CN103364371B - The absorption coefficient of atmospheric aerosol Novel differential measurement method of coaxial-type photothermal interference - Google Patents
The absorption coefficient of atmospheric aerosol Novel differential measurement method of coaxial-type photothermal interference Download PDFInfo
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Abstract
The invention discloses the new method that a kind of absorption coefficient of atmospheric aerosol double passage differential based on coaxial-type photothermal interference is measured, utilize modulated carrier laser to be formed through aerosol sample region to be measured to interfere, design two path interferometric light paths, the baseline phase drift that one of them Air conduct measurement causes due to environment temperature gradual change and Platform Vibration, total phase place change that another Air conduct measurement gasoloid absorption exciting laser and baseline phase drift cause, both difference obtain gasoloid and absorb caused phase changing capacity, on the basis of interfering amplification factor to be demarcated, realize the on-line checkingi of gasoloid absorption coefficient.The present invention can also be used for the Concentration Testing of the specific aerosol component according to " fingerprint " absorption characteristic; Instant invention overcomes the impact of variation of ambient temperature and measuring table vibration, eliminate the adjustment that phase inversion is not good enough, the operating distance of exciting laser and exploring laser light is doubled, have easy to operate, detection speed fast, be easy to miniaturization, detection sensitivity high.
Description
Technical field:
The present invention relates to a kind of double passage differential new method of measuring utilizing photothermal interference to detect absorption coefficient of atmospheric aerosol, exciting laser and interact through the interfering beam in gasoloid region to be measured and cause the change of interferometric phase, aerocolloidal absorption coefficient to be measured can be measured in real time according to phase place change, and monitor gasoloid absorption coefficient development law in time.Select the exciting laser of specific " fingerprint " wavelength, specific gasoloid trace constituent and concentration thereof can be determined.
Background technology:
It is much more complicated than greenhouse gases that atmospheric aerosol absorbs the Radiative Forcing caused, and is one of the most uncertain factor during Radiative Forcing calculates, greatly have impact on the accuracy of atmospherical model.The shortage of gasoloid absorption information has become one of subject matter in the Atmospheric Correction research of the research of Aerosol radiation climatic effect and Spaceborne Remote Sensing Application.When laser transmits in an atmosphere, the laser energy that gasoloid absorbs conducts to air, causes the fluctuating of air index, makes beam distribution become complicated; Superlaser also can produce thermal blooming effects and air punctures, and changes high power laser light by propagation in atmosphere to the energy density distribution in target, directly affects design and the development of engineering system.On-line measurement obtains the absorption coefficient of atmospheric aerosol, more adequately can not only assess the Changing Pattern of gasoloid complex index of refraction especially imaginary index, the transport property research in an atmosphere of in-depth laser, and the accuracy that Aerosol radiation forces calculating can be improved, deepen the understanding of climatic effect and Changing Pattern.
In air, the on-line measurement of gasoloid absorption coefficient also has much reality and potential purposes.As the detection of methane content in mine, the detection of the harmful gas such as silane, arsenic hydride, hydrogen phosphide in semiconductor production workshop, the field such as life science and medical diagnosis is to the detection etc. of its constituents of interest.In these applications above-mentioned, the concentration of each composition to be measured is often at ppm(10
-6) magnitude even below, therefore design has the gasoloid absorption coefficient detection technique of high sensitivity, high selectivity, the fast feature such as response and real-time non-destructive, gas with various composition is utilized usually to have the characteristic of difference " fingerprint " absorbing wavelength, select the laser of specific wavelength, the concentration of composition to be measured can be determined, thus carry out prevention or emergence treatment scheme.
