System and method for eliminating secondary diffraction spectrum influence of grating spectrum system

Abstract

The invention provides a system and method for eliminating secondary diffraction spectrum influence of a grating spectrum system, and belongs to the field of grating spectrums.The eliminating system comprises a second filter, a third filter and double slits, the second filter and the third filter correspond to one slit in the double slits respectively, and the second filter and the third filter correspond to the other slit in the double slits respectively. The central wavelength and the passband width of the second filter plate and the third filter plate are matched with the slit distance of the double slits, separation of a second-level diffraction spectrum and a first-level diffraction spectrum is realized by utilizing the matching and design of the double slits and the optical filters, and the influence of the second-level diffraction spectrum of the grating spectrometer is eliminated. According to the invention, an optical filter does not need to be used for suppressing a secondary spectrum, so that the transmittance of the system is improved, the reflected light of the detector protection glass cannot be reflected by the optical filter to form relatively strong stray light, and the stray light formed by secondary diffraction light is reduced.

Description

Technical Field

[0001] The invention belongs to the field of grating spectroscopy, and in particular relates to a system and method for eliminating the influence of secondary diffraction spectrum of a grating spectroscopy system. Background Art

[0002] Grating spectrometer is an instrument that can disperse composite light and obtain energy information of different wavelengths. As a spectroscopic device, the grating has the characteristic of nearly linear dispersion, but due to the existence of multi-order diffraction of the grating, the energy of the useful light is reduced, and the other orders of light are reflected multiple times in the optical path, increasing the source of stray light. Among them, the second-order diffraction has the most serious impact, which is mainly reflected in spectrometers with a relatively wide spectral range, especially in the ultraviolet, visible and near-infrared bands.

[0003] When the spectral range is relatively wide, the short-wave second-order diffraction spectrum and the long-wave first-order diffraction spectrum will overlap. If a spectrometer mainly uses the +1st-order diffraction spectrum of the grating, according to the grating equation:

[0004] ;

[0005] Among them, α is the incident angle, β is the diffraction angle, N is the grating constant, m is the diffraction order, is the wavelength.

[0006] like Figure 1 As shown, the existing grating spectrometer includes a slit 1, a collimator 2, a grating 3, a focusing mirror 4, and a planar array detector 6, which are arranged in sequence to form the 0th order diffraction of the slit, the 1st order diffraction of the slit, and the 2nd order diffraction of the slit. In the case where the wavelength range of the light source is not limited, the +2nd order diffraction spectrum of the 400nm light is very close to the +1st order spectrum of the 800nm. If no processing is done, the signal at 800nm ​​will be greatly interfered, and the spectral information cannot be accurately obtained. Filters are usually used to suppress the secondary diffraction light, that is, a filter is placed in the secondary diffraction light area, so that the long wave passes through to the detector, and the short wave secondary diffraction light is reflected. However, since the secondary diffraction light is reflected and reflected multiple times with other elements of the optical system, stray light will still be formed. Although it is greatly weakened, it is still not negligible. Secondly, the existence of the secondary diffraction suppression filter may cause short-wavelength light to reflect back and forth between the detector protective glass and the secondary diffraction suppression filter to cause stray light.

[0007] In the prior art, filters are inserted into the optical system of the grating spectrometer to limit the secondary spectrum, such as Figure 2 As shown, the first filter 5 divides a glass plate into two areas, such as Figure 3As shown. The blank area on the left is a non-coated area that can transmit the full-band spectrum, and the film layer in the coated area on the right is a long-wave pass. For example, for a spectrometer with a band range of 380~1000nm, the coated area needs to block the transmission of light less than 500nm. Since within this band, the secondary diffraction spectrum of 380nm~500nm may overlap with the primary spectrum of 760nm~1000nm, the coated area should transmit light of 760nm~1000nm. When designing, a margin is usually left. Generally, the coated area can be designed to transmit 550nm~1000nm and cut off 380nm~550nm. In the optical path setting, the primary spectrum of 380nm~600nm can pass through the blank area on the left, and the primary spectrum of 600nm~1000nm can pass through the coated area, so as to ensure that the primary spectrum passes and the secondary spectrum is filtered. However, its coated area is long-wave-transmissive and has an extremely high reflectivity for short-waves, which may cause ghost images. After the short-wave passes through the blank area on the left and reaches the detector protective glass, it will be reflected by about 4% by the protective glass. If the reflected light is reflected by the coated area again, this part of the light will reach the detector again, forming strong stray light.

