incident residual linearly polarized light to a second beam collector. The second beam collector collects the incident second residual laser beam. A vacuum gauge detects the vacuum state. A molecular pump maintains the vacuum state in the ultra-high vacuum cavity and can adjust the evacuation if the vacuum state is unstable. The 10.8 eV laser is incident on a LiF prism 229 within the vacuum cavity. The difference in refractive index between the 114nm and driving 343nm light by the LiF prism 229 separates the 114nm and 343nm light along their spatial propagation paths, thus achieving monochromaticization of the 10.8 eV EUV light. The 10.8 eV laser beam is reflected by the EUV reflector, changing its propagation direction. An extreme ultraviolet (EUV) mirror is fixed on a biaxial electrically controlled vacuum-compatible mirror mount on a two-dimensional vacuum electrically controlled displacement stage. An external controller manipulates the stage's forward, backward, left, and right positions, as well as the mirror mount's offset and pitch, to adjust the final emission direction of the 10.8 eV laser. An aluminum EUV laser detection screen can be inserted into the 10.8 eV laser emission direction within the ultra-high vacuum square cavity via an ultra-high vacuum magnetic rod. The outer side of the screen is coated with phosphor to develop the 10.8 eV EUV laser beam profile for observation. 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. An EUV photodiode is placed inside the dark chamber to measure the 10.8 eV incident photocurrent, thereby calculating the 10.8 eV optical power and luminous flux. The entire ultra-high vacuum square cavity combines 10.8 eV focusing and monochromatic measurement functions.

[0034] Figure 3 A model diagram of a generation cell and a vacuum chamber provided according to an embodiment of the present invention is shown, such as... Figure 3 As shown, Figure 3The 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 right-hand circular polarization test result 504 indicates that the present invention currently outputs right-hand circularly polarized extreme ultraviolet pulsed laser. Therefore, it can be seen that the solution of the present invention can output extreme ultraviolet pulsed laser with tunable polarization.

[0037] Because the 343nm laser undergoes a four-wave mixing process with inert gas in the generation cell, the spatial distribution of the transmitted inert gas is uniform, and there is no phase-matching condition as with nonlinear crystals affected by the polarization direction of the incident laser. Furthermore, the optical devices that pass through the 10.8 eV generated laser do not exhibit selectivity regarding the laser polarization direction. Therefore, the inventors discovered that the polarization characteristics of the 10.8 eV extreme ultraviolet laser generated in this process depend solely on the polarization characteristics of the incident 343 nm driving laser, and these polarization characteristics can be maintained in subsequent systems. This invention introduces a polarization-tuning optical element group before the 343nm light incident lens, and by adjusting the polarization characteristics of the 343 nm driving light, the polarization characteristics of the 10.8 eV extreme ultraviolet light at the end-user can be adjusted.

[0038] Compared to existing technologies, this invention utilizes a combination of several low-cost, miniaturized polarization optical elements to obtain an extreme ultraviolet (EUV) pulsed laser with the same polarization characteristics and tunable polarization, generated by four-wave mixing of inert gas, through adjustment of the polarization characteristics of the driving light. Due to the narrow bandwidth of the fundamental frequency spectrum and the efficient monochromaticity and dispersion compensation achieved throughout the generation process, the generated EUV pulsed laser exhibits outstanding energy resolution in practical applications, such as as a source for angle-resolved photoelectron spectroscopy (ARPS). Furthermore, since 10.8 eV EUV light has a higher photon energy than UV light generated by frequency conversion from a single nonlinear crystal, this EUV laser source offers both a wide momentum space coverage and retains the requirement for polarization tunability in ARPS applications.

