JPH0668458B2 - Fourier transform spectrophotometer - Google Patents

Description

TECHNICAL FIELD The present invention relates to a Fourier transform type spectrophotometer.

(B) Conventional technology In a Fourier transform type spectrophotometer, a sampling pulse is formed from interference fringes of light having a wavelength shorter than the measurement wavelength range. A Fourier transform far-infrared spectrophotometer forms a sampling pulse from the interference fringes of He-Ne laser light. The one-time photometric output is sampled to obtain interferogram data. In order to increase the S / N ratio of the measurement, the interferometer scans multiple times, and the interferograms of each time are integrated. In this case, however, since the interferograms of each time are integrated in the same phase, It is necessary to set one same phase point as the origin, but it was difficult to determine this origin accurately. Normally, the center of the interferogram center burst (the peak of the interference light that appears at the position where the optical path difference between the two optical paths of the interferometer is 0) is taken as the origin, but some He-
There are interference fringes of Ne laser light, and it is difficult to determine which of them is the true center berth center. Alternatively, there is a method of mechanically detecting the origin, but even in this case, it is difficult to accurately determine the origin.

(C) Problems to be Solved by the Invention The present invention is to provide a means for accurately detecting the origin in the case of integrating interferograms in a Fourier transform type spectrophotometer.

D. Means for solving the problem: The interferogram data obtained by one scan in the interferometer is temporarily stored in the first memory, and the reference waveform data of the interferogram center burst is stored in the third memory. The data in the vicinity of the center verse of the interferogram obtained by the above-described one scanning is stored in a small amount and overlapped with the data in the third memory, and the displacement amount that best matches is detected. The center position of the center burst is detected in the data of the interferogram in the first memory, and the position corresponds to the center of the accumulated center burst of the interferogram in the main memory. The data of was transferred to the main memory and integrated.

(E) When the interferometer scans once, the interferogram data at that time is temporarily stored in the first memory, this data is transferred to the main memory, and the interferogram is integrated in each scan in the main memory. At this time, if the reference waveform of the center burst of the interferogram is superimposed on the data in the vicinity of the center burst in the data of the interferogram in the first memory and the overlapping position is gradually shifted. , Where the waveforms of both center bursts are best matched. At this time, since the data position in the first memory which overlaps with the center position in the reference center burst waveform is the center of the center burst in the interferogram in the first memory,
Since this position corresponds to the center burst center position in the interferogram in the main memory, if the data in the first memory is transferred and added to the main memory, the respective interferograms can be added with their origins aligned. .

F. Embodiment FIG. 1 shows an embodiment of the present invention. I is an interferometer and mv is a moving mirror. P is a main light source and L is a He-Ne laser. D1 is a photodetector that receives the interference light of the main light source, D2 is He-
It is a photodetector that receives the interference light of the Ne laser. Photo detector
The output waveform of D2 draws a waveform of one cycle each time one fringe of the laser interference light moves. This output waveform is shaped into a rectangular wave by the waveform shaper F, and the rising edge of the rectangular wave is generated by the sampling pulse forming circuit C. Is detected and a sampling pulse is output. Therefore, one sampling pulse is output for each laser interference fringe. G is opened in the gate circuit by the sampling pulse output from the circuit C, and sends the output signal of the photodetector D1 to the interface If. The interface If holds the output signal of the photodetector D1 output through the gate G and performs A / D conversion. CPU is this A / D
The converted data is stored in the first memory M1.

The first memory M1 is a memory for temporarily storing interferogram data when one scan is performed by the moving mirror of the interferometer, and this data is the photodetector D1 as described above.
Is sampled for each stripe of the interference fringes of the laser light. Similarly, the second memory M2 is a memory for temporarily storing data near the center burst of the interferogram. Therefore, the contents are the same as the data in the vicinity of the center burst in the data in the first memory. The third memory M3 stores the data obtained by integrating the data in the vicinity of the center burst of the interferogram for each scanning of the interferometer by aligning the origins. The fourth memory M4 is a main memory for accumulating the interferogram, and reads out the data of n laser light interference fringes from the first memory for each scanning of the interferometer and accumulates the data in the fourth memory. It is a thing.

With the above configuration, the CPU performs the following control and data processing to integrate the interferogram. In the following description, simply the sampling data is the interferogram data sampled for each stripe of the laser light interference fringes, and the n-sampling data is the sampling at intervals of n laser interference fringes. It is the interferogram data that was created.

In the Nth scan of the interferometer, N- is stored in the fourth memory M4.
The result of accumulating the sampling data of n skips up to the first scan by matching the origins is stored. Also the third
The memory M3 is centered on the center of the center burst of the interferogram in scanning up to N-1 times
The data in which the sampling data at the points are integrated is stored. In the Nth scan, the CPU stores the sampling data in the first memory M1. At the same time, 21 pieces of sampling data continuing from the scanning start point are normalized with the maximum value among them being 1, and then stored in the second memory M2.
While the moving mirror of the interferometer goes back to the starting point of scanning, the CPU
The data of the second memory M2 is shifted by one sampling point while being superimposed on the data of the third memory M3, and the shift number at which the best match is detected. Thus, in the data in the first memory M1, it is possible to know which sampling data is the center of the center burst from the data corresponding to the starting point of the scanning, and the sampling data is used as the data of the origin of the interferogram in the Nth scanning. As a result, the n skipped sampling data is read from it, added to the data of each corresponding address of the fourth memory M4, and the contents of the fourth memory are replaced with this addition result. Further, the origin determined by the above-mentioned operation is matched, and the seven consecutive sampling data in the second memory M2 are added to the data of the corresponding address of the third memory, and the addition result is halved to the third value. Rewrite the contents of memory.

In the first scan (N = 1), the contents of the third and fourth memories are 0, and in this case, the sampling data is stored in the first memory M1 and before and after including the maximum value in the data.
The sampling data of the point is normalized and stored in the third memory M3, and the sampling data of n skips is read from the first memory and stored in the fourth memory M4 with the sampling data of the maximum value as the origin. In this way, the above-described operation is performed when N = 2 or more.

That is, in this embodiment, the data in the vicinity of the reference center burst is the data in the vicinity of the center burst of the interferogram in the first scan, and the subsequent interferograms are in phase with the first interferogram.

The above operation is illustrated in FIG. In Figure 2
M1 indicates the data stored in the first memory M1, and 0, 1, 2 ... On the horizontal axis scale are address numbers. Similarly, M2 is the second
The data stored in the memory M2, M3 is the data in the third memory M3, and M4 is the data in the fourth memory M4. The curve indicated by the dotted line in M2 of FIG. 2 is from the second memory M2 to i in FIG.
The data from the i-th to the i + 6-th data are shown in the state of being superimposed on the data in M3. Change i from 0 to 14 and search for the best match. If i is io at that time, the origin of the interferogram is io + third in M1. Then, the io + third data of the M1 data is put into the first address of M4, and the data of M1 is read every nth address from io + 3 address and is integrated with the data of M4.

The operation of shifting the data of M2 and overlaying it with the data of M3 to search for the best match is the data of each address of M2 (Di + k)
And the data of each address of M3 is Ek. Here k is 0
The number of 6 and i is the number which changes sequentially from 1 to 15.

Change i from 1 to 15 and find i that minimizes Ki in the above equation.

Effect According to the present invention, since the origin can be accurately adjusted in the integration of interferograms, the distortion of the spectrum obtained with the improvement of the S / N ratio is eliminated, and the reproducibility, the linearity between the sample concentration and the absorbance, etc. An improvement is obtained.

[Brief description of drawings]

FIG. 1 is a block diagram of one embodiment of the present invention, and FIG. 2 is a graph explaining the operation of the same embodiment.

Claims (1)

[Claims] 1. A first memory for temporarily storing data of an interferogram obtained by one scan of an interferometer, and accumulated data of accumulating interferograms of each scan of the interferometer. It has a main memory to be stored and a third memory to store the data in the center burst of the interferogram, which is the reference,
The data in the vicinity of the center burst of the interferogram for each scan is shifted and overlapped with the data of the reference center burst in the third memory to obtain the best match. A Fourier transform spectrophotometer for detecting the origin and adding it to the data in the main memory.