A semi-confocal lens, two-photon laser-induced fluorescence system and application

Abstract

The application discloses a kind of semi-confocal lens, two-photon laser-induced fluorescence system and application, the semi-confocal lens includes inner lens and outer lens;Wherein, inner lens is embedded in the middle of outer lens;The mirror surface diameter of the inner lens is 10-20mm, and focal length is 250-350mm;The mirror surface diameter of the outer lens is 80-120mm, and focal length is 310-450mm.Two-photon laser-induced fluorescence system includes laser, and after laser is reflected by laser reflector, it is focused at the focal point of the inner lens of semi-confocal lens, after two photons are absorbed in the atom of focusing place, transition to higher energy level, then de-excitation and emit photon produce fluorescence, and the fluorescence produced is received by the outer lens of semi-confocal lens, and after being reflected by fluorescence reflector, it is focused by focusing lens and received by photomultiplier tube.The application also provides a kind of two-photon laser-induced fluorescence system in strong background two-photon absorption laser-induced fluorescence hydrogen atom neutral gas density measurement application.

Description

Technical Field

[0001] This invention belongs to the field of laser-induced fluorescence, and particularly relates to a semi-confocal lens for fluorescence detection in high-temperature plasma environments, a two-photon laser-induced fluorescence system, and their applications. Background Technology

[0002] Boundary neutral particles play a crucial role in tokamaks. They directly influence tokamak operation and plasma confinement: neutral particles are important for LH mode transitions and sump formation; they affect ion flow and ion flow shear near the outermost closed magnetic surface; they act as particle sources entering the sump region and even the plasma core; they participate in plasma momentum transport and charge exchange friction effects; and neutral particle studies can provide important parameters for physical processes such as wall material recycling and divertor de-targeting. However, despite their important role, there are currently no effective methods for neutral particle diagnostics. The fast ionization gauge is a method currently used to measure neutral particle density and temperature in high-temperature hydrogen plasmas, but it is susceptible to perturbations in the neutral particle density profile, making it difficult to obtain accurate local neutral particle temperature and density information.

[0003] Two-photon laser-induced fluorescence (TALIF) utilizes two photons to excite ground-state hydrogen atoms, and then diagnoses hydrogen atom parameters by measuring their fluorescence. In principle, TALIF can measure the density, temperature, directional velocity, and magnetic field information of neutral hydrogen atoms. Currently, this diagnostic system is widely used in linear devices for measuring the density and directional velocity of neutral particles.

[0004] Researchers at the Max Planck Institute, including Krychowiak, designed a device for measuring the density of helium atoms at the helium outlet of a TEXTOR tokamak using a laser-induced fluorescence system. They compared experimental results with simulation results to calculate the helium atom density at the helium outlet. Elliott of West Virginia University successfully measured the density and temperature of deuterium atoms using a two-photon laser-induced fluorescence system on the HIT-SI3 spherical tokamak. However, there are currently no experiments measuring deuterium atoms in high-temperature tokamas. The main reason is that in high-temperature tokamas, the high-temperature plasma cooling at the boundary region generates fluorescence through effects such as recombination with electrons. This fluorescence includes the fluorescence band measured by the TALIF system, and the light intensity is very high, making it difficult to separate the fluorescence signal from the background light.

[0005] In laser-induced fluorescence measurements, ground-state particles are typically excited by a focused laser from one side, while fluorescence signals are collected from the other side to achieve the optimal signal-to-noise ratio and avoid interference from the laser. However, this setup presents several challenges when used in high-temperature plasma environments such as tokamak devices. First, observing from both sides requires two windows, and tokamak observation windows are very limited. Second, due to the high degree of freedom, optical path adjustment is difficult, and finding the focal point requires a process. Third, the laser path from the vertically incident window is relatively long, potentially leading to energy loss due to plasma scattering during incidence. Furthermore, conventional confocal lenses, which require a single focal point, struggle to achieve a large mirror size with a short focal length. Summary of the Invention

[0006] To address the shortcomings of existing technologies, this invention provides a semi-confocal lens, a two-photon laser-induced fluorescence system, and their applications for fluorescence detection in high-temperature plasma environments.

