JPH11148898A - Isotope analyzer - Google Patents

Abstract

(57) [Summary] [PROBLEMS] To stably and accurately detect the intensity of a light absorption spectrum. A selection circuit (15) is switched so that a temperature detection circuit (6) and a temperature control circuit (7) of a semiconductor laser (1) are connected, and the light wavelength of the laser light (L) is roughly adjusted.
Is switched to the lock-in amplifier 13 side for detecting the 3f component, and fine adjustment is performed to lock the optical wavelength to the zero cross point of the 3f component. In this case, the light wavelength is locked by the light absorption spectrum itself, so that an accurate light wavelength can be obtained. Therefore, the intensity of the light absorption spectrum can be detected stably and 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 sample cell 9, a light source, and a light source. Detection element 10, oscillation circuit 11, lock-in amplifier 12, control unit 14, and current control circuit 18
have.

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 calculates a difference between a temperature set value given from the control unit 14 and the measured temperature value, and according to the calculated difference, a temperature control element integrally attached to the holding block 2. 5 is controlled.

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 stabilized at a desired set temperature given from the control unit 14.

Further, the semiconductor laser 1 is driven by a current supplied from a current control circuit 18 which outputs a stabilized current according to a set value given from the control unit 14.

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 18, added to the stabilization current in the current control circuit 18, and supplied from the current control circuit 18 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 set value of the output current from the control unit 14 increases proportionally, the current control circuit 18
Increases monotonically, and the optical wavelength of the semiconductor laser 1 monotonically increases in accordance with the increase in the driving current. In this case, the light detection element 10 can detect the intensity of the predetermined light absorption spectrum by setting the variable range of the light wavelength to the 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, and the intensity of the light absorption spectrum is detected by the lock-in amplifier 12 which detects the 2f component.

By controlling the ratio of the two predetermined light absorption spectra thus detected by the controller 14, the isotope ratio can be detected by the isotope analyzer shown in FIG. it can.

[0024]

Generally, the FM modulation efficiency of the optical wavelength of the semiconductor laser 1 is determined by a combination of the chip temperature of the semiconductor laser 1 and the driving current supplied to the semiconductor laser 1. , The FM modulation efficiency changes. When the FM modulation efficiency changes, the lock-in amplifier 12 that detects the 2f component
, The intensity of the light absorption spectrum detected fluctuates, and the detection accuracy decreases.

Although it is relatively easy to supply a stable drive current from the current control circuit 18 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 given from the control unit 14.

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. Therefore, the FM modulation efficiency 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]

SUMMARY OF THE INVENTION The present invention relates to a semiconductor laser 1 for outputting a laser beam L in an isotope analyzer for detecting an isotope ratio from an optical absorption spectrum of an isotope, for example, as shown in FIG. 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; and supplying a constant drive current to the semiconductor laser. A constant current circuit 8, 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 isotope sample gas 9, A lock-in amplifier 12 for detecting the 2f component of the light absorption spectrum, a lock-in amplifier 13 for detecting the 3f component of the light absorption spectrum, and an input to the temperature control circuit. A selection circuit 15 for selecting from the output of the temperature detection circuit or the output of the lock-in amplifier for detecting the 3f component, and the coarse adjustment of the light wavelength of the laser light by the output of the temperature detection circuit and the 3f component. The light wavelength is locked by using the fine adjustment of the light wavelength by the output of the lock-in amplifier to be detected, and the intensity of the light absorption spectrum is detected and detected by the lock-in amplifier output for detecting the 2f component. The isotope ratio is detected from an intensity ratio of a light absorption spectrum.

According to the present invention, the light wavelength is locked by the output of the lock-in amplifier that detects the 3f component after the rough adjustment of the light wavelength of the laser light based on the output of the temperature detection circuit. The light wavelength is locked in the spectrum itself, and the light absorption spectrum can be detected stably. As a result, the isotope ratio can be obtained with high accuracy.