[0008] In the prior art, there is also a method of suppressing the secondary diffraction spectrum by using a linear gradient filter. The characteristic of the linear gradient filter is that the central wavelength of the light transmitted changes along the gradient direction. If the linear gradient filter is placed in front of the photosensitive surface of the detector, each pixel can only receive a very narrow wavelength range. Even if the short-wave secondary diffraction spectrum and the long-wave primary spectrum are mixed together, they can be effectively filtered out, thereby maximally suppressing the secondary diffraction spectrum and stray light of other wavelengths. However, its cost is high and its gradient rate is limited, so the size of the photosensitive surface of the selected detector must also match, resulting in the limitation of the detector, the large system volume, and the reduced system signal-to-noise ratio. Summary of the invention

[0009] The present invention provides a system and method for eliminating the influence of the secondary diffraction spectrum of a grating spectrum system. Firstly, the ghost images and stray light caused by the secondary diffraction spectrum and multiple reflections of light by the secondary diffraction filter in the existing spectrum system are reduced, thereby improving the luminous flux of the spectrum system. Secondly, miniaturization design is performed while reducing the stray light.

[0010] In order to achieve the above object, the present invention adopts the following technical solution:

[0011] A system for eliminating the influence of a secondary diffraction spectrum of a grating spectrometer system comprises a second filter, a third filter and a double slit, wherein the second filter and the third filter correspond to one slit of the double slit respectively, the central wavelength and passband width of the second filter and the third filter and the slit distance of the double slit are matched, and the separation of the secondary diffraction spectrum and the first-order diffraction spectrum is achieved by using the matching and design of the double slit and the filter, so as to eliminate the influence of the secondary diffraction spectrum of the grating spectrometer.

[0012] The present invention also provides a grating spectrum system, including the above-mentioned system for eliminating the influence of the secondary diffraction spectrum of the grating spectrum system, including a collimator, a grating, a focusing mirror and a planar array detector; the light passes through the front optical system and reaches the filter in front of the double slit, wherein the wavelength is The light passes through the first slit, the wavelength is The light passes through the second slit, and after passing through the collimator, grating and focusing mirror, the slit images of different wavelengths are imaged at different positions on the area array detector; .

[0013] The present invention also provides a method for eliminating the influence of the secondary diffraction spectrum of the grating spectrum system applied to the above-mentioned grating spectrum system, comprising the following steps:

[0014] Step 1, determine the working band of the grating spectrum system;

[0015] Step 2, design the optical path distribution of double slits;

[0016] Step 3, adjust the slit spacing and wavelength;

[0017] Step 4: According to the grating equation, determine the constraints of the slit spacing and wavelength;

[0018] Step 5, determine the calculation formula of the slit spacing;

[0019] Step 6: Verify the wavelength range and slit spacing;

[0020] Step 7: Implement grating spectrum system design to eliminate the influence of secondary diffraction spectrum.

[0021] Beneficial effects:

[0022] 1. The present invention reasonably distributes the working wavelength of the spectrometer to two slits and utilizes the gap between the first-order diffraction spectrum and the second-order diffraction spectrum to separate the spectra of different wavelengths and different diffraction orders in space, thereby solving the aliasing problem of the second-order diffraction spectrum and the first-order diffraction spectrum without using a filter;

[0023] 2. The present invention does not need to use a filter to suppress the secondary spectrum, thereby improving the transmittance of the system, and the reflected light of the detector protection glass will not be reflected by the filter to form relatively strong stray light, thereby reducing the stray light formed by the secondary diffraction light. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 It is a schematic diagram of the aliasing of the secondary diffraction spectrum and the primary spectrum;

[0025] Figure 2 is a schematic diagram of inserting a filter;

[0026] Figure 3 It is a schematic diagram of the partition;

[0027] Figure 4 It is a schematic diagram of a system for eliminating the influence of the secondary diffraction spectrum of a grating spectrum system of the present invention.

