JPH0665971B2 - Fourier transform spectrophotometer - Google Patents

Description

Detailed Description of the Invention a. BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a means for phase-matching interferograms when integrating interferograms in a Fourier transform type spectrophotometer.

B. 2. Description of the Related Art A Fourier transform spectrophotometer obtains a spectrum of measurement light by Fourier transforming an interferogram obtained by moving a moving mirror of an interferometer, and improves the S / N ratio of the interferogram. To do so, the movement of the movable mirror is repeated, and the interferograms obtained each time are integrated, that is, superposed, so that noise is averaged. in this case,
The interferogram obtained for each scan of the movable mirror must be correctly phased and integrated. For this reason, conventionally, a subinterferometer linked to the main interferometer was used to detect the peak of the delta-function-like interferogram obtained by making visible white light incident on the subinterferometer. Then, a method was used in which points corresponding to the position of this peak were made to coincide with each other and integrated. However, this method requires a sub-interferometer, which complicates the apparatus configuration, and requires the user to adjust the interferometer, which is troublesome to handle.

In the interferometer, at the position of the moving mirror where the optical paths of the two light beams split into two are equal, the lights of all wavelengths overlap in phase, so the maximum peak (center burst) appears in the interferogram at this position. In this case, the center burst should be detected and the interferograms should be integrated so that they overlap, but if the transmittance of the sample is small or the wavelength distribution of the transmitted light is narrow as in a narrow band filter. In the narrow case, the center burst is not so large, or several peaks of the same degree appear, and the center burst cannot be unambiguously determined because it cannot be distinguished from noise. Therefore, this method cannot be generally used. There is also a method of providing a means for detecting the position of the movable mirror and performing phase matching of the interferogram by a signal emitted when the movable mirror passes a specific position, but the specific position shifts when the temperature changes. However, the installation environment of the device must be kept constant, and the economical efficiency becomes a problem. With this kind of thing,
The method described at the beginning is considered practical.

C. DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention The present invention aims to provide an inexpensive means which can accurately and surely perform phase matching of interferograms without using a subinterferometer.

D. Means for Solving Problems Providing a means for collecting data on the position of the moving mirror during scanning and a means for detecting that the moving mirror has passed a specific position on the device, and a control means is provided to For each scan, the difference between the data of the position of the moving mirror taken when the moving mirror passed the above-mentioned specific position and the maximum value of the interferogram and the data of the position of the moving mirror obtained by the scanning at that time are When it is within a preset range, the maximum value is determined to be the center burst of the interferogram at that time, and the interferogram obtained by each scan is matched with the determined center burst. I tried to add it.

E. The positional relationship between the position of the movable mirror and the position detecting means where the optical path lengths of the two light beams of the working interferometer are equal to each other is structurally determined even if it is affected by temperature. Therefore, for example, when the specific position detecting means is arranged at the position of the movable mirror where the optical path lengths of the two light fluxes are equal, the peak overlapping the specific position detection signal can be confirmed as the center burst in the interferogram. Of course, the position of the specific position detection means is not limited to the above position. The interferogram is generally measured in the infrared Fourier transform spectrophotometer by sampling the output of the photodetector every time the moving mirror moves a fixed distance, for example, half the wavelength of the laser light of the He-Ne laser. Therefore, it is possible to obtain the position data of the movable mirror by counting the number of times of sampling, and it can be determined that the peak including the number of data after the specific position detection signal is the center burst. .

F. Embodiment FIG. 1 shows an embodiment of the present invention. Reference numeral 1 is a fixed mirror, 2 is a moving mirror, and 3 is a beam splitter, and these constitute a Michelson-type interferometer. 4 is an infrared light source,
Reference numeral 5 is a sample cell and 6 is a main photodetector. Reference numeral 7 denotes a He-Ne laser, the interference image of which is detected by the photodetector 8. This detector output changes by one cycle every time the movable mirror 2 moves by a half wavelength of the He-Ne laser light. Then, the waveform of this output is shaped and the sampling circuit 9 is controlled. Further, by counting the number of times of sampling, data on the position of the movable mirror during scanning is obtained. That is, the laser 7, the detector 8, the sampling circuit 9, the counting means (in the data processing device 10) and the like constitute a means for collecting the data of the position of the movable mirror during scanning. Reference numeral 10 is a computer of data processing means, which takes in the output of the main photodetector 6 sampled by the sampling circuit 9. A position detector 11 detects the central position of the magnet of the object to be detected which is integrated with the movable mirror 2. Since the sign of this detection signal changes when the center between both poles of the magnet passes the front surface of the position detection, the comparator 12 compares the output of the detector 11 with 0 level, and the output of the comparator 12 is inverted. Therefore, the position of the movable mirror 2 is detected. Reference numeral 13 denotes a memory, which is an area f that stores and collects the collected interferogram data one after another and an area t that stores the interferogram obtained by the scanning of the moving mirror this time. The interferograms are provided, and the interferograms are integrated in the area f by performing phase alignment of the interferogram and transferring the data to the area f. In the memory 13, the maximum value of the data of the center point of the center burst (maximum peak) and several points in the vicinity thereof among the data of the interferogram being accumulated, that is, the interferogram stored in the area f, is set to 1 as the maximum value. The maximum value of the file F that stores the data and the data of the corresponding points including the maximum peak from the interferogram data collected this time is set to 1
A file T that is standardized and stored in is prepared.

