C-T light path structure suitable for near-infrared band Raman spectrometer and application

Abstract

The invention belongs to the technical field of optical instruments, and particularly discloses a C-T light path structure suitable for a near-infrared band Raman spectrometer and application, and the C-T light path structure comprises an entrance slit unit, a self-adaptive aperture unit, a collimation unit, a diffraction unit, a focusing unit and a detection unit; the adaptive aperture unit is located behind the entrance slit unit and coincides with an object space focal plane of the collimation unit, the diffraction unit is located on a reflection light path of the collimation unit, and the detection unit is located on an image space focal plane of the focusing unit; the entrance slit unit comprises an entrance slit which is connected with an SMA905 optical fiber; the self-adaptive aperture unit comprises a diaphragm, the collimation unit comprises a collimating mirror, the diffraction unit comprises a plane scribed line diffraction grating, and the focusing unit comprises a focusing mirror and a cylindrical mirror. The optical path system provided by the invention not only realizes a compact structure, but also ensures the stability, high resolution and detection precision of the system.

Description

Technical Field

[0001] The invention belongs to the technical field of optical instruments, and in particular relates to a CT optical path structure suitable for a near-infrared band Raman spectrometer and its application. Background Art

[0002] Raman spectrometer is a spectral analysis instrument based on Raman scattering effect, which is widely used in molecular structure analysis. By irradiating the sample with laser, Raman spectrometer can detect the frequency shift information in the scattered spectrum to identify the chemical composition and molecular structure of the substance. Due to its high sensitivity, non-destructiveness and ability to detect extremely low concentration substances, Raman spectrometer is widely used in many fields such as chemical research, biomedicine, drug testing and food safety.

[0003] With the rapid development of modern technology, low-wavenumber, high-resolution Raman spectrometers have gradually become the focus of research. Traditional Raman spectrometers mostly work in the visible light band and are easily interfered by sample fluorescence, resulting in a decrease in signal quality. In order to reduce fluorescence interference, more and more studies have shifted the working band of Raman spectroscopy to the near-infrared region (NIR), which significantly weakens the influence of fluorescence background and is particularly suitable for the analysis of high-fluorescence samples of biological tissues and complex chemical materials. The optical path design of Raman spectrometers is the key to achieving high-precision and high-sensitivity detection. The Czerny-Turner (CT) optical path structure is a classic and widely used design in spectrometers. It consists of two mirrors and a diffraction grating, which is designed for dispersion and spectroscopy. The CT optical path has high spectral resolution, compact structure and good flexibility, and is widely used in spectral analysis from ultraviolet to infrared bands.

[0004] The existing Czerny-Turner (CT) optical path structure has been widely used in spectrometers, especially in high-resolution and sensitive spectral detection. However, with the rapid development of modern technology and higher requirements for spectrometer performance, the limitations of the CT optical path have begun to emerge, especially in the contradictions between resolution and system volume, incident aperture and energy utilization. In the design of spectrometers, spectral resolution is always a crucial indicator. In order to improve the resolution, it is usually necessary to rely on a long optical path and a diffraction grating with high-density lines. Although this can theoretically enhance the ability to separate the spectrum, it also directly leads to a significant increase in the volume of the system. Especially in the design of portable and miniaturized spectrometers, the long optical path makes it difficult to reduce the volume of the device, hindering the trend of modern spectrometers towards integration and compactness. The contradiction between the demand for high resolution and volume limitations has become increasingly obvious. At the same time, the CT optical path is also faced with the mutual constraints between the incident aperture and volume. In order to improve the signal strength, increasing the incident aperture can effectively increase the light flux entering the optical path. However, the increased light flux requires larger optical components, especially the size of the reflector and grating, which further leads to the expansion of the system volume. This pursuit of greater light flux conflicts with the need for miniaturization, forcing the CT optical path to compromise between light flux and volume in design. Such compromise often comes at the expense of the compactness of the system, affecting its application prospects in miniature spectrometers. In addition, the contradiction between the incident aperture and energy utilization efficiency has gradually become a core issue in the design of CT optical paths. Although a larger aperture can introduce more light energy, the divergence of the light beam increases accordingly. For the CT optical path, the optical components of the system require collimated parallel light beams to ensure the efficient operation of the diffraction grating. When multimode fiber is used for input, the divergent light beam cannot be fully captured by the grating and reflector, resulting in a decrease in energy utilization efficiency. This loss of efficiency directly affects the intensity and detection accuracy of the spectral signal, especially in near-infrared detection that requires high sensitivity. A more complicated situation occurs in wide-band applications. The diffraction efficiency of the diffraction grating of the CT optical path is not consistent in different wavelength ranges. Especially in wide-band applications from ultraviolet to near-infrared, the diffraction efficiency varies significantly with wavelength, resulting in a decrease in spectral resolution and sensitivity. This efficiency inhomogeneity further exacerbates the limitations of CT optical paths in wide-band applications, limiting their performance in application scenarios that require efficient full-band spectral splitting. These technical contradictions of CT optical path structures in traditional spectrometer design show that despite its obvious advantages in spectral dispersion capability, in the process of modern spectrometers developing towards high resolution, compactness, and high efficiency, issues such as optical path volume, incident aperture, and energy utilization still need to be resolved. Summary of the invention

