Optical fiber enhanced Raman spectrum background silicon noise multi-scale filtering method and system

Abstract

An optical fiber enhanced Raman spectrum background silicon noise multi-scale filtering method is characterized by comprising the following steps that an optical fiber enhanced Raman spectrum background silicon noise multi-scale system is assembled at one end of a hollow-core optical fiber in a mechanical mode, and back Raman signals of the hollow-core optical fiber are collected; selecting an optimal parameter of a diaphragm clear aperture, and performing radial spatial filtering by adopting an adjustable diaphragm to filter background silicon noise parasitizing around the irregular-shaped Raman signal of the target gas; selecting an optimal parameter of the width of the slit, and realizing longitudinal spatial filtering through the slit; optimal parameters of CCD pixel rows are selected, transverse filtering is achieved by means of selective integration of the CCD pixel rows, and a multi-scale filtering result of the background silicon noise of the optical fiber enhanced Raman spectrum is obtained.

Description

Technical Field

[0001] The present invention relates to the field of gas analysis, and more specifically, to a method and system for multi-scale filtering of background silicon noise in fiber-enhanced Raman spectroscopy. Background Art

[0002] Raman spectroscopy is an analytical technique based on the Raman scattering effect. It can provide information about the vibration and rotation of molecules and is used for qualitative and quantitative analysis of substances. In gas detection, Raman spectroscopy can be used to identify gas components and measure their concentrations.

[0003] Hollow core fiber (HCF) is a special optical fiber structure with a hollow core, allowing light to transmit through air or other gases. This structure is particularly useful in gas detection because the interaction length between light and gas is increased, thereby improving detection sensitivity.

[0004] However, hollow-core fibers are made of silicon-based materials (such as silica). When excitation light propagates through the fiber, the silicon generates a Raman scattering signal, known as background silicon noise. This interferes with the Raman signal of the target gas, reducing the signal-to-noise ratio and sensitivity of detection. Therefore, filtering out background silicon noise is a core challenge in improving Raman spectroscopy performance.

[0005] Spatial filtering technology is currently widely used, but traditional spatial filters have complex structures (typically consisting of a focusing lens, pinhole, and collimating lens). They require extremely high adjustment precision, and micron-level deviations can cause mode coupling failure. Furthermore, they cannot completely eliminate stray light caused by higher-order modes or defects. The invention patent (202311208192.0) combines an adjustable aperture with a Raman signal imaging device to filter out background silicon noise, but this method loses some of the Raman signal of the target gas (irregular shape) while still retaining fluorescence interference along the longitudinal axis.

[0006] In summary, existing methods for filtering background silicon noise have limitations in terms of system complexity, flexibility, and filtering effectiveness. Therefore, a practical approach is urgently needed to advance the practical application of hollow-core fiber Raman gas detection. Summary of the Invention

[0007] In order to solve the deficiencies in the prior art, the present invention provides a method and system for multi-scale filtering of background silicon noise in fiber-enhanced Raman spectroscopy.

[0008] The present invention adopts the following technical solutions.

[0009] The first aspect of the present invention relates to a multi-scale filtering method for background silicon noise in fiber-enhanced Raman spectroscopy. The method comprises the following steps: mechanically assembling a multi-scale system for background silicon noise in fiber-enhanced Raman spectroscopy at one end of a hollow-core optical fiber to collect a back-scattered Raman signal from the hollow-core optical fiber; selecting optimal parameters for the aperture of an aperture, using an adjustable aperture to perform radial spatial filtering, and filtering out background silicon noise parasitic around the irregularly shaped Raman signal of a target gas; selecting optimal parameters for the width of a slit 3, and achieving longitudinal spatial filtering through the slit; selecting optimal parameters for a CCD pixel row, and achieving lateral filtering by means of selective integration of the CCD pixel row to obtain a multi-scale filtering result for background silicon noise in fiber-enhanced Raman spectroscopy.