[0028] Among them, the reference numerals are: slit 1, collimating mirror 2, grating 3, focusing mirror 4, first filter 5, planar array detector 6, front mirror 7, double slit 8, second filter 9, third filter 10, first slit 11, second slit 12. DETAILED DESCRIPTION

[0029] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0030] like Figure 4 As shown, a system for eliminating the influence of the secondary diffraction spectrum of a grating spectroscopy system according to an embodiment of the present invention comprises a second filter 9, a third filter 10, and a double slit 8; the second filter 9 and the third filter 10 respectively correspond to one of the slits in the double slit 8, and the central wavelength and the passband width of the second filter 9 and the third filter 10 as well as the slit distance of the double slit 8 are matched, and the coordination and design of the double slit 8 and the filter are utilized to realize the separation of the secondary diffraction spectrum and the first-order diffraction spectrum, thereby eliminating the influence of the secondary diffraction spectrum of the grating spectrometer.

[0031] The embodiment of the present invention also provides a grating spectrum system, including the above elimination system, including a collimator 2, a grating 3, a focusing mirror 4 and a planar array detector 6; the light passes through the front optical system and reaches the filter in front of the double slit, wherein the band is The light passes through the first slit, the wavelength is After the light passes through the second slit, passes through the collimator 2, the grating 3 and the focusing mirror 4, the slit images of different wavelengths are imaged at different positions on the area array detector 6; and .

[0032] The present invention also provides a method for eliminating the influence of the secondary diffraction spectrum of the grating spectrum system applied to the above-mentioned grating spectrum system, comprising the following steps:

[0033] Step 1, determine the working band of the grating spectrum system;

[0034] Step 2, design the optical path distribution of double slits;

[0035] Step 3, adjust the slit spacing and wavelength;

[0036] Step 4: According to the grating equation, determine the constraints of the slit spacing and wavelength;

[0037] Step 5, determine the calculation formula of the slit spacing;

[0038] Step 6: Verify the wavelength range and slit spacing;

[0039] Step 7: Implement grating spectrum system design to eliminate the influence of secondary diffraction spectrum.

[0040] Specifically, assuming that the working band of the spectrometer is ~ , < < . Set the wavelength to ~ The light of passes through the first slit 11 in the double slit 8 alone, and the wavelength is ~ The light passes through the second slit 12. By adjusting the slit spacing and wavelength , so that ~ The primary spectrum is just at the wavelength Between the zero-order light and the first-order spectrum, ~ The primary spectrum is just at ~ The area between the primary spectrum and the secondary spectrum is avoided to avoid the problem of inaccurate spectrum acquisition caused by the aliasing between spectra of different wavelengths and different levels.

[0041] Combining the above conditions with the spectrometer's specific parameters, such as the grating constant, the first-order spectral dispersion length, etc., the slit spacing and .

[0042] According to the grating equation: ;

[0043] Among them, α is the incident angle, β is the diffraction angle, N is the grating constant, m is the diffraction order, is the wavelength. According to the above principle, the following two conditions need to be met:

[0044] (1) The 0th-order image and the 1st-order image of the first slit 11 (wavelength ) is larger than the first-order dispersion angle (wavelength) of the second slit 12. ~ The angle between );

[0045] (2) First-order diffraction of the second slit 12 (wavelength ) and second-order diffraction (wavelength ) is larger than the first-order dispersion angle (wavelength) of the first slit 11. ~ Since the light passes through two slits and is collimated by collimator 2, the incident angles reaching the grating are the same. The incident angle is assumed to be 0. The specific analysis is as follows:

[0046] Condition 1: ;

[0047] in, Indicates the wavelength of the first slit 11 The first-order diffraction angle is Indicates the wavelength of the second slit 12 The first-order diffraction angle is Indicates the wavelength of the second slit 12 The first order diffraction angle.

[0048] Condition 2: ;

[0049] in, Indicates the wavelength of the first slit The first-order diffraction angle is Indicates the second wavelength The second diffraction angle.

[0050] Combining the two inequalities, we can get:

[0051] Condition 1: ;

[0052] Condition 2: ;

[0053] Finally, the two conditions are equivalent:

[0054] ;

[0055] If the wavelength range is 380nm~1000nm, then , then the slit spacing d can be solved based on the constraint that the light rays of each diffraction order do not overlap.

[0056] ;

[0057] ;

[0058] Where f is the focal length determined by the optical design, assuming that the system object-image ratio is 1:1.

[0059] Preferably, the components used in the present invention are all transmissive components, including lenses and gratings, and reflective optical components may also be used.

[0060] Preferably, the slit is not limited to a mechanical slit or a photolithography slit, and a double aperture may also be used.

