KR101394219B1 - Method of trace gas analysis and apparatus performing the same - Google Patents

Abstract

A spectroscopic device according to an embodiment of the present invention includes a laser light source, a resonator, and an optical switch. Wherein the spectroscopic device comprises a laser light source for providing an input laser to the resonator, and a resonator having a resonance frequency corresponding to the resonance frequency of the resonator while moving the specific mirror when a voltage of a specific waveform is applied to a piezo- A resonator for tracking the frequency of the input laser, and a voltage value applied to the piezo when the resonance frequency of the resonator coincides with the frequency of the input laser, And a device for acquiring and analyzing the signal.

Description

TECHNICAL FIELD [0001] The present invention relates to a method for analyzing trace gas and a spectroscopic apparatus using the same,

Embodiments of the present invention relate to a method for analyzing trace gas and a spectroscopic apparatus for performing the method.

Trace gas analysis is a technique for analyzing the types and concentrations of gases having a concentration of less than parts per million (ppm). This analysis technique is essential for many industries such as environment, defense, safety, food hygiene, . Representative analytical techniques that have been introduced so far include chemical analysis techniques (chromatography), electrochemical sensors, and laser spectroscopy techniques. Laser spectroscopy is one of the most promising analytical methods because it has the highest sensitivity and real - time analysis. However, laser spectroscopy has not been widely used in the industrial field because it requires too much technical requirement to realize high sensitivity.

In an embodiment of the present invention, a plurality of mirrors in a resonator are inclined at a specific angle with respect to an optical axis, so that reflected light reflected by the first mirror of the input laser by the laser light source and returned to the laser light source, And returning to the laser light source a part of the resonator mode which passes through the resonator mode and returns to the laser light source. The present invention also provides a spectroscopic apparatus for performing the method.

In one embodiment of the present invention, as the resonance frequency of the resonator tracks the frequency of the input laser while moving a specific one of the plurality of mirrors according to the application of a voltage having a specific waveform, the frequency of the input laser and the resonance frequency A method of analyzing a very small amount of gas capable of ensuring a sufficient crossing time of the resonance frequency and a spectroscopic apparatus for implementing the method.

In one embodiment of the present invention, when the laser frequency is matched to the resonator resonance frequency, the laser frequency is automatically latched to the resonator resonance frequency, so that light of a sufficiently high intensity is formed inside the resonator, Gas analyzing method capable of stably obtaining a gas having a large signal acquisition rate, and a spectroscopic apparatus for performing the method.

The problems to be solved by the present invention are not limited to the above-mentioned problem (s), and another problem (s) not mentioned can be clearly understood by those skilled in the art from the following description.

Among the embodiments, the spectroscopic device includes a laser light source, a resonator, and an optical switch. Wherein the spectroscopic device comprises a laser light source for providing an input laser to the resonator, and a resonator having a resonance frequency corresponding to the resonance frequency of the resonator while moving the specific mirror when a voltage of a specific waveform is applied to a piezo- A resonator for tracking the frequency of the input laser and an optical switch for blocking the input laser when the resonance frequency of the resonator matches the frequency of the input laser.

In one embodiment, the spectroscopic device may further comprise a photodetector for acquiring and analyzing an attenuation signal generated in the resonator while blocking the input laser.

In one embodiment, the plurality of mirrors may spatially separate the first reflected light and the second reflected light of the input laser.

In one embodiment, the first reflected light is reflected light reflected by the first mirror of the plurality of mirrors and returned to the laser light source, and the second reflected light passes through the first mirror to return to the laser light source. It may be part of the resonant frequency of the resonator.

In one embodiment, the resonator may be used as at least one of a linear resonator or a V-shaped resonator depending on at least one of the number and type of the plurality of mirrors.

In one embodiment, the linear resonator may include two opposing mirrors that are inclined at different angles about the optical axis.

In one embodiment, the V-shaped resonator may comprise two mirrors having the same radius of curvature as the length of the resonator.

In one embodiment, the V-shaped resonator may further comprise a plane mirror for providing the first reflected light to the laser light source when the optical switch is a photoacoustic modulator.

In one embodiment, the piezo may move the particular mirror by a distance greater than a half wavelength of the laser light source.

In one embodiment, the voltage of the particular waveform is determined by the sum of the voltage due to the specific function that causes the amplitude to increase with time and the frequency to decrease and the voltage applied to the piezo just before the voltage of the particular waveform is applied .

