CN204924934U - Multicomponent gas is detection device simultaneously based on two kinds of quantum cascade laser spectrum - Google Patents
Multicomponent gas is detection device simultaneously based on two kinds of quantum cascade laser spectrum Download PDFInfo
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- CN204924934U CN204924934U CN201520638006.1U CN201520638006U CN204924934U CN 204924934 U CN204924934 U CN 204924934U CN 201520638006 U CN201520638006 U CN 201520638006U CN 204924934 U CN204924934 U CN 204924934U
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Abstract
The utility model relates to a laser spectrum detects gentle physical examination and surveys technical field, specifically is multicomponent gas is detection device simultaneously based on two kinds of quantum cascade laser spectrum. Arbitrary ripples function generator exports the current drive signal of high -frequency modulation signal sexual periodicity signal as the laser instrument that only superpose in the arbitrary half -period, it drives to cascade the laser instrument through the current control unit to room temperature modulus of continuity wherein infrared quantum, the laser instrument sends the laser signal, in proper order through the three -dimensional governing system of focus collimation, first speculum, sample absorption cell and off axis paraboloidal mirror back reflection arrive first detector, first detector turns into the signal of telecommunication after through the data acquisition unit with the laser signal and the computer is given in the transmission, the computer carries out analysis processes to the signal of telecommunication and reachs the gaseous information that awaits measuring. The utility model discloses utilizing two kinds of spectrum methods to detect gas simultaneously, having the detection sensitivity height, measurement accuracy is high, need not outer land mark gas and proofreaies and correct, and the light path is adjusted portably, and the response soon and advantage such as system stability height.
Description
Technical field
The utility model relates to laser spectrum and detects and gas detection technology field, is specially a kind of multicomponent gas based on the sub-cascade laser spectrum of two amounts pick-up unit simultaneously.
Background technology
Traditional gas componant detection method mainly contains chemical method and optical means.Chemical method needs to carry out pre-service to analysans usually, and process is complicated, consuming time, the previous status of destructible sample and generation secondary pollution; It is strong and respond the advantages such as fast that optical spectroscopic method has untouchable, non-demolition, selectivity, the continuous analysis of real-time in-situ can be realized, make it be widely used in the fields such as atmosphere environment supervision, industrial treatment control, combusting component detection and breath diagnosis.
Conventional optical spectroscopic method has direct absorption spectroscopy and frequency-modulated spectroscopy.Direct absorption spectroscopy is a kind of direct detecting method based on Lambert-Beer's law, the method is by analyzing the faint variable quantity of light intensity, the information such as the concentration of detected sample, speed, temperature can be finally inversed by, but there is the shortcomings such as be subject to various electronics and optical noise is disturbed, sensitivity is limited.Wavelength modulation spectroscopy is in conjunction with phase lock-in detecting principle, realizes the high sensitivity Indirect Detecting Method of restraint speckle, but needs to be corrected rear (gas correction) by concentration known sample, could obtain the concentration information of other unknown samples, comparatively complicated.
Middle infrared spectral region (2.5-25 μm) contains the Base Band of majority of gas molecule vibrational-rotational level, becomes the desirable wave band of high sensitivity Trace gas detection.Quantum cascade laser (QCL) is as a kind of novel semiconductor laser, have that volume is little, the life-span long, low in energy consumption, line width, power are relatively high and be easy to integrated feature, the perfect light source of infrared trace-gas sensors research in becoming.The wide wavelength tuning range of QCL and fast response characteristic can realize high resolving power, high-sensitivity detection while multiple gases molecule.Could realize compared to traditional LTS laser time sharing multiplexed detection technology based on multiple near infrared laser Time share scanning the method that multiple gases analyzes simultaneously, system is compacter, and effective measuring period is higher.
In existing research, utilization qc laser is as light source, the direct absorption spectroscopy of independent employing or frequency-modulated spectroscopy carry out gas detect and all obtain practical application, as: China Patent Publication No. is respectively the patent of invention of CN102175641A and CN104596987A.The former discloses a kind of trace gas detection device based on intermediate infrared quantum cascade laser direct absorption spectrum and method, the method utilizes pulsed quantum cascade laser as light source,, there is the shortcomings such as be subject to various electronics and optical noise interference, limited, the gas concentration inversion method reliability of sensitivity and measuring accuracy be low in the direct absorption spectroscopy of independent employing; Latter discloses 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, the method utilizes continuous quantity qc laser as light source, independent employing frequency-modulated spectroscopy, the extra gas of existence needs frequently corrects, high pressure downforce adds the shortcomings such as broad effect desensitization and reliability.
In practical application, above-mentioned two kinds of classic methods are all not ideal enough.The utility model is intended adopting and is utilized direct absorption spectroscopy and frequency-modulated spectroscopy to detect gas simultaneously, this kind of method can overcome defect existing when only adopting a kind of spectrographic technique to carry out gas detect, up to the present, not yet find any about adopting above-mentioned two kinds of researchs detected single component gas or multicomponent gas based on quanta cascade laser spectrum method simultaneously.
