JPS6112530B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an infrared spectrometer using a laser beam as a light source.

Infrared spectroscopy, which determines the presence and chemical structure of specific substances based on the absorption spectrum of infrared rays, is an analytical method that has been used for a long time. An apparatus for performing such an analysis requires a spectroscopic means for infrared rays in the wavelength band used for the analysis, and this requires a prism or a highly accurate diffraction grating.

In contrast, the present inventors previously filed a patent application filed in 1973-
In No. 128465, we proposed a spectroscopic analyzer using a laser made of a lead-containing alloy semiconductor as the measurement light source. This type of semiconductor laser has the property of changing its emission wavelength depending on the operating current, element temperature, etc.
The emission wavelength can be swept at a predetermined speed within a certain range by external control. Therefore, if the relationship between the control factors and the emission wavelength is sufficiently calibrated, a diffraction grating, prism, etc. are not necessary. For this calibration, a part of the laser beam is split and transmitted through a standard cell sealed with a transparent material whose absorption spectrum is known, and the spectrum of the transmitted light is compared with the absorption spectrum of the object to be measured.

However, this type of semiconductor laser currently has some instability, and fluctuations in emission intensity, emission wavelength, etc. are likely to occur. In particular, if the emission wavelength fluctuates and light is emitted at a wavelength different from the wavelength corresponding to the absorption peak of the measurement target, both the absorption by the measurement target and the absorption by the standard cell will become weaker, resulting in a disadvantageous reduction in analysis accuracy. There is.

The present invention has been made in view of the above points, and is a novel method that uses a semiconductor laser with a variable emission wavelength as a light source and includes means for normalizing the emission wavelength of the laser using a signal obtained from a standard cell. The purpose of this invention is to provide an infrared spectroscopic analysis device.

An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a system diagram showing the structure of an example of an atmospheric pollution component analyzer to which the present invention is applied.
A laser consisting of ternary semiconductors of tin (Sn) and tellurium (Te) is used. This type of laser emits infrared rays with a wavelength of several μm or more as coherent light, and the emission wavelength can be changed by changing the supply current, ambient temperature, etc. to the same element. Similar properties are slightly observed in gallium arsenide (GaAs)-based semiconductor laser devices, but the range is extremely narrow. In comparison, the wavelength variable range of the ternary semiconductor is much wider; for example, as will be described later, it is possible to variably control the emission wavelength over a range of about 1 μm just by changing the supply current. Reference numeral 2 denotes a current supply power source, which outputs a direct current including an alternating current component, as will be described later. The light emitted from the semiconductor laser 1 is interrupted by the chopper 3, and enters the deflection/branching system 4 as intermittent light. This part divides the optical path of the laser beam into two, one of which is incident on the deflection/focusing system 5, and the other is incident on another detector to be described later. The deflection/focusing system 5 is for focusing the incident laser light and projecting it as parallel light into the gas to be analyzed, and can be easily constructed by a combination of well-known Cassegrain mirrors, semi-transparent mirrors, etc.

The infrared rays entering the deflection/focusing system 5 are converted into parallel light, pass through the gas 6 to be analyzed, are further reflected by the bending reflector 7, and are sent back to the deflection/focusing system 5 as shown in 8. I'm going home. The purpose of reciprocating the infrared rays in this way is to lengthen the optical path and increase the amount of absorption by the gas 6 to be analyzed. Note that hereinafter, the deflection/branching system 4 will be referred to as a first optical system, and the deflection/focusing system 5 will be referred to as a second optical system.

Now, the infrared rays after being absorbed by the gas 7 to be analyzed once pass through the correction cell 9, and then are focused and incident on the first infrared detector 10, where they are converted into electrical signals. The other branched infrared rays exiting the deflection/branching system 4 enter the second infrared detector 12 and become an electrical signal. The output signals of both infrared detectors 10 and 12 are applied as inputs to a divider 11, and the output e ₂ of the second infrared detector 12 is applied to the first infrared detector 10.
The output e is subjected to an operation (division) that divides it by ₁ . By applying this calculation output to, for example, a self-recording oscillograph, a spectral absorption spectrum of the gas 6 to be analyzed can be obtained. However, the reason why it is possible to obtain the above spectrum using a laser that originally emits light of a constant wavelength as a light source is that, as will be described later, in the present invention, a semiconductor laser whose oscillation wavelength can be variably controlled is used, and external control (this implementation This is because the laser oscillation frequency is swept by controlling the power supply in the example. Note that L ₁ , L ₂ , and L ₃ are focusing infrared lenses. The correction cell 9 is for calibrating the system gain.

Here, since the second detector 12 receives infrared rays that do not pass through the gas 6 to be analyzed, its output _e2 reflects only the operating state of the semiconductor laser 1, regardless of the type and state of the gas. Therefore, as described above, if e ₁ /e ₂ is calculated by the divider 11, the signal e ₁ containing absorption spectrum information has been normalized by e ₂ , so the emission of the semiconductor laser Variations in intensity due to factors that are difficult to control can be corrected. Since the above-mentioned normalized signal appears at the output terminal 13 of the divider 11, by applying this signal to a recording or display device, the absorption spectrum of the gas 6 to be analyzed can be obtained without being affected by fluctuations in the light source. can be observed. In this embodiment, the optical wavelength is swept by controlling the supply current of the power supply 2 for supplying current. That is, the oscillation wavelength is continuously changed by supplying from the power supply 2 to the laser 1 a current having a waveform in which a gentle sawtooth wave is superimposed on a direct current sufficient for laser oscillation. However, the method for controlling the emission wavelength itself is essentially the same as the method previously proposed by the present inventors and already described in the specification of Japanese Patent Application No. 128465/1983. The repetition frequency of the above-mentioned sawtooth wave must also take into account the characteristics of the recording or display device,
Furthermore, since the analyzer of the present invention has extremely high resolution, the repetition frequency is preferably 1 Hz or less.
It is desirable to set it to around 0.1Hz.

Up to this point, it has been assumed that the relationship between the current and the oscillation (emission) wavelength for one particular unit of laser is constant unless other conditions change. However, in the case of a semiconductor laser made of an alloy semiconductor containing lead, there is a possibility of deterioration due to excessive current, heat generation, etc., and when deterioration occurs, the emission wavelength changes. In such a case, the laser beam before passing through the gas to be analyzed may be incident on a standard gas cell, and the signal obtained by receiving the infrared rays after passing through the gas cell with an infrared detector may be used. This can be achieved by simply inserting a standard gas cell between the first optical system 4 and the lens _L2 , but in FIG. (hereinafter referred to as the first divider) system and an embodiment has been shown in which it is used in place of the first divider system. In FIG. 2, the parts other than the semi-transparent mirror 14 are the same as in FIG. 1. Although the optical system and the like before lens _L2 are omitted, they are all the same as in Fig. 1.

The standard gas cell 15 contains a gas that is thought to be contained in the gas to be analyzed, for example, if the target to be analyzed is the atmosphere and you want to investigate its pollution, SO ₂ ,
A predetermined number of moles of NO ₂ , NO, etc. are sealed. The laser beam, that is, infrared rays after passing through the standard gas cell 15 is focused by a focusing lens L ₃ and
The light enters the infrared detector 16 and is photoelectrically converted. The photoelectric conversion output e ₃ of the detector 16 is applied to a divider 17, and the output e ₁ of the first infrared detector 10 is applied to the divider 17 through a buffer circuit 18 to convert e ₁ into e ₃ The divider 17 performs the operation of dividing by
e ₁ / to the output terminal 19 of (hereinafter referred to as the second divider)
An output proportional to e ₃ is obtained. This output corresponds to the absorption by the object of measurement (in this case, the atmosphere) normalized by the absorption by the standard cell 15. Since the absorption spectrum of the gas in the standard cell is known, even if the emission wavelength is deviated due to deterioration of the semiconductor laser, this will not cause a measurement error. Note that the changeover switch 20 is for switching between the output of the first divider 11 and the output of the second divider 17. Although a single changeover switch is used in the example shown in this figure, it is also possible to use an interlocking switch. If the input of the first divider 11 is also switched at the same time as the outputs of both dividers are switched, the buffer circuit 1
8 can be omitted.

Next, the timing circuit 21 is for detecting the absorption peak and activating the division circuit within the required time including this peak. This timing circuit has a memory function, and the first
The time point at which the strongest absorption occurs in the second oscillation frequency sweep is memorized, and the control signal can be issued only within a required time width before and after the maximum absorption time point during the second sweep. Therefore, it is convenient to use this timing circuit when it is desired to precisely observe the maximum absorption point, but it can be omitted for qualitative analysis.

Note that the above sweep uses a sawtooth wave. Therefore, the time until the wavelength corresponding to the peak of gas absorption is detected is detected using the first sawtooth wave, and subsequent measurements are performed at that timing.

The measurement time width is the time including the peak waveform. That is, it is the time from the rise to the fall of the peak waveform.

The spectroscopic analyzer of the present invention described above uses a semiconductor laser with variable emission wavelength as a light source, and therefore has advantages such as no need for spectroscopic means (diffraction grating, etc.) and easy wavelength control. Of course, as a countermeasure against fluctuations and deterioration of the light emission intensity of the laser, the measured values are normalized using non-absorbing laser light, so the operation is extremely stable, and the peak point of light absorption is Since measurements are carried out at Therefore, the present invention is extremely advantageous when applied to air pollution monitoring devices and other active type spectroscopic analyzers that utilize infrared rays.

[Brief explanation of drawings]

FIG. 1 is a system diagram showing one embodiment of a spectroscopic analyzer according to the present invention, and FIG. 2 is a system diagram of essential parts showing another embodiment of the spectroscopic analyzer according to the present invention. 1: Tunable wavelength semiconductor laser, 2: Power supply, 3:
Chiyotsupa, 4: first optical system, 5: second optical system,
6: Measurement object (atmosphere), 7: Bending mirror, 9: Correction cell, 10: First infrared detector, 11: First divider, 12: Second infrared detector, 13: Output terminal, 14: Semi-transparent mirror, 15: Standard gas cell, 1
6: Third infrared detector, 17: Second divider, 1
8: buffer circuit, 19: output terminal of second divider, 20: changeover switch, 21: timing circuit.

Claims (1)

[Claims] 1. A light source that oscillates a laser beam whose wavelength can be varied, a wavelength control means that sweeps and controls the wavelength of the laser beam, an optical branching means that branches the beam of the laser beam, and a light source that oscillates a laser beam whose wavelength can be varied; A main infrared detector receives the branched light that is not absorbed by the analyte, a sub-infrared detector receives the branched light that is not absorbed by the analyte, and the timing at which a predetermined period of time has elapsed from the start of wavelength sweep until the maximum absorption of the branched light occurs in the analyte is memorized. It comprises a timing circuit and a divider inputting the outputs of the main infrared detector and the sub-infrared detector, respectively, and a predetermined time from the rise to the fall of the peak waveform at which the maximum absorption occurs at the stored timing. An infrared spectroscopic analysis device characterized in that the divider output is obtained in a width.