When illumination is mapped on particulate, particulate absorbs optical radiation energy and causes air Warm status such as temperature, air pressure and density etc. on light transmission path to change, and when incident light is subject to modulating, the localized heat state of air just produces periodically change.By measuring the degree size of this change, aerocolloidal absorption coefficient to be measured can be obtained.Optical thermo method is based upon on basis that certain character of sample gas that incidenting laser radiation energy hot-cast socket causes changes and realizes detection, and adopt the incident laser of higher luminous power to improve detection sensitivity, this is the feature that general absorption spectrum does not have.What measure due to optical thermo method is the thermal diffusion result of light absorption, this result is to the scattering of gas componant and reflect insensitive, therefore optical thermo method is in scattering with to reflect the method for difference that the absorptiometry in the medium that coexists obtains absorption characteristic compared with the scattering of delustring deduction more accurate, moreover the detecting device of optical thermo method can Fast Restoration, " poisoning " reaction can not be produced, do not need long integration to reach detectability, therefore utilize photo-thermal effect to detect practical application very attractive and the market outlook of gasoloid absorption coefficient.
The successful Application of optical thermo method on gasoloid absorption coefficient composition and Concentration Testing is optoacoustic spectroscopy, the air pressure change that optoacoustic spectroscopy utilizes photo-thermal effect to produce, the detection of gasoloid absorption coefficient is realized by measuring the acoustical signal converted by the luminous energy of molecule absorption, but optoacoustic spectroscopy must complete in optical resonator, is subject to many limitations.
Change due to air themperature state causes the refractive index light path generation in other words subtle change of beam path, and this variable quantity can be obtained by the method for phase-detection, and photothermal interference method has very highland high sensitivity in phase-detection.Under the condition that earth atmosphere light is propagated, phase fluctuation presents saturated phenomenon unlike light intensity fluctuation, and the scope of application thus based on the phase fluctuation result of perturbation theory will much larger than light intensity fluctuation.The power of photothermal interference signal depends on the size of gasoloid absorption coefficient to be measured and exciting laser power.H.B.Lin etc. measure the absorption characteristic of ammonium sulfate by photothermal interference, but its measurement result is very easy to the interference being subject to extraneous vibration, strongly limit the application of interferometric method.M.A.Owens etc. utilize plated film Jamin plate and filled gold plate etc. to combine the synchro control achieving reference path and signal light path, regulate interferometric phase to be in phase inversion all the time not good enough, and carried out meticulous measurement according to absorption characteristic to ammonia by piezoelectric ceramics; In order to solve the impact of vibration on result, suspend in cavity detection system being placed in acoustical material, practical operation is got up very loaded down with trivial details.A.Sedlacek etc. adopt Zigzag type Jamin structure to simplify the double light design of interference device, but Zigzag type structure still needs with piezoelectric ceramics regulating rotary not good enough mutually, and the optical surface of prism needs to use N
2continue to purge to keep clean, should use still inconvenient.
Make a general survey of the development of photothermal interference method, 3 bottleneck problems always existed limit its application: 1, the vibration of measuring table; 2, the dynamic adjustments that phase inversion is not good enough; 3, the operating distance of exciting laser and exploring laser light.What measure due to photothermal interference method is phase changing capacity, and the disturbance of mechanical vibration to light path is enough to have an impact the phase information of measurement result, and the common method solving vibration is shielded by measuring equipment special material.In order to ensure the linear relationship between phase change amount and modulated laser power, it is not good enough that interfering beam must be in phase inversion, usual employing low frequency piezoelectric ceramics feedback circuit realizes, the frequency of feedback circuit and the frequency of exciting laser relatively time just bother very much.In order to increase the operating distance of exciting laser and exploring laser light, early stage often utilize the material of the exciting laser that to be all-trans through exploring laser light realize both coaxial, but exciting laser to light path, impact is brought to the heating of reflecting material, therefore many employing exciting lasers and exploring laser light keep the mode of certain angle now, are realized the interaction distance met the demands by reduction angle or increase sample cell length.
