CN104596987A - Mid-infrared spectroscopy-based trace gas detection method and device combining long-optical-path open light path with wavelength modulation technique - Google Patents
Mid-infrared spectroscopy-based trace gas detection method and device combining long-optical-path open light path with wavelength modulation technique Download PDFInfo
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Abstract
The invention discloses mid-infrared spectroscopy-based trace gas detection method and device combining a long-optical-path open light path with a wavelength modulation technique. The detection device mainly consists of a continuous wave quantum cascade laser (CW-QCL), a laser driving and controlling unit, a plane mirror, a beam splitter, a visible laser, a reference gas pool, mercury, tellurium and cadmium (MCT) detector, an off-axis parabolic mirror, a corner reflector, a digital lock-in-amplifier and a computer. By using the CW-QCL as a light source, long-optical-path open light path is combined with the wavelength modulation technique to detect multi-component trace gas with high sensitivity.
Description
Technical field
The invention belongs to environmental science and field of spectroscopy, be specifically related to a kind of based on mid-infrared spectral Long open path in conjunction with the trace gas detection method of wavelength-modulation technique and device, can realize measuring polycomponent atmospheric trace gas real-time continuously.
Background technology
Trace gas detection plays key effect in a lot of field, such as environmental monitoring, climatic study, industrial stokehold, agricultural, food industry, volcanology, medical diagnosis and national security.At present to have developed polytype, based on the gas detecting instrument of different detection principle, such as gas chromatograph, mass spectrometer, chemiluminescent analyzer, electrochemical sensor etc.In recent years, the application carrying out trace gas detection based on laser spectrum tech more and more comes more extensive, because this technology can realize high sensitivity (detection limit is low to moderate sub-ppb concentration), high selectivity (can distinguish isotope and isomerism molecule), multicomponent are measured, and without the need to sample preparation and pre-concentration process simultaneously.But LASER Light Source feature comprises radiation wavelength, tuning range, live width, power and working temperature etc., and suitable detecting strategy is vital to the detection successfully realizing trace gas.
At present, tunable near-infrared laser light source is widely used for detection and the Leakage inspection of multiple trace gas in air.It combines with the multi-channel gas absorption cell of low pressure usually, realizes the highly sensitive detection to tested gas.Near-infrared band is attractive to detection at the gas molecule of ppm magnitude or higher concentration, but near-infrared band covers the general frequency of molecule or sum of fundamental frequencies absorbs, its absorption intensity usually than in infrared fundamental frequency absorb a weak 1-2 order of magnitude.And, the method of multi-channel gas absorption cell is adopted to need extracting gases, easy introducing measuring error, and acquisition is sampling point information, point is measured can not represent large area of space exactly, and especially in the poor air of mixing, and Long open path system obtains is the average information of whole measured zone air, insensitive to the fluctuation of local, the region be also applicable to bad environments, should not sampling.
The fundamental frequency that middle-infrared band covers a large amount of trace gas absorbs, and quantum cascade laser (QCL) is one of desirable mid-infrared light source of development in recent years, and it has, and tuning range is wide, output power is high, can the feature such as working and room temperature.Compared with near-infrared laser instrument, another advantage based on the open light path surveying instrument of QCL is that middle-infrared band penetrates the ability of smog and dust by force, affects little by gasoloid in air.But work in open atmosphere, the difficulty of detection mainly comes from the Absorption Line broadening and atmospheric turbulence that atmospheric pressure causes.Line broadening reduces the contrast of Absorption Line, reduces the sensitivity of measurement.The sensitivity reduced is compensated by long light path in some degree, but the maximum length of light path is subject to the restriction of atmospheric attenuation and turbulent flow.Because QCL exports the power high (usual tens mW) of light, the decay of several kilometers of distances is no longer a serious problem.But atmospheric turbulence causes detectable signal amplitude random variation, when scan time of single spectrum line compared with the characteristic time of turbulent flow processes quite or longer time, atmospheric turbulence can make detectable signal obviously distort.And adopting wavelength rapid scanning can make measure spectrum not by the impact of atmospheric turbulence, this is necessary to the measurement of Long open path.In addition, adopt QCL to be that to export the angle of divergence of light large as the shortcoming of light source, light beam will through hundreds of the rice even long light path of several kilometers, and light beam needs to expand to reduce the angle of divergence.