[0010] The optimal parameters of the aperture are selected, and the adjustable aperture is used for radial spatial filtering to filter out the background silicon noise surrounding the Raman signal of the irregular shape of the target gas, including: fixing the width of the slit and the photosensitive pixels of the CCD; setting the aperture of the aperture from the reference value D base1 =(D-1.5mm), obtain the Raman spectrum of the laboratory ambient air every 0.5mm, and calculate the signal-to-noise ratio of the N2 Raman characteristic peak under this condition; when the signal-to-noise ratio of the N2 Raman characteristic peak decreases for the first time, stop increasing the aperture of the diaphragm, and record the aperture D corresponding to the maximum signal-to-noise ratio. max1 ; From the reference value D base2 =(D max1 -0.5mm), the Raman spectrum of the laboratory ambient air is obtained every 0.1mm, and the signal-to-noise ratio of the N2 Raman characteristic peak under this condition is calculated; when the signal-to-noise ratio of the N2 Raman characteristic peak decreases for the first time, the increase of the aperture of the diaphragm is stopped, and the aperture corresponding to the maximum signal-to-noise ratio D is recorded at the same time. max2 , which is the optimal aperture D of the diaphragm opt ;

[0011] D is the standard aperture of the diaphragm, which is calculated as follows:

[0012]

[0013] Where λ is the wavelength of the excitation light,

[0014] L0 is the focal length of the lens that couples the laser into the hollow-core fiber.

[0015] MFD is the mode field diameter of the hollow-core fiber, which is 0.75 of the core diameter of the hollow-core fiber.

[0016] Select the optimal parameters of the slit width to achieve longitudinal spatial filtering through the slit, including: the clear aperture D of the fixed aperture opt , CCD photosensitive pixels; set the slit width from the reference value W base1=(W-15μm), obtain the Raman spectrum of the laboratory ambient air every 5μm, and calculate the signal-to-noise ratio of the N2 Raman characteristic peak under this condition; when the signal-to-noise ratio of the N2 Raman characteristic peak decreases for the first time, stop increasing the slit width and record the slit width W corresponding to the maximum signal-to-noise ratio. max1 ; From the reference value W base2 =(W max1 -5μm), the Raman spectrum of the laboratory ambient air is acquired every 1μm, and the signal-to-noise ratio of the N2 Raman characteristic peak under this condition is calculated; when the signal-to-noise ratio of the N2 Raman characteristic peak decreases for the first time, the increase in the slit width is stopped, and the slit width W corresponding to the maximum signal-to-noise ratio is recorded. max2 , which is the optimal slit width W opt ;

[0017] W is the standard clear aperture of the slit, which is calculated as follows:

[0018]

[0019] Wherein, L1 is the focal length of the optical lens.

[0020] Select the optimal parameters of the CCD pixel row, use the CCD pixel row selective integration to achieve lateral filtering, and obtain the multi-scale filtering results of the fiber-enhanced Raman spectroscopy background silicon noise, including: the fixed aperture is D opt The width of the slit is W opt ; Select the middle row 1, middle row 3, middle row 5, middle row 7, middle row 9, middle row 11, and middle row 13 as the photosensitive pixels of the CCD in sequence; obtain the Raman spectrum of the laboratory ambient air under each setting, and calculate the signal-to-noise ratio of the N2 Raman characteristic peak under each setting; when the signal-to-noise ratio of the N2 Raman characteristic peak decreases for the first time, stop increasing the number of CCD pixel rows; and record the number of pixel rows N corresponding to the maximum signal-to-noise ratio max , which is the optimal number of CCD pixel rows N opt .

[0021] The second aspect of the present invention relates to a fiber-enhanced Raman spectroscopy background silicon noise multi-scale filtering system, which is used to implement a fiber-enhanced Raman spectroscopy background silicon noise multi-scale filtering method according to the first aspect of the present invention; the system includes an aperture 1, an optical lens 2, a slit 3, an optical lens 4, a diffraction grating 5, an optical lens 6, a charge-coupled device 7, and an optical darkroom 8, which are sequentially arranged on the optical path; the aperture 1 is mechanically assembled at the light input end of the optical lens 2; the optical darkroom 8 is used to integrate the slit 3, optical lens 4, diffraction grating 5 and optical lens 6, and to fix, protect and provide an optical darkroom for the above-mentioned components.

[0022] The aperture of the diaphragm is continuously adjustable in the range of 0 to 15 mm, and the adjustment accuracy is 0.1 mm.

[0023] The optical lens is a standard Nikkor lens with a focal length L1 of 85mm, a maximum aperture of f / 1.8, a minimum aperture of f / 16, and a light-clearance diameter of 67mm.

