JPH1048047A - Measuring method of interferogram - Google Patents

Abstract

PROBLEM TO BE SOLVED: To increase the number of data to be measured per unit time, and improve the measuring efficiency, by sampling the interferogram output from an analyzing part, in the both of the going and returing movements of a movable mirror in an interferometer. SOLUTION: The measurement of the interferogram IF is performed by reciprocating a movable mirror of an interferometer in the X, Y directions. The first CPU 15 performs the sampling of the interferogram IF converted into a digital signal in the going movement of the movable mirror in the X direction, during a period indicated by the code t1 -t2 , and stores the same in a memory as the data. Then the first CPU 15 performs the sampling of the interferogram IF converted into a digital signal in the returing movement of the movable mirror in the Y direction during a period indicated by t3 -t4 . In the period t3 -t4 , the data stored in the memory of the first CPU 15 is transferred to the second CPU 16 at a high speed. The second CPU adds and averages this data.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to a method for measuring an interferogram used in Fourier transform spectroscopy.

[0002]

2. Description of the Related Art One of the measuring apparatuses using Fourier transform spectroscopy is a Fourier transform infrared spectrometer (FTIR).
This FTIR is configured, for example, as shown in FIG. That is, in this figure, 1 is an analysis unit, and 2 is a data processing unit that processes an interferogram output from the analysis unit 1. The analysis unit 1 includes an infrared light source 3, an interferometer 7 including a beam splitter 4, a fixed mirror 5, a movable mirror 6 that is moved in parallel in the X and Y directions by a driving mechanism (not shown) to scan, a measurement sample, and the like. And a cell 8 to which infrared light L from the infrared light source 3 is irradiated via the interferometer 7, and a semiconductor detector 9.

[0003] The data processing unit 2 is composed of, for example, a computer. The data processor 2 adds and averages interferograms, and outputs the averaged output of the interferogram with a fast Fourier transform.
ier Transform (hereinafter, simply referred to as FFT) to obtain an absorption spectrum.

FIG. 4 schematically shows a configuration of a signal processing system in the conventional FTIR. In FIG. 4, reference numeral 10 denotes an interferometer output from a detector 9 of the analyzer 1 (see FIG. 3). A preamplifier for appropriately amplifying the gram IF, an A / D converter 11, and a CPU 12 for performing control and calculation. Reference numeral 13 denotes a drive circuit of the interferometer 7 (see FIG. 3), and reference numeral 14 denotes a personal computer (hereinafter, simply referred to as a personal computer) including a display device and a memory device.

[0005] In the FTIR having the above configuration, analysis can be performed as follows. That is, the comparison sample or the measurement sample is stored in the cell 8, respectively, and the cell 8 is irradiated with infrared light L from the infrared light source 3, and the interferogram IF of the comparison sample and the measurement sample is measured. These interferograms IF are each subjected to FFT in the data processing unit 2 to obtain a power spectrum, then the ratio of the power spectrum of the measurement sample to the power spectrum of the comparison sample is obtained, and the transmittance spectrum or the absorbance spectrum is obtained. Perform qualitative or quantitative analysis.

When sampling the interferogram IF, the movable mirror 6 in the interferometer 7 is used.
The direction in which the optical path length between the beam splitter 4 and the movable mirror 6 (hereinafter simply referred to as the optical path length) decreases (the direction indicated by the arrow X in FIG. 3) and the direction in which the optical path length increases (FIG. 3)
The scanning is performed so as to reciprocate (in the direction indicated by an arrow Y in FIG. 5), but conventionally, data sampling is performed in one reciprocating operation of the movable mirror 6 as shown in FIG. When sampling is performed in only one of the backward movements and sampling is not performed, the CPU 1
2 is an external device such as a personal computer for performing data calculations and 1
4 was performed.

[0007]

However, in the above-mentioned sampling method, even if the movable mirror 6 is returned to the start point of the scan at a high speed, it may not be possible to start the next scan. And the amount of data that can be measured per unit time is reduced, and the measurement efficiency is not always good. With this, there is room for improvement in S / N per fixed measurement time. Was.

The present invention has been made in consideration of the above-mentioned matters, and has as its object to provide a method of measuring an interferogram which can increase the number of data that can be measured per unit time and improve the measurement efficiency. It is to be.

[0009]

According to the present invention, there is provided a Fourier transform spectroscopy in which light from a light source is applied to a cell via an interferometer. The ferrogram is sampled both when the movable mirror moves forward and backward in the interferometer.

According to the method for measuring the interferogram, the amount of data that can be measured per unit time increases,
As the measurement efficiency improves, the S per fixed measurement time
/ N is improved.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described below with reference to the drawings. In the following description,
The same reference numerals as those shown in FIGS. 3 and 4 indicate the same or corresponding components.

