CN116598877B - Vacuum ultraviolet light source generating equipment and application system - Google Patents

Vacuum ultraviolet light source generating equipment and application system Download PDF

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CN116598877B
CN116598877B CN202310863783.5A CN202310863783A CN116598877B CN 116598877 B CN116598877 B CN 116598877B CN 202310863783 A CN202310863783 A CN 202310863783A CN 116598877 B CN116598877 B CN 116598877B
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light
optical fiber
air
vacuum ultraviolet
vacuum
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CN116598877A (en
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马雪岩
路声跃
邓勇开
刘运全
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Peking University
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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N23/00—Investigating or analysing materials by the use of wave or particle radiation, e.g. X-rays or neutrons, not covered by groups G01N3/00 – G01N17/00, G01N21/00 or G01N22/00
    • G01N23/22—Investigating or analysing materials by the use of wave or particle radiation, e.g. X-rays or neutrons, not covered by groups G01N3/00 – G01N17/00, G01N21/00 or G01N22/00 by measuring secondary emission from the material
    • G01N23/227—Measuring photoelectric effect, e.g. photoelectron emission microscopy [PEEM]
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N23/00—Investigating or analysing materials by the use of wave or particle radiation, e.g. X-rays or neutrons, not covered by groups G01N3/00 – G01N17/00, G01N21/00 or G01N22/00
    • G01N23/22—Investigating or analysing materials by the use of wave or particle radiation, e.g. X-rays or neutrons, not covered by groups G01N3/00 – G01N17/00, G01N21/00 or G01N22/00 by measuring secondary emission from the material
    • G01N23/227—Measuring photoelectric effect, e.g. photoelectron emission microscopy [PEEM]
    • G01N23/2273—Measuring photoelectron spectrum, e.g. electron spectroscopy for chemical analysis [ESCA] or X-ray photoelectron spectroscopy [XPS]
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
    • H01S3/005—Optical devices external to the laser cavity, specially adapted for lasers, e.g. for homogenisation of the beam or for manipulating laser pulses, e.g. pulse shaping
    • H01S3/0071—Beam steering, e.g. whereby a mirror outside the cavity is present to change the beam direction
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
    • H01S3/005—Optical devices external to the laser cavity, specially adapted for lasers, e.g. for homogenisation of the beam or for manipulating laser pulses, e.g. pulse shaping
    • H01S3/0085—Modulating the output, i.e. the laser beam is modulated outside the laser cavity
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
    • H01S3/10—Controlling the intensity, frequency, phase, polarisation or direction of the emitted radiation, e.g. switching, gating, modulating or demodulating
    • H01S3/106—Controlling the intensity, frequency, phase, polarisation or direction of the emitted radiation, e.g. switching, gating, modulating or demodulating by controlling devices placed within the cavity
    • H01S3/108—Controlling the intensity, frequency, phase, polarisation or direction of the emitted radiation, e.g. switching, gating, modulating or demodulating by controlling devices placed within the cavity using non-linear optical devices, e.g. exhibiting Brillouin or Raman scattering
    • H01S3/109—Frequency multiplication, e.g. harmonic generation

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  • Electromagnetism (AREA)
  • Engineering & Computer Science (AREA)
  • Optics & Photonics (AREA)
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  • General Health & Medical Sciences (AREA)
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  • Nonlinear Science (AREA)
  • Optical Couplings Of Light Guides (AREA)

Abstract

The application relates to the field of optics, and provides vacuum ultraviolet light source generating equipment and an application system, wherein the equipment comprises: the vacuum ultraviolet light source generated by the pulse laser, the frequency doubling crystal, the double-color-field optical fiber coupling module, the optical fiber clamping and air path module and the harmonic monochromatization and focusing module can be applied to an optoelectronic detecting instrument. The pulse laser outputs fundamental frequency light, and the fundamental frequency light and the frequency doubling light are collinearly transmitted through the frequency doubling crystal. The double-color-field optical fiber coupling module is used for coupling fundamental frequency light and frequency doubling light into the hollow optical fiber in the optical fiber clamping and gas circuit module; the optical fiber clamping and gas circuit module is used for enabling fundamental frequency light and frequency doubling light to pass through the hollow optical fiber and obtaining mixed light beams through cascade mixing treatment; and the harmonic monochromatization and focusing module is used for monochromatizing the mixed light beam to obtain a vacuum ultraviolet light source and focusing the vacuum ultraviolet light source on the surface of a target sample in the photoelectron detecting instrument. The problem of the limitation of the existing ultraviolet light source generation is solved, and an application scene is provided.

Description

Vacuum ultraviolet light source generating equipment and application system
Technical Field
The application relates to the technical field of optics, in particular to vacuum ultraviolet light source generation equipment and an application system.
Background
Optoelectronic detection instruments (e.g., optoelectronic spectrometers and light-emitting electron microscopes, etc.) are important technological means for studying solid electronic properties. Because the detection sensitivity of multiphoton ionization is extremely low, an ultraviolet light source with higher single photon energy (higher than the work function of a substance) has important significance for the application of an optoelectronic detection instrument. Currently, ultraviolet light sources mainly include gas discharge lamps, synchrotron radiation or free electron lasers, gas higher harmonics, and lower harmonics generated by nonlinear crystals or rare gases. A gas discharge lamp is a conventional light source capable of generating a continuous light source with a single photon energy up to several tens eV (photon energy unit), but the application range of the light source is limited to a probe instrument without a time resolution characteristic; the synchrotron radiation light source or the free electron laser can output pulse light sources with energy up to tens to hundreds eV, but the large-scale laser device has high cost and huge volume; the gas higher harmonic is a desktop harmonic light source, but the mode requires the driving laser to have higher single pulse energy and shorter pulse width, and the instantaneous electric field intensity is required to be compared with the electric field intensity of atoms per se; vacuum ultraviolet light source can be obtained by utilizing nonlinear crystal or rare gas to generate low-order harmonic wave, but the scheme can only realize a single nonlinear process by designing the angle of crystal optical axis or gas pressure so as to obtain single frequency output.
Disclosure of Invention
The application provides a vacuum ultraviolet light source generating device and an application system, which can simultaneously generate multiple orders of harmonic waves, and can select one order of harmonic waves to be applied to an optoelectronic detecting instrument so as to solve the problem of limitation of the existing ultraviolet light source.
The application provides a vacuum ultraviolet light source generating device, the vacuum ultraviolet light source generating device comprises a pulse laser, a frequency doubling crystal, a bicolor field optical fiber coupling module, an optical fiber clamping and air circuit module and a harmonic monochromatization and focusing module, wherein:
the pulse laser is used for outputting fundamental frequency light;
the frequency doubling crystal is used for converting a part of the fundamental frequency light into frequency doubling light, and the frequency doubling light and the rest part of the fundamental frequency light are collinearly transmitted to obtain parallel combined light;
the double-color-field optical fiber coupling module is used for sequentially carrying out beam splitting treatment, focusing treatment and beam combining treatment on the parallel beam combining light to obtain focused beam combining light, and the focus of the focused beam combining light is located on the front end face of the hollow optical fiber in the optical fiber clamping and gas circuit module;
the optical fiber clamping and air path module is used for forming stable air pressure gradient distribution in the hollow optical fiber so that the focused combined light passes through the hollow optical fiber and then is subjected to cascade mixing treatment to obtain a mixed light beam;
The harmonic monochromatization and focusing module is used for carrying out monochromatization treatment on the mixed light beam to obtain a vacuum ultraviolet light source.
According to the vacuum ultraviolet light source generating device provided by the application, the bicolor field optical fiber coupling module comprises a beam splitter, a delay line, a reflector, a wave plate, a polaroid, a focusing lens and a beam combiner, wherein:
the beam splitter is used for splitting the parallel beam combination light;
the delay line is used for adjusting the time delay amount of the fundamental frequency light and the frequency doubling light so as to enable the fundamental frequency light and the frequency doubling light to be time-coincident at the front end face of the hollow optical fiber;
the reflecting mirror is used for adjusting the propagation directions of the fundamental frequency light and the frequency doubling light;
the wave plate and the polaroid are used for adjusting the polarization direction and the light intensity of the fundamental frequency light and the frequency doubling light;
the focusing lens is used for focusing the fundamental frequency light and the frequency doubling light;
and the beam combining lens is used for carrying out beam combining treatment on the fundamental frequency light and the frequency doubling light to obtain the focusing beam combining light.
