JPH01282434A - Fourier spectroscope - Google Patents

Abstract

PURPOSE:To achieve a reduction in calculation time with a Fourier transform, by a method wherein an optical path of an interferometer for acquiring an interferogram is provided with an optical BPF and light with a desired wave number range sigma1-sigma2 wherein sigma2=(1+1/m)sigma1 passes among sample lights with the maximum wave number sigmaM to sample an interferogram data. CONSTITUTION:A sample light from an aperture 14 is divided in two with a beam splitter 18 through a collimation lens 16 to be reflected separately with a fixed mirror 20 and a mobile mirror 22 and combined and coupled 24 with the splitter 18 to be incident into a photo detector 26. An output signal of the detector 26 is amplified 30 to be converted 32 into digital from analog. A control unit 28 shifts a passage area of an interfering light to a wave number transmission range sigma1-sigma2 set 37 and a mobile mirror 22 moves by one step each through a mobile mirror driver 33. here, the sigma1 and sigma2 are set for sigma=(1+1/m)sigma1 (wherein m represents integer). Moreover, a data converted 32 into digital from analog is written into an interferogram memory 34. The data in the memory 34 undergoes a Fourier transform 40 to be outputted 42.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to an infrared or visible Fourier spectrometer, and in particular, the present invention relates to a Fourier spectrometer in the infrared or visible range. Concerning the Fourier spectrometer that extracts well.

Conventional technology 1: In Fourier spectroscopy, interferogram data is
FT (fast Fourier transform) is applied to restore the original spectral data. Here, the N-point interferogram data is converted into N-point spectral data.

[Problems to be Solved by the Invention] However, when trying to improve the wave number resolution or expanding the observed wave number range, the value of N increases. Especially in the visible range, the number of data points becomes extremely large.

This increase in the number of data points causes two problems. 1
One is an increase in PFT calculation time due to an increase in the number of data points, and the other is an increase in the dynamic range of the A/D converter when acquiring interferogram data.

In the case of continuous spectra, the interferogram will have a large center burst, and the number of bits of the A/D converter must be increased accordingly to improve the measurement accuracy of the reconstructed spectrum. As a result, the price of the A/D converter, the conversion speed, and the word length per data point increase, which also affects the overall data processing speed.

While it is true that the Fourier interferometer is often used to perform qualitative analysis using the entire reconstructed spectral waveform, there are also many cases where information about only a specific region of a wide range of spectral data is sufficient.

This is especially true in quantitative analysis, such as the analysis of impurities in semiconductors. This also applies to measurements such as FT Raman. Conventionally, even in such cases, it is necessary to perform FFT on all data points to restore the spectrum, resulting in the aforementioned problems of increased FFT calculation time and increased dynamic range of the A/D converter. was.

A blur filtering method is a method for reducing the number of data points.

In the blur filtering method, if you want to obtain the spectrum of only the band σN to σN out of the sample light in the entire wavenumber range 0 to σN, interferogram data is sampled at an interval of I/(2σN) or less, and the spectrum of the band σ1 to σN is obtained. After performing a convolution operation with a 5ine function on the interferogram surface corresponding to the filter of σN, it is necessary to further sample (thin out) the data resulting from this operation. Therefore, calculation time cannot be reduced much.

SUMMARY OF THE INVENTION In view of the above problems, it is an object of the present invention to provide a Fourier spectrometer that can shorten calculation time without reducing wave number resolution and narrow the dynamic range required by an A/D converter.

[Means for Solving the Problems] In order to achieve this object, the Fourier spectrometer according to the present invention includes an interferometer that acquires an interferogram of sample light, and an interferometer that is arranged in the optical path of the interferometer and that σ*−(1+I/m)σ out of the sample light of σN.

(m is a positive integer) desired wave number range (σ1 to σN)
The interferogram data obtained by the interferometer and the optical bandpass filter that transmits the light of h°
≦1 / [2 (σN - σN)) sampling means for sampling at an interval h', and Fourier transform means for obtaining spectral data by performing Fourier transform on the sampled interferogram data. .

[Example code] (1) One example An embodiment of the present invention will be described based on the drawings.

FIG. 1 shows the main part configuration of a Fourier spectrometer according to an embodiment of the present invention.

In this example, for the sake of simplicity, the spectrum S(
σ) is assumed to have two bright lines on a linear baseline as shown in FIG. 2(a). Further, suppose that we are interested only in these two emission lines and want to obtain only the spectrum in the wave number range σ1 to σN that includes these two emission lines out of the entire wave number range O to σ.

As shown in FIG. 1, this embodiment shows a case in which a continuously variable wavelength interference filter 12 is installed in an ordinary Michelson interferometer 10.

The Michelson interferometer 10 is for temporally acquiring an interferogram of sample light by scanning a movable mirror, and includes an aperture 14 and a collimating lens 16 that collimates the sample light from the aperture 14. , a beam splitter 18 that splits the light beam from the collimating lens 16 into two, a fixed mirror 20 that reflects one of the split light beams and moves it backwards, and a moving 1m that reflects the other of the split light beams and moves it backwards! 22, an imaging lens 24 that images the interference light combined by the beam splitter 18, and a photodetector 26 that is placed at the imaging position and detects the light intensity.

The continuously variable wavelength interference filter 12 is arranged in the optical path between the imaging lens 24 and the photodetector 26. The continuously variable wavelength interference filter 12 has a disk shape, and the transmitted wavelength changes continuously or stepwise along the circumferential direction. The transmission band of the optical path portion of the continuously variable wavelength interference filter 12 is determined by the drive control from the control unit 28.
The disk is rotated by the lugs and changes continuously.

