JPS61148331A - Fourier transform type spectrophotometer - Google Patents

Abstract

PURPOSE:To achieve a phase matching eliminating a subinterferometer and adjusting points, by making the current interferogram (IF) overlap the IF in the course of integration for scanning of a moving mirror up to the previous one being shifted slightly to perform a phase matching for integration determining optimum correlation. CONSTITUTION:The output of a main photodetector 6 is sampled with a sampling circuit 10 by scanning a moving mirror 2 to take into a computer 10 and the IF in the course of integration upto previous operation is stored into an area (f) of a memory 11 while the current IF done into the area (t) thereby, both are also stored into an F file and a T file respectively. The computer 10 takes data of the T file sequentially to overlap the data of the F file in the corresponding number and finds the optimum mutual correlation to minimize the square sum of difference between both data at each point. Thus, the phase matching is done for e integration of IFs can be done by data processing alone to eliminate subinterferometer, thereby automatically discarding data mixed with abnormal noises.

Description

DETAILED DESCRIPTION OF THE INVENTION A. Field of Industrial Application The present invention relates to means for phasing interferograms when integrating interferograms in a Fourier transform spectrophotometer.

- Conventional technology Fourier transform spectrophotometers obtain the spectrum of the measurement light by Fourier transforming the interferogram obtained by moving the interferometer's movable mirror, but the S/N ratio of the interferogram is In order to improve this, the movable mirror is moved repeatedly, and the interferograms obtained each time are superimposed, or integrated, to average out the noise. In this case, the interferogram for each scan of the moving mirror needs to be integrated with the correct phase, but in the past, to avoid this, a sub-interferometer linked to the main interferometer was used, and the sub-interferometer had visible white light. A method is used in which the peak of a delta function-like interferogram obtained by incident light is detected, and the points corresponding to the top of this peak are matched with each other in the interferogram of the main interferometer and integrated. Ta. However, this method requires a sub-interferometer, which complicates the device configuration, and requires the user to adjust the interferometer, making it difficult to handle.

C. Problems to be Solved by the Invention The present invention addresses the structural complexity of the conventional phase matching means in integrating interferograms, Try overlapping the interferograms obtained this time with a slight shift in relation to For example, one way to find the cross-correlation is to overlay the current interferogram on the interferogram that is currently being integrated, with a slight shift, and find the overlapping pattern that minimizes the sum of the squares of the differences between the two at each point. A method such as this is used.

E. Effect As described above, the present invention performs phase matching using the interferogram itself, so a sub-interferometer is not necessary.
There is no adjustment required by the user, and phase alignment can be achieved simply by processing the measurement result data.

Embodiment FIG. 1 shows an embodiment of the present invention. 1 is a fixed mirror of the interferometer, 2 is a movable mirror, and 3 is a beam splitter, which constitute a Michelson interferometer. 4 is an infrared light source, 5 is a sample cell, and 6 is a main photodetector. 7 is H
It is an e-Ne laser, and 8 is a photodetector that receives interference fringes of light from the laser. Since the interference of the light from the He-Ne laser causes one cycle of brightness and darkness to change every time the movable mirror 2 moves by half a wave, the output of the photodetector 8 is shaped into a waveform and used as a sampling pulse to control the sampling circuit 9. , the output of the main photodetector 6 is sampled. Reference numeral 10 denotes a computer serving as a control means, which takes in the output of the main photodetector sampled as described above. This is the interferogram data. Reference numeral 11 denotes a memory, in which there are two areas called F file and T file: area f for storing interferograms in the middle of integration, area t for storing interferograms collected during the current moving mirror scan. Elijah is ready.

It is not necessary to perform the calculation for determining the correlation between the interferogram in the middle of integration and the currently collected interferogram for the entire interferogram. The interferogram has a peak (center burst) where the optical path difference between the fixed mirror and the movable mirror is maximum at 0, and since the signal is large here, it is sufficient to find the correlation in the vicinity area including the center burst. It is. The interferogram data shows that the movable mirror captures the half-wave component α of the He-Ne laser light.
Since the samples are sampled every time the sample moves by 316 μm, the calculation for calculating the correlation is performed with a shift of one sampling interval. The correlation calculation is performed as follows. FIG. 2 is a flowchart of the operation of the calculation. The calculation operation will be explained below.

Extract seven pieces of data near the center burst of the interferogram that is being integrated from the f area of the memory, normalize the data so that the maximum value is 1, and store the data in the f area of the memory.
Store in a file 2).

The interferogram data obtained from this moving mirror scan is stored in the T area of the memory, so the data of 27 points before and after including the maximum value is extracted, standardized, and stored in the T file of the memory ( mouth). Here? Let the data of the file be Fk (k=1°2, river 7) and the data of the T file be Tj (j=1.2...21). Set the subscript j of the data T/ in the T file to l = 8 -1, set S = 1, and go to e. Then, compare Ps with the previous calculation result P8-1 (profit, Ps (if Ps-1, add 1 to 8 and set it as 82B+1) and return to (to) the operation), and (in the step of profit, Ps≧ 2 days for P8-1
Since 1 is the minimum, compare 1.2 days-1 with the reference value A. If Ps-1 (A, then Fk and Tj are in phase and overlap. At this time, Fl and T8-1 are data of the same y, so the data of the currently collected interferogram stored in the t area of the memory is changed to Fl of the interferogram being integrated, which is stored in the f area of the memory and the data corresponding to TS-J. In the relationship corresponding to the data corresponding to f
Example of moving to Elijah and adding. P in the step
s) If it turns out to be A, the current interferogram will be rejected as containing a large amount of noise. (fart)
If the result of adding 1 to 8 in step is 21, then Tj
There are only 96 pieces of data remaining, which cannot be overlapped with the 7 pieces of data of Fl, and the fact that the minimum value does not appear in Ps after reaching this point is also rejected as noise has been introduced in the current scan.

The meaning of the above-mentioned operations will be explained with reference to FIG. F in FIG. 3 indicates data of the F file, which is data of seven points of k=1 to 7. T in Figure 3 is T file data, z = 1
This is data for 27 points of ~2γ.

From these 27 points of data, l=1~7tl=2~8,...
Take the ranges in order and superimpose them on the graph in Figure 3 F,
We find the range 1 = 8 that has the best weight.

G. Effects According to the present invention, phase alignment of the interferogram integration stage is performed only by data processing, eliminating the need for a sub-interferometer or the like in terms of equipment, and furthermore, there is no need for abnormalities during scanning of the moving mirror. If noise is mixed in, the data can be automatically rejected, so methods such as using a sub-interferometer or detecting the position of a moving mirror to align the phase are also ``stronger'' against noise.

[Brief explanation of drawings]

FIG. 1 is a plan view and block diagram of an embodiment of the present invention, FIG. 2 is a flowchart of the operation in the embodiment, and FIG. 3 is a graph explaining the operation. Agent Patent Attorney Kosuke TsuneFigure 2

Claims (1)

[Claims] A file F that extracts, normalizes and stores data near the maximum value of the interferogram in the middle of integration, and a file T that normalizes and stores data near the maximum value of the interferogram from the current moving mirror scan. , find the correlation between the data of file F and the data of file T, detect the data of file T that corresponds to the data of file F, and use the correspondence relationship to determine the data of the interferogram from the current moving mirror scan. A Fourier transform spectrophotometer equipped with a control means that adds the interferogram data to the interferogram data being integrated.