CN115615953A - Differential absorption laser radar light source for detecting harmful gas in atmospheric environment - Google Patents
Differential absorption laser radar light source for detecting harmful gas in atmospheric environment Download PDFInfo
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Abstract
The invention discloses a differential absorption laser radar light source for detecting harmful gas in atmospheric environment, which comprises: the laser system comprises a laser pumping source, an optical system, a dye laser resonant cavity and an optical frequency doubling system, wherein tuning of output laser wavelength and generation of dual-wavelength laser are realized by adjusting a dispersion element in a light path; and then nonlinear optical frequency doubling is realized through a frequency doubling crystal, and the laser radar light source is used as a dual-wavelength differential absorption laser radar light source of an ultraviolet band and can be used for trace detection of sulfur dioxide, carbon disulfide and other atmospheric harmful gases.
Description
Technical Field
The invention belongs to the technical field of dye lasers and lasers, and particularly relates to a differential absorption laser radar light source for detecting harmful gases in an atmospheric environment and a method for generating dual-wavelength laser.
Background
In recent years, the large urban population in China is rapidly developed in economy and industrialization, the artificial emission is also sharply increased along with the improvement of the living standard of people, and the composite pollution caused by atmospheric particulates and ozone becomes the main pollution problem in the large urban area. Considering the wide distribution of atmospheric particulates, ozone and NO 2 、SO 2 Etc. which cause serious harm to human health, ecosystems, etc., and may cause some changes such as warming of climate, etc., thereby to particulate matter, ozone, NO in the atmospheric environment 2 、SO 2 The research on optical and physical properties, the research on the formation reasons and influencing factors, and the like, are of great significance.
The laser radar applied to the atmospheric environment detection technology is a very common detection instrument, has high spatial and temporal resolution, can continuously monitor the vertical distribution of atmospheric pollutants such as atmospheric particulates, ozone and the like for a long time, and has been widely applied worldwide. The laser radar is the most common atmospheric environment detection technology, and has different specific applications aiming at different atmospheric pollutants. For aerosol represented by atmospheric particulates, a multi-wavelength polarization laser radar based on Mie scattering is generally adopted; for the reactive gases and greenhouse gases in the atmosphere, such as ozone and NO 2 、SO 2 Etc., differential absorption lidar technology is commonly employed. As an active optical remote sensing technology, the differential absorption laser radar technology has the characteristics of high spatial resolution, high detection sensitivity, large measurement range and the like, can realize the targets which are difficult to realize by the conventional technical means such as horizontal and vertical spatial distribution detection of atmospheric trace gas, overhead source exhaust gas monitoring and the like, and has unique application value in the remote sensing monitoring of atmospheric gas concentration.
There are many research directions for the differential absorption lidar technology, and the light source selection of the differential absorption lidar technology has been diversified up to now, wherein the research on the tunable dual-wavelength laser as the lidar light source has gradually become one of the objects of major attention of many researchers in recent years. Existing ways of generating tunable dual-wavelength laser light include nonlinear frequency conversion, active ion level splitting, etc., but these systems are relatively complex in design and more cumbersome to operate. The method of generating two-wavelength laser based on dye laser is an emerging technological means in recent years, but the biggest problem in the implementation of the method is that the devices utilize gain regions of the same space or adjacent spaces of the same dye, and the relative intensities of light of two wavelengths are difficult to control due to mode competition. And the adjustment of the two wavelengths is mutually restricted, and can not be completely independent. In summary, how to accurately select and generate the detection wavelength and the reference wavelength required for detection is the key of the entire lidar system.
Disclosure of Invention
In order to overcome the defects of the prior art, the invention provides a differential absorption laser radar light source for detecting harmful gases in atmospheric environment, SO that a laser with continuously tunable dual wavelengths can be obtained and used as the differential absorption laser radar light source, and therefore, the detection wavelength and the reference wavelength required by detection can be accurately selected and generated for effectively detecting SO in the atmospheric environment 2 、CS 2 And the concentration of harmful gases.
