Gas absorption spectrometer

Abstract

The laser light frequency is stabilized even when the incidence of light into the resonator is blocked in order to obtain a ring-down signal. [Solution] The gas absorption spectrometer comprises a first light source (11), a first resonator (40), an optical modulator (20) arranged in the optical path between the first light source and the first resonator, and a frequency stabilization circuit (30) arranged so as to form a negative feedback circuit between the first light source and the optical modulator. The frequency stabilization circuit (30) includes a second light source (31) and an optical stabilization unit (300).

Description

Technical Field

[0001] The present disclosure relates to a gas absorption spectrometer for determining the concentration of a target component in a gas using cavity ring-down absorption spectroscopy (CRDS).

Background Art

[0002] As one of the gas absorption spectroscopy methods, cavity ring-down absorption spectroscopy (CRDS) is known. CRDS is a spectroscopic method for highly sensitively determining the concentration of a target component contained in a gas in a resonator by increasing the effective optical path length using a resonator (cavity).

[0003] In CRDS, laser light is input from a light source into the resonator. The laser light input into the resonator is accumulated in the resonator. After the laser light is sufficiently accumulated in the resonator, the input of the laser light into the resonator is blocked. Thereafter, the attenuation of the light leaking from the resonator is measured. The gas absorption spectrometer acquires the output signal of the photodetector as a "ring-down signal". The gas absorption spectrometer measures the concentration of the target component contained in the gas in the resonator by calculating the attenuation time constant (ring-down time) using the acquired ring-down signal.

[0004] Non-Patent Document 1 discloses a gas absorption spectrometer in which a feedback system operating based on the PDH (Pound-Drever-Hall) method is inserted into the optical path from the light source toward the resonator. According to the gas absorption spectrometer described in Non-Patent Document 1, narrowing of the line width of the laser light can be realized.

Prior Art Documents

Non-Patent Documents

[0005]

Non-Patent Document 1

[0006] In CRDS, it is necessary to interrupt the incidence of light into the resonator in order to acquire the ring-down signal. Therefore, in conventional gas absorption spectrometers such as those described in Non-Patent Literature 1, there is a timing when the light returning to the feedback system is interrupted. Consequently, when the incidence of light into the resonator is resumed, there is a risk that the wavelength of light optimal for the resonator and the wavelength of light incident on the resonator will be out of sync. As a result, the gas absorption spectrometer cannot perform PDH lock after acquiring the ring-down signal, and the laser light frequency cannot be stabilized, resulting in a problem.

[0007] The present invention was made to solve these problems, and its objective is to stabilize the frequency of laser light even when the incidence of light into the resonator is blocked in order to obtain a ring-down signal. [Means for solving the problem]

[0008] The gas absorption spectrometer according to this disclosure is a gas absorption spectrometer for measuring gas components, comprising: a first light source that outputs a first laser beam used for measuring gas components; a first resonator into which the first laser beam is input; an optical modulator arranged in the optical path between the first light source and the first resonator; and a frequency stabilization circuit arranged between the first light source and the optical modulator so as to form a negative feedback circuit, wherein the frequency stabilization circuit comprises: a second light source that outputs a second laser beam for stabilizing the first laser beam; and an optical stabilization unit for stabilizing the second laser beam. [Effects of the Invention]

[0009] According to this disclosure, the frequency of the laser light can be stabilized even when the incidence of light into the resonator is blocked in order to acquire a ring-down signal. [Brief explanation of the drawing]

[0010] [Figure 1] This diagram schematically shows the configuration of a gas absorption spectrometer. [Figure 2] This is a conceptual diagram to explain modal frequencies. [Figure 3] This diagram schematically shows the detailed configuration of the frequency stabilization circuit. [Figure 4] This diagram schematically shows the configuration of the frequency stabilization circuit related to the first modified example. [Figure 5] This diagram schematically shows the configuration of the frequency stabilization circuit related to the 2nd modified example. [Modes for carrying out the invention]

[0011] This embodiment will be described in detail below with reference to the drawings. In the following description, the same or corresponding parts in the drawings will be denoted by the same reference numerals, and their descriptions will not be repeated.