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

Claims

1. A polarization-tunable extreme ultraviolet pulsed laser generator, characterized in that, The device includes: a fiber laser, a beam stabilization system, a frequency conversion module, a dichroic mirror, a first beam collector, a third-harmonic reflector, a polarization tuning module, an inert gas frequency conversion module, and a focusing-monochromatic-detection module, wherein: The fiber laser is used to generate fundamental frequency laser; The beam direction stabilization system is used to stabilize the output direction of the fundamental frequency laser; wherein, the beam direction stabilization system includes a first electrically controlled mirror, a second mirror, a third electrically controlled mirror, and a fourth electrically controlled mirror. Waveplate, beam splitter cube, first plano-convex lens, third mirror, second plano-convex lens, fourth mirror, filter, spot position analyzer, fifth mirror, second A waveplate, wherein: a first electrically controlled reflector is disposed in the laser emission direction of the fiber laser, used to reflect the fundamental frequency laser generated by the fiber laser back to the first reflector; the first electrically controlled reflector is equipped with a stepper motor and piezoelectric ceramic to adjust the propagation direction of the fundamental frequency laser when the beam propagation is unstable according to the feedback from the beam position analyzer; the first reflector is used to reflect the incident fundamental frequency laser back to a second reflector; the second reflector is used to reflect the incident fundamental frequency laser back to the second electrically controlled reflector; the second electrically controlled reflector is used to reflect the incident fundamental frequency laser back to the first reflector. Waveplate, the second electrically controlled reflector is equipped with a stepper motor and piezoelectric ceramic to adjust the propagation direction of the fundamental frequency laser when the beam propagation is unstable according to the feedback from the beam position analyzer; first Waveplates are used to separate the sampled reference light from the fundamental frequency laser for beam stability assessment; beam splitters are used to separate the first... Waveplate-separated sampling reference light is incident on a first plano-convex lens, and fundamental frequency laser light is incident on a fifth reflecting mirror. The first plano-convex lens performs a first beam-shrinking process on the sampling reference light before it is incident on a third reflecting mirror. The third reflecting mirror reflects the first beam-shrinking sampled reference light to a second plano-convex lens. The second plano-convex lens performs a second beam-shrinking process on the incident sampling reference light before it is incident on a fourth reflecting mirror. The fourth reflecting mirror reflects the second processed sampling reference light to a filter. The filter attenuates the power of the incident sampling reference light to meet the requirements of beam spot analysis. A beam spot position analyzer performs optical disc sharing on the filtered sampling reference light to determine the beam propagation stability and provides feedback to the first and second electrically controlled reflecting mirrors when the beam propagation is unstable. The fifth reflecting mirror reflects the fundamental frequency laser light to the second... Wave plate; second Waveplates are used to adjust the polarization direction of the fundamental frequency laser and direct it into the frequency conversion module; The frequency conversion module is used to perform a third-harmonic operation on the fundamental frequency laser to obtain a third-harmonic linearly polarized laser and the first residual laser. The dichroic mirror is used to separate the third-harmonic linearly polarized laser and the remaining laser, and to direct the third-harmonic linearly polarized laser into the reflector, while the remaining laser is directed into the first beam collector. The first beam collector is used to collect the first remaining laser beam; The third-harmonic reflector is used to reflect the third-harmonic linearly polarized laser light incident through 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 a second residual laser. The focusing-monochrome-detection module is used to separate the extreme ultraviolet laser and the second residual laser, and to detect the optical power and luminous flux of the extreme ultraviolet laser.

2. The extreme ultraviolet pulsed laser generator according to claim 1, characterized in that, The fiber laser is a ytterbium-doped fiber laser, used to generate a fundamental frequency laser with a wavelength of 1030 nm.

3. The extreme ultraviolet pulsed laser generator according to claim 2, characterized in that, The frequency conversion module includes a third plano-convex lens, a first BBO crystal, a second BBO crystal, and a fourth plano-convex lens, wherein: The third and fourth plano-convex lenses are used to form the first focusing lens group, which is used to adjust the intersection of the fundamental frequency laser to be located in 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 515nm based on the fundamental frequency laser. The second-harmonic light and the remaining fundamental frequency laser from the first laser are injected into the second BBO crystal together. The second BBO crystal is used to generate a third-harmonic linearly polarized laser with a center wavelength of 343nm based on the incident second-harmonic light and the first remaining fundamental frequency laser. The third-harmonic linearly polarized laser, the remaining second-harmonic light, and the second remaining fundamental frequency laser are all incident on the dichroic mirror.

