Confocal gas optical fiber Raman probe

Abstract

The invention discloses a confocal gas optical fiber Raman probe, and belongs to the field of Raman detection, the confocal gas optical fiber Raman probe mainly comprises a probe body and a hollow optical fiber gas Raman sensor, the probe body comprises a laser excitation light path and a spectrum collection light path, the spectrum collection optical path comprises a reflective lens, a dichroscope, a first confocal lens, a pinhole filter, a second confocal lens, a Raman optical filter, a spectrum collection lens and a spectrum collection optical fiber which are connected in sequence, and a set of confocal optical system is formed through the reflective lens, a plurality of confocal lenses and other devices; excitation laser is accurately focused on the inlet end face of the hollow optical fiber gas Raman sensor through the reflection-type lens and the adjusting device of the reflection-type lens. The laser is repeatedly excited in the gas Raman sensor, and the laser is emitted from the end surface and then is coupled into the collection light path by the reflective lens at the tail end, so that simultaneous collection of forward and backward Raman signals is realized, and finally, the Raman signal of the gas is remarkably enhanced. According to the gas optical fiber Raman probe, the technical problems of low efficiency and high background of conventional gas Raman detection are solved, the Raman signal intensity is improved, and the application range and scene of gas Raman detection are expanded.

Description

Technical Field

[0001] The present invention relates to the field of Raman detection, and in particular to a confocal gas fiber Raman probe. Background Art

[0002] Traditional fiber optic Raman probes are widely used in Raman spectroscopy of liquids and solids due to their flexibility and miniaturization. However, in gas Raman detection, conventional fiber optic Raman probes have the following problems: 1. Low efficiency: The density of gas molecules is low, and the signal excitation and collection efficiency is insufficient; 2. High background noise: Laser scattering on the surface of optical components and material fluorescence interference are serious; 3. Unable to simultaneously collect forward and backward gas Raman signals: Traditional optical path design only supports single-directional signal collection, and the signal strength is insufficient.

[0003] Therefore, there is an urgent need for a new type of fiber optic Raman probe with high efficiency, low background noise and high signal intensity. Summary of the Invention

[0004] The purpose of the present invention is to overcome the problems of low efficiency, high background noise and low signal strength of existing fiber optic Raman probes. A confocal gas fiber optic Raman probe is provided. Through a reflective lens, a confocal optical path, a reflective lens focus adjustment device and a hollow fiber optic gas sensor, the signal-to-noise ratio and detection sensitivity of the gas Raman signal are significantly improved.

[0005] The object of the present invention is achieved through the following technical solutions: A confocal gas fiber Raman probe, comprising: The probe body includes a laser excitation optical path and a spectrum collection optical path. The laser excitation optical path includes a laser incident optical fiber, a laser collimator, a laser line filter, a laser reflector, a dichroic mirror, and a reflective lens connected in sequence. The spectrum collection optical path includes a reflective lens, a dichroic mirror, a first confocal mirror, a pinhole filter, a second confocal mirror, a Raman filter, a spectrum collection mirror, and a spectrum collection optical fiber connected in sequence. The hollow fiber gas Raman sensor comprises a hollow fiber, the front end of the hollow fiber is connected to the reflective lens, and the rear end of the hollow fiber is provided with a total reflection mirror.

[0006] In some embodiments, the inner wall of the hollow optical fiber is coated with a metal film layer with high reflectivity.

[0007] In some embodiments, a gas sealing window is provided at the front end of the hollow-core optical fiber.

[0008] In some embodiments, the distance between the gas sealing window and the end face of the hollow optical fiber is not less than 3 mm, and the window thickness of the gas sealing window is less than 1 mm.

[0009] In some embodiments, the probe body is also provided with an adjustment device for adjusting the focus of the reflective lens, and the adjustment device is connected to the reflective lens through a reflector seat. The adjustment device includes a focus horizontal adjustment device and a focus vertical adjustment device; the focus horizontal adjustment device includes a horizontal fine-tuning screw connected to the reflector seat and a horizontal adjustment spring mechanism.

[0010] In some embodiments, the focus vertical adjustment device includes an angle adjustment screw connected to the reflector seat and an angle adjustment spring mechanism.