[0012] <Configuration of a gas absorption spectrometer> Figure 1 is a schematic diagram showing the configuration of a gas absorption spectrometer 1 according to this embodiment. The gas absorption spectrometer 1 comprises a measurement QCL (Quantum Cascade Laser) 11, an AOM (Acousto-Optic Modulator) 20, a frequency stabilization circuit 30, a CRDS resonator 40, a photodetector (PD) 60, and a controller 70.

[0013] The measurement QCL11 is an example of a first light source that outputs a first laser beam used for measuring gas components. The measurement QCL11 is configured to have a variable laser beam oscillation frequency according to commands from the controller 70. Specifically, the measurement QCL11 is a distributed feedback type quantum cascade laser (QCL).

[0014] AOM20 is located in the optical path between the measurement QCL11 and the CRDS resonator 40. AOM20 is an example of an optical modulator. AOM20 is an optical switch (switch) that rapidly switches between outputting and blocking laser light from the measurement QCL11 to the CRDS resonator 40. AOM20 switches the input (incident) of light to the CRDS resonator 40 between ON and OFF. When an ON command for outputting light is applied from the controller 70, AOM20 enters the ON state, outputting laser light from the measurement QCL11 to the CRDS resonator 40. When an OFF command for blocking light is applied from the controller 70, AOM20 enters the OFF state, not outputting laser light from the measurement QCL11 to the CRDS resonator 40. When switching the input of light between ON and OFF, AOM20 may switch the frequency in addition to switching the optical path.

[0015] The CRDS resonator 40 is located in the optical path between the AOM 20 and the photodetector 60. The CRDS resonator 40 is an example of a first resonator. The CRDS resonator 40 is composed of a container (cell) that can seal the sample gas and has an inlet tube 44 for introducing the sample gas inside before the start of measurement and an outlet tube 45 for discharging the sample gas to the outside after the end of measurement. The inlet tube 44 is provided with an inlet valve 46. The outlet tube 45 is provided with an outlet valve 47. The controller 70 controls the opening and closing of the inlet valve 46 and the outlet valve 47.

[0016] A pair of mirrors 41 and 42 are provided inside the CRDS resonator 40. The mirrors 41 and 42 are positioned opposite each other inside the CRDS resonator 40 so that light reflects between them. At least one of the mirrors 41 and 42 is concave in shape to facilitate the meeting of the stability requirements for the CRDS resonator 40. Furthermore, the mirrors 41 and 42 are made of materials with high reflectivity (for example, about 99.9%) so that the amount of light leaking out of the CRDS resonator 40 is extremely small. Note that the number of mirrors placed inside the CRDS resonator 40 is not limited to two, but may be three or more. In other words, it may be a resonator in which mirrors are arranged so that light reflects between them, or a resonator in which mirrors are arranged in a ring shape so that light reflects in one direction.

[0017] A piezoelectric element 43 is placed on mirror 42. The piezoelectric element 43 drives the mirror 42, which constitutes the CRDS resonator 40, according to a command from the controller 70, thereby displacing the mirror 42 in the direction of the optical axis. This changes the resonator length of the CRDS resonator 40. Note that the piezoelectric element may be placed on mirror 41 instead of mirror 42, or on both mirror 41 and mirror 42.

[0018] The photodetector 60 is, for example, a photodiode. The photodetector 60 detects the weak light extracted from the mirror 42 of the CRDS resonator 40 as the output light of the CRDS resonator 40, and outputs a detection signal to the controller 70. For the photodetector 60, for example, a liquid nitrogen cooled InSb (indium antimonide) detector can be employed.

[0019] A beam splitter 51 is provided in the optical path between the measurement QCL 11 and the AOM 20. The beam splitter 51 branches the laser light output from the measurement QCL 11 into an optical path toward the AOM 20 and an optical path toward the frequency stabilization circuit 30.

[0020] The controller 70 includes a processor 71 such as a CPU (Central Processing Unit) or an FPGA (Field-Programmable Gate Array), a memory 72 such as a ROM (Read Only Memory) and a RAM (Random Access Memory), and an input / output port (not shown).

