An equal-wavenumber division banding noise reduction method for an infrared Fourier transform spectrometer

Abstract

The application discloses an equal-wavenumber division waveband noise reduction method for an infrared Fourier transform spectrometer, and is applied to fine spectral detection with wide spectral range and ultrahigh resolution. When designing a low-temperature infrared Fourier transform spectrometer, a low-temperature filter wheel is arranged in an optical path in front of a detector, and the low-temperature filter wheel is driven by a low-temperature motor. A plurality of filters are arranged on the filter wheel, the central wavelengths of the filters are different, the central wavelength intervals are different, the central wavelengths and the bandwidths of the filters are designed according to equal central spectral intervals, each filter has a narrow bandwidth, and according to a spectral range of a required detection target, a corresponding filter is selected to realize spectral detection with ultrahigh spectral resolution of a concerned spectral range. For the infrared Fourier transform spectrometer with high spectral resolution and wide spectral bandwidth, the measurement brings the advantage of reducing noise caused by out-of-band photons on the detector, and low temperature of the filter reduces infrared background and photon noise caused by the filter body.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of infrared optical instrument technology, and particularly relates to an equal-wavenumber division waveband noise reduction method for an infrared Fourier transform spectrometer. BACKGROUND

[0002] For satellite atmospheric composition limb remote sensing detection, high spectral resolution and large spectral bandwidth are required, and the target temperature is low. For solar magnetic field infrared spectrum detection, high spectral resolution and a very small field of view are required, and the signal is weak. The spectral resolution index of the atmospheric super radiation spectrometer currently under research is 0.015 wave number, the detection waveband range is 3.2-15.4 μm, and the detection limb atmosphere (Ministry of Science and Technology National Key Research and Development Plan Project - Atmospheric Radiation Super Spectrum Detection Technology - Approval No. 2016YFB0500600) is detected. The spectral resolution index of the solar magnetic field measurement spectrometer under research is 0.004 wave number, and the front field of view is 1.5 angular seconds (National Major Fund Project - Mid-Infrared Observation System for Accurate Measurement of Solar Magnetic Field - Approval No. 11427901).

[0003] The characteristics of the super high spectral resolution infrared Fourier transform spectrometer are as follows: the spectral resolution is extremely high, the spectral bandwidth is large, and the instrument has the ability to cover a continuous spectrum range. As a result, the energy of a spectral element bandwidth is small and the photon noise is large. The super high spectral resolution infrared Fourier transform spectrometer mainly comprises an interferometer and an energy collection system. By designing low-temperature interferometer technology, low-temperature adjustable field stop technology, and the like, the infrared background of the interferometer and the field stop can be reduced, and thus the background noise of the entire spectrometer system can be reduced. In this case, it is more necessary to cool the filter wheel. For some specific requirements, for example: to expand the application requirements, the wider the continuous spectrum range that the instrument can cover, the better, and the higher the spectral resolution, the more precise the instrument detects the spectral line. However, at the same time, the energy of a spectral element bandwidth will be smaller. When performing super high spectral resolution detection, sometimes the spectrum range is concerned, and sometimes the spectrum range is concerned. If the light of the entire spectrum range is incident on the detector at the same time, the photon noise will be large, and the signal-to-noise ratio of the instrument will be affected.

[0004] The present application proposes a method for designing a low-temperature filter wheel to reduce the noise caused by out-of-band photons and the infrared background of the super high spectral resolution infrared Fourier transform spectrometer. When performing spectral detection, the filter corresponding to the spectrum range of the detection target is selected to reduce the out-of-band photon noise. The filter wheel is arranged in a low-temperature vacuum, and the infrared background of the filter wheel device itself is also reduced.

[0005] The smaller the field of view of the instrument detector unit, the lower the temperature of the detected target in front, and the smaller the signal, which requires a lower filter temperature. For example, the temperature of the follow-up optical design of the super radiation atmospheric spectrometer is 90K, and the temperature of the follow-up optical design of the solar magnetic field spectrometer is 80K. SUMMARY

[0006] The purpose of the present application is to provide an equal wave number division wave band noise reduction method for an infrared Fourier transform spectrometer.

