CN111238644B - White light interference removing method for interference spectrum of DFDI instrument - Google Patents
White light interference removing method for interference spectrum of DFDI instrument Download PDFInfo
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- G—PHYSICS
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- G01J—MEASUREMENT OF INTENSITY, VELOCITY, SPECTRAL CONTENT, POLARISATION, PHASE OR PULSE CHARACTERISTICS OF INFRARED, VISIBLE OR ULTRAVIOLET LIGHT; COLORIMETRY; RADIATION PYROMETRY
- G01J3/00—Spectrometry; Spectrophotometry; Monochromators; Measuring colours
- G01J3/28—Investigating the spectrum
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- G—PHYSICS
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- G01J—MEASUREMENT OF INTENSITY, VELOCITY, SPECTRAL CONTENT, POLARISATION, PHASE OR PULSE CHARACTERISTICS OF INFRARED, VISIBLE OR ULTRAVIOLET LIGHT; COLORIMETRY; RADIATION PYROMETRY
- G01J3/00—Spectrometry; Spectrophotometry; Monochromators; Measuring colours
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Abstract
The invention relates to a white light interference removing method for interference spectrum of a DFDI instrument, which can accurately analyze phase information of interference fringes and accurately measure the sight of an observed starAnd (4) the speed. The method comprises the following steps: step 1: according to the spectral wave number range delta k, determining the total number N of discrete sampling points in the wave number direction and the sampling rate k of the detector along the dispersion directionintΔ k/N; step 2: determining the optical path difference d of the fixed delay interferometer module in the instrument according to the formula (12), and selecting the maximum value 1/2kint(ii) a And step 3: fourier transform is carried out on the two-dimensional interference spectrum acquired by the instrument along the wave number direction, and interference information is converted into a frequency domain space; and 4, step 4: in the frequency domain space, filtering out +/-d frequency terms of interference fringe information S1 caused by white light by utilizing band-pass or high-pass filtering; and 5: and performing inverse Fourier transform on the filtered interference spectrum frequency domain information to obtain the mole fringes S2 caused by the sidereal absorption lines.
Description
The technical field is as follows:
the invention relates to the technical field of optics, in particular to a white light interference removing method for interference spectrum of a DFDI instrument.
Background art:
the apparent velocity method is one of the most important methods for finding out-of-system planets, and is to indirectly estimate the existence of planets by measuring the change of the apparent velocity of stars by using the spectral Doppler periodic movement generated by the traction of planets on main stars. When the apparent speed of the star changes in a sine law, it shows that at least one planet exists around the star.
The dispersion Fixed optical path difference Interferometer (DFDI) is a new type of viewing direction velocity method realization technology, mainly composed of Fixed Delay Interferometer and medium and low resolution post-dispersion device. The DFDI instrument effectively combines the advantages of an interferometer and a spectrometer, can realize the detection precision equivalent to a high-precision echelle grating by using a medium-low resolution dispersion device, greatly reduces the volume of the instrument, effectively reduces the sensitivity of the instrument to the environmental influence, has excellent cost performance, and is powerful supplement of the traditional sight direction speed realization technology.
The DFDI instrument measures the change of the apparent velocity of the observation star by detecting the phase change of the interference fringe corresponding to the absorption line of the observation star, and further detects the planets existing around the observation star. According to the working principle of the DFDI instrument, the two-dimensional interference spectrum obtained by the stellar spectrum through the DFDI instrument is composed of two parts: the first is interference fringes caused by white light (uniform continuous light) and moire fringes caused by the absorption lines of the stellar spectrum.
However, the phase information required for measuring the apparent velocity of the star exists in the moire fringes caused by the absorption line of the spectrum of the star, and the interference fringes caused by the white light interfere with the phase information, so that the phase resolved from the two-dimensional interference spectrum acquired by the DFDI instrument is inaccurate, and the measured apparent velocity of the star is inaccurate. While the fixed optical path difference of the DFDI instrument is different, interference fringes caused by white light also have different interference on phase information. White light interference is therefore an obstacle to DFDI instruments accurately measuring the apparent directional velocity of stars.
The invention content is as follows:
the invention aims to provide a method for removing white light interference of interference spectrum of a DFDI instrument, which solves the problem that the white light interference influences the accurate measurement of the apparent velocity of a fixed star of the DFDI instrument in the prior art, can accurately analyze the phase information of interference fringes and can accurately measure the apparent velocity of the observed fixed star.
