JPH11142328A - Isotope analyzer - Google Patents

Abstract

(57) Abstract: To stably and accurately detect the intensity of a light absorption spectrum, stabilize the FM modulation efficiency of a light wavelength at the time of measurement. A peak detection circuit detects a peak position of two optical absorption spectra of an isotope to be measured from a peak value output of each 2f component obtained by a lock-in amplifier and a sweep signal of a sweep control circuit. The arithmetic circuit 14 obtains the shift amount and the peak position interval information, and outputs the obtained information. By correcting the set value (bias) of the temperature control circuit 7 through the offset correction circuit 16 in accordance with the output of the arithmetic circuit 14, the peak positions of the two light absorption spectra of the isotope to be measured can be kept constant. it can.
Therefore, the FM modulation efficiency of the light wavelength at the time of measurement is stabilized, and the light absorption spectrum can be detected stably, so that the isotope ratio can be detected with high accuracy.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an isotope analyzer for irradiating a sample gas containing an isotope with light and detecting an isotope ratio from the intensity of each light absorption spectrum of the isotope.

[0002]

2. Description of the Related Art First, the background of the invention will be described. The method of tracing isotope changes should be used for diagnosing diseases in the medical industry, researching photosynthesis and plant metabolism in the agricultural field, and tracing ecosystems in the earth science field. Can be.

[0003] Isotopes used in these applications include nitrogen and carbon. In carbon, there are stable isotopes of ¹² C having a mass number of ¹² and ¹³ C having a mass number of 13,
These stable isotopes are easy to handle because they are not exposed to radiation as radioisotopes, and their use in the medical field is being accelerated.

Conventionally, there is an infrared spectrometer as an isotope analyzer for such an application. An infrared spectrometer is a device that uses a lamp having a wide emission wavelength range in the infrared region as a light source, selects a light wavelength using a dispersive spectroscope, and observes the light absorption spectrum of the isotope. However, since the light absorption spectrum wavelengths of the isotopes are very close, the light wavelength selection performance of the dispersive spectrometer is impeded, and sufficient light wavelength resolution characteristics cannot be obtained. The measurement accuracy was not sufficient.

[0005] Another isotope analyzer is a mass spectrometer. A mass spectrometer can measure isotopes with high accuracy because it measures the mass of a molecule itself. However, there are disadvantages in that the device is large, difficult to handle, and very expensive.

As a technique for solving these problems, a laser spectroscopic analysis technique has been receiving attention. In this laser spectroscopic analysis method, high light wavelength resolution can be obtained with a small device by using a narrow band semiconductor laser as a light source. Therefore, the operability is improved, and the accuracy of isotope measurement is sufficient.

In this laser spectroscopic analysis method, a predetermined light wavelength is obtained by stabilizing the temperature and current of a semiconductor laser used as a light source, and the light intensity of a laser beam after passing through a sample gas is changed by gas molecules. The light absorption spectrum intensity is measured.

[0008] However, the light wavelength of the semiconductor laser is sensitive to environmental conditions such as temperature and is easily changed. Therefore, stabilization of the optical wavelength with high accuracy has become a key technology in laser spectroscopic analysis techniques, a so-called key technology.

FIG. 4 shows a configuration of a conventional isotope analyzing apparatus to which a laser spectroscopic analysis technique is applied.

The isotope analyzing apparatus shown in FIG. 4 comprises a semiconductor laser 1, a holding block 2, a collimating lens 3, a temperature detecting element 4, a temperature controlling element 5, a temperature detecting circuit 6, a temperature controlling circuit 7, a current controlling circuit 8, Sample cell 9, light detection element 10, oscillation circuit 11, lock-in amplifier 12, peak detection circuit 1
3b, an arithmetic circuit 14 and a sweep control circuit 15a.

First, the operation of the optical system will be described. Laser light L emitted from the semiconductor laser 1 fixed on the holding block 2 is converted into parallel laser light L via the collimating lens 3. The laser light L is transmitted after being absorbed in the sample cell 9 into which the sample gas to be measured is introduced, and the absorption spectrum intensity is detected by the photodetector 10.