Utility model content
For the problems of the prior art, the utility model provides a kind of using INFRARED QUANTUM CASCADE LASERS in the continuous mode of room temperature operation as light source, utilize direct absorption spectroscopy and frequency-modulated spectroscopy, without the need to extraneous gas correction, high sensitivity, high-precision gas-detecting device simultaneously.
For realizing above technical purpose, the technical solution of the utility model is:
Based on the multicomponent gas pick-up unit simultaneously of the sub-cascade laser spectrum of two amounts, comprise INFRARED QUANTUM CASCADE LASERS in any wave function generator, room temperature continuous mode, focussed collimated three-dimensional regulation system, the first catoptron, absorption of sample pond, off axis paraboloidal mirror, the first detector, data acquisition unit and computing machine, in described room temperature continuous mode, INFRARED QUANTUM CASCADE LASERS has temperature control unit and current control unit;
Described any wave function generator exports the current drive signal of cyclical signal as INFRARED QUANTUM CASCADE LASERS in room temperature continuous mode of only superposition modulated signal within any semiperiod, and described current drive signal is driven the Injection Current of INFRARED QUANTUM CASCADE LASERS in room temperature continuous mode by current control unit;
In described room temperature continuous mode, INFRARED QUANTUM CASCADE LASERS sends laser signal as light source;
Described focussed collimated three-dimensional regulation system carries out focussed collimated to laser signal;
Laser signal after focussed collimated is coupled to absorption of sample pond by described first catoptron;
Described absorption of sample pond is filled with gas to be measured, described laser signal in absorption of sample pond by gas molecules sorb after shine off axis paraboloidal mirror;
Laser signal is gathered the first detector by described off axis paraboloidal mirror;
The laser signal received is converted into electric signal by data acquisition unit and is transferred to computing machine by described first detector;
Described computing machine carries out analyzing and processing to electric signal and draws gas information to be measured.
During work, any wave function generator exports the current drive signal of cyclical signal as laser instrument of only superposition modulated signal within any semiperiod, by current control unit, the Injection Current of INFRARED QUANTUM CASCADE LASERS in room temperature continuous mode is driven, laser instrument sends the laser signal of certain frequency scope, then absorption of sample pond is coupled into by the first catoptron after laser signal line focus collimation three-dimensional regulation system focussed collimated, laser signal in absorption of sample pond by gas molecules sorb after shine off axis paraboloidal mirror, off axis paraboloidal mirror is gathered on the first detector, then after light signal is changed into electric signal by data acquisition unit, be transferred to computing machine carry out analyzing and processing, computing machine is to carrying out direct absorption spectroanalysis not with modulation signal, to carrying out Wavelength modulation spectroscopy analysis with modulation signal.
As can be seen from foregoing description, the technical program has the following advantages:
(1) arbitrarily wave function generator export only within any semiperiod the cyclical signal of superposition modulated signal can not only meet the demand simultaneously realizing direct absorption spectroscopy and frequency-modulated spectroscopy, and modulation signal wherein can make the index of modulation optimization respectively of different molecular, realize optimization and detect each molecule, thus improve system sensitivity; By reducing sampled pressure, avoiding high pressure downforce and adding the molecule self or intermolecular absorption disturbing effect that broad effect causes, improve the reliability of systematic survey.
(2) the gas information of the direct absorption spectrum inverting of high s/n ratio is utilized, for the Wavelength modulation spectroscopy analytical gas information process based on Labview digital servo-control provides correction, namely other sample concentration information to be analyzed is finally inversed by more accurately by Wavelength modulation spectroscopy after correction, two kinds of spectrographic techniques are learnt from other's strong points to offset one's weaknesses, and realize highly sensitive and high-precision gas analysis.
(3) directly absorption spectrum analyzing method absorbs the method for Depth Inverse gas concentration information compared to traditional absorption line center position that only utilizes, little by noise, inversion algorithm reliability and degree of accuracy higher; Wavelength modulation spectroscopy analytical approach utilizes multiple linear regression analysis algorithm to carry out inverting to the sample message of unknown concentration, carry out compared with correction with only utilizing single peak value size in second harmonic signal in conventional correction methods, be not subject to the impact of various noise, measuring error is little.
As improvement, also comprise instruction light source, the second catoptron and half-reflecting half mirror, described half-reflecting half mirror is located between focussed collimated three-dimensional regulation system and the first catoptron, described instruction light source produces visible light signal, visible light signal is reflexed to half-reflecting half mirror by described second catoptron, and visible light signal reflects by described half-reflecting half mirror again and the laser signal that itself and INFRARED QUANTUM CASCADE LASERS in the room temperature continuous mode of coming through half-reflecting half mirror transmission are sent is coaxial;
The pilot light of the laser signal utilizing visible ray to export as INFRARED QUANTUM CASCADE LASERS in sightless room temperature continuous mode, the position in the first catoptron and absorption of sample pond is regulated according to pilot light hot spot distribution character of minute surface in absorption of sample pond, hot spot is distributed more much more even, namely order of reflection is higher, and coupling efficiency is higher, thus obtains most high coupling efficiency, when coupling efficiency is higher, effective light path is longer, and interference of light noise is lower, measurement sensistivity and measuring accuracy higher.