[0011] In some embodiments, achieving confocal requires the following conditions to be met: , , ; Among them, F1 represents the focal length of the laser collimator, NA1 represents the numerical aperture of the laser incident fiber, F2 represents the focal length of the reflective lens, NA2 represents the numerical aperture of the hollow-core fiber, d2 represents the inner diameter of the hollow-core fiber, d3 represents the aperture of the pinhole filter, F3 represents the focal length of the first confocal lens, F4 represents the focal length of the second confocal lens, d4 represents the core diameter of the spectrum collection fiber, and F5 represents the focal length of the spectrum collection lens.

[0012] In some embodiments, the hollow fiber gas Raman sensor is detachably connected to the probe body.

[0013] It should be further explained that the technical features corresponding to the above embodiments can be combined or replaced with each other to form a new technical solution if there is no conflict.

[0014] Compared with the prior art, the present invention has the following beneficial effects: 1. The present invention's spectral collection optical path forms a confocal optical system using a reflective lens, multiple confocal mirrors, and other components. The excitation laser passes through the reflective lens and its adjustment device and is precisely focused onto the inlet end face of the hollow-core fiber gas Raman sensor. The laser is repeatedly excited within the gas Raman sensor. After exiting the end face, the laser is coupled back into the collection optical path by the reflective lens at the end, achieving efficient and reliable coupling. This allows for the simultaneous collection of both forward and reverse Raman signals, significantly enhancing the gas Raman signal. Ultimately, this improves Raman signal collection efficiency and signal strength, expanding the scope and application scenarios of gas Raman detection.

[0015] 2. In some examples, the inner wall of the hollow-core optical fiber of the present invention is coated with a high-reflectivity metal film layer, which prevents the laser from directly hitting the optical fiber matrix, allowing the laser to be reflected within the hollow-core optical fiber. The laser repeatedly excites the atmosphere within the hollow-core optical fiber, thereby reducing background interference and increasing signal strength.

[0016] 3. In some examples, a gas-sealed window is provided at the front end of the hollow optical fiber of the present invention to isolate the test gas; this prevents the test gas from being disturbed by external gases, thereby ensuring the accuracy of the test. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 This is a schematic diagram of the structure of a confocal gas fiber Raman probe according to an embodiment of the present invention; Figure 2 A schematic diagram of an adjustment device for horizontally adjusting focus according to an embodiment of the present invention; Figure 3 A schematic diagram of an adjustment device for vertically adjusting focus according to an embodiment of the present invention; Figure 4 This is a schematic diagram of the detachable connection between the hollow fiber gas Raman sensor and the probe body according to an embodiment of the present invention.

[0018] 1-probe body; 200-laser incident fiber; 201-laser fiber end face; 202-laser beam; 203-laser collimator; 204-laser line filter; 205-laser reflector; 301-reflective lens; 302-adjustment device; 303-reflective lens optical axis; 304-parallel optical axis adjustment direction; 305-rotation adjustment direction around the optical axis; 400-hollow fiber gas Raman sensor; 401-gas sealing window; 402 - hollow-core fiber end face; 403 - hollow-core fiber; 404 - hollow-core fiber output light; 405 - total reflection mirror; 501 - dichroic mirror; 502 - Raman beam; 503 - first confocal mirror; 504 - pinhole filter; 505 - second confocal mirror; 506 - Raman filter; 507 - spectrum collection mirror; 508 - spectrum collection fiber end face; 509 - spectrum collection fiber; 601 - fiber bundle outer tube; 602 - laser incident fiber outer end; 603 -External end of the spectrum collection optical fiber; 30201-Horizontal fine-tuning screw; 30202-Parallel movement direction of the reflective lens; 30203-Reflector mount; 30204-Horizontal adjustment spring mechanism; 30205-Horizontal adjustment support position; 30206-Parallel light beam; 30207-Converging light beam; 30208-Horizontal movement direction of the focus; 30210-Angle adjustment screw; 30211-Angle adjustment spring mechanism; 30212-Rotation direction of the reflective lens; 30213-Vertical movement direction of the focus; 4001-Top screw; 4002-VCR connector. DETAILED DESCRIPTION

[0019] The technical solutions of the present invention are described clearly and completely below in conjunction with the accompanying drawings. Obviously, the described embodiments are part of the embodiments of the present invention, rather than all of the embodiments. The components of the embodiments of the present application generally described and shown in the drawings herein can be arranged and designed in various different configurations. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0020] It should be noted that the defects existing in the solutions in the above-mentioned prior art are the results obtained by the inventor after practice and careful research. Therefore, the discovery process of the above-mentioned problems and the solutions proposed in the embodiments of this application below for the above-mentioned problems should be the contributions made by the inventor to this application in the process of invention and creation, and should not be understood as technical contents known to technical personnel in this field.