Next, the operation of stabilizing the light wavelength of the semiconductor laser 1 will be described. The semiconductor laser 1 and the temperature detecting element 4 are fixed on the holding block 2 with high adhesion. For this reason, the thermal conductivity between the semiconductor laser 1 and the temperature detecting element 4 is kept good, and the temperature of the semiconductor laser 1 and the temperature detecting element 4 becomes substantially the same as the temperature of the holding block 2. Therefore, the temperature of the semiconductor laser 1 can be detected by the temperature detecting element 4.

The temperature information of the semiconductor laser 1 detected by the temperature detecting element 4 is converted into an electric signal by a temperature detecting circuit 6 and input to a temperature control circuit 7 as a measured temperature value.

The temperature control circuit 7 controls the temperature control element 5 integrally attached to the holding block 2 so as to have a set value selected in advance so as to obtain a predetermined light wavelength.

The temperature control element 5 heats or absorbs heat under the control of the temperature control circuit 7, and is fixed on the temperature control element 5 while maintaining good thermal conductivity.
The temperature of the

By forming the temperature control loop as described above, the temperature of the semiconductor laser 1 is controlled by the temperature control circuit 7.
It stabilizes at the set temperature.

The semiconductor laser 1 has a sweep control circuit 1
It is driven by a current supplied from a current control circuit 8 that outputs a stabilized current according to an input signal from 5a.

Therefore, the above-mentioned stabilization of the set temperature,
In other words, by stabilizing the chip temperature of the semiconductor laser 1 and stabilizing the drive current supplied to the semiconductor laser 1, the light wavelength of the laser light L can be stabilized.

Next, the operation of detecting the light absorption spectrum will be described.

The oscillation circuit 11 generates a modulation signal of a frequency f for modulating the driving current of the semiconductor laser 1. The modulation signal having the frequency f is input to the current control circuit 8, added to the stabilized current in the current control circuit 8, and added to the current control circuit 8.
Is supplied to the semiconductor laser 1 as a drive current. By modulating the drive current of the semiconductor laser 1, the light wavelength of the laser light L is FM-modulated.

When the sweep control circuit 15a controls the current control circuit 8 so that the output current set value increases proportionally, the drive current supplied from the current control circuit 8 to the semiconductor laser 1 monotonously increases. As the drive current increases,
The light wavelength of the semiconductor laser 1 monotonically increases and is swept.
In this case, the intensity of the predetermined light absorption spectrum can be detected by the light detection element 10 by setting the light wavelength sweep to a range where the predetermined light absorption spectrum exists.

When the light wavelength is FM-modulated at the frequency f, the light absorption spectrum waveform is replaced by the 2f signal, so that the intensity of the light absorption spectrum can be detected by the lock-in amplifier 12 for detecting the 2f component. .

The peak detection circuit 13b extracts the peak value of the 2f component of the light absorption spectrum as the light wavelength is swept. The arithmetic circuit 14 selects the intensity of the light absorption spectrum corresponding to two predetermined isotopes from the peak value information of the 2f component obtained from the peak detection circuit 13b and the light wavelength control information obtained from the sweep control circuit 15a, By taking the ratio of these intensities, the isotope ratio can be detected by the isotope analyzer shown in FIG.

[0024]

Generally, the FM modulation efficiency of the optical wavelength of the semiconductor laser 1 has a characteristic that varies depending on the chip temperature of the semiconductor laser 1 and the driving current supplied to the semiconductor laser 1. . However, the optical wavelength F
When the M modulation efficiency changes, the intensity of the light absorption spectrum detected by the lock-in amplifier 12 that detects the 2f component fluctuates, causing a problem that the detection accuracy decreases.

Although it is relatively easy to supply a stable drive current from the current control circuit 8 to the semiconductor laser 1,
It is not easy to stabilize the chip temperature of the semiconductor laser 1.

The reason is that the interposition of the holding block 2 is indispensable for the thermal contact between the semiconductor laser 1 and the temperature detecting element 4.
Even if the semiconductor laser 1 and the temperature detecting element 4 are fixed with high adhesion on top of each other and the mutual heat conduction is maintained well, thermal fluctuation elements such as a proportional increase in the driving current are repeated in the semiconductor laser 1. When the temperature is applied or the environmental temperature changes, the chip temperature of the semiconductor laser 1 and the temperature detecting element 4
This is because there is a delicate gap from the detected temperature. As a result, the chip temperature of the semiconductor laser 1 has a value slightly different from the set temperature of the temperature control circuit 7.