[0007] The technical solution of this invention is as follows:

[0008] According to a first aspect of the present invention, a semi-confocal lens is provided, the semi-confocal lens comprising an inner lens and an outer lens; wherein the inner lens is embedded in the middle of the outer lens; the inner lens has a mirror diameter of 10-20mm and a focal length of 250-350mm; the outer lens has a mirror diameter of 80-120mm and a focal length of 310-450mm.

[0009] Furthermore, the inner lens uses magnesium fluoride as the lens material; the outer lens uses H-K9L glass as the lens material.

[0010] According to a second aspect of the present invention, a two-photon laser-induced fluorescence system is provided, comprising the aforementioned semi-confocal lens.

[0011] Furthermore, the two-photon laser-induced fluorescence system includes a laser. The laser emitted from the laser is reflected by a laser mirror and focused at the focal point of the inner lens of a semi-confocal lens. At the focal point, atoms absorb two photons, transition to a higher energy level, and then de-excite and emit photons to generate fluorescence. The generated fluorescence is received by the outer lens of the semi-confocal lens. The fluorescence divergence angle after passing through the outer lens is between 0.15 degrees and 30 degrees. After being reflected by a fluorescence mirror placed at a distance of 200-3500 mm from the confocal lens, with a length, width, and thickness of 150-300 mm, 100-200 mm, and 10-30 mm respectively, the fluorescence is focused by a focusing lens placed at a distance of 500-4000 mm from the confocal lens and is received by a photomultiplier tube.

[0012] According to a third aspect of the present invention, an application of a two-photon laser-induced fluorescence system in the measurement of the density of neutral hydrogen atoms under strong background two-photon absorption laser-induced fluorescence is provided.

[0013] Furthermore, the application includes the following steps:

[0014] Step S1: Measure the single-pulse laser energy of lasers at different wavelengths;

[0015] Step S2: Use Gaussian curve fitting to find the laser excitation center wavelength;

[0016] Step S3: Measure the intensity of two-photon laser-induced fluorescence signal of krypton atoms under different gas pressures, calculate the krypton atom density using the ideal gas law, establish the relationship between the krypton atom density and the laser-induced fluorescence signal intensity, and calculate the hydrogen atom density accordingly.

[0017] Further, step S3 includes:

[0018] The expression for the intensity relationship of two-photon laser-induced fluorescence signal of krypton atoms is as follows:

[0019] I TALIF,Kr =1.558×10 -23 n Kr (1)

[0020] Among them, I TALIF,Kr n represents the intensity of the two-photon laser-induced fluorescence signal of krypton atoms. Kr This represents the density of krypton atoms.

[0021] The density of hydrogen atoms is calculated using the following expression:

[0022]

[0023]

[0024] Where, n H Hydrogen atoms represent density, I TALIF I0 represents fluorescence intensity, I0 represents laser intensity, and A0< / 32 σ is the Einstein transition coefficient, τ is the excited state lifetime, and σ is the Einstein transition coefficient. (2) λ represents the two-photon excitation scattering cross section, λ represents the laser wavelength, and γ represents the ratio of the efficiency of the fluorescence system.

[0025] Furthermore, the application also includes:

[0026] The relationship between hydrogen atom density and two-photon laser-induced fluorescence signal is as follows:

[0027] n H =8.7332×10 20 ITsALIF,H (4).

[0028] According to a fourth aspect of the present invention, a two-photon laser-induced fluorescence system is provided for the application of biological component measurement, chemical product component measurement, impurity detection, material detection, or propulsion plume research.

[0029] Compared with existing technologies, the advantages of this invention are as follows: This invention proposes a semi-confocal lens for fluorescence detection in high-temperature plasma environments. This semi-confocal lens is a short focal length, large mirror diameter semi-confocal lens, which saves window space and reduces the degree of freedom in optical path adjustment while obtaining a larger solid angle, enhancing the fluorescence signal to collect as much fluorescence as possible. This semi-confocal lens receives fluorescence from the same direction of laser incident light, which reduces the degree of freedom in the optical path, facilitating adjustment; it also reduces the number of windows occupied by the tokamak, which is beneficial for device installation and window reservation. Compared with existing confocal lenses, the semi-confocal lens does not require the outer lens focal point to coincide with the inner lens focal point, thus requiring less stringent material requirements for the outer lens, resulting in lower cost, and making it easier to obtain higher light transmittance. Attached Figure Description

[0030] 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.