Based on middle infrared spectrum and a set of Long open path measurement mechanism of tunable diode laser absorption spectroscopy (TDLAS) Integration ofTechnology, the highly sensitive detection to polycomponent trace gas can be realized, have the advantages that the response time is fast, detection sensitivity is high, the defect of existing trace gas detection method and device can be made up.
Summary of the invention
The object of this invention is to provide a kind of based on mid-infrared spectral Long open path in conjunction with the trace gas detection method of wavelength-modulation technique and device, using continuous wave quantum cascade laser (CW-QCL) as light source, long light path and wavelength-modulation technique combine and reduce detection detectability, improve detection sensitivity; Adopt wavelength rapid scanning, eliminate the impact that atmospheric turbulence splits road detectable signal of giving out light.Be integrated with a set of Long open path pick-up unit based on CW-QCL, change the laser instrument that centre wavelength is different, the measurement of different trace gas molecules can be switched, make up the deficiency of existing trace gas detection method and device, provide a kind of fast, represent large, the highly sensitive polycomponent trace gas detection method in region and device.
Technical scheme of the present invention is as follows: a kind of based on the trace gas detection method of mid-infrared spectral Long open path in conjunction with wavelength-modulation technique, it specifically comprises the following steps:
Using the continuous wave quantum cascade laser at room temperature worked as light source, quantum cascade laser works under laser instrument drives the control with control module; The beam splitter front light path of quantum cascade laser setting gradually plane mirror and infrared transmission is 8:2 with reflected energy ratio and is all-trans to visible ray, the effect of plane mirror regulates infrared beam, the light beam that quantum cascade laser is sent is all adjustable on direction up and down, obtains larger range of adjustment with this; The mid-infrared light bundle that quantum cascade laser sends is invisible, and conveniently optical path adjusting arranges the visible laser of an outgoing ruddiness, and its ruddiness sent is through the coupling infra-red light of beam splitter reflection with beam splitter transmission; The front light path of the infrared light of beam splitter reflection sets gradually plane mirror, reference gas pond and mercury-cadmium tellurid detector, the effect of plane mirror regulates the infrared beam of beam splitter reflection, make this light beam all adjustable on direction up and down, the effect in reference gas pond is filled with calibrating gas to carry out the sampling of reference signal and the demarcation of concentration, the signal of outgoing behind mercury-cadmium tellurid detector detection reference gas pond; Then off axis paraboloidal mirror and off axis paraboloidal mirror are set in the front of beam splitter transmitted light path, off axis paraboloidal mirror and off axis paraboloidal mirror are installed in about one, on support that five dimensions such as all around and pitching are adjustable, make the light beam after infrared light and ruddiness coupling can realize expanding, reduce beam divergence angle; The infrared light expanded after off axis paraboloidal mirror and off axis paraboloidal mirror and ruddiness coupled light beam are successively by plane mirror and plane mirror, plane mirror and plane mirror coordinate adjustment in order to change beam exit direction, make coupled light beam all adjustable on direction up and down, obtain larger range of adjustment with this; Coupled light beam after plane mirror and plane mirror enters in open atmosphere through the central through hole of off axis paraboloidal mirror, through about 400m light path angle of arrival reverberator, after corner reflector reflection, the former road of light beam returns, and focuses on mercury-cadmium tellurid detector by off axis paraboloidal mirror; The reference signal that mercury-cadmium tellurid detector and mercury-cadmium tellurid detector detect respectively and open optical path signal are all through digital lock-in amplifier, be demodulated into second harmonic signal, these second harmonic signals are by the high-speed data acquisition card collection in computing machine and carry out retrieving concentration by the program based on Labview.