[0007] The technical solution of the present application is as follows:

[0008] The method for scanning and detecting the spectral band covered by the instrument by using a low-temperature filter wheel is designed to finely detect the specific target spectrum. The low-temperature filter wheel is controlled by a low-temperature driving device, and a plurality of filters are installed on the filter wheel. Each filter has a different center wavelength, and the center wavelengths of each filter have different spacings. The center wavelengths and bandwidths of each filter are designed to be equal in center spectral distance, and each filter has a narrow bandwidth. For different detection spectral bands of interest, the corresponding spectral band filter is selected to achieve fine spectral detection of the ultra-high spectral resolution of the concerned spectral band, and to reduce the noise caused by the infrared background and out-of-band photons on the detector.

[0009] The total bandwidth of the filters on the low-temperature filter wheel needs to cover the starting wavelength to the ending wavelength of the spectral instrument detection band, and the center wavelengths of each filter are designed to be equal in center spectral distance. Let the starting wavelength of the infrared Fourier transform spectrometer detection band be W b micron, and the ending wavelength be W e micron, divide the entire band into n sub-bands, and design n filters, each corresponding to a sub-band. The filter number is set as i, and the center wavelength of the i-th filter is set as λ 中心-i . As shown in Figure 1 and Figure 2 .

[0010] The band is divided according to the equal wave number width:

[0011] The starting wave number and the ending wave number of the i-th filter are set as σ i and σ i+1 , and the calculation formula is:

[0012]

[0013]

[0014] The starting wavelength and the ending wavelength corresponding to the i-th filter are set as λ i and λ i+1 , and the calculation formula is:

[0015]

[0016]

[0017] The center wavelength of the i-th filter is λ 中心-i The calculation formula is:

[0018]

[0019] The calculation formula of the wavelength bandwidth of the i-th filter is:

[0020]

[0021] The interval of the center wavelengths is not equal, the center wavelengths and the bandwidths are designed according to equal center spectral distance, each filter has the characteristics of narrow bandwidth, and the spectrum is scanned and detected by selecting different waveband filters during detection.

[0022] The advantages of the present application are that the waveband is divided by using the filter wheel, the out-of-band photons are blocked, the noise is reduced, the low-temperature design of the filter wheel reduces the infrared radiation background and noise thereof, and the signal-to-noise ratio of the instrument is improved; in the case that the spectral brightness characteristic of the target changes slowly, the center wavelengths and the bandwidths of the filters are designed according to equal center spectral distance (i.e. equal wave number width), the dynamic range of the interference signal is basically unchanged when the waveband is switched, the AD of the electronic system does not need to be replaced, and the implementation of the electronic data acquisition system is very beneficial. BRIEF DESCRIPTION OF DRAWINGS

[0023] Figure 1 It is an equal wave number width division filter waveband schematic diagram;

[0024] In the figure:

[0025] 1 - the first filter;

[0026] 2 - the second filter;

[0027] i - the i-th filter;

[0028] n-1 - the n-1-th filter;

[0029] n - the n-th filter;

[0030] σ1 - the starting wave number of the first filter;

[0031] σ2 - the ending wave number of the first filter;

[0032] σ i - the starting wave number of the i-th filter;

[0033] σ 中心-i - the center wave number of the i-th filter;

[0034] σ i+1 — the i-th filter start wavelength;

[0035] σ n — the n-th filter start wavelength;

[0036] σ n+1 — the n-th filter end wavelength;

[0037] σ— wavelength coordinate.