In order to achieve the purpose, the invention adopts the technical scheme that:
a method for removing white light interference of interference spectrum of DFDI instrument is characterized in that: the method comprises the following steps:
step 1: determining the total number N of discrete sampling points in the wave number direction and the sampling rate k of the detector along the dispersion direction according to the spectral wave number range Deltak received by the detector and the instrument adopted in the design of the DFDI instrumentint＝Δk/N；
Step 2: DFDI instrument is determined according to the following equationSelecting the maximum value of 1/2k as the optical path difference d of the middle fixed delay interferometer moduleint；
And step 3: fourier transform is carried out on the two-dimensional interference spectrum acquired by the DFDI instrument along the wave number direction, and interference information is converted into a frequency domain space;
and 4, step 4: in the frequency domain space, filtering out +/-d frequency terms of interference fringe information S1 caused by white light by utilizing band-pass or high-pass filtering;
and 5: and performing inverse Fourier transform on the filtered interference spectrum frequency domain information to obtain mole fringes S2 caused by the sidereal absorption line, and finishing the extraction of the interference fringes containing accurate phase information.
The two-dimensional interference spectrum S acquired by the DFDI instrument is fourier-transformed in the wave number direction and converted into frequency domain information F [ S ] ═ F [ S1] + F [ S2 ].
In the frequency domain space, F' [ S ] ═ F [ S2] is obtained by filtering ± d frequency terms of the interference fringe information S1 caused by white light using band-pass or high-pass filtering.
And performing inverse Fourier transform on the F' S to extract Mohr stripes S2 containing accurate phase information and eliminate interference of white light on the phase information.
Compared with the prior art, the invention has the following advantages and effects:
1. according to the working principle of the DFDI instrument, the distribution characteristics of effective information (effective phase information carried by mole fringes caused by absorption lines) and interference information (interference phase information carried by interference fringes caused by white light interference) in a two-dimensional interference spectrum acquired by the DFDI instrument are quantitatively described and analyzed, based on the difference of the distribution characteristics of the two information, the interference fringes caused by white light are effectively eliminated through proper frequency domain filtering, the mole fringes caused by the absorption lines of the stellar spectrum are extracted, and therefore the phase information of the interference fringes can be accurately analyzed, and the apparent velocity of an observed star can be accurately measured.
2. The method for removing the white light interference from the interference spectrum of the DFDI instrument provided by the invention strictly controls the distribution characteristics of the related white light interference from the design stage of the instrument by selecting reasonable instrument parameters, and further effectively eliminates the white light interference through proper frequency domain filtering after the two-dimensional interference spectrum is obtained subsequently.
Description of the drawings:
FIG. 1 is a flowchart of the process of the present invention.
The specific implementation mode is as follows:
the present invention will be described in detail with reference to specific embodiments.
The invention relates to a method for removing white light interference from a two-dimensional interference spectrum acquired by a DFDI instrument based on the working principle of the DFDI instrument.
According to the working principle of the DFDI instrument, after an observed stellar spectrum enters the DFDI instrument, interference information is loaded through the fixed delay interferometer, then the stellar spectrum enters the spectrometer for post-dispersion, and finally the stellar two-dimensional interference spectrum is obtained by the detector, wherein one dimension represents the wavelength dispersion direction, and the other dimension represents the interference fringe direction changing along with the optical path difference.
If p (k) represents the stellar spectrum (k represents the wave number), according to the interference principle, the stellar spectrum passes through a fixed delay interferometer to form complex color spectrum interference fringes at a slit, then the complex color spectrum interference fringes pass through a spectrometer to be dispersed, and finally a star two-dimensional interference spectrum S is formed at a detectorcod(k) I.e. DFDI acquired sidereal interference spectrum Scod(k) Equivalent to the ideal interference fringe I after the diffraction of the complex color spectrum interference fringeideal(k) And the spectrometer modulation function lsf (k), as shown in equations (1), (2), where k1 and k2 represent the wavenumber range covered by the stellar spectrum entering the system, and d represents the fixed optical path difference.
And the absorption lines in the stellar spectra can be approximated by a gaussian distribution, i.e. p (k) can be expressed by equation (3). Wherein A represents the absorption intensity of the absorption line, kaRepresents the central wave number of the absorption line as ka＝1/λa(λaCentral wavelength), Δ kaRepresents the half height width of the absorption line wave number of
(ΔλaWavelength full width at half maximum).