[0031] Figure 1 This is a design schematic diagram of a semi-confocal lens;

[0032] Figure 2 This is a schematic diagram of the optical path of a semi-confocal lens;

[0033] Figure 3 A schematic diagram of a two-photon laser-induced fluorescence system;

[0034] Figure 4 This is a schematic diagram of the fluorescence optical path of a semi-focusing lens and a focusing lens;

[0035] Figure 5 This is a graph showing the measurement results of hydrogen atom density under different gas pressures inside a vacuum chamber under discharge conditions.

[0036] In the diagram, 1-inner lens; 2-outer lens; 3-laser optical path; 4-fluorescent optical path; 5-laser; 6-laser reflector; 7-fluorescent reflector; 8-focal point; 9-semi-confocal lens; 10-focusing lens; 11-photomultiplier tube. Detailed Implementation

[0037] 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.

[0038] It should be noted that, unless otherwise specified, the features in the following embodiments and implementation methods can be combined with each other.

[0039] like Figure 1 As shown, this invention proposes a semi-confocal lens for fluorescence detection in a high-temperature plasma environment. The semi-confocal lens includes an inner lens 1 and an outer lens 2, and the positional connection relationship between the inner lens 1 and the outer lens 2 is as follows: Figure 1 As shown; wherein, inner lens 1 is embedded in the opening of outer lens 2, the mirror diameter of inner lens 1 is 10-20mm, and the focal length is 250-350mm; the mirror diameter of outer lens 2 is 80-120mm, and the focal length is 310-450mm. The opening on the left side of outer lens 2 has a diameter of 17mm and a depth of 10mm, and the opening on the right side has a diameter of 20mm and a depth of 10mm. The two lenses are bonded together with Norland 61 UV-curable adhesive.

[0040] It should be noted that the inner lens 1 in the semi-confocal lens provided by this invention has a mirror diameter of 10-20mm and a focal length of 250-350mm; the outer lens 2 has a mirror diameter of 80-120mm and a focal length of 310-450mm. This semi-confocal lens is a short focal length, large mirror diameter semi-confocal lens. The short focal length and large mirror diameter can obtain a larger solid angle, enhance the fluorescence signal, and collect as much fluorescence as possible.

[0041] Furthermore, the inner lens 1 uses magnesium fluoride or other quartz glass with a transmittance of more than 75% for light in the 190-250nm range as the lens material; the outer lens 2 uses H-K9L glass or other glass with a transmittance of more than 90% for light in the 400-760nm range as the lens material.

[0042] Exemplarily, this example designs a semi-confocal lens, in which an inner lens 1 and an outer lens 2 are connected by cementing. The inner lens 1 uses magnesium fluoride as the lens material, with a mirror diameter of 20mm and a focal length of 315mm. The magnesium fluoride lens material is more conducive to ultraviolet light transmission. The outer lens 2 uses H-K9L glass, with a mirror diameter of 100mm and a focal length of 360mm. H-K9L glass is relatively inexpensive and has good transmittance in the visible light range, which can reduce costs when manufacturing larger semi-confocal lenses. However, H-K9L glass has a low refractive index, and the thickness of the raw material for cutting lenses is limited. Therefore, in engineering, achieving the same focal length for both the outer and inner lenses and a large semi-confocal lens is very expensive, and a large curvature reduces fluorescence transmittance. This semi-confocal outer lens has a transmittance of over 99% for light in the wavelength range of 600nm-750nm, and the inner lens has a transmittance of over 80% for light near the wavelength of 205nm.

[0043] This invention relates to a method where the focal length of the outer lens 2 is greater than that of the inner lens 1, thereby reducing the lens curvature and obtaining a larger fluorescence receiving solid angle. However, there is some diffusion of the subsequent light, which can be addressed by using a larger focusing lens to receive and focus the fluorescence, achieving the purpose of collecting the fluorescence and detecting it with a photomultiplier tube.

[0044] This example provides a schematic diagram of a semi-confocal lens optical path, with laser optical path 3 and fluorescence optical path 4 as shown. Figure 2 As shown, the laser source emits laser light, which is focused to the focal point by the inner lens 1, and the de-excited fluorescence is collected by the outer lens 2.

[0045] Specifically, a laser beam is incident perpendicularly to the inner lens of a semi-confocal lens, and the incident laser beam is focused at the focal point of the inner lens. At the focal point, an atom absorbs two photons, transitions to a higher energy level, and after a period of time (the half-life of a 3D hydrogen atom is approximately 16 ns), de-excites and emits photons, producing fluorescence. The generated fluorescence is received by the outer lens of the semi-confocal lens, and finally, a lens is placed behind it to focus the fluorescence, which is then received by a photomultiplier tube.

[0046] like Figure 3 and Figure 4 As shown, this invention proposes a two-photon laser-induced fluorescence system. The system includes a laser 5. The laser emitted from the laser 5 is reflected by a laser mirror 6 and then focused at the focal point of the inner lens of a semi-confocal lens 9. At the focal point, atoms absorb two photons and transition to a higher energy level. After a period of time, they de-excite and emit photons, generating fluorescence. The generated fluorescence is received by the outer lens of the semi-confocal lens. The fluorescence divergence angle after passing through the outer lens is between 0.15 degrees and 30 degrees. After being reflected by a fluorescence mirror 7, the fluorescence is focused by a focusing lens 10 and received by a photomultiplier tube 11.

[0047] Furthermore, in this example, the fluorescent reflector 7 is placed at a distance of 200-3500mm from the confocal lens, and its length, width, and thickness are designed to be 150-300mm, 100-200mm, and 10-30mm, respectively. The focusing lens 10 is placed at a distance of 500-4000mm from the confocal lens, and its diameter is 120-300mm, with a focal length of 300-700mm.

[0048] This invention also proposes an application of a two-photon laser-induced fluorescence system in the measurement of the neutral gas density of hydrogen atoms under strong background two-photon absorption laser-induced fluorescence, the application specifically including the following steps:

[0049] Step S1: Measure the single-pulse laser energy of lasers of different wavelengths.

[0050] Specifically, the energy of the laser was measured at three points: the laser emission point, after reflection by two mirrors, and finally upon impact within the vacuum chamber. The energy of the emitted laser pulse was approximately 2 mJ. After reflection by the two mirrors, the laser pulse energy decreased to approximately 1 mJ. Inside the vacuum chamber, the energy of the 205 nm laser pulse was 0.71 mJ, and the energy of the 204 nm laser pulse was 0.56 mJ.

[0051] Step S2: Use Gaussian curve fitting to find the laser excitation center wavelength.

[0052] Specifically, in this example, the excitation wavelength of the krypton atoms is λ. Kr =204.171nm, the excitation wavelength of hydrogen atoms is λ H =205.122nm.

[0053] Step S3: Measure the intensity of two-photon laser-induced fluorescence signal of krypton atoms under different gas pressures, calculate the krypton atom density using the ideal gas law, establish the relationship between the krypton atom density and the laser-induced fluorescence signal intensity, and substitute it into the formula to calculate the hydrogen atom density.

[0054] The expression for the intensity relationship of two-photon laser-induced fluorescence signal of krypton atoms is as follows:

[0055] I TALIF，Kr =1.558×10 -23 n Kr #(1)

[0056] Among them, I TALIF，Kr n represents the intensity of the two-photon laser-induced fluorescence signal of krypton atoms. Kr This represents the density of krypton atoms.

[0057] The density of hydrogen atoms is calculated using the following expression:

[0058]

[0059]

[0060] Where, n H Hydrogen atoms represent density, I TALIF I0 represents fluorescence intensity, I0 represents laser intensity, and A0< / 32 σ is the Einstein transition coefficient, τ is the excited state lifetime, and σ is the Einstein transition coefficient. (2) λ represents the two-photon excitation scattering cross section, λ represents the laser wavelength, and γ represents the ratio of the efficiency of the fluorescence system.

[0061] The efficiency of the fluorescence path is mainly affected by the characteristics of the photomultiplier tube. For hydrogen atoms, the photomultiplier tube response is 78 mA / W, while for the 826 nm spectral line produced by krypton atoms, the photomultiplier tube response is 2.8 mA / W. Calculations show γ = 0.0359 and χ = 0.0187.

