JPS603609B2 - Interferometry spectrometer - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an interferometric spectroscopic apparatus, and more particularly to an interferometric spectroscopic apparatus using a Michelson type interferometer and equipped with an extremely inexpensive frequency analyzer.

In recent years, the seriousness of problems such as environmental pollution has been recognized, and various devices have come to be used to measure the concentration of specific gases in the atmosphere.

For example, one method is to perform gas analysis using an infrared spectrometer, and in such cases, a spectrometer suitable for measuring the concentration of characteristic gases in the atmosphere is capable of highly sensitive detection. Something is desirable. One such spectrometer is a Michelson interferometer type spectrometer, which is an extremely bright spectrometer because it can separate incident light into spectra without dispersing it. However, in a Michelson interferometer type spectrometer, the signal corresponding to the amount of light directly obtained as a result of the operation of the spectrometer does not represent intensity as an explicit function of energy, and therefore must be inversely Fourier transformed. Therefore, an interferometric spectrometer using a Michelson interferometer type spectrometer is provided with means for inversely Fourier transforming the signal from the photodetector. The conventional interferometry spectrometer uses a small computer as a means for performing this inverse Fourier transform, which makes the device extremely expensive. For example, in gas analysis for pollution measurement, the main target of measurement is only a few specific harmful gases, so some of the infrared light source light that is absorbed when passing through the measurement sample is If the light intensity at the main absorption wavelength of a specific gas can be known, it can be used for quantitative analysis, and it is not necessarily necessary to measure the intensity over all wavelengths. In view of these points, the present invention aims to eliminate the drawbacks of conventional devices, and provides an extremely inexpensive and simple interference spectroscopy device.One embodiment of the present invention will be described in detail below based on the drawings. . FIG. 1 is a schematic diagram of an embodiment of the apparatus. In the drawing, reference numeral 1 indicates a light source to be separated that generates light to be separated, and light 2 from the light source enters a lens 3 and is parallelized. The parallel light enters a beam splitter 4 arranged at an angle of 450 with respect to Toko.

Reference numeral 5 denotes a reference light source such as a helium neon laser that generates a monochromatic light serving as a reference light, which is provided to enable accurate spectroscopic measurements even when the reciprocating mirror 9 has slight variations in speed. Monochromatic light from a light source 6 and lenses 7
After the light is made into parallel light, it enters the beam splitter 4.

8 is a fixed mirror having a mirror surface parallel to the light beam, and 9 is a reciprocating mirror having a mirror surface perpendicular to the mirror surface of the fixed mirror.

One end of the reciprocating mirror is adapted to be reciprocated by a known drive mechanism 10, such as that used in loudspeakers, for example, consisting of a voice coil and a permanent magnet. Among the reciprocating movements, the forward movement is performed at a constant speed. A photodetector 11 is provided to detect the light from the reference light source 5 reflected by the beam splitter 4 . 12 is the beam splitter 4
This is a condensing lens for condensing the light reflected by the photodetector 11.

The output end of the photodetector 11 is connected via an amplifier 13 to a waveform shaping circuit for converting it into a transistor logic signal suitable for digital processing, and the output signal of the waveform shaping circuit 14 is output from the circuit 14. A phase-locked loop circuit 1 for dividing the frequency of an output signal by a factor of N or multiplying it by a factor of N according to a predetermined setting value.
5. Here N' and N are integers chosen for each measurement. The output signal of the phase-locked loop circuit 15 is the output signal of the phase-locked loop circuit 1.
5 is supplied to a phase shifter 16 for changing the phase of the output signal. A second photodetector 17 is arranged corresponding to the photodetector 11 to detect the light from the light source 1 to be analyzed that is reflected by the beam splitter 4.
18 is a condensing lens for condensing the light from the light source 1 to be analyzed reflected by the beam splitter 4 onto the photodetector 17.

The output terminal of the photodetector 17 is supplied via an amplifier 19 to two phase detectors to which a reference signal from the phase shifter 16 is supplied. The output signal of the phase detector 20 is supplied to a recorder 22 via a low-pass filter 21. All of the signal processing in the various circuits described above is performed effectively only while the reciprocating mirror 9 is moving at a constant speed. In the apparatus configured as described above, for example, as the light source 1 to be analyzed, the light source light of an infrared spectrometer having a spectrum as shown in FIG. 2a, which has passed through the sample gas, is selected.

In FIG. 2a, for example, ``A'' is the main absorption peak of sulfur dioxide gas at wavelength ^, and ``A'' is the main absorption peak of nitrogen dioxide gas at wavelength 2. The spectrum of the reference beam 6 is as shown in FIG. 2b. A portion 2a of the light 2 from the light source 1 to be separated having such a wavelength distribution is reflected by the beam splitter 4, then reflected by the fixed mirror 8, and further transmitted through the beam splitter 4. A portion 2b of the light 2 from the light source 1 to be separated passes through the beam splitter 4, is reflected by the reciprocating mirror 9, is reflected by the beam splitter 4, and travels on the same optical path as the light 2a. cause interference. In exactly the same way, light 6 from the reference light source 5 also has a component 6a that is reflected by the beam splitter 4 and then reflected by the fixed mirror 8, and a component 6 that is reflected by the reciprocating mirror 9 and then reflected by the beam splitter 4.
b travels on the same optical path and causes interference. The drive mechanism 10 is driven to cause the reciprocating mirror 9 to move forward at a constant speed V. As a result, as is well known, the photodetector 17 receives a signal as shown in FIG. 3a, which has a spectrum as shown in FIG. When converted, a signal having a frequency as shown in FIG. 3b (wherein is the wavelength of the reference light source) whose spectrum is shown in FIG. 2b is obtained. The signal from the detector 11 is supplied to an amplifier 13 and amplified, and then supplied to a waveform shaping circuit 14 where the signal is shaped into a signal as shown in FIG. 4a. For example, to find the intensity of the light from the light source 1 to be spectralized at the wavelength input, the song is ＊畔. Find a set of integers N, and N,' such that

As a result, the output signal of the phase-locked loop circuit 15 becomes as shown in FIG. 4b. The output signal is passed through the phase shifter 16
Two phase detectors are supplied via the phase detector. Phase detector 201
This is supplied with a signal as shown in FIG. 3a, which is detected by the phase detector 20 based on the signal provided by the phase shifter 16 shown in FIG. 4b. The detected signal has a high frequency component set in a low-pass filter 21 and is recorded on a recorder 22 as a DC output.
Therefore, if the phase is changed appropriately using the phase shifter 16, the recorder 2
The signal value of the DC signal recorded in 2 increases or decreases. By observing the signal value and adjusting the amount of phase shift by the phase shifter 16 so that the recorded value is maximized, the frequency corresponding to the wavelength included in the signal supplied to the phase detector 20 can be adjusted. The phase of the signal component that has the same frequency matches the phase of the reference signal that is supplied from the phase shifter 16 and has the same frequency, and the recorder 22 receives the light at the wavelength input in FIG. 2a as shown in FIG. 4c. The output corresponding to intensity 1, is recorded. Similarly, in the same figure, in order to obtain an output corresponding to a light intensity of 12 at wavelength input 2, we find a pair of integers N2 and N2' that looks stylish, put it in the phase-locked loop circuit 15, and change the waveform. Set the frequency of No. 14 to be multiplied by the frequency.

As a result, the frequency of the output signal of the waveform shaping circuit 14 is multiplied by the phase-locked loop circuit 15 as shown in FIG. 4d, for example. In this case, the mochi transfer 16 corresponds to the wavelength input 2 contained in the signal shown in FIG. A component having the same frequency is detected by the phase shifter 16 and two phase detectors based on a reference signal having almost the same frequency and the same phase, and a signal in which various harmonic components are superimposed on the DC component is detected. can get.

The harmonic components of the signal are cut off by a low-pass filter 21, and a DC signal component corresponding to the light intensity 12 at wavelength input 2 in FIG. 2a as shown in FIG. 4e is recorded on the recorder 22. By obtaining a signal output corresponding to such light intensities 1, 12, it is possible to know the concentration of a specific gas in the atmosphere. Incidentally, when viewed in terms of wavelength order, velocity unevenness occurs in the reciprocating speed of the reciprocating mirror 9, but the effect caused by such causes is that the light from the light source 1 to be separated and the light from the reference light source 5 Since the two components are added equally, the resulting errors in the measurement are kept to a very small extent.

The embodiment described above is only one embodiment of the present invention, and in reality, the dynamic range of the phase detector 20 may be kept below a certain level, or the S/N ratio may be improved. A bandpass filter is provided before the phase detector 20,
Unnecessary frequency components may be cut in advance.

As is clear from the above description, according to the present invention, it is possible to measure the light intensity of a specific wavelength without using a small computer for inverse Fourier transform, and therefore an inexpensive interferometry device is provided. .

[Brief explanation of the drawing]

Fig. 1 is a schematic diagram showing an embodiment of the present invention, Fig. 2 shows an example of the spectral waveform of light generated from the light source 1 to be analyzed and the reference light source 5, and Fig. 3 shows the inverse Fourier transform. 2 shows the output signal of the photodetector which is converted into the spectral waveform shown in FIG. 2, and FIG. 4 illustrates the output signal of each component of the embodiment device shown in FIG. are doing. 1... Light source to be separated, 2... Light source light to be separated, 3, 7, 12, 18""" lens, 4... Beam splitter, 5... See Light source, 6...
Reference light source light, 8... Fixed mirror, 9... Reciprocating mirror, 10... Drive mechanism, 11, 17...
...Photodetector, 13,19...Amplifier, 1
4... Waveform shaping circuit, 15... Phase locked loop circuit, 16... Phase shifter, 20...
... Phase detector, 21 ... Low-pass filter, 22
...Recorder. 2rl figure next 2 figures 3 figures inferior. figure

Claims (1)

[Claims] 1. A Michelson interferometer onto which light from a light source to be separated is projected, a mechanism for moving the mirror surface of the Michelson interferometer in parallel at a constant speed, and a mechanism for detecting the interfered light to be separated in the Michelson interferometer. a first photodetector; a reference light source for projecting monochromatic light onto the Michelson interferometer; and a second photodetector for detecting the interfered reference light in the Michelson interferometer. a frequency conversion circuit for converting the frequency of the output signal of the second photodetector to an arbitrary frequency, and a phase shifter for shifting the phase of the output signal of the frequency conversion circuit by an arbitrary amount. and a circuit for detecting the phase of the output signal of the first photodetector using the output signal of the phase shifter as a reference signal, and means for recording or displaying a signal based on the output of the circuit. An interference spectrometer characterized by: