阅读说明：本技术 波长可调谐的单色真空紫外光源输出装置及方法 (Wavelength-tunable monochromatic vacuum ultraviolet light source output device and method ) 是由 俞盛锐 李万涛 凌彩宁 杨文绍 简继文 于 2020-07-09 设计创作，主要内容包括：本发明公开了一种波长可调谐的单色真空紫外光源输出装置及方法。本发明将激光系统产生的两束基频光以小角度斜入射至混频系统中的聚焦透镜的边缘,四波混频产生的真空紫外光及残留的基频光因在同一介质中的折射率不同而以不同角度从聚焦透镜中出射,从而将真空紫外光与基频光进行分离,此设计在保证真空紫外光源单色性的同时,因无需增加额外的光学元件而使真空紫外光源的能量损耗降至最小；当需要改变真空紫外光源波长之时,除改变基频光的波长之外,只需调节透镜偏离中心位置的距离,而基频光的入射方向及真空紫外光源的出射方向始终不变,从而简化了将基频光引入混频系统的光路系统,也使所输出的真空紫外光源兼具可调谐性及可准直性。(The invention discloses a wavelength tunable monochromatic vacuum ultraviolet light source output device and method. Two beams of fundamental frequency light generated by a laser system are obliquely incident to the edge of a focusing lens in a frequency mixing system at a small angle, vacuum ultraviolet light generated by four-wave frequency mixing and residual fundamental frequency light are emitted from the focusing lens at different angles due to different refractive indexes in the same medium, so that the vacuum ultraviolet light is separated from the fundamental frequency light, and the design ensures the monochromaticity of the vacuum ultraviolet light source and simultaneously reduces the energy loss of the vacuum ultraviolet light source to the minimum due to no need of adding additional optical elements; when the wavelength of the vacuum ultraviolet light source needs to be changed, the distance of the lens from the center position is only needed to be adjusted except for changing the wavelength of the fundamental frequency light, and the incident direction of the fundamental frequency light and the emergent direction of the vacuum ultraviolet light source are always unchanged, so that the introduction of the fundamental frequency light into a light path system of the frequency mixing system is simplified, and the output vacuum ultraviolet light source has tunability and collimation.)

1. The monochromatic vacuum ultraviolet light source output device with tunable wavelength is characterized by comprising a mixing system, a laser system and a detection system;

the frequency mixing system mainly comprises an adjustable frequency mixing pool (1), a fixed frequency mixing pool (2) and a gas distribution system (3), wherein a focusing lens (4) is arranged in the adjustable frequency mixing pool (1), and the position of the focusing lens (4) can be moved back and forth and left and right through an external adjusting mechanism, so that fundamental frequency light is incident to the edge of the focusing lens (4), and necessary conditions are provided for preparing a monochromatic vacuum ultraviolet light source; the installation direction of the fixed mixing pool (2) is consistent with the incidence direction of the fundamental frequency light for four-wave mixing, and the incidence point of the fundamental frequency light just falls in the center of a window sheet (5) arranged at the front end of the fixed mixing pool (2); the focusing lens (4) and the window sheet (5) separate the frequency mixing system into an independent chamber, the gas distribution system (3) vacuumizes the independent chamber, and nonlinear medium gas (6) required by four-wave frequency mixing is conveyed to the independent chamber;

the laser system mainly comprises a pumping source (7), a first dye laser (8) and a second dye laser (9), wherein laser output by the pumping source (7) is respectively used for pumping the first dye laser (8) and the second dye laser (9); fundamental frequency light output by the first dye laser (8) is frequency-doubled by the frequency doubling crystal (10) to generate a first laser beam omega required by four-wave mixing₁The laser light output by the second dye laser (9) is used as the second laser light omega required by four-wave mixing₂(ii) a First beam of laser light omega₁With a second laser beam omega₂The light is reflected for many times by a high-reflection mirror (11), and is collinearly incident into the mixing system at the same time under the action of a double-convex lens (12) and is focused at the same point; laser omega₁And omega₂Generating three beams of laser light via four-wave mixing or frequency tripling in a mixing system: 3 omega₁，2ω₁+ω₂，2ω₁-ω₂；

The detection system mainly comprises a vacuum cavity (13), a vacuum pump (14), a light source detector (15) and an observation window (16), wherein the vacuum cavity (13) is vacuumized by the vacuum pump (14) to maintain a vacuum environment required by vacuum ultraviolet light source transmission; the light source detector (15) can transmit the laser 2 omega of the focusing lens (4)₁-ω₂Namely, the intensity of the vacuum ultraviolet light source is detected; the observation window (16) can observe the separated laser omega₁And ω₂Whether the light penetrates through the window or not ensures the monochromaticity of the vacuum ultraviolet light source.

2. The output device of claim 1, wherein the focusing lens (4) is a plano-convex lens made of magnesium fluoride or lithium fluoride.

3. The output device of claim 1, wherein the window plate (5), the lenticular lens (12) and the viewing window (16) are made of fused silica.

4. A wavelength tunable monochromatic vacuum ultraviolet light source output device according to claim 1, characterized in that the nonlinear dielectric gas (6) selected by the four-wave mixing is krypton, ω₁The corresponding vacuum wavelength is 212.5nm, omega₂Can be continuously tunable within the range of 400-850 nm.

5. The output device of the monochromatic vacuum ultraviolet light source with tunable wavelength as claimed in claim 1, wherein the linking portions between the adjustable mixing tank (1) and the fixed mixing tank (2) and between the adjustable mixing tank and the vacuum chamber (13) are sealed by rubber rings, so as to ensure the vacuum degree requirement of each portion and the convenience of repeated disassembly.

6. The output device of the monochromatic vacuum ultraviolet light source with tunable wavelength as claimed in claim 1, wherein the probe of the light source detector (15) in the vacuum part is a round metal target made of copper, and the head of the non-vacuum part connected with the probe is an oscilloscope.

7. The method for outputting the monochromatic vacuum ultraviolet light source with tunable wavelength adopts the device of claim 1, and is characterized in that:

laser omega₁And omega₂The vacuum ultraviolet light 2 omega generated by four-wave mixing is obliquely incident to the edge of a focusing lens (4) in the mixing system at a small angle₁-ω₂And residual fundamental frequency light omega₁、ω₂The light is emitted from the focusing lens (4) at different angles due to different refractive indexes, so that the separation between the vacuum ultraviolet light source and the fundamental frequency light is realized;

when the wavelength of the vacuum ultraviolet light source needs to be changed, the laser omega is changed₂Only the distance of the focusing lens (4) from the center position needs to be adjusted, and the fundamental frequency light omega₁And omega₂The incident direction of the vacuum ultraviolet light source and the emergent direction of the vacuum ultraviolet light source are always unchanged.

Technical Field

The invention relates to a wavelength tunable monochromatic vacuum ultraviolet light source output device and method, which realize the separation between a vacuum ultraviolet light source and other light sources by adjusting the distance of a focusing lens from the center position and the wavelength of fundamental frequency light for four-wave mixing, thereby obtaining the monochromatic vacuum ultraviolet light source with unchanged emergent direction, tunable wavelength and minimum energy loss rate.

Background

Since the invention of laser in 1960, the advantages of high brightness, monochromaticity, collimation and the like provide an important experimental tool for detecting atoms, molecules and free radicals in physicochemical research. At present, commercial lasers can only generate stronger laser light in the visible and ultraviolet regions, limited by the influence of the absorption characteristics of the laser medium. However, most of the electron excited states of atoms, molecules or radicals are located in the vacuum ultraviolet region, and therefore, the photoexcited ionization detection based on the laser technique often employs multiphoton ionization in the visible light band.