[0005] The purpose of the present invention is to overcome the defects of the prior art and provide a CT optical path structure and application suitable for a near-infrared band Raman spectrometer.

[0006] In order to achieve the above purpose, the technical solution of the present invention is: a CT optical path structure suitable for a near-infrared band Raman spectrometer, comprising an incident slit unit, an adaptive aperture unit, a collimation unit, a diffraction unit, a focusing unit and a detection unit; the adaptive aperture unit is located behind the incident slit unit and coincides with the object-side focal plane of the collimation unit, the diffraction unit is located on the reflected light path of the collimation unit, and the detection unit is located on the image-side focal plane of the focusing unit; the incident slit unit comprises an incident part and a slit part; the adaptive aperture unit comprises an aperture, the collimation unit comprises a collimating lens, the diffraction unit comprises a plane ruled diffraction grating, the focusing unit comprises a focusing lens and a cylindrical lens, and the detection unit is located on the image-side focal plane of the focusing unit.

[0007] In a preferred embodiment of the present invention, the adaptive aperture unit is used to adjust the light flux of the entrance pupil so that the light passing through the measured medium in the optical fiber enters the CT optical path; the collimation unit is used to collimate the incident light so that the incident light becomes parallel light, and the parallel light is reflected to the plane ruled diffraction grating; the diffraction unit is used to split the incident parallel light, and reflect the same wavelength in the split light beam to the focusing unit; the focusing unit is used to focus and collimate the split light beam, and the monochromatic light of the same wavelength is gathered to the detection unit; the detection unit is used to collect and convert the optical signal focused by the focusing unit for subsequent processing.

[0008] In a preferred embodiment of the present invention, the size of the incident slit is (0.03-0.07) mm*(2-4) mm, preferably 0.05 mm*3 mm.

[0009] In a preferred embodiment of the present invention, the aperture size is selected according to the actual light path design size and the required luminous flux. Taking into account that the addition of the aperture will result in the loss of a portion of the luminous flux, it is not advisable to select a too small aperture for a portable instrument. The optional range is 2mm*2mm-4mm*4mm according to actual usage. The hollow size of the aperture is preferably 0.6mm*0.6mm, and the overall size of the aperture is preferably 2mm*2mm. The material of the aperture is aluminum alloy.

[0010] In a preferred embodiment of the present invention, the collimator is a concave reflector with a curvature radius of -95 mm. The angle α between the incident light and the outgoing light of the collimator can be between 8 and 10°.

[0011] In a preferred embodiment of the present invention, the light incident angle i of the planar ruled diffraction grating is selected according to the required resolution and the overall optical path volume setting, and the optional range is 8-12° according to the actual application situation. The light exit angle θ is calculated by the grating equation based on the selected grating scale and the wavelength range used in the optical path, combined with the light incident angle i, and is preferably 47-50°. The grating lines can be selected to be 0.86-1.4 lines / μm according to the length of the CMOS.

[0012] In a preferred embodiment of the present invention, the focusing mirror is a concave reflector with a curvature radius of -102 mm. The angle β between the incident light and the outgoing light of the focusing mirror is optimized according to the selected CMOS pixel size combined with the grating angle and the collimator angle. The optional range is 28-32° according to actual application conditions. The curvature radius of the cylindrical mirror is -5 mm.

[0013] In a preferred embodiment of the present invention, the detection unit receives diffraction light of +1 order, and the number of detector pixels and pixel size are flexibly selected according to the selection of grating lines. The present invention preferably has 2048 pixels and a pixel size of 14μm*200μm.