In order to achieve the purpose, the invention adopts the following technical scheme:
the invention relates to a differential absorption laser radar light source for detecting harmful gas in atmospheric environment, which is characterized by comprising the following components: the device comprises a laser pumping source, an optical system, a dye laser resonant cavity and an optical frequency doubling system; YAG solid laser device, wherein the laser pump source is Nd of pulse working mode; the optical system includes: frequency doubling crystals, half-wave plates, polarizing plates, total reflection mirrors and cylindrical lenses; the dye laser resonant cavity comprises: blazed grating, dye cell, output coupling mirror; the optical frequency doubling system comprises: the device comprises a polarizer, a transmission reflector, a nonlinear frequency doubling crystal, a bicolor wave plate and a beam combiner;
laser emitted by the laser pump source passes through the frequency doubling crystal and then outputs frequency doubling laser, the laser passes through the half-wave plate and the output energy adjustment of the polaroid in sequence, the total reflection mirror is used for folding the optical path to obtain pump light, and the pump light forms linear light spot pump light to irradiate into the dye cell from the side after being shaped by the cylindrical lens;
the dye pool is filled with an ethanol solution of Nile red as a gain medium of the dye laser resonant cavity, and the ethanol solution, the blazed grating and the output coupling mirror together form the laser resonant cavity, so that the linear light spot pumping light generates dye laser in the laser resonant cavity, is output from the right side of the output coupling mirror after wavelength tuning, and finally outputs frequency doubling laser after frequency doubling treatment of a polarizer, a transmission reflector, a nonlinear frequency doubling crystal, a bicolor wave plate and a beam combiner in sequence, namely the differential absorption laser radar light source.
The differential absorption laser radar light source of the invention is also characterized in that: and a total reflection mirror is arranged below the blazed grating of the dye laser resonant cavity, and the total reflection mirror, the dye cell, the blazed grating and the output coupling mirror form a laser resonant cavity with a Littman-Metcalf configuration.
The dye laser in the laser resonant cavity is generated according to the following process:
rotating a dye cell filled with an ethanol solution of nile red clockwise, and forming a certain angle with a main optical axis of dye laser, so that a linear laser track and an annular laser track exist in a dye laser resonant cavity at the same time; the two keep stable in the cavity and oscillate back and forth, finally forming dual-wavelength laser output.
The dual-wavelength dye laser is used for tuning the wavelength according to the following steps:
step 1a, rotating the blazed grating to simultaneously change the incident angle of a linear laser track and an annular laser track, so as to change the oscillation wavelength of the linear laser track and the annular laser track in the dye laser resonant cavity;
and 2a, keeping the rotation angle of the blazed grating unchanged, and translating the blazed grating from far to near to the dye pool, so that the wavelength interval of the dual-wavelength dye laser is continuously changed in the translation range to realize wavelength tuning.
The dual-wavelength dye laser is used for wavelength tuning according to the following steps:
step 1b, keeping the angle and the position of the blazed grating unchanged, and simultaneously changing the incident angle of a linear laser track and an annular laser track by rotating the total reflection mirror, so as to change the oscillation wavelength of the linear laser track and the annular laser track in the dye laser resonant cavity;
and 2b, keeping the rotation angle of the blazed grating and the total reflection mirror unchanged, and translating the total reflection mirror from far to near to the blazed grating, so that the wavelength interval of the dual-wavelength dye laser is continuously changed in the translation range to realize wavelength tuning.
Compared with the prior art, the invention has the beneficial effects that:
1. the invention utilizes the solvation color development characteristic of organic laser dye Nile red and combines the grating resonant cavity to tune the laser wavelength, thereby realizing the dye laser output with continuously adjustable wavelength. The technology for tuning the wavelength through the dispersion element can utilize a motor to control rotation or translation, realizes precise tuning, and has simple operation and convenient integration.
2. The invention can realize the continuous tunable output of the dual-wavelength dye laser by utilizing the total internal reflection system consisting of the blazed grating, the dye cell and the output coupling mirror and by precise tuning. The means for realizing the dual-wavelength laser output is novel, and compared with other technical means such as nonlinear optics and the like, the dual-wavelength laser is easier to obtain; in addition, by replacing a laser gain medium, namely laser dye, the dual-wavelength laser output covering the wide spectral range of ultraviolet, visible light and near infrared can be realized, and the application range and the utilization value of the dual-wavelength laser output are immeasurable.
3. The invention can realize double frequency and triple frequency of output dye laser by using an optical frequency doubling system to obtain double-wavelength laser light sources of 190-220 nm and 290-330 nm, the wavelength interval is continuously adjustable within the range of 0.2-2.5 nm, and the invention can be used for the complete machine research and development of differential absorption laser radars and provides light source technical support for trace detection of harmful gases such as sulfur dioxide, carbon disulfide and the like in atmospheric environment.
4. The invention has simple integral structure and easy operation, can integrate the laser pumping source, the resonant cavity and the optical frequency doubling system into a whole, and has relatively low equipment cost and wide application.
Drawings
FIG. 1 is an optical path diagram of a differential absorption lidar light source in embodiment 1 of the invention;
FIG. 2 is a schematic diagram showing the trace of the oscillating laser in the dye laser resonator in example 1 of the present invention;
fig. 3 is a tunable dual wavelength laser spectrum obtained by rotating a grating in embodiment 1 of the present invention;
fig. 4 is a laser spectrum of a two-wavelength interval continuously varied by translating a blazed grating in embodiment 1 of the present invention;
FIG. 5 is a light path diagram of a differential absorption lidar light source in a Littman-Metcalf configuration in example 2 of the present invention;
FIG. 6 is a schematic diagram showing the locus of a two-wavelength oscillation laser in a dye laser resonator in example 2 of the present invention;
fig. 7 is a tunable dual wavelength laser spectrum obtained by rotating the holomirror in embodiment 2 of the present invention;
fig. 8 is a laser spectrum with continuously changing two wavelength intervals obtained by translating the total reflection mirror in embodiment 2 of the present invention.
Detailed Description
Example 1: as shown in fig. 1, a differential absorption lidar light source for harmful gas detection in an atmospheric environment comprises: the device comprises a laser pumping source 1, an optical system, a dye laser resonant cavity and an optical frequency doubling system; wherein, the laser pump source 1 is Nd: YAG solid laser in pulse working mode; the optical system includes: frequency doubling crystal 2, half-wave plate 3, polaroid 4, total reflection mirror 5 and cylindrical lens 6; the dye laser resonator includes: blazed grating 7, dye cell 8, output coupling mirror 9; the optical frequency doubling system comprises: the device comprises a polarizer 10, a transmission reflector 11, a nonlinear frequency doubling crystal 12, a bicolor wave plate 13 and a light beam combiner 14;
laser emitted by a laser pump source 1 passes through a frequency doubling crystal 2 and then outputs frequency doubling laser, the laser sequentially passes through a half-wave plate 3 and output energy adjustment of a polaroid 4, a light path is folded by a total reflection mirror 5 to obtain pump light, and the pump light forms linear facula pump light to irradiate into a dye cell 8 from the side after being shaped by a cylindrical lens 6;
the dye cell 8 is filled with an ethanol solution of nile red as a gain medium of the dye laser resonant cavity, and forms the laser resonant cavity together with the blazed grating 7 and the output coupling mirror 9, so that linear spot pump light generates dye laser in the laser resonant cavity, is output from the right side of the output coupling mirror 9 after wavelength tuning, and finally outputs frequency-doubled laser after frequency doubling treatment sequentially through a polarizer 10, a transmission reflecting mirror 11, a nonlinear frequency doubling crystal 12, a two-color wave plate 13 and a beam combiner 14, namely the differential absorption laser radar light source.
The dual-wavelength dye laser in the laser resonant cavity in this embodiment 1 is generated as follows:
the dye cell 8 is filled with a nile red/ethanol solution with proper concentration as a gain medium of the dye laser; excited radiation generates fluorescence in the dye cell 8 through the side irradiation of a 532nm pumping light source, stable laser oscillation is formed through the feedback of a resonant cavity formed by the blazed grating 7 and the output coupling mirror 9, and finally dye laser with single wavelength is output to the right;
fig. 2 is a schematic diagram showing the trajectory of the laser light of two-wavelength oscillation in the dye laser resonator in example 1. Rotating a dye cell 8 filled with an ethanol solution of nile red clockwise, and forming a certain angle with a main optical axis of dye laser, so that a linear laser track 101 and an annular laser track 102 exist in a dye laser resonant cavity at the same time; the two keep stable in the cavity and oscillate back and forth, finally forming dual-wavelength laser output.
In specific implementation, the wavelength tuning of the dual-wavelength dye laser is carried out according to the following steps:
step 1a, simultaneously changing the incident angle of a linear laser track 101 and an annular laser track 102 by rotating a blazed grating 7, so as to change the oscillation wavelength of the linear laser track 101 and the annular laser track 102 in a dye laser resonant cavity; when the dye pool is horizontally placed, only one laser track exists in the resonant cavity, namely a linear laser track 101; when the dye cell is tilted clockwise by a slight angle, another laser track appears in the cavity due to total internal reflection, i.e. a ring-shaped laser track 102, coexisting with the linear laser track. The two keep stable and oscillate back and forth in the resonant cavity, and the dual-wavelength laser output is finally formed due to different lengths of oscillation tracks. Fig. 3 is a laser spectrum obtained in the optical path of example 1, and a continuously tunable dual-wavelength laser output from 626.6nm to 697.8nm can be realized by rotating the grating by 3 °, with a tuning range as high as 71.2nm;
and 2a, keeping the rotation angle of the blazed grating 7 unchanged, and translating the blazed grating from far to near to the dye pool 8, so that the wavelength interval of the dual-wavelength dye laser is continuously changed in the translation range to realize wavelength tuning. When the rotation angle of the grating is kept unchanged and the grating is translated from near to far, the total length of the resonant cavity is increased, so that in order to form a closed cavity structure, the incident angle of the ring-shaped laser track 102 is inevitably changed, and the oscillation wavelength of the ring-shaped laser track is changed; meanwhile, the incident angle of the linear laser track 101 is only dependent on the grating rotation angle and does not change, and thus the oscillation wavelength thereof does not change. Finally, a laser spectrum with a continuously changing two-wavelength interval can be obtained from the output end, as shown in fig. 4. By translation, a dual-wavelength laser light source with a wavelength interval continuously changing in the range of 0.7-5 nm can be obtained. After frequency doubling, the dual-wavelength interval is 0.35-2.5 nm, and an important reference basis can be provided for the preparation of a differential absorption laser radar light source.