The present invention is directed to above-mentioned three factors, propose the absorption coefficient of atmospheric aerosol Novel differential measurement method of coaxial-type photothermal interference, formed by modulated carrier laser and interfere, two detection is adopted to interfere passage, in it and the interference channel measurements of modulated excitation laser action contains phase place baseline change that the gradual and Platform Vibration of environment temperature causes and the periodic phase that modulated excitation laser causes changes, and the phase place baseline change that another passage measures ambient temperature is gradual and Platform Vibration causes, obtained by difference method and absorb by gasoloid the phase changing capacity caused merely, obtain aerocolloidal absorption coefficient to be measured, fundamentally break away from environment temperature change, Platform Vibration and the not good enough restriction of phase inversion, adopt coaxial interference mode, make the interaction distance of exciting laser and optical interference circuit expand as the twice of non-coaxial mode.This invention greatly simplify the operation of photothermal interference, improves the detectivity of photothermal interference.
Summary of the invention:
The object of the invention is the deficiency for existing conventional gasoloid absorption coefficient measuring technique, there is provided a kind of and form two interference detection passages by modulated carrier laser, utilize difference method to obtain and absorb by gasoloid the phase changing capacity caused merely, the method for on-line measurement gasoloid absorption coefficient to be measured; The method has broken away from the not good enough restriction of variation of ambient temperature, Platform Vibration and phase inversion; And make the interaction distance of exciting laser and optical interference circuit expand as the twice of non-coaxial mode, adopt the laser instrument of Wavelength tunable, the method effectively can also determine the concentration of specific aerosol component, has that principle is simple, detection sensitivity is high, be easy to the features such as miniaturization.
The technical solution used in the present invention is:
A kind of absorption coefficient of atmospheric aerosol Novel differential measurement method of coaxial-type photothermal interference, it is characterized in that: include carrier wave laser, the front light path of carrier wave laser is equipped with beam splitter, the incident light of carrier wave laser is divided into two-beam through beam splitter, the front light path of two-beam is disposed with optoisolator respectively, optical circulator, optical collimator, two described optical collimators are positioned at the front end of detection cell, the rear end of detection cell is provided with high reflective mirror, reflection and transmission is there is respectively in two-beam at collimating apparatus end face, reflected light returns along former road, reflect former road by high reflective mirror after the detected sample gas zones of transmitted light after testing in pond to return, through after the detected sample gas in detection cell again through optical collimator end face, the reflected light of this transmitted light and optical collimator end face forms interference light, described two-way interference light enters photodetector by optical circulator, wherein a road interfering beam detects baseline wander as baseline correction light path, another road interfering beam detects the phase place change summation that the gentle gel absorption exciting laser of baseline wander causes, described exciting laser is the light modulated away from interference light wavelength that signal generator produces, on the basis of interfering amplification factor to be demarcated, realize the on-line checkingi of gasoloid absorption coefficient.
The absorption coefficient of atmospheric aerosol Novel differential measurement method of described coaxial-type photothermal interference, it is characterized in that: described exciting laser front light path is provided with light splitting piece, the reflected light path of light splitting piece is provided with light power meter, the transmitted light path of light splitting piece is provided with light reflection mirror one, the reflected light path of light reflection mirror one is provided with light reflection mirror two, light reflection mirror one, light reflection mirror two to be located in detection cell wherein on a road interfering beam respectively, described exciting laser in detection cell and detection optical interference circuit to interact a segment distance.
The absorption coefficient of atmospheric aerosol Novel differential measurement method of described coaxial-type photothermal interference, is characterized in that: described detection cell and optical interference circuit are fixed on the as far as possible large fixed support of counterweight to reduce the vibration of measuring table.
The absorption coefficient of atmospheric aerosol Novel differential measurement method of described coaxial-type photothermal interference, it is characterized in that: described sample gas enters detection cell by the hybrid chamber of gas compounding system, the carrier gas of described gas compounding system comprises pure nitrogen and pretreated air, sample gas and the air direct injected of different moisture content can be prepared, its hybrid chamber serves the effect of Buffer Pool, eliminates the adverse effect of aspiration pump vibration to optical interference circuit measurement result.
The absorption coefficient of atmospheric aerosol Novel differential measurement method of described coaxial-type photothermal interference, it is characterized in that: the described optical interference circuit through detection cell is coaxially reverse, therefore the interaction distance of exciting laser and detection optical interference circuit is that exciting laser institute covers 2 times that detect optical interference circuit length.