[0014] In a preferred embodiment of the present invention, the detection unit is a CMOS linear array image detector.

[0015] The above-mentioned CT optical path structure suitable for near-infrared band Raman spectrometer is applied in the Raman spectrometer.

[0016] Compared with the prior art, the present invention has the following beneficial effects:

[0017] 1..The CT optical path structure of the present invention adds a central hollow aluminum alloy device as an aperture, so that the optical system can effectively limit the excessive scattering area caused by the 0.22 aperture of the optical fiber when responding to different design needs, such as portable and handheld Raman spectrometers. It can not only effectively eliminate the stray light caused by improper optical fiber coupling in the system while ensuring the overall energy utilization of the optical path, but also keep the optical path structure simple, small in size and low in cost, and can be used in portable Raman instruments and handheld Raman instruments in the near-infrared band.

[0018] 2. The CT optical path structure of the present invention uses a plane ruled diffraction grating as a dispersion element to reduce absorption. By adjusting the angle and distance of the collimator, grating, and focusing lens, the overall resolution of the optical path can be 2 cm in the full band. -1 , which greatly improves the detection accuracy of this optical system when applied, and greatly compresses the volume of the optical path system while ensuring that the resolution is high enough. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 The optical path principle diagram of the CT optical path structure of the present invention is applicable to the infrared band Raman spectrometer;

[0020] Figure 2 This is a light path simulation diagram of the CT light path structure applicable to the infrared band Raman spectrometer of the present invention;

[0021] Figure 3 This is a physical modeling diagram of the optical path of the CT optical path structure applicable to the infrared band Raman spectrometer of the present invention;

[0022] In the figure: 1-incident slit unit, 2-adaptive aperture unit, 3-collimation unit, 4-diffraction unit, 5-focusing unit, 6-focusing mirror, 7-cylindrical mirror, 8-detection unit. DETAILED DESCRIPTION

[0023] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is described in more detail below with reference to the accompanying drawings and specific embodiments, but the protection scope of the present invention is not limited to these embodiments.

[0024] The present invention discloses a CT optical path structure suitable for a near-infrared band Raman spectrometer, aiming to solve the problem that the optical path volume and resolution cannot be taken into account in the current portable and handheld Raman instruments, and the incident aperture and the optical path volume are difficult to be compatible. This CT optical system proposes an adaptive aperture design for the first time, which effectively controls the light flux by minimizing the optical path volume, so that the detection unit can detect extremely low-energy light signals. This design overcomes the defect of the traditional cross-type Czerny-Turner structure that the system volume increases due to the excessive aperture of the laser fiber. The present invention introduces a cylindrical mirror on the basis of a focusing mirror, and its main function is to further collimate and focus the light after passing through the focusing mirror. Its key advantage is to control the light beam more accurately. The cylindrical mirror can effectively improve the focusing quality and collimation effect of the light beam, ensuring that the light beam can fall on the photosensitive surface of the detector with extremely high precision. This not only improves the spectral resolution of the system, but also improves the energy utilization efficiency, thereby enhancing the spectrometer's ability to detect weak signals. In general, the CT optical system not only retains the advantages of the CT optical path, but also combines the characteristics of adaptive aperture, which greatly improves the energy utilization efficiency of the spectrometer and significantly improves the resolution and portability of the system.

[0025] like Figure 1As shown, the CT optical path structure of the present invention applicable to the infrared band Raman spectrometer is composed of the following parts: an incident slit unit 1, an aperture adaptation unit 2, a collimation unit 3, a diffraction unit 4, a focusing unit 5 and a detection unit 8. Among them, the incident slit unit 1 is used as the incident slit of the CT optical path, through which the light in the optical fiber is guided into the optical path system to ensure that the spot size of the subsequent light beam meets the requirements of the subsequent optical system. The incident slit unit includes an incident part SMA905 seat and a slit part. The adaptive aperture unit 2 is used as the aperture designed this time, located behind the incident slit, to adjust the light flux. Under a specific optical design, the adaptive aperture unit can effectively control the angle and divergence of the incident light, optimize the shape of the light beam entering the spectrometer, reduce the entry of redundant light beams, and thus improve the overall optical efficiency of the system; the collimation unit 3 is a concave reflector, used as a collimation device, responsible for collimating the incident light incident in concentric circles through the adaptive aperture unit into a parallel light beam. The parallel light beam is the basis of spectral dispersion in the CT optical path, and its collimation will directly affect the resolution of the subsequent spectrum and the accuracy of the spectral signal. The collimation unit 3 hits the parallel light onto the plane diffraction line grating in the diffraction unit 4; the diffraction unit 4 is located on the reflection light path of the collimation unit 3, and has two functions, one is to split the incident light, and the other is to reflect the split light beam to the focusing unit 5; the focusing unit 5 is composed of a concave reflector 6 and a cylindrical mirror 7, which is used to collimate and focus the received split light beam. The concave reflector reflects light of different wavelengths, and the cylindrical mirror further focuses and collimates the light beam, so that the final light beam falls accurately on the photosensitive surface of the detector; the detection unit 8 is located on the image focal plane of the focusing unit 5, and is used to receive the light signal of the target after splitting in the incident direction, and convert it into an electrical signal for subsequent signal processing.

