Wavelength-tunable monochromatic vacuum ultraviolet light source output device and method

Abstract

The present invention discloses a wavelength-tunable monochromatic vacuum ultraviolet light source output device and method. The present invention makes two beams of fundamental frequency light generated by a laser system obliquely incident at a small angle to the edge of a focusing lens in a frequency mixing system. The vacuum ultraviolet light generated by four-wave mixing and the residual fundamental frequency light are emitted from the focusing lens at different angles due to different refractive indices in the same medium, thereby separating the vacuum ultraviolet light from the fundamental frequency light. This design ensures the monochromaticity of the vacuum ultraviolet light source and minimizes the energy loss of the vacuum ultraviolet light source because no additional optical elements are required. When the wavelength of the vacuum ultraviolet light source needs to be changed, in addition to changing the wavelength of the fundamental frequency light, it is only necessary to adjust the distance of the lens from the center position, while the incident direction of the fundamental frequency light and the emission direction of the vacuum ultraviolet light source remain unchanged, thereby simplifying the optical path system for introducing the fundamental frequency light into the frequency mixing system, and also making the output vacuum ultraviolet light source both tunable and collimable.

Description

Technical Field

[0001] The present invention relates to a wavelength-tunable monochromatic vacuum ultraviolet light source output device and method, which realizes separation between the vacuum ultraviolet light source and other light sources by adjusting the distance that a focusing lens deviates from a central position and the wavelength of a fundamental frequency light used for four-wave mixing, thereby obtaining a monochromatic vacuum ultraviolet light source with an unchanged emission direction, tunable wavelength and minimum energy loss rate. Background Art

[0002] Since the invention of laser in 1960, it has provided an important experimental tool for the detection of atoms, molecules and free radicals in physical and chemical research due to its advantages such as high brightness, monochromaticity and collimation. At present, limited by the absorption characteristics of laser media, commercial lasers can only produce strong lasers in the visible and ultraviolet regions. However, the electronic excited states of most atoms, molecules or free radicals are located in the vacuum ultraviolet region, so the photo-induced ionization detection based on laser technology often uses multi-photon ionization in the visible light band.

[0003] Compared with single-photon ionization technology, the detection sensitivity of multi-photon ionization is extremely low. In order to improve the detection efficiency, the use of vacuum ultraviolet light source as the ionization source in experiments is the only effective solution. However, in addition to the excimer laser developed using fluorine gas discharge technology, which can produce a fixed vacuum ultraviolet light source with several special wavelengths, the only devices that can output wavelength-tunable vacuum ultraviolet light sources are large lasers such as synchrotron radiation and free electron lasers. These devices are extremely expensive, bulky, and complex in structure. In particular, free electron lasers can only serve a single experimental line station in the same time period, which greatly reduces the efficiency of the entire light source.

[0004] In view of this, general laboratories often use the optical nonlinear effect of four-wave mixing technology to generate wavelength-tunable vacuum ultraviolet light sources as ionization sources. The so-called four-wave mixing technology is an intermodulation phenomenon in nonlinear optics, in which the interaction between two or three wavelengths produces two or a new wavelength. At present, the most common nonlinear media in four-wave mixing are gases such as krypton, xenon, and mercury vapor. For example, krypton, in the electronic ground state (4p 6 ) krypton atoms are excited to an electronic excited state (4p) by absorbing two photons of 212.5 nm (ω1) through two-photon resonance. 5 5p), and then stimulated radiation to 4p under 845nm (ω2) laser induction. 5 5s, and finally transitions back to the ground state and emits 121.6nm vacuum ultraviolet light. The wavelength of the laser involved in the whole process satisfies the formula: ω VUV=2ω1-ω2, by adjusting the wavelength of ω2, a wavelength-tunable vacuum ultraviolet light source can be obtained. However, in the process of four-wave mixing, in addition to the difference frequency light 2ω1-ω2, the sum frequency light 2ω1+ω2 and the triple frequency light 3ω1 will also be generated at the same time, and the fundamental frequency lights ω1 and ω2 used for four-wave mixing will also remain. Usually, the wavelengths of the sum frequency light and the triple frequency light are in the extreme ultraviolet region and cannot pass through the focusing lens or window made of magnesium fluoride or lithium fluoride at the front end of the mixing cell, but the fundamental frequency lights ω1 and ω2 in the visible or ultraviolet band can pass through the optical components made of magnesium fluoride or lithium fluoride, resulting in the final vacuum ultraviolet light source being mixed with light sources of other bands. Summary of the invention

[0005] In view of the above-mentioned deficiencies in the prior art, the technical problem to be solved by the present invention is to provide a wavelength-tunable monochromatic vacuum ultraviolet light source output device and method.