As improvement, also comprise beam splitter, with reference to absorption cell and the second detector, described beam splitter is located between focussed collimated three-dimensional regulation system and the first catoptron, for by the laser signal beam splitting after focussed collimated three-dimensional regulation system focussed collimated, part laser signal enters with reference to absorption cell through beam splitter reflection, another part laser signal is transmitted to the first catoptron through beam splitter, described reference absorption cell is single-pass absorption cell and is filled with pure gas to be measured, the described laser signal entered with reference to absorption cell is shone the second detector after gas molecules sorb, the laser signal received is converted into electric signal by data acquisition unit and is transferred to computing machine by described second detector, described computing machine carries out analyzing and processing to electric signal and draws the central frequency deviation information of INFRARED QUANTUM CASCADE LASERS in room temperature continuous mode and fed back to current control unit, described current control unit is according to the central frequency deviation information received, carry out current compensation, stablize the centre frequency of INFRARED QUANTUM CASCADE LASERS in room temperature continuous mode,
Utilize the central frequency deviation information obtaining INFRARED QUANTUM CASCADE LASERS in room temperature continuous mode with reference to absorption cell light path, the bias current of INFRARED QUANTUM CASCADE LASERS in room temperature continuous mode is adjusted in real time according to central frequency deviation information, realize the real-time lock to laser center wavelength, improve pick-up unit stability and measuring accuracy.
As improvement, also comprise beam splitter, etalon and the second detector, described beam splitter is located between focussed collimated three-dimensional regulation system and the first catoptron, for by the laser signal beam splitting after focussed collimated three-dimensional regulation system focussed collimated, part laser signal is through beam splitter reflection Engage of standard tool, another part laser signal is transmitted to the first catoptron through beam splitter, the laser signal of described Engage of standard tool shines the second detector after producing in etalon and interfering, the laser signal received is converted into electric signal by data acquisition unit and is transferred to computing machine by described second detector, described computing machine carries out to the electric signal received the relative wavelength tuning range that analyzing and processing draws INFRARED QUANTUM CASCADE LASERS in room temperature continuous mode.
Etalon optical circuit is utilized to obtain the relative wavelength tuning range of INFRARED QUANTUM CASCADE LASERS in room temperature continuous mode, again in conjunction with the molecule line parameter provided in HITRAN spectra database, realize the Absolute Calibration to INFRARED QUANTUM CASCADE LASERS wavelength tuning range in room temperature continuous mode, thus improve measuring accuracy.
As the improvement had with reference to absorption cell light path or etalon optical circuit, also comprise instruction light source, the second catoptron, described instruction light source produces visible light signal, visible light signal is reflexed to beam splitter by described second catoptron, and visible light signal reflects by described beam splitter again and the laser signal that itself and INFRARED QUANTUM CASCADE LASERS in the room temperature continuous mode of coming through beam splitter transmission are sent is coaxial;
The pilot light of the laser signal utilizing visible ray to export as INFRARED QUANTUM CASCADE LASERS in sightless room temperature continuous mode, the position in the first catoptron and absorption of sample pond is regulated according to pilot light hot spot distribution character of minute surface in absorption of sample pond, hot spot is distributed more much more even, namely order of reflection is higher, and coupling efficiency is higher, thus obtains most high coupling efficiency, when coupling efficiency is higher, effective light path is longer, and interference of light noise is lower, measurement sensistivity and measuring accuracy higher.
As preferably, described focussed collimated three-dimensional regulation system is made up of two plane mirrors and an off axis paraboloidal mirror, and two catoptrons become 45 degree of placements, overall three-dimensional adjustable;
The off axis paraboloidal mirror of focussed collimated three-dimensional regulation system is utilized to be converged to by laser beam in first catoptron, by second catoptron, beam emissions is exported again, this system can realize three-dimensional carries out focussed collimated adjustment to the light beam that INFRARED QUANTUM CASCADE LASERS in room temperature continuous mode sends, and avoids feedback light to be coupled to INFRARED QUANTUM CASCADE LASERS in room temperature continuous mode and causes disturbing effect.
As preferably, described absorption of sample pond is the adjustable HERRIOTT type multiple reflectance cell based on two concave mirrors of effective light path;
Adopt the HERRIOTT type multiple reflectance cell based on two concave mirrors that effective light path is adjustable, according to the height of gas concentration to be measured in applied environment, effective total optical path can be selected.
As preferably, the cyclical signal that described any wave function generator produces is low frequency periodic triangular wave or sawtooth wave, and the modulation signal that cyclical signal only superposes within any semiperiod is high_frequency sine wave;
The slope conversion trend comparison of triangular wave is delayed, close with the electric current dependency characteristic of middle INFRARED QUANTUM CASCADE LASERS, sinusoidal wave as modulation signal, is convenient to signal receiving.