[0062] Substituting equations (1) and (3) and related parameters into equation (2), the relationship between hydrogen atom density and two-photon laser-induced fluorescence signal is finally obtained as follows:

[0063] n H =8.7332×10 20 I TALIF，H #(4)

[0064] The hydrogen atom density under different gas pressures inside the vacuum chamber can be calculated using equation (4), and the results are as follows: Figure 5 As shown. By Figure 5 It can be seen that the neutral particle density increases with increasing air pressure. This result shows that the two-photon laser-induced fluorescence system can calculate the neutral particle density at the measurement point under different conditions using equation (4) and the intensity of the fluorescence signal.

[0065] It should be noted that the two-photon laser-induced fluorescence system proposed in this invention can also be applied to the measurement of biological components, the measurement of chemical product components, the detection of impurities, the detection of materials, or the study of propulsion plumes.

[0066] The above embodiments are only used to illustrate the design concept and features of the present invention, and their purpose is to enable those skilled in the art to understand the content of the present invention and implement it accordingly. The protection scope of the present invention is not limited to the above embodiments. Therefore, all equivalent changes or modifications made based on the principles and design ideas disclosed in the present invention are within the protection scope of the present invention.

Claims

1. A two-photon laser-induced fluorescence system, characterized in that, The laser (5) is emitted from the laser (5). After being reflected by the laser mirror (6), the laser is focused at the focal point of the inner lens (1) of the semi-confocal lens (9). After the atom at the focal point absorbs two photons, it jumps to a higher energy level, then de-excites and emits photons to generate fluorescence. The generated fluorescence is received by the outer lens (2) of the semi-confocal lens, and after being reflected by the fluorescence mirror (7), the fluorescence is focused by the focusing lens (10) and received by the photomultiplier tube (11). The semi-confocal lens includes an inner lens (1) and an outer lens (2); wherein the inner lens (1) is embedded in the middle of the outer lens (2); the inner lens (1) has a mirror diameter of 10-20mm and a focal length of 250-350mm; the outer lens (2) has a mirror diameter of 80-120mm and a focal length of 310-450mm. The inner lens (1) is made of magnesium fluoride or other quartz glass with a transmittance of more than 75% for light in the 190-250nm range; the outer lens (2) is made of H-K9L glass or other glass with a transmittance of more than 90% for light in the 400-760nm range.

2. The application of the two-photon laser-induced fluorescence system of claim 1 in the measurement of the neutral gas density of hydrogen atoms under strong background two-photon absorption laser-induced fluorescence.

3. The application according to claim 2, characterized in that, The application includes the following steps: Step S1: Measure the single-pulse laser energy of lasers at different wavelengths; Step S2: Use Gaussian curve fitting to find the laser excitation center wavelength; Step S3: Measure the intensity of two-photon laser-induced fluorescence signal of krypton atoms under different gas pressures, calculate the krypton atom density using the ideal gas law, establish the relationship between the krypton atom density and the laser-induced fluorescence signal intensity, and calculate the hydrogen atom density accordingly.

4. The application according to claim 3, characterized in that, Step S3 includes: The expression for the intensity relationship of two-photon laser-induced fluorescence signal of krypton atoms is as follows: I TALIF,Kr =1.558×10 -23 n Kr (1) Among them, I TALIF,Kr n represents the intensity of the two-photon laser-induced fluorescence signal of krypton atoms. Kr Indicates the density of krypton atoms; The density of hydrogen atoms is calculated using the following expression: Where, n H Hydrogen atoms represent density, I TALIF I0 represents fluorescence intensity, I0 represents laser intensity, and A0< / 32 σ is the Einstein transition coefficient, τ is the excited state lifetime, and σ is the Einstein transition coefficient. (2) λ represents the two-photon excitation scattering cross section, λ represents the laser wavelength, and γ represents the ratio of the efficiency of the fluorescence system.

5. The application according to claim 3, characterized in that, The application also includes: The relationship between hydrogen atom density and two-photon laser-induced fluorescence signal is as follows: n H =8.7332×10 20 I TALIF,H (4)。 6. The application of the two-photon laser-induced fluorescence system of claim 1 in the measurement of biological components, the measurement of chemical product components, the detection of impurities, the detection of materials, or the study of propulsion plumes.

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