[0006] The technical solution adopted by the present invention is:

[0007] The device of the present invention is composed of a frequency mixing system, a laser system and a detection system.

[0008] The mixing system mainly includes an adjustable mixing cell, a fixed mixing cell and a gas distribution system. A focusing lens is installed inside the adjustable mixing cell, and its position can be moved forward, backward, left and right through an external adjustment mechanism so that the fundamental frequency light falls on the edge of the focusing lens, providing the necessary conditions for preparing a monochromatic vacuum ultraviolet light source; the installation direction of the fixed mixing cell is consistent with the incident direction of the fundamental frequency light used for four-wave mixing, and the incident point of the fundamental frequency light just falls on the center of the window installed at the front end of the fixed mixing cell; the focusing lens and the window isolate the mixing system into an independent chamber, which is evacuated by the gas distribution system and the nonlinear medium gas required for four-wave mixing is transported to the independent chamber.

[0009] The laser system mainly includes a pump source, a first dye laser and a second dye laser. The laser output by the pump source is used to pump the first dye laser and the second dye laser respectively. The fundamental frequency light output by the first dye laser is frequency-doubled by a frequency-doubling crystal to generate the first laser beam ω1 required for four-wave mixing, and the laser output by the second dye laser is used as the second laser beam ω2 required for four-wave mixing. The lasers ω1 and ω2 are reflected multiple times by a high-reflection mirror, and under the action of a double convex lens, they are collinearly incident into the mixing system at the same time and focused on the same point. The lasers ω1 and ω2 are subjected to four-wave mixing or triple frequency doubling in the mixing system to generate three laser beams: 3ω1, 2ω1+ω2, and 2ω1-ω2.

[0010] The detection system mainly includes a vacuum chamber, a vacuum pump, a light source detector and an observation window. The vacuum chamber is evacuated by a vacuum pump to maintain the vacuum environment required for the transmission of the vacuum ultraviolet light source; the light source detector detects the intensity of the vacuum ultraviolet light source 2ω1-ω2 that can pass through the focusing lens; the observation window can observe whether the separated lasers ω1 and ω2 pass through the window to ensure the monochromaticity of the vacuum ultraviolet light source.

[0011] Preferably, the focusing lens is a plano-convex lens made of magnesium fluoride or lithium fluoride, and its focal length is sufficient to focus the monochromatic ultraviolet light source onto the light source detector, and effectively separate the light emitted at different refraction angles (with very small differences), so that the vacuum ultraviolet light source is confined within the light source detector, while the remaining light sources can pass through the observation window.

[0012] The window piece, the double convex lens and the observation window are made of furnace quartz.

[0013] The nonlinear medium gas is krypton gas, the laser wavelength corresponding to ω1 is 212.5 nm, and ω2 can be continuously tuned in the range of 200 to 850 nm.

[0014] The connection parts between the adjustable frequency mixing tank, the fixed frequency mixing tank and the vacuum chamber are all sealed by rubber rings to ensure the vacuum degree requirements of each part and the convenience of repeated disassembly.

[0015] The probe of the light source detector in the vacuum part is a copper metal target, and the meter head of the non-vacuum part connected to the probe is an oscilloscope.

[0016] The method for preparing a wavelength-tunable monochromatic vacuum ultraviolet light source using the above device is as follows:

[0017] The lasers ω1 and ω2 are incident at a small angle to the edge of the focusing lens in the mixing system. The vacuum ultraviolet light 2ω1-ω2 generated by four-wave mixing and the residual fundamental frequency light ω1 and ω2 are emitted from the focusing lens at different angles due to different refractive indices, realizing the separation between the vacuum ultraviolet light source and the fundamental frequency light. This design ensures the monochromaticity of the vacuum ultraviolet light source while minimizing the energy loss of the vacuum ultraviolet light source because no optical elements are required. When the wavelength of the vacuum ultraviolet light source needs to be changed, in addition to changing the wavelength of the laser ω2, it is only necessary to adjust the distance of the focusing lens from the center position (including the front and back, left and right positions). The incident direction of the fundamental frequency light ω1 and ω2 and the emission direction of the vacuum ultraviolet light source remain unchanged. This not only simplifies the optical path system for introducing the fundamental frequency light into the mixing system, but also ensures that the vacuum ultraviolet light source output by this device has both tunability and collimability.