4. The extreme ultraviolet pulsed laser generator according to claim 3, characterized in that, The dichroic mirror is used to separate the third-harmonic linearly polarized laser, the remaining second-harmonic light, and the second remaining fundamental frequency laser. The third-harmonic linearly polarized laser is then directed into the reflector, while the remaining second-harmonic light and the second remaining fundamental frequency laser are directed into the first beam collector as the first remaining laser.

5. The extreme ultraviolet pulsed laser generator according to claim 4, characterized in that, The third-harmonic reflector is a first 343nm reflector.

6. The extreme ultraviolet pulsed laser generator according to claim 5, characterized in that, The polarization tuning module includes a first 343nm Wave plate, 343nm Wave plate, second 343nm Wave plate, wherein: First 343nm Waveplates are used to adjust the third harmonic linearly polarized light to S-type or P-type linear polarization according to application requirements; 343nm Waveplates are used to adjust the polarization of linear third harmonic lasers to be left-handed or right-handed circularly polarized, depending on the application requirements. Second 343nm Waveplates are used to adjust the polarization direction of third-harmonic linearly or circularly polarized lasers according to application requirements.

7. The extreme ultraviolet pulsed laser generator according to claim 6, characterized in that, The inert gas frequency conversion module includes a fifth plano-convex lens, an inert gas generation cell, and a LiF lens window, wherein: The inert gas generation cell is used to provide an inert gas cavity and a gas filling and discharging circuit for performing a third harmonic operation on linearly polarized light to obtain an extreme ultraviolet laser with a wavelength of 114 nm. The extreme ultraviolet laser and the remaining third harmonic linearly polarized light are together injected into the focusing-monochrome-detection module. The fifth plano-convex lens and the LiF lens window together form the second focusing lens group, which is used to focus the extreme ultraviolet laser.

8. The extreme ultraviolet pulsed laser generator according to claim 7, characterized in that, The focusing-monochrome-detection module includes a LiF prism, an extreme ultraviolet (EUV) mirror, an EUV laser detection screen, a second 343nm mirror, a second beam collector, a vacuum gauge, and a molecular pump. The LiF prism, EUV mirror, EUV laser detection screen, second 343nm mirror, and second beam collector are configured in an ultra-high vacuum chamber, wherein: The LiF prism is used to separate the extreme ultraviolet laser from the remaining third-harmonic linearly polarized light, and to direct the extreme ultraviolet laser into the extreme ultraviolet mirror, while the remaining third-harmonic linearly polarized light is directed into the second 343nm mirror as the second remaining laser. Extreme ultraviolet (EUV) reflectors are used to reflect incident EUV laser light onto an EUV laser detection screen. Extreme ultraviolet laser detection screen is used to detect and develop extreme ultraviolet laser beams in order to observe the profile of the extreme ultraviolet laser beam. The second 343nm reflector is used to reflect the incident residual linearly polarized light to the second beam collector; The second beam collector is used to collect the second remaining laser beam. Vacuum gauges are used to detect vacuum conditions; Molecular pumps are used to maintain the vacuum state in ultra-high vacuum chambers and can adjust the evacuation when the vacuum state is unstable.

9. The extreme ultraviolet pulsed laser generator according to claim 8, characterized in that, The extreme ultraviolet laser detection screen includes: a fluorescent screen, an extreme ultraviolet photodiode, and a detection bottle casing, wherein: The fluorescent screen has slits to allow extreme ultraviolet laser light to enter the dark chamber inside the screen; Extreme ultraviolet photodiodes are used to measure extreme ultraviolet laser current to calculate optical power and luminous flux.

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