A Superfluid Helium Flow Field Visualization Optical Path System Based on Molecular Fluorescence Technology

Abstract

This invention discloses a superfluid helium flow field visualization optical path system based on molecular fluorescence technology, including a 905nm nanosecond laser, a 1073nm fiber laser, and a 1099nm fiber laser. The 1073nm fiber laser and the 1099nm fiber laser generate laser beams, which are then combined into a first beam by a first beam combiner. The laser beam generated by the 905nm nanosecond laser is deformed by a convex lens group, then redirected by a first plane mirror and combined with the first optical path by a second beam combiner to become a second beam. The second beam sequentially passes through a mechanical gate and an optical chopper, then is redirected by a second plane mirror, deformed by a concave-convex lens group and a convex-concave lens group, and finally redirected by a third plane mirror to enter a cryogenic constant-temperature cavity. The cryogenic constant-temperature cavity contains He2. * Superfluid helium in an excimer cloud generates 640nm fluorescence under the excitation of a second light beam. The fluorescence signal is captured by a high-speed camera and transmitted to a computer, enabling the measurement and calculation of the superfluid helium flow field velocity. This invention allows for higher-precision measurement and analysis of superfluid helium flow fields.

Description

Technical Field

[0001] This invention relates to the field of superfluid field visualization technology, specifically to a superfluid helium flow field visualization optical path system based on molecular fluorescence technology. Background Technology

[0002] The extremely high thermal conductivity and very low viscosity of superfluid helium make it widely used as a cooling medium in many advanced devices and large scientific installations. For example, Chinese patent document CN107965940A discloses a superfluid helium cryogenic system; Chinese patent document CN113969883A discloses a cryogenic compressor and a superfluid helium cryogenic system. However, due to the extreme ambient temperature and unique properties of superfluid helium itself, theoretical and experimental research on superfluid helium is very limited.

[0003] Flow field visualization technology, as a classic flow field measurement technique, has advantages such as non-contact, high precision, and global measurement. After decades of development, it has mature systems and methods in classical fluids, and therefore has also been applied to the study of superfluid helium flow fields.

[0004] Unlike classical fluids, superfluid helium follows Landau's two-fluid model, meaning it contains both a constant-fluid component and a superfluid component, each with its own density and velocity fields. The superfluid component is inviscid and entropy-free, while the constant-fluid component is viscous and entropy-rich. When their velocities are low, traditional flow field visualization techniques can still distinguish between them. However, as their velocities increase, mutual friction occurs, causing the superfluid helium to enter a quantum turbulent state. Numerous random quantum vortices are generated within the superfluid component, causing the constant and superfluid components to couple and become entangled. At this point, traditional flow field visualization techniques cannot distinguish between the constant and superfluid components, thus hindering high-precision measurements of the superfluid helium flow field.

[0005] Molecular fluorescence tracing of superfluid helium flow fields is a newly emerging flow field visualization technique in recent years. Its principle is based on the ionization of He atoms in superfluid helium to produce He2. * Excimer clouds are excited by lasers of specific wavelengths, causing energy level transitions. The transitioned clouds decay, generating fluorescence signals of specific wavelengths during this process. Analysis of these fluorescence signals allows for the visualization and measurement of the superfluid helium flow field. Compared to traditional flow field visualization methods, the molecular tracing method utilizes He2... * The excimer clouds have an even smaller particle size of approximately 0.1 nm, making them less susceptible to being bound by quantum vortex lines and exhibiting good following behavior towards normal fluids. Furthermore, due to the... *Excimer clouds are generated from He atoms in superfluid helium. Therefore, they also have the advantages of being pollution-free, not interfering with the flow field, and having near-neutral buoyancy, which can enable high-precision measurement of superfluid helium flow fields.

[0006] However, despite the significant advantages of molecular fluorescence tracing, current research remains limited to theoretical studies and verification of technical feasibility, lacking mature experimental protocols and supporting experimental platforms.

[0007] Therefore, there is an urgent need to develop a visualization system for superfluid helium flow fields suitable for molecular fluorescence tracing, so as to achieve high-precision measurement and analysis of superfluid helium flow fields. Summary of the Invention

[0008] This invention provides a superfluid helium flow field visualization optical path system based on molecular fluorescence technology. By using laser to excite molecular fluorescence, it is possible to achieve high-precision tracing and imaging of superfluid helium flow fields.

[0009] A superfluid helium flow field visualization optical path system based on molecular fluorescence technology includes a 905nm nanosecond laser generator, a 1073nm fiber laser generator, and a 1099nm fiber laser generator.

[0010] The 1073nm fiber laser generator and the 1099nm fiber laser generator generate fiber laser beams, which are then combined into a first beam by a first beam combiner. The laser generated by the 905nm nanosecond laser generator is deformed by a first set of cylindrical convex lenses, and then redirected by a first plane mirror and combined with the first optical path by a second beam combiner to become a second beam.

[0011] The second beam passes through a mechanical optical gate and an optical chopper in sequence, and is then turned by the second plane mirror. After being deformed by the second set of cylindrical concave and convex lens groups and the third set of cylindrical convex and concave lens groups, it is turned by the third plane mirror and enters the cryogenic constant temperature cavity.

[0012] The low-temperature constant temperature cavity contains He2 * The superfluid helium in the excimer cloud generates 640nm fluorescence under the excitation of a second beam. The movement of the fluorescence signal is captured by a high-speed camera and transmitted to a computer. The computer can perform high-precision analysis and measurement of the superfluid helium flow field characteristics based on the image data.

[0013] Furthermore, the cryogenic constant temperature cavity is filled with superfluid helium with a temperature below 2.17K.

[0014] Furthermore, the 1099nm fiber laser generator and the 1073nm fiber laser generator are controlled by a first controller; the 905nm nanosecond laser generator is controlled by a second controller; the mechanical optical gate and the optical chopper are controlled by a third controller; and the high-speed camera is controlled by a fourth controller.

[0015] The first controller, second controller, third controller, and fourth controller are all connected to a computer.

[0016] Furthermore, the cryogenic constant temperature cavity is provided with a first optical window and a second optical window; the second light beam enters the cryogenic constant temperature cavity through the first optical window, and the high-speed camera captures and photographs fluorescence signals through the second optical window.

[0017] Furthermore, the first set of cylindrical convex lenses includes a first cylindrical convex lens and a second cylindrical convex lens, and the distance between the first cylindrical convex lens and the second cylindrical convex lens is the sum of the focal lengths of the two lenses.

[0018] Furthermore, the second set of cylindrical concave and convex lens groups includes a first cylindrical concave lens and a third cylindrical convex lens, and the distance between the first cylindrical concave lens and the third cylindrical convex lens is the focal length difference between the two lenses.

[0019] Furthermore, the third set of cylindrical convex and concave lens groups includes a fourth cylindrical convex lens and a second cylindrical concave lens, and the distance between the fourth cylindrical convex lens and the second cylindrical concave lens is the focal length difference between the two lenses.

[0020] Furthermore, the nanosecond laser emitted by the 905nm nanosecond laser generator is used to excite the fluorescence signal, while the fiber laser emitted by the 1073nm fiber laser generator and the 1099nm fiber laser generator is used to delay the attenuation of the fluorescence signal.

[0021] Furthermore, the first beam becomes a circular beam after being deformed by the first set of cylindrical convex mirrors.

[0022] Furthermore, after the second beam is distorted by the second set of cylindrical concave and convex lens groups and the third set of cylindrical convex and concave lens groups, the energy density of the 905nm laser should meet the requirement of ≥2.5mJ / cm². 2 .

[0023] Compared with the prior art, the present invention has the following beneficial effects:

[0024] The superfluid helium flow field visualization optical path system provided by this invention utilizes molecular fluorescence technology, which effectively solves the problem in traditional flow field visualization techniques where tracer particles easily combine with quantum vortices in superfluid helium, thus failing to accurately reflect flow field information. The system designed in this invention can achieve higher precision superfluid helium flow field measurement. Attached Figure Description

[0025] To more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0026] Figure 1 This is a schematic diagram of the overall structure of a superfluid helium flow field visualization optical path system based on molecular fluorescence technology according to the present invention.