[0024] The width of the slit is continuously adjustable in the range of 0 to 300 μm, and the adjustment accuracy is 1 μm.

[0025] The diffraction grating 5 is a transmission grating with a blazing wavelength of 610 nm and a line density of 1200 l / mm. The diffraction grating 5 is mounted on a precision rotation stage, and its angle with the optical axis can be adjusted with an adjustment accuracy of 1°.

[0026] The optical darkroom is made of metal and composite materials through mechanical processing. The inner wall is laser etched to form a sub-millimeter rough surface, and the inner wall is sprayed with a nano-level aluminum oxide black layer to absorb stray light.

[0027] The beneficial effect of the present invention lies in that, compared with the prior art, the fiber-enhanced Raman spectroscopy background silicon noise multi-scale filtering method and system of the present invention addresses the shortcomings of traditional fiber-enhanced Raman background silicon noise filtering methods, adopts an adjustable aperture to perform radial spatial filtering, and filters out most of the background silicon noise parasitic around the irregularly shaped Raman signal of the target gas; realizes longitudinal spatial filtering through a slit; and realizes lateral filtering with the help of selective integration of charge-coupled device (CCD) pixel rows.

[0028] The beneficial effects of the present invention also include:

[0029] By adjusting the aperture, slit width, and number of CCD pixel rows, this system is adaptable to Raman applications on HCFs of various fiber core sizes, offering high flexibility. Its modular components require simple assembly and assembly, eliminating the need for precise adjustments and reducing system complexity. It effectively filters radial, longitudinal, and transverse background silicon noise, achieving a practical filtering efficiency of 90% or higher. The proposed system is compact and robust, making it well-suited for installation and field deployment. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 This is a schematic diagram of the structure of the multi-scale filtering system for background silicon noise in fiber-enhanced Raman spectroscopy;

[0031] Figure 2 Schematic diagram of the multi-scale filtering principle of background silicon noise in fiber-enhanced Raman spectroscopy;

[0032] Figure 3 Schematic diagram of the application of the multi-scale filtering system for background silicon noise in fiber-enhanced Raman spectroscopy. DETAILED DESCRIPTION

[0033] In order to make the purpose, technical solutions and advantages of the present invention clearer and more accurate, the technical solutions of the present invention are described in detail below through multiple specific embodiments. The embodiments used in the present invention are only used to explain the present invention and are not intended to limit the content of the present invention.

[0034] like Figure 1-3 The first aspect of the present invention relates to a multi-scale filtering method for background silicon noise in fiber-enhanced Raman spectroscopy, the method comprising the following steps:

[0035] Step 1: mechanically assemble a fiber-enhanced Raman spectroscopy background silicon noise multi-scale system at one end of a hollow-core optical fiber to collect the back Raman signal of the hollow-core optical fiber;

[0036] Step 2: Select the optimal parameters of the aperture and use the adjustable aperture to perform radial spatial filtering to filter out the background silicon noise surrounding the Raman signal of the irregular shape of the target gas.

[0037] Step 3, selecting the optimal parameters of the slit 3 width to achieve longitudinal spatial filtering through the slit;

[0038] Step 4: Select the optimal parameters of the CCD pixel row, use the CCD pixel row selective integration to achieve lateral filtering, and obtain the multi-scale filtering results of the background silicon noise of the fiber-enhanced Raman spectroscopy.

[0039] In this example, the wavelength of the laser is 532 nm, and the output laser power is 1.5 W; the aperture of the optical lens 2 and the optical lens 4 is set to f / 1.8; the aperture of the optical lens 6 is set to f / 1.4; the focal length L0 of the lens 9 is 60 mm; the core diameter of the hollow-core antiresonant fiber 10 is 26 μm (the mode field diameter is 0.75 of the core diameter), and the length is 2 m.