[0018] The present invention has the following advantages and beneficial effects: the present invention does not need to add additional optical elements, and only needs to use the focusing lens used for nonlinear medium gas sealing and light beam convergence in the mixing system to split the light, thereby ensuring that the energy loss of the prepared monochromatic vacuum ultraviolet light source is reduced to a minimum; according to the wavelength of the prepared light source, the position of the focusing lens off the center is adjusted by a transmission mechanism to ensure that the incident direction of the fundamental frequency light and the emitting direction of the vacuum ultraviolet light source remain unchanged, thereby greatly simplifying the operation process of the device, and making the output monochromatic vacuum ultraviolet light source both tunable and collimable. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 It is a structural schematic diagram of the present invention, Figure 2 Schematic diagram of light splitting using a focusing lens.

[0020] Among them, 1. adjustable mixing cell, 2. fixed mixing cell, 3. gas distribution system, 4. focusing lens, 5. window, 6. nonlinear medium gas, 7. pump source, 8. first dye laser, 9. second dye laser, 10. frequency doubling crystal, 11. high reflective mirror, 12. double convex lens, 13. vacuum chamber, 14. vacuum pump, 15. light source detector, 16. observation window. DETAILED DESCRIPTION

[0021] The following is combined with Figure 1 The present invention is further described in detail with reference to the accompanying drawings and embodiments.

[0022] like Figure 1 As shown, this implementation case consists of a frequency mixing system, a laser system and a detection system.

[0023] The mixing system mainly includes an adjustable mixing cell 1, a fixed mixing cell 2 and a gas distribution system 3. A focusing lens 4 is installed inside the adjustable mixing cell 1, and its position can be moved forward, backward, left and right through an external adjustment mechanism so that the fundamental frequency light falls on the edge of the focusing lens 4, providing the necessary conditions for preparing a monochromatic vacuum ultraviolet light source; the installation direction of the fixed mixing cell 2 is consistent with the incident direction of the fundamental frequency light used for four-wave mixing, and the incident point of the fundamental frequency light just falls on the center of the window 5 installed at the front end of the fixed mixing cell 2; the focusing lens 4 and the window 5 isolate the mixing system into an independent chamber, which is evacuated by the gas distribution system 3 and the nonlinear medium gas 6 required for four-wave mixing is transported to the independent chamber.

[0024] The laser system mainly includes a pump source 7, a first dye laser 8 and a second dye laser 9. The laser light output by the pump source 7 is used to pump the first dye laser 8 and the second dye laser 9 respectively. The fundamental frequency light output by the first dye laser 8 is frequency-doubled by a frequency-doubling crystal 10 to generate the first laser beam ω1 required for four-wave mixing. The laser light output by the second dye laser 9 is used as the second laser beam ω2 required for four-wave mixing. The laser light ω1 and ω2 are reflected multiple times by a high-reflection mirror 11, and under the action of a double convex lens 12, they are collinearly incident into the mixing system at the same time and focused on the same point. The laser light ω1 and ω2 are subjected to four-wave mixing or triple frequency doubling in the mixing system to generate three laser beams: 3ω1, 2ω1+ω2, and 2ω1-ω2.

[0025] The detection system mainly includes a vacuum chamber 13, a vacuum pump 14, a light source detector 15 and an observation window 16. The vacuum chamber 13 is evacuated by the vacuum pump 14 to maintain the vacuum environment required for the transmission of the vacuum ultraviolet light source; the light source detector 15 detects the intensity of the vacuum ultraviolet light source 2ω1-ω2 that can pass through the focusing lens 4; the observation window 16 can observe whether the separated lasers ω1 and ω2 pass through the window to ensure the monochromaticity of the vacuum ultraviolet light source.

[0026] Method for outputting a tunable monochromatic vacuum ultraviolet light source using the above device:

[0027] The lasers ω1 and ω2 are incident obliquely at a small angle to the edge of the focusing lens 4 in the mixing system. The vacuum ultraviolet light 2ω1-ω2 generated by four-wave mixing and the residual fundamental frequency lights ω1 and ω2 are emitted from the focusing lens 4 at different angles due to their different refractive indices, thereby realizing the separation between the vacuum ultraviolet light source and the fundamental frequency light. This design ensures the monochromaticity of the vacuum ultraviolet light source while minimizing the energy loss of the vacuum ultraviolet light source because no optical elements need to be added. When it is necessary to change the wavelength of the vacuum ultraviolet light source, in addition to changing the wavelength of the laser ω2, it is only necessary to adjust the distance of the focusing lens 4 from the center position, and the incident direction of the fundamental frequency lights ω1 and ω2 and the emission direction of the vacuum ultraviolet light source remain unchanged. This not only simplifies the optical path system for introducing the fundamental frequency light into the mixing system, but also ensures that the vacuum ultraviolet light source output by this device has both tunability and collimability.

[0028] The specific implementation process of the present invention is as follows:

[0029] 1. Select a plano-convex thin lens (center thickness h) with a curvature radius of R and a size of 1 inch as the focusing lens. Its initial center position falls exactly on the central axis of the vacuum cavity. Set the center position of the focusing lens at the initial position as the origin, the central axis of the vacuum cavity, that is, the propagation path of the vacuum ultraviolet light after emission, as the x-axis, and the left and right adjustment axis of the focusing lens as the y-axis. For details, see Figure 2 Annotation.

[0030] 2. Select wavelength λvuv The vacuum ultraviolet light is used as the design basis of the mixing system, and the installation direction of the fixed mixing cell, that is, the angle θ between it and the central axis of the vacuum chamber, is designed as:

[0031] θ=arcsin(d y n λvuv / R)-arcsin(d y / R)

[0032] Among them, d y is the distance that the focusing lens deviates from the initial center position in the y-axis direction, n λvuv is the initially selected refractive index of vacuum ultraviolet light in the focusing lens, d y In addition to ensuring that the value is within the radius of the focusing lens, it is also necessary to leave a certain space for adjusting the position of the focusing lens on the y-axis when the wavelength of the vacuum ultraviolet light changes.

[0033] 3. When the fundamental frequency light ω1 and ω2 are incident on the mixing system at θ, the vacuum ultraviolet light beam generated by the mixing is emitted in the x-axis direction. Near the light source detector, the distance difference between the fundamental frequency light ω1 and ω2 and the center of the vacuum ultraviolet light beam is:

[0034] Δy=[h-R+(Rd y ) 1 / 2 ]tan[θ1-arcsin(d y / R)]+Ltanθ2

[0035] Where h is the center thickness of the focusing lens, θ1 = arcsin(d y n λvuv / R / n ω1,ω2 ) is the refraction angle of the fundamental frequency light at the incident surface (convex surface) of the focusing lens, θ2 = arcsin{n ω1,ω2 sin[θ1-arcsin(d y / R)]} is the refraction angle of the fundamental frequency light on the exit surface (plane) of the focusing lens, L is the initial center position, that is, the distance from the origin to the light source detector. After selecting a suitable R value, the design value of L ensures that the focus of the vacuum ultraviolet light after passing through the focusing lens is located near the position of the light source detector, and the distance difference between the fundamental frequency light ω1 and ω2 and the center of the vacuum ultraviolet light beam is sufficient to effectively separate the light emitted at different refraction angles (the difference is very small), so that the vacuum ultraviolet light source is confined within the light source detector, while the fundamental frequency light can pass through the observation window.

[0036] 4. Change the wavelength of the fundamental frequency light ω2, and the wavelength of the vacuum ultraviolet light source generated by four-wave mixing is changed from λ vuv Change to λ' vuv When the focusing lens is moved from the initial position (0, dy ) becomes (d' x ,d' y ), where, since θ remains unchanged, d' y It can be obtained by arcsin(d y n λvuv / R)-arcsin(d y / R)=arcsin(d' y n' λvuv / R)-arcsin(d' y / R) to find the numerical solution, and d' x Then:

[0037] d' x =(Rd y ) 1 / 2 -(Rd' y ) 1 / 2

[0038] When d' x When >0, the focusing lens moves along the positive direction of the x-axis, otherwise, it moves along the negative direction of the x-axis. At this time, the vacuum ultraviolet light source still emits along the x-axis, and the distance difference between the fundamental frequency light ω1 and ω'2 and the center of the vacuum ultraviolet light beam becomes:

[0039] Δy'=[h-R+(Rd' y ) 1 / 2 ]tan[θ'1-arcsin(d' y / R)]+(Ld' x )tanθ'2

[0040] θ'1=arcsin(d' y n' λvuv / R / n ω1,ω '2)

[0041] θ'2=arcsin{n ω1,ω '2sin[θ'1-arcsin(d' y / R)]}

[0042] 5. Use the observation window to observe whether the fundamental frequency light is emitted, and use the light source detector to detect the intensity of the output vacuum ultraviolet light source.