The light beam that incident light is divided into two-beam identical in quality through beam splitter, two-way interference light is formed through reflection and transmission, environment temperature gradual change is identical with the impact of Platform Vibration on two-way interference light, both difference realize the Measurement accuracy of photothermal phase knots modification, avoid the adjustment of traditional photothermal interference for quadrature point, expand the dynamic range of survey frequency and measurement concentration.
Present invention achieves the absorption coefficient of atmospheric aerosol direct-detection for open atmosphere environment; Select specific " fingerprint " absorbing wavelength, the online composition that can realize trace gas is determined and Concentration Testing; Exciting laser fluctuation of energy coordinates energy meter to obtain the degree of accuracy being improved result of calculation by light splitting piece.
Optical fiber is electrical isolation, corrosion resistant optical transmission medium, lightweight, volume is little and short-distance transmission can ignore optical energy loss and polarization state change, coaxial-type photothermal interference is realized by single-mode fiber.
Theoretical foundation of the present invention is:
The heat-conduction coefficient of air is very little (is 0.026Wm at 298.2K temperature
-1k
-1), the heat transfer process of air wants much slow relative to the excited state relaxation processes that gasoloid absorbs, and therefore thinks that the heating of sample air is instantaneous and completes and be confined to be rational within exciting beam.
Suppose that the collision relaxation after gasoloid absorbs luminous energy in air causes temperature rising Δ T, under gasoloid absorbs unsaturated prerequisite, the ascending amount of this temperature can be expressed as:
Wherein P
ebe the power of excitation laser (excitedlaser), α is the absorption coefficient of particulate, and l is the action length of exciting beam and exploring laser light bundle, a
ebe exciting laser beam radius, ρ and C is density and the thermal capacitance of air, f
efor the modulating frequency of exciting laser, its dutycycle is 1:1, this frequency response environment noise and mechanical vibration insensitive.
The change of atmospheric temperature causes the subtle change of refractive index, according to Ge Lasidun-Dai Er (Gladstone-Dale) law:
Δn=((n-1)/T
0)ΔT（2）
Wherein, n is the mean refractive index of testing sample, T
0for the absolute temperature of testing sample.
There is corresponding change owing to being subject to the change of air refraction in the detecting light beam light path through this region, its variable quantity is by the change Δ φ of detecting light beam interferometric phase
eshow.For the axis reflector formula structure described in this patent, the action length of exciting beam and exploring laser light bundle (maximum when both overlap, but light path is subject to the impact that optical device expands with heat and contract with cold) rising to 2l, λ is the wavelength of detecting light beam, then:
Δφ
e=2π·2l·Δn/λ（3）
The variation delta φ of interferometric phase
efrequency and the modulating frequency f of exciting laser
eidentical, simultaneous (1), (2) and (3) formula:
Gasoloid absorption coefficient is:
Utilize mutually responsive lock-in amplifier as detecting device, can noise beyond effectively filtering modulating frequency, improve the antijamming capability of system.The absorption coefficient of particulate is proportional to and and phase change amount Δ φ from amplifier signal S out
elinear, be expressed as:
α∝S=AΔφ
e（6）
Wherein A is for interfering amplification factor, can be demarcated obtain by preparation aerosol sample.
Suppose that the initial interference light beam that modulated laser is formed is cosine form:
x(t)=Bcos(ωt)（7）
Wherein a road interfering beam is behind sample area, and its expression formula is:
x
1(t)=Bcos(ωt+φ
1)（8）
Wherein φ
1mainly from change and the Platform Vibration of environment temperature, when Platform Vibration is little, φ
1it is a gradual amount.Another beam interferometer light beam through sample area and and exciting laser effect after, its expression formula is:
x
2(t)=Bcos(ωt+φ
2)（9）
Wherein φ
2=φ
1+ Δ φ
e, Δ φ
eit is the phase changing capacity that modulated excitation laser causes.