However, since the light wavelength at which the light absorption spectrum exists is physically constant and does not fluctuate, a predetermined light wavelength can be obtained at a different driving current value by an amount corresponding to a shift of the actual chip temperature of the semiconductor laser 1. Will be.
In this case, the chip temperature and the average driving current of the semiconductor laser 1 detected by the temperature detecting element 4 at the time of observation of the light absorption spectrum are different from the initial conditions. For this reason, the FM modulation efficiency of the light wavelength changes, and the detection level of the lock-in amplifier 12 that detects the 2f component changes.

The slight difference between the chip temperature of the semiconductor laser 1 and the temperature detected by the temperature detection element 4 is caused by the fact that the chip itself of the semiconductor laser 1, more precisely, the light emitting point in the chip and the temperature detection element 4 are physically different. This is a problem that cannot be avoided because it cannot be integrated with a computer.

The present invention has been made in view of the above-described problems, and it is possible to stabilize the FM modulation efficiency of a light wavelength at the time of measuring a light absorption spectrum and to stably detect the light absorption spectrum. It is an object of the present invention to provide an isotope analyzer capable of determining an isotope ratio with high accuracy.

[0030]

According to the present invention, there is provided an isotope analyzer for detecting an isotope ratio from a light absorption spectrum of an isotope to be measured, as shown in FIGS. 1 and 3, for example.
A semiconductor laser 1 for outputting laser light L, a temperature detection circuit 6 for detecting the temperature of the semiconductor laser, a temperature control circuit 7 for controlling the temperature of the semiconductor laser so that the detected temperature becomes a set value, A current control circuit 8 for controlling a drive current of the semiconductor laser, a sweep control circuit 15a for performing a sweep of an optical wavelength of the semiconductor laser based on a sweep signal,
15b, an oscillation circuit 11 for modulating the frequency of the semiconductor laser with a frequency f, a light detection element 10 for detecting a light absorption spectrum from the laser light transmitted through the sample gas of the isotope to be measured, and a detected measurement A lock-in amplifier 12 for detecting each 2f component of two light absorption spectra of the target isotope;
A peak detection circuit 13a for detecting each peak value of the component,
An arithmetic circuit 1 for obtaining and outputting information on the amount of shift between the peak positions of two light absorption spectra of the isotope to be measured and the peak position interval from the sweep signal and the output of the peak detection circuit.
4 and the temperature control circuit 7 according to the output of the arithmetic circuit.
And an offset correction circuit 16 that corrects the set values of the two isotopes. The peak positions of the two light absorption spectra of the isotope to be measured are held constant, and the intensities of the light absorption spectra are detected. The isotope ratio is detected from an intensity ratio of an absorption spectrum.

According to the present invention, the shift amount of the peak position and the peak position interval information of the two light absorption spectra of the isotope to be measured are obtained from the peak value output of each 2f component and the sweep signal obtained by the lock-in amplifier. The peak value of the two light absorption spectra of the isotope to be measured is kept constant by correcting the set value of the temperature control circuit through the offset correction circuit in accordance with the output of the calculation circuit. Then, the intensity of the light absorption spectrum is detected, and the isotope ratio is detected from the intensity ratio of each detected light absorption spectrum, so that the FM modulation efficiency of the light wavelength at the time of measurement is stabilized. Since the light absorption spectrum can be detected stably, the isotope ratio can be detected with high accuracy.

In this case, for example, as shown in FIG. 1, the sweep control circuit 15a may control the current control circuit 8 to sweep the light wavelength of the semiconductor laser 1.

Further, for example, as shown in FIG. 3, the sweep control circuit 15b may control the temperature control circuit 7 to sweep the light wavelength of the semiconductor laser 1.

[0034]

An embodiment of the present invention will be described below with reference to the drawings. In the drawings referred to below, components corresponding to those shown in FIG. 4 are denoted by the same reference numerals, and detailed description thereof will be omitted.

FIG. 1 shows a configuration of an isotope analyzing apparatus according to an embodiment of the present invention.

The isotope analyzer of FIG. 1 includes a semiconductor laser 1, a holding block 2, a collimating lens 3, a temperature detecting element 4, a temperature controlling element 5, a temperature detecting circuit 6, a temperature controlling circuit 7, a current controlling circuit 8, Sample cell 9, light detection element 10, oscillation circuit 11, lock-in amplifier 12, peak detection circuit 1
3a, an arithmetic circuit 14, a sweep control circuit 15a, and an offset correction circuit 16.