[0021] The controller 70 controls each device constituting the gas absorption spectroscopic apparatus 1. Specifically, the controller 70 outputs a command for scanning the oscillation frequency of the laser light to the laser driver 12, or outputs the above-described on signal or off signal to the AOM 20. The controller 70 outputs a command for introducing the sample gas into the CRDS resonator 40 to the introduction valve 46, or outputs a command for discharging the sample gas to the outside of the CRDS resonator 40 to the discharge valve 47.

[0022] ]>The controller 70 applies a voltage for displacing the mirror 42 to the piezo element 43. The controller 70 executes various data processes. The various data processes include a process of calculating the concentration (absolute concentration) of the target component contained in the sample gas based on the detection signal from the photodetector 60.

[0023] The controller 70 may be configured by dividing it into two or more units for each function. For example, the controller 70 may be divided into a unit that controls each device and a unit that performs various data processing.

[0024] <Measurement principle using cavity ring-down spectroscopy (CRDS)> The measurement principle of cavity ring-down absorption spectroscopy in gas absorption spectrometer 1 will be explained. Generally, resonance occurs in a resonator when the frequency of the light irradiated onto the resonator is a specific frequency. Hereinafter, the frequency of the laser light input to the CRDS resonator 40 will be referred to as the "laser frequency," and the frequency of light in which resonance can occur in the CRDS resonator 40 will be referred to as the "mode frequency."

[0025] Figure 2 is a conceptual diagram illustrating mode frequencies. As shown in Figure 2, multiple mode frequencies exist at predetermined frequency intervals. Hereafter, the interval between two adjacent mode frequencies will be referred to as the "free spectral range" (FSR).

[0026] If the laser frequency does not match any of the mode frequencies, no light power is stored in the CRDS resonator 40. On the other hand, if the laser frequency matches any of the mode frequencies, light power is stored in the CRDS resonator 40.

[0027] The controller 70 determines whether sufficient laser light power has been stored in the CRDS resonator 40 based on the output signal of the photodetector 60. If the controller 70 determines that sufficient laser light power has been stored in the CRDS resonator 40, it outputs an off signal to the AOM 20. This blocks the light input to the CRDS resonator 40.

[0028] As a result, the light stored in the CRDS resonator 40 travels back and forth between mirror 41 and mirror 42 many times (usually several thousand to tens of thousands of times). As this light travels back and forth between mirrors 41 and 42, it is gradually attenuated due to losses from reflection leakage between mirrors 41 and 42 and absorption by the target component in the sample gas. Therefore, the output light from the CRDS resonator 40 leaking from mirror 42 is gradually attenuated. In a CRDS, by using the CRDS resonator 40 to increase the distance the light travels through the sample gas (effective optical path length), it is possible to detect light absorption by the target component even if the absorption is extremely small.

[0029] The controller 70 acquires the signal detected by the photodetector 60 as a "ring-down signal" while the light input to the CRDS resonator 40 is blocked. The controller 70 calculates the decay time constant of the acquired ring-down signal as the "ring-down time". From the calculated ring-down time, the controller 70 calculates the concentration of the target component contained in the sample gas.

[0030] <Configuration of the frequency stabilization circuit> Figure 3 is a schematic diagram illustrating the detailed configuration of the frequency stabilization circuit 30. As shown in Figure 3, the frequency stabilization circuit 30 comprises a reference QCL 31, a highly stable resonator 33, a PDH circuit 34, a PLL (Phase Locked Loop) circuit 35, photodetectors (PDs) 36, 37, beam splitters 52-54, and a mirror 61.

[0031] The light stabilization unit 300 is comprised of a highly stable resonator 33, a PDH circuit 34, a PLL circuit 35, photodetectors 36, 37, beam splitters 52-54, and a mirror 61.

[0032] The frequency stabilization circuit 30 stabilizes the laser light from the reference QCL 31 relative to the high-stability resonator 33. The high-stability resonator 33, the PDH circuit 34, and the photodetector 36 operate according to the PDH (Pound-Drever-Hall) method. The PDH circuit 34 stabilizes the laser light from the reference QCL 31 relative to the high-stability resonator 33 by performing PDH control.