Accompanying drawing explanation
Fig. 1 is the structural representation of the utility model embodiment one;
Fig. 2 is the structural representation of the utility model embodiment two;
Fig. 3 is the structural representation of the utility model embodiment three;
Fig. 4 is the structural representation of the utility model embodiment four;
Fig. 5 is any wave function generator output waveform and the first detector output waveform contrast schematic diagram;
The contrast schematic diagram of the Wavelength modulation spectroscopy second harmonic signal that Fig. 6 is original direct absorption signal that in embodiment four, first detector exports, direct absorption spectrum after background normalization and Labview digital servo-control demodulate;
Reference numeral: 1. any wave function generator, 2. temperature control unit, 3. current control unit, 4. INFRARED QUANTUM CASCADE LASERS in room temperature continuous mode, 5. focussed collimated three-dimensional regulation system, 6. the first catoptron, 7. absorption of sample pond, 8. off axis paraboloidal mirror, 9. the first detector, 10. data acquisition unit, 11. computing machines, 12. beam splitters, 13. with reference to absorption cell, 14. second detectors, 15. instruction light sources, 16. second catoptrons, 17. half-reflecting half mirrors.
Embodiment
Composition graphs 1, describes first embodiment of the present utility model in detail, but does not do any restriction to claim of the present utility model.
As shown in Figure 1, based on the multicomponent gas pick-up unit simultaneously of the sub-cascade laser spectrum of two amounts, comprise INFRARED QUANTUM CASCADE LASERS 4 in any wave function generator 1, room temperature continuous mode, focussed collimated three-dimensional regulation system 5, first catoptron 6, absorption of sample pond 7, off axis paraboloidal mirror 8, first detector 9, data acquisition unit 10 and computing machine 11, in described room temperature continuous mode, INFRARED QUANTUM CASCADE LASERS 4 has temperature control unit 2 and current control unit 3.
During work, any wave function generator 1 exports the current drive signal of cyclical signal as INFRARED QUANTUM CASCADE LASERS 4 in room temperature continuous mode of only superposition modulated signal within any semiperiod, current drive signal is driven by INFRARED QUANTUM CASCADE LASERS 4 in current control unit 3 pairs of room temperature continuous modes, in room temperature continuous mode, INFRARED QUANTUM CASCADE LASERS 4 sends laser signal as light source, the first catoptron 6 is incided after laser signal line focus collimation three-dimensional regulation system 5 focussed collimated, laser signal is coupled to absorption of sample pond 7 by the first catoptron 6, absorption of sample pond 7 is filled with gas to be measured, laser signal in absorption of sample pond 7 by gas molecules sorb after shine off axis paraboloidal mirror 8, laser signal is gathered the first detector 9 by off axis paraboloidal mirror 8, the laser signal received is converted into electric signal by data acquisition unit 10 and is transferred to computing machine 11 by the first detector 9, computing machine 11 is to carrying out direct absorption spectroanalysis not with modulation signal in the electric signal received, to carrying out Wavelength modulation spectroscopy analysis with modulation signal.
Utilize any wave function generator 1 to export only within any semiperiod the cyclical signal of superposition modulated signal can not only meet the demand simultaneously realizing direct absorption spectroscopy and frequency-modulated spectroscopy, and modulation signal wherein can make the index of modulation optimization respectively of different molecular, realize optimization detection, thus improve system sensitivity; By reducing sampled pressure, avoiding high pressure downforce and adding the molecule self or intermolecular absorption disturbing effect that broad effect causes, improve the reliability of systematic survey.
Utilize the gas information that the direct absorption spectrum of high s/n ratio is finally inversed by, for the Wavelength modulation spectroscopy analytical gas information process based on Labview digital servo-control provides correction, namely other sample concentration information to be analyzed is finally inversed by more accurately by Wavelength modulation spectroscopy after correction, two kinds of spectrographic techniques are learnt from other's strong points to offset one's weaknesses, and realize highly sensitive and high-precision gas analysis.
Composition graphs 2, describes second embodiment of the present utility model in detail, but does not do any restriction to claim of the present utility model.
In order to improve detection system stability and measuring accuracy further, as shown in Figure 2, the basis of embodiment one increases with reference to absorption cell light path, specifically comprise beam splitter 12, with reference to absorption cell 13 and the second detector 14, pure gas to be measured is filled with reference to absorption cell 13, beam splitter 12 is arranged between dimension focussed collimated three-dimensional regulation system 5 and the first catoptron 6, by beam splitter 12, the laser signal after collimation is carried out beam splitting, a part reflexes to reference to absorption cell 13 through beam splitter 12, and a part is transmitted to the first catoptron 6 through beam splitter 12.