[0038] Figure 2 is a filter wheel wavelength division schematic diagram;

[0039] In the figure:

[0040] Wb— detection band start wavelength;

[0041] We— detection band end wavelength;

[0042] λ1— the 1st filter start wavelength;

[0043] λ2— the 1st filter end wavelength;

[0044] λ i — the i-th filter start wavelength;

[0045] λ 中心-i — the i-th filter center wavelength;

[0046] λ i+1 — the i+1-th filter end wavelength;

[0047] λ n — the n-th filter start wavelength;

[0048] λ n+1 — the n-th filter start wavelength;

[0049] λ— wavelength coordinate. DETAILED DESCRIPTION

[0050] A specific design example is given below:

[0051] Observe the solar spectrum, filter temperature: 90K, set the spectrometer detection band wavelength range requirements: start wavelength W b = 10 μm, end wavelength W e = 13 μm, design the number of sub-bands n = 6, i.e. design 6 filters, divide the wave bands of each filter according to the equal wavelength width, and calculate the center wavelength of each filter according to the formula:

[0052]

[0053] The center wavelength of each filter is obtained:

[0054] B1 = 10.2 μm;

[0055] B2 = 10.617 μm;

[0056] B3 = 11.069 μm;

[0057] B4 = 11.561 μm;

[0058] B5 = 12.1 μm;

[0059] B6 = 12.69 μm.

[0060] According to the filter bandwidth calculation formula:

[0061]

[0062] The filter bandwidth range is obtained:

[0063] Δλ1 = 0.4 μm;

[0064] Δλ2 = 0.433 μm;

[0065] Δλ3 = 0.471 μm;

[0066] Δλ4 = 0.514 μm;

[0067] Δλ5 = 0.563 μm;

[0068] Δλ6 = 0.619 μm.

[0069] According to the filter starting wavelength and ending wavelength calculation formula:

[0070]

[0071]

[0072] The six filter band design parameters are:

[0073] Filter No. Filter center wavelength (pm) Start wavelength (pm) End wavelength (pm) Filter 1 10.2 10 10.4 Filter 2 10.617 10.4 10.833 Filter 3 11.069 10.833 11.304 Filter 4 11.561 11.304 11.818 Filter 5 12.1 11.818 12.381 Filter 6 12.69 12.381 13

[0074] When performing spectral detection, according to the detection target wavelength range, the corresponding low-temperature filter is selected, further reducing the noise caused by the infrared background and out-of-band photons on the detector, and improving the signal-to-noise ratio of the instrument.

Claims

1. An equal-wavenumber division band noise reduction method for an infrared Fourier transform spectrometer, characterized in that: The method uses a cryogenic filter wheel to scan and detect the spectral range covered by the instrument, and to finely detect the specific target spectral range of interest; the cryogenic filter wheel is controlled by a cryogenic driving device, and a plurality of filters are installed on the filter wheel, each filter has a different center wavelength, the center wavelengths of the filters are not equally spaced, the center wavelengths and bandwidths of the filters are designed to be equally spaced, and each filter has a narrow bandwidth characteristic; it selects the filter of the corresponding spectral range for different detection spectral ranges of interest to achieve fine spectral detection of the spectral range of interest with ultra-high spectral resolution, and reduces the noise caused by infrared background and out-of-band photons on the detector; The total bandwidth of the filters on the low-temperature filter wheel needs to cover the start wavelength to the end wavelength of the spectrometer detection waveband, and the center wavelengths of the filters are designed to be equal in center spectral distance; the start wavelength of the infrared Fourier transform spectrometer detection waveband is W b microns, and the end wavelength is W e microns, the entire waveband is divided into n sub-wavebands, and n filters are designed, each corresponding to a sub-waveband; the filter serial number is set as i, and the center wavelength of the i-th filter is set as λ 中心-i ; The bands are divided according to equal-wavenumber width: The start and end wave numbers of the ith filter are set as σ i and σ i+1 The calculation formula is: The starting wavelength and the ending wavelength corresponding to the i-th filter are respectively set as λ i and λ i+1 , and the calculation formula is: The center wavelength λi of the i-th filter is 中心-i The calculation formula is: The wavelength bandwidth calculation formula of the i-th filter is: The center wavelengths are not equally spaced, the center wavelengths and bandwidths are designed to be equally spaced, each filter has a narrow bandwidth characteristic, and the spectrum is scanned and detected by selecting different band filters during detection.

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