The spectrometer modulation function lsf (k) can also be expressed in simplified terms of the central spot of the airy disk caused by diffraction and aberration using a Gaussian distribution, i.e. using equation (4), where Δ k0(Δλ0) Is a key factor affecting the size of the airy disk and is determined by the grating resolution gr, as shown in equation (5).
Combining the formula (2), the formula (3) and the formula (4), the sidereal interference spectrum S can be obtainedcod(k) Comprises the following steps:
S(k)＝S1+S2 (6)
i.e. sidereal interferenceSpectrum Scod(k) Consists of two parts of interference fringes S1 of uniform continuous light and mole fringes S2 caused by absorption lines. And the absorption line information is contained at S2, regardless of S1. And S1 interferes with the phase difference before and after Doppler shift, so that the inversion apparent velocity precision is often very low when the fixed optical path difference is small, and the inversion precision also fluctuates greatly as the optical path difference becomes larger.
As can be seen from equations (7) and (8), the phases of S1 and S2 are shown in equations (9) and (10), respectively.
φS1＝2πdk (9)
The interference spectrum acquired by the DFDI instrument is two-dimensional, where one dimension varies along the optical path difference d and the other dimension varies along the wavenumber k. For a certain wave number k, the two frequencies are different in the stripe direction (the optical path difference d is variable), the frequency of S1 is k, the frequency of S2 is k
Meanwhile, for a certain optical path difference d, the two frequencies are also different in the wavenumber direction (the wavenumber k is a variable), the frequency of S1 is d, and the frequency of S2 is d
I.e., the frequency of S2 is lower than the frequency of S1. Setting the central wavelength lambda of the absorption lineaIs 800nm and half-height width delta lambdaaAt 0.02nm and a grating resolution gr of 15000, it can be calculated that the frequency of S2 is only about 12.3% of the frequency of S1 in the wavenumber direction. Therefore, in the wavenumber direction, the interference fringes S1 caused by white light can be filtered out by a high-pass/band-pass filter, thereby extracting the moir fringes S2 caused by the sidereal absorption lines.
In the invention, Fourier transform is adopted to convert signals into frequency domain. The variable in the wavenumber direction is the wavenumber k, and if Fourier transform is performed in the Δ k range, the frequency domain resolution is 1/Δ k, where Δ k is shown by equation (11), where k isintRepresenting the sampling rate of the detector along the dispersion direction and N representing the total number of discrete sample points over a range of deltak in the beam direction.
Δk＝kint×N (11)
The cos function in S1 can be extended to a combination of exponential functions, i.e., S1 contains both + d and-d frequency terms. In order to filter out the frequency terms d of S1 sufficiently, the frequency d should be chosen to be an integer multiple of the frequency domain resolution 1/Δ k. According to the periodicity of the Fourier transform, the highest frequency after the transform is
I.e. the frequency d should take a value as shown in equation (12). That is, in order to completely remove interference fringe information caused by white light from the two-dimensional interference spectrum acquired by the DFDI instrument, the optical path difference d should be selected according to the formula (12), and the optical path difference d and the sampling rate k of the detector along the dispersion directionintAre closely related.
By integrating the processes, the method for removing the white light interference aiming at the interference spectrum of the DFDI instrument provided by the invention comprises the following specific steps:
step 1: according to the spectral wave number range Deltak received by the detector and the instrument adopted in the design of the DFDI instrument, the total number N of discrete sampling points in the wave number direction (the number of pixels of the detector in the wave number direction) and the sampling rate k of the detector along the dispersion direction are determinedint＝Δk/N。
Step 2: determining the optical path difference d of the fixed delay interferometer module in the DFDI instrument according to equation (12), typically selecting the maximum value 1/2kint。
And step 3: and Fourier transformation is carried out on the two-dimensional interference spectrum acquired by the DFDI instrument along the wave number direction, and interference information is converted into a frequency domain space.
And 4, step 4: in the frequency domain space, d frequency terms of interference fringe information S1 caused by white light are filtered out by using band-pass or high-pass filtering.
And 5: and performing inverse Fourier transform on the filtered interference spectrum frequency domain information to obtain mole fringes S2 caused by the sidereal absorption lines, namely completing the extraction of the interference fringes containing accurate phase information.
Example (b):
assuming a spectral wavenumber range Δ k received by the DFDI instrument, the detector employed has a number of pixels N in the wavenumber direction.