In this case, for example, as shown in FIG. 3, the gain is inversely proportional to the output of the lock-in amplifier for detecting the 2f component between the photodetector and the lock-in amplifier for detecting the 3f component. Controlled variable gain amplifier 17
And a DC amplifier 16 for detecting a change in output power of the light detecting element is provided on the output side of the light detecting element, and the intensity of the light absorption spectrum is obtained by an output of a lock-in amplifier for detecting the 2f component. When detecting the output of the lock-in amplifier for detecting the 2f component as a value normalized by the output of the DC power,
Taking the ratio can increase the accuracy of isotope ratio detection. Further, by the action of the variable gain amplifier, it is possible to prevent a change in the level of the 3f component used for the optical wavelength stability control, and to enhance the stability of the optical wavelength.

[0033]

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 the configuration of an isotope analyzing apparatus according to one embodiment of the present invention.

The example of the isotope analyzer shown in 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 constant current circuit 8, It has a sample cell 9, a light detection element 10, an oscillation circuit 11, lock-in amplifiers 12, 13, a control unit 14, and a selection circuit 15.

In the isotope analyzer of FIG. 1, a single mode DFB (distributed feedback) laser or the like can be used as the semiconductor laser 1. 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 heat conductivity, is used in order 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 detection circuit 6, a resistance value detection differential amplifier circuit is used.

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

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

A single-pass or multi-pass cell made of glass or metal is used as the sample cell 9.

As the light detecting element 10, the semiconductor laser 1 is used.
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 InGaAs, which can detect an infrared wavelength band of about 2.0 μm, is suitable.

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

As the lock-in amplifiers 12 and 13, a chopping amplifier, an LPF and a mixer circuit are used.

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

As the selection circuit 15, an analog switch, a photo MOS relay or the like is used.

First, the operation of the optical system in 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. The detected intensity signal is a lock-in amplifier 1 that detects the 2f component of the light absorption spectrum.
2 and 3f component of the light absorption spectrum are input to the lock-in amplifier 13 and used for detection and control described later.

Next, the operation of stabilizing the light wavelength of the semiconductor laser 1 will be described. In the isotope analyzer of FIG. 1, stabilization of the light wavelength is achieved in two stages.

First, the first stage (coarse adjustment) of light wavelength stabilization 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 inputted to the selecting circuit 15 as a measured temperature value.

In the first stage of the optical wavelength stabilization, the control unit 14 switches the selection circuit 15 so that the measured temperature value output from the temperature detection circuit 6 becomes the input to the temperature control circuit 7 (at the position shown in the drawing). ), The temperature control circuit 7 sets the chip temperature set value of the semiconductor laser 1 at which a light wavelength at which a predetermined light absorption spectrum exists (a known light wavelength λ0) is obtained.
Give to.

The temperature control circuit 7 calculates the difference between the temperature set value supplied from the control unit 14 and the measured temperature value supplied through the temperature detection circuit 6, and integrates with the holding block 2 according to the calculated difference. It controls the temperature control element 5 which is mounted in a fixed manner.

The temperature control element 5 heats or absorbs heat under the control of the temperature control circuit 7 to change 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 stabilized at a desired set temperature given from the control unit 14.

At this time, the semiconductor laser 1 is
Is driven by a constant drive current supplied from the constant current circuit 8 that outputs a stabilized drive current according to the set value set in the constant current circuit 8.

By stabilizing the chip temperature of the semiconductor laser 1 and the driving current supplied to the semiconductor laser 1 in this manner, the first stage of the light wavelength is stabilized.

While stabilizing the optical wavelength in the first stage, 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 constant current circuit 8. , And generates reference signals of frequencies 2f and 3f to be supplied to the lock-in amplifiers 12 and 13 for detecting the frequency 2f component and the frequency 3f component, respectively, and supplies the reference signals to the lock-in amplifiers 12 and 13, respectively.