Spectral line characteristic for gas to be measured chooses suitable gaseous absorption line, drive at the electric current of quantum cascade laser and load sawtooth scan signal and high frequency sinusoidal modulation signal, sawtooth scan signal is the output wavelength changing laser instrument, and high frequency sinusoidal modulation signal is used to the harmonic detecting realizing lock-in amplifier; The setting of sweep signal frequency will make the scan period be less than the characteristic time of atmospheric turbulence, realizes wavelength rapid scanning; By the target absorption line regulating the temperature parameter of loading current and temperature controller to make the scanned selection of the centre wavelength of laser instrument; When quantum cascade laser working temperature is certain, the wavelength tuning range that the one-period of sawtooth scan signal is corresponding can reach 1cm
-1above, if the position of the Absorption Line of two different moleculars can be scanned within this scan period, can realize measuring while these two kinds of gas molecules;
Be filled with the normal concentration sample gas of gas to be measured to reference gas pond, obtain second harmonic signal and the 2f signal of the calibrating gas of gas to be measured, then background deduction and light intensity normalized are carried out to this reference signal;
The second harmonic signal of the open light path of continuous acquisition, utilizes the reference signal measured to carry out multilinear fitting to the open light path 2f signal after light intensity normalized, obtains the concentration value of gas to be measured.
The present invention provides a kind of based on the trace gas sniffer of mid-infrared spectral Long open path in conjunction with wavelength-modulation technique in addition, comprise continuous wave quantum cascade laser, laser instrument drives and control module, plane mirror, beam splitter, visible laser, plane mirror, reference gas pond, mercury-cadmium tellurid detector, off axis paraboloidal mirror, off axis paraboloidal mirror, plane mirror, plane mirror, off axis paraboloidal mirror, corner reflector, mercury-cadmium tellurid detector, digital lock-in amplifier and computing machine, described quantum cascade laser works under laser instrument drives the control with control module, the beam splitter front light path of described quantum cascade laser setting gradually plane mirror and infrared transmission is 8:2 with reflected energy ratio and is all-trans to visible ray, described visible laser is the He-Ne laser instrument of the 633nm of outgoing ruddiness, and the light beam that its ruddiness sent reflects through described beam splitter is coupled with the infrared beam of described beam splitter transmission, the front light path of the infrared light of described beam splitter reflection sets gradually plane mirror, reference gas pond and mercury-cadmium tellurid detector, the front of described beam splitter transmitted light path arranges off axis paraboloidal mirror and off axis paraboloidal mirror, the infrared light expanded after described off axis paraboloidal mirror and off axis paraboloidal mirror and ruddiness coupled light beam are successively by plane mirror and plane mirror, coupled light beam after described plane mirror and plane mirror enters in open atmosphere through the central through hole of off axis paraboloidal mirror, through about 400m light path angle of arrival reverberator, after described corner reflector reflection, the former road of light beam returns, and focuses on mercury-cadmium tellurid detector by described off axis paraboloidal mirror, the signal of described mercury-cadmium tellurid detector and the detection of described mercury-cadmium tellurid detector is all through digital lock-in amplifier, be demodulated into second harmonic signal, these second harmonic signals are by the high-speed data acquisition card collection in computing machine and carry out retrieving concentration by the program based on Labview.
The present invention's advantage is compared with prior art as follows:
(1) the present invention can realize in real time, online, monitoring is compared with the concentration change information of the trace gas within the scope of large regions continuously.
(2) the present invention can realize the highly sensitive detection to polycomponent trace gas, has the advantages that the response time is fast, detection sensitivity is high, detection accuracy is high, can make up the defect of existing trace gas detection method and device.
(3) the present invention can realize detecting while multicomponent gas, such as, while CH in measurement environment air
4and N
2the concentration of O.
Accompanying drawing explanation
Fig. 1 is structure principle chart of the present invention, and in figure, solid line represents light path, and dotted line represents electric signal transmission direction.
Fig. 2 is instance graph of the present invention, and wherein (a) is CH
4and N
2the second harmonic reference signal of O calibrating gas, (b) is the open light path CH to detection
4and N
2o second harmonic signal carries out the signal of multilinear fitting.
Embodiment
The present invention is further illustrated below in conjunction with accompanying drawing and specific embodiment.
