CN104515742B

CN104515742B - Method for improving cavity ring-down time measurement accuracy

Info

Publication number: CN104515742B
Application number: CN201410789135.0A
Authority: CN
Inventors: 朱小明; 王晓东; 李丙玉; 颜昌翔
Original assignee: Changchun Institute of Optics Fine Mechanics and Physics of CAS
Current assignee: Changchun Institute of Optics Fine Mechanics and Physics of CAS
Priority date: 2014-12-17
Filing date: 2014-12-17
Publication date: 2017-01-18
Anticipated expiration: 2034-12-17
Also published as: CN104515742A

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

A kind of method improving cavity ring-down time certainty of measurement

Technical field

The present invention relates to trace gas detects picosecond time interval measurement field, particularly to a kind of improve cavity decline swing when Between certainty of measurement method.

Background technology

Cavity ring-down spectroscopy technology (crds, cavity ring-down spectrum) it is that a kind of recent two decades develop The trace gas Detection Techniques come, the resonator that its core technology is made up of ultra-high reflectivity speculum, narrow linewidth laser And wavelength locking technology and precise time-time-interval e measurement technology.In terms of measurement trace gas, the isotopic content of trace element There are very many advantages, such as measurement data is unrelated with laser power fluctuation, do not need standard sample gas, certainty of measurement pole High, can complete to measure in real time, need not calibrate for a long time, field unattended measurement etc..

Due to cavity ring-down spectroscopy commercial measurement high precision, specular reflectivity and time resolution are required also very High.As shown in subordinate list one, in the long 41cm in chamber, specular reflectivity is 0.9999, and linear function is under 5.13 and room temperature normal pressure, divide Distinguish 30ppbv methane gas content when, time resolution be 4.5ns；And when gas concentration resolution ratio is 1ppbv, the time Certainty of measurement is 0.15ns.On the premise of in chamber, specular reflectivity can not improve, time resolution brings up to from 4.5ns 0.15ns, this proposes high requirement to time measurement system.The present invention is exactly directed to this situation, from ring-down time starting point Be accurately positioned to improve the precision of time measurement with two aspects of accurate measurement at ring-down time interval.

Content of the invention

The invention solves the problems that technical problem of the prior art, provide a kind of side improving cavity ring-down time certainty of measurement Method.

In order to solve above-mentioned technical problem, technical scheme is specific as follows:

A kind of method improving cavity ring-down time certainty of measurement, comprises the following steps:

Step one, unlatching laser instrument, and by wavelength feedback regulating system, the feature of wavelength locking under test gas is inhaled Receive in the range of spectral line；

Step 2, adjustment cavity length, and monitoring detector amplitude output signal；

Step 3, repeat step two, until detector output signal amplitude reaches the upper threshold value of setting, stop adjustment chamber Long, and close laser instrument；

Step 4, resonator no longer have energy input, and freedom of entry declines the stage of swinging, and energy is gradually decayed, when detector is defeated When going out signal amplitude again for setting upper threshold value, timing starts；

Step 5, freely declining to swing proceeds, and energy is decayed further, when detector output signal amplitude reaches under setting During threshold value, timer expiration swings end it is believed that declining；

Step 6, calculating cavity free ring-down time constant；

Step 7, suction under test gas, repeat step one to six, obtain the free ring-down time containing under test gas normal Number；

Step 8, according to data such as the cavity that records and the free ring-down time constants containing under test gas, calculate in chamber Gas concentration.

The present invention has a following beneficial effect:

The method of the raising cavity ring-down time certainty of measurement of the present invention, rapidly switches off semiconductor laser using electric current, Alleviate the impact to measurement data for the conditions of streaking.

The method of the raising cavity ring-down time certainty of measurement of the present invention, accurately sets upper lower threshold value by high accuracy dac, Reduce adc continuous sampling and judge that caused measure error, it is often more important that setting by dual threshold, eliminates closing laser The impact to measurement for the light energy input during device.

Brief description

With reference to the accompanying drawings and detailed description the present invention is described in further detail.

Fig. 1 is System Working Principle schematic diagram.

Fig. 2 declines for light intensity in chamber and swings curve synoptic diagram.

Specific embodiment

The invention thought of the present invention is: during time of measuring interval, has several factors to lead to the decline of certainty of measurement, wherein It is important that the positioning precision of initial time.The present invention exactly be directed to this problem, in terms of two improve to initial when The positioning precision carved, and then improve the certainty of measurement of time interval in the measurement of cavity ring-down spectroscopy.

Specifically, the method for the raising cavity ring-down time certainty of measurement of the present invention, comprises the following steps:

Open laser instrument, and by wavelength feedback regulating system by the characteristic absorpting spectruming line model of wavelength locking under test gas In enclosing；

Adjustment cavity length, and monitoring detector amplitude output signal, set until detector output signal amplitude reaches Fixed upper threshold value, stopping adjustment chamber is long, and closes laser instrument；

When detector output signal amplitude is to set upper threshold value again, timing starts；

When detector output signal amplitude reaches setting lower threshold value, timer expiration；

Calculate cavity free ring-down time constant；

Suction under test gas, repeat the above steps, obtain the free ring-down time constant containing under test gas；

According to the data such as the cavity recording and the free ring-down time constant containing under test gas, calculate intracavity gas dense Degree.