[0026] like Figure 2 As shown, the working principle of a CT optical path system suitable for an infrared band Raman spectrometer is as follows: the incident light enters the CT optical path through the incident slit unit and the adaptive aperture unit, is reflected by the collimation unit, and propagates to the diffraction unit 21 as a plane light wave. The diffraction unit 21 diffracts and splits the complex light hitting the grating surface, and reflects a divergent light beam. The divergent light beam is double-focused and collimated by the focusing unit, and the monochromatic light of the same wavelength is focused on the detector located on the focal plane of the holographic concave grating 21, and the detector collects spectral data.

[0027] In this optical system, the collimator is a concave reflector with a radius of curvature of -95mm, an angle of 9° between the incident and outgoing light rays, a distance of 45.302mm from the aperture, and is located directly behind the aperture. The incident angle and diffraction angle of the plane diffraction ruled grating are 21° and -48.472° respectively, and the existing commercial grating template can be selected for customization. The distance between the collimator and the collimator is -40mm, and it is located in the upper left of the collimator. The focusing mirror is a concave reflector with a radius of curvature of -102, an angle of 30.468° between the incident and outgoing light rays, a distance of 49.217mm from the plane ruled diffraction grating, and is located in the upper right of the plane ruled diffraction grating. The glass material of the concave reflector is preferably K9 from Chengdu Guangming. The cylindrical lens is a cylindrical lens made of BK7 from Chengdu Guangming, with a thickness of 3mm, a radius of curvature of -5, a distance from the focusing lens of -42mm, and is located on the upper left of the focusing lens. The detector is a linear array CMOS of Hamamatsu S11693-01, with an effective photosensitive length of 28.672mm, an actual use length of 24mm, 2048 pixels, and a pixel size of 14μm*200μm. Due to the existence of the cylindrical lens, the fixed Y axis is the optical axis direction, and the corresponding image plane setting should also be rotated 90° along with the cylindrical lens.

[0028] like Figure 3 As shown, in actual application of the present invention, the specific lens fixing mode can be selected as a bottom and side double fixing mode, and an integrated molding cutting process is adopted to minimize the deviation.

[0029] Table 1 Spot and resolution of CT optical path structure suitable for infrared band Raman spectrometer

[0030]

[0031] As shown in Table 1, after calculating the full-band 2 wave number resolution and setting the corresponding wavelength, the light spots corresponding to the adjacent resolution rays on the image plane are completely separated, and according to Figure 1 As shown by the ruler, the overall volume is 5cm*6cm*3cm.

[0032] Table 2. RMS details of the CT optical path structure for infrared Raman spectrometers

[0033]

[0034] As shown in Table 2, according to the detector pixel size and the optical axis direction as the Y axis, after the detector is rotated by a corresponding angle, the maximum Y axis size of the light spot is 12 μm and the minimum is 5.08 μm, which is completely consistent with the detector pixel Y axis width of 14 μm.

[0035] Based on the above structural setting, the CT-type structural imaging system based on the holographic concave grating of the present invention has the following characteristics: a hollow aperture made of aluminum alloy is introduced into the optical path, and a precise opening design is made at the center of the aperture to achieve remarkable results in limiting the influence of stray light; the addition of the aperture not only strictly controls the aperture on the object side, limiting its maximum value to 0.125, but also effectively improves the light flux while maintaining the compact volume of the system. This design greatly improves the stray light problem in fiber coupling, thereby reducing the light scattering caused by improper fiber aperture, ensuring the signal detection accuracy of the optical system, and enhancing the ability to capture weak Raman signals.