As shown in Figure 1, of the present invention a kind of based on the trace gas sniffer of mid-infrared spectral Long open path in conjunction with wavelength-modulation technique, comprise quantum cascade laser 1 (QCL1), laser instrument drives and control module 2, plane mirror 3, beam splitter 4, visible laser 5, plane mirror 6, reference gas pond 7, mercury-cadmium tellurid detector 8 (MCT8), off axis paraboloidal mirror 9, off axis paraboloidal mirror 10, plane mirror 11, plane mirror 12, off axis paraboloidal mirror 13, corner reflector 14, mercury-cadmium tellurid detector 15 (MCT15), digital lock-in amplifier 16 and computing machine 17, using the continuous wave QCL1 at room temperature worked as light source, QCL1 works under laser instrument drives the control with control module 2, the plane mirror 3 that the front light path of QCL1 sets gradually gold-plated film and the beam splitter 4 that infrared transmission is 8:2 with reflected energy ratio and is all-trans to visible ray, regulate plane mirror 3, the infrared beam that QCL1 is sent is all adjustable on direction up and down, the mid-infrared light bundle that QCL1 sends is invisible, conveniently optical path adjusting, the He-Ne visible laser 5 of the 633nm of an outgoing ruddiness is set, regulate QCL1, plane mirror 3 and visible laser 5 that the visible red that the infrared light of beam splitter 4 transmission and beam splitter 4 reflect is coupled, in the coupling optical path adjustment of later step, visible red is as pilot light, the front light path of the infrared light that beam splitter 4 reflects sets gradually the plane mirror 6 of gold-plated film, reference gas pond 7 and mercury-cadmium tellurid detector 8 (MCT8) that length is 10cm, the infrared beam that adjustment plane mirror 6 makes beam splitter 4 reflect is by reference to gas cell 7, the effect in reference gas pond 7 is the calibrating gas being filled with the concentration known of gas to be measured when gathering reference signal and concentration calibration, and mercury-cadmium tellurid detector 8 (MCT8) detects the signal of transmission behind reference gas pond, focal length is set in the front of beam splitter 4 transmitted light path and is respectively the off axis paraboloidal mirror 9 of the gold-plated film of 50.8mm and 152mm and the off axis paraboloidal mirror 10 of gold-plated film, off axis paraboloidal mirror 9 and off axis paraboloidal mirror 10 are installed in about one, on support that five dimensions such as all around and pitching are adjustable, judge according to ruddiness hot spot, regulate off axis paraboloidal mirror 9 and off axis paraboloidal mirror 10 to make infrared light and ruddiness coupled light beam realize expanding, reduce beam divergence angle, the infrared light expanded after off axis paraboloidal mirror 9 and off axis paraboloidal mirror 10 and ruddiness coupled light beam are successively by the plane mirror 11 of gold-plated film and the plane mirror 12 of gold-plated film, plane mirror 11 and plane mirror 12 coordinate adjustment, in order to change beam exit direction, coupled light beam is made to enter in open atmosphere by the central through hole of the off axis paraboloidal mirror 13 of gold-plated film, the diameter of off axis paraboloidal mirror 13 is 101mm, is the through hole of 12mm with the diameter being parallel to collimated light beam, then light beam arrives through the open atmosphere of about 400m light path the hollow corner reflector 14 that clear aperature is 98mm, after corner reflector 14 reflects, the former road of light beam returns, focus on the mercury-cadmium tellurid detector 15 (MCT15) the same with mercury-cadmium tellurid detector 8 (MCT8) performance parameter by off axis paraboloidal mirror 13, whole light path reaches about 800m, the reference signal that mercury-cadmium tellurid detector 8 (MCT8) and mercury-cadmium tellurid detector 15 (MCT15) detect respectively and open optical path signal are all through digital lock-in amplifier 16, be demodulated into second harmonic signal, these second harmonic signals are by the high-speed data acquisition card collection in computing machine 17 and carry out concentration automatic inversion by the program based on Labview.
First the spectral line characteristic for gas to be measured chooses suitable gaseous absorption line, drive at the electric current of QCL1 and load sawtooth scan signal and high frequency sinusoidal modulation signal, sawtooth scan signal is the output wavelength changing laser instrument, and high frequency sinusoidal modulation signal is used to the harmonic detecting realizing lock-in amplifier; Sweep signal frequency f
1setting the scan period of signal will be made to be less than the characteristic time of atmospheric turbulence, realize wavelength rapid scanning, in order to eliminate measure in the impact of atmospheric turbulence; By the target absorption line regulating the temperature parameter of loading current and temperature controller to make the scanned selection of the centre wavelength of laser instrument; When QCL1 working temperature is certain, the wavelength tuning range that the one-period of sawtooth scan signal is corresponding can reach 1cm
-1above, if the position of the Absorption Line of two different moleculars can be scanned within this scan period, can realize measuring while these two kinds of gas molecules; Sinusoidal modulation signal is divided into two-way, and the loading current that a road is input to QCL1 is modulated, and an other road is as the reference signal of digital lock-in amplifier 16.
Then the standard sample gas of the concentration known of gas to be measured is filled with to reference gas pond 7, regulate the modulation parameter of digital lock-in amplifier 16, obtain the second harmonic signal (2f signal) of gas standard gas to be measured, then background deduction and light intensity normalized are carried out, with the reference 2f signal after the high-speed data acquisition card acquisition process in computing machine 17 with reference to 2f signal to this.
Gather the second harmonic signal of open light path, the 2f signal splitting road of giving out light carries out light intensity normalized, the open light path 2f signal of reference 2f signal to process that utilization is measured above carries out multilinear fitting, obtain the concentration value of gas to be measured, whole data acquisition and retrieving concentration process have the program based on Labview automatically to realize; Repeat above step, realize continuous signal collection and retrieving concentration.
The basis of carrying out gas concentration inverting based on multilinear fitting is: in the second-harmonic detection of gas absorption weak (product of gas molecules sorb coefficient and absorption light path is much smaller than 1), second harmonic signal and initial beam intensity I
0, light path l and absorb gas concentration c between pass be:
I
2f∝I
0cl
Select the QCL1 of proper operation parameter, can detect two kinds of gases simultaneously, in the one-period interscan of sweep signal to the Absorption Line of two gas molecules, this needs the cross jamming of consideration two Absorption Lines, the basis of eliminating two gas cross interference thinks that the 2f signal of open light path is the linear superposition of the 2f signal of two gases to be measured, obtains thus:
Here c
1and c
2represent the concentration of two kinds of gases to be measured of open atmosphere respectively, c
1rand c
2rthe concentration of reference path two kinds of calibrating gas respectively, I
2f-openand I
0-open2f signal and the initialize signal of the open light path measured respectively, I
2f-1rand I
0-1r2f signal and the initialize signal of the reference path of the first gas to be measured respectively, I
2f-2rand I
0-2r2f signal and the initialize signal of the reference path of the second gas to be measured respectively, L
openand l
roptical path length corresponding to open light path and reference path respectively.
In order to continuous coverage exactly, often spend 2 hours, need to demarcate the inverting of gas concentration: the calibrating gas passing into variable concentrations in reference cell, measure the concentration of these calibrating gas, find out the relation curve of measured value and given value according to these measurement concentration values and concentration known value, then according to this relation, the gas concentration value measured is revised.
In a word, the present invention combines the measurement TDLAS technology of trace gas concentration and the wavelength-modulation technique technology of Testing of Feeble Signals, have developed a set of based on middle infrared spectrum long light path multicomponent gas sniffer, can realize CH in large regions ambient atmosphere
4, N
2the monitoring of the high sensitivity of the trace gas concentration such as O, CO, high precision, real-time online.Utilize trace gas detection system of the present invention effectively can make up the defect of conventional measurement techniques.
Non-elaborated part of the present invention belongs to the known technology of those skilled in the art.
The above; be only the embodiment in the present invention; but protection scope of the present invention is not limited thereto; any people being familiar with this technology is in the technical scope disclosed by the present invention; the conversion or replacement expected can be understood; all should be encompassed in and of the present inventionly comprise within scope, therefore, protection scope of the present invention should be as the criterion with the protection domain of claims.
Claims (10)
1., based on the trace gas detection method of mid-infrared spectral Long open path in conjunction with wavelength-modulation technique, it is characterized in that: it specifically comprises the following steps:
Using the continuous wave quantum cascade laser (1) at room temperature worked as light source, quantum cascade laser (1) works under laser instrument drives the control with control module (2); The beam splitter (4) the front light path of quantum cascade laser (1) setting gradually plane mirror (3) and infrared transmission is 8:2 with reflected energy ratio and is all-trans to visible ray, the effect of plane mirror (3) regulates infrared beam, the light beam that quantum cascade laser (1) is sent is all adjustable on direction up and down, obtains larger range of adjustment with this; The mid-infrared light bundle that quantum cascade laser (1) sends is invisible, conveniently optical path adjusting, arrange the visible laser (5) of an outgoing ruddiness, its ruddiness sent is through the coupling infra-red light of beam splitter (4) reflection with beam splitter (4) transmission; The front light path of the infrared light that beam splitter (4) reflects sets gradually plane mirror (6), reference gas pond (7) and mercury-cadmium tellurid detector (8), the effect of plane mirror (6) regulates the infrared beam that beam splitter (4) reflects, make this light beam all adjustable on direction up and down, the effect in reference gas pond (7) is filled with calibrating gas to carry out the sampling of reference signal and the demarcation of concentration, the signal of outgoing behind mercury-cadmium tellurid detector (8) detection reference gas pond; Then off axis paraboloidal mirror (9) and off axis paraboloidal mirror (10) are set in the front of beam splitter (4) transmitted light path, off axis paraboloidal mirror (9) and off axis paraboloidal mirror (10) are installed in about one, on support that five dimensions such as all around and pitching are adjustable, make the light beam after infrared light and ruddiness coupling can realize expanding, reduce beam divergence angle; The infrared light expanded after off axis paraboloidal mirror (9) and off axis paraboloidal mirror (10) and ruddiness coupled light beam are successively by plane mirror (11) and plane mirror (12), plane mirror (11) and plane mirror (12) coordinate adjustment in order to change beam exit direction, make coupled light beam all adjustable on direction up and down, obtain larger range of adjustment with this; Coupled light beam after plane mirror (11) and plane mirror (12) enters in open atmosphere through the central through hole of off axis paraboloidal mirror (13), through about 400m light path angle of arrival reverberator (14), after corner reflector (14) reflection, the former road of light beam returns, and focuses on mercury-cadmium tellurid detector (15) by off axis paraboloidal mirror (13); The reference signal that mercury-cadmium tellurid detector (8) and mercury-cadmium tellurid detector (15) detect respectively and open optical path signal are all through digital lock-in amplifier (16), be demodulated into second harmonic signal, these second harmonic signals are by the high-speed data acquisition card collection in computing machine (17) and carry out retrieving concentration by the program based on Labview;
Spectral line characteristic for gas to be measured chooses suitable gaseous absorption line, upper loading sawtooth scan signal and high frequency sinusoidal modulation signal is driven at the electric current of quantum cascade laser (1), sawtooth scan signal is the output wavelength changing laser instrument, and high frequency sinusoidal modulation signal is used to the harmonic detecting realizing lock-in amplifier; The setting of sweep signal frequency will make the scan period be less than the characteristic time of atmospheric turbulence, realizes wavelength rapid scanning; By the target absorption line regulating loading current and working temperature to make the centre wavelength scanning selection of laser instrument; When quantum cascade laser (1) working temperature is certain, the wavelength tuning range that the one-period of sawtooth scan signal is corresponding can reach 1cm
-1above, if the position of the Absorption Line of two different moleculars can be scanned within this scan period, can realize measuring while these two kinds of gas molecules;
Be filled with the normal concentration sample gas of gas to be measured to reference gas pond (7), obtain second harmonic signal and the 2f signal of the calibrating gas of gas to be measured, then background deduction and light intensity normalized are carried out to this reference signal;
The second harmonic signal of the open light path of continuous acquisition, utilizes the reference signal measured to carry out multilinear fitting to the open light path 2f signal after light intensity normalized, obtains the concentration value of gas to be measured.