Example 2: a total reflection mirror 15 is arranged below the blazed grating 7 of the dye laser resonant cavity, and forms a Littman-Metcalf structured laser resonant cavity together with the dye cell 8, the blazed grating 7 and the output coupling mirror 9, as shown in fig. 5.
The dual-wavelength dye laser in the laser resonant cavity with the Littman-Metcalf configuration is generated according to the following process:
the dye cell 8 is filled with a nile red/ethanol solution with a proper concentration to be used as a gain medium of the dye laser; excited radiation generates fluorescence in the dye cell 8 through side irradiation of a 532nm pumping light source, the fluorescence is stably oscillated in the dye laser resonant cavity, and finally dye laser with single wavelength output to the right is formed;
fig. 6 is a schematic diagram showing the trajectory of the two-wavelength oscillation laser in the dye laser resonator in example 2. Rotating a dye cell 8 filled with an ethanol solution of nile red clockwise, and forming a certain angle with a main optical axis of dye laser, so that a linear laser track 103 and an annular laser track 104 exist in a dye laser resonant cavity at the same time; the two keep stable in the cavity and oscillate back and forth, finally forming the dual-wavelength laser output.
The wavelength tuning of the dual-wavelength dye laser in the laser resonant cavity with the Littman-Metcalf configuration is carried out according to the following steps:
step 1b, keeping the angle and the position of the blazed grating 7 unchanged, and simultaneously changing the incident angle of the linear laser track 103 and the annular laser track 104 by rotating the total reflection mirror 15, so as to change the oscillation wavelength of the linear laser track 103 and the annular laser track 104 in the dye laser resonant cavity; when the dye cell is tilted clockwise by a small angle, two laser tracks, namely a linear laser track 103 and a ring laser track 104, exist simultaneously in the resonant cavity due to Total Internal Reflection (TIR). They remain stable and oscillate back and forth, ultimately forming a dual wavelength laser output. Fig. 7 shows the continuously tunable dual-wavelength laser output from 634.4nm to 663.3nm realized by rotating the total reflection mirror by 2.1 ° in embodiment 2, and the tuning range covers 29nm.
And 2b, keeping the rotation angles of the blazed grating 7 and the all-reflection mirror 15 unchanged, and translating the all-reflection mirror 15 from far to near to the blazed grating 7, so that the wavelength interval of the dual-wavelength dye laser is continuously changed in the translation range to realize wavelength tuning. The angle between the blazed grating 7 and the total reflection mirror 15 is not changed, the position of the blazed grating 7 is kept unchanged, the distance between the blazed grating 7 and the total reflection mirror 15 is changed by translating the total reflection mirror, and a dual-wavelength laser light source with the wavelength interval continuously changed within the range of 1.5 nm-4 nm can be obtained, and the tuning result is shown in fig. 8. After frequency doubling, the dual-wavelength interval is 0.75-2 nm, and an important reference basis can be provided for the preparation of a differential absorption laser radar light source.
In summary, the differential absorption lidar light source for detecting harmful gas in atmospheric environment and the method for generating dual-wavelength laser utilize solvation color development characteristic and excellent laser characteristic of organic laser dye nile red, and realize continuous tunable laser output of two wavelengths in a large range of 620 nm-700 nm through precise tuning in a total internal reflection system formed by a grating resonant cavity and a dye cell; meanwhile, a nonlinear optical frequency doubling system is utilized to realize frequency doubling and frequency tripling of output laser to obtain 190-220 nm and 290-330 nm dual-wavelength laser sources, the wavelength interval is continuously adjustable within the range of 0.2-2.5 nm, and the laser source can be used for the complete machine research and development of differential absorption laser radars and provide important support for the light source technology for trace detection of harmful gases such as sulfur dioxide, carbon disulfide and the like in the atmospheric environment.