Compared with the single photon ionization technology, the multi-photon ionization detection sensitivity is extremely low, and in order to improve the detection efficiency, the experimental adoption of a vacuum ultraviolet light source as an ionization source is the only effective solution. However, in addition to excimer lasers developed by fluorine discharge technology that can generate several fixed vacuum ultraviolet light sources of specific wavelengths, devices that can output wavelength tunable vacuum ultraviolet light sources are only large lasers such as synchrotron radiation and free electron lasers. These devices are extremely expensive, bulky and complex in construction, and in particular the free electron laser can only serve a single experimental line station in the same time period, resulting in a considerable loss of efficiency of use of the whole light source.

In view of this, the ordinary laboratory often produces the wavelength tunable vacuum ultraviolet light source as the ionization source by means of the optical nonlinear effect of four-wave mixing technology. The so-called four-wave mixing technique is an intermodulation phenomenon in nonlinear optics, in which the interaction between two or three wavelengths produces two or one new wavelength. Currently, the most common of four-wave mixingThe non-linear medium is krypton gas, xenon gas, mercury vapor and the like. E.g. krypton, in the electronic ground state (4 p)⁶) Absorbs two 212.5nm (omega) krypton atoms by two-photon resonance₁) Is then excited to the electronic excited state (4 p)⁵5p) and then at 845nm (ω)₂) Stimulated radiation to 4p under laser induction⁵And (3) a certain virtual state near 5s finally transits to the ground state and emits vacuum ultraviolet light with the wavelength of 121.6nm, wherein the wavelength of the laser related in the whole process meets the formula: omega_VUV＝2ω₁-ω₂By adjusting omega₂The wavelength of the vacuum ultraviolet light source can be tunable. However, in the four-wave mixing process, the difference frequency light 2 ω is removed₁-ω₂Outside, sum frequency light 2 omega₁+ω₂ Triple frequency light 3 omega₁Also simultaneously generating fundamental frequency light omega for four-wave mixing₁And ω₂May remain. In general, the wavelengths of the sum-frequency light and the triple-frequency light are in the extreme ultraviolet region, and cannot pass through a focusing lens or a window made of magnesium fluoride or lithium fluoride at the front end of the mixing cell, but the fundamental frequency light ω in the visible light or ultraviolet band is not transmitted through the focusing lens or the window₁And ω₂But can transmit the optical element made of magnesium fluoride or lithium fluoride, so that the finally prepared vacuum ultraviolet light source is mixed with light sources in other wave bands.

Disclosure of Invention

Aiming at the defects in the prior art, the technical problem to be solved by the invention is to provide a monochromatic vacuum ultraviolet light source output device with tunable wavelength and a method thereof.

The technical scheme adopted by the invention is as follows:

the device of the invention consists of a frequency mixing system, a laser system and a detection system.

The frequency mixing system mainly comprises an adjustable frequency mixing pool, a fixed frequency mixing pool and a gas distribution system, wherein a focusing lens is arranged in the adjustable frequency mixing pool, and the position of the focusing lens can be moved back and forth and left and right through an external adjusting mechanism, so that the fundamental frequency light falls on the edge of the focusing lens, and necessary conditions are provided for preparing a monochromatic vacuum ultraviolet light source; the installation direction of the fixed mixing pool is consistent with the incidence direction of the fundamental frequency light for four-wave mixing, and the incidence point of the fundamental frequency light just falls in the center of a window sheet installed at the front end of the fixed mixing pool; the focusing lens and the window plate separate the frequency mixing system into an independent chamber, the independent chamber is vacuumized by the gas distribution system, and nonlinear medium gas required by four-wave frequency mixing is conveyed to the independent chamber.