[0021] In response to the technical problems pointed out in the background technology, the embodiments provided by the present invention are as follows: like Figure 1 As shown, a confocal gas fiber Raman probe comprises: The probe body 1 includes a laser excitation optical path and a spectrum collection optical path. The laser excitation optical path includes a laser incident optical fiber 200, a laser collimating mirror 203, a laser line filter 204, a laser reflector 205, a dichroic mirror 501, and a reflective lens 301 connected in sequence. The spectrum collection optical path includes a reflective lens 301, a dichroic mirror 501, a first confocal mirror 503, a pinhole filter 504, a second confocal mirror 505, a Raman filter 506, a spectrum collection mirror 507, and a spectrum collection optical fiber 509 connected in sequence. The hollow-core fiber gas Raman sensor 400 includes a hollow-core fiber 403 , the front end of which is connected to the reflective lens 301 , and the rear end of which is provided with a total reflection mirror 405 ; The optical fiber bundle includes a laser branch and a spectrum signal branch. The laser branch is connected to the laser incident optical fiber 200 , and the spectrum signal branch is connected to the spectrum collection optical fiber 509 .

[0022] Specifically, the laser input fiber 200 is a continuous optical fiber. The laser input fiber outer end 602 outside the probe body 1 is connected to the laser. The laser fiber end face 201 inside the probe body 1 is located at the focus of the laser collimator 203, and collimates the divergent laser beam into parallel light. After passing through the laser line filter 204, it is transmitted to the dichroic mirror 501 by the laser reflector 205. The dichroic mirror 501 reflects the laser beam to the reflective lens 301, which precisely focuses the parallel laser light onto the hollow fiber end face 402 of the gas Raman sensor 400. A gas sealing window 401 is also provided at the light incident port of the gas Raman sensor 400 to isolate the test gas. The inner wall of the hollow-core fiber 403 of the gas Raman sensor 400 is coated with a metal film. This metal film confines incoming laser light, allowing it to propagate within the hollow-core fiber 403 and continuously excite the gas's Raman signal during propagation. The Raman signal light propagates in both directions along the axis of the hollow-core fiber 403. The light 404 emitted from the hollow-core fiber 403, consisting of both the laser light and the gas's Raman signal light, is then reflected back into the hollow-core fiber 403 by a total reflection mirror 405. The reflected laser light is reused to excite the gas Raman signal, while the Raman signal light is simultaneously transferred back into the hollow-core fiber 403. This mechanism significantly enhances the excitation and collection capabilities of the gas Raman signal.

[0023] The Raman signal light and the reflected laser light transmitted from the hollow core fiber 403 are collimated by the reflective lens 301. The dichroic mirror 501 reflects the reverse reflected laser beam and transmits the Raman signal light and a small amount of leaked laser light 502. The Raman signal light and a small amount of leaked laser light 502 pass through the first confocal lens 503 and are focused on the pinhole filter 504 at its focal point. The pinhole filter 504 blocks the non-parallel incident scattered laser light and other fluorescent background light, allowing only the parallel incident light to pass through the pinhole and be collimated into parallel light by the second confocal lens 505. The Raman filter 506 has a very high suppression effect on the parallel incident laser light, while transmitting the Raman signal light. In this way, the Raman signal light and the laser portion of the small amount of leaked laser light 502 are filtered out, and only the Raman signal light passes through. The Raman signal light is focused by the collecting lens 507 on the end face 508 of the spectrum collection fiber and transmitted to the outside of the spectrum collection fiber through the spectrum collection fiber 509.

[0024] The optical fiber branch end face 508 of the optical fiber bundle for collecting spectrum and the hollow optical fiber end face 402 of the gas Raman sensor form a confocal optical system under the action of the excitation optical path in the probe body 1, the reflective lens 301 and the spectrum collection optical path; The reflective lens 301 in the probe body 1 uses a reflective surface of a metal medium, eliminating the background fluorescence and interfering Raman signal light generated by the lens material after the laser passes through the lens objective lens in the conventional optical fiber probe; Furthermore, the gas sensor 400 has a gas sealing window 401 at the light entrance for sealing. The distance between the gas sealing window 401 and the hollow fiber end face 402 of the gas Raman sensor is at least 3 mm, and the thickness of the gas sealing window 401 is less than 1 mm. Under the confocal optical system, the fluorescence background and Raman interference signal of the gas sealing window 401 are effectively suppressed. Furthermore, the optical system consisting of the first confocal lens 503, the pinhole filter 504, and the second confocal lens 505 can effectively block the scattered laser light on the surface of the optical device from entering the collection fiber. Combined with the Raman filter 506, the laser suppression rate of the fiber Raman probe can reach OD12, which is much higher than the OD6 of a conventional fiber Raman probe. This is very beneficial for long-term integration of gas Raman testing.

