Laser gas analyzer

Abstract

To provide a laser type gas analyzer with which it is possible to reduce measurement errors due to influences of optical interference noise.SOLUTION: The present invention comprises a light emitting unit (10) that has a laser element (12) that emits laser light, and a modulation light generation unit (11) that supplies a drive current to the laser element so as to be swept and modulated in a wavelength band that includes the light absorption wavelength of absorption line spectrum of the gas to be measured; and a light receiving unit (20) that has a light receiving element (22) that receives laser light, and a received light signal processing unit (21) that analyzes the gas to be measured, with respect to the detection signal, on the basis of the amplitude of a lock-in detection waveform obtained by detecting a lock-in at a multiply-by-n frequency of the modulating frequency. The invention is further characterized by acquiring the optical interference waveform profile of optical interference noise, separating the optical interference noise based on the lock-in detection waveform and the optical interference waveform profile, and analyzing the gas to be measured.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a laser gas analyzer for analyzing the presence or absence and concentration of a measurement target gas existing in a space.

Background Art

[0002] Gas molecules in a gaseous state have an absorption line spectrum representing their respective unique light absorption wavelengths and absorption intensities. Also, laser light is light with a narrow spectral line width at a specific wavelength. A laser gas analyzer causes a laser element to emit laser light having a light absorption wavelength absorbed by a measurement target gas that is a gaseous gas molecule, causes the measurement target gas to absorb the laser light, and detects the presence or absence of the measurement target gas based on the amount of absorption of the laser light at the light absorption wavelength. In addition, since the amount of absorption of the laser light at the light absorption wavelength is proportional to the concentration of the measurement target gas, the laser gas analyzer can also detect the concentration.

[0003] A conventional technique of a laser gas analyzer for performing such gas analysis is disclosed in, for example, Patent Document 1. The laser gas analyzer of Patent Document 1 performs detection by wavelength modulation spectroscopy. A wavelength tunable laser element emits laser light whose wavelength is swept by a drive current and modulated at a specific frequency, the laser light is detected by a light receiving element, a lock-in amplifier performs lock-in detection of the signal at a frequency double of the modulation frequency, and the gas concentration is calculated from the amplitude of this lock-in detection waveform.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] Incidentally, in laser gas analyzers, optical interference noise can be superimposed on the received signal when light from overlapping laser beams with different path lengths is received, such as reflected light from the end faces of optical elements such as optical elements and lenses placed along the laser beam path.

[0006] Optical interference noise appears superimposed on the lock-in detection waveform of the gas being measured, resulting in errors in gas concentration measurement. Generally, measures are taken to reduce reflected light due to end-face reflection, such as angling the windows and lenses of the optical elements that make up the device, or applying anti-reflective coatings.

[0007] However, when the absorption intensity of the absorption line spectrum of the gas being measured is small, or when measuring low-concentration gases, the absorption amplitude of the lock-in detection waveform becomes small, which leads to a relatively large effect of optical interference noise and a significant error in gas concentration measurement.

[0008] Furthermore, due to the nonlinearity between laser wavelength and current, and between light intensity and current, the resulting waveform is not a constant sine wave. Instead, it exhibits changes such as increasing or decreasing amplitude and phase reversal, making it difficult to remove optical interference noise using simple frequency filters or sine wave fitting.

[0009] Therefore, the present invention was made to solve the above problems and aims to provide a laser gas analyzer that can reduce measurement errors due to the influence of optical interference noise. [Means for solving the problem]

[0010] The present invention relates to a laser gas analyzer for performing gas analysis of a target gas present in a space to be measured, comprising: a light-emitting unit having a laser element that emits laser light in a wavelength band including the optical absorption wavelength of the absorption line spectrum of the target gas; a modulated light generation unit that supplies a drive current to the laser element so that the wavelength is swept and modulated in a wavelength band including the optical absorption wavelength of the absorption line spectrum of the target gas; a light-receiving unit having a light-receiving element that receives the laser light that has passed through the space to be measured; and a light-receiving signal processing unit that performs analysis of the target gas based on the amplitude of a lock-in detection waveform obtained by lock-in detection at the modulation frequency or a multiple of the frequency of the detection signal output from the light-receiving element, and an optical interference waveform profile of optical interference noise is acquired, and the optical interference noise is separated based on the lock-in detection waveform and the optical interference waveform profile to perform analysis of the target gas.