[0027] In the diagram: 1-1099nm fiber laser generator; 2-905nm nanosecond laser generator; 3-Second controller; 4-High-speed camera; 5-Fourth controller; 6-Computer; 7-Second cylindrical concave mirror; 8-Third cylindrical convex mirror; 9-Third controller; 10-Second beam combiner; 11-1073nm fiber laser generator; 12-First controller; 13-First beam combiner; 14-Second cylindrical convex mirror; 15-First cylindrical convex mirror; 16-Cryogenic cavity; 17-Mechanical optical gate; 18-First plane mirror; 19-Optical chopper; 20-Second plane mirror; 21-First cylindrical concave mirror; 22-Fourth cylindrical convex mirror; 23-First optical window; 24-Third plane mirror; 25-He2 * Excimer cloud; 26 - Second optical window. Detailed Implementation

[0028] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0029] like Figure 1 As shown, a superfluid helium flow field visualization optical path system based on molecular fluorescence technology includes an optical path system consisting of a 1073nm fiber laser generator 11, a 1099nm fiber laser generator 1, a 905nm nanosecond laser generator 2, a high-speed camera 4, a mechanical optical gate 17, an optical chopper 19, and a computer 6.

[0030] In the optical path system, the 1073nm fiber laser generator 11 and the 1099nm fiber laser generator 1 emit lasers under the control of the computer 6 and the first controller 12, and then the first beam combiner 13 combines them into the first beam.

[0031] In a preferred embodiment of the present invention, the 1073nm fiber laser generator 11 can have a power of 2W and a laser beam diameter of 5mm. The 1099nm fiber laser generator 1 can have a power of 3W and a laser beam diameter of 5mm.

[0032] After the 905nm nanosecond laser generator 2 emits laser light under the control of the computer 6 and the second controller 3, the laser light passes sequentially through a set of first cylindrical convex mirrors 15 and second cylindrical convex mirrors 14 with a specific focal length ratio perpendicular to the functional direction, so that the laser beam is transformed into a circular beam. After being turned by the first plane mirror 18, the laser beam is combined with the first beam by the second beam combiner 10 to form a second beam.

[0033] In a preferred embodiment of the present invention, the energy of the 905nm nanosecond laser generator 2 can be 902μJ, and the laser beam size can be 3*6mm.

[0034] In a preferred embodiment of the present invention, the first plane mirror 18 can redirect the 905nm laser by 90°.

[0035] As a preferred embodiment of the present invention, the focal length of the first cylindrical convex lens 15 can be selected as 3cm, the focal length of the second cylindrical convex lens 14 can be selected as 6cm, the laser energy loss rate is 0.48%, and the distance between the two can be selected as 9cm.

[0036] The second beam passes sequentially through the mechanical optical gate 17 and the optical chopper 19, and is then redirected by the second plane mirror 20. The optical chopper 19 and the mechanical optical gate 17 are controlled by the third controller 9 and the computer 6 to control the on / off state and frequency of the second beam.

[0037] In a preferred embodiment of the present invention, the second plane mirror 20 can redirect the second beam by 90°.

[0038] The second beam passes sequentially through a set of first cylindrical concave mirrors 21 and third cylindrical convex mirrors 8 with a specific focal length ratio and a horizontal functional direction, and a fourth cylindrical convex mirror 22 and second cylindrical concave mirrors 7 with a specific focal length ratio and a vertical functional direction, and is then deflected by a third plane mirror 24.

[0039] In a preferred embodiment of the present invention, the focal length of the first cylindrical concave mirror 21 can be selected as 10cm, the focal length of the third cylindrical convex mirror 8 can be selected as 20cm, the laser energy loss rate is 0.48%, and the distance between the two can be selected as 10cm.

[0040] In a preferred embodiment of the present invention, the focal length of the fourth cylindrical convex mirror 22 can be selected as 30cm, the focal length of the second cylindrical concave mirror 7 can be selected as 10cm, the laser energy loss rate is 0.48%, and the distance between the two can be selected as 20cm.

[0041] In a preferred embodiment of the present invention, the size of the 905nm laser beam, after continuous deformation, is 0.2*1.2cm. Considering energy loss, its energy density is:

[0042]

[0043] This value is ≥2.5 mJ / cm 2 To meet the energy requirements for activation.

[0044] In a preferred embodiment of the present invention, the third plane mirror 24 can redirect the second beam by 90°.

[0045] The second beam passes through the cryogenic cavity 16 with the first optical window 23, exciting He2 in the superfluid helium within it. * The excimer cloud 25 generates a 640nm fluorescence signal. The high-speed camera 4 captures the generated fluorescence signal through the second optical window 26, and the fourth controller 5 and computer 6 control the capture, and then feed the data back to the computer for processing and analysis.