Among the embodiments, a method of analyzing a trace gas, which is performed in a spectroscope including a laser light source, a resonator, and an optical switch, is a method in which when a voltage of a specific waveform is applied to a piezo- A step of keeping the resonance frequency of the resonator coincident with the frequency of the laser light source while making the resonance frequency of the resonator coincide with the frequency of the laser light source, And acquiring and analyzing the resonator attenuation signal.

In one embodiment, the step of tracking the frequency of the input laser with the resonant frequency of the resonator may further comprise moving the specific mirror by a distance greater than a half wavelength of the laser light source.

In one embodiment, the plurality of mirrors may include two opposing mirrors that are inclined at different angles about an optical axis.

In one embodiment, the plurality of mirrors may spatially separate the first reflected light and the second reflected light of the input laser.

In one embodiment, the first reflected light is reflected light reflected by the first mirror of the plurality of mirrors and returned to the laser light source, and the second reflected light passes through the first mirror to return to the laser light source. May be part of the resonant frequency of the resonator.

In one embodiment, the plurality of mirrors may further comprise a flat mirror for providing the first reflected light to the laser light source when optical switching is performed by a photoacoustic modulator.

The details of other embodiments are included in the detailed description and the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS The advantages and / or features of the present invention, and how to accomplish them, will become apparent with reference to the embodiments described in detail below with reference to the accompanying drawings. It should be understood, however, that the invention is not limited to the disclosed embodiments, but is capable of many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, To fully disclose the scope of the invention to those skilled in the art, and the invention is only defined by the scope of the claims. Like reference numerals refer to like elements throughout the specification.

According to an embodiment of the present invention, a plurality of mirrors in a resonator are finely tilted with respect to an optical axis by a specific angle, so that reflected light reflected by the first mirror of the input laser by the laser light source and returned to the laser light source The present invention is to provide a method for analyzing a trace amount of gas and a spectroscopic apparatus for performing the same, wherein a part of the resonator mode passing through the first mirror and returning to the laser light source is spatially separated and returned to the laser light source.

According to an embodiment of the present invention, by applying a voltage of a specific waveform to move a specific mirror among a plurality of mirrors, a sufficient intersection time between the frequency of the input laser and the resonance frequency of the resonator can be secured at a high repetition rate.

According to an embodiment of the present invention, when the resonance frequency of the resonator coincides with the frequency of the laser light source, the laser frequency is automatically locked to the resonance frequency of the resonator, so that the attenuation signal having a sufficiently high signal- Can be obtained.

1 is a block diagram illustrating a spectroscopic apparatus according to an embodiment of the present invention.
2 is a block diagram illustrating a spectroscope according to another embodiment of the present invention.
Fig. 3 is a view for explaining generation of an attenuation signal in the resonator in Fig.
4 is a view for explaining the resonator of Fig.
5 is a graph illustrating a voltage applied to the piezo of FIG.
FIGS. 6 and 7 are graphs showing a result of obtaining a high sensitivity spectrum for trace amount of ethane gas using a spectroscope according to an embodiment of the present invention.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

The spectrometer of the present invention is based on Cavity Ring Down Spectroscopy (CRDS), which is one of the laser spectroscopy methods. The process of obtaining the gas spectrum using CRDS is as follows. First, an input laser by a laser light source is incident on a resonator composed of a pair of high reflectance (R> 99.9%) mirrors. The laser trapped inside the resonator is very slowly exuded out of the mirror due to the low transmittance of the mirror. However, if a specific gas is present inside the resonator, the attenuation time of the laser of a specific wavelength trapped by the resonator is shortened by the absorption effect of the gas existing in the resonator. When the attenuation time is measured while changing the frequency of the laser light source to measure the absorption spectrum of the gas, absorption of the gas greatly affects the change of the attenuation time, unlike the reflectance of the mirror which is very insensitive to the wavelength.

Since the laser trapped inside the resonator reciprocates within the resonator by a path of several km (or more) on average until it exits the resonator, even if the absorption coefficient of the gas in the resonator is very small, Change. This is a major reason for the high sensitivity of CRDS analysis.

At least one of the pulsed lasers can be selected as the light source for the CRDS. However, in recent years, since the spectroscopic apparatus can be downsized and high sensitivity can be easily realized, continuous oscillation lasers are widely used. The present invention relates to a CW-CRDS using a continuous oscillation laser.