Claims

1. A wavelength tunable monochromatic vacuum ultraviolet light source output device, characterized in that: The device consists of a frequency 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); a focusing lens (4) is installed inside the adjustable frequency mixing pool (1), and its position can be moved forward and backward, left and right through an external adjustment mechanism, so that the fundamental frequency light is incident on the edge of the focusing lens (4), providing the necessary conditions for preparing a monochromatic vacuum ultraviolet light source; the installation direction of the fixed frequency mixing pool (2) is consistent with the incident direction of the fundamental frequency light used for four-wave mixing, and the incident point of the fundamental frequency light just falls on the center of the window (5) installed at the front end of the fixed frequency mixing pool (2); the focusing lens (4) and the window (5) isolate the frequency mixing system into an independent chamber, which is evacuated by the gas distribution system (3), and the nonlinear medium gas (6) required for four-wave mixing is transported to the independent chamber; The laser system mainly comprises a pump source (7), a first dye laser (8) and a second dye laser (9); the laser light output by the pump source (7) is used to pump the first dye laser (8) and the second dye laser (9) respectively; the fundamental frequency light output by the first dye laser (8) is frequency-doubled by a frequency-doubling crystal (10) to generate a first laser beam ω1 required for four-wave mixing; the laser light output by the second dye laser (9) is used as a second laser beam ω2 required for four-wave mixing; the first laser beam ω1 and the second laser beam ω2 are reflected multiple times by a high-reflection mirror (11), and under the action of a double convex lens (12), they are collinearly incident into the mixing system at the same time and focused on the same point; the laser beams ω1 and ω2 are subjected to four-wave mixing or triple frequency doubling in the mixing system to generate three laser beams: 3ω1, 2ω1+ω2, and 2ω1-ω2; The detection system mainly comprises a vacuum chamber (13), a vacuum pump (14), a light source detector (15) and an observation window (16). The vacuum chamber (13) is evacuated by the vacuum pump (14) to maintain a vacuum environment required for the transmission of a vacuum ultraviolet light source; the light source detector (15) detects the intensity of the laser light 2ω1-ω2 that can pass through the focusing lens (4), that is, the vacuum ultraviolet light source; and the observation window (16) can observe whether the separated laser light ω1 and ω2 pass through the window to ensure the monochromaticity of the vacuum ultraviolet light source.

2. The wavelength tunable monochromatic vacuum ultraviolet light source output device according to claim 1, characterized in that: The focusing lens (4) is a plano-convex lens made of magnesium fluoride or lithium fluoride.

3. The wavelength tunable monochromatic vacuum ultraviolet light source output device according to claim 1, characterized in that: The window sheet (5), the double convex lens (12) and the observation window (16) are made of furnace quartz.

4. The wavelength tunable monochromatic vacuum ultraviolet light source output device according to claim 1, characterized in that: The nonlinear medium gas (6) selected for the four-wave mixing is krypton gas, the vacuum wavelength corresponding to ω1 is 212.5 nm, and ω2 can be continuously tuned within the range of 400 to 850 nm.

5. The wavelength tunable monochromatic vacuum ultraviolet light source output device according to claim 1, characterized in that: The connecting parts between the adjustable frequency mixing tank (1), the fixed frequency mixing tank (2) and the vacuum chamber (13) are all sealed by rubber rings, thereby ensuring the vacuum requirements of each part and the convenience of repeated disassembly.

6. The wavelength tunable monochromatic vacuum ultraviolet light source output device according to claim 1, characterized in that: The probe of the light source detector (15) in the vacuum part is a copper circular metal target, and the meter head of the non-vacuum part connected to it is an oscilloscope.

7. A wavelength tunable monochromatic vacuum ultraviolet light source output method, using the device of claim 1, characterized in that: The lasers ω1 and ω2 are incident at a small angle on the edge of a focusing lens (4) in the mixing system, and the vacuum ultraviolet light 2ω1-ω2 generated by four-wave mixing and the residual fundamental frequency lights ω1 and ω2 are emitted from the focusing lens (4) at different angles due to different refractive indices, thereby achieving separation between the vacuum ultraviolet light source and the fundamental frequency light; When the wavelength of the vacuum ultraviolet light source needs to be changed, in addition to changing the wavelength of the laser ω2, it is only necessary to adjust the distance of the focusing lens (4) away from the center position, and the incident direction of the fundamental frequency light ω1 and ω2 and the emitting direction of the vacuum ultraviolet light source remain unchanged.

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