By Hilbert transform, (8) formula and (9) formula are converted into:
x
1′(t)=Bsin(ωt+φ
1)（10）
x
2′(t)=Bsin(ωt+φ
2)（11）
(11) * (8)-(10) * (9):
X(t)=Bsin(Δφ
e)（12）
(9) * (8)+(11) * (10):
Y(t)=Bcos(Δφ
e)（13）
Phase changing capacity Δ φ
efor:
(5) formula of substitution, obtains aerocolloidal absorption coefficient to be measured in real time.
The invention has the beneficial effects as follows:
The present invention establishes the method for photothermal interference method real-time online measuring absorption coefficient of atmospheric aerosol, obtain environmental factors and periodic modulation exciting laser to signal base line phase change by two optical interference circuits, utilize method of difference obtain aerocolloidal absorption coefficient to be measured and with between development law; The present invention is measured as in site measurement to gasoloid absorption coefficient, and detection sensitivity is high, easy and simple to handle.
Advantage of the present invention is:
1, achieve the real-time online non-contact measurement of gasoloid absorption coefficient under atmospheric environment, maintain original state of air to be measured to greatest extent;
2, optical fiber type axis reflector structure achieves the multiplication of exciting beam and interfering beam operating distance;
3, the measuring principle of gasoloid absorption coefficient is simple, easy to operate, detection speed is fast;
4, different from conventional suction spectrum, photothermal interference method can improve the detection sensitivity of gasoloid absorption coefficient by improving exciting laser power;
5, the phase change amount acquisition pattern of modulation /demodulation carrier wave laser signal avoids the mutually not good enough adjustment of conventional interference method transfer, and the length of optical interference circuit and initial phase do not require equal, expands the dynamic range of survey frequency and measurement concentration;
6, double passage differential measurement eliminates the impact of environment temperature gradual change and Platform Vibration etc., and a calibration point is just enough to correct interference amplification factor in theory;
7, without absorbing with regard to no signal, being a kind of measuring technique of zero background signal, using adjustable wavelength laser, the concentration of special component can be measured.
Accompanying drawing illustrates:
Fig. 1 is that the measuring principle schematic diagram of gasoloid absorption coefficient is (coaxial in detection cell through the light path (hollow arrow) after the incident light (filled arrows) of collimating apparatus end face and total reflective mirror reflection, the coaxial detection light path that exciting laser light path and transmitted light, reflected light form becomes low-angle angle, while ensureing absorption length, avoid the light path perturbation that the breathing of catoptron own causes; It is power in order to dynamic monitoring exciting laser that light splitting piece adds energy meter, to determine gasoloid absorption coefficient more accurately.
Fig. 2 is the fundamental diagram (the equal propagating co-axial of ghost line, described separately is for convenience of description) of an optical interference circuit in two interference passages.
Fig. 3 is that (sample that can prepare comprises testing sample preparation process figure: 1. pure nitrogen does the variable concentrations aerosol sample of carrier gas, 2. the pure nitrogen containing variable concentrations steam does the variable concentrations aerosol sample of carrier gas, 3. zero air does the variable concentrations aerosol sample of carrier gas, 4. zero air containing variable concentrations steam does the variable concentrations aerosol sample of carrier gas, 5. ambient atmosphere).
Embodiment:
As shown in Figure 1, a kind of absorption coefficient of atmospheric aerosol Novel differential measurement method of coaxial-type photothermal interference, include carrier wave laser 1, the front light path of carrier wave laser 1 is equipped with beam splitter 2, the incident light of carrier wave laser 1 is divided into two-beam through beam splitter 2, the front light path of two-beam is disposed with optoisolator 3 respectively, optical circulator 5, optical collimator, two optical collimators are positioned at the front end of detection cell 7, the rear end of detection cell 7 is provided with high reflective mirror 8, reflection and transmission is there is respectively in two-beam at collimating apparatus end face 6, reflected light returns along former road, reflect former road by high reflective mirror 8 behind the detected sample region of transmitted light after testing in pond 7 to return, through after the detected sample in detection cell 7 again through optical collimator end face 6, the reflected light of this transmitted light and optical collimator end face 6 forms interference light, described two-way interference light enters photodetector by forming interfering beam after optical circulator 5, wherein a road interfering beam detects baseline wander as baseline correction light path, another road interfering beam detects the phase place change summation that the gentle gel absorption exciting laser 11 of baseline wander causes, described exciting laser is away from interference light wavelength, the directional light modulated by signal generator 12, on the basis of interfering amplification factor to be demarcated, realize the on-line checkingi of gasoloid absorption coefficient.