2., based on the trace gas sniffer of mid-infrared spectral Long open path in conjunction with wavelength-modulation technique, comprise continuous wave quantum cascade laser (1), laser instrument drives and control module (2), plane mirror (3), beam splitter (4), visible laser (5), plane mirror (6), reference gas pond (7), mercury-cadmium tellurid detector (8), off axis paraboloidal mirror (9), off axis paraboloidal mirror (10), plane mirror (11), plane mirror (12), off axis paraboloidal mirror (13), corner reflector (14), mercury-cadmium tellurid detector (15), digital lock-in amplifier (16) and computing machine (17), it is characterized in that: described quantum cascade laser (1) works under laser instrument drives the control with control module (2), the beam splitter (4) the front light path of described quantum cascade laser (1) setting gradually plane mirror (3) and infrared transmission is 8:2 with reflected energy ratio and is all-trans to visible ray, the He-Ne laser instrument that described visible laser (5) is the 633nm of outgoing ruddiness, the light beam that its ruddiness sent reflects through described beam splitter (4) is coupled with the infrared beam of described beam splitter (4) transmission, the front light path of the infrared light that described beam splitter (4) reflects sets gradually plane mirror (6), reference gas pond (7) and mercury-cadmium tellurid detector (8), the front of described beam splitter (4) transmitted light path arranges off axis paraboloidal mirror (9) and off axis paraboloidal mirror (10), the infrared light expanded after described off axis paraboloidal mirror (9) and off axis paraboloidal mirror (10) and ruddiness coupled light beam are successively by plane mirror (11) and plane mirror (12), coupled light beam after described plane mirror (11) and plane mirror (12) enters in open atmosphere through the central through hole of off axis paraboloidal mirror (13), through about 400m light path angle of arrival reverberator (14), after described corner reflector (14) reflection, the former road of light beam returns, and focuses on mercury-cadmium tellurid detector (15) by described off axis paraboloidal mirror (13), the signal that described mercury-cadmium tellurid detector (8) and described mercury-cadmium tellurid detector (15) detect is all through digital lock-in amplifier (16), be demodulated into second harmonic signal, these second harmonic signals are by the high-speed data acquisition card collection in computing machine (17) and carry out retrieving concentration by the program based on Labview.
3. according to claim 2 based on the trace gas sniffer of mid-infrared spectral Long open path in conjunction with wavelength-modulation technique, it is characterized in that: described quantum cascade laser (1) is the semiconductor laser of radiation wavelength in middle-infrared band, belong to distributed feedback continuous wave laser, at room temperature work, do not need liquid nitrogen refrigerating, output power 20mW.
4. according to claim 2 based on the trace gas sniffer of mid-infrared spectral Long open path in conjunction with wavelength-modulation technique, it is characterized in that: described plane mirror (3), plane mirror (6) and plane mirror (11) and plane mirror (12) all surface gold-plating films, to infrared reflectivity more than 95%, to visible reflectance more than 80%.
5. according to claim 2 based on the trace gas sniffer of mid-infrared spectral Long open path in conjunction with wavelength-modulation technique, it is characterized in that: described beam splitter (4) is the beam splitter being 8:2 to infrared transmission with reflected energy ratio and being all-trans to visible red.
6. according to claim 2 based on the trace gas sniffer of mid-infrared spectral Long open path in conjunction with wavelength-modulation technique, it is characterized in that: the He-Ne laser instrument of described visible laser (5) to be radiation wavelength be 633nm, output power 30mW.
7. according to claim 2 based on the trace gas sniffer of mid-infrared spectral Long open path in conjunction with wavelength-modulation technique, it is characterized in that: described mercury-cadmium tellurid detector (8) and mercury-cadmium tellurid detector (15) have same running parameter, are all response spectrum scopes be 2-12um, effective detectivity is greater than 10
9cmHz
1/2the infrared photovoltaic type detector of/W, thermoelectric cooling, does not need liquid nitrogen refrigerating.
8. according to claim 2 based on the trace gas sniffer of mid-infrared spectral Long open path in conjunction with wavelength-modulation technique, it is characterized in that: described off axis paraboloidal mirror (9) and off axis paraboloidal mirror (10) focal length are respectively 50.8mm and 152mm, surface gold-plating film.
9. according to claim 2 based on the trace gas sniffer of mid-infrared spectral Long open path in conjunction with wavelength-modulation technique, it is characterized in that: the diameter of described off axis paraboloidal mirror (13) is 101mm, is the through hole of 12mm with the diameter being parallel to collimated light beam.
10. according to claim 2 based on the trace gas sniffer of mid-infrared spectral Long open path in conjunction with wavelength-modulation technique, it is characterized in that: the hollow corner reflector that described corner reflector (14) is clear aperature 98mm; Described high-speed data acquisition card is 2 passages, and sampling rate is 20M/s.
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