[0011] One aspect of the present invention is characterized by performing optical interference measurement with a modulation amplitude smaller than the modulation amplitude used when measuring the concentration of the target gas, obtaining a lock-in detection waveform of the optical interference, obtaining interference length and phase information from the lock-in detection waveform of the optical interference, and obtaining the optical interference waveform profile based on the interference length and the phase information. [Effects of the Invention]

[0012] According to the present invention, measurement errors due to optical interference noise can be reduced. This makes it possible to provide a laser-type gas analyzer that can measure the gas concentration of a target gas with high accuracy and stability. [Brief explanation of the drawing]

[0013] [Figure 1] This is an overall configuration diagram of the laser gas analyzer according to this embodiment. [Figure 2] This is a waveform diagram of a lock-in detection signal with superimposed optical interference noise. [Figure 3] This is a flowchart diagram using a laser gas analyzer according to this embodiment. [Figure 4]It is a waveform diagram of the laser sweep drive current during optical interference measurement and gas concentration measurement in the laser gas analyzer according to this embodiment. [Figure 5] It is a waveform diagram obtained and processed by the flowchart of FIG. 4. [Figure 6] It is a graph showing the relationship between the NH3 concentration and the concentration calculation error in this embodiment and the conventional example. [Figure 7] It is a conceptual diagram showing the signal processing circuit of the laser gas analyzer according to this embodiment. [Figure 8] It is an example of a waveform diagram of waveform analysis and filtering executed by the laser gas analyzer according to this embodiment.

Mode for Carrying Out the Invention

[0014] Hereinafter, the laser gas analyzer according to the embodiment of the present invention will be described in detail with reference to the accompanying drawings. Note that the present invention is not limited to the following embodiments, and can be appropriately modified and implemented without changing the gist thereof.

[0015] <Overall Configuration Diagram of Laser Gas Analyzer> FIG. 1 is an overall configuration diagram of a laser gas analyzer according to an embodiment of the present invention. As shown in FIG. 1, the laser gas analyzer 1 includes a light emitting unit 10 and a light receiving unit 20.

[0016] The laser gas analyzer 1 analyzes the measurement target gas existing in the measurement target space. In the laser gas analyzer 1, the laser light 30 emitted from the light emitting unit 10 is irradiated onto the measurement target gas flowing through the inside (measurement target space) of the walls 50a and 50b constituting the gas tube. The laser light 30 transmitted through the measurement target gas enters the light receiving unit 20, and a specific gas concentration can be obtained from the detected light amount. Also, if the gas concentration is 0 or less than a predetermined value, it can be detected that there is no gas, and thus the presence or absence of gas can also be detected.

[0017] The light emitting unit 10 and the light receiving unit 20 are detachably attached to the walls 50a and 50b that constitute the gas pipe. The walls 50a and 50b are the walls of a pipe or the like where a specific gas exists, and holes are formed in each of them. The flanges 51a and 51b are fixed to those holes by welding or the like. The optical axis adjustment flanges 52a and 52b provided on the light emitting unit 10 and the light receiving unit 20 are mechanically detachably attached to these flanges 51a and 51b. The light emitting unit 10 and the light receiving unit 20 are arranged at opposite positions with the walls 50a and 50b interposed therebetween, and the position can be adjusted by the optical axis adjustment flanges 52a and 52b.

[0018] The optical axis adjustment flange 52a can adjust the emission angle of the laser beam 30, and the optical axis adjustment flange 52b can adjust the incident angle of the laser beam 30. With the optical axis adjustment flanges 52a and 52b, the laser beam 30 emitted from the light emitting unit 10 is received by the light receiving unit 20 with the maximum light amount.

[0019] [Light emitting unit 10] The light emitting unit 10 will be described. As shown in FIG. 1, the light emitting unit 10 includes a modulation light generation unit 11, a laser element 12, a collimating lens 13, a light emitting unit window plate 14, a light emitting unit container 15, and an optical axis adjustment flange 52a. As shown in FIG. 1, the modulation light generation unit 11, the laser element 12, and the collimating lens 13 are arranged inside the light emitting unit container 15. The light emitting unit container 15 isolates the built-in components from the outside air and protects them from wind, rain, dust, dirt, and the like.

[0020] The modulation light generation unit 11 generates a drive current that is generated such that the wavelength is repeatedly swept and modulated in a wavelength band including the light absorption wavelength of the absorption line spectrum of the measurement target gas. Then, the modulation light generation unit 11 supplies a drive current for emitting the modulated laser light to the laser element 12. Thereby, for gas concentration analysis, modulated light with wavelength modulation can be irradiated according to the light absorption characteristics of the measurement target gas.

[0021] The laser element 12 emits light at the central wavelength λ1 of a specific absorption line spectrum absorbed by the gas being measured, and at wavelengths around that wavelength. The emission wavelength of the laser element 12 is variably controlled by drive current and temperature control.

[0022] The laser element 12 is temperature-controlled so that its emission center wavelength is the center wavelength λ1 of the absorption line spectrum of the gas being measured. Furthermore, the laser light 30 emitted from the laser element 12 is controlled by a drive current supplied from the modulation light generation unit 11 to sweep wavelengths around the center wavelength of the absorption line spectrum of the gas being measured over time. In addition, it is modulated by superimposing an appropriate sine wave to enable highly sensitive measurement by wavelength modulation spectroscopy (WMS). Wavelength modulation spectroscopy is also called the 2f detection method.

[0023] The laser element 12 used is not particularly limited, but may be, for example, a DFB laser diode (Distributed Feedback Laser Diode), a VCSEL (Vertical Cavity Surface Emitting Laser), or a DBR laser diode (Distributed Bragg Reflector Laser Diode).

[0024] The collimating lens 13 is made of a material that has high transmittance at the central wavelength λ1 of the absorption line spectrum of the gas being measured, and at wavelengths around it. The collimating lens 13 converts the laser light 30 into nearly parallel light, allowing it to be transmitted to the light receiving unit 20 while suppressing loss due to diffusion.

[0025] The light-emitting point of the laser element 12 is positioned near the focal point of the collimating lens 13. The light emitted from the laser element 12 diffuses as it enters the collimating lens 13 and is converted into laser light 30, which is approximately parallel light. In this embodiment, the collimating lens 13 is used as the parallel light conversion unit, but this is not intended to limit the invention to a collimating lens. For example, a parabolic mirror can be used instead of the collimating lens 13 as the parallel light conversion unit.

[0026] The laser beam 30, which is nearly parallel, passes through the light-emitting window plate 14 and propagates into the interior of the walls 50a and 50b, that is, into the space where the gas containing the gas to be measured exists. The light-emitting window plate 14 is provided so as to create a hole in a part of the light-emitting container 15 and seal it. The light-emitting window plate 14 is in the optical path of the laser beam 30 and allows the laser beam 30 to pass through while preventing the gas containing the specific gas to be measured from entering the interior of the light-emitting unit 10. As a result, each component placed inside the light-emitting container 15 does not come into direct contact with the gas, and each component inside the light-emitting container 15 is protected.

[0027] [Light receiving section 20] The light-receiving unit 20 will now be described. The light-receiving unit 20 is composed of a light-receiving signal processing unit 21, a light-receiving element 22, a light-collecting lens 23, a light-receiving unit window plate 24, and a light-receiving unit container 25. The light-receiving unit container 25 houses the light-receiving element 22, optical components, and electrical and electronic circuits, and isolates them from the outside air to protect them from wind, rain, dust, and dirt.

[0028] The light-receiving unit 20 receives laser light 30 that has passed through the light-receiving unit window plate 24 and analyzes the light absorbed by the gas to be measured according to its absorption characteristics. The light-receiving unit window plate 24 is provided by making a hole in a part of the light-receiving unit container 25 and sealing it. The light-receiving unit window plate 24 is located in the optical path of the laser light 30, allowing the laser light 30 to pass through while preventing gas containing the specific gas to be measured from entering the interior of the light-receiving unit 20. As a result, the components placed inside the light-receiving unit 20 do not come into direct contact with the gas, thus protecting the interior. The laser light 30 is focused by the focusing lens 23 and incident on the light-receiving element 22. In this embodiment, a focusing lens 23 is used, but a parabolic mirror, a doublet lens, or a diffractive lens can be used instead of the focusing lens 23.

[0029] The photodetector 22 receives the laser light 30 that has passed through the gas to be measured. A photodetector with sensitivity at the central wavelength λ of the absorption line spectrum of the gas to be measured, and at the surrounding wavelengths, can be selected. The received signal from the photodetector 22 is sent as an electrical signal to the photodetector signal processing unit 21.

[0030] The focusing lens 23 is made of a material with high transmittance at the central wavelength λ1 of the absorption line spectrum of the gas being measured, and at wavelengths around it. Because the laser light 30 is focused onto the photodetector 22 by the focusing lens 23, a high signal intensity can be obtained. The light-receiving signal processing unit 21 processes the electrical signal received by the light-receiving element 22 to calculate the gas concentration.

[0031] <Background leading to this embodiment> In the laser gas analyzer 1, the wavelength is linearly swept within the wavelength band containing the optical absorption wavelength of the absorption line spectrum of the gas to be measured. Lock-in detection is performed at the modulation frequency or a frequency multiple of that frequency (generally the second harmonic), and the gas concentration is calculated by determining how many times larger the amplitude of the detected lock-in detection waveform is than that of the spanned gas waveform.

[0032] Figure 2 is a waveform diagram of the lock-in detection signal. As shown in Figure 2, the lock-in detection signal may be wavy. This is because, in the laser gas analyzer 1, laser light with different optical path lengths is received due to end-face reflection of the optical elements, etc., causing waves with different optical path lengths to overlap, reinforce or cancel each other out, resulting in superimposed optical interference noise. Note that the optical interference noise is superimposed on the entire lock-in detection signal shown in Figure 2. Also, in Figure 2, the horizontal axis represents time, and the vertical axis represents the signal level of the lock-in detection waveform.

[0033] The lock-in detection waveform shown in Figure 2 has a shape that is approximated by the second derivative of the absorption line spectrum. As shown in Figure 2, a wave-like waveform characteristic of optical interference is superimposed on the signal indicating the absorption of the gas being measured. This causes errors during gas concentration measurement, and in particular, when the absorption intensity of the absorption line of the gas being measured is small, or when measuring low-concentration gases, the absorption amplitude of the lock-in detection waveform becomes small, and the effect of optical interference noise becomes relatively larger, making the error more pronounced.

[0034] Therefore, after diligent research, the inventors have succeeded in providing a laser-type gas analyzer that can separate optical interference noise from the lock-in detection signal and reduce measurement errors caused by the influence of optical interference noise.

[0035] <Regarding the separation of optical interference noise> Figure 3 is a flowchart illustrating the laser gas analyzer according to this embodiment. Figure 4 is a waveform diagram of the drive current during optical interferometry measurement and gas concentration measurement in the laser gas analyzer according to this embodiment. Figure 5 is a waveform diagram acquired and processed in the flowchart of Figure 4.

[0036] In the optical interference measurement step S01 shown in Figure 3, the modulation amplitude of the laser sweep drive current supplied to the laser element 12 is set to a small value to minimize the absorption of the target gas, and the received waveform is acquired by adjusting it so that only optical interference appears in the signal waveform. Here, "small modulation amplitude" means smaller than the modulation amplitude of the laser sweep drive current supplied during gas concentration measurement, and is not limited to that, but is adjusted to a modulation amplitude of 1 / 10 to 1 / 50 of that of normal gas concentration measurement. The laser sweep drive current adjusted to a small modulation amplitude is shown in Figure 4(a). In this way, by making the laser sweep drive current smaller than the modulation amplitude during gas concentration measurement, the absorption of the target gas can be made so small that it can be ignored, and the lock-in detection waveform acquired with a small modulation amplitude can be adjusted so that only optical interference appears. As a result, in the optical interference measurement step S01, for example, the lock-in detection waveform of optical interference shown in Figure 5(a) can be acquired. As shown in Figure 5(a), if the baseline of the lock-in detection waveform of optical interference is sloped, it is preferable to correct the slope of the baseline by polynomial fitting.

[0037] Specifically, points where the lock-in detection waveform intersects zero are extracted, and the average time between each point is obtained as the optical interference period. Then, from the obtained period (ΔT), considering the laser sweep drive current profile shown in Figure 4(a) and the characteristics of the laser element 12 (wavelength λ∝current I), Δλ (repeated interference pitch (nm)) is calculated by converting to wavelength, and the slope of the baseline is corrected as shown in Figure 5(b).

[0038] Next, the absorption wavelength (center wavelength) of the gas being measured is set to λ1, and the interference length L (optical path difference of the interfering light) of the optical interference is calculated from (Equation 1) below. L=λ1 2 / Δλ (Equation 1) Furthermore, the phase Θ of the optical interference waveform is obtained from the displacement at a reference time (for example, the laser emission start time).

[0039] Next, in the optical interference profile acquisition step S02 shown in Figure 3, based on the acquired interference length L and phase information, the optical interference profile of the received waveform shown in Figure 5(c) is acquired by taking into account the laser sweep drive current profile during gas concentration measurement (see Figures 4(b) and 4(c)), laser characteristics, and photodetector characteristics. In other words, in the optical interference measurement step S01 in Figure 3, the modulation amplitude of the laser sweep drive current supplied to the laser element 12 is set to a small value to acquire the lock-in detection waveform of the optical interference. Therefore, it is necessary to derive an optical interference profile based on the modulation amplitude during actual gas concentration measurement.

[0040] Here, gas concentration measurements can be performed multiple times (n times, where n is 2 or more) after optical interference measurement, as shown in Figures 4(b) and 4(c), and the timing and number of optical interference measurements can be adjusted as appropriate. For example, optical interference measurements can be performed periodically at an arbitrarily set frequency, such as once per minute if the temporal changes in interference are large, or once a day if the changes are small, depending on the measurement environment conditions, thereby enabling stable measurements.

[0041] Next, in the optical interference noise separation step S03 shown in Figure 3, the target gas absorption waveform is separated by fitting using the optical interference profile acquired in step S02.

[0042] Figure 5(d-1) shows the optical interference waveform, and Figure 5(d-2) shows the measurement waveform during gas concentration measurement. Figure 5(d-1) is the lock-in detection waveform acquired during the optical interference measurement in Figure 4(a), and Figure 5(d-2) is the lock-in detection waveform acquired during the gas concentration measurement in Figures 4(b) and 4(c). The measurement waveform shown in Figure 5(d-2) is a superposition of a span gas waveform without optical interference (with optical interference removed) and a constant multiple of the optical interference waveform. Therefore, using the optical interference profile acquired in step S02 of Figure 3, optical interference noise is separated from the absorption waveform during gas concentration measurement shown in Figure 5(d-2) by fitting (matrix calculation) to obtain the target gas absorption waveform shown in Figure 5(d-3). This makes it possible to obtain the target gas absorption waveform without superimposed optical interference noise.

[0043] Next, in the concentration calculation step S04 shown in Figure 3, the ratio of the target gas absorption waveform and the span gas waveform, after separating the optical interference noise, is determined to calculate the gas concentration. For example, as shown in Figure 5(e), the square root of the sum of the amplitudes (Ax, Ay) of the lock-in detection waveforms X and Y (the magnitude of the composite vector) contains concentration information. Therefore, the target gas concentration can be calculated from the ratio of the value obtained from the target gas absorption waveform separated during gas concentration measurement and the absorption waveform during span gas measurement.

[0044] Figure 6 shows the simulation results of the relationship between NH3 concentration and concentration calculation error, based on the absorption cross-section of the absorption line database, assuming an ammonia meter with a path length of 1 m (optical path length 1 m) and an interference length of 100 mm for optical interference noise. In the conventional example, optical interference noise was not separated, and the concentration was calculated based on the lock-in detection waveform obtained during gas concentration measurement. As shown in Figure 6, in the conventional example, the error became large near zero concentration where the absorption amplitude was small and the proportion of optical interference increased relatively. On the other hand, in the example, the steps shown in Figure 3 were performed to separate the optical interference noise. As a result, the concentration calculation error in the example was reduced to almost constant levels, and in particular, the concentration calculation error could be set sufficiently low even near zero concentration where the error was large in the conventional example.

[0045] In this embodiment, to effectively achieve optical interference separation, it is desirable that the modulated light generation unit 11 shown in Figure 1 be composed of a low-distortion digital-to-analog converter (DAC). In laser gas analyzers disclosed in Patent Document 1, concentration detection is performed by measuring the harmonic component (generally the second harmonic) of the modulation frequency, utilizing the fact that distortion occurs when modulated laser light is absorbed by the gas being measured. For this reason, low-distortion analog oscillators that oscillate at a specific frequency have often been used. On the other hand, in recent years, DAC elements have become more precise and less distorted in fields such as high-resolution audio, and some have achieved distortion rates that are significantly lower than the total harmonic distortion rate (around -80 to -90 dB) of conventional low-distortion analog oscillators (for example, model number AK4499EQ (manufactured by Asahi Kasei Corporation); total harmonic distortion rate -125 dB). By using such a low-distortion, high-precision DAC, it becomes possible to drive the laser with any waveform while possessing the low-distortion modulation performance necessary for gas concentration measurement, thus enabling implementation without increasing the scale of the circuit.