In the isotope analyzer of FIG. 1, as the semiconductor laser 1, a single mode DFB (distributed feedback) laser or the like can be used. And carbon isotopes ( ¹² C,
^In the measurement of ¹³ C), an infrared wavelength region of about 1.5 to 2.0 μm is effective because it has high sensitivity.

As the holding block 2, a metal such as copper, which is plated with gold and has good thermal conductivity, is used to suppress heat radiation and increase the adhesion to the semiconductor laser 1 and the like.

As the collimating lens 3, a glass or a plus-chip aspheric lens suitable for the light wavelength of the semiconductor laser 1 is used.

As the temperature detecting element 4, a platinum thin film temperature sensor or a thermistor is used.

As the temperature control element 5, a Peltier element or a heater is used.

As the temperature detecting circuit 6, a resistance value detecting differential amplifier circuit is used.

As the temperature control circuit 7, a difference circuit and PI
A D (proportional-integral-derivative) circuit is used.

As the current control circuit 8, a resistance load feedback type operation circuit is used.

As the sample cell 9, a single-pass or multi-pass cell made of glass or metal is used.

The semiconductor laser 1 is used as the photodetector 10.
Use a photodiode suitable for the light wavelength of For the measurement of carbon isotopes ( ¹² C, ¹³ C) as isotopes, 1.5 to
Ge or I capable of detecting an infrared wavelength band of about 2.0 μm
nGaAs or the like is suitable.

As the oscillation circuit 11, a PLL circuit or a digital clock generation circuit is used.

As the lock-in amplifier 12, a chopping amplifier, an LPF and a mixer circuit are used.

As the peak detection circuit 13a, a sample hold, an A / D converter and an MPU are used.

As the arithmetic circuit 14, an MPU, a memory element, an A / D / D / A converter and the like are used.

A D / A converter or the like is used as the sweep control circuit 15a.

The offset correction circuit 16 has a D / A
Use converters, variable gain amplifiers and / or look-up tables.

The optical system around the semiconductor laser 1 is
For stabilizing the temperature for the purpose of stabilizing the light wavelength, it may be housed in a vacuum or low-pressure container.

First, the operation of the optical system of the isotope analyzing apparatus configured as described above will be described. Laser light L emitted from the semiconductor laser 1 fixed on the holding block 2 is converted into parallel laser light L via the collimating lens 3. This laser light L is transmitted after being absorbed in the sample cell 9 into which the sample gas to be measured is introduced, and the absorption spectrum intensity is detected by the light detection element 10.

Next, the light wavelength stabilizing action on the semiconductor laser 1 will be described. The semiconductor laser 1 and the temperature detecting element 4 are fixed on the holding block 2 with high adhesion. For this reason, the thermal conductivity between the semiconductor laser 1 and the temperature detecting element 4 is kept good, and the temperature of the semiconductor laser 1 and the temperature detecting element 4 becomes substantially the same as the temperature of the holding block 2. Therefore, the temperature of the semiconductor laser 1 can be detected by the temperature detecting element 4.

The temperature information of the semiconductor laser 1 detected by the temperature detecting element 4 is converted into an electric signal by the temperature detecting circuit 6 and input to the temperature control circuit 7 as a measured temperature value. The temperature control circuit 7 controls the temperature control element 5 so that a predetermined value is obtained in advance so as to obtain a predetermined light wavelength.

The temperature control element 5 heats or absorbs heat under the control of the temperature control circuit 7 and changes the temperature of the holding block 2 which is thermally fixed on the temperature control element 5 in a good condition.

By forming the temperature control loop as described above, the temperature of the semiconductor laser 1 is controlled by the temperature control circuit 7.
It stabilizes at the set temperature.

At this time, the semiconductor laser 1 is driven by a current supplied from a current control circuit 8 which outputs a stabilized current according to an input signal from a sweep control circuit 15a.

As described above, by stabilizing the chip temperature of the semiconductor laser 1 and the drive current supplied to the semiconductor laser 1, the light wavelength can be stabilized.