FIGS. 1 and 2 show an embodiment of the present invention. First, FIG. 1 schematically shows a configuration for implementing an interferogram measurement method according to the present invention, and shows an example of a configuration of a signal processing system in FTIR, for example. In this figure, 15 to 17 are A / D converters 11
1 to 3C provided in series with each other on the output side of
PU. Reference numeral 18 denotes a drive circuit of the interferometer 7, and reference numeral 19 denotes, for example, a personal computer as an external device, which includes an appropriate display device and a memory device.

More specifically, the first CPU 15
The data converted into a digital signal by the / D converter 11 is fetched, transferred to the second CPU 16 at a high speed, and the drive circuit 18 of the interferometer 7 is controlled. Then, the second CPU 16 adds and averages the data transferred at a high speed from the first CPU 15 and outputs the added average output by the FFT.
Then, an absorption spectrum is obtained, and the data signal is
Output to CPU17. Also, the third CPU 17
The spectrum data from the CPU 16 is output to the personal computer 19. Further, the personal computer 19 displays the spectrum on the screen based on the data sent from the third CPU 17, and stores the spectrum data in the memory.

Next, a method for measuring an interferogram according to the present invention will be described with reference to FIGS. The cell 8 accommodates the comparative sample or the measurement sample, respectively, and irradiates the cell 8 with infrared light L from the infrared light source 3,
The interferogram IF of the comparative sample and the measurement sample is measured. The measurement of the interferogram IF is performed by moving the movable mirror 6 in the interferometer 7 with the arrow X in FIG.
This is performed by reciprocating in the Y direction. The interferogram IF at this time is converted into an electric signal by the detector 9, appropriately amplified by the preamplifier 10, and then converted into a digital signal by the A / D converter 11.

[0015] Then, the period shown in FIG. 2 Oite code t ₁ ~t _2, when moving e.g. forward in the arrow X direction in the movable mirror 6 in FIG. 3, the interferogram IF the first 1CPU15 is converted into the digital signal Is sampled and stored as data in its memory.

Next, when the movable mirror 6 moves backward in the direction of arrow Y in FIG. 3 during a period indicated by reference numerals t _{3 to} t ₄ in FIG. 2, the first CPU 15 samples the interferogram IF converted into a digital signal. I do. Then, in the period t ₃ ~t _4, data taken into the memory of the 1CPU15 is fast forwarded to the 2CPU16. Then, the second CPU 16 adds and averages the data transferred at a high speed and outputs the added average output of the FFT.
Then, data of an absorption spectrum is obtained.

The processed data is supplied to a third CPU 17.
Is sent to the personal computer 19, and is displayed as an absorption spectrum on a screen of a display device attached to the personal computer 19 or stored in a memory device.

Hereinafter, the above-described processing is repeatedly and continuously performed. That is, data sampling is performed both when the movable mirror 6 moves forward and backward. By doing so, the number of data that can be measured per unit time can be increased, the measurement efficiency is almost doubled, and therefore a high S / N can be obtained with a short measurement time.

In the above embodiment, three CPUs 15
~ 17 are provided, but are not limited to this.
Depending on the capacity of the CPU, two of them may be used, or four or more CPUs may be used. Further, if the CPU can perform very high-speed processing, only one of them may be used. It may be.

Further, the present invention is not limited to the processing of the interferogram in the above-mentioned FTIR, but it is needless to say that it can be applied to the processing of an interferogram widely used in Fourier transform spectroscopy.

[0021]

As described above, according to the present invention, the amount of data that can be measured per unit time is increased, and the measurement efficiency is improved. Therefore, a high S / N can be obtained in a short measurement time, and the accuracy can be improved. High measurement can be performed.

[Brief description of the drawings]

FIG. 1 is a diagram schematically showing a configuration for implementing an interferogram measurement method of the present invention.

FIG. 2 is a diagram illustrating the operation of the measurement method.

FIG. 3 is a diagram schematically showing a configuration of a general FTIR.

FIG. 4 is a diagram schematically showing a configuration for implementing a conventional interferogram processing method.

FIG. 5 is a diagram for explaining the conventional method.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Analysis part, 3 ... Light source, 6 ... Movable mirror, 7 ... Interferometer,
8: cell, L: light, IF: interferogram.

Claims (1)

[Claims] In a Fourier transform spectroscopy in which light from a light source is irradiated to a cell via an interferometer, an interferogram output from an analysis unit is used when the movable mirror in the interferometer moves forward and backward. A method for measuring an interferogram, characterized in that sampling is performed during both movements.