Exciting laser 11 front light path is provided with light splitting piece 9, the reflected light path of light splitting piece 9 is provided with light power meter 10, the transmitted light path of light splitting piece 9 is provided with light reflection mirror 1, the reflected light path of light reflection mirror 1 is provided with light reflection mirror 2 14, light reflection mirror 1, light reflection mirror 2 14 are located on the optical interference circuit of a wherein road interfering beam in detection cell 7 respectively, described exciting laser 11 in detection cell 7 and detection optical interference circuit angle 2
owithin, both interact a segment distance.
Detection cell 7 and optical interference circuit are fixed on the as far as possible large fixed support of counterweight to reduce the vibration of measuring table.
Sample gas enters detection cell via the hybrid chamber of gas compounding system, the carrier gas of described gas compounding system comprises pure nitrogen and pretreated air, sample gas and the air direct injected of different moisture content can be prepared, its hybrid chamber serves the effect of Buffer Pool, eliminates the adverse effect of aspiration pump vibration to optical interference circuit measurement result.
Optical interference circuit through detection cell 7 is coaxially reverse, therefore the interaction distance of exciting laser 11 and detection optical interference circuit be exciting laser 11 covers 2 times that detect optical interference circuit length.
Embodiment
1, select armouring single-mode fiber as the transmission medium of carrier wave laser 1, utilize visible ray such as HeNe laser to form optical interference circuit as carrier wave by optical fiber, interference light and incident carrier wave laser are separated by optical circulator 5.The anti-film reflectivity of increasing of optical collimator end face 6 is arranged between 26% ~ 30%, make formed interfere reflected light and transmitted intensity roughly equal;
2, for same atmospheric aerosol, the absorption coefficient of exciting laser 11 correspondence of different wave length is different.Selection can not form the laser of interfering as exciting laser with carrier wave laser 11.Take into account exciting laser beam diameter, and the angle between exciting laser and interfering beam, regulate the mirror width on support to control at about 5mm by being positioned at exciting laser;
3, in order to the measurement result of two optical interference circuits does not interfere with each other, 8cm ~ 12cm is arranged on by reflecting the two parallel beam distances that former road returns through high reflective mirror 8, optical collimator and high reflective mirror 8 are fixed on the as far as possible little material of deformation coefficient as on pottery, distance is between the two arranged on 20cm ~ 24cm, and the angle of interfering beam and exciting light beam controls 1
o~ 2
o, the interaction distance controls at about 10cm;
4, select tempered glass to make detection cell 7, detection cell 7 select counterweight as far as possible large center rest fixed, the optical fiber resilient material through detection cell 7 is filled, and is reduced to minimum by the vibration of detection cell 7 pairs of optical interference circuits;
5, because ammonia has absorption cross section 56atm considerably when 273K
-1cm
-1, therefore select ammonia as the gasoloid standard model demarcated.The ammonia of normal concentration by osmos tube with certain speed (μ g/min) to exosmosis, continue at an upper portion thereof to purge pure nitrogen, by flow controller at times dynamic dilution go out ammonia sample from low to high, excitation laser selects that energy is 2W, wavelength is the CO of 9.22 μm
2laser instrument, by the cooperation of light splitting piece 9 and light power meter 10, the dynamic range of record exciting laser energy, improves the degree of accuracy of demodulation signal processing;
6, substitute into formulae discovery and go out phase changing capacity Δ φ corresponding to the ammonia sample of variable concentrations
e, utilize a road optical interference circuit tracer signal baseline with the change φ of environmental factor
1, utilize another road optical interference circuit property measuring period modulation signal φ
2, obtain the absorption intensity S that modulated excitation laser beam causes, calibrate and interfere amplification factor A;
7, by sample preparation system, correct and interfere amplification factor, investigate configure the absorption coefficient of sample;
8, the hybrid chamber of sample system is considered as Buffer Pool, ambient atmosphere to be left intact direct injected through hybrid chamber, investigates the absorption coefficient of exciting laser corresponding wavelength;
9, when wanting the concentration of certain composition in atmospheric sounding, select this composition " fingerprint " absorbing wavelength as exciting laser; If detect be Absorption Line comparatively close several aerosol component time, select the adjustable laser instrument of output wavelength, as detection while methane, ammonia and carbon monoxide can select the DFB semiconductor laser of 2.3 μm.