Reflex to the laser signal with reference to absorption cell 13, the second detector 14 is shone after pure gas absorption to be measured in referenced absorption cell 13, the laser signal received is converted into electric signal by data acquisition unit 10 and is transferred to computing machine 11 by the second detector 14, computing machine 11 pairs of electric signal carry out analyzing and processing and draw the central frequency deviation information of INFRARED QUANTUM CASCADE LASERS 4 in room temperature continuous mode and feed back to current control unit 3, current control unit 3 is according to central frequency deviation information, the bias current of INFRARED QUANTUM CASCADE LASERS 4 in room temperature continuous mode is adjusted in real time, realize the real-time lock to laser signal wavelength, thus improve detection system stability and measuring accuracy, its detailed process is utilize to be filled with the spectral signal that pure gas to be measured obtains high s/n ratio, analyze the change of absorption line center, the bias current of real-time adjustment amount qc laser also feeds back in its control module the real-time lock realized its wavelength, solve the problem of laser frequency drift, thus improve system stability and measuring accuracy, can be used for the normalized of quantum cascade laser light intensity with reference to absorption cell signal simultaneously.
Reference absorption cell 13 in such scheme also may instead be etalon, and the laser signal inciding etalon shines the second detector 14 after producing and interfering, the laser signal received is converted into electric signal by data acquisition unit 10 and is transferred to computing machine 11 by the second detector 14, computing machine 11 carries out to the electric signal received the relative wavelength tuning range that analyzing and processing draws INFRARED QUANTUM CASCADE LASERS 4 in room temperature continuous mode, realize the Absolute Calibration to INFRARED QUANTUM CASCADE LASERS 4 wavelength tuning range in room temperature continuous mode, thus raising measuring accuracy, its principle is the interference fringe information utilizing the laser signal of INFRARED QUANTUM CASCADE LASERS 4 in the Free Spectral Range of etalon and room temperature continuous mode to be produced by etalon, the relative Repeat realizing laser output wavelength corrects, again in conjunction with the molecule line parameter provided in HITRAN spectra database, the absolute range that can realize laser output wavelength corrects, thus direct for time domain absorption signal is transformed into frequency field, for the concentration information of direct absorption spectrum inverting testing sample.
Also can use with reference to absorption cell light path and etalon optical circuit simultaneously, not only solve the problem of laser frequency drift but also the wavelength tuning range of laser instrument is corrected, to obtain more accurate measurement result.
Composition graphs 3, describes the 3rd embodiment of the present utility model in detail, but does not do any restriction to claim of the present utility model.
In order to improve systematic survey sensitivity and the measuring accuracy of embodiment one further, as shown in Figure 3, in the basis of embodiment one upper increase pilot light light path, specifically comprise instruction light source 15, second catoptron 16 and half-reflecting half mirror 17, half-reflecting half mirror 17 is arranged between focussed collimated three-dimensional regulation system 5 and the first catoptron 6.
Instruction light source 15 produces visible light signal, visible light signal is reflexed to half-reflecting half mirror 17 by the second catoptron 16, visible light signal reflects and makes it coaxial with the laser signal of coming through half-reflecting half mirror 17 transmission by half-reflecting half mirror 17 again, the pilot light of the laser signal utilizing visible ray to export as INFRARED QUANTUM CASCADE LASERS 4 in sightless room temperature continuous mode, the position in the first catoptron 6 and absorption of sample pond 7 is regulated according to pilot light hot spot distribution character of minute surface in absorption of sample pond 7, hot spot is distributed more much more even, namely order of reflection is higher, coupling efficiency is higher, when coupling efficiency is higher, effective light path is longer, interference of light noise is lower, measurement sensistivity and measuring accuracy are also higher.
Composition graphs 4, describes the 4th embodiment of the present utility model in detail, but does not do any restriction to claim of the present utility model.
In order to improve systematic survey sensitivity and the measuring accuracy of embodiment two further, as shown in Figure 3, in the basis of embodiment two upper increase pilot light light path, specifically comprise instruction light source 15 and the second catoptron 16.
Instruction light source 15 produces visible light signal, visible light signal is reflexed to beam splitter 12 by the second catoptron 16, visible light signal reflects and makes it coaxial with the laser signal of coming through beam splitter 12 transmission by beam splitter 12 again, the pilot light of the laser signal utilizing visible ray to export as INFRARED QUANTUM CASCADE LASERS 4 in sightless room temperature continuous mode, the position in the first catoptron 6 and absorption of sample pond 7 is regulated according to pilot light hot spot distribution character of minute surface in absorption of sample pond 7, hot spot is distributed more much more even, namely order of reflection is higher, coupling efficiency is higher, when coupling efficiency is higher, effective light path is longer, interference of light noise is lower, measurement sensistivity and measuring accuracy are also higher.