[0040] Specifically, the laser is focused by lens 9 and enters the core of the hollow-core optical fiber; the laser is transmitted in the core, interacts with the gas, and generates a Raman signal, which is distributed approximately circularly in space; the laser is also scattered by the antiresonant ring and inner wall in the cladding, generating a silicon Raman signal (i.e., background silicon noise), which is distributed radially in space and envelops the gas Raman signal. The (gas and silicon) Raman signal generated in the hollow-core optical fiber is transmitted in the reverse direction and collimated by lens 9; it is first radially spatially filtered by aperture 1 to filter out most of the background silicon noise parasitic around the target gas (irregular shape) Raman signal; it is then collected by optical lens 2 and focused on the plane of slit 3; the Raman signal is axially spatially filtered by slit 3 to filter out the background silicon noise remaining in the axial direction; it is then collimated by optical lens 4, diffracted and split by grating 5, and then collected by optical lens 6 and focused on the pixel row of CCD7; by selecting the pixel row of CCD7, the background silicon noise is integrated and filtered to filter out the background silicon noise remaining in the lateral direction; the pixel row of CCD7 detects the Raman scattering signal and converts the optical signal into an electrical signal for output for analysis.

[0041] The optimal parameter selection process for aperture 1 is as follows:

[0042] The width of the slit 3 is fixed to 10 μm, the middle row of photosensitive pixels of CCD 7 is selected, and the integration time is 60 s. The other experimental conditions remain unchanged. The aperture of the diaphragm 1 is changed from the reference value D base1 = (D-1.5mm), the Raman spectrum of the laboratory ambient air was obtained every 0.5mm, and the N2 Raman characteristic peak (2327cm -1 ) of the signal-to-noise ratio (SNR). Wherein, the signal intensity is defined as the peak height I of the N2 Raman characteristic peak h , the noise is defined as the spectral baseline between 1800 and 1900 cm -1 The standard deviation σ, and SNR=I h / σ. D is calculated as follows:

[0043]

[0044] Where λ is the wavelength of the excitation light; MFD is the mode field diameter of the hollow-core fiber, which is 0.75 of the core diameter of the hollow-core fiber.

[0045] Compare the signal-to-noise ratio of the series N2 Raman characteristic peak obtained in the first calculation. When it first decreases, stop increasing the aperture of aperture 1. At the same time, record the aperture D corresponding to the maximum signal-to-noise ratio. max1 .

[0046] The aperture of diaphragm 1 is changed from the reference value D base2 =(D max1-0.5mm), the Raman spectrum of the laboratory ambient air was obtained every 0.1mm, and the N2 Raman characteristic peak (2327cm -1 ) of the signal-to-noise ratio.

[0047] Compare the signal-to-noise ratio of the series N2 Raman characteristic peak obtained by the second calculation. When it decreases for the first time, stop increasing the aperture of aperture 1. At the same time, record the aperture D corresponding to the maximum signal-to-noise ratio. max2 , which is the optimal aperture D of the aperture 1 opt .

[0048] Furthermore, the optimal parameter selection process for the width of slit 3 is as follows:

[0049] The clear aperture of fixed aperture 1 is D opt The middle row of CCD7's photosensitive pixels was selected and the integration time was 60s. The other experimental conditions remained unchanged. The width of slit 3 was set to the base value Wbase1 = (W-15μm). The Raman spectrum of the laboratory ambient air was acquired every 5μm, and the N2 Raman characteristic peak (2327cm) under this condition was calculated. -1 ) of the signal-to-noise ratio (SNR). Wherein, the signal intensity is defined as the peak height I of the N2 Raman characteristic peak h , the noise is defined as the spectral baseline between 1800 and 1900 cm -1 The standard deviation σ, and SNR=I h / σ. W is calculated as follows:

[0050]

[0051] L0 is the focal length of lens 9, and L1 is the focal length of optical lens 2. Compare the signal-to-noise ratio of the Raman characteristic peak of series N2 obtained by the first calculation. When it first decreases, stop increasing the width of slit 3; at the same time, record the slit width W corresponding to the maximum signal-to-noise ratio. max1 .

[0052] The width of the slit 3 is increased from the reference value W base2 =(W max1 -5μm), the Raman spectrum of the laboratory ambient air was obtained every 1μm, and the N2 Raman characteristic peak (2327cm -1 ) of the signal-to-noise ratio.

[0053] Compare the signal-to-noise ratio of the series N2 Raman characteristic peak obtained by the second calculation. When it decreases for the first time, stop increasing the width of slit 3; at the same time, record the slit width W corresponding to the maximum signal-to-noise ratio. max2 , which is the optimal width W of the slit 3 opt .