[0046] The embodiments described above provide a detailed explanation of the technical solutions and beneficial effects of the present invention. It should be understood that the above descriptions are merely specific embodiments of the present invention and are not intended to limit the present invention. Any modifications, additions, and equivalent substitutions made within the scope of the principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A superfluid helium flow field visualization optical path system based on molecular fluorescence technology, characterized in that, Including a 905nm nanosecond laser generator (2), a 1073nm fiber laser generator (11), and a 1099nm fiber laser generator (1); The 1073nm fiber laser generator (11) and the 1099nm fiber laser generator (1) generate fiber laser beams, which are then combined into a first beam by a first beam combiner (13); the laser generated by the 905nm nanosecond laser generator (2) is deformed by a first set of cylindrical convex lenses, and then turned by a first plane mirror (18) and combined with the first optical path by a second beam combiner (10) to become a second beam. The second beam passes through the mechanical light gate (17) and the optical chopper (19) in sequence, and is then turned by the second plane mirror (20) and deformed by the second set of cylindrical concave and convex lens groups and the third set of cylindrical convex and concave lens groups in sequence, before being turned by the third plane mirror (24) and entering the low temperature constant temperature cavity (16). The cryogenic constant temperature cavity (16) contains He2 * The superfluid helium of the excimer cloud (25) generates 640nm fluorescence under the excitation of the second beam. The movement of the fluorescence signal is captured by a high-speed camera (4) and transmitted to a computer (6). The computer (6) performs high-precision analysis and measurement of the superfluid helium flow field characteristics based on the image data.

2. The superfluid helium flow field visualization optical path system based on molecular fluorescence technology according to claim 1, characterized in that, The 1099nm fiber laser generator (1) and the 1073nm fiber laser generator (11) are controlled by the first controller (12); the 905nm nanosecond laser generator (2) is controlled by the second controller (3); the mechanical optical gate (17) and the optical chopper (19) are controlled by the third controller (9); and the high-speed camera (4) is controlled by the fourth controller (5). The first controller (12), the second controller (3), the third controller (9) and the fourth controller (5) are all connected to the computer (6).

3. The superfluid helium flow field visualization optical path system based on molecular fluorescence technology according to claim 1, characterized in that, The low-temperature constant temperature cavity (16) is provided with a first optical window (23) and a second optical window (26); the second beam enters the low-temperature constant temperature cavity (16) through the first optical window (23), and the high-speed camera (4) captures and photographs the fluorescence signal through the second optical window (26).

4. The superfluid helium flow field visualization optical path system based on molecular fluorescence technology according to claim 1, characterized in that, The first set of cylindrical convex lenses includes a first cylindrical convex lens (15) and a second cylindrical convex lens (14), and the distance between the first cylindrical convex lens (15) and the second cylindrical convex lens (14) is the sum of the focal lengths of the two lenses.

5. The superfluid helium flow field visualization optical path system based on molecular fluorescence technology according to claim 1, characterized in that, The second set of cylindrical concave and convex lens groups includes a first cylindrical concave lens (21) and a third cylindrical convex lens (8), and the distance between the first cylindrical concave lens (21) and the third cylindrical convex lens (8) is the focal length difference between the two lenses.

6. The superfluid helium flow field visualization optical path system based on molecular fluorescence technology according to claim 1, characterized in that, The third set of cylindrical convex and concave lens groups includes a fourth cylindrical convex lens (22) and a second cylindrical concave lens (7), and the distance between the fourth cylindrical convex lens (22) and the second cylindrical concave lens (7) is the focal length difference between the two lenses.

7. The superfluid helium flow field visualization optical path system based on molecular fluorescence technology according to claim 1, characterized in that, The nanosecond laser emitted by the 905nm nanosecond laser generator (2) is used to excite the fluorescence signal, and the fiber laser emitted by the 1073nm fiber laser generator (11) and the 1099nm fiber laser generator (1) is used to delay the decay of the fluorescence signal.

8. The superfluid helium flow field visualization optical path system based on molecular fluorescence technology according to claim 1, characterized in that, The first beam becomes a circular beam after being deformed by the first set of cylindrical convex mirrors.

9. The superfluid helium flow field visualization optical path system based on molecular fluorescence technology according to claim 1, characterized in that, After the second beam is distorted by the second set of cylindrical concave and convex lenses and the third set of cylindrical convex and concave lenses, the energy density of the 905nm laser should meet the requirement of ≥2.5mJ / cm². 2 .

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