[0036] The present invention uses commercial templates to customize the plane ruled diffraction grating, which effectively reduces the manufacturing cost. Under certain volume requirements, a grating ruled line density of 1.2 lines / μm is selected to greatly enhance the grating's spectroscopic ability. At the same time, the selection of the grating blaze angle matches the characteristics of the near-infrared band, ensuring efficient spectroscopic effects within the full spectrum. The present invention introduces a cylindrical mirror in the focusing unit, which plays a vital role in light beam focusing and collimation. The cylindrical mirror further improves the focusing accuracy of the light beam, so that monochromatic light of the same wavelength can be accurately focused on the detector, thereby significantly improving the resolution and detection accuracy of the system. Through the synergistic effect of the cylindrical mirror and the concave reflector, the optical path system of the present invention not only achieves a compact structure, but also ensures the stability and high resolution of the system, and is particularly suitable for miniature and portable Raman spectrometers.

[0037] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that the technical solutions described in the aforementioned embodiments may still be modified, or some or all of the technical features thereof may be replaced by equivalents. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A CT optical path structure suitable for a near-infrared Raman spectrometer, characterized in that: It includes an incident slit unit, an adaptive aperture unit, a collimating unit, a diffraction unit, a focusing unit and a detection unit; the adaptive aperture unit is located behind the incident slit unit and coincides with the object-side focal plane of the collimating unit, the diffraction unit is located on the reflected light path of the collimating unit, and the detection unit is located on the image-side focal plane of the focusing unit; the incident slit unit includes an incident part and a slit part; The adaptive aperture unit includes an aperture, the collimating unit includes a collimating mirror, the diffraction unit includes a plane ruled diffraction grating, the focusing unit includes a focusing mirror and a cylindrical mirror, and the detection unit is located on the image-side focal plane of the focusing unit.

2. The CT optical path structure suitable for near-infrared Raman spectrometer according to claim 1, characterized in that: The adaptive aperture unit is used to adjust the light flux of the entrance pupil so that the light passing through the measured medium in the optical fiber enters the CT optical path; the collimation unit is used to collimate the incident light so that the incident light becomes parallel light and reflects the parallel light to the plane ruled diffraction grating; the diffraction unit is used to split the incident parallel light and reflect the same wavelength in the split light beam to the focusing unit; the focusing unit is used to focus and collimate the split light beam and gather the monochromatic light of the same wavelength to the detection unit; the detection unit is used to collect and convert the optical signal focused by the focusing unit for subsequent processing.

3. The CT optical path structure suitable for near-infrared Raman spectrometer according to claim 1, characterized in that: The size of the incident slit is (0.03-0.07) mm*(2-4) mm.

4. The CT optical path structure suitable for Raman spectrometer according to claim 1, characterized in that: The size of the aperture is 2mm*2mm-4mm*4mm, and the material of the aperture is aluminum alloy.

5. The CT optical path structure suitable for near-infrared Raman spectrometer according to claim 1, characterized in that: The collimator is a concave reflector with a curvature radius of -95 mm. The angle between the incident light and the outgoing light of the collimator is α=8-10°.

6. The CT optical path structure suitable for near-infrared Raman spectrometer according to claim 1, characterized in that: The light incident angle i of the plane ruled diffraction grating is 8-12°, the light exit angle θ is 47-50°, and the grating ruled line length is 0.86-1.4 lines / μm.

7. The CT optical path structure suitable for near-infrared Raman spectrometer according to claim 1, characterized in that: The focusing mirror is a concave reflector with a curvature radius of -102 mm. The angle β between the incident light and the outgoing light of the focusing mirror is 28-32°. The curvature radius of the cylindrical mirror is -5 mm.

8. The CT optical path structure suitable for near-infrared Raman spectrometer according to claim 1, characterized in that: The detection unit receives diffraction light of +1 order, the number of detector pixels is 2048, and the pixel size is 14 μm*200 μm.

9. The CT optical path structure suitable for near-infrared Raman spectrometer according to claim 1, characterized in that: The detection unit is a CMOS linear array image detector.

10. Application of the CT optical path structure suitable for a near-infrared band Raman spectrometer according to any one of claims 1 to 9 in a Raman spectrometer.

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