The output signal of the photodetector 26 is amplified by an amplifier 30,
Digital conversion is performed by an A/D converter 32.

The control unit 28 supplies the drive pulse to the continuously variable wavelength interference filter 12 to set the transmission range of the interference light to the wave number transmission range σ1 to σN set by the setting device 37, and also supplies the drive pulse to the movable mirror drive device 33. Supply and move mirror 2
2 in a straight line one step at a time. Here σ1, σN
is set to satisfy σN=(t+l/m)σ1 (m is a positive integer).

Furthermore, the control unit 28 controls the A/D converter 3
2, a conversion signal is supplied at an interval h' that satisfies the following condition (the amount of change in the optical path difference between the two light beams in the interferometer 10), and the interferogram data is sampled and digitally converted.

h≦! /(σN+σN) h'=1/(2(σN-σ+))=h nn is a positive integer The data sequentially obtained from the A/D converter 32 is written to the interferogram memory 34, and A discretized two-sided interferogram is created in 34.

Figure 2(b) is a continuously variable wavelength interference filter! (c) shows the convolution S(σ) of S(σ) with the comb function (shah function) utwh(σ), and (c) shows the modeled transmission characteristic F(σ) of 2. d)
is the filter function F(σ) and the comb function E1. Convolution with h(σ) F (σ)eta +zh((F )
, and (e) is the product of (c) and (d) (S (7F ) @ 1LLIBh (ff )) (F (
cr )Oul+zh(σ)) is shown.

Here, 1. h indicates the period. In general, the product and convolution on the spectral surface correspond to the convolution and product on the interferogram surface, respectively.

If sampling is performed at the above interval h (provided that the equal sign holds), the interferogram memory 34 will contain (
A discretized interferogram obtained by Fourier transforming a) is written, as described above.

If you sample with , interferogram memory 3
4, a discretized interferogram obtained by Fourier transforming (f) is written.

Next, the fast Fourier transformer 40 performs Fourier transform on the data in the interferogram memory 34 (
A spectrum in the wave number range θ to (σN-σl) shown in f) is obtained and supplied to the spectrum output device 42. This spectral data is visualized and extracted from the spectral output device 42.

In this way, conventional, normal measurements! /(2σN)
Interferogram data that had to be sampled at intervals of 1/(2(σN-σI))
It is only necessary to sample at the following intervals, and the sampling interval can be made wider by σIl/(2(σN-σN)) than in the past. Therefore, the interferogram to be supplied to the fast Fourier transformer 40, which requires a long calculation time. The number of data points N can be reduced to N(σN-σN)/σ, and the PFT calculation time can be significantly shortened.

Furthermore, by passing through the continuously variable wavelength interference filter 12, the peak of the interferogram is dispersed to both sides, so that the necessary dynamic range of the A/D converter 32 is
It can be reduced to (σN - σN)/σ engineering times. Here, K is ≧1, and when the sample light spectrum is completely white light, K=1.

Furthermore, by passing the filter 12, as shown in FIG.
) and (b), and the total calculation time can be further shortened.

(2) Expansion Note that the present invention includes various other modifications.

For example, in the above embodiment, the continuously variable wavelength interference filter 12 is used as the optical bandpass filter, but for example, a plurality of interference filters having different transmission wavenumber ranges may be prepared, and these may be adjusted according to the target wavenumber range. It may be configured to switch.

It goes without saying that various types of interferometers for creating interferograms can be used, for example, those that spatially form an interferogram and obtain it.

[Effects of the Invention] As explained above, according to the Fourier spectrometer according to the present invention, an optical bandpass filter is disposed in the optical path of the interferometer for obtaining an interferogram, and σ of the sample light with the maximum wave number σN is *= (1+1/m)σ1 (m is a positive integer) Light in the target wave number range (σN to σN) is transmitted, and the interferogram data obtained by the interferometer is expressed as h°≦1 /(2(σN - σN)), and Fourier transform is performed on the sampled interferogram data, which reduces the number of sampling points of interferogram data and also reduces the complexity of the above-mentioned complicated composure. Since there is no need to perform a silane calculation, the calculation time can be shortened, the dynamic range of the A/D converter can be reduced, and there is an excellent effect that the wave number resolution is not degraded.

[Brief explanation of the drawing]

1 and 2 relate to one embodiment of the present invention, with FIG. 1 being a block diagram of the main parts of a Fourier spectrometer, and FIG. 2 being a waveform diagram on a spectral plane for explaining the operation. In the figure, 10: Michelson interferometer! 2: Continuously variable interference filter 16: Collimating lens 18: Beam splitter 20: Fixed mirror 22: Moving mirror 24: Imaging lens 26: Photodetector 34: Interferogram memory 40: Fast Fourier transformer 42 Varnish vector output device

Claims (1)

[Claims] An interferometer (10
), and is placed in the optical path of the interferometer, and transmits light in the target wave number range (σ_1 to σ_2) where σ_2 = (1 + 1/m) σ_1 (m is a positive integer) out of the sample light with the maximum wave number σ_N. The interferogram data obtained by the optical bandpass filter (12) and the interferometer are adjusted so that h'≦1/
It has a sampling means (28) that samples at an interval h of {2(σ_2-σ_1)}, and a Fourier transform means (40) that obtains spectral data by performing Fourier transform on the sampled interferogram data. A Fourier spectrometer characterized by: