CN104515750A - Method for improving resonant cavity ring-down measurement accuracy - Google Patents
Method for improving resonant cavity ring-down measurement accuracy Download PDFInfo
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- CN104515750A CN104515750A CN201410787501.9A CN201410787501A CN104515750A CN 104515750 A CN104515750 A CN 104515750A CN 201410787501 A CN201410787501 A CN 201410787501A CN 104515750 A CN104515750 A CN 104515750A
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Abstract
The invention discloses a method for improving resonant cavity ring-down measurement accuracy. The method comprises the following steps: (1) a laser with a continuous wavelength is started, the drive current and temperature are adjusted to enable the laser to work on a target wavelength, and the wavelength is locked using a wavelength monitor; (2) laser beams are converted to S linearly polarized light by a polarizer; (3) the S linearly polarized light is incident to the resonant cavity via a collimating mirror and a pattern matching mirror, and accumulates energy in the cavity through resonance; (4) a detector is used to receive the resonant cavity outgoing lights, and the semiconductor laser is shut down and a ring-down process is started when the light intensity reaches a set upper threshold value; (5) when the energy received by the detector reaches a set lower threshold value, the ring-down process is considered to be ended, and then the ring-down time of the energy from the upper threshold value to the lower threshold value is recorded, and the gas concentration is calculated according to Lambert-Beer law. The method provided by the invention eliminates the impact of P light component on the ring-down and improves the measurement accuracy.
Description
Technical field
The present invention relates to trace gas concentration fields of measurement, specifically relate to a kind of cavity resonant that improves and decline and swing the method for measuring accuracy.
Background technology
Cavity ring-down spectroscopy (CRDS, Cavity Ring-down Spectrum) be a kind of trace gas concentration Detection Techniques grown up in nearly twenty or thirty year, by selecting measurement gas characteristic absorption peak, its selective absorbing characteristic coordinates long light path to decline to swing and accurately measure trace gas content, generally can reach ppm or ppb magnitude (to swing distance relevant to the absorption peak strength of gas and declining).This technology is widely used in CH at present
4, N
2o, CO, CO
2, the measurement of the gas concentrations such as HF, is also widely used in these gas isotope content fields of measurement.
A core technology high reflectance resonator cavity of cavity ring-down spectroscopy, and the key forming resonator cavity is high reflectivity mirror, general reflectivity requirements is 99.99% or higher, and the meaning of high reflectance has 2 points: one, obtains higher intra-cavity energy and add up when opening laser instrument; Its two, less Mirror reflection loss, obtains longer declining and swings length.When the reflectivity of thrihedral reflector is 99.999%, when chamber long for 0.5m time, when light intensity attenuation is 0.3 of initial beam intensity, order of reflection is 40000, decline swing through distance be 20km.And when reflectivity is 99.99%, decline when swinging 5000 times, relative light intensity drops to 0.2.This shows the importance of reflectivity in CRDS measuring method.
The resonator cavity of current use mostly is two mirror chamber and three mirror cavities.In two mirror chambeies, wherein should install precise driving device after a catoptron and flow out emergent ray path again, installment and debugging has inconvenience more.In three mirror cavity structure, for light, another installs drive unit for beam projecting after spherical mirror to two plane high reflection mirrors one, and structure greatly simplifies, and therefore applies widely.But three mirror cavity has a defect to be that the P component of natural light and S component reflectivity are inconsistent with incident angle change, and the decay of P light reflectivity is very fast, and the decay of S light reflectivity is very little.And can find out that the height of reflectivity directly affects to decline and swing length from introduce before, thus affect measuring accuracy.
The method of current most popular acquisition high reflectance is plated film, according to use wavelength and Coating Materials, is reached the reflectivity of setting by control thickness and coating layers.Multi-layer mirror has its feature, and when oblique incidence, P light and S light component can with incident angle and wavelength variations, fig. 1 illustrates 45 degree incident time, the 29 layers of TiO used in system
2and SiO
2the relation of high-reflecting film P light and S light reflectivity and wavelength.When using wavelength in 1450nm – 1620nm interval, S light reflectivity remains on more than 99.99%, and P light reflectivity is no more than 36%, and big ups and downs, level off to 0 especially time minimum.If use P light and the common energy value of S light to measure ring-down time, due to the rapid loss of P light, cause the non-exponential of energy to decay, cause measuring accuracy to decline.
Summary of the invention
The present invention will solve technical matters of the prior art, provides a kind of cavity resonant that improves to decline and swing the method for measuring accuracy.
In order to solve the problems of the technologies described above, technical scheme of the present invention is specific as follows:
Improve cavity resonant to decline and swing a method for measuring accuracy, comprise the following steps:
Step one, unlatching continuous wavelength laser instrument, make it be operated in target wavelength by adjustment drive current and temperature, and use Wavelength monitor to lock;
Step 2, laser beam are converted to S linearly polarized light through the polarizer;
Step 3, S linearly polarized light incide in resonator cavity through collimating mirror and pattern match mirror, and at chamber interior resonance cumlative energy;
Step 4, use detector receive resonator cavity emergent light, when light intensity reaches setting upper threshold value, close semiconductor laser, start the process of swinging that declines;
Step 5, the energy received when detector reach the lower threshold value of setting, think that the process of swinging that declines terminates, and the ring-down time recording by upper threshold value to lower threshold value, calculates gas concentration by langbobier law.
