CN104515742A - Method for improving cavity ring-down time measurement accuracy - Google Patents
Method for improving cavity ring-down time measurement accuracy Download PDFInfo
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- CN104515742A CN104515742A CN201410789135.0A CN201410789135A CN104515742A CN 104515742 A CN104515742 A CN 104515742A CN 201410789135 A CN201410789135 A CN 201410789135A CN 104515742 A CN104515742 A CN 104515742A
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Abstract
The invention relates to a method for improving cavity ring-down time measurement accuracy. The method comprises the following steps: starting a laser and locking the wavelength within the range of characteristic spectrum lines of the gas to be tested according to a wavelength looped system; adjusting the length of a resonant cavity while monitoring the amplitude of signals output by a detector; stopping adjusting the length of the resonant cavity until the amplitude of the signals output by the detector reaches a set upper threshold value, and then shutting down the laser; starting timing when the amplitude of the signals output by the detector reaches the set upper threshold value again; stopping timing when the amplitude of the signals output by the detector reaches a set lower threshold value; calculating the free ring-down time constant of the cavity; pumping the gas to be tested into the cavity and repeating the previous steps to obtain the free ring-down time constant of the cavity containing the gas to be tested; calculating the concentration of the gas in the cavity according to data such as the free ring-down time constant of the cavity and that of the cavity containing the gas to be tested. According to the invention, the semiconductor laser is quickly shut down through electric current, which reduces the impact of the tailing on the measurement data.
Description
Technical field
The present invention relates to trace gas detection picosecond time interval measurement field, particularly a kind of method improving cavity ring-down time measuring accuracy.
Background technology
Cavity ring-down spectroscopy technology (CRDS, Cavity Ring-down Spectrum) be the trace gas Detection Techniques that a kind of recent two decades grows up, the resonator cavity that its core technology is made up of ultra-high reflectivity catoptron, narrow linewidth laser and wavelength locking technology and precise time-time-interval measuring technique.In the isotopic content measuring trace gas, trace element, have advantages much more very, such as measurement data and laser power fluctuate have nothing to do, do not need standard model gas, measuring accuracy high, can complete real-time measurement, for a long time without the need to calibrating, field unattended measurement etc.
Because cavity ring-down spectroscopy commercial measurement precision is high, require also very high to specular reflectance and time resolution.As shown in subordinate list one, the long 41cm in chamber, specular reflectance is 0.9999, linear function be 5.13 and room temperature normal pressure under, when differentiate the methane gas content of 30ppbv, time resolution is 4.5ns; And when gas concentration resolution is 1ppbv, time resolution is 0.15ns.Under the prerequisite that specular reflectance can not improve in chamber, time resolution brings up to 0.15ns from 4.5ns, and this proposes high requirement to time measurement system.The present invention, just for this situation, improves the precision of time measurement from the accurate location of ring-down time starting point and accurate measurement two aspects at ring-down time interval.
Summary of the invention
The present invention will solve technical matters of the prior art, provides a kind of method improving cavity ring-down time measuring accuracy.
In order to solve the problems of the technologies described above, technical scheme of the present invention is specific as follows:
Improve a method for cavity ring-down time measuring accuracy, comprise the following steps:
Step one, unlatching laser instrument, and pass through wavelength feedback regulating system by wavelength locking within the scope of the characteristic absorpting spectruming line of gas to be measured;
Step 2, adjustment cavity length, and monitoring detector amplitude output signal;
Step 3, repetition step 2, until detector output signal amplitude reaches the upper threshold value of setting, stop adjustment chamber long, and close laser instrument;
Step 4, resonator cavity no longer include energy input, and freedom of entry declines the stage of swinging, and energy is decayed gradually, and when detector output signal amplitude is again for setting upper threshold value, timing starts;
Step 5, freely decline to swing and proceed, energy is decayed further, when detector output signal amplitude reaches setting lower threshold value, and timer expiration, thinking declines swings end;
Step 6, the free ring-down time constant of calculating cavity;
Step 7, suction gas to be measured, repeat step one to six, obtain the free ring-down time constant containing gas to be measured;
The data such as the cavity that step 8, basis record and the free ring-down time constant containing gas to be measured, calculate intracavity gas concentration.
The present invention has following beneficial effect:
The method of raising cavity ring-down time measuring accuracy of the present invention, uses electric current to turn off semiconductor laser fast, alleviates the impact of conditions of streaking on measurement data.