The constant current circuit 8 adds 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. It is known that when the light wavelength is subjected to FM modulation at a frequency f and the lock-in amplifier 13 detects the frequency 3f component at the light wavelength where the light absorption spectrum exists, a third-order differential waveform of the light absorption spectrum is obtained. .

Next, with reference to FIG.
The stage (fine adjustment) will be described. 2A is a waveform of an optical absorption spectrum, FIG. 2B is a 1f waveform, FIG. 2C is a 2f waveform,
FIG. 2d shows the 3f waveform. The 1f waveform is the first derivative waveform of the light absorption spectrum waveform shown in FIG. 2a, the 2f waveform is the second derivative waveform of the light absorption spectrum waveform shown in FIG. 2a, and the 3f waveform is the light absorption spectrum waveform shown in FIG. 2a. 3
These are respectively equivalent to the second derivative waveform.

The light spectrum absorption lines appearing as the light absorption spectrum waveforms shown in FIGS. 2A to 2D are extremely steep waveforms, and the chip temperature and the temperature detecting element of the semiconductor laser 1 as described in the section of the prior art. The light wavelength of the semiconductor laser 1 is shifted due to a delicate difference from the detected temperature of No. 4, that is, a slight offset of the chip temperature.
For this reason, it is difficult to obtain a strictly known light wavelength λ0 by control using only the detected temperature.

Therefore, in the second stage of light wavelength stabilization, the control unit 14 switches the selection circuit 15 so that the output of the lock-in amplifier 13 for detecting the 3f component is input to the temperature control circuit 7. In this state, the temperature control circuit 7 controls the temperature control element 5 so that the output of the lock-in amplifier 13 for detecting the 3f component can obtain a light wavelength at which the zero cross point Z2 shown in FIG. Control chip temperature.

Locking the light wavelength to the zero cross point Z2 of the 3f component is nothing less than locking the light wavelength to the light absorption spectrum itself. At this time, the chip temperature of the semiconductor laser 1 is always kept constant under the condition that the drive current stabilized for the semiconductor laser 1 is supplied from the constant current circuit 8, so that the second stage The light wavelength is stabilized.

In order to lock the light wavelength to the zero cross point Z2 in the second stage of stabilizing the light wavelength, the so-called fine adjustment stage, the light wavelength must be locked in the first stage of the stabilization of the light wavelength, the so-called coarse adjustment stage. To zero-cross points Z1 and Z3
It is a precondition that control is performed within the range (see FIG. 2d).

To satisfy this precondition, heat conduction between the semiconductor laser 1, the holding block 2, the temperature detecting element 4 and the temperature controlling element 5 is improved, and the temperature detecting circuit 6 and the temperature controlling circuit 7 detect the heat. It is necessary to keep the control error small in advance. However, in the first stage of light wavelength stabilization, near the light wavelength where the light absorption spectrum exists,
The semiconductor laser 1 is sent from the control unit 14 to the temperature control circuit 7.
2D is controlled so that the chip temperature continuously increases proportionally, and the light wavelength is previously set to zero cross points Z1 to Z in FIG.
By providing a function to confirm that it is within the range of 3,
The required specifications required can be reduced.

As a control signal input to the temperature control circuit 7 for stabilizing the light wavelength, the first-order differential waveform shown in FIG. 2B can be used. Since the power change remains as an offset, it is not suitable for obtaining high control accuracy.

In the isotope analyzer of FIG. 1, the optical system around the semiconductor laser 1 may be housed in a vacuum or low-pressure container for stabilizing the temperature for stabilizing the light wavelength. Good.

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

It is known that when the light wavelength is subjected to FM modulation of the frequency f and the 2f component is detected by the lock-in amplifier 12 at the light wavelength where the light absorption spectrum exists, a second-order differential waveform as shown in FIG. 2C is obtained. Have been. This 2
The next derivative waveform is effective for improving detection accuracy, such as showing a peak at the center point of the light absorption spectrum and removing an offset error caused by dark current of the photodetector 10.