The laser system mainly comprises a pumping source, a first dye laser and a second dye laser, wherein lasers output by the pumping source are respectively used for pumping the first dye laser and the second dye laser; fundamental frequency light output by the first dye laser generates a first laser beam omega required by four-wave mixing after frequency multiplication by the frequency multiplication crystal₁The laser light output by the second dye laser is used as the second laser light omega required by four-wave mixing₂(ii) a Laser omega₁And omega₂The light is reflected for multiple times by a high-reflection mirror and is collinearly incident into the frequency mixing system at the same time under the action of the double-convex lens and is focused on the same point; laser omega₁And omega₂Generating three beams of laser light via four-wave mixing or frequency tripling in a mixing system: 3 omega₁，2ω₁+ω₂，2ω₁-ω₂。

The detection system mainly comprises a vacuum cavity, a vacuum pump, a light source detector and an observation window, wherein the vacuum cavity is vacuumized by the vacuum pump to maintain a vacuum environment required by vacuum ultraviolet light source transmission; light source detector can be passed through focusing lens's vacuum ultraviolet light source 2 omega₁-ω₂Detecting the intensity of (c); the observation window can observe the separated laser omega₁And ω₂Whether the light penetrates through the window or not ensures the monochromaticity of the vacuum ultraviolet light source.

Preferably, the focusing lens is a plano-convex lens made of magnesium fluoride or lithium fluoride, and the focal length of the plano-convex lens is enough to focus the monochromatic ultraviolet light source to the light source detector, and effectively separate the light emitted at different refraction angles (with little difference), so that the vacuum ultraviolet light source is bound in the light source detector, and the rest light sources can penetrate through the observation window.

The window sheet, the biconvex lens and the observation window are made of melting furnace quartz.

The nonlinear medium gas is krypton gas,ω₁the corresponding laser wavelength is 212.5nm, omega₂Can be continuously tunable within the range of 200-850 nm.

The adjustable mixing tank, the fixed mixing tank and the connecting part between the adjustable mixing tank and the vacuum cavity are sealed by rubber rings, so that the vacuum degree requirement of each part and the convenience of repeated disassembly are ensured.

The probe of the light source detector on the vacuum part is a metal target made of copper, and the gauge outfit of the non-vacuum part connected with the probe is an oscilloscope.

The method for preparing the monochromatic vacuum ultraviolet light source with tunable wavelength by using the device comprises the following steps:

laser omega₁And omega₂The vacuum ultraviolet light 2 omega generated by four-wave mixing is obliquely incident to the edge of a focusing lens in a mixing system at a small angle₁-ω₂And residual fundamental frequency light omega₁、ω₂The light source is emitted from the focusing lens at different angles due to different refractive indexes, so that the separation between the vacuum ultraviolet light source and the fundamental frequency light is realized, and the energy loss of the vacuum ultraviolet light source is minimum due to no need of adding optical elements while the monochromaticity of the vacuum ultraviolet light source is ensured. When the wavelength of the vacuum ultraviolet light source needs to be changed, the laser omega is changed₂In addition to the wavelength of (a), only the distance (including the front and back and left and right positions) of the focusing lens from the center position needs to be adjusted, and the fundamental frequency light omega₁And omega₂The incident direction and the emergent direction of the vacuum ultraviolet light source are always unchanged, so that the light path system for introducing the fundamental frequency light into the mixing system is simplified, and the vacuum ultraviolet light source output by the device is ensured to have tunability and collimation.

The invention has the following advantages and beneficial effects: according to the invention, no additional optical element is needed, and only a focusing lens used for nonlinear medium gas sealing and light beam convergence in a frequency mixing system is used for light splitting, so that the energy loss of the prepared monochromatic vacuum ultraviolet light source is reduced to the minimum; according to the wavelength of the prepared light source, the position of the focusing lens deviating from the center is adjusted by using the transmission mechanism, the incident direction of the fundamental frequency light and the emergent direction of the vacuum ultraviolet light source are ensured to be invariable all the time, the operation process of the device is greatly simplified, and the output monochromatic vacuum ultraviolet light source has tunability and collimation.

Drawings

Fig. 1 is a schematic structural diagram of the present invention, and fig. 2 is a schematic diagram of light splitting by using a focusing lens.