Fig. 2 is the fundamental diagram of an optical interference circuit in two interference passages, and number in the figure represents respectively:
1. the interference light that is made up of 8 and 9 through the reflected light 10. of collimating apparatus end face through the transmitted light 9. carrier wave laser of collimating apparatus through reflected light 8. reflected light of high reflective mirror of carrier wave laser 2. optoisolator 3. optical circulator 4. collimating apparatus end face 5. carrier wave laser-transmitting light 6. high reflective mirror 7. carrier wave laser.
Claims (5)
1. the absorption coefficient of atmospheric aerosol Novel differential measurement method of a coaxial-type photothermal interference, it is characterized in that: include carrier wave laser, the front light path of carrier wave laser is equipped with beam splitter, the incident light of carrier wave laser is divided into two-beam through beam splitter, the front light path of two-beam is disposed with optoisolator respectively, optical circulator, optical collimator, two optical collimators are positioned at the front end of detection cell, the rear end of detection cell is provided with high reflective mirror, reflection and transmission is there is respectively in two-beam at collimating apparatus end face, reflected light returns along former road, reflect former road by high reflective mirror after the detected sample gas zones of transmitted light after testing in pond to return, through after the detected sample gas in detection cell again through optical collimator end face, the reflected light of this transmitted light and optical collimator end face forms interference light, two-way interference light enters photodetector by optical circulator, wherein a road interfering beam detects baseline wander as baseline correction light path, another road interfering beam detects the phase place change summation that the gentle gel absorption exciting laser of baseline wander causes, described exciting laser is the light modulated away from interference light wavelength that signal generator produces, on the basis of interfering amplification factor to be demarcated, realize the on-line checkingi of gasoloid absorption coefficient.
2. the absorption coefficient of atmospheric aerosol Novel differential measurement method of coaxial-type photothermal interference according to claim 1, it is characterized in that: described exciting laser front light path is provided with light splitting piece, the reflected light path of light splitting piece is provided with light power meter, the transmitted light path of light splitting piece is provided with light reflection mirror one, the reflected light path of light reflection mirror one is provided with light reflection mirror two, light reflection mirror one, light reflection mirror two are located on the optical interference circuit of a wherein road interfering beam in detection cell respectively, described exciting laser in detection cell and detection optical interference circuit to interact a segment distance.
3. the absorption coefficient of atmospheric aerosol Novel differential measurement method of coaxial-type photothermal interference according to claim 1, is characterized in that: described detection cell and optical interference circuit are fixed on the as far as possible large fixed support of counterweight.
4. the absorption coefficient of atmospheric aerosol Novel differential measurement method of coaxial-type photothermal interference according to claim 1, it is characterized in that: described sample gas enters detection cell by the hybrid chamber of gas compounding system, the carrier gas of described gas compounding system comprises pure nitrogen and pretreated air, can prepare sample gas and the air direct injected of different moisture content.
5. the absorption coefficient of atmospheric aerosol Novel differential measurement method of coaxial-type photothermal interference according to claim 1, it is characterized in that: the described optical interference circuit through detection cell is coaxially reverse, therefore the interaction distance of exciting laser and detection optical interference circuit is that exciting laser institute covers 2 times that detect optical interference circuit length.
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