When the intensity of the light absorption spectrum is detected by the 2f component, if the FM modulation efficiency of the light wavelength fluctuates, the detection result fluctuates. However, in the isotope analyzing apparatus to which the present invention is applied, the chip temperature and the average driving current of the semiconductor laser 1 are always kept constant when observing a predetermined light absorption spectrum. The FM modulation efficiency of the wavelength becomes constant, and the intensity of the light absorption spectrum can be detected stably. Thus, the intensity of the light absorption spectrum, that is, the intensity P2 shown in FIG. 2C is obtained.

In order to detect the isotope ratio, it is necessary to detect the intensities of two predetermined light absorption spectra.
4 is a chip temperature value of the semiconductor laser 1 set in the temperature control circuit 7 or a semiconductor laser 1 set in the constant current circuit 8.
Is changed, the stabilization operation of the first and second light wavelengths is performed at two light wavelengths, thereby detecting the intensity P2 of the light absorption spectrum of each isotope. Intensity P2 of two detected predetermined light absorption spectra
By obtaining the ratio in the control unit 14, the isotope ratio can be detected with high accuracy.

In the above-described embodiment, a case has been described in which the intensity of the light absorption spectrum is obtained as the intensity P2 in the 2f component shown in FIG. 2c. However, the tertiary differential waveform shown in FIG. There are also zero cross points Z1, Z3 corresponding to the bottom peak points P1, P2 of the next differential waveform. Therefore, the applicant of this application is disclosed in Japanese Patent Application No. Hei.
As proposed in the specification and drawings of No. 93, by using polarity selection using an inverting amplifier together, in FIG.
The light wavelength can also be locked at the bottom peak points P1 and P3. In this case, it is possible to detect the intensity of the light absorption spectrum as peak-to-peak. Such a detection method is effective for high-precision detection in which the drift of the detection level of the lock-in amplifier 12 that detects the 2f component cannot be ignored.

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 constant current circuit 8. , Sample cell 9, photodetector 10,
Oscillation circuit 11, lock-in amplifiers 12, 13, control unit 1
4, a selection circuit 15, a DC amplifier 16, and a variable gain amplifier 17. An operational amplifier is used as the DC amplifier 16 and the variable gain amplifier 17.

In the example shown in FIG. 3, the operation and basic operation of the optical system are the same as those in the example shown in FIG. Therefore, the operation added to the example of FIG. 1 will be described for the example of FIG.

In the example of FIG. 3, 2f is connected between the photodetector 10 and the lock-in amplifier 13 for detecting the 3f component.
A variable gain amplifier 17 whose gain is controlled in inverse proportion to the detection level of the lock-in amplifier 12 for detecting a component is inserted. Accordingly, even under the condition that the light absorption spectrum intensity of the gas for which the isotope ratio is detected is different, the level of the 3f component used for the light wavelength stabilization control can be prevented from changing, and the accuracy of the light wavelength stabilization can be improved. .

Further, in the example of FIG.
Is input to the control unit 14 via the DC amplifier 16. Thereby, when detecting the intensity of two predetermined light absorption spectra, the semiconductor laser 1
, The output power of the semiconductor laser 1 that changes as the set values of the chip temperature and the drive current change. In the control unit 14, the lock-in amplifier 1
2, the detection level of the 2f component, that is, the intensity P2, is divided by the output power S2 detected by the DC amplifier 16 and normalized, and then the ratio is taken, whereby the detection accuracy of the isotope ratio can be further improved. .

Instead of the means for stabilizing the level change of the 3f component used for the optical wavelength stabilization control by the variable gain amplifier 17, it is proposed in the specification and the drawings of the above-mentioned Japanese Patent Application No. Hei 8-110993. In addition, a photodetector that receives transmitted laser light from a sample cell filled with a reference gas is provided in parallel with a photodetector that receives transmitted laser light from a sample cell as a measurement target, and divided into two by a beam splitter. By configuring one of the laser beams L to be incident on the sample cell in which the reference gas is sealed, the level of the 3f component for controlling the light wavelength stabilization can be stably obtained by the output of the attached photodetector. It is also possible to

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, since the light wavelength is locked by the output of the lock-in amplifier for detecting the 3f component, the light wavelength is locked by the light absorption spectrum itself. The effect is achieved.

Since the light wavelength is locked based on the 3f component of the light absorption spectrum, an accurate light wavelength can be obtained, and the light absorption spectrum can be detected stably. As a result, the isotope ratio can be increased. The effect that accuracy can be obtained is achieved.

In addition, since there is basically no need to sweep the light wavelength, it is possible to obtain an effect that the measurement can be performed in a short time, that is, the measurement can be speeded up.

Further, the output current of the constant current circuit, which can easily stabilize the current output, is used as the drive current of the semiconductor laser.
Since the wavelength is locked to the light absorption spectrum itself, the chip temperature of the semiconductor laser can be fixed (locked) to the initial state, and as a result, the effect of stabilizing the FM modulation efficiency is achieved.

[Brief description of the drawings]

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

FIGS. 2A and 2B are waveform diagrams provided for explaining a fine adjustment operation of an optical wavelength. FIG. 2A is a waveform diagram of an optical absorption spectrum, and FIG. 2B is a 1f (first-order differential) waveform of the optical absorption spectrum. Figure,
FIG. 2C is a 2f (second derivative) waveform diagram of the light absorption spectrum, and FIG. 2D is a 3f (third derivative) waveform diagram of the light absorption spectrum.

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 ... Constant current circuit 9 ... Sample cell 10 ... Light detection element 11 ... Oscillation circuit 12, 13 ... lock-in amplifier 14 ... control unit 15 ... selection circuit 16 ... DC amplifier 17 ... variable gain amplifier 18 ... current control circuit

Claims (2)

[Claims] 1. An isotope analyzer for detecting an isotope ratio from an optical absorption spectrum of an isotope, a semiconductor laser for outputting a laser beam, a temperature detection circuit for detecting a temperature of the semiconductor laser, and a detected temperature. A temperature control circuit that controls the temperature of the semiconductor laser so that a set value is obtained, a constant current circuit that supplies a constant drive current to the semiconductor laser, an oscillation circuit that modulates a frequency of the semiconductor laser, A photodetector that detects a light absorption spectrum from the laser light transmitted through the isotope sample gas; a lock-in amplifier that detects a 2f component of the light absorption spectrum; and a lock that detects a 3f component of the light absorption spectrum. An input of the temperature control circuit, an output of the temperature detection circuit or an output of a lock-in amplifier for detecting the 3f component. A coarse adjustment of the light wavelength of the laser light by an output of the temperature detection circuit and a fine adjustment of the light wavelength by an output of a lock-in amplifier for detecting the 3f component. Locking a light wavelength, detecting an intensity of the light absorption spectrum by an output of a lock-in amplifier detecting the 2f component, and detecting the isotope ratio from an intensity ratio of the detected light absorption spectrum. Isotope analyzer. 2. The device according to claim 1, wherein a gain is controlled in inverse proportion to an output of the lock-in amplifier detecting the 2f component between the photodetector and the lock-in amplifier detecting the 3f component. A variable gain amplifier, a DC amplifier for detecting a change in output power of the photodetector is provided on the output side of the photodetector, and the light absorption is performed by an output of a lock-in amplifier for detecting the 2f component. When detecting the intensity of the spectrum, the 2f
An isotope analyzing apparatus, wherein an output of a lock-in amplifier for detecting a component is detected as a value normalized by an output of the DC amplifier.