The method of raising cavity ring-down time measuring accuracy of the present invention, upper lower threshold value is accurately set by high precision DAC, reduce ADC continuous sampling judge caused by measuring error, the more important thing is and to be set by dual threshold, eliminate and to close in laser procedures luminous energy input to the impact of measuring.
Accompanying drawing explanation
Below in conjunction with the drawings and specific embodiments, the present invention is described in further detail.
Fig. 1 is System Working Principle schematic diagram.
Fig. 2 is that in chamber, light intensity declines and swings curve synoptic diagram.
Embodiment
Invention thought of the present invention is: during measuring intervals of TIME, has several factors to cause the decline of measuring accuracy, and wherein the most important is the positioning precision of initial time.The present invention, just for this problem, improves the positioning precision to initial time from two aspects, and then improves the measuring accuracy in the time interval in the measurement of cavity ring-down spectroscopy.
Specifically, the method for raising cavity ring-down time measuring accuracy of the present invention, comprises the following steps:
Open laser instrument, and pass through wavelength feedback regulating system by wavelength locking within the scope of the characteristic absorpting spectruming line of gas to be measured;
Adjustment cavity length, and monitoring detector amplitude output signal, until detector output signal amplitude reaches the upper threshold value of setting, stop adjustment chamber long, and close laser instrument;
When detector output signal amplitude is again for setting upper threshold value, timing starts;
When detector output signal amplitude reaches setting lower threshold value, timer expiration;
Calculate the free ring-down time constant of cavity;
Suction gas to be measured, repeats above-mentioned steps, obtains the free ring-down time constant containing gas to be measured;
According to data such as the cavity recorded and the free ring-down time constants containing gas to be measured, calculate intracavity gas concentration.
Illustrate step of the present invention below in conjunction with accompanying drawing 1 and accompanying drawing 2 to realize.
Improve a method for cavity ring-down time measuring accuracy, comprise the following steps:
Step one, device power-on, open laser instrument 2, controller 101 drives the wavelength of 103 adjustment laser instruments 2 by temperature-driven 102 and electric current, and monitors wavelength variations with Wavelength monitor (not providing in figure), and by wavelength locking within the scope of gas characteristic absorption line;
Step 2, length by the long regulon in chamber (not providing in figure) adjustment resonator cavity 3, and monitor resonator cavity 3 output intensity with detector 4;
Step 3, repetition step 2, until the signal amplitude that detector 4 exports reaches the upper threshold value V1 (the t1 moment in accompanying drawing 2) of setting, stop adjustment chamber long, and drive 103 closedown laser instruments 2 by electric current;
Step 4, resonator cavity 3 no longer include energy input, and freedom of entry declines the stage of swinging, and energy is decayed gradually, and when detector 4 amplitude output signal is setting upper threshold value V1 (the t2 moment in accompanying drawing 2) again, timing starts;
Step 5, freely decline to swing and proceed, energy is decayed further, and when detector 4 amplitude output signal reaches setting lower threshold value V2 (in accompanying drawing 2 t3 moment), timing stops, and thinking declines swings end;
Step 6, comparer 5 and time measurement module 6, by the time interval length between t2 to t3, calculate the free ring-down time constant of cavity;
Step 7, suction gas to be measured, repeat step one to six, obtain the free ring-down time constant containing gas to be measured;
The data such as the cavity that step 8, basis record and the free ring-down time constant containing gas to be measured, calculate intracavity gas concentration.
Cavity ring-down spectroscopy measuring process is as follows:
First laser instrument is opened, by regulating system, laser wavelength is adjusted in the characteristic absorpting spectruming line of gas, then wavelength locking, adjustment cavity length, when light beam closes laser instrument when chamber interior resonance makes energy be increased to setting upper threshold value, at this moment no longer include energy input in chamber, enter the stage of swinging of declining, until intra-cavity energy decays to setting lower threshold value, the process of swinging that declines terminates.Decaying to time interval between lower threshold value by measuring energy from upper threshold value, ring-down time constant can be calculated, thus calculate the concentration of gas to be measured in chamber.2 points can be found out: one, when intra-cavity energy runs up to setting upper threshold value, the closing velocity of laser instrument will affect the positioning precision of initial time from the above-mentioned course of work; Two, ring-down time interval is longer, then the impact of time measurement module self measuring error on measuring accuracy is less.
