Optical system of scattering-type cloud particle detector
Technical field
The present invention has designed a kind of cloud particle detector that receives based on single-mode fiber coupling output semiconductor laser, scattering multi-angle.Use single-mode fiber coupling output semiconductor laser and square hole diaphragm development cloud particle detector, by using square hole to cut away the marginal portion of Gaussian beam, the top that only keeps Gaussian beam, utilize the 4f optical system that square hole is imaged on and measure the center, sensitizing range, measuring the approximate flat top beam of center, sensitizing range generation, solve the illumination unevenness problem, use the square hole diaphragm to produce square light beam, it is identical to make particle pass time of illuminated area, the time width of electric pulse is identical, is easy to follow-up electronics and handles.The cloud particle detector of invention has two scattared energy receiving systems, receives particle scattering from forward direction and rear flank to two angles, according to the ratio of two angle output electric signal, can infer the phase of cloud particle.
Background technology
Increasing rain artificially is one of most important activity of weather modification, has very high social benefit and economic benefit.Moisture is converted into precipitation more in the cloud in order to make, thereby reaches the purpose that increases rain, and the action need of increasing rain artificially carries out the catalysis operation opportune moment at the suitable position of cloud body.But, because the factor such as complicated and changeable of cloud body, only according to the very difficult district broadcast that determines accurately in the cloud of the resulting information of more ground observation methods, this accuracy to the catalysis decision-making makes a big impact, and structure therefore how to understand cloud system accurately is the focus of weather modification problem in science.Utilizing aircraft directly to fly into cloud system inside, effectively observe, is the research method that modern age, cloud physics adopted always.Since the seventies in last century, the U.S. has developed the sub-measuring system of airborne cloud particle (PMS) of a cover robotization, this cover instrument all is being greatly improved aspect automatic measurement and the detection accuracy at present, wherein the scattering-type cloud particle probe is an ingredient in this cover instrument, and its measurement range is 0.5-47um.
At present, state-of-the-art scattering-type cloud particle measuring system function operation principle is as follows, and system uses the continuous laser of 658nm as lighting source, and the illuminating bundle cross section is 200 * 180um, and the measurement sensitizing range size of formation is 2mm * 180um.Cloud particle probe is installed in the aircraft outside, and the Laser Transmission direction is perpendicular to the direction of aircraft flight, can think during aircraft flight that particle passes laser beam perpendicular to beam direction, particle passes scattering laser energy in the process, direct light is attached to the mirror reversal bright dipping road of being all-trans on the collecting lens, monitoring in order to energy of lasers, scattared energy between scattered light collection mirror is collected 4-12 °, the light of collecting is divided into 33/66% two parts (detection channels and quality control passage) by spectroscope, uses photodetector to survey respectively.Wherein its face of quality control passage has aperture, when particle range observation center is far away, according to the viewpoint of how much imagings then the position of imaging change (front and back change), and the light of part is blocked by diaphragm, therefore the situation of quality control channel energy less than detection channels appear, it is few more that distance focal point then quality control far away more passage is surveyed the energy that obtains, and the detection channels energy does not change substantially, then basis relation between the two can be given up distance focal point particle far away.On electronics, the electric signal that detection channels and quality control passage come out at first is exaggerated, carry out quality control by comparer then, use the multi channel signals analyser that the signal of detection channels is analyzed simultaneously, comparer be output as 0 or the digital signal of 5V give DSP, as the basis for estimation that receives and reject, if high level is then given computing machine with the signal of analyser output by the RS232 serial ports, if low level, then system does not write down this particle.
Finding in the O﹠M for a long time, with regard to opticator, mainly there is the problem of the following aspects for above-mentioned scattering-type cloud particle measuring system.(1) system uses the semiconductor laser of free space output, the branch that in the transmission course of light, has fast axle, slow axis, through hot spot behind the segment distance is elliptical shape, and not only zlasing mode is in X-axis, Y-axis difference, and is unfavorable for design, processing, the processing of subsequent optical system; (2) 200 * 180um light beam in the system is to be formed by diaphragm, because the diaphragm aperture is very little, must consider the diffraction in the wave optics, therefore, after laser arrives the optical absorption body, its size is far above this size of 200um * 180um, because particle scattering energy itself is very little, must highly suppress direct light, the area that increases catoptron can increase the inhibition degree of direct light, but simultaneously also loss scattered light, and be near 0 ° scattered light, make scattered light be subjected to very big decay; (3) the direct light total reflective mirror directly is glued on the scattered light collecting lens owing to can not use adjustment rack (being afraid of scattered light is blocked); (4) do not have narrow band pass filter in the receiving system, and the detection of cloud particle generally is to carry out by day, a lot of parasitic lights enter receiving system, influence the signal to noise ratio (S/N ratio) of system; (5) this system can only obtain the size information of cloud particle, can not obtain the phase of cloud particle.The development of Modern Optics Technology provides necessary condition for improving this system, by adopting modern photoelectric device, designing in conjunction with tight geometrical optics wave optics, should be able to obtain being better than the sub-detection system of cloud particle of this system.
Summary of the invention
The technical matters that the present invention solves: by using single-mode fiber coupling output semiconductor laser, non-sphere collimation mirror, square hole diaphragm and 4f transformation system, both produced the even illumination of the laser that needs, solve the diffraction problem in the light beam cutting process again, improved the purity that scattered light receives; The cloud particle detector of invention has two receiving angles, according to the ratio of two angle output electric signal, can infer the phase of cloud particle.
Technical solution of the present invention is as follows:
A kind of optical system of scattering-type cloud particle detector: comprise that transmitting optics unit, forward scattering probe unit and rear flank are to the scatter sounding unit;
Described transmitting optics unit comprises: single-mode fiber coupling output laser (1), non-sphere collimation mirror (2), square hole diaphragm (3), 4f optical system; Described 4f optical system comprises fourier transform lens (4), inverse-Fourier transform lens (6) and first total reflective mirror (5);
Described forward scattering probe unit comprises: forward scattering light collecting lens (9), first narrow band pass filter (10), second total reflective mirror (11), first photodetector (12), convergent lens (13), Amici prism (14), second photodetector (15), aperture (16), the 3rd photodetector (17);
Described rear flank comprises to the scatter sounding unit: light collection lens (20), the 4th photodetector (21) are received to scattering in second narrow band pass filter (19), rear flank;
The light of described single-mode fiber coupling output laser (1) optical fiber connector output uses aspheric mirror (2) to collimate, the collimation back uses square hole diaphragm (3) to go cutting, fourier transform lens (4) conversion through the 4f optical system, by first total reflective mirror (5) light after the conversion is turned over 90 ° then, send into inverse-Fourier transform lens (6), square hole diaphragm (3) is imaged onto the middle i.e. center between first window glass (7), second window glass (8) of measured zone; It is identical to locate beam characteristics at this centre position beam characteristics and square hole diaphragm (3), diffraction phenomena is not obvious, therefore, with this point be one of the center among a small circle in, form evenly illumination, because particle is identical through the time of light beam, the time domain specification that produces electric signal is identical simultaneously, eliminate edge effect, be easy to subsequent treatment.
After the forward scattering light of particle is received by scattered light receiver lens (9), filter parasitic light through narrow band pass filter (10) and send into second total reflective mirror (11), second total reflective mirror (11) center drilling, allow direct light directly by measuring by first photodetector (12), second total reflective mirror (11) reflected light is sent into convergent lens (13), divide two parts through Amici prism (14) with light again after the convergence, wherein transmitted light is surveyed by second photodetector (15), and wherein reflected light enters the 3rd photodetector (17) through aperture (16);
The rear flank of particle filters parasitic light to scattered light through second narrow band pass filter (19), is received to scattered light collecting lens (20) by the rear flank, and is surveyed by the 4th photodetector (21);
System receives the scattering of cloud particle on both direction, collect forward scattering and rear flank respectively to scattering, can infer the phase of particle to be measured according to the output of photodetector on the both direction.
Scattering-type cloud particle detection system light path may further comprise the steps:
(1) laser of single-mode fiber coupling output laser is exported from optical fiber connector;
(2) non-sphere collimation mirror becomes directional light with the output of its optical fiber connector, and its spot size is 2mm;
(3) use laser beam after the square hole diaphragm of 300um * 300um goes to cut shaping, only be suitable in the middle of the Gaussian beam part relatively uniformly;
(4) use the 4f optical system that being imaged onto of the square hole on the square hole diaphragm measured sensitizing range (center position between first window glass and second window glass);
(5) all radiating portion elements are isolated by window glass and outside air;
(6) all forward scattering receiving devices are isolated by window glass and outside air;
(7) the forward scattering lens are collected 13 ° with interior light signal, comprise direct signal and scattered signal;
(8) utilize narrow band pass filter to suppress the parasitic light of collecting, increase signal to noise ratio (S/N ratio);
(9) use 45 ° of total reflective mirrors that scattered light is all-trans, perforate in the middle of this total reflective mirror, the size in hole is passed through direct light fully.
(10) scattered light is focused on by convergent lens;
(11) scattered light after Amici prism will focus on is divided into 3: 1 two parts, Amici prism anti-3 saturating 1;
(12) Amici prism reflecting part corresponding mass control channel, the detector front is put an aperture and is used for quality control, and the transmission part is directly surveyed by photodetector;
(13) rear flank isolates by window glass and ambient atmosphere to the scattered portion optical element;
(14) narrow band pass filter is used to suppress the noise that parasitic light causes;
(15) collecting lens focuses on detector with the rear flank to scattering, is used for the detection of rear flank to scattared energy;
Laser instrument is that optical fiber coupling output laser is a continuous wave laser among the present invention, and wavelength is 685nm, and output power is 35mW.The work bore of said non-sphere collimation mirror is 2mm, and the angle of divergence of collimation back laser is less than 1mrad.Said square hole diaphragm square hole size is 300um * 300um.The 4f optical system comprises fourier transform lens, total reflective mirror, inverse-Fourier transform lens.Fourier transform lens carries out Fourier transform to the light through the square hole diaphragm, total reflective mirror changes 90 degree with the transmission direction of light, but do not change the character of light, the inverse-Fourier transform lens carry out inverse-Fourier transform to the light of incident, and the picture of square hole is presented on and measures in the middle of the sensitizing range the most at last.
Described first, second, third window glass is quartzy dull and stereotyped, is used for sealing optical transmitting system, forward scattering receiving system, rear flank respectively to receiving system.
Described scattered light receiver lens is used for receiving forward scattering and rear flank respectively to scattering, and the reception solid angle that receiver lens became is respectively 4-13 °, 128.5-141.5 °.It is 685nm that described narrow band pass filter center sees through wavelength, and bandwidth is 10nm, and transmitance is 99% in the bandwidth.Described total reflective mirror (11) is all-trans for 685nm45 °, and there is a square hole at the center, can allow the direct light of laser directly pass through, and is radiated on the detector, is used to monitor the shake of energy of lasers.
Described convergent lens (13) converges to detector with the particle scattering light signal, differs very little after the convergence, near diffraction limit.Described Amici prism is divided into 3: 1 two parts with scattered light signal.Described aperture (16) is used for the control of search coverage, and its diameter is 200um.Described photodetector (12), (15), (17), (21) are respectively applied for laser power supervision, forward scattering detection, the detection of forward scattering quality control passage, rear flank to scatter sounding.
The advantage that the present invention compared with prior art has is:
The present invention is directed to two problems of edge effect in Beam Control difficulty in the cloud particle detector development process and the instrument use, by using single-mode fiber coupling output semiconductor laser, square hole diaphragm and 4f optical system development cloud particle detector, and, can obtain the sub-phase information of cloud particle by multi-angle collection scattered light.The free output facula of semiconductor laser is generally ellipse, and oval hot spot is wayward, therefore, this ellipse light spot is converged enter single-mode fiber, and the hot spot of optical fiber connector output is a Gaussian beam, is ideal Laser Transmission pattern; Edge effect is one of main source of error of water dust particle detector, by using the square hole diaphragm to cut away the marginal portion of Gaussian beam, only keep the top of Gaussian beam, use the 4f optical system to reduce diffractive effect, produce approximate flat top beam, eliminate edge effect; The cloud particle detector of invention has two scattared energy receiving systems, receives particle scattering from forward direction and rear flank to two angles, according to the ratio of two angle output electric signal, can infer the phase of cloud particle.
(1) use single-mode fiber coupling output laser, the zlasing mode of output is good, and hot spot is that circular light spot is easy to handle; Use aspheric mirror that optical fiber output light is collimated, the laser beam divergence behind the collimation is little and beam diameter is little;
(2) utilize the square hole diaphragm to go to cut Gaussian beam, utilize the 4f optical system to eliminate the influence of diffraction system;
(3) total reflective mirror center drilling in system allows direct light directly pass, and in order to the monitoring energy of lasers, has reduced the difficulty of optics processing.
(4) in the scattering receiving course, use narrow band pass filter, the noise that the parasitic light when the inhibition instrument works by day causes.
(5) use the reception of multi-direction scattering, not only receive forward scattering, and the receiver side back scattering, utilize forward scattering can obtain the size of particle, utilize the ratio of two direction scatterings can obtain the phase information of particle.
Description of drawings:
Fig. 1 is the light path synoptic diagram of scattering-type cloud particle detector
Among the figure: 1-single-mode fiber coupling output laser; The 2-non-sphere collimation mirror; 3-square hole diaphragm; The 4-fourier transform lens; 5-first total reflective mirror; 6-inverse-Fourier transform lens; 7-first window glass; 8-second window glass; 9-forward scattering light collecting lens; 10-first narrow band pass filter; 11-second total reflective mirror; 12-first photodetector; The 13-convergent lens; The 14-Amici prism; 15-second photodetector; The 16-aperture; 17-the 3rd photodetector; 18-the 3rd window glass; 19-second narrow band pass filter; 20-collects mirror to scattering in the rear flank; 21-the 4th photodetector.
Embodiment:
As shown in Figure 1, this is the scattering-type cloud particle detector of Benq in novel light path, and it uses single-mode fiber coupling output semiconductor laser as lighting source, uses non-sphere collimation mirror with laser alignment; Utilize square hole diaphragm and 4f transformation system, both produced the even illumination of the laser that needs, solved the diffraction problem in the light beam cutting process again, improved the purity that scattered light receives; When receiving scattering, use narrow band pass filter, improved the signal to noise ratio (S/N ratio) when instrument works by day; The cloud particle detector of invention has two receiving angles, not only can obtain the size of cloud particle, and can infer the phase of cloud particle according to the ratio of two scattered through angles intensity.
This system is by a single-mode fiber coupling output laser 1, non-sphere collimation mirror 2, square hole diaphragm 3, fourier transform lens 4, first total reflective mirror 5, inverse-Fourier transform lens 6, first window glass 7, second window glass 8, forward scattering light collecting lens 9, first narrow band pass filter 10, second total reflective mirror 11, first photodetector 12, convergent lens 13, Amici prism 14, second photodetector 15, aperture 16, the 3rd photodetector 17, the 3rd window glass 18, second narrow band pass filter 19, mirror 20 is collected to scattering in the rear flank, the 4th photodetector 21 is formed.
Wherein single-mode fiber coupling output laser 1 is used for producing the single mode continuous laser of 685nm, in native system as lighting source, wherein non-sphere collimation mirror 2 is used for the laser of optical fiber connector output is collimated, aspheric mirror has better collimation effect with respect to spherical mirror, and the angle of divergence of collimation back laser is less than 1mrad.Wherein square hole diaphragm 3 is used to cut laser beam, only gets the center section of Gaussian beam, produces approximate uniform illumination.Fourier transform lens 4 carries out Fourier transform through the laser of diaphragm cutting.First total reflective mirror 5 turns over 90 ° with the light after the conversion, does not change the character of light.Inverse-Fourier transform lens 6 carry out inverse-Fourier transform to light, make the picture of its final square hole become center (center between first window glass and second window glass) in search coverage.