[0025] Furthermore, an adjusting device 302 for adjusting the focus of the reflective lens 301 is provided in the probe body 1 , and the reflective lens 301 is mounted on the adjusting device 302 to achieve precise confocal adjustment.

[0026] Specifically, the adjustment device is connected to the reflective lens 301 via a reflector mount 30203. The adjustment device 302 includes a horizontal focus adjustment device and a vertical focus adjustment device. The horizontal focus adjustment device enables fine-tuning along the reflective lens optical axis 303 parallel to the laser transmission direction, while the vertical focus adjustment device enables fine-tuning in the rotational direction around the reflective lens optical axis 303. The horizontal focus adjustment device includes a horizontal fine-tuning screw 30201 connected to the reflector mount 30203 and a horizontal adjustment spring mechanism 30204. The vertical focus adjustment device includes an angle adjustment screw 30210 connected to the reflector mount 30203 and an angle adjustment spring mechanism 30213.

[0027] like Figure 2 As shown, the parallel light beam 30206 is incident on the reflective lens 301 and is focused into a convergent light beam 30207. Due to the tolerance of mechanical and optical components, there will be a certain deviation between the focus and the hollow optical fiber 403 in the horizontal direction. By adjusting the horizontal fine-tuning screw 30201, the reflector base 30203 will move parallel in the horizontal direction under the action of the horizontal fine-tuning screw 30201 and the horizontal adjustment spring mechanism 30204, and the reflective lens 301 is fixed on the reflector base 30203. Correspondingly, the reflective lens 301 will move along the parallel movement direction 30202 of the reflective lens, so that the focus of the convergent light beam 30207 will move in the horizontal movement direction 30208 of the focus, so that the focus can be adjusted to the same vertical plane as the hollow optical fiber 403 through the focus horizontal adjustment device; wherein, the horizontal adjustment spring mechanism 30204 is also connected to a horizontal adjustment support position 30205, and the horizontal adjustment support position 30205 is used to limit the horizontal adjustment spring mechanism 30204 at the other end, that is, one end of the spring is limited, so that the accumulated elastic potential energy keeps the reflector seat 30203 in contact with the horizontal fine-tuning screw 30201 and is driven in both directions to perform a linear micro-displacement movement.

[0028] like Figure 3As shown, by adjusting the angle adjustment screw 30210, the reflector base 30203 drives the reflective lens 301 to generate rotational motion along the optical axis of the reflective lens 301 under the action of the angle adjustment spring mechanism 30211. In this way, the focus of the converged light beam 30207 will move in the focus vertical movement direction 30208. In this way, the focus can be adjusted to be on the same horizontal plane as the hollow-core optical fiber 403 through the focus vertical adjustment device. By adjusting the parallelism and angle, the parallel light beam incident on the reflective lens 301 can always be accurately focused into the inner hole of the hollow-core optical fiber 403; according to the principle of optical path reversibility, the signal light excited in the hollow-core optical fiber 403 will be collimated into a parallel light beam 30206 by the reflective lens 301 after being emitted from the end face of the hollow-core optical fiber 403, so that the probe can collect both forward and backward gas Raman signals.

[0029] Preferably, the reflective lens 301 may be an off-axis parabolic reflector. The optical fiber bundle is provided with an optical fiber bundle outer tube 601 , which is protected by stainless steel to prevent optical fiber displacement caused by bending or vibration.

[0030] Furthermore, to realize the confocal optical system, the following conditions need to be met: , , ; Among them, F1 represents the focal length of the laser collimator 203, NA1 represents the numerical aperture of the laser incident optical fiber 200, F2 represents the focal length of the reflective lens 301, NA2 represents the numerical aperture of the hollow-core optical fiber 403, d2 represents the inner diameter of the hollow-core optical fiber 403, d3 represents the aperture of the pinhole filter 504, F3 represents the focal length of the first confocal lens 503, F4 represents the focal length of the second confocal lens 505, d4 represents the core diameter of the spectrum collection optical fiber 509, and F5 represents the focal length of the spectrum collection lens 507.