In above-mentioned 4 embodiments:
1. arbitrarily cyclical signal be periodically low frequency triangular wave or sawtooth wave in the current drive signal that exports of wave function generator 1, and the modulation signal only superposed in any semiperiod of cyclical signal is high_frequency sine wave.Do not add the semiperiod of modulation signal for generation of direct absorbing laser spectral signal, for inverting gas concentration information, add the laser spectrum absorption signal of semiperiod for generation of band modulation of modulation signal, by based on Labview digital servo-control demodulation techniques, export the wavelength modulation signal of high s/n ratio, and the amplitude of sinusoidal modulation signal, frequency and phase place can distinguish optimization according to the absorption characteristic of different molecular, the optimization index of modulation is modulated amplitude (cm
-1) and molecular absorption line live width (cm
-1) ratio.
As shown in Figure 5, be the laser diode current drive signal waveform of any wave function generator 1 output and the comparison of wave shape schematic diagram of the first detector 9 output.
2. in room temperature continuous mode, centered by INFRARED QUANTUM CASCADE LASERS 4, emission wavelength is the quantum cascade laser of 4.56 microns, and this wavelength is applicable to steam (H
2o), carbon monoxide (CO) and laughing gas (N
2o) measure while three kinds of gas absorption spectras, this laser diode current tuning rate can reach kHz magnitude.When needs are to other gas molecule Measurement and analysis, the output wavelength of quantum cascade laser correspondingly selects the wavelength being applicable to other gas molecules sorb spectrum.
3. focussed collimated three-dimensional regulation system 5 is made up of two plane mirrors and an off axis paraboloidal mirror, can realize three-dimensional carries out focussed collimated to the light beam that quantum cascade laser sends.Laser beam converges in first catoptron by off axis paraboloidal mirror, then beam emissions is exported by second catoptron, and two catoptrons become 45 degree of arrangements.
4. absorption of sample pond 7 is the adjustable HERRIOTT type multiple reflectance cell based on two concave mirrors of effective light path, can according to the height of gas concentration to be measured in applied environment, select effective total optical path, by gas circulator, gaseous sample to be measured is pumped into absorption of sample pond 7.
5. reference absorption cell 13 is single-pass absorption cell.
6. the gas to be measured in absorption of sample pond 7 is the potpourri of steam, carbon monoxide and laughing gas; Correspondingly, with reference to the pure gas to be measured in absorption cell 13 to be concentration be 100% carbon monoxide or laughing gas.When gas and changing to be measured in absorption of sample pond 7, be also changed accordingly with reference to the pure gas to be measured in absorption cell 13.
7. etalon can select Fabry – P é rot interferometer or germanium etalon;
8. the first detector 9 and the second detector 14 are mercury-cadmium tellurid detector;
9. directly absorption spectrum and Wavelength modulation spectroscopy analysis principle are distinguished as follows:
(1) direct absorption spectroanalysis inverting gas concentration process is based on Lambert-Beer's law and least square fitting algorithm,
In formula (1), S (T) is the strong S of molecular absorption line (unit: cm time temperature T (unit: K)
-1/ molucule), L is for effectively to absorb light path, and N (T, P) is the number density of molecule total under temperature T and P (unit: atm) condition, and I (v) is absorption of sample pond 7 transmitted light intensity, and namely the first detector 9 outputs signal; I
0v () is absorption of sample pond 7 incident intensity, by carrying out order polynomial fits acquisition in I (v) without absorption portion.Absorption of sample pond 7 pressure condition is depended in the selection of least square fitting process center line pattern type, and pattern function has Guass function (being less than 10mbar), Lorentz function (being greater than 100mbar) and Voigt function (between 10-100mbar).
Compared to classic method, the absorption line center position that only utilizes as used in the patent of invention of China Patent Publication No. CN102175641A absorbs the method for Depth Inverse gas concentration information, this method by noise little, inversion algorithm reliability and degree of accuracy higher.
(2) second harmonic detection signal I in Wavelength modulation spectroscopy analysis
2fwith sample concentration C direct proportionality:
I
2f∝ I
0α CL formula (2)
In formula (2), I
0for initial beam intensity, α is that molecule absorption absorbs (unit: cm
-1), L is effective total optical path (unit: cm).
Only utilize single peak value size in second harmonic signal to correct in conventional correction methods, be subject to various noise, error is large, and this method utilizes multiple linear regression analysis algorithm to carry out inverting to the sample message of unknown concentration, and formula is:
In formula (3),
for the second harmonic sampled signal matrix of unknown concentration sample,
for the second harmonic sampled signal matrix of concentration known sample, X is sampling channel number, k
1, k
2, k
3for multiple linear regression coefficient, coefficient k
1the concentration being multiplied by known sample is the concentration value of unknown sample:
In formula (4), X is different molecular kind, and this algorithm improves the reliability of system compensation in wavelength modulation spectrum technology.
As shown in Figure 6, the Wavelength modulation spectroscopy second harmonic signal contrast schematic diagram that the original direct absorption signal exported for the first detector 9 in embodiment four, the direct absorption spectrum after background normalization and Labview digital servo-control demodulate.