The device comprises an adjustable mixing pool, a fixed mixing pool, a gas distribution system, a focusing lens, a window 5, a window 6, nonlinear medium gas 7, a pumping source 8, a first dye laser 9, a second dye laser 10, a frequency doubling crystal 11, a high-reflection mirror 12, a biconvex lens 13, a vacuum cavity 14, a vacuum pump 15, a light source detector 16 and an observation window.

Detailed Description

The present invention will be described in further detail with reference to the accompanying fig. 1 and the embodiments.

As shown in fig. 1, the present embodiment is composed of a mixing system, a laser system and a detection system.

The frequency mixing system mainly comprises an adjustable frequency mixing pool 1, a fixed frequency mixing pool 2 and a gas distribution system 3, wherein a focusing lens 4 is arranged in the adjustable frequency mixing pool 1, and the position of the focusing lens 4 can be moved back and forth and left and right through an external adjusting mechanism, so that the fundamental frequency light falls on the edge of the focusing lens 4, and necessary conditions are provided for preparing a monochromatic vacuum ultraviolet light source; the installation direction of the fixed mixing pool 2 is consistent with the incidence direction of the fundamental frequency light for four-wave mixing, and the incidence point of the fundamental frequency light just falls in the center of a window 5 arranged at the front end of the fixed mixing pool 2; the focusing lens 4 and the window 5 separate the mixing system into a single chamber, which is evacuated by the gas distribution system 3 and supplied with the nonlinear medium gas 6 required for four-wave mixing.

The laser system mainly comprises a pumping source 7, a first dye laser 8 and a second dye laser 9, wherein laser output by the pumping source 7 is respectively used for pumping the first dye laser 8 and the second dye laser 9; fundamental frequency light output by the first dye laser 8 is frequency-doubled by the frequency doubling crystal 10 to generate a first laser beam omega required by four-wave mixing₁The laser light output from the second dye laser 9 is used as the second laser light for four-wave mixingω₂(ii) a Laser omega₁And omega₂The light is reflected for multiple times by a high-reflection mirror 11, and is collinearly incident into the frequency mixing system at the same time under the action of a double-convex lens 12 and is focused at the same point; laser omega₁And omega₂Generating three beams of laser light via four-wave mixing or frequency tripling in a mixing system: 3 omega₁，2ω₁+ω₂，2ω₁-ω₂。

The detection system mainly comprises a vacuum cavity 13, a vacuum pump 14, a light source detector 15 and an observation window 16, wherein the vacuum cavity 13 is vacuumized by the vacuum pump 14 to maintain a vacuum environment required by vacuum ultraviolet light source transmission; the light source detector 15 can transmit the vacuum ultraviolet light source 2 omega of the focusing lens 4₁-ω₂Detecting the intensity of (c); the observation window 16 can observe the separated laser omega₁And ω₂Whether the light penetrates through the window or not ensures the monochromaticity of the vacuum ultraviolet light source.

The method for outputting the tunable monochromatic vacuum ultraviolet light source by using the device comprises the following steps:

laser omega₁And omega₂The vacuum ultraviolet light 2 omega generated by four-wave mixing is obliquely incident to the edge of a focusing lens 4 in the mixing system at a small angle₁-ω₂And residual fundamental frequency light omega₁、ω₂The light is emitted from the focusing lens 4 at different angles due to different refractive indexes, so that the separation between the vacuum ultraviolet light source and the fundamental frequency light is realized, and the energy loss of the vacuum ultraviolet light source is minimum due to no need of adding optical elements while the monochromaticity of the vacuum ultraviolet light source is ensured; when the wavelength of the vacuum ultraviolet light source needs to be changed, the laser omega is changed₂Only the distance of the focusing lens 4 from the center position needs to be adjusted, and the fundamental frequency light omega₁And omega₂The incident direction and the emergent direction of the vacuum ultraviolet light source are always unchanged, so that the light path system for introducing the fundamental frequency light into the mixing system is simplified, and the vacuum ultraviolet light source output by the device is ensured to have tunability and collimation.