[0054] Furthermore, the optimal parameter selection process for the CCD7 pixel row is as follows:

[0055] The clear aperture of fixed aperture 1 is D opt , the width of slit 3 is W opt The integration time is 60s, and the other experimental conditions remain unchanged. The photosensitive pixels of CCD7 are selected in sequence, the middle row 1, the middle row 3, the middle row 5, the middle row 7, the middle row 9, the middle row 11, the middle row 13, etc., to obtain the Raman spectrum of the laboratory ambient air under each setting, and calculate the N2 Raman characteristic peak (2327cm -1 ) of the signal-to-noise ratio (SNR). Wherein, the signal intensity is defined as the peak height I of the N2 Raman characteristic peak h , the noise is defined as the spectral baseline between 1800 and 1900 cm -1 The standard deviation σ, and SNR=I h / σ.

[0056] Compare the calculated signal-to-noise ratio of the series N2 Raman characteristic peaks. When it first decreases, stop increasing the number of pixel rows of CCD7. At the same time, record the number of pixel rows N corresponding to the maximum signal-to-noise ratio. max , which is the optimal number of pixel rows N of CCD7 opt .

[0057] The system first uses aperture 1 to perform radial spatial filtering to remove most of the background silicon noise parasitic around the irregularly shaped Raman signal of the target gas; then it uses the slit to achieve longitudinal spatial filtering; finally, it uses the charge-coupled device (CCD) pixel row selective integration to achieve lateral filtering.

[0058] The second aspect of the present invention relates to a fiber-enhanced Raman spectroscopy background silicon noise multi-scale filtering system; the system is implemented using the method described in the first aspect of the present invention; the system specifically includes: an aperture 1, an optical lens 2, a slit 3, an optical lens 4, a diffraction grating 5, an optical lens 6, a charge-coupled device 7, and an optical darkroom 8.

[0059] The Fiber-Enhanced Raman Spectroscopy Background Silicon Noise Multiscale Filtering System can be used in a variety of hollow-core fiber-enhanced Raman spectroscopy applications (gases, liquids, etc.). During operation, the components within the device are fixed; the device and the optical fiber are relatively fixed, but different types of optical fibers can be replaced.

[0060] The aperture 1 described in the present invention has a continuously adjustable aperture within a range of 0 to 15 mm, with an adjustment accuracy of 0.1 mm. It is used for radial spatial filtering to remove the majority of the background silicon noise that is parasitic around the (irregularly shaped) Raman signal of the target gas and is distributed radially in a circular pattern. During use, the aperture 1 is mechanically mounted to the light input end of the optical lens 2, with the aperture 1 located on the optical axis.

[0061] The optical lens 2 described herein is a standard Nikkor lens with a focal length L1 of 85 mm, a maximum aperture of f / 1.8, a minimum aperture of f / 16, and a clear diameter of 67 mm. Optical lens 2 is mechanically mounted in optical darkroom 8, with its center positioned on the optical axis. It is used to collect the target gas Raman signal and focus it on the plane of slit 3.

[0062] The slit 3 described in the present invention is composed of two sheet metals arranged side by side in the same plane. The metal sheets are mechanically connected to a differential head outside the optical darkroom 8 for adjusting the slit width. The slit width is continuously adjustable within the range of 0 to 300 μm with an adjustment accuracy of 1 μm. The slit is located on the focal plane of the optical lens 2 and is used for axial spatial filtering to filter out the background silicon noise remaining in the axial direction after radial spatial filtering.

[0063] The optical lens 4 described in the present invention is a standard Nikkor lens with a focal length L2 of 85 mm, a maximum aperture of f / 1.8, a minimum aperture of f / 16, and a clear diameter of 67 mm, and is used for collimating the target gas Raman signal.

[0064] The diffraction grating 5 described in the present invention is a transmission grating with a blaze wavelength of 610 nm and a groove density of 1200 l / mm. It is used for diffraction spectrometry of Raman scattered light from the target gas, that is, to separate Raman scattered light of different wavelengths. During use, the diffraction grating 5 is mounted on a precision rotation stage, and its angle with the optical axis can be adjusted with an accuracy of 1°. The rotation stage is also mechanically connected to the micrometer head outside the optical darkroom 8.