In sum, the detection of gas with multiple constituents device based on the sub-cascade laser spectrum of two amounts described in the utility model has the following advantages:
1. to have fast response characteristic, in the room temperature continuous mode of wide tunable range, INFRARED QUANTUM CASCADE LASERS 4 is as excitation source, utilize any wave function generator 1 to export only within any semiperiod the cyclical signal of superposition modulated signal as the current drive signal of INFRARED QUANTUM CASCADE LASERS 4 in room temperature continuous mode, achieve and utilize direct absorption spectroscopy and frequency-modulated spectroscopy to detect multicomponent gas simultaneously simultaneously, utilize the gas information of the direct absorption spectrum inverting of high s/n ratio, for the Wavelength modulation spectroscopy analytical gas information process based on Labview digital servo-control provides correction, namely other sample concentration information to be analyzed is finally inversed by more accurately by Wavelength modulation spectroscopy after correction, two kinds of spectrographic techniques are learnt from other's strong points to offset one's weaknesses, realize highly sensitive and high-precision gas analysis,
2., during frequency-modulated spectroscopy Multi-Component Gas Analyzing, the modulation signal that any wave function generator 1 exports can make the index of modulation optimization respectively of different molecular, realizes optimization and detects each molecule, thus improve system sensitivity; By reducing sampled pressure, avoiding high pressure downforce and adding the molecule self or intermolecular absorption disturbing effect that broad effect causes, improve the reliability of systematic survey;
3. directly absorption spectrum analyzing method absorbs the method for Depth Inverse gas concentration information compared to traditional absorption line center position that only utilizes, little by noise, inversion algorithm reliability and degree of accuracy higher; Wavelength modulation spectroscopy analytical approach utilizes multiple linear regression analysis algorithm to carry out inverting to the sample message of unknown concentration, carry out compared with correction with only utilizing single peak value size in second harmonic signal in conventional correction methods, be not subject to the impact of various noise, measuring error is little;
4. utilize the central frequency deviation information obtaining INFRARED QUANTUM CASCADE LASERS 4 in room temperature continuous mode with reference to absorption cell light path, the bias current of INFRARED QUANTUM CASCADE LASERS 4 in room temperature continuous mode is adjusted in real time according to central frequency deviation information, realize the real-time lock to laser center wavelength, improve pick-up unit stability and measuring accuracy.
5. utilize etalon optical circuit to obtain the relative wavelength tuning range of INFRARED QUANTUM CASCADE LASERS 4 in room temperature continuous mode, again in conjunction with the molecule line parameter provided in HITRAN spectra database, realize the Absolute Calibration to INFRARED QUANTUM CASCADE LASERS 4 wavelength tuning range in room temperature continuous mode, thus improve measuring accuracy;
6. the laser coupled utilizing pilot light light path to improve INFRARED QUANTUM CASCADE LASERS 4 output in room temperature continuous mode enters the coupling efficiency in absorption of sample pond 7, coupling efficiency is higher, effective light path is longer, and interference of light noise is lower, thus improves measurement sensistivity and measuring accuracy;
Therefore, compared to traditional LTS laser time sharing multiplexed detection device based on multiple near infrared laser Time share scanning, the utility model more compact structure, effective measuring period is higher; Compared to single spectrum detection device, the utility model not only overcomes the loaded down with trivial details problem that the not enough and wavelength modulation spectrum technology of direct absorption spectroscopy techniques sensitivity needs extra gas to correct, and have that detection sensitivity is high, measuring accuracy is high, optical path adjusting is easy, be convenient to safeguard, respond soon, high system stability advantages.
Be understandable that, above about specific descriptions of the present utility model, the technical scheme described by the utility model embodiment is only not limited to for illustration of the utility model.Those of ordinary skill in the art should be appreciated that and still can modify to the utility model or equivalent replacement, to reach identical technique effect, uses needs, as long as meet all within protection domain of the present utility model.
Claims (8)
1. based on the multicomponent gas pick-up unit simultaneously of the sub-cascade laser spectrum of two amounts, it is characterized in that: comprise any wave function generator (1), INFRARED QUANTUM CASCADE LASERS (4) in room temperature continuous mode, focussed collimated three-dimensional regulation system (5), first catoptron (6), absorption of sample pond (7), off axis paraboloidal mirror (8), first detector (9), data acquisition unit (10) and computing machine (11), in described room temperature continuous mode, INFRARED QUANTUM CASCADE LASERS (4) has temperature control unit (2) and current control unit (3),
Described any wave function generator (1) exports the current drive signal of cyclical signal as INFRARED QUANTUM CASCADE LASERS (4) in room temperature continuous mode of only superposition modulated signal within any semiperiod, and described current drive signal is driven the Injection Current of INFRARED QUANTUM CASCADE LASERS (4) in room temperature continuous mode by current control unit (3);
In described room temperature continuous mode, INFRARED QUANTUM CASCADE LASERS (4) sends laser signal as light source;
Described focussed collimated three-dimensional regulation system (5) carries out focussed collimated to laser signal;
Laser signal after focussed collimated is coupled to absorption of sample pond (7) by described first catoptron (6);
Described absorption of sample pond (7) is filled with gas to be measured, described laser signal in absorption of sample pond (7) by gas molecules sorb after shine off axis paraboloidal mirror (8);
Laser signal is gathered the first detector (9) by described off axis paraboloidal mirror (8);
The laser signal received is converted into electric signal by data acquisition unit (10) and is transferred to computing machine (11) by described first detector (9);
Described computing machine (11) carries out analyzing and processing to electric signal and draws gas information to be measured.