The specific implementation operation process of the invention is as follows:

1. a plano-convex thin lens (center thickness h) with the curvature radius of R and the size of 1 inch is selected as a focusing lens, the initial center position of the plano-convex thin lens is just on the central axis of the vacuum cavity, the central position of the focusing lens at the initial position is set as the origin, the central axis of the vacuum cavity, namely the propagation path after the vacuum ultraviolet light is emitted, is set as the x axis, and the left and right adjusting axes of the focusing lens are set as the y axis, which is specifically shown in the figure 2.

2. Selecting wavelength as lambda_vuvThe vacuum ultraviolet light as the design benchmark of mixing system, the installation direction of fixed mixing pool, the included angle theta between it and the vacuum cavity center axis is designed as follows:

θ＝arcsin(d_yn_λvuv/R)-arcsin(d_y/R)

wherein d is_yThe distance of the focusing lens from the initial center position in the y-axis direction, n_λvuvRefractive index of the vacuum ultraviolet light in the focusing lens initially selected, d_yThe value of (1) not only ensures that a certain space is reserved for the position adjustment of the focusing lens on the y axis when the vacuum ultraviolet wavelength is changed within and outside the radius range of the focusing lens.

3. When fundamental frequency light omega₁And omega₂The light beam of the vacuum ultraviolet light generated by mixing is emitted in the direction of the x axis when the light beam is incident to the mixing system by theta, and the fundamental frequency light omega is near the light source detector₁And omega₂The difference in distance from the beam center of the vacuum ultraviolet light is:

Δy＝[h-R+(R-d_y)^1/2]tan[θ₁-arcsin(d_y/R)]+Ltanθ₂

where h is the center thickness of the focusing lens, θ₁＝arcsin(d_yn_λvuv/R/n_ω1,ω2) Is the refraction angle of the fundamental frequency light on the incident surface (convex surface) of the focusing lens, theta₂＝arcsin{n_ω1,ω2sin[θ₁-arcsin(d_y/R)]The refraction angle of the fundamental frequency light on the exit surface (plane) of the focusing lens, L is the initial central position, namely the distance between the origin and the light source detector, after a proper R value is selected, the design value of L ensures that the focus of the vacuum ultraviolet light passing through the focusing lens is positioned near the position of the light source detector, and the fundamental frequency light omega is₁And omega₂The difference in distance from the center of the beam of vacuum ultraviolet light is sufficient to effectively separate light exiting at different (minimally different) refraction angles, such that the vacuum ultraviolet light source is confined within the light source detector and the fundamental frequency light is transmitted through the viewing window.

4. Changing fundamental frequency light omega₂Wavelength of vacuum ultraviolet light source generated by four-wave mixing of light of wavelength λ_vuvIs changed to lambda'_vuvThen, the position of the focusing lens is changed from the initial position (0, d)_y) Become (d'_x,d'_y) Wherein d 'since θ remains constant'_yCan be composed of arcsin (d)_yn_λvuv/R)-arcsin(d_y/R)＝arcsin(d'_yn'_λvuv/R)-arcsin(d'_y/R) obtaining a numerical solution, and d'_xThen it is:

d'_x＝(R-d_y)^1/2-(R-d'_y)^1/2

when d'_x>When 0, the focusing lens moves along the positive direction of the x axis, otherwise, the focusing lens moves along the negative direction of the x axis, at the moment, the vacuum ultraviolet light source still emits along the x axis, and the fundamental frequency light omega₁And ω'₂The difference in distance from the beam center of the vacuum ultraviolet light becomes:

Δy'＝[h-R+(R-d'_y)^1/2]tan[θ'₁-arcsin(d'_y/R)]+(L-d'_x)tanθ'₂

θ'₁＝arcsin(d'_yn'_λvuv/R/n_ω1,ω'₂)

θ'₂＝arcsin{n_ω1,ω'₂sin[θ'₁-arcsin(d'_y/R)]}

5. and observing whether the fundamental frequency light is emitted or not by using an observation window, and detecting the intensity of the output vacuum ultraviolet light source by using a light source detector.