[0046] In this embodiment, measurement errors due to optical interference noise can be reduced, and accurate gas concentrations can be calculated. Furthermore, in this embodiment, even if, in addition to optical interference noise, gas interference noise other than that of the gas being measured is superimposed on the lock-in detection waveform, each noise component can be analyzed and separated by the waveform analysis and filtering processing unit shown in Figure 7.

[0047] Figure 7 shows an example of a signal processing circuit, in which, after lock-in detection, waveform analysis and filtering are performed, and then the concentration is calculated. The processing unit that performs waveform analysis and filtering may be incorporated into the processing unit that calculates the concentration, or it may be a separate, independent circuit processing unit. The processing unit that performs waveform analysis and filtering analyzes the lock-in detection waveform and, through fitting processing, separates the measurement waveform during gas concentration measurement into the target gas absorption waveform and various types of noise such as optical interference noise.

[0048] The lock-in detection waveform during gas concentration measurement shown in Figure 8(a) may be superimposed with offset base noise shown in Figure 8(b), optical interference noise shown in Figure 8(c), gas interference noise shown in Figure 8(d), etc. In this case, it is difficult to identify and separate each type of interference noise unless the measurement conditions are appropriately changed according to the type of interference noise. By appropriately changing the measurement conditions, the processing unit that performs waveform analysis and filtering in the signal processing circuit shown in Figure 7 can appropriately analyze the noise waveform and appropriately separate each type of noise such as optical interference noise and gas interference noise, thereby obtaining a target gas absorption waveform that is not superimposed with various types of noise (Figure 8(e)). In addition, by sharing data and coordinating between the light-emitting unit and the light-receiving unit via the communication line 40 shown in Figure 7, for example, by adjusting the laser sweep drive current during gas concentration measurement shown in Figures 4(b) and 4(c) so that the modulation wavelength of the gas interference noise is outside the range, it is possible to control the superposition of other gas interference noise during subsequent gas concentration measurements, thereby enabling a high-precision reduction of measurement errors. [Industrial applicability]

[0049] The laser gas analyzer of the present invention is ideal for measuring and controlling combustion exhaust gases in boilers, waste incineration, and other applications. It is also useful as an analyzer for various other applications, including gas analysis for steelmaking [blast furnaces, converters, heat treatment furnaces, sintering (pellet equipment), coke ovens], fruit and vegetable storage and aging, biochemistry (microorganisms) [fermentation], air pollution [incinerators, flue gas desulfurization / denitrification], exhaust gas from internal combustion engines of automobiles and ships (de-testing), disaster prevention [explosive gas detection, toxic gas detection, combustion gas analysis of new building materials], plant cultivation, chemical analysis [petroleum refining plants, petrochemical plants, gas generation plants], environmental applications [surface concentration, tunnel concentration, parking lot, building management], and various physical and chemical experiments. [Explanation of symbols]

[0050] 1: Laser gas analyzer 10: Light-emitting part 11: Modulated light generation unit 12: Laser element 13: Collimating lenses 14: Light-emitting window panel 15: Light-emitting part container 20: Light receiving part 21: Light receiving signal processing unit 22: Photodetector 23: Focusing lens 24: Light-receiving window plate 25: Light-receiving container 30: Laser light 40: Communication lines 50a, 50b: Wall 51a, 51b: Flange 52a, 52b: Optical axis adjustment flange

Claims

[Claim 1] A laser gas analyzer that performs gas analysis of a target gas present in a space to be measured, A laser element that emits laser light in a wavelength band that includes the optical absorption wavelength of the absorption line spectrum of the gas to be measured, A light-emitting unit having a modulated light generation unit that supplies a drive current to the laser element such that the wavelength is swept and modulated in a wavelength band that includes the optical absorption wavelength of the absorption line spectrum of the gas to be measured, A light-receiving element that receives the laser light that has passed through the space to be measured, The system includes a light receiving unit which performs analysis of the target gas based on the amplitude of a lock-in detection waveform obtained by lock-in detection at the modulation frequency or a multiple thereof with respect to the detection signal output from the light receiving element, A laser gas analyzer characterized by performing optical interference measurement with a modulation amplitude smaller than the modulation amplitude used when measuring the concentration of the target gas, obtaining a lock-in detection waveform of the optical interference, obtaining interference length and phase information from the lock-in detection waveform of the optical interference, obtaining an optical interference waveform profile of the optical interference noise based on the interference length and phase information, separating the optical interference noise based on the lock-in detection waveform and the optical interference waveform profile, and performing analysis of the target gas.

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