[0065] The optical lens 6 described in the present invention is a standard Nikkor lens with a focal length L3 of 50 mm, a maximum aperture of f / 1.4, a minimum aperture of f / 16, and a clear diameter of 62 mm. It is used to collect the Raman signal of the target gas and focus it on the pixel row plane of the charge-coupled device 7.

[0066] The charge coupled device 7 (CCD) described in the present invention has two functions: on the one hand, it integrates and filters the background silicon noise by selecting the pixel rows of the CCD; on the other hand, it is used to detect the Raman scattering signal of the target gas and convert the optical signal into an electrical signal output for analysis.

[0067] The optical darkroom 8 of the present invention is used to integrate the slit 3, optical lens 4, diffraction grating 5 and optical lens 6, and also serves to fix and protect the above components and provide an optical darkroom. It is made of metal materials (such as aluminum alloy) and composite materials (such as carbon fiber reinforced plastic) through mechanical processing, and the inner wall is laser etched to form a submillimeter rough surface, which uses multiple scattering to consume stray light energy; at the same time, the inner wall is sprayed with a nano-scale aluminum oxide black layer (such as Martin ) is used to absorb stray light to suppress background (shot) noise as much as possible.

[0068] Finally, it should be noted that the above embodiments are intended only to illustrate the technical solutions of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art will appreciate that the technical solutions of the present invention still include modifications or equivalent substitutions that may be made to the specific embodiments of the present invention. Any modifications or equivalent substitutions that do not depart from the spirit and scope of the present invention are intended to be covered by the claims of the present invention.

Claims

1. A multi-scale filtering method for background silicon noise in fiber-enhanced Raman spectroscopy, characterized in that: The method comprises the following steps: The fiber-enhanced Raman spectroscopy background silicon noise multi-scale system is mechanically assembled at one end of the hollow-core fiber to collect the back Raman signal of the hollow-core fiber. The optimal parameters of the aperture are selected, and an adjustable aperture is used for radial spatial filtering to filter out the background silicon noise surrounding the Raman signal of the irregular shape of the target gas. Select the optimal parameters of the slit width to achieve longitudinal spatial filtering through the slit; The optimal parameters of CCD pixel rows are selected, and lateral filtering is achieved with the help of CCD pixel row selective integration to obtain the multi-scale filtering results of background silicon noise in fiber-enhanced Raman spectroscopy.

2. The multi-scale filtering method for background silicon noise in fiber-enhanced Raman spectroscopy according to claim 1, characterized in that: The method of selecting the optimal parameters of the aperture and using the adjustable aperture to perform radial spatial filtering to filter out background silicon noise surrounding the irregularly shaped Raman signal of the target gas comprises: Fixed slit width and CCD photosensitive pixels; Set the aperture of the diaphragm from the reference value D base1 =(D-1.5mm), obtain the Raman spectrum of the laboratory ambient air every 0.5mm, and calculate the signal-to-noise ratio of the N2 Raman characteristic peak under this condition; When the signal-to-noise ratio of the N2 Raman characteristic peak decreases for the first time, stop increasing the aperture of the diaphragm and record the aperture D corresponding to the maximum signal-to-noise ratio. max1 ; From the reference value D base2 =(D max1 -0.5mm), the Raman spectrum of the laboratory ambient air was acquired every 0.1mm, and the signal-to-noise ratio of the N2 Raman characteristic peak under this condition was calculated; When the signal-to-noise ratio of the N2 Raman characteristic peak decreases for the first time, stop increasing the aperture of the diaphragm and record the aperture D corresponding to the maximum signal-to-noise ratio. max2 , which is the optimal aperture D of the diaphragm opt ; D is the standard aperture of the diaphragm, which is calculated as follows: Where λ is the wavelength of the excitation light, L0 is the focal length of the lens that couples the laser into the hollow-core fiber. MFD is the mode field diameter of the hollow-core fiber, which is 0.75 of the core diameter of the hollow-core fiber.