[0031] Furthermore, the first confocal lens 503, the second confocal lens 505, and the spectrum collection lens 507 are designed to optimize chromatic and spherical aberration. The gas Raman sensor 400 and both end faces of the hollow-core fiber 403 within it are coated with a metal film to prevent the laser from entering the sidewalls of the hollow-core fiber 403 and generating fluorescence and Raman interference signals.

[0032] Furthermore, the hollow fiber gas Raman sensor 400 is connected to the probe body 1 by a detachable mechanical connection, such as Figure 4As shown, the two are fixed with a top screw 4001, so that the hollow-core fiber gas Raman sensor 400 can be implanted in a closed system before the fiber Raman probe is installed, improving the ability to assemble in a small space; the laser incident end of the hollow-core fiber 403 is designed with a groove that fits the top screw 4001. Depending on the installation conditions, the laser incident end of the hollow-core fiber 403 can be designed with a VCR connector 4002, thereby ensuring a higher leakage rate (10 -9 Pa·m 3 / s), in an environment where the leakage rate requirement is not high, threads can also be used with O-rings for sealing.

[0033] The above specific implementation methods are detailed descriptions of the present invention. It cannot be considered that the specific implementation methods of the present invention are limited to these descriptions. For ordinary technicians in the technical field to which the present invention belongs, they can make several simple deductions and substitutions without departing from the concept of the present invention, which should be regarded as falling within the scope of protection of the present invention.

Claims

1. A confocal gas fiber Raman probe, characterized in that: include: The probe body includes a laser excitation optical path and a spectrum collection optical path. The laser excitation optical path includes a laser incident optical fiber, a laser collimator, a laser line filter, a laser reflector, a dichroic mirror, and a reflective lens connected in sequence. The spectrum collection optical path includes a reflective lens, a dichroic mirror, a first confocal mirror, a pinhole filter, a second confocal mirror, a Raman filter, a spectrum collection mirror, and a spectrum collection optical fiber connected in sequence. The hollow fiber gas Raman sensor comprises a hollow fiber, the front end of the hollow fiber is connected to the reflective lens, and the rear end of the hollow fiber is provided with a total reflection mirror.

2. A confocal gas fiber Raman probe according to claim 1, characterized in that: The inner wall of the hollow optical fiber is plated with a metal film layer with high reflectivity.

3. The confocal gas fiber Raman probe according to claim 1, characterized in that: A gas sealing window is provided at the front end of the hollow optical fiber.

4. A confocal gas fiber Raman probe according to claim 3, characterized in that: The distance between the gas sealing window and the end face of the hollow optical fiber is not less than 3 mm, and the window thickness of the gas sealing window is less than 1 mm.

5. The confocal gas fiber Raman probe according to claim 1, characterized in that: The probe body is also provided with an adjusting device for adjusting the focus of the reflective lens. The adjusting device is connected to the reflective lens through a reflector seat. The adjusting device includes a horizontal focus adjusting device and a vertical focus adjusting device.

6. The confocal gas fiber Raman probe according to claim 5, characterized in that: The focus horizontal adjustment device includes a horizontal fine-tuning screw connected to the reflector seat and a horizontal adjustment spring mechanism; the focus vertical adjustment device includes an angle adjustment screw connected to the reflector seat and an angle adjustment spring mechanism.

7. The confocal gas fiber Raman probe according to claim 1, characterized in that: The following conditions must be met to achieve confocal imaging: ， ， ； Among them, F1 represents the focal length of the laser collimator, NA1 represents the numerical aperture of the laser incident fiber, F2 represents the focal length of the reflective lens, NA2 represents the numerical aperture of the hollow-core fiber, d2 represents the inner diameter of the hollow-core fiber, d3 represents the aperture of the pinhole filter, F3 represents the focal length of the first confocal lens, F4 represents the focal length of the second confocal lens, d4 represents the core diameter of the spectrum collection fiber, and F5 represents the focal length of the spectrum collection lens.

8. The confocal gas fiber Raman probe according to claim 1, characterized in that: The hollow fiber gas Raman sensor is detachably connected to the probe body.

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