For high sensitivity, the resonator decay time must be long and the signal to noise ratio must be high. In particular, for high S / N ratios, the frequency of the input laser must match the resonant frequency of the resonator for a sufficiently long time (decay time level). However, in a resonator using a mirror having a very high reflectance, the frequency linewidth of the laser is often narrower than the resonance frequency linewidth of the resonator. However, since the frequency of the laser oscillates rapidly in a range much larger than the line width of the resonator resonance frequency, The attenuation signal having a high S / N ratio can not be obtained.

In order to obtain a resonator attenuation signal having a high S / N ratio, servo-locking method in which the frequency of the input laser is matched with the resonance frequency of the resonator for a long time has been widely used by using a feedback electronic circuit and a light element. However, in this case, expensive components such as a feedback electronic circuit, a laser frequency modulation device, and the like are additionally required, which complicates the system, makes it difficult to operate, and increases the cost of the system. Although CRDS spectroscopy has the advantage of being the best among other analytical techniques, the CRDS spectroscope has not been widely used in the field and remains in laboratory level research.

Hereinafter, a spectroscope according to an embodiment of the present invention will be described in detail to solve the above problems.

FIG. 1 is a block diagram illustrating a spectroscope according to an embodiment of the present invention, and FIG. 2 is a block diagram illustrating a spectroscope according to another embodiment of the present invention.

1 and 2, a spectroscopic apparatus 100 includes a laser light source 101, a resonator 102, and an optical switch 103, and may include a plurality of lenses 104, a photodetector 105, a trigger signal generator 106, a computing device 107, a voltage signal amplifier 108, an optical switch control unit 109, a ramp signal generator 110 and a polarizer 111. [

The laser light source 101 provides the input laser to the resonator 102 and receives the reflected light reflected from the input laser from the resonator 102. In one embodiment, the laser light source 101 may include at least one of a DFB diode laser of an external resonator diode laser.

The resonator 102 may further include a plurality of mirrors 112 and a piezo 122.

The plurality of mirrors 112 are formed by a first reflected light 114 reflected by the first mirror 112a of the input laser beam by the laser light source 101 and a second reflected light 114 passing through the first mirror 112a 115). For example, the first reflected light may be reflected by the first mirror 112a and returned to the laser light source, and the second reflected light may pass through the first mirror 112a and return to the laser light source 101, 0.0 > 102 < / RTI >

In one embodiment, the plurality of mirrors 112 may be two opposing mirror pairs, and each of the plurality of mirrors 112 may be configured to be inclined at different angles with respect to the optical axis. In one embodiment, the plurality of mirrors 112 may be configured to be tilted at a small angle of the order of a few mrads. As described above, since the plurality of mirrors 112 are inclined at different angles with respect to the optical axis, the optical alignment of the resonator is slightly deviated, so that the first reflected light and the second reflected light of the input laser by the laser light source 101 Can be separated.

Of the plurality of mirrors 112, a particular mirror may be mounted on the piezo 122. The piezo 122 can move the mounted mirror by a distance equal to or longer than a half wavelength of the input laser by the laser light source 101, and can be formed in a ring shape. The piezo 122 may move a specific one of the plurality of mirrors as the voltage of the particular waveform is applied.

In one embodiment, the resonator 102 is configured such that, when a voltage of a particular waveform is applied to a piezo 122 with a particular mirror of a plurality of mirrors 112, the resonance of the resonator 102 The frequency tracks the frequency of the corresponding input laser as quickly as possible.

The resonator 102 may be used as at least one of a linear resonator and a V-shaped resonator according to at least one of the number and shape of the plurality of mirrors 112. [

In one embodiment, the resonator 102 can be used as a linear resonator if the plurality of mirrors 112 are two mirror pairs facing each other.

In another embodiment, the resonator 102 can be used as a V-shaped resonator when using two mirrors or three mirrors. The V-type resonator is a V-shaped folded linear resonator. If two mirrors are used, the length of the V-shaped resonator should be configured to be equal to the radius of curvature of the mirror. That is, if two mirrors are used, the resonator must be configured to be confocal. A V-shaped resonator using three mirrors consists of two curved mirrors and one flat mirror. If three mirrors are used, the radius of curvature of the plurality of mirrors in the V-shaped resonator may be arbitrarily selected.

The resonator 102 may be configured to include an additional mirror depending on the type of the optical switch 103. [ In one embodiment, the resonator 102 is used as a V-shaped resonator, and when the optical switch 103 is a photoacoustic modulator, the first reflected light 114 and the second reflected light 115 are combined together into a laser light source 101 Must be provided. To this end, the resonator 102 may further include a partial reflection mirror 112c so that the first reflection light can be provided to the laser light source 101. [

The optical switch 103 cuts off the input laser under the control of the optical switch control unit 109.

In one embodiment, the optical switch 103 may include a photoacoustic modulator (AOM) as in FIG. 1 and may include an optoelectronic modulator (EOM) as in FIG. If the optical switch 103 is used as an optoelectronic modulator (EOM) as in FIG. 2, the spectroscopic apparatus 100 may further include a polarizer 111. [

The optical switch 103 is disposed between the laser light source 101 and the resonator 102 and passes the input laser from the laser light source 101 to the resonator 102. The reflected light reflected by the resonator 102 is transmitted to the laser And supplies it to the light source 101. When a photoacoustic modulator is used as the optical switch 103, the input laser by the laser light source 101 passes through the optical switch 103 two times, and the frequency corresponding to twice the frequency of the optical switch 103 Change.

The photodetector 105 acquires and provides the resonator 102 attenuation signal to the computing device 107 when the resonant frequency of the resonator 102 matches the frequency of the input laser.

The trigger signal generator 106 generates a TTL pulse signal having a specific delay time when the signal of the photodetector 105 exceeds a predetermined threshold value.

The computing device 107 is synchronized with the pulse signal of the trigger signal generator 106 to generate a voltage signal of a particular waveform applied to the piezo 122 while analyzing the resonator attenuation signal obtained at the photodetector 105 And perform the operation. In one embodiment, the computing device 107 may further include an analog-to-digital converter 117 and a digital-to-analog converter 127. The analog-to-digital converter 117 converts the attenuation signal of the resonator 102 by the photodetector 105 into a digital signal and the digital-to-analog converter 127 converts the voltage signal of the programmed specific waveform applied to the piezo- And converts it into a signal.

The voltage signal amplifier 108 amplifies the voltage signal of the specific waveform generated by the computing device 107 and provides it to the piezo 122. [

The optical switch control unit 109 controls the optical switch 103 to block the input laser. In one embodiment, the optical switch control 109 can control the optical switch 103 to block the input laser when the frequency of the resonator 102 matches the frequency of the input laser by the laser light source 101 . In another embodiment, the optical switch control section 109 controls the optical switch 103 to block the input laser according to the TTL pulse signal generated by the trigger signal generator 106. [

Fig. 3 is a view for explaining generation of an attenuation signal in the resonator in Fig.

Referring to FIG. 3, it is clear that the resonator attenuation signal is generated in the pulse laser 301, but a step-by-step understanding is required for the attenuation signal to be generated in the continuous oscillation laser 302. That is, a step in which the frequency of the corresponding input laser coincides with the resonant frequency of the resonator, and a light of sufficiently strong intensity is formed inside the resonator while the two frequencies coincide over a sufficient period (damping time level) The input laser is cut off and the resonator attenuation signal is generated.

4 is a view for explaining the resonator shown in Fig.

4, the resonator 102 may be used as at least one of the linear resonator 410 and the V-shaped resonator 420, 430 depending on the number of the plurality of mirrors 112 inside.

The linear resonator 410 may include two opposing mirror pairs that are slightly tilted at different angles with respect to the optical axis. The two pairs of mirrors in the linear resonator 410 are configured to be tilted by a specific angle with respect to the optical axis so as to be slightly deviated from the optical alignment and the first reflected light 412 and the second reflected light 412 of the input laser 411 413 may be spatially separated and fed back to the corresponding laser.

V-shaped resonators 420 and 430 are in the form of a V-shaped folded linear resonator and may include two mirrors or three mirrors. When including two mirrors, the length of the V-shaped resonator should be configured to be equal to the radius of curvature of the mirror (420). That is, if two mirrors are used, the resonator must be configured to be confocal. The V-shaped resonator 430 using three mirrors is composed of two curved mirrors and one flat mirror. If three mirrors are used, the radius of curvature of the plurality of mirrors in the V-shaped resonator may be chosen arbitrarily. In the V-shaped resonator, a flat mirror 112c is additionally required to provide a part of the first reflected light, particularly, to the corresponding laser light source.

5 is a graph illustrating the voltage applied to the piezo in Fig.

Referring to FIG. 5, the piezo 122 may receive a specific type of voltage and move a specific mirror among a plurality of mirrors to track the frequency of the input laser. More specifically, by varying the length of the resonator using a modulated sinusoidal function (whose frequency gradually decreases) whose amplitude and period gradually increase with time, the resonator resonant frequency can quickly track the frequency of the corresponding input laser have. In one embodiment, the voltage of a particular waveform applied to the piezo 122 can be calculated by: < EMI ID = 1.0 >

[Equation 1]

V _out = V _sig + V _off

V _out : voltage applied to the piezo,

V _sig : amplitude increases and frequency decreases over time

 A voltage in the form of a modulated sinusoidal function,

V _off : the fixed voltage applied just before the new tracking phase

The maximum slope of V _sig should be below a certain criterion so that the time during which the frequency of the input laser and the resonance frequency of the resonator overlap can be assured. The large initial value of V _sig is for maximizing the time point when the resonance frequency of the resonator matches the frequency of the input laser. Referring in more detail to the V _sig, beginning early time point on the amplitude of the modulated sine wave corresponds to the free spectral distance of the resonator (102) (Free Spectral Range) voltage in the form of the amplitude and frequency the same sine wave, and the modulated sine wave continuously Respectively.

V _off Is within the range of the voltage corresponding to the free spectral range of the resonator 102. [ V _off (Plus) subtracting the voltage corresponding to the free spectrum distance from the present value is the final V _off .

6 is a graph showing a result of obtaining a high sensitivity spectrum for trace amount of ethane gas using a spectroscope according to an embodiment of the present invention.

Referring to FIG. 6, the configuration of the spectroscopic apparatus 100 for obtaining a high sensitivity spectrum for trace amount of ethane gas is as follows. The same or corresponding contents as those described above with reference to FIG. 1 will be omitted for the configuration or operation of the spectroscopic apparatus 100, but those skilled in the art will be able to fully understand the embodiment of FIG.

The laser light source 101 used an external resonator diode laser (ECDL) (New Focus, velocity 6300), which can change the wavelength within a range of 1.65 - 1.68 μm and has a line width less than 1 MHz. The resonator 102 is formed of a deformed linear resonator having a length of 1 m using two mirrors having a reflectance of 99.998% or more (1.65 - 1.68 mm) and a radius of curvature of 2 m. The optical switch 103 uses a photoacoustic modulator (80 MHz) and uses a -1 st order deflected input laser. The deflected beam of the photoacoustic modulator is matched to the resonant mode of the resonator 102 as much as possible using two convex lenses. The photodetector 105 measures the attenuation signal of the resonator 102 using a low noise and very high gain photodiode (NewFocus, 2053FS) and measures the attenuation of the resonator 102 using a digitizer with a resolution of 14 bits and a bandwidth of 200 MHz (Gage Compuscope 14100 ) Was used to obtain the signal of the photodiode.

Reference numeral 610 is a graph showing the attenuation signal of the resonator 102 when the resonance frequency of the resonator 102 and the frequency of the input laser coincide and reference numeral 720 indicates a frequency of about 200 Hz The attenuation signal of the resonator 102 generated by the resonator 102 is shown. The X axis of each graph 610 and 620 represents time, and the Y axis represents a resonator attenuation signal. According to the graphs 610 and 620, the signal-to-noise ratio is very good as about 3000: 1 and the attenuation time is 168.6 us, which means that an extremely long resonator attenuation signal can be stably obtained at a very high speed of several hundreds Hz .

7 is a graph showing a result of obtaining a high sensitivity spectrum for trace amount of ethane gas using a spectroscope according to another embodiment of the present invention.

Referring to FIG. 7, the configuration of a spectroscopic apparatus 100 for obtaining a high sensitivity spectrum for trace amount of ethane gas is as follows. The same or corresponding contents as those described above with reference to FIG. 1 are omitted for the configuration or operation of the spectroscopic apparatus 100, but those skilled in the art will be able to fully understand the embodiment of FIG.

7 is a spectrum of the ethane gas measured at a wavelength of 1678.6 nm using the spectroscopic apparatus 100 of FIG. The concentration of ethane gas was 1 ppm, and the measurement time per data point was 1 second. The spectrum is for the strongest absorption line in the wavelength band that can be measured with this spectrometer, and the analytical sensitivity to ethane from the S / N ratio of the signal is about 200 ppt (0.2 ppb).