1) Determining the total number of discrete sampling points in the wavenumber direction to be N, and the sampling rate of the detector along the dispersion direction to be kint＝Δk/N。
2) Determining optical path difference d of fixed delay interferometer module in DFDI instrument according to formula (12), and selecting maximum value 1/2k of dint。
3) The two-dimensional interference spectrum S acquired by the DFDI instrument is fourier-transformed in the wave number direction and converted into frequency domain information F [ S ] ═ F [ S1] + F [ S2 ].
4) In the frequency domain space, F' [ S ] ═ F [ S2] is obtained by filtering ± d frequency terms of the interference fringe information S1 caused by white light using band-pass or high-pass filtering.
5) And performing inverse Fourier transform on the F' [ S ] to extract Moire fringes S2 containing accurate phase information, thereby removing the interference of white light on the phase information.
The above-described embodiments are merely illustrative of the principles and effects of the present invention, and some embodiments may be applied, and it will be apparent to those skilled in the art that various changes and modifications may be made without departing from the inventive concept of the present invention, and these embodiments are within the scope of the present invention.
Claims (4)
1. A white light interference removing method for an interference spectrum of a dispersion fixed optical path difference interferometer is characterized by comprising the following steps: the method comprises the following steps:
step 1: according to the spectral wave number range Dk received by the detector and the instrument adopted in the design of the dispersion fixed optical path difference interferometer, the total number N of discrete sampling points in the wave number direction and the sampling rate k of the detector along the dispersion direction are determinedint＝Dk/N；
Step 2: determining the optical path difference d of a fixed delay interferometer module in the dispersion fixed optical path difference interferometer according to the following formula, and selecting the maximum value 1/2kint；
And step 3: fourier transform is carried out on the two-dimensional interference spectrum acquired by the dispersion fixed optical path difference interferometer along the wave number direction, and the two-dimensional interference spectrum is converted into a frequency domain space;
and 4, step 4: in the frequency domain space, filtering out +/-d frequency terms of interference fringe information S1 caused by white light by utilizing band-pass or high-pass filtering;
and 5: and performing inverse Fourier transform on the filtered interference spectrum frequency domain information to obtain mole fringes S2 caused by the sidereal absorption line, and finishing the extraction of the interference fringes containing accurate phase information.
2. The method for removing white light interference in the interference spectrum of the dispersion fixed optical path difference interferometer according to claim 1, wherein: the two-dimensional interference spectrum S acquired by the dispersion-fixed optical path difference interferometer is fourier-transformed in the wave number direction, and is converted into frequency domain information F [ S ] ═ F [ S1] + F [ S2 ].
3. The method for removing white light interference in the interference spectrum of the dispersion fixed optical path difference interferometer according to claim 1, wherein: in the frequency domain space, F' [ S ] ═ F [ S2] is obtained by filtering ± d frequency terms of the interference fringe information S1 caused by white light using band-pass or high-pass filtering.
4. The method of claim 3, wherein the method comprises: and performing inverse Fourier transform on the F' S to extract Mohr stripes S2 containing accurate phase information and eliminate interference of white light on the phase information.
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| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPH01167621A (en) * | 1987-12-23 | 1989-07-03 | Nippon Telegr & Teleph Corp <Ntt> | Light spectrum analyzer |
| CN102818786A (en) * | 2012-08-17 | 2012-12-12 | 中国科学院上海光学精密机械研究所 | Sinusoidal phase modulation parallel complex frequency domain optical coherence tomography imaging system and method |
| CN106644075A (en) * | 2016-11-17 | 2017-05-10 | 天津津航技术物理研究所 | Efficient de-noising method for Fourier spectrograph |
| CN110399646A (en) * | 2019-07-01 | 2019-11-01 | 西安工业大学 | A kind of DFDI instrument models method for building up for being outer planet detection |
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| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPH01167621A (en) * | 1987-12-23 | 1989-07-03 | Nippon Telegr & Teleph Corp <Ntt> | Light spectrum analyzer |
| CN102818786A (en) * | 2012-08-17 | 2012-12-12 | 中国科学院上海光学精密机械研究所 | Sinusoidal phase modulation parallel complex frequency domain optical coherence tomography imaging system and method |
| CN106644075A (en) * | 2016-11-17 | 2017-05-10 | 天津津航技术物理研究所 | Efficient de-noising method for Fourier spectrograph |
| CN110399646A (en) * | 2019-07-01 | 2019-11-01 | 西安工业大学 | A kind of DFDI instrument models method for building up for being outer planet detection |
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