The laser instrument used in cavity ring-down spectroscopy is semiconductor laser, laser wavelength can be regulated by temperature and drive current two kinds of modes, because rate temperature change is relatively slowly a lot, adopt the mode of adjustment electric current, laser wavelength is shifted out rapidly characteristic absorpting spectruming line scope, be equivalent to close laser instrument, for the constant current source that the additional driving circuit of parallel DAC produces, this process just can complete in 30ns.Even the so short time, be still difficult to accept for cavity ring-down spectroscopy measuring technique, can be confirmed by table 1.If select intra-cavity energy to arrive the moment of upper threshold value as initial time, in laser instrument closing process, intra-cavity energy is still in quick increase, therefore, after intra-cavity energy arrives upper threshold value, laser instrument is closed, when intra-cavity energy drops to upper threshold value again, timing starts, and sees accompanying drawing 2.Be upper lower threshold value comparative level by high-precision DAC output voltage, ultrahigh-speed comparator produces and compares output, at this moment accurately can provide the ring-down time length between lower threshold value.
Relation table between table 1. Measuring Time precision and gas concentration
Above data design conditions are: the long 41cm in chamber, and cavity mirrors reflectivity is 0.9999, standard atmospheric pressure, and room temperature (25 DEG C), linear function is 5.13.
Obviously, above-described embodiment is only for clearly example being described, and the restriction not to embodiment.For those of ordinary skill in the field, can also make other changes in different forms on the basis of the above description.Here exhaustive without the need to also giving all embodiments.And thus the apparent change of extending out or variation be still among the protection domain of the invention.
Claims (3)
1. improve a method for cavity ring-down time measuring accuracy, it is characterized in that, comprise the following steps:
Step one, unlatching laser instrument, and pass through wavelength feedback regulating system by wavelength locking within the scope of the characteristic absorpting spectruming line of gas to be measured;
Step 2, adjustment cavity length, and monitoring detector amplitude output signal;
Step 3, repetition step 2, until detector output signal amplitude reaches the upper threshold value of setting, stop adjustment chamber long, and close laser instrument;
Step 4, resonator cavity no longer include energy input, and freedom of entry declines the stage of swinging, and energy is decayed gradually, and when detector output signal amplitude is again for setting upper threshold value, timing starts;
Step 5, freely decline to swing and proceed, energy is decayed further, when detector output signal amplitude reaches setting lower threshold value, and timer expiration, thinking declines swings end;
Step 6, the free ring-down time constant of calculating cavity.
2. the method improving cavity ring-down time measuring accuracy as claimed in claim 1, is characterized in that, also comprise after step 6:
Step 7, suction gas to be measured, repeat step one to six, obtain the free ring-down time constant containing gas to be measured.
3. the method improving cavity ring-down time measuring accuracy as claimed in claim 2, is characterized in that, also comprise after step 7:
The data such as the cavity that step 8, basis record and the free ring-down time constant containing gas to be measured, calculate intracavity gas concentration.
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Cited By (4)
| Publication number | Priority date | Publication date | Assignee | Title |
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| CN107389604A (en) * | 2017-06-26 | 2017-11-24 | 中国科学院光电研究院 | A kind of laser, which declines, swings detection method |
| CN107561009A (en) * | 2017-09-12 | 2018-01-09 | 中国科学院长春光学精密机械与物理研究所 | Resonator output intensity determines method, system and measuring apparatus, concentrations detectors |
| CN109959623A (en) * | 2017-12-25 | 2019-07-02 | 内蒙古光能科技有限公司 | A kind of sampling system and its method of sampling of CRDS gas concentration detector |
| CN114166766A (en) * | 2021-12-06 | 2022-03-11 | 中国科学院合肥物质科学研究院 | Gas measurement method based on amplitude modulation cavity enhanced absorption spectrum technology |
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Cited By (6)
| Publication number | Priority date | Publication date | Assignee | Title |
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| CN107389604A (en) * | 2017-06-26 | 2017-11-24 | 中国科学院光电研究院 | A kind of laser, which declines, swings detection method |
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| CN107561009A (en) * | 2017-09-12 | 2018-01-09 | 中国科学院长春光学精密机械与物理研究所 | Resonator output intensity determines method, system and measuring apparatus, concentrations detectors |
| CN109959623A (en) * | 2017-12-25 | 2019-07-02 | 内蒙古光能科技有限公司 | A kind of sampling system and its method of sampling of CRDS gas concentration detector |
| CN114166766A (en) * | 2021-12-06 | 2022-03-11 | 中国科学院合肥物质科学研究院 | Gas measurement method based on amplitude modulation cavity enhanced absorption spectrum technology |
| CN114166766B (en) * | 2021-12-06 | 2024-05-14 | 中国科学院合肥物质科学研究院 | Gas measurement method based on amplitude modulation cavity enhanced absorption spectrum technology |
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