While the present invention has been described in connection with what is presently considered to be practical exemplary embodiments, it is to be understood that the invention is not limited to the disclosed embodiments. Therefore, the scope of the present invention should not be limited to the described embodiments, but should be determined by the scope of the appended claims and equivalents thereof.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it is to be understood that the invention is not limited to the disclosed exemplary embodiments, but, on the contrary, Modification is possible. Accordingly, the spirit of the present invention should be understood only in accordance with the following claims, and all equivalents or equivalent variations thereof are included in the scope of the present invention.

100: Spectroscopic device
101: Laser light source
102: Resonator
103: Optical switch
104: a plurality of lenses
105: Photodetector
106: Trigger signal generator
107: computing device
108: Voltage signal amplifier
109: Optical switch control section
110: lamp signal generator
111: Polarizer
112: a plurality of lenses
117: Analog-to-digital converter
122: Piezo
127: Digital-to-Analog Converter

Claims (17)

A spectroscope including a laser light source, a resonator, and an optical switch,
A laser light source for providing an input laser to the resonator;
A resonator for tracking the frequency of the input laser corresponding to the resonance frequency of the resonator while moving the specific mirror when a voltage of a specific waveform is applied to a piezo having a specific mirror among a plurality of mirrors; And
And an optical switch for blocking the input laser when the resonance frequency of the resonator matches the frequency of the input laser,
Wherein the voltage of the specific waveform is determined by a sum of a voltage due to a specific function which causes the amplitude to increase with time and a frequency to decrease and a voltage to be applied to the piezo just before the voltage of the specific waveform is applied.
The method according to claim 1,
Further comprising a photodetector for blocking the input laser and acquiring an attenuation signal generated in the resonator.
2. The apparatus of claim 1, wherein the plurality of mirrors
And separates the first reflected light and the second reflected light reflected from the input laser spatially.
The method of claim 3,
The first reflected light is reflected light reflected by the first mirror of the plurality of mirrors and returned to the laser light source, and the second reflected light passes through the first mirror to return to the laser light source, And a part thereof.
The resonator according to claim 1, wherein the resonator
Wherein the resonator is used as at least one of a linear resonator and a V-shaped resonator according to at least one of the number and kind of the plurality of mirrors.
The resonator according to claim 5, wherein the linear resonator
And two mirrors facing each other, which are inclined at different angles about the optical axis.
6. The V-shaped resonator according to claim 5, wherein the V-
Wherein the resonator comprises two mirrors having the same radius of curvature as the length of the resonator.
The resonator of claim 7, wherein the V-shaped resonator
And a plane mirror for providing the first reflected light to the laser light source when the optical switch is a photoacoustic modulator.
2. The method of claim 1,
And the specific mirror is moved by a distance equal to or longer than a half wavelength of the laser light source.
delete A method for analyzing a trace gas in a spectroscopic apparatus including a laser light source, a resonator, and an optical switch,
Tracking the frequency of the input laser by the laser light source while the resonant frequency of the resonator is moving while moving the specific mirror when a voltage of a certain waveform is applied to a piezo-mounted piezo-mirror among the plurality of mirrors;
Fixing a voltage value applied to the piezo when the resonance frequency of the resonator matches the frequency of the input laser and blocking reception of the input laser; And
Receiving the input laser and acquiring and analyzing an attenuation signal generated in the resonator,
The voltage of the particular waveform
Wherein the amplitude is determined by the sum of the voltage due to the specific function that causes the amplitude to increase with time and the frequency to decrease and the voltage applied to the piezo just before the voltage of the particular waveform is applied.
12. The method of claim 11, wherein the resonant frequency of the resonator tracks the frequency of the input laser by the laser light source
Further comprising moving the specific mirror by a distance equal to or greater than a half wavelength of the laser light source.
12. The system of claim 11, wherein the plurality of mirrors
Characterized in that it comprises two opposing mirrors which are inclined at different angles about the optical axis.
14. The system of claim 13, wherein the plurality of mirrors
Wherein the first reflected light and the second reflected light reflected from the input laser are spatially separated from each other.
15. The method of claim 14,
The first reflected light is reflected light reflected by the first mirror of the plurality of mirrors and returned to the laser light source, and the second reflected light passes through the first mirror to return to the laser light source, And a part of the gas is analyzed.
14. The system of claim 13, wherein the plurality of mirrors
Further comprising a planar mirror for providing the first reflected light to the laser light source when optical switching is performed by a photoacoustic modulator.
delete

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