3. The multi-scale filtering method for background silicon noise in fiber-enhanced Raman spectroscopy according to claim 2, characterized in that: The method of selecting the optimal parameters of the slit width and implementing longitudinal spatial filtering through the slit includes: Fixed aperture D opt , CCD photosensitive pixels; Set the slit width from the reference value W base1 =(W-15μm), obtain the Raman spectrum of the laboratory ambient air every 5μm, and calculate the signal-to-noise ratio of the N2 Raman characteristic peak under this condition; When the signal-to-noise ratio of the N2 Raman characteristic peak decreases for the first time, the slit width is stopped from increasing, and the slit width W corresponding to the maximum signal-to-noise ratio is recorded. max1 ; From the reference value W base2 =(W max1 -5μm), the Raman spectrum of the laboratory ambient air was acquired every 1μm, and the signal-to-noise ratio of the N2 Raman characteristic peak under this condition was calculated; When the signal-to-noise ratio of the N2 Raman characteristic peak decreases for the first time, the slit width is stopped from increasing, and the slit width W corresponding to the maximum signal-to-noise ratio is recorded. max2 , which is the optimal slit width W opt ; W is the standard clear aperture of the slit, which is calculated as follows: Wherein, L1 is the focal length of the optical lens.

4. The multi-scale filtering method for background silicon noise in fiber-enhanced Raman spectroscopy according to claim 4, characterized in that: The method selects the optimal parameters of the CCD pixel row, uses the CCD pixel row selective integration to achieve lateral filtering, and obtains the multi-scale filtering results of the fiber-enhanced Raman spectroscopy background silicon noise, including: The fixed aperture is D opt The width of the slit is W opt ; Select the middle 1st row, middle 3rd row, middle 5th row, middle 7th row, middle 9th row, middle 11th row and middle 13th row of CCD photosensitive pixels in sequence; Obtain the Raman spectrum of the laboratory ambient air under each setting and calculate the signal-to-noise ratio of the N2 Raman characteristic peak under each setting; When the signal-to-noise ratio of the N2 Raman characteristic peak decreases for the first time, the number of CCD pixel rows is stopped from increasing; at the same time, the number of pixel rows N corresponding to the maximum signal-to-noise ratio is recorded. max , which is the optimal number of CCD pixel rows N opt .

5. A multi-scale filtering system for background silicon noise in fiber-enhanced Raman spectroscopy, characterized by: The system is used to implement the multi-scale filtering method for background silicon noise of fiber-enhanced Raman spectroscopy according to claims 1-4; The system includes an aperture 1, an optical lens 2, a slit 3, an optical lens 4, a diffraction grating 5, an optical lens 6, a charge coupled device 7, and an optical darkroom 8, which are sequentially arranged on the optical path; The aperture 1 is mechanically assembled on the light input end of the optical lens 2; The optical darkroom 8 is used to integrate the slit 3, the optical lens 4, the diffraction grating 5 and the optical lens 6, and to fix, protect and provide an optical darkroom for the above-mentioned components.

6. The fiber-enhanced Raman spectroscopy background silicon noise multi-scale filtering system according to claim 5, characterized in that: The aperture of the diaphragm is continuously adjustable within the range of 0 to 15 mm, and the adjustment accuracy is 0.1 mm.

7. The fiber-enhanced Raman spectroscopy background silicon noise multi-scale filtering system according to claim 5, characterized in that: The optical lens is a standard Nikkor lens with a focal length L1 of 85 mm, a maximum aperture of f / 1.8, a minimum aperture of f / 16, and a light-clearance diameter of 67 mm.

8. The fiber-enhanced Raman spectroscopy background silicon noise multi-scale filtering system according to claim 5, characterized in that: The width of the slit is continuously adjustable within the range of 0 to 300 μm, and the adjustment accuracy is 1 μm.

9. The fiber-enhanced Raman spectroscopy background silicon noise multi-scale filtering system according to claim 5, characterized in that: The diffraction grating 5 is a transmission grating with a blazing wavelength of 610 nm and a line density of 1200 l / mm; The diffraction grating 5 is mounted on a precision rotation stage, and its angle with the optical axis can be adjusted with an adjustment accuracy of 1°.

10. The fiber-enhanced Raman spectroscopy background silicon noise multi-scale filtering system according to claim 5, characterized in that: The optical darkroom is made of metal and composite materials through mechanical processing. The inner wall is formed into a sub-millimeter rough surface through laser etching, and the inner wall is sprayed with a nano-scale aluminum oxide black layer to absorb stray light.

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