The present invention has following beneficial effect:
Raising cavity resonant of the present invention declines and swings the method for measuring accuracy, and employing reflectivity is two sides level crossing and a spherical mirror of 99.999% (normal incidence), composition high sharpness reflection resonator cavity.It is simple that many mirrors resonator cavity has structure, is beneficial to and installs driven unit and arrange light path; Light source adopts narrow linewidth semiconductor laser, is regulated by drive current and temperature, uses Wavelength monitor monitoring adjustment process, makes wavelength locking in target wavelength.
Accompanying drawing explanation
Below in conjunction with the drawings and specific embodiments, the present invention is described in further detail.
When Fig. 1 is 45 degree of incidence, the 29 layers of TiO used in system
2and SiO
2the relation schematic diagram of high-reflecting film P light and S light reflectivity and wavelength.
Fig. 2 is that raising cavity resonant of the present invention declines the schematic diagram of a kind of embodiment of method of swinging measuring accuracy.
Reference numeral in figure is expressed as:
1-semiconductor laser; The 2-polarizer; 3-collimating mirror; 4-pattern match mirror; 5-high reflectance level crossing; 6-high reflectance level crossing; 7-spherical mirror and drive unit; 8-detector.
Embodiment
Below in conjunction with accompanying drawing, the present invention is described in detail.
As shown in Figure 2, the raising cavity resonant of the present invention method of swinging measuring accuracy that declines comprises the following steps:
Open semiconductor laser 1, make it be operated in target wavelength by adjustment drive current and temperature, and use Wavelength monitor to lock.
The S linearly polarized light vertical with level crossing surface is converted to through the polarizer 2.
Collimate through collimating mirror 3 and after pattern match mirror 4 matched shape, incide in the resonator cavity that is made up of high reflectance level crossing 5, high reflectance level crossing 6, spherical mirror and drive unit 7, and cumlative energy.
Resonator cavity emanated energy is gathered by detector 8, and when energy reaches setting upper threshold value, close laser instrument, the process of swinging that declines starts.
Energy starts to decline to swing in resonator cavity, until the energy that detector 8 receives reaches lower threshold value, thinks that the process of swinging that declines terminates, and the ring-down time recording by upper threshold value to lower threshold value, calculates gas concentration by langbobier law.
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 cavity resonant to decline and swing a method for measuring accuracy, it is characterized in that, comprise the following steps:
Step one, unlatching continuous wavelength laser instrument, make it be operated in target wavelength by adjustment drive current and temperature, and use Wavelength monitor to lock;
Step 2, laser beam are converted to S linearly polarized light through the polarizer;
Step 3, S linearly polarized light incide in resonator cavity through collimating mirror and pattern match mirror, and at chamber interior resonance cumlative energy.
2. raising cavity resonant as claimed in claim 1 declines and swings the method for measuring accuracy, it is characterized in that, also comprises after step 3:
Step 4, use detector receive resonator cavity emergent light, when light intensity reaches setting upper threshold value, close semiconductor laser, start the process of swinging that declines.
3. raising cavity resonant as claimed in claim 2 declines and swings the method for measuring accuracy, it is characterized in that, also comprises after step 4:
Step 5, the energy received when detector reach the lower threshold value of setting, think that the process of swinging that declines terminates, and the ring-down time recording by upper threshold value to lower threshold value, calculates gas concentration by langbobier law.
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| CN201410787501.9A CN104515750A (en) | 2014-12-17 | 2014-12-17 | Method for improving resonant cavity ring-down measurement accuracy |
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| CN201410787501.9A CN104515750A (en) | 2014-12-17 | 2014-12-17 | Method for improving resonant cavity ring-down measurement accuracy |
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Citations (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US20090244541A1 (en) * | 2008-03-26 | 2009-10-01 | Bincheng Li | Cavity ring-down apparatus and method for measuring reflectivity of highly reflective mirrors |
| CN102252825A (en) * | 2011-04-14 | 2011-11-23 | 西安电子科技大学 | System for measuring loss of optical resonant cavity based on optical cavity ring-down method |
| CN102884413A (en) * | 2010-03-02 | 2013-01-16 | 利康股份有限公司 | Method and apparatus for the photo-acoustic identification and quantification of analyte species in a gaseous or liquid medium |
| CN103471815A (en) * | 2013-09-11 | 2013-12-25 | 中国科学院光电技术研究所 | Method for simultaneously measuring S-polarized light reflectivity and P-polarized light reflectivity of high reflecting mirror |
-
2014
- 2014-12-17 CN CN201410787501.9A patent/CN104515750A/en active Pending
Patent Citations (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US20090244541A1 (en) * | 2008-03-26 | 2009-10-01 | Bincheng Li | Cavity ring-down apparatus and method for measuring reflectivity of highly reflective mirrors |
| CN102884413A (en) * | 2010-03-02 | 2013-01-16 | 利康股份有限公司 | Method and apparatus for the photo-acoustic identification and quantification of analyte species in a gaseous or liquid medium |
| CN102252825A (en) * | 2011-04-14 | 2011-11-23 | 西安电子科技大学 | System for measuring loss of optical resonant cavity based on optical cavity ring-down method |
| CN103471815A (en) * | 2013-09-11 | 2013-12-25 | 中国科学院光电技术研究所 | Method for simultaneously measuring S-polarized light reflectivity and P-polarized light reflectivity of high reflecting mirror |
Non-Patent Citations (2)
| Title |
|---|
| 方茗 等: "光栅反射镜作为激光器后腔镜输出基横模线偏振光", 《中国激光》 * |
| 杨秋霞: "连续波腔衰荡光谱技术特性及在气体浓度测量中应用研究", 《中国博士学位论文全文数据库 信息科技辑》 * |
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