[0061] Preferably, a slit is used, and the second filter 9 and the third filter 10 are placed along the slit direction, and the planar array detector 6 is used to record the spectral data, which is equivalent to two spectrometers using a set of optical systems. The band ranges of the two spectrometers do not have the phenomenon of second-order diffraction spectrum aliasing, but when combined together, a larger working spectrum range can be achieved without the influence of second-order diffraction spectrum aliasing.

Claims

1. A system for eliminating the influence of secondary diffraction spectrum of a grating spectrum system, characterized in that: The invention comprises a second filter, a third filter and a double slit, wherein the second filter and the third filter correspond to one slit of the double slit respectively, the central wavelength and the passband width of the second filter and the third filter and the slit distance of the double slit are matched, and the coordination and design of the double slit and the filter are utilized to realize the separation of the secondary diffraction spectrum and the first-order diffraction spectrum, and eliminate the influence of the secondary diffraction spectrum of the grating spectrometer.

2. A grating spectroscopy system, comprising the system for eliminating the influence of secondary diffraction spectrum of a grating spectroscopy system according to claim 1, characterized in that: It includes a collimator, a grating, a focusing mirror and an array detector; the light passes through the front optical system and reaches the filter in front of the double slit, and the band is The light passes through the first slit, the wavelength is The light passes through the second slit, and after passing through the collimator, grating and focusing mirror, the slit images of different wavelengths are imaged at different positions on the area array detector; .

3. A method for eliminating the influence of the secondary diffraction spectrum of a grating spectrum system according to claim 1, characterized in that: The steps include: Step 1, determine the working band of the grating spectrum system; Step 2, design the optical path distribution of double slits; Step 3, adjust the slit spacing and wavelength; Step 4: According to the grating equation, determine the constraints of the slit spacing and wavelength; Step 5, determine the calculation formula of the slit spacing; Step 6: Verify the wavelength range and slit spacing; Step 7: Implement grating spectrum system design to eliminate the influence of secondary diffraction spectrum.

4. The method for eliminating the influence of the secondary diffraction spectrum of a grating spectrum system according to claim 3 is characterized in that: In step 1, it is assumed that the working band of the spectrometer is ,in .

5. The method for eliminating the influence of the secondary diffraction spectrum of a grating spectrum system according to claim 3, characterized in that: In step 2, the wavelength range The light passes through the first slit in the double slit, and the wavelength range The light passes through the second slit in the double slit.

6. The method for eliminating the influence of the secondary diffraction spectrum of a grating spectrum system according to claim 3, characterized in that: The step 3 comprises: making The primary spectrum is just at the wavelength between the zero-order light and the first-order spectrum; The first-order spectrum is just at The area between the primary and secondary spectra.

7. The method for eliminating the influence of the secondary diffraction spectrum of a grating spectrum system according to claim 3, characterized in that: The grating equation in step 4 is sin(α)+sin(β)=Nmλ; Among them, α is the incident angle, which is assumed to be 0, β is the diffraction angle, N is the grating constant, m is the diffraction order, and λ is the wavelength.

8. The method for eliminating the influence of the secondary diffraction spectrum of a grating spectrum system according to claim 3, characterized in that: The constraints in step 4 are: The constraints on the diffraction angle are: ； ； Further simplified to: ； ； Finally, we conclude: ; in, Indicates the wavelength of the first slit The first-order diffraction angle is Indicates the wavelength of the second slit The first-order diffraction angle is Indicates the wavelength of the second slit The first-order diffraction angle is Indicates the wavelength of the first slit The first-order diffraction angle is Indicates the second wavelength The second diffraction angle.

9. The method for eliminating the influence of the secondary diffraction spectrum of a grating spectrum system according to claim 3, characterized in that: In step 5, the slit spacing d is calculated according to the constraints of the focal length f of the optical system and the diffraction angle: ； 。 10. The method for eliminating the influence of the secondary diffraction spectrum of a grating spectrum system according to claim 8, characterized in that: The step 6 comprises: If the wavelength range is 380 nm ~ 1000 nm, then according to the above constraints, The value range is: 620nm ≤ ≤ 1000 nm.

11. The method for eliminating the influence of the secondary diffraction spectrum of a grating spectrum system according to claim 3, characterized in that: The step 7 comprises: Design and install double slits, filters, collimators, gratings, focusing mirrors and array detectors; Adjust the parameters of each component, including the slit spacing, the central wavelength of the filter and the passband width, to ensure that the grating spectroscopy system effectively eliminates the influence of the secondary diffraction spectrum and improves the accuracy of spectral measurement.

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