Next, the operation of detecting the light absorption spectrum will be described. While stabilizing the optical wavelength, the oscillation circuit 11 generates a modulation signal having a frequency f for modulating the driving current of the semiconductor laser 1 and supplies the modulation signal to the current control circuit 8.
The current control circuit 8 adds the current change due to the supplied modulation signal of the frequency f to the stabilized drive current and outputs the result. By modulating the drive current of the semiconductor laser 1 in this manner, the light wavelength is FM-modulated.

In such a state, the sweep control circuit 1
When 5a controls the current control circuit 8 so that the output current set value increases proportionally, the drive current of the semiconductor laser 1 continuously and monotonically increases, and accordingly, the light wavelength is swept.
By performing the light wavelength sweep in a range where the light absorption spectra of two predetermined isotopes exist, the intensity of the predetermined light absorption spectrum can be detected. When the light wavelength is FM-modulated at the frequency f, the light absorption spectrum waveform is replaced by the 2f signal, and therefore the 2f component (second derivative component)
The intensity of the light absorption spectrum can be detected by the lock-in amplifier 12 that detects

The peak detection circuit 13a extracts the peak value of the 2f component of the light absorption spectrum as the light wavelength is swept. The arithmetic circuit 14 selects the intensity of the light absorption spectrum corresponding to two predetermined isotopes from the peak information of the 2f component obtained by the peak detection circuit 13a and the light wavelength control information obtained from the sweep control circuit 15a. The isotope ratio is detected by calculating the ratio of these intensities.

Next, with reference to FIGS. 2A and 2B, a description will be given of a mechanism in which a variation in FM modulation efficiency occurs. 2A shows the initial state of the light absorption spectrum waveform, and FIG. 2B shows the light absorption spectrum waveform after the thermal fluctuation element is repeatedly applied to the semiconductor laser 1 by continuous measurement. 2A and 2B, the horizontal axis represents the control value of the wavelength variable element, that is, the drive current of the semiconductor laser 1 or the chip temperature, and the vertical axis represents the signal of the 2f component of the laser light L detected by the photodetector 10. Shows the strength.

As described above, the driving power of the semiconductor laser 1 is
Sweep the flow to change the light wavelength and observe the light absorption spectrum
In the example of the isotope analyzer shown in FIG.
The temperature of the chip of the semiconductor laser 1
There is a minute gap in the detected temperature between
Will come. Then, the drive current different from the initial state
, A predetermined light wavelength can be obtained.
Of the 2f component of the light absorption spectrum obtained by
As shown in FIGS. 2A and 2B,¹²CO _TwoThe pea
From position B to position B '(hereinafter, also referred to as position B → B').
Say. Go to¹³CO_TwoPeak position from position E
Move to position E '(position E → E'). In this case, drive
The change in optical wavelength when sweeping the current is generally non-linear.
Therefore, the distance between the position B and the position B ′ (also referred to as the displacement amount)
U. ) BB 'and the distance between position E and position E'
Also called. ) EE 'are not the same interval.

However, since the wavelength of the light absorption spectrum is physically invariable, this displacement phenomenon is caused by a change in the state of the system that controls the light wavelength, and the horizontal axis represents the control value of the wavelength variable element. , The driving current or the chip temperature of the semiconductor laser) changes nonlinearly.

In general, the FM modulation efficiency of the light wavelength of the semiconductor laser 1 has a characteristic that changes depending on the chip temperature of the semiconductor laser 1 and the drive current. For this reason, when these combinations change when obtaining a predetermined light wavelength, the FM modulation efficiency of the light wavelength also changes. When the FM modulation efficiency of the optical wavelength of the semiconductor laser 1 changes, the lock-in amplifier 12
Fluctuates in the intensity of the 2f component of the light absorption spectrum detected by the above, and it becomes impossible to observe the light absorption spectrum with high accuracy.

As described above, in the isotope analyzer of FIG. 1, when the sweep control circuit 15a controls the current control circuit 8 so that the output current set value increases proportionally based on a predetermined sweep signal, the semiconductor The drive current of the laser 1 monotonically increases, and the light wavelength is swept accordingly. At this time, the arithmetic circuit 14 determines the predetermined sweep signal and the peak detection circuit 1
3a, peak values b and b 'and peak values e,
e ′, the positional deviation amount BB ′ and the positional deviation amount E
E ′ is obtained, and an initial peak position interval BE and a changed peak position interval B′E ′ are obtained.