According to the vacuum ultraviolet light source generating device provided by the application, the optical fiber clamping and air path module comprises the hollow optical fiber, an optical fiber connector, an air inlet device, an air inlet cavity, an optical inlet window, an air exhaust cavity, a vacuum pipeline and a first air exhaust pump, wherein:
The air inlet device comprises a first air cylinder, a first pressure reducing valve, an air pressure controller and a first air pipe, wherein an air outlet of the first air cylinder is connected with one end of the air pressure controller through the first pressure reducing valve and the first air pipe, the other end of the air pressure controller is connected with the air inlet cavity through the first air pipe, and the front end of the hollow optical fiber is positioned in the air inlet cavity;
the light inlet window is used for separating the air inlet cavity from the atmospheric environment;
the first air pump is connected with the air extraction cavity through the vacuum pipeline, and the rear end of the hollow optical fiber is positioned in the air extraction cavity;
and the air inlet device and the air inlet cavity are used for introducing air to the front end of the hollow optical fiber, the first air pump, the vacuum pipeline and the air suction cavity are used for sucking air to the rear end of the hollow optical fiber, and stable air pressure gradient distribution is formed in the hollow optical fiber, so that the focused combined light passes through the hollow optical fiber to obtain the mixed light beam.
According to the vacuum ultraviolet light source generating device provided by the application, the optical fiber clamping and gas circuit module further comprises a pre-air extracting device, wherein the pre-air extracting device comprises a pre-air extracting pipeline and a gas valve, and the pre-air extracting device comprises the following components:
In a state that the gas valve is opened, the first air pump pumps air to the air inlet device and the air inlet cavity except the first gas cylinder through the pre-pumping pipeline, and simultaneously, the first air pump pumps air to the air pumping cavity at the rear end of the hollow optical fiber through the vacuum pipeline;
and in a state of closing the gas valve, stable pressure gradient distribution is formed inside the hollow optical fiber through the gas inlet device and the first air pump.
According to the vacuum ultraviolet light source generating device provided by the application, in the optical fiber clamping and air path module, the connection mode between the hollow optical fiber and the air inlet cavity and the connection mode between the hollow optical fiber and the air exhaust cavity are as follows:
the hollow optical fiber is arranged on the optical fiber connector, and the fixing and sealing between the hollow optical fiber and the optical fiber connector are realized through vacuum sealant;
the air inlet cavity and the air exhaust cavity are connected with the optical fiber connector, and sealing between the air inlet cavity and the optical fiber connector and sealing between the air exhaust cavity and the optical fiber connector are achieved through the rubber ring.
According to the vacuum ultraviolet light source generating device provided by the application, the optical fiber clamping and gas circuit module further comprises a coupling efficiency monitoring device, wherein:
the coupling efficiency monitoring device comprises a coupling efficiency monitoring cavity and an optical power meter;
the fundamental frequency light or the frequency doubling light passing through the hollow optical fiber enters the coupling efficiency monitoring cavity, and the fundamental frequency light or the frequency doubling light is led into the optical power meter through a reflecting mirror in the coupling efficiency monitoring cavity;
measuring the optical power of the fundamental frequency light or the frequency doubling light by the optical power meter, and adjusting the coupling efficiency of the hollow optical fiber according to the optical power;
and under the condition that the coupling efficiency of the hollow optical fiber is adjusted, adjusting a reflecting mirror in the coupling efficiency monitoring cavity so that the light beam emitted from the hollow optical fiber passes through the coupling efficiency monitoring cavity to reach the harmonic monochromatization and focusing module without obstruction.
According to the vacuum ultraviolet light source generating device provided by the application, the harmonic monochromatization and focusing module comprises a vacuum cavity, wherein a vacuum ultraviolet concave reflecting mirror, a vacuum ultraviolet plane reflecting mirror, a vacuum ultraviolet triple prism and a vacuum ultraviolet focusing lens are arranged in the vacuum cavity, and the harmonic monochromatization and focusing module comprises:
Collimating the mixed beam by the vacuum ultraviolet concave reflector;
the propagation direction of the mixed light beam in front of the vacuum ultraviolet triple prism is regulated through the vacuum ultraviolet concave reflecting mirror and the vacuum ultraviolet plane reflecting mirror;
the mixed light beam is divided into the fundamental frequency light, the frequency doubling light and the multi-level subharmonic by the vacuum ultraviolet triple prism;
and using one of the multiple subharmonics as the vacuum ultraviolet light source for focusing treatment through the vacuum ultraviolet focusing lens.
According to the vacuum ultraviolet light source generating device provided by the application, the harmonic monochromatization and focusing module further comprises an air cooling device, wherein:
the air cooling device comprises a second air bottle, a second pressure reducing valve, a second air pipe, an air inlet valve and a second air extracting pump;
the second air cylinder, the second pressure reducing valve, the second air pipe and the air inlet valve are used for feeding air into the vacuum cavity, the second air extracting pump is used for extracting air from the vacuum cavity, stable air flow is formed in the vacuum cavity, and the optical element in the vacuum cavity is cooled.
According to the vacuum ultraviolet light source generating device provided by the application, the harmonic monochromatization and focusing module further comprises a vacuum ultraviolet light inlet window and a vacuum ultraviolet light outlet window, wherein:
The vacuum environment of the optical fiber clamping and air path module and the harmonic monochromatization and focusing module are mutually independent through the vacuum ultraviolet light inlet window;
through the vacuum ultraviolet light outlet window, the harmonic monochromatization and focusing module and the vacuum environment of other interconnection devices are mutually independent.
According to the vacuum ultraviolet light source generating device provided by the application, the harmonic monochromatization and focusing module further comprises an observation window and a scintillation crystal, wherein:
and the observation window is used for observing fluorescent light spots formed on the scintillation crystal by the irradiation of the vacuum ultraviolet light source.
The application also provides a vacuum ultraviolet light source application system, which comprises a target sample, an optoelectronic detecting instrument and the vacuum ultraviolet light source generating equipment, wherein the vacuum ultraviolet light source generating equipment generates a vacuum ultraviolet light source, and focuses the vacuum ultraviolet light source on the surface of the target sample so as to excite photoelectrons to escape from the surface of the target sample, and the escaped photoelectrons are received by a detector in the optoelectronic detecting instrument.
The application provides vacuum ultraviolet light source generating equipment and an application system, wherein the vacuum ultraviolet light source generating equipment comprises a pulse laser, a frequency doubling crystal, a double-color-field optical fiber coupling module, an optical fiber clamping and gas circuit module and a harmonic monochromatization and focusing module, wherein the double-color-field optical fiber coupling module is used for sequentially carrying out beam splitting treatment, focusing treatment and beam combination treatment on fundamental frequency light and frequency doubling light to obtain focused combined light, the focus of the focused combined light is arranged on the front end face of a hollow optical fiber in the optical fiber clamping and gas circuit module, then the focused combined light enters the hollow optical fiber in the optical fiber clamping and gas circuit module, under the condition that stable air pressure gradient distribution is formed inside the hollow optical fiber, the mixed light is obtained after the hollow optical fiber, the mixed light enters a harmonic monochromatization and focusing module, the harmonic monochromatization and focusing module is used for grading the mixed light to obtain the vacuum ultraviolet light source, and the vacuum ultraviolet light source is obtained through beam combination treatment, mixing treatment and monochromatization treatment on fundamental frequency light and frequency doubling treatment. Solves the problem of limitation and high cost of the prior vacuum ultraviolet light source.
Drawings
In order to more clearly illustrate the application or the technical solutions of the prior art, the following description will briefly explain the drawings used in the embodiments or the description of the prior art, and it is obvious that the drawings in the following description are some embodiments of the application, and other drawings can be obtained according to these drawings without inventive effort for a person skilled in the art.