[0033] A feedback optical path runs from the reference QCL31 through beam splitters 53 and 54 to the high-stability resonator 33, and further through the photodetector 36 and PDH circuit 34 back to the reference QCL31, thereby PDH-locking the laser beam to the high-stability resonator 33 (the laser beam is locked to the high-stability resonator 33 according to the PDH method). Inside the high-stability resonator 33, a pair of mirrors (not shown) are provided, similar to the CRDS resonator 40. However, the reflectivity of the mirrors in the high-stability resonator 33 is lower than that of the mirrors in the CRDS resonator 40. If the reflectivity of the mirrors is too high, PDH locking becomes difficult. For this reason, mirrors with reflectivity sufficient to stably perform PDH locking are used in the high-stability resonator 33. Alternatively, a narrow-linewidth gas absorption line may be used instead of the high-stability resonator 33.

[0034] The PLL circuit 35 can synchronize the phase of the laser beam of the measurement QCL 11 with the phase of the laser beam of the reference QCL 31 through a phase-locked loop.

[0035] The PLL circuit 35 performs PLL control using the beat signal generated when the laser beam output from the reference QCL 31 and the laser beam output from the measurement QCL 11 are interfered with. This controls the linewidth of the laser beam output from the measurement QCL 11 to match the linewidth of the narrowed laser beam (already narrowed) output from the reference QCL 31.

[0036] The details of the frequency stabilization circuit 30 are described below. The reference QCL 31 outputs laser light toward the high-stability resonator 33. Beam splitters 53 and 54 are arranged in the optical path between the reference QCL 31 and the high-stability resonator 33. Beam splitter 53 splits the laser light output from the reference QCL 31 into two beams, which are then incident on beam splitter 52 and beam splitter 54. The laser light traveling from beam splitter 53 toward beam splitter 54 is incident on the high-stability resonator 33.

[0037] The laser light output from the highly stable resonator 33 is returned to the beam splitter 54. The beam splitter 54 guides the laser light output from the highly stable resonator 33 to the photodetector 36. The photodetector 36 outputs a signal corresponding to the intensity of the laser light. The signal output from the photodetector 36 is input to the PDH circuit 34.

[0038] The PDH circuit 34 frequency-stabilizes the laser beam relative to the high-stability resonator 33 according to the PDH (Pound-Drever-Hall) method. The PDH circuit 34 may include, for example, a generator, a phase shifter, a mixer, a low-pass filter, a servo circuit, and a laser driver, as is common in circuits operating according to the PDH method. The PDH circuit 34 stabilizes the frequency of the laser beam by providing feedback to the reference QCL 31 based on the laser beam detected by the photodetector 36.

[0039] The laser beam from the measurement QCL 11 is input to the frequency stabilization circuit 30 via the beam splitter 51. The laser beam incident on the frequency stabilization circuit 30 from the beam splitter 51 is guided to the beam splitter 52 by the mirror 61. Therefore, the laser beam from the reference QCL 31 (frequency stabilized) and the laser beam from the measurement QCL are input to the beam splitter 52.

[0040] The beam splitter 52 outputs a combined laser beam to the photodetector 37, which is a combination of the laser beam (frequency stabilized) from the reference QCL 31 and the laser beam from the measurement QCL. The photodetector 37 detects the beat of the combined light from the laser beam from the measurement QCL 11 and the laser beam from the reference QCL 31. The photodetector 37 outputs the detection signal to the PLL circuit 35.

[0041] The PLL circuit 35 synchronizes the phase of the laser beam from the measurement QCL 11 with the phase of the laser beam from the reference QCL 31 via a phase-locked loop. The beat frequency is stabilized by the phase-locked loop. The signal for stabilizing the beat frequency is fed back from the PLL circuit 35 to the measurement QCL 11.

[0042] The PLL circuit 35 detects a beat signal by superimposing the laser beam output from the measurement QCL 11 and the laser beam output from the reference QCL 31. The PLL circuit 35 may also sweep the frequency of the beat signal. This allows the laser beam output from the measurement QCL 11 to have its linewidth narrowed, and the wavelength of the laser beam output from the measurement QCL 11 to be swept to a size appropriate for spectral measurement.

[0043] For example, if the reference beat frequency (the target frequency to be stabilized) is set to 100 MHz, then by stabilizing the laser beam output from the measurement QCL 11 to match that 100 MHz, it is possible to output laser beam from the measurement QCL with a wavelength shifted by 100 MHz from the reference QCL 31. In this way, the beat frequency can be controlled depending on the circuit design of the PLL circuit 35 that performs the PLL control.

[0044] As shown in Figure 3, the frequency stabilization circuit 30 in this embodiment forms a feedback loop between the measurement QCL 11 and the AOM 20 to stabilize the frequency of the laser light output from the measurement QCL 11. Alternatively, it is conceivable to provide some kind of frequency stabilization circuit so that feedback is formed between the measurement QCL 11 and the AOM 20, and between the AOM 20 and the CRDS resonator 40.

[0045] However, in CRDS, it is necessary to block the incidence of light into the CRDS resonator 40 in order to acquire the ring-down signal. Therefore, if a frequency stabilization circuit is installed between the measurement QCL11 and AOM20, the supply of laser light to the frequency stabilization circuit will be interrupted while the incidence of light into the CRDS resonator is blocked. In this case, when the incidence of light into the CRDS resonator is resumed, there is a risk that the wavelength of light optimal for the CRDS resonator and the wavelength of light incident on the CRDS resonator will be out of sync. As a result, the gas absorption spectrometer will have the problem of not being able to perform PDH lock after acquiring the ring-down signal.

[0046] Therefore, in this embodiment, a configuration is adopted to stabilize the laser light output from the measurement QCL11 without including the CRDS resonator 40 in the feedback optical system. That is, in this embodiment, as shown in Figure 3, a reference optical system (frequency stabilization circuit 30) including a reference QCL31 and a highly stable resonator 33 is provided separately from the optical system of the measurement QCL11, and PDH locking is performed in the reference optical system.

[0047] The frequency stabilization circuit 30, which constitutes the reference optical system, performs PDH lock on the highly stable resonator 33 to stabilize the linewidth of the laser beam output from the reference QCL 31. The frequency stabilization circuit 30 further provides a feedback signal to the measurement QCL 11 using the beat signal between the linewidth-stabilized laser beam from the reference QCL 31 and the laser beam from the measurement QCL 11.

[0048] For example, when a feedback signal is applied to the measurement QCL11 to completely stabilize the beat signal, a laser beam with the same linewidth as the reference QCL31 is output from the measurement QCL11. The frequency stabilization circuit 30 is an example of a frequency stabilization circuit arranged such that a negative feedback circuit is configured between the first light source and the optical modulator.

[0049] According to this embodiment, the laser light of the measurement QCL 11 can be stabilized without including the CRDS resonator 40 in the feedback optical system for frequency stabilization. As a result, even when the incidence of light to the CRDS resonator 40 is blocked, a signal for stabilizing the beat frequency can be continuously supplied from the frequency stabilization circuit 30 to the measurement QCL 11.

[0050] Therefore, according to this embodiment, the frequency of the laser light can be stabilized even when the incidence of light to the CRDS resonator 40 is blocked in order to acquire a ring-down signal. According to this embodiment, the oscillation frequency of the measurement QCL 11 can be narrowed without using the CRDS resonator 40. Therefore, the effect of easily modularizing the light source is also achieved. In general, since the linewidth of the laser light resonating in a CRDS resonator is extremely narrow, it is technically difficult to perform PDH lock on the CRDS resonator. In this embodiment, since it is not necessary to perform PDH lock on the CRDS resonator, the design of the gas absorption spectrometer can be simplified.

[0051] In this embodiment, the oscillation frequency of the measurement QCL11 is narrowed by the frequency stabilization circuit 30. This reduces the difficulty of PDH locking to the high-finesse CRDS resonator 40.

[0052] <Example 1> Next, Modification 1 will be explained using Figure 4. Figure 4 is a schematic diagram showing the configuration of the frequency stabilization circuit 30A related to Modification 1. In the frequency stabilization circuit 30A related to Modification 1, an optical feedback section 39 is employed instead of a circuit configuration that operates according to the PDH (Pound-Drever-Hall) method. The optical feedback section 39 includes a gain layer and a passive layer. Light incident on the optical feedback section 39 undergoes multiple resonances within the optical feedback section 39. As a result, wavelength-stabilized light is output from the optical feedback section 39.

[0053] In the modified example 1, the light stabilization unit 300A is composed of an optical feedback unit 39, a PLL circuit 35, a photodetector 37, and a mirror 61.

[0054] <Modification 2> Next, Modification 2 will be explained using Figure 5. Figure 5 is a schematic diagram showing the configuration of the frequency stabilization circuit 30B related to Modification 2. In the explanation so far, frequency stabilization circuits 30 and 30A having an AOM20 have been given as examples. However, the frequency stabilization circuit does not have to have an AOM20. Figure 5 shows a frequency stabilization circuit 30B that does not have an AOM20.

[0055] The frequency stabilization circuit 30B may also be switched to a non-resonant state by changing the current of the light source. By changing the current flowing through the light source, the oscillation frequency of the laser changes. This makes it possible to switch the CRDS resonator 40 between a resonant state and a non-resonant state. In this case, two methods are possible: one in which the locked target frequency is switched while maintaining the PLL lock, and another in which the PLL lock is released only when performing a ring-down measurement to switch the frequency, and the PLL is locked again after the ring-down measurement is completed.

[0056] Both of these methods involve switching the frequency using a frequency stabilization circuit instead of an AOM. The optical stabilization unit 300B shown in Figure 5 has a switching circuit 38 for switching the frequency input to the PLL circuit 35 between ON and OFF. Therefore, the frequency stabilization circuit 30B has the function of switching the frequency, thereby switching the optical input to the CRDS resonator 40 and performing ring-down measurement. The frequency stabilization circuit 30B shown in Figure 5 is an example of a frequency stabilization circuit arranged so that a negative feedback circuit is configured between the first light source and the first resonator.

[0057] In modified example 2, the light stabilization unit 300B is composed of a highly stable resonator 33, a PDH circuit 34, a PLL circuit 35, photodetectors 36, 37, beam splitters 52-54, a mirror 61, and a switching circuit 38.

[0058] [Pattern] Those skilled in the art will understand that the embodiments and their modifications described above are specific examples of the following embodiments.

[0059] (Section 1) The gas absorption spectrometer according to the present disclosure is a gas absorption spectrometer for measuring gas components, comprising: a first light source that outputs a first laser beam used for measuring gas components; a first resonator into which the first laser beam is input; an optical modulator arranged in the optical path between the first light source and the first resonator; and a frequency stabilization circuit arranged between the first light source and the optical modulator so as to form a negative feedback circuit, wherein the frequency stabilization circuit comprises: a second light source that outputs a second laser beam for stabilizing the first laser beam; and an optical stabilization unit for stabilizing the second laser beam.

[0060] In the gas absorption spectrometer described in paragraph 1, the frequency of the laser light can be stabilized even when the incidence of light to the resonator is blocked in order to acquire a ring-down signal.

[0061] (Section 2) In the gas absorption spectrometer described in Section 1, the photostabilization unit includes a second resonator into which the second laser beam is input, and a PDH (Pound-Drever-Hall) circuit for performing PDH lock on the second resonator.

[0062] In the gas absorption spectrometer described in paragraph 2, the second laser beam can be stabilized by performing a PDH (Pound-Drever-Hall) lock on the second resonator.

[0063] (Clause 3) In the gas absorption spectrometer described in paragraph 1 or 2, the frequency stabilization circuit further comprises a PLL (Phase Locked Loop) that synchronizes the phase of the first laser beam with the phase of the second laser beam by a phase-locked loop.

[0064] In the gas absorption spectrometer described in paragraph 3, the phase of the first laser beam can be synchronized with the phase of the second laser beam, thereby stabilizing the first laser beam.

[0065] (Section 4) In the gas absorption spectrometer described in Section 3, the PLL circuit is configured to detect a beat signal by superimposing the first laser beam and the second laser beam, and to sweep the frequency of the beat signal.

[0066] In the gas absorption spectrometer described in paragraph 4, the frequency of the first laser beam can be swept.

[0067] (Clause 5) In the gas absorption spectrometer described in any one of paragraphs 1 to 4, the gas absorption spectrometer further comprises a controller that measures gas components using cavity ring-down spectroscopy.

[0068] In the gas absorption spectrometer described in Section 5, the gas components can be measured by the controller.

[0069] (Item 6) In the gas absorption spectrometer described in any one of Items 1 to 5, the optical modulator switches the input of light to the first resonator or the frequency of the first resonator.

[0070] In the gas absorption spectrometer described in paragraph 6, the input of light to the first resonator or the frequency of the first resonator is switched by an optical modulator.

[0071] (Section 7) The gas absorption spectrometer according to the present disclosure is a gas absorption spectrometer for measuring gas components, comprising: a first light source that outputs a first laser beam used for measuring gas components; a first resonator into which the first laser beam is input; and a frequency stabilization circuit arranged such that a negative feedback circuit is formed between the first light source and the first resonator, wherein the frequency stabilization circuit comprises: a second light source that outputs a second laser beam for stabilizing the first laser beam; and an optical stabilization unit for stabilizing the second laser beam.

[0072] In the gas absorption spectrometer described in paragraph 7, the frequency of the laser light can be stabilized even when the incidence of light to the resonator is blocked in order to acquire a ring-down signal.

[0073] The embodiments disclosed herein should be considered in all respects to be illustrative and not restrictive. The scope of the present invention is indicated by the claims rather than by the description of the embodiments above, and all modifications within the meaning and scope equivalent to the claims are intended to be included. [Explanation of Symbols]

[0074] 1 Gas absorption spectrometer, 11 Measurement QCL, 20 AOM, 30, 30A, 30B Frequency stabilization circuit, 31 Reference QCL, 33 High-stability resonator, 34 PDH circuit, 35 PLL circuit, 36, 37, 60 Photodetector (PD), 39 Optical feedback section, 40 CRDS resonator, 41, 42 Mirror, 43 Piezo element, 44 Inlet tube, 45 Outlet tube, 46 Inlet valve, 47 Outlet valve, 51, 52, 53, 54 Beam splitter, 61 Mirror, 70 Controller, 71 Processor, 72 Memory, 300, 300A, 300B Optical stabilization section.

Claims

1. A gas absorption spectrometer for measuring gas components, A first light source that outputs a first laser beam used for measuring the aforementioned gas components, A first resonator into which the first laser beam is input, An optical modulator is arranged in the optical path between the first light source and the first resonator, The system comprises a frequency stabilization circuit arranged so as to form a negative feedback circuit between the first light source and the optical modulator, The frequency stabilization circuit is A second light source that outputs a second laser beam for stabilizing the first laser beam, A gas absorption spectrometer comprising a photostabilization unit for stabilizing the second laser beam.

2. The aforementioned light stabilization unit is The second resonator into which the second laser beam is input, The gas absorption spectrometer according to claim 1, further comprising a PDH circuit for performing PDH (Pound-Drever-Hall) locking on the second resonator.

3. The gas absorption spectrometer according to claim 1 or 2, wherein the frequency stabilization circuit further comprises a Phase Locked Loop (PLL) circuit that synchronizes the phase of the first laser beam with the phase of the second laser beam by a phase-locked loop.

4. The gas absorption spectrometer according to claim 3, wherein the PLL circuit is configured to detect a beat signal by superimposing the first laser beam and the second laser beam, and to sweep the frequency of the beat signal.

5. The gas absorption spectrometer according to claim 1 or claim 2, further comprising a controller that measures the gas components using cavity ring-down spectroscopy.

6. The gas absorption spectrometer according to claim 1, wherein the optical modulator switches the input of light to the first resonator or the frequency of the first resonator.

7. A gas absorption spectrometer for measuring gas components, A first light source that outputs a first laser beam used for measuring the aforementioned gas components, A first resonator into which the first laser beam is input, The system comprises a frequency stabilization circuit arranged so as to form a negative feedback circuit between the first light source and the first resonator, The frequency stabilization circuit is A second light source that outputs a second laser beam for stabilizing the first laser beam, A gas absorption spectrometer comprising a photostabilization unit for stabilizing the second laser beam.

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