The offset correction circuit 16 calculates the position shift amount BB ', the position shift amount EE', and the peak position interval BE.
The temperature control circuit 7 performs feedback control based on the information of the peak position interval B'E 'and the peak position interval B'E' so that the peak position of the light absorption spectrum does not deviate from the position B → B 'and the position E → E'. In this way, the light absorption spectra of two given isotopes are respectively converted to a fixed light wavelength FM.
It is possible to observe at the modulation efficiency, and it is possible to stably measure the isotope ratio.

The operation of the arithmetic circuit 14 and the offset correction circuit 16 will be described more specifically. At a predetermined chip temperature of the semiconductor laser 1, a predetermined sweep signal,
That is, when the control value (the drive current value of the semiconductor laser 1 in the embodiment of FIG. 1) X of the wavelength variable element is changed between X = P to Q (see FIG. 2A), the control value X becomes X = The control value X = E (or X = E) when the offset value of B (or X = E) and the amplitude value from the offset value are X = B to E
At the time of B), it is assumed that the peak value b and the peak value e are obtained to obtain a constant light wavelength FM modulation efficiency.

In the initial state, the predetermined chip temperature value of the semiconductor laser 1 and the set value of the temperature control circuit 7 match, and the control value X = B and the amplitude value X = BE are maintained. However, the chip temperature value of the semiconductor laser 1 changes due to the repetition of the sweep. Is one to one
Does not change. Therefore, if the initial temperature set value is maintained, the peak position shifts to the control value X = B '(peak value b') and the control value X = E '(peak value e'). It becomes impossible to observe the light absorption spectrum with a constant light wavelength FM modulation efficiency.

Therefore, control value X = B and control value X =
E, in other words, the offset correction circuit 16 corrects the set value of the temperature control circuit 7 so that the peak values of the two light absorption spectra are obtained in the predetermined current value range. At this time, the correction direction (whether the correction amount is a positive value or a negative value) and the correction amount can be obtained by measuring the set temperature value and the direction of the positional shift in advance.

In the above-described correction method, the control value X = B and the control value X = B due to the minute gap between the chip temperature and the detected temperature between the temperature detection element 4 and the offset, that is, the chip temperature. In order to correct the deviation of E, the offset correction circuit 16 changes the set value of the temperature control circuit 7, that is, the bias, so that the initial state (control value X = B, amplitude value X = B to E) is restored. In this case, this method is sufficient.
However, in order to more accurately return to the initial state after the change in the chip temperature, the offset correction circuit 16 needs to adjust the bias of the temperature control circuit 7 according to the position shift amount BB 'or the position shift amount EE'. And the deviation amount of the peak position interval (BE-B'E 'difference or BE
/ B′E ′) may be configured to change the scale factor (scale factor) of the predetermined sweep signal of the sweep control circuit 15a. Sweep control circuit 15a is D / A
When constituted by a converter, by changing the scale factor, the amplitude of the sweep signal supplied to the current control circuit 8, that is, the output voltage value changes.

In the example of the isotope analyzer of FIG. 1, the intensity of the light absorption spectrum is determined by the peak value b and the peak value e in FIG. 2A.
Or the absolute value of the ratio or b- (a + c) / 2, e- (d
+ G) / 2 can be obtained as the absolute value of the ratio of the calculated values.

FIG. 3 shows the configuration of another embodiment of the present invention.

The isotope analyzing apparatus shown in FIG. 3 includes a semiconductor laser 1, a holding block 2, a collimating lens 3, a temperature detecting element 4, a temperature controlling element 5, a temperature detecting circuit 6, a temperature controlling circuit 7, and a current controlling circuit 8. , Sample cell 9, photodetector 1
0, an oscillation circuit 11, a lock-in amplifier 12, a peak detection circuit 13a, a calculation circuit 14, a sweep control circuit 15b, and an offset correction circuit 16.

In the example of FIG. 3, the operation and the basic operation of the optical system are the same as those of FIG. 3, except that the sweep of the light wavelength is performed by changing the temperature of the semiconductor laser 1 via the temperature control circuit 7 by the sweep control circuit 15b. Same as one example.

In the example shown in FIG. 3, the arithmetic circuit 14
The position shift amount of the peak value of the light absorption spectrum detected by the peak detection circuit 13a and the peak interval information are output to the offset correction circuit 16. Offset correction circuit 16
The temperature control circuit 7 based on the amount of displacement of the peak value.
Is changed, and if necessary, the scale factor of the sweep control circuit 15b is changed based on the peak interval information.

The sweep control circuit 15b combines the output signal from the offset correction circuit 16 with the transmission signal in the initial state and, for example, adds and outputs the resultant signal to correct the positional deviation of the light absorption spectrum. In the example of FIG. 3, the current control circuit 8 outputs a constant drive current that is stabilized in accordance with a set value selected so that a predetermined light wavelength is obtained in advance, and supplies the same to the semiconductor laser 1.

With such a configuration, also in the isotope analyzing apparatus shown in FIG. 3, it is possible to observe the light absorption spectra of two predetermined isotopes at a constant light wavelength FM modulation efficiency. The isotope ratio can be stably measured.

The present invention is not limited to the above-described embodiment, but can adopt various configurations without departing from the gist of the present invention.

[0082]

As described above, according to the present invention, the peak positions of the two light absorption spectra of the isotope to be measured are determined from the peak value output of each 2f component and the sweep signal obtained by the lock-in amplifier. The shift amount and the peak position interval information are obtained and output by the arithmetic circuit, and the set value of the temperature control circuit is corrected through the offset correction circuit in accordance with the output of the arithmetic circuit, thereby obtaining the light absorption spectrum of two predetermined isotopes. Can be observed at a constant light wavelength FM modulation efficiency.

As a result, the abundances of the two isotopes can be stably detected, and as a result, the isotope ratio can be measured with high accuracy.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration of an embodiment of the present invention.

2A and 2B are waveform diagrams for explaining the phenomenon of FM modulation efficiency fluctuation of light wavelength, where FIG. 2A is a 2f (second derivative) waveform diagram of an optical absorption spectrum in an initial state, and FIG. FIG. 3 is a 2f (second derivative) waveform diagram of the light absorption spectrum of FIG.

FIG. 3 is a block diagram showing a configuration of another embodiment of the present invention.

FIG. 4 is a block diagram showing a configuration of a conventional technique.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Semiconductor laser 2 ... Holding block 3 ... Collimating lens 4 ... Temperature detection element 5 ... Temperature control element 6 ... Temperature detection circuit 7 ... Temperature control circuit 8 ... Current control circuit 9 ... Sample cell 10 ... Light detection element 11 ... Oscillation circuit 12: lock-in amplifier 13a, 13b: peak detection circuit 14: arithmetic circuit 15a, 15b: sweep control circuit 16: offset correction circuit

Claims (3)

[Claims] 1. An isotope analyzer for detecting an isotope ratio from an optical absorption spectrum of an isotope to be measured, a semiconductor laser for outputting a laser beam, a temperature detection circuit for detecting a temperature of the semiconductor laser, A temperature control circuit for controlling the temperature of the semiconductor laser so that the temperature becomes a set value, a current control circuit for controlling a drive current of the semiconductor laser, and sweeping an optical wavelength of the semiconductor laser based on a sweep signal. A sweep control circuit; an oscillation circuit that modulates the semiconductor laser at a frequency f; a photodetector that detects a light absorption spectrum from the laser light transmitted through the sample gas of the isotope to be measured; and a detected measurement. A lock-in amplifier for detecting each 2f component of the two light absorption spectra of the target isotope; and a 2f component for each 2f component obtained by the lock-in amplifier. A peak detection circuit for detecting a peak value; and a calculation for obtaining and outputting information on a peak position shift amount and peak position interval information of two light absorption spectra of the isotope to be measured from the sweep signal and the output of the peak detection circuit. And an offset correction circuit that corrects the set value of the temperature control circuit according to the output of the arithmetic circuit, and holds the peak positions of the two light absorption spectra of the isotope to be measured constant. An isotope analyzing apparatus, wherein the isotope ratio is detected from the intensity ratio of each detected light absorption spectrum, and the isotope ratio is detected. 2. The apparatus according to claim 1, wherein the sweep control circuit controls the current control circuit to sweep the light wavelength of the semiconductor laser. 3. The isotope analyzer according to claim 1, wherein said sweep control circuit controls said temperature control circuit to sweep the light wavelength of said semiconductor laser.