FIG. 1 is a schematic diagram of a vacuum ultraviolet light source generating apparatus and an application system according to the present application;
FIG. 2 is a schematic diagram of a dual-color-field fiber coupling module in a vacuum ultraviolet light source generating device provided by the application;
FIG. 3 is a schematic diagram of an optical fiber clamping and air path module in a vacuum ultraviolet light source generating device provided by the application;
fig. 4 is a schematic diagram of a harmonic monochromating and focusing module in a vacuum ultraviolet light source generating apparatus provided by the present application.
Detailed Description
For the purpose of making the objects, technical solutions and advantages of the present application more apparent, the technical solutions of the present application will be clearly and completely described below with reference to the accompanying drawings, and it is apparent that the described embodiments are some embodiments of the present application, not all embodiments. All other embodiments, which can be made by those skilled in the art based on the embodiments of the application without making any inventive effort, are intended to be within the scope of the application.
Referring to fig. 1, the vacuum ultraviolet light source generating apparatus provided in this embodiment includes a pulse laser, a frequency doubling crystal, a dual-color-field optical fiber coupling module, an optical fiber clamping and gas path module, and a harmonic monochromatization and focusing module, and the vacuum ultraviolet light source generated by the vacuum ultraviolet light source generating apparatus provided in this embodiment can be applied to an optoelectronic detecting instrument.
The pulse laser is used for outputting fundamental frequency light. The output fundamental frequency light irradiates on the frequency doubling crystal. And the frequency doubling crystal is used for converting part of the fundamental frequency light into frequency doubling light. The frequency multiplication light and the residual fundamental frequency light are collinearly transmitted to obtain parallel combined light. The parallel beam combination light enters the double-color-field optical fiber coupling module. The double-color-field optical fiber coupling module is used for sequentially carrying out beam splitting treatment, focusing treatment and beam combining treatment on the parallel beam combining light to obtain focused beam combining light.
The focused beam-combining light enters the optical fiber clamping and gas circuit module. The focus of the focused beam combining light falls on the front end face of the hollow optical fiber in the optical fiber clamping and gas circuit module, and the fundamental frequency light and the frequency doubling light are coupled into the hollow optical fiber. Under the condition that stable air pressure gradient distribution is formed inside the hollow optical fiber, the mixed beam is obtained by cascade mixing treatment after the focused combined beam passes through the hollow optical fiber. The mixed light beam enters a harmonic monochromatization and focusing module, and the harmonic monochromatization and focusing module is used for carrying out monochromatization treatment on the mixed light beam to obtain a vacuum ultraviolet light source, and focusing the vacuum ultraviolet light source on the surface of a target sample in the photoelectron detecting instrument.
According to the embodiment, parallel beam combination light is obtained by frequency doubling of fundamental frequency light output by the pulse laser, then the parallel beam combination light is subjected to beam splitting treatment, focusing treatment and beam combination treatment to obtain focused beam combination light, the focused beam combination light is coupled into the hollow fiber, and then the vacuum ultraviolet light source is obtained through cascade mixing treatment and monochromatization treatment, so that the problems of limitation and high cost of the existing generated ultraviolet light source are solved, and an application scene of the vacuum ultraviolet light source is provided.
In one embodiment, the dual-color-field optical fiber coupling module provided by the embodiment of the application comprises a beam splitter, a delay line, a reflector, a wave plate, a polaroid, a focusing lens and a beam combiner, wherein:
referring to fig. 2, the beam splitter is configured to split the fundamental frequency light and the frequency-doubled light into two beams, and in this embodiment, the fundamental frequency light is transmitted completely, and the frequency-doubled light is reflected completely; the fundamental frequency light can be totally reflected and the frequency doubling light can be totally transmitted. Fig. 2 is a diagram illustrating an example in which fundamental frequency light is transmitted entirely and frequency-multiplied light is reflected entirely. After passing through the beam splitter, the fundamental frequency light passes through the reflector 4, the reflector 5 and the reflector 6, reaches the 1/2 wave plate 1 and the polaroid 1, and then reaches the focusing lens 1. The 1/2 wave plate 1 can rotate the polarization direction of the fundamental frequency light, the polaroid 1 can transmit the fundamental frequency light with specific polarization components, and the combination of the two can enable the fundamental frequency light behind the polaroid 1 to have any polarization direction and any light intensity. In order to achieve optimal coupling of the fundamental light in the hollow fiber, the focal diameter of the fundamental light needs to be equal to the mode field diameter of the hollow fiber. Therefore, the focal length is selected Is used as the focusing lens 1, wherein MFD is the mode field diameter of the hollow fiber, +.>Is the wavelength of fundamental frequency light, < >>Is the diameter of the spot of the parallel fundamental frequency light before the focusing lens 1. In the embodiment of the application, the position of the focusing lens 1 is adjustable along the propagation direction of the fundamental frequency light, so that the optical path length of the fundamental frequency light from the focusing lens 1 to the front end face of the hollow optical fiber is equal to the focal length of the focusing lens 1, the focal point of the fundamental frequency light is located on the front end face of the hollow optical fiber, and the coupling efficiency of the hollow optical fiber is optimized. In a preferred embodiment of the application, the focusing lens 1 can be placed on a displacement stage for fine tuning in the micrometer scale.
The frequency-doubled light is reflected by the beam splitter, passes through the reflector 1, the reflector 2 and the reflector 3, reaches the 1/2 wave plate 2 and the polaroid 2, and then reaches the focusing lens 2. Wherein, the 1/2 wave plate 2 can rotate the polarization direction of the frequency doubling light,the polarizer 2 can transmit the frequency multiplication light of specific polarization components, and the two can be combined to ensure that the frequency multiplication light behind the polarizer 2 has any polarization direction and any light intensity. In order to achieve optimal coupling of the doubled light in the hollow fiber, the focal diameter of the doubled light needs to be equal to the mode field diameter of the hollow fiber. Therefore, the focal length is selected Wherein MFD is the mode field diameter of the hollow fiber, +.>For doubling the wavelength of the light, +.>Is the spot diameter of the parallel doubled light before the focusing lens 2. In the embodiment of the application, the position of the focusing lens 2 is adjustable along the propagation direction of the frequency doubling light, so that the optical path length of the frequency doubling light from the focusing lens 2 to the front end face of the hollow optical fiber is equal to the focal length of the focusing lens 2, the focal point of the frequency doubling light is located on the front end face of the hollow optical fiber, and the coupling efficiency of the hollow optical fiber is optimized. In a preferred embodiment of the application, the focusing lens 2 may be placed on a displacement stage for fine tuning in the micrometer scale.
It is worth to say that, the cascade mixing conversion efficiency in the hollow fiber is related to the relative polarization directions of the fundamental frequency light and the frequency doubling light, and when the polarization directions of the two light beams are the same, the cascade mixing conversion efficiency in the hollow fiber is the highest, and in addition, the cascade mixing conversion efficiency is related to the light intensity of the two light beams. The 1/2 wave plate 1 and the polaroid 1 on the fundamental frequency light path and the 1/2 wave plate 2 and the polaroid 2 on the frequency doubling light path are adjusted, so that the fundamental frequency light and the frequency doubling light in the hollow optical fiber have the same polarization direction, and the light intensity of the two light beams can be adjusted to optimize cascade mixing conversion efficiency.
In order to drive the cascade mixing process in the hollow fiber, the fundamental frequency light and the frequency doubling light need to be time coincident at the front end face of the hollow fiber. Neglecting the dispersion of BBO crystal, before beam splitter, the fundamental frequency light and frequency doubling light in parallel beam combining light are coincident in natural time. After the beam splitter, the two beams of light are respectively transmitted along different tracks, and after the beam splitter, the two beams of light are combined into one beam again. If the two beams of light respectively experience equal optical paths from the beam splitter to the beam combiner, the two beams of light simultaneously reach the beam combiner. After the beam combining lens, the two beams of light are used as focused beam combining light to co-linearly propagate along the same track, and the relative time delay of the two beams of light caused by the optical element passing through in the co-linear propagation process is basically negligible, so that the two beams of light are basically time-coincident on the front end face of the optical fiber. In order to make two beams of light respectively experience equal optical paths from the beam splitter to the beam combiner, in the bicolor field optical fiber coupling module, two reflectors in the optical path of one beam of light (fundamental frequency light or frequency doubling light) can be synchronously moved, and the optical path of the beam of light from the beam splitter to the beam combiner is adjusted to be equal to the optical path of the other beam of light from the beam splitter to the beam combiner, so that time superposition of the two beams of light after the beam combiner is realized, and the delay line is called. In a preferred embodiment of the application, the two mirrors can be placed on the same displacement stage to achieve fine tuning in the micrometer scale. The delay line in this embodiment may be disposed on the optical path of the fundamental frequency light, or may be disposed on the optical path of the frequency-doubled light.
Fig. 2 illustrates an example in which a delay line is provided on the optical path of the frequency-multiplied light, and the mirror 1 and the mirror 2 are placed on a displacement stage to constitute the delay line. By adjusting the displacement table, the reflector 1 and the reflector 2 synchronously move in the direction of an arrow in fig. 2, the optical path of the frequency doubling light relative to the fundamental frequency light can be adjusted, and the two light beams reach the front end face of the hollow optical fiber at the same time after being combined by the beam combining mirror, so that the cascade mixing process under the combined action of the two light beams is realized. The beam combining lens can combine two beams into one beam in a mode of transmitting fundamental frequency light and reflecting frequency doubling light; the two light beams can be combined into one light beam by transmitting the frequency doubling light and reflecting the fundamental frequency light. In the example of fig. 2, the beam combiner combines two beams into one beam by transmitting the frequency-doubled light and reflecting the fundamental frequency light as focused combined beam. After passing through the reflecting mirror 7 and the reflecting mirror 8, the focused combined light is aligned with the hollow optical fiber in the optical fiber clamping and gas path module, so that the focus of the focused combined light is on the front end surface of the hollow optical fiber.
According to the embodiment, through the arrangement and the position relation of various lenses in the double-color-field optical fiber coupling module, two beams of light can reach the front end face of the hollow optical fiber of the optical fiber clamping and gas circuit module at the same time, and the two beams of light can be respectively optimally coupled in the hollow optical fiber.
In one embodiment, the optical fiber clamping and air path module provided by the embodiment of the application comprises a hollow optical fiber, an optical fiber connector, an air inlet device, an air inlet cavity, an optical inlet window, an air exhaust cavity, a vacuum pipeline and a first air exhaust pump, wherein:
referring to fig. 3, a schematic diagram of an optical fiber clamping and air channel module according to an embodiment of the present application is shown, and an air inlet device includes a first air cylinder, a first pressure reducing valve, an air pressure controller, and a first air pipe. The gas outlet of the first gas cylinder is connected with one end of the air pressure controller through a first pressure reducing valve and a first gas pipe. The other end of the air pressure controller is connected with the air inlet cavity through a first air pipe. Preferably, the first air pipe directly connected with the air inlet cavity is a soft air pipe, so that the position of the air inlet cavity is allowed to be adjustable, and the hollow optical fiber is convenient to install. The front end of the air inlet cavity is provided with an optical window, the optical window is a flange window provided with a window sheet, and the window sheet needs to have higher transmittance for fundamental frequency light and frequency doubling light, and is preferably a fused quartz window sheet. The light inlet window may separate the air inlet cavity from the atmosphere. The front end of the hollow optical fiber is positioned at the rear end of the air inlet cavity. The focusing beam-combining light reaches the front end of the hollow optical fiber from the light inlet window through the air inlet cavity. The rear end of the hollow optical fiber is positioned in the pumping cavity. The first air pump is connected with the air suction cavity through a vacuum pipeline.
Rare gases may be utilized in hollow fiber as the nonlinear gaseous medium for the cascade mixing process. Because the nonlinear coefficient of xenon is large, the harmonic conversion efficiency is high, and the gas in the first gas cylinder is preferably xenon. In one embodiment of the application, xenon is conveyed to the front end of the hollow optical fiber through the air inlet device and the air inlet cavity, and the rear end of the hollow optical fiber is pumped through the first pumping pump, the vacuum pipeline and the pumping cavity, so that stable air pressure gradient distribution is formed inside the hollow optical fiber, and the mixed light beam is obtained through cascade mixing treatment after the focused combined light passes through the hollow optical fiber. A mixed light beam is emitted from the rear end face of the hollow fiber, and the mixed light beam contains the remaining fundamental frequency light component, frequency multiplication light component and multiple harmonics.
The two ends of the hollow optical fiber are respectively fixed in the air inlet cavity and the air pumping cavity through optical fiber connectors. Since a stable air pressure gradient distribution is formed inside the hollow optical fiber, good air tightness must be maintained between the hollow optical fiber and the air intake chamber and the air exhaust chamber. In an embodiment of the present application, optical fiber connectors are respectively installed at two ends of the hollow optical fiber, and the vacuum sealant can be used to fix and seal the hollow optical fiber and the optical fiber connectors. The vacuum sealant is arranged at the contact position of the tail end of the optical fiber connector and the hollow optical fiber, so that the light beam and the vacuum sealant are prevented from acting. The fiber connectors at the two ends of the hollow fiber are respectively arranged on the air inlet cavity and the air exhaust cavity, and sealing can be realized by using rubber rings. In a preferred embodiment of the application, the air inlet or the air outlet can be secured and sealed to the fiber optic connector by means of adapter flanges. Specifically, two flanges with matched interfaces are customized according to the type of the optical fiber connector, namely one surface of the flange is provided with a knife edge, so that the connection with an air inlet cavity or an air exhaust cavity can be realized, the sealing is realized through a copper gasket, the other surface of the flange is provided with an interface matched with the optical fiber connector, the mechanical connection with the optical fiber connector can be realized, and the sealing is realized through placing a rubber ring between the flange and the copper gasket. In a preferred embodiment of the present application, the air inlet chamber is mountable on a displacement table for movement in the direction of the hollow optical fiber to facilitate installation of the hollow optical fiber.
In one embodiment, the optical fiber clamping and gas circuit module provided by the embodiment of the application further comprises a coupling efficiency monitoring cavity. The coupling efficiency monitoring cavity is used for monitoring the coupling efficiency of the fundamental frequency light or the frequency doubling light in the hollow optical fiber. Fundamental frequency light or frequency doubling light is focused on the front end face of the hollow optical fiber, transmitted by the hollow optical fiber, and then emitted from the rear end face of the hollow optical fiber to enter the coupling efficiency monitoring cavity. A rotatable reflecting mirror is arranged in the coupling efficiency monitoring cavity. When the reflector is regulated to make the outgoing beam outgoing from the monitoring window, the optical power meter may be used to monitor the optical power of the output light, and the angle of the reflector or the position of the focusing lens in the double-color-field optical fiber coupling module may be regulated based on the output optical power to optimize the coupling efficiency of the fundamental frequency light or the frequency doubling light in the hollow optical fiber. Upon completion of the coupling efficiency adjustment, a stable air pressure gradient profile is formed inside the hollow fiber as previously described, focusing the combined light beam through the hollow fiber to produce a mixed light beam. By adjusting the rotatable mirror within the coupling efficiency monitoring cavity, the beam exiting the optical fiber can pass through the coupling efficiency monitoring cavity unobstructed to reach the harmonic monochromatization and focusing module.
In an embodiment of the present application, the fiber clamping and gas circuit module further designs a pre-air pumping device, wherein the pre-air pumping device comprises a pre-air pumping pipeline and three gas valves. The optical fiber clamping and air path module can have air in the module after the first installation is completed, or the air in the external environment can slowly leak into the module after the module stops running for a period of time. Once the air exists in the module, the air is pumped out firstly to realize a vacuum environment, and then pure xenon gas pressure gradient distribution can be obtained in the hollow optical fiber through the air inlet device and the first air pump. Without the pre-evacuation device, the first pump can only evacuate air through the hollow fiber to the air intake device and the air intake chamber other than the first air bottle, which is very slow due to the small inside diameter of the hollow fiber. The pre-air exhausting device can be used for rapidly exhausting air in the air inlet device and the air inlet cavity except the first air bottle. Under the state of opening three gas valves, the valve of the first gas cylinder is closed, the first pressure reducing valve, the air pressure controller and the first air pump are opened, the first air pump can rapidly pump air to all air inlet devices and air inlet cavities except the first gas cylinder through the pre-pumping pipeline, and the vacuum environment is rapidly realized by pumping air to the air inlet cavities through the vacuum pipeline. Under the state of closing the three gas valves, the valve of the first gas cylinder, the first pressure reducing valve, the gas pressure controller and the first air pump are opened, xenon in the first gas cylinder can enter the gas inlet cavity through the gas pressure controller, reach the air pumping cavity through the hollow optical fiber and then reach the first air pump, so that stable gas pressure gradient distribution is formed inside the hollow optical fiber. By arranging three gas valves on the pre-pumping pipeline, xenon can flow through the pre-pumping pipeline as little as possible in the state of closing the three gas valves, so that the consumption of the xenon is saved and the cost is reduced.
According to the embodiment, through the optical fiber clamping and air path module, the air pressure gradient distribution inside the hollow optical fiber is realized, after the focusing beam combining light is coupled into the hollow optical fiber, the cascade mixing process occurs through the interaction with xenon inside the hollow optical fiber, mixed light beams containing different orders of harmonic waves can be generated, and the mixed light beams are emitted from the rear end face of the hollow optical fiber and reach the harmonic monochromatization and focusing module.
In one embodiment of the application, the harmonic monochromatization and focusing module comprises a vacuum cavity, wherein a vacuum ultraviolet concave reflecting mirror, a vacuum ultraviolet plane reflecting mirror, a vacuum ultraviolet triple prism and a vacuum ultraviolet focusing lens are arranged in the vacuum cavity, and the harmonic monochromatization and focusing module further comprises a vacuum ultraviolet light inlet window, a vacuum ultraviolet light outlet window, an air cooling device, an observation window and a scintillation crystal. Wherein:
as shown in fig. 4, the harmonic monochromatization and focusing module mainly comprises a vacuum cavity, wherein a vacuum ultraviolet concave reflector (optionally an aluminum film concave reflector coated with a magnesium fluoride protective film), a vacuum ultraviolet plane reflector (optionally an aluminum film plane reflector coated with a magnesium fluoride protective film), a vacuum ultraviolet prism (optionally a lithium fluoride prism or a magnesium fluoride prism) and a vacuum ultraviolet focusing lens (optionally a lithium fluoride focusing lens or a magnesium fluoride focusing lens) are arranged in the vacuum cavity. The mixed light beam emitted from the rear end face of the hollow optical fiber is in a divergent state, and the vacuum ultraviolet concave reflecting mirror collimates the mixed light beam into a parallel state. The vacuum ultraviolet concave reflecting mirror and the vacuum ultraviolet plane reflecting mirror jointly regulate the propagation direction of the mixed light beam in front of the vacuum ultraviolet triple prism. The vacuum ultraviolet concave reflecting mirror and the vacuum ultraviolet plane reflecting mirror can be exchanged in sequence, and the mixed light beam can be collimated by the vacuum ultraviolet concave reflecting mirror and then transmitted in a specific direction by the vacuum ultraviolet plane reflecting mirror, or can be collimated by the vacuum ultraviolet plane reflecting mirror and then transmitted in the specific direction by the vacuum ultraviolet concave reflecting mirror. Regardless of the front-to-back sequence of the vacuum ultraviolet concave mirror and the vacuum ultraviolet plane mirror, the optical path from the rear end face of the hollow optical fiber to the vacuum ultraviolet concave mirror is equal to the focal length of the vacuum ultraviolet concave mirror. In fig. 4, the mixed beam passes through the vacuum ultraviolet concave mirror and then passes through the vacuum ultraviolet plane mirror. After passing through the vacuum ultraviolet triple prism, the fundamental frequency light component (omega in fig. 4), the frequency multiplication light component (2 omega in fig. 4) and the multi-order harmonic wave (3 omega-7 omega in fig. 4 represent from the third harmonic wave to the seventh harmonic wave) in the mixed light beam are emitted at different angles, so that the spatial separation is realized. It should be noted that the cascade mixing conversion efficiency is affected by various factors such as the optical power of the fundamental frequency light and the frequency-doubled light in the hollow fiber, and the air pressure gradient distribution in the hollow fiber. And, the higher the harmonic order, the lower the harmonic intensity. Depending on experimental conditions, the observable harmonic order may be lower than the seventh harmonic, or may be higher than the seventh harmonic. Under the condition of higher cascade mixing conversion efficiency, the hollow fiber can generate up to tens of orders of harmonic waves through cascade mixing, but due to the limitation of the absorption boundary of the vacuum ultraviolet triple prism, the highest order which can be observed through the vacuum ultraviolet triple prism is generally nine orders of harmonic waves.
The vacuum cavity comprises a vacuum ultraviolet light inlet window and a vacuum ultraviolet light outlet window, the vacuum ultraviolet light inlet window and the vacuum ultraviolet light outlet window are double-sided knife edge flanges provided with vacuum ultraviolet window sheets, and the vacuum ultraviolet window sheets can be lithium fluoride window sheets or magnesium fluoride window sheets. The vacuum cavity is connected with the optical fiber clamping and gas circuit module through the vacuum ultraviolet light inlet window and is connected with the application module (photoelectron detecting instrument) of the vacuum ultraviolet light source through the vacuum ultraviolet light outlet window. The vacuum ultraviolet light inlet window separates the vacuum environments of the optical fiber clamping and gas circuit module and the harmonic monochromatization and focusing module, so that the vacuum environments of the two modules are not affected; the vacuum ultraviolet light outlet window separates the vacuum environments of the harmonic monochromatization and focusing module and the application module (photoelectron detecting instrument) of the vacuum ultraviolet light source, so that the vacuum environments of the two modules are not affected.
The vacuum chamber further comprises an air cooling device. The air cooling device comprises a second air bottle, a second pressure reducing valve, a second air pipe, an air inlet valve and a second air extracting pump. The gas in the second cylinder may be nitrogen. And the second air cylinder, the second pressure reducing valve, the second air pipe and the air inlet valve are used for feeding air into the vacuum cavity, and meanwhile, the second air extracting pump is used for extracting air from the vacuum cavity, so that stable nitrogen air flow can be formed in the vacuum cavity, and the optical element in the vacuum cavity is cooled.
The vacuum chamber further comprises a viewing window and a scintillation crystal. The different orders of harmonic wave irradiated on the scintillation crystal (yttrium aluminum garnet crystal optionally doped with cerium) through the vacuum ultraviolet triple prism can generate fluorescent light spots. The shape of the fluorescent light spot reflects the cross-sectional shape of the harmonic light beam, and the relative brightness of the fluorescent light spot reflects the relative intensity of the harmonic light beam. A camera may be used to record the light spot on the scintillation crystal through the viewing window.
After passing through the vacuum ultraviolet triple prism, fundamental frequency light, frequency multiplication light and multiple order harmonic waves in the mixed light beam are emitted at different angles, and any order harmonic wave can be selected as a vacuum ultraviolet light source to be applied to an optoelectronic detecting instrument. The following is an illustration of a sixth harmonic as a vacuum ultraviolet light source for an optoelectronic probe, as shown in fig. 4. The angle formed by the propagation direction of the light beam in front of the triangular prism and the propagation direction after passing through the triangular prism is called the deflection angle, and when the deflection angle is minimum, the aberration of the light beam is minimum. Therefore, the optical path is designed so that the sixth harmonic propagates through the vacuum ultraviolet prism at a minimum deflection angle and is incident on the target sample surface in the optoelectronic probe. According to the refraction law of light, the deflection angle of the sixth harmonic wave passing through the vacuum ultraviolet triple prism has a corresponding relation with the incidence angle when the sixth harmonic wave enters the vacuum ultraviolet triple prism, wherein under a certain specific incidence angle, the deflection angle is the smallest when the sixth harmonic wave passes through the vacuum ultraviolet triple prism, and the smallest deflection angle is that . After passing through the vacuum ultraviolet triple prism, the sixth harmonic passes through the vacuum ultraviolet focusing lens. The position of the vacuum ultraviolet focusing lens along the transmission direction of the sixth harmonic is adjustable, so that the optical path of the sixth harmonic from the vacuum ultraviolet focusing lens to the surface of the target sample is equal to the focal length of the vacuum ultraviolet focusing lens aiming at the sixth harmonic, and the focal point of the sixth harmonic is located on the surface of the target sample in the photoelectron detecting instrument. In a preferred embodiment of the application, vacuum ultraviolet focusingThe lens can be arranged on a displacement table to realize micron-scale precise adjustment. Preferably, after passing through the vacuum ultraviolet triple prism, the fundamental frequency light and the frequency doubling light can be absorbed by the optical trap, and other order harmonics except for the sixth harmonic can be absorbed by the baffle 1 and the baffle 2.
Since the sixth harmonic is a vacuum ultraviolet light source, the ray track of the sixth harmonic can be traced only in a vacuum environment and by means of the scintillation crystal, which brings difficulty to the construction of the optical path. However, in this embodiment, the mixed beam passes through the vacuum ultraviolet concave mirror, the vacuum ultraviolet plane mirror and then the vacuum ultraviolet prism, so that the basic construction of the optical path can be completed in the atmospheric environment, and the operation is simple and easy. Before the vacuum ultraviolet triple prism, the mixed light beam contains frequency multiplication light components, and the frequency multiplication light is visible light, so that the propagation direction of the mixed light beam before the vacuum ultraviolet triple prism can be determined by utilizing the frequency multiplication light components in the mixed light beam. After the vacuum ultraviolet triple prism, although the sixth harmonic is spatially separated from the fundamental frequency light and the frequency-doubled light, there is a correlation in the light propagation direction thereof. When the sixth harmonic passes through the vacuum ultraviolet triple prism with the minimum deflection angle, the deflection angle of the frequency multiplication light after passing through the vacuum ultraviolet triple prism is . The propagation direction of the frequency multiplication light passing through the vacuum ultraviolet triple prism is deflected relative to the propagation direction of the mixed light beam before the vacuum ultraviolet triple prism by adjusting the position and the angle of the vacuum ultraviolet triple prismAngle, the sixth harmonic wave can pass through the vacuum ultraviolet prism and then be deflected by the minimum deflection angle +.>Propagation. Therefore, the basic adjustment of the position and angle of the vacuum ultraviolet concave reflector, the vacuum ultraviolet plane reflector and the vacuum ultraviolet triple prism can be completed in the atmosphere environment by utilizing the frequency multiplication light component in the mixed light beam. Due to unavoidable errors in the construction process of the optical path, after passing through the vacuum ultraviolet triple prism, the propagation direction and the construction of six harmonicsThere may be a slight deviation in the gauge direction. Further, the concave mirror and the planar mirror may be carefully adjusted in a vacuum environment to allow the sixth harmonic to be incident on the surface of the target sample.
According to the embodiment, different orders of harmonic waves in the mixed light beam are spatially separated through the vacuum ultraviolet triple prism, wherein any order of harmonic waves can be selected as a vacuum ultraviolet light source, the problem of limitation and high cost of the existing ultraviolet light source generation is solved, and an application scene of the ultraviolet light source is provided.
In one embodiment of the present application, the vacuum ultraviolet light source generating device and the application system provided by the present application generate an ultraviolet light source and apply the following specific implementation operation processes:
the fiber laser outputs a pulsed laser light with a wavelength of 1030nm, called fundamental frequency light. First, the fundamental frequency light passes through BBO crystal to generate frequency doubling light with wavelength of 515nm, and the frequency doubling light and the rest fundamental frequency light co-linearly propagate in parallel light state, which is called parallel beam combining light.
The parallel beam combination light enters the double-color-field optical fiber coupling module and is divided into two beams of light after passing through the beam splitter. The two light beams are respectively transmitted on the two light paths, and are combined again after the beam combining lens. On the respective light paths of the two beams, fundamental frequency light is focused by a focusing lens 1, and frequency doubling light is focused by a focusing lens 2, and then the combined beam light after the beam combining lens is focused combined beam light. In order to optimize the coupling efficiency of the optical fiber, on the one hand, the reflection mirror can be adjusted to align the fundamental frequency light and the frequency doubling light to the optical fiber, and on the other hand, the positions of the focusing lens 1 and the focusing lens 2 can be adjusted along the propagation direction of the light beam, so that the focuses of the fundamental frequency light and the frequency doubling light fall on the front end face of the hollow optical fiber. The specific operation steps are as follows: first, the fundamental frequency light is blocked, the reflecting mirror 7 and the reflecting mirror 8 are adjusted to align the frequency-doubled light to the optical fiber, the output light power is monitored by the coupling efficiency monitoring cavity to be the highest, and then the displacement table below the focusing lens 2 is adjusted to be the highest. After the adjustment of the frequency doubling optical coupling efficiency is completed, frequency doubling light is blocked, the reflector 5 and the reflector 6 are adjusted to enable the fundamental frequency light to be aligned with the optical fiber, so that the output light power is highest, and then the displacement table below the focusing lens 1 is adjusted to enable the output light power to be highest. After the hollow fiber coupling efficiency is optimized, a reflecting mirror in a coupling efficiency monitoring cavity is rotated to enable a light beam emitted from the rear end of the hollow fiber to enter a harmonic monochromatization and focusing module.
In the double-color-field optical fiber coupling module, two light beams have the same polarization direction when reaching the front end face of the hollow optical fiber and have enough light intensity to drive a cascade mixing process in the hollow optical fiber by adjusting the 1/2 wave plate 1 and the polaroid 1 on the fundamental frequency optical fiber and the 1/2 wave plate 2 and the polaroid 2 on the frequency doubling optical fiber. The reflector 1 and the reflector 2 are arranged on a displacement table to form a delay line, and the displacement table in the delay line is adjusted to enable the two beams of light to be overlapped in time after passing through the beam combining mirror. Preferably, a sum frequency BBO crystal capable of generating a frequency tripling signal by sum frequency of fundamental frequency light and frequency doubling light is placed on a collinear light path after the beam combiner, the optical axis direction of the sum frequency BBO crystal is adjusted to meet a phase matching condition, a displacement table in a delay line is adjusted, and when the frequency tripleing signal is observed, it is indicated that the time coincidence of the fundamental frequency light and the frequency doubling light is realized after the beam combiner. Because the relative time delay of the two light beams brought by the optical element passing through in the collinear propagation process of the two light beams after the beam combining lens is basically negligible, the two light beams are basically time-coincident on the front end face of the optical fiber. After the above operation is completed, the sum frequency BBO crystal is moved out of the optical path. In the subsequent operation, if the air pressure gradient distribution is realized in the optical fiber clamping and air circuit module, the fluorescent light spots generated by multi-level harmonic irradiation on the scintillation crystal can be observed in the harmonic monochromatization and focusing module, and the brightness of the fluorescent light spots can be further regulated by observing the brightness of the fluorescent light spots, so that the fluorescent light spots are brightest, and the cascade mixing conversion efficiency is enhanced by regulating the light intensity of two light beams respectively passing through the polaroid 1 and the polaroid 2 and the displacement table in the delay line. This operation will not be described in detail later.
After the operation is finished, the focused beam combination light emitted by the double-color-field optical fiber coupling module reaches the optical fiber clamping and air path module. In this embodiment, the nonlinear gas medium participating in the cascade mixing process may be xenon, i.e. the gas in the first gas cylinder may be xenon. After the optical fiber clamping and the air circuit module are installed, air exists in the module, and the air in the module should be pumped out first. The specific operation is as follows: and closing the first air bottle valve, opening the first pressure reducing valve, opening the air pressure controller, opening the three air valves, opening the first air extracting pump, and pumping out the air in the module. After the vacuum environment is realized, three gas valves are closed, a first gas bottle valve is opened, a first pressure reducing valve is opened, and a gas pressure controller is opened, so that the gas pressure at the front end of the hollow optical fiber is 1000Torr (Torr, pressure unit). The pressure at the rear end of the hollow fiber was about 0Torr due to the action of the first pump. Under the condition, stable air pressure gradient distribution is realized inside the hollow fiber, and fundamental frequency light and frequency doubling light generate cascade mixing process in the hollow fiber, generate multiple-order harmonic waves such as triple frequency and quadruple frequency … …, and output mixed light beams. The mixed light beam exits from the rear end face of the hollow fiber.
After the operation is finished, the mixed light beam output by the optical fiber clamping and air path module reaches the harmonic monochromatization and focusing module. In this module, the different order harmonics are first observed using a scintillation crystal. The specific operation is as follows:
firstly, setting up a light path in the module, enabling the mixed light beam to be collimated into a parallel state through a vacuum ultraviolet concave reflecting mirror, and enabling the mixed light beam to enter a vacuum ultraviolet triple prism according to a specific propagation direction through adjusting the vacuum ultraviolet concave reflecting mirror and a vacuum ultraviolet plane reflecting mirror. After passing through the vacuum ultraviolet triple prism, fundamental frequency light, frequency multiplication light and different orders of harmonic waves are spatially separated, and a scintillation crystal is placed in the expected propagation direction of the harmonic waves. Preferably, a rotary table can be arranged below the vacuum ultraviolet triple prism, and the vacuum ultraviolet triple prism is rotated, so that different subharmonics can be irradiated on the scintillation crystal to generate fluorescent light spots. After the light path is built, the vacuum cavity is closed. And opening a second air pump, and opening a valve, a second pressure reducing valve and an air inlet valve on the second air bottle to ensure that a certain nitrogen air flow is kept in the cavity, and cooling an optical element in the cavity so as to ensure that the transmissivity of the transmission element is stable. Preferably, a vacuum gauge may be mounted on the vacuum chamber, and the pressure is monitored by means of the vacuum gauge, and the inlet valve is adjusted so that the pressure in the chamber is about 30mbar (millibar, pressure unit). At this time, the vacuum ultraviolet triple prism is rotated, and fluorescent light spots generated by different order harmonics are observed on the scintillation crystal.
Then, the intensity and the shape of the reference light spot are selected according to the requirement, and specific order subharmonics are selected as vacuum ultraviolet light sources to be applied to an optoelectronic detecting instrument. In order to make the vacuum ultraviolet light source focus on the surface of the target sample after passing through the vacuum ultraviolet triple prism, special design and construction of the light path are needed. The following description uses the sixth harmonic wave as a vacuum ultraviolet light source of the photoelectron detecting instrument, and the specific operation is as follows:
1. the theoretical propagation direction of the sixth harmonic wave on the surface of the target sample is obtained by utilizing visible light after passing through a vacuum ultraviolet triple prism. The method comprises the following steps: and (3) independently leading a beam of visible light to strike the target sample, and placing a vacuum ultraviolet focusing lens by utilizing the beam of visible light to ensure that the visible light does not change the propagation direction after passing through the vacuum ultraviolet focusing lens and still strikes the surface of the target sample. The distance between the vacuum ultraviolet focusing lens and the surface of the target sample is approximately equal to the focal length of the vacuum ultraviolet focusing lens for the sixth harmonic. Preferably, the vacuum ultraviolet focusing lens is placed on a displacement stage, which can be adjusted during subsequent operations to bring the sixth harmonic focus to the target sample surface. Before the vacuum ultraviolet focusing lens, two scintillation crystals with through holes at the centers are used along the visible light propagation direction, wherein the diameter of each through hole is smaller than the diameter of each light spot, and the through holes are aligned to the visible light spot centers. The connecting line direction of the two through holes is the theoretical propagation direction of the sixth harmonic wave which passes through the vacuum ultraviolet triple prism and then strikes the surface of the target sample.
2. And adjusting the positions and angles of the vacuum ultraviolet concave reflecting mirror, the vacuum ultraviolet plane reflecting mirror and the vacuum ultraviolet triple prism according to the theoretical propagation direction of the light path. The specific operation is as follows: knowing the theoretical propagation direction of the sixth harmonic wave passing through the vacuum ultraviolet prism and striking on the surface of the target sample, and according to the minimum deflection angle of the sixth harmonic wave passing through the vacuum ultraviolet prismThe theoretical propagation direction of the mixed beam before it enters the vacuum ultraviolet prism can be known. By adjusting the vacuum ultraviolet concave reflector and the vacuum ultraviolet planeAnd a reflecting mirror which can enable the mixed light beam to enter the vacuum ultraviolet triple prism along the theoretical propagation direction. It is known that when the sixth harmonic is at the minimum deviation angle +.>When passing through the vacuum ultraviolet triple prism, the deflection angle of the frequency multiplication light after passing through the vacuum ultraviolet triple prism is +.>. The position and the angle of the vacuum ultraviolet triple prism are adjusted, so that the propagation direction of the frequency multiplication light passing through the vacuum ultraviolet triple prism is deviated relative to the propagation direction of the mixed light beam before the vacuum ultraviolet triple prism>The angle can lead the six harmonics to pass through the vacuum ultraviolet prism and then to be at the minimum deflection angle +.>Along the theoretical propagation direction striking the surface of the target sample. Preferably, after the vacuum ultraviolet triple prism, optical traps may be placed in the propagation directions of fundamental frequency light and frequency-doubled light, and the barriers 1 and 2 may be placed in the propagation directions of other orders except for the sixth harmonic for absorbing light beams except for the sixth harmonic.
The above operations can be completed in the atmosphere, and the difficulty in constructing the light path caused by the fact that the sixth harmonic is invisible in the atmosphere is solved. After the operation is finished, the vacuum cavity is closed, an air cooling device on the vacuum cavity is started, and the mixed light beam reaches the harmonic monochromatization and focusing module. After the mixed beam is split by the vacuum ultraviolet triple prism, six harmonics basically propagate along the theoretical propagation direction striking the surface of the target sample. Therefore, a sixth harmonic fluorescence spot will be observed on a scintillation crystal centered at a through-hole, where the diameter of the through-hole needs to be smaller than the spot diameter. Due to unavoidable errors in the light path construction process, the center of the sixth harmonic fluorescent light spot may deviate from the center of the through hole. Further, the sixth harmonic fluorescent light spot is aligned with the through holes on the two scintillation crystals by carefully adjusting the vacuum ultraviolet concave mirror and the vacuum ultraviolet planar mirror. After the above operation is completed, the two scintillation crystals are moved out of the optical path, and six harmonics are hit on the surface of the target sample. The displacement table below the vacuum ultraviolet focusing lens is adjusted, so that the sixth harmonic focus can fall on the surface of the target sample.
The apparatus embodiments described above are merely illustrative, wherein the elements illustrated as separate elements may or may not be physically separate, and the elements shown as elements may or may not be physical elements, may be located in one place, or may be distributed over a plurality of network elements. Some or all of the modules may be selected according to actual needs to achieve the purpose of the solution of this embodiment. Those of ordinary skill in the art will understand and implement the present invention without undue burden.
From the above description of the embodiments, it will be apparent to those skilled in the art that the embodiments may be implemented by means of software plus necessary general hardware platforms, or of course may be implemented by means of hardware. Based on this understanding, the foregoing technical solution may be embodied essentially or in a part contributing to the prior art in the form of a software product, which may be stored in a computer readable storage medium, such as ROM/RAM, a magnetic disk, an optical disk, etc., including several instructions for causing a computer device (which may be a personal computer, a server, or a network device, etc.) to execute the method described in the respective embodiments or some parts of the embodiments.
Finally, it should be noted that: the above embodiments are only for illustrating the technical solution of the present application, and are not limiting; although the application has been described in detail with reference to the foregoing embodiments, it will be understood by those of ordinary skill in the art that: the technical scheme described in the foregoing embodiments can be modified or some technical features thereof can be replaced by equivalents; such modifications and substitutions do not depart from the spirit and scope of the technical solutions of the embodiments of the present application.

Claims (9)

1. The utility model provides a vacuum ultraviolet light source generating device which characterized in that, vacuum ultraviolet light source generating device includes pulse laser, frequency doubling crystal, double-color field fiber coupling module, optic fibre centre gripping and gas circuit module and harmonic monochromatization and focusing module, wherein:
the pulse laser is used for outputting fundamental frequency light;
the frequency doubling crystal is used for converting a part of the fundamental frequency light into frequency doubling light, and the frequency doubling light and the rest part of the fundamental frequency light are collinearly transmitted to obtain parallel combined light;
the double-color-field optical fiber coupling module is used for sequentially carrying out beam splitting treatment, focusing treatment and beam combining treatment on the parallel beam combining light to obtain focused beam combining light, and the focus of the focused beam combining light is located on the front end face of the hollow optical fiber in the optical fiber clamping and gas circuit module;
The optical fiber clamping and air path module is used for forming stable air pressure gradient distribution in the hollow optical fiber so that the focused combined light passes through the hollow optical fiber and then is subjected to cascade mixing treatment to obtain a mixed light beam;
the harmonic monochromatization and focusing module is used for carrying out monochromatization treatment on the mixed light beam to obtain a vacuum ultraviolet light source;
the bicolor field optical fiber coupling module comprises a beam splitter, a delay line, a reflector, a wave plate, a polaroid, a focusing lens and a beam combiner, wherein:
the beam splitter is used for splitting the parallel beam combination light;
the delay line is used for adjusting the time delay amount of the fundamental frequency light and the frequency doubling light so as to enable the fundamental frequency light and the frequency doubling light to be time-coincident at the front end face of the hollow optical fiber;
the reflecting mirror is used for adjusting the propagation directions of the fundamental frequency light and the frequency doubling light;
the wave plate and the polaroid are used for adjusting the polarization direction and the light intensity of the fundamental frequency light and the frequency doubling light;
the focusing lens is used for focusing the fundamental frequency light and the frequency doubling light;
the beam combining lens is used for combining the fundamental frequency light and the frequency doubling light to obtain the focused combined light;
The optical fiber clamping and air path module comprises the hollow optical fiber, an optical fiber connector, an air inlet device, an air inlet cavity, an optical inlet window, an air exhaust cavity, a vacuum pipeline and a first air pump, wherein:
the air inlet device comprises a first air cylinder, a first pressure reducing valve, an air pressure controller and a first air pipe, wherein an air outlet of the first air cylinder is connected with one end of the air pressure controller through the first pressure reducing valve and the first air pipe, the other end of the air pressure controller is connected with the air inlet cavity through the first air pipe, and the front end of the hollow optical fiber is positioned in the air inlet cavity;
the light inlet window is used for separating the air inlet cavity from the atmospheric environment;
the first air pump is connected with the air extraction cavity through the vacuum pipeline, and the rear end of the hollow optical fiber is positioned in the air extraction cavity;
and the air inlet device and the air inlet cavity are used for introducing air to the front end of the hollow optical fiber, the first air pump, the vacuum pipeline and the air suction cavity are used for sucking air to the rear end of the hollow optical fiber, and stable air pressure gradient distribution is formed in the hollow optical fiber, so that the focused combined light passes through the hollow optical fiber to obtain the mixed light beam.
2. The vacuum ultraviolet light source generating apparatus of claim 1, wherein the fiber clamping and gas circuit module further comprises a pre-evacuation device comprising a pre-evacuation conduit and a gas valve, wherein:
in a state that the gas valve is opened, the first air pump pumps air to the air inlet device and the air inlet cavity except the first gas cylinder through the pre-pumping pipeline, and simultaneously, the first air pump pumps air to the air pumping cavity at the rear end of the hollow optical fiber through the vacuum pipeline;
and in a state of closing the gas valve, stable pressure gradient distribution is formed inside the hollow optical fiber through the gas inlet device and the first air pump.
3. The vacuum ultraviolet light source generating apparatus according to claim 2, wherein in the optical fiber clamping and air path module, a connection manner between the hollow optical fiber and the air intake chamber, and a connection manner between the hollow optical fiber and the air exhaust chamber are:
the hollow optical fiber is arranged on the optical fiber connector, and the fixing and sealing between the hollow optical fiber and the optical fiber connector are realized through vacuum sealant;
The air inlet cavity and the air exhaust cavity are connected with the optical fiber connector, and sealing between the air inlet cavity and the optical fiber connector and sealing between the air exhaust cavity and the optical fiber connector are achieved through the rubber ring.
4. The vacuum ultraviolet light source generating apparatus of claim 3, wherein the fiber clamping and gas circuit module further comprises a coupling efficiency monitoring device, wherein:
the coupling efficiency monitoring device comprises a coupling efficiency monitoring cavity and an optical power meter;
the fundamental frequency light or the frequency doubling light passing through the hollow optical fiber enters the coupling efficiency monitoring cavity, and the fundamental frequency light or the frequency doubling light is led into the optical power meter through a reflecting mirror in the coupling efficiency monitoring cavity;
measuring the optical power of the fundamental frequency light or the frequency doubling light by the optical power meter, and adjusting the coupling efficiency of the hollow optical fiber according to the optical power;
and under the condition that the coupling efficiency of the hollow optical fiber is adjusted, adjusting a reflecting mirror in the coupling efficiency monitoring cavity so that the light beam emitted from the hollow optical fiber passes through the coupling efficiency monitoring cavity to reach the harmonic monochromatization and focusing module without obstruction.
5. The vacuum ultraviolet light source generating apparatus according to claim 1, wherein the harmonic monochromating and focusing module comprises a vacuum chamber having a vacuum ultraviolet concave mirror, a vacuum ultraviolet plane mirror, a vacuum ultraviolet triple prism, and a vacuum ultraviolet focusing lens disposed therein, wherein:
collimating the mixed beam by the vacuum ultraviolet concave reflector;
the propagation direction of the mixed light beam in front of the vacuum ultraviolet triple prism is regulated through the vacuum ultraviolet concave reflecting mirror and the vacuum ultraviolet plane reflecting mirror;
the mixed light beam is divided into the fundamental frequency light, the frequency doubling light and the multi-level subharmonic by the vacuum ultraviolet triple prism;
and using one of the multiple subharmonics as the vacuum ultraviolet light source for focusing treatment through the vacuum ultraviolet focusing lens.
6. The vacuum ultraviolet light source generating apparatus of claim 5, wherein the harmonic monochromating and focusing module further comprises an air cooling device, wherein:
the air cooling device comprises a second air bottle, a second pressure reducing valve, a second air pipe, an air inlet valve and a second air extracting pump;
The second air cylinder, the second pressure reducing valve, the second air pipe and the air inlet valve are used for feeding air into the vacuum cavity, the second air extracting pump is used for extracting air from the vacuum cavity, stable air flow is formed in the vacuum cavity, and the optical element in the vacuum cavity is cooled.
7. The vacuum ultraviolet light source generating apparatus of claim 6, wherein the harmonic monochromating and focusing module further comprises a vacuum ultraviolet light-in window and a vacuum ultraviolet light-out window, wherein:
the vacuum environment of the optical fiber clamping and air path module and the harmonic monochromatization and focusing module are mutually independent through the vacuum ultraviolet light inlet window;
through the vacuum ultraviolet light outlet window, the harmonic monochromatization and focusing module and the vacuum environment of other interconnection devices are mutually independent.
8. The vacuum ultraviolet light source generating apparatus of claim 7, wherein the harmonic monochromatization and focusing module further comprises a viewing window and a scintillation crystal, wherein:
and the observation window is used for observing fluorescent light spots formed on the scintillation crystal by the irradiation of the vacuum ultraviolet light source.
9. A vacuum ultraviolet light source application system comprising a target sample, an optoelectronic detection instrument, and a vacuum ultraviolet light source generating device as claimed in any one of claims 1 to 8, the vacuum ultraviolet light source generating device generating a vacuum ultraviolet light source and focusing the vacuum ultraviolet light source on a surface of the target sample to excite photoelectrons to escape from the surface of the target sample, the escaping photoelectrons being received by a detector in the optoelectronic detection instrument.
CN202310863783.5A 2023-07-14 2023-07-14 Vacuum ultraviolet light source generating equipment and application system Active CN116598877B (en)

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