First, an outline of the operation of the data processing means 10 will be described. The data processing means counts the number of data samplings from the beginning of the scanning of the moving mirror, and the sampling data is used as the addressing data when storing it in the t area of the memory 13. This is the number of the sampled data. Further, as described above, this count value becomes the data of the position of the movable mirror. When receiving the position detection signal of the position detector at the specific position, the data processing means stores the number n2 of the sampling data immediately before that. After the scanning of the moving mirror is completed once, the maximum value is obtained from the sampled interferogram data, and the data number n1 is detected to calculate N = n1-n2. If the above-mentioned maximum value is the data of the top of the center burst, the value of N is a value that is not much different from the fixed number determined structurally. Therefore, if N is within a certain reference range, the maximum value can be determined to be the peak of the center burst. In this embodiment, a more elaborate determination is added to this, and if the maximum value of the interferogram in the current scanning is once determined to be the peak of the center burst as described above, the maximum value is centered around this maximum value. The data in the range is standardized and stored in the file T, and the data is overlapped with the standardized data (in the file F) near the center burst of the interferogram during the integration by slightly shifting them. Correlation is calculated, and the interferogram data collected this time (in the t area of the memory) is converted to the interferogram data in the middle of integration in the f area according to the correspondence relationship between both data when the correlation is the best. Add up. On the other hand, when the above-mentioned N is out of the reference range, or when a good correlation cannot be obtained by the above-described calculation of the correlation, the data collected this time is regarded as having abnormal noise and is discarded.

FIG. 2 is a flow chart of the operation of the data processing means 10. In step (a), it is checked whether it is the first time of the interferogram integration. At the first time, the numerical value NO designed in advance is set as the reference value of N mentioned above (b). Next, in the step (c), the above-mentioned N = n2-n1 is obtained, and in the step (d), A = | N-No | is compared with the reference value Ao. Ideally, | N−No | should be 0, not practically 0. When | N−No | is Ao or less, the operation proceeds to step (e) to check whether it is the first integration or not. At the first time, there is no interferogram in the middle of integration that should be correlated, so the operation is ( F), the data of the interferogram stored in the t area of the sampled memory is put into the f area, and one interferogram measurement operation is completed. If | N-No> becomes Ao in step (d), the operation goes to step (h) to check whether the set gain of the automatic gain adjustment unit in the amplifier 14 in FIG. 1 is the maximum or not. However, when it is not the maximum, the data collected this time is rejected (re). When A> Ao, do not immediately discard the data and place the step (h) in the case where the gain of the amplifier 14 is set to the maximum in a sample with a very low transmittance, the center burst does not always stand out. Since it does not happen, the maximum value in the interferogram is treated according to the peak of the center bust, and the peaks are overlapped each time thereafter, and integration is performed. Therefore, if it is the first time of integration, n2-n1 = N is newly set to No (nu) and the operation proceeds to (f). After the second integration, the correlation calculation between the data in the file F and the current data in the file T is performed after the step (e) (g). In this correlation calculation, the data of the file T is shifted by one by the data number, and the file F is moved.
By the method of subtracting from the data of, and finding the place where the sum of squares of the difference is the minimum, the correlation is not established when the sum of the least squares is larger than a certain value E in the step (r). The data at that time is rejected, and when the least sum of squares becomes smaller than a certain value, the operation proceeds to step. When the data is discarded three times in a row, for example, it is considered that there is a problem with the sample or the device. Therefore, an error display (e) is displayed and the measurement is stopped.

G. Effect As described above, in the present invention, when integrating the interferograms, the center burst is detected to align the phases, and the phases are aligned by matching the bursts. No need for high precision equipment,
If there is no adjustment point necessary for the user and the detection of the center burst is called the maximum peak, there is a possibility that the center burst may be mistaken when abnormal noise is introduced, and depending on the sample, the center burst may be mistaken. The burst may not show a prominent peak and thus the center burst may be erroneously detected. However, in the present invention, a means for detecting the position of the movable mirror is also used, and the center detection on the interferogram from the position detection signal. Since the range in which the burst should exist is limited, it is possible to provide an inexpensive and easy-to-handle phase adjusting means for the interferogram without misidentifying the center burst.

[Brief description of drawings]

FIG. 1 is a plan view and a block diagram of an embodiment of the present invention, and FIG. 2 is a flow chart of the operation in the embodiment.

Claims (1)

[Claims] 1. A memory for additionally storing an interferogram obtained by each scanning of a moving mirror, a memory for storing an interferogram obtained by a current scanning of a moving mirror, and a moving memory. It is equipped with a means for collecting data on the position of the mirror during scanning, a specific position detecting means for detecting that the movable mirror has passed a specific position on the device, and a control means. The preset value is the difference between the position data of the moving mirror sampled when the moving mirror passes the specific position for each time and the position data corresponding to the maximum value of the interferogram obtained in this scanning. , The maximum value is determined to be the center burst of the interferogram at that time, and the interferogram obtained by each scan is determined as the center bar determined above. A Fourier transform type spectrophotometer, characterized in that the interferograms are stored in a memory that stores the interferograms in an additive manner.