2. the multicomponent gas based on the sub-cascade laser spectrum of two amounts according to claim 1 pick-up unit simultaneously, it is characterized in that: also comprise instruction light source (15), second catoptron (16) and half-reflecting half mirror (17), described half-reflecting half mirror (17) is located between focussed collimated three-dimensional regulation system (5) and the first catoptron (6), described instruction light source (15) produces visible light signal, visible light signal is reflexed to half-reflecting half mirror (17) by described second catoptron (16), visible light signal reflects by described half-reflecting half mirror (17) again and the laser signal that itself and INFRARED QUANTUM CASCADE LASERS (4) in the room temperature continuous mode of coming through half-reflecting half mirror (17) transmission are sent is coaxial.
3. the multicomponent gas based on the sub-cascade laser spectrum of two amounts according to claim 1 pick-up unit simultaneously, is characterized in that: also comprise beam splitter (12), with reference to absorption cell (13) and the second detector (14);
Described beam splitter (12) is located between focussed collimated three-dimensional regulation system (5) and the first catoptron (6), for by the laser signal beam splitting after focussed collimated three-dimensional regulation system (5) focussed collimated, part laser signal enters with reference to absorption cell (13) through beam splitter (12) reflection, and another part laser signal is transmitted to the first catoptron (6) through beam splitter (12);
Describedly be filled with pure gas to be measured with reference to absorption cell (13) for single-pass absorption cell, described in the laser signal entered with reference to absorption cell (13) shone the second detector (14) after gas molecules sorb;
The laser signal received is converted into electric signal by data acquisition unit (10) and is transferred to computing machine (11) by described second detector (14);
Described computing machine (11) carries out analyzing and processing to electric signal and draws the central frequency deviation information of INFRARED QUANTUM CASCADE LASERS (4) in room temperature continuous mode and fed back to current control unit (3);
Described current control unit (3), according to the central frequency deviation information received, carries out current compensation, stablizes the centre frequency of INFRARED QUANTUM CASCADE LASERS (4) in room temperature continuous mode.
4. the multicomponent gas based on the sub-cascade laser spectrum of two amounts according to claim 1 pick-up unit simultaneously, is characterized in that: also comprise beam splitter (12), etalon and the second detector (14);
Described beam splitter (12) is located between focussed collimated three-dimensional regulation system (5) and the first catoptron (6), for by the laser signal beam splitting after focussed collimated three-dimensional regulation system (5) focussed collimated, part laser signal enters etalon through beam splitter (12) reflection, and another part laser signal is transmitted to the first catoptron (6) through beam splitter (12);
The laser signal of described Engage of standard tool shines the second detector (14) after producing in etalon and interfering;
The laser signal received is converted into electric signal by data acquisition unit (10) and is transferred to computing machine (11) by described second detector (14);
Described computing machine (11) carries out to the electric signal received the relative wavelength tuning range that analyzing and processing draws INFRARED QUANTUM CASCADE LASERS (4) in room temperature continuous mode.
5. the multicomponent gas based on the sub-cascade laser spectrum of two amounts according to claim 3 or 4 is pick-up unit simultaneously, it is characterized in that: also comprise instruction light source (15) and the second catoptron (16), described instruction light source (15) produces visible light signal, visible light signal is reflexed to beam splitter (12) by described second catoptron (16), visible light signal reflects by described beam splitter (12) again and the laser signal that itself and INFRARED QUANTUM CASCADE LASERS (4) in the room temperature continuous mode of coming through beam splitter (12) transmission are sent is coaxial.
6. the multicomponent gas based on the sub-cascade laser spectrum of two amounts according to claim 1,2,3 or 4 is pick-up unit simultaneously, it is characterized in that: described focussed collimated three-dimensional regulation system (5) is made up of two plane mirrors and an off axis paraboloidal mirror, two catoptrons become 45 degree of placements, overall three-dimensional adjustable.
7. the multicomponent gas based on the sub-cascade laser spectrum of two amounts according to claim 1,2,3 or 4 is pick-up unit simultaneously, it is characterized in that: described absorption of sample pond (7) is the adjustable HERRIOTT type multiple reflectance cell based on two concave mirrors of effective light path.
8. the multicomponent gas based on the sub-cascade laser spectrum of two amounts according to claim 1,2,3 or 4 is pick-up unit simultaneously, it is characterized in that: the cyclical signal that described any wave function generator (1) exports is low frequency periodic triangular wave or sawtooth wave, the modulation signal that cyclical signal only superposes within any semiperiod is high_frequency sine wave.
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