Claims (5)
1. A differential absorption lidar light source for harmful gas detection in an atmospheric environment, comprising: the device comprises a laser pumping source (1), an optical system, a dye laser resonant cavity and an optical frequency doubling system; YAG solid laser of pulse working mode is adopted as the laser pumping source (1); the optical system includes: the frequency doubling crystal (2), a half-wave plate (3), a polarizing plate (4), a total reflection mirror (5) and a cylindrical lens (6); the dye laser resonant cavity comprises: a blazed grating (7), a dye cell (8) and an output coupling mirror (9); the optical frequency doubling system comprises: a polarizer (10), a transmission reflector (11), a nonlinear frequency doubling crystal (12), a bicolor wave plate (13) and a beam combiner (14);
laser emitted by the laser pumping source (1) passes through the frequency doubling crystal (2) and then outputs frequency doubling laser, then passes through the half-wave plate (3) and the polaroid (4) in sequence to adjust output energy, the total reflection mirror (5) folds a light path to obtain pumping light, and the pumping light forms linear light spot pumping light to irradiate into the dye cell (8) from the side after being shaped by the cylindrical lens (6);
the dye cell (8) is filled with an ethanol solution of Nile red as a gain medium of a dye laser resonant cavity, and forms a laser resonant cavity together with the blazed grating (7) and the output coupling mirror (9), so that the linear light spot pump light generates dye laser in the laser resonant cavity, is output from the right side of the output coupling mirror (9) after wavelength tuning, and finally outputs frequency-doubled laser after frequency doubling treatment of a polarizer (10), a transmission reflector (11), a nonlinear frequency doubling crystal (12), a bicolor wave plate (13) and a beam combiner (14) in sequence, namely the differential absorption laser radar light source.
2. The differential absorption lidar light source of claim 1, wherein: and a total reflection mirror (15) is arranged below the blazed grating (7) of the dye laser resonant cavity, and the dye cell (8), the blazed grating (7) and the output coupling mirror (9) together form a laser resonant cavity with a Littman-Metcalf configuration.
3. The differential absorption lidar light source of claim 1 or claim 2, wherein the dye laser within the lasing cavity is generated by:
clockwise rotating a dye cell (8) filled with an ethanol solution of Nile red, and forming a certain angle with a main optical axis of dye laser, so that a linear laser track (101) and an annular laser track (102) exist in a dye laser resonant cavity at the same time; the two keep stable in the cavity and oscillate back and forth, finally forming dual-wavelength laser output.
4. The lidar light source of claim 1, wherein the dual wavelength dye laser is wavelength tuned by:
step 1a, simultaneously changing the incidence angle of a linear laser track (101) and an annular laser track (102) by rotating the blazed grating (7), thereby changing the oscillation wavelength of the linear laser track (101) and the annular laser track (102) in the dye laser resonant cavity;
and 2a, keeping the rotation angle of the blazed grating (7) unchanged, and translating the blazed grating from far to near to the dye pool (8), so that the wavelength interval of the dual-wavelength dye laser is continuously changed in the translation range to realize wavelength tuning.
5. The differential absorption lidar light source of claim 2, wherein the dual wavelength dye laser is wavelength tuned by:
step 1b, keeping the angle and the position of the blazed grating (7) unchanged, and simultaneously changing the incidence angle of a linear laser track (103) and an annular laser track (104) by rotating the total reflection mirror (15), so as to change the oscillation wavelength of the linear laser track (103) and the annular laser track (104) in the dye laser resonant cavity;
and 2b, keeping the rotation angles of the blazed grating (7) and the total reflection mirror (15) unchanged, and translating the total reflection mirror (15) from far to near to the blazed grating (7), so that the wavelength interval of the dual-wavelength dye laser is continuously changed in the translation range to realize wavelength tuning.
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| CN109755853A (en) * | 2019-03-12 | 2019-05-14 | 中国科学技术大学 | A kind of dye laser device of Nile red organic solvent as gain media |
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| CN109755853A (en) * | 2019-03-12 | 2019-05-14 | 中国科学技术大学 | A kind of dye laser device of Nile red organic solvent as gain media |
| CN110635348A (en) * | 2019-10-29 | 2019-12-31 | 中国科学技术大学 | Nile red dye laser for acid detection |
| CN112202043A (en) * | 2020-08-31 | 2021-01-08 | 西安电子科技大学 | Coumarin C440 and C460 co-doped dye tunable laser |
| CN114354531A (en) * | 2021-12-30 | 2022-04-15 | 合肥工业大学 | Plastic identification system of double-wavelength coherent light source based on near infrared |
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