Below in conjunction with the accompanying drawings 1 and accompanying drawing 2 illustrate the present invention step realize.

Step one, device power-on, open laser instrument 2, and controller 101 passes through temperature-driven 102 and electric current drives 103 regulations The wavelength of laser instrument 2, and monitor wavelength change with Wavelength monitor (in figure does not provide), and wavelength locking is inhaled in gas characteristic Receive in the range of spectral line；

Step 2, transit chamber long adjustment unit (in figure is not given) adjust the length of resonator 3, and are monitored with detector 4 Resonator 3 output intensity；

Step 3, repeat step two, until the signal amplitude of detector 4 output reaches the upper threshold value v1 of setting (in accompanying drawing 2 The t1 moment), stop adjustment chamber long, and by electric current drive 103 close laser instruments 2；

Step 4, resonator 3 no longer have energy input, and freedom of entry declines the stage of swinging, and energy is gradually decayed, when detector 4 Amplitude output signal is to set upper threshold value v1 (the t2 moment in accompanying drawing 2) again, and timing starts；

Step 5, freely declining to swing proceeds, and energy is decayed further, when detector 4 amplitude output signal reaches setting During lower threshold value v2 (t3 moment in accompanying drawing 2), timing stops swinging end it is believed that declining；

Step 6, comparator 5 and time measurement module 6, by the time interval length between t2 to t3, calculate cavity freely Ring-down time constant；

Cavity ring-down spectroscopy measurement process is as follows:

First turn on laser instrument, by regulating system, laser wavelength is adjusted in the characteristic absorpting spectruming line of gas, so Wavelength locking afterwards, adjusts cavity length, when light beam makes energy close laser instrument when increasing to setting upper threshold value in chamber interior resonance, At this moment no longer there is energy input in chamber, enter and decline the stage of swinging, until intra-cavity energy decays to setting lower threshold value, decline and swing process knot Bundle.Decay 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 under test gas in chamber.Can be seen that from the above-mentioned course of work at 2 points: one, when intra-cavity energy runs up to setting upper-level threshold During value, the closing velocity of laser instrument will affect the positioning precision of initial time；2nd, ring-down time is spaced longer, then time measurement The impact to certainty of measurement for module itself measure error is less.

Used in cavity ring-down spectroscopy, laser instrument is semiconductor laser, can pass through temperature and two kinds of driving current Mode adjusts laser wavelength, because rate temperature change is relatively slowly a lot, by the way of adjustment electric current, by laser instrument ripple Long rapid removal characteristic absorpting spectruming line scope, is equivalent to and closes laser instrument, the perseverance that additional drive circuit produces for parallel dac Stream source, this process just can complete in 30ns.Even the so short time, cavity ring-down spectroscopy e measurement technology is come Say still difficult to accept, can be confirmed by table 1.If reaching the moment of upper threshold value as initial time from intra-cavity energy, In laser instrument closing process, intra-cavity energy still increases quick, therefore after intra-cavity energy reaches upper threshold value, closes laser Device, when intra-cavity energy is re-lowered to upper threshold value, timing starts, and sees accompanying drawing 2.It is upper by high-precision dac output voltage Lower threshold value comparative level, ultrahigh-speed comparator producing ratio relatively exports, when at this moment can accurately provide declining between lower threshold value and swinging Between length.

Relation table between table 1. time of measuring precision and gas concentration

Data above design conditions are: the long 41cm in chamber, and cavity mirrors reflectivity is 0.9999, standard atmospheric pressure, room temperature (25 DEG C), Linear function is 5.13.

Obviously, above-described embodiment is only intended to clearly illustrate example, and the not restriction to embodiment.Right For those of ordinary skill in the art, can also make on the basis of the above description other multi-forms change or Change.There is no need to be exhaustive to all of embodiment.And the obvious change thus extended out or Change among still in the protection domain of the invention.

Claims

1. a kind of method improving cavity ring-down time certainty of measurement is it is characterised in that comprise the following steps:

Step one, open laser instrument, and by wavelength feedback regulating system by the characteristic absorpting spectrum of wavelength locking under test gas In the range of line；

Step 3, repeat step two, until detector output signal amplitude reaches the upper threshold value of setting, stopping adjustment chamber is long, and Close laser instrument；

Step 4, resonator no longer have energy input, and freedom of entry declines the stage of swinging, and energy is gradually decayed, when detector exports letter When number amplitude is to set upper threshold value again, timing starts；

Step 5, freely declining to swing proceeds, and energy is decayed further, when detector output signal amplitude reaches setting lower threshold value When, timer expiration swings end it is believed that declining；

Step 6, calculating cavity free ring-down time constant.

2. the method improving cavity ring-down time certainty of measurement as claimed in claim 1 is it is characterised in that after step 6 Also include:

Step 7, suction under test gas, repeat step one to six, obtain the free ring-down time constant containing under test gas.

3. the method improving cavity ring-down time certainty of measurement as claimed in claim 2 is it is characterised in that after step 7 Also include:

Cavity and the free ring-down time constant data containing under test gas that step 8, basis record, calculate intracavity gas dense Degree.