First window glass 7 is used for sealing optical transmitting system, and itself and ambient atmosphere are isolated.Second window glass 8 is used for sealing the forward direction receiving system, and itself and ambient atmosphere are isolated.The reception solid angle that forward scattering light collecting lens 9 is become is respectively 13 °.First narrow band pass filter is used for suppressing to enter the parasitic light of forward direction receiving system.Second total reflective mirror, 11 center drillings allow direct light directly pass through, and making the light that finally enters forward scatter system is 4-13 °.Photodetector 12 is used for the measurement of system's direct light, can be in order to the detection laser energy variation.Convergent lens 13 converges to detector with the particle scattering light signal, differs very little after the convergence, near diffraction limit.Amici prism 14 is divided into 3: 1 two parts with scattered light signal, and anti-3 saturating 1.Second photodetector 15 is used for obtaining the size of particle size, and its amplitude size is relevant with particle size.Aperture 16 is used for the control of search coverage, and its diameter is 200um.The 3rd photodetector 17 is used for quality control, according to the ratio of itself and second detector, can determine whether particle is surveying sensitive area.
The 3rd window glass 18 is used for sealed sides back scattering receiving system, and the rear flank is kept apart to scattering receiving element and outside air.Second narrow band pass filter 19 is used for suppressing the parasitic light of approaching side back scattering receiving element, improves signal to noise ratio (S/N ratio).To scattering, the solid angle of reception is 128.5-141.5 ° to rear flank that scattered light collecting lens 20 is used for receiving particle in the rear flank.The 4th photodetector 21 is used for the backward scattered detection of particle side.
Specific implementation process below in conjunction with the description of drawings scattering-type cloud particle detector.
During system works, open the power supply of optical fiber coupling output laser 1, the laser instrument bright dipping, the optical fiber afterbody has single-mode laser output, and the angle of divergence of output laser is decided by the numerical aperture of used optical fiber.The laser of dispersing collimates through aspheric mirror 2, the spot diameter of non-sphere collimation mirror output is 2mm, a triangle of laser is little to be 1mrad, characteristic according to single-mode optics, this moment, the energy distribution of hot spot was according to the rotational symmetric Gauss's hot spot of Gaussian function, the intermediate energy that is hot spot is big, radially reduces gradually.For obtaining approximate even illumination, place the square hole diaphragm 3 of a 300um * 300um at the light path center position.At the place, rear surface of being close to diaphragm, the beam shape that sees through is near square hole, but because orifice size is less, if there are not other optical lenses, along with the transmission of light, diffraction phenomena is very serious.For this reason, use the 4f optical system, the light that diaphragm comes out at first carries out Fourier transform through fourier transform lens 4, form frequency plane, carry out inverse-Fourier transform with identical 6 pairs of light of fourier transform lens again, the picture of aperture is become measuring center, sensitizing range (center between first window glass and second window glass), be equal to the hot spot characteristic at diaphragm place, can produce approximate even illumination in the characteristic of this position hot spot.The particle that passes the measurement sensitizing range is laser scattering towards periphery, and scattering process is followed the Mie scattering theory, and because particle is very little, can regard pointolite as.
The forward scattering light of particle is received by scattered light receiver lens 9, and filter the parasitic light of other wavelength of the system of entering with a narrow band pass filter 10, the solid angle of its reception is 13 ° to the maximum, but because near 0 °, scattered light and direct incident light can't separate, therefore, one 45 ° of total reflective mirrors 11 are placed in the optical filter back, and perforate in the middle of this total reflective mirror allows direct incident light pass through, this part light can be surveyed with first photodetector 12, variation that can monitoring laser power.Total reflective mirror 11 center drillings cause 0-4 ° to be lost with interior scattered light, scattered light in 4-13 ° enters and is reflected, assemble with convergent lens 13, converging light is divided into two parts by Amici prism 14 before entering detector, and this Amici prism is divided into anti-saturating 3: 1 two parts with flashlight.Transmitted light is directly surveyed by second photodetector 15, and its amplitude output signal is relevant with the particle size size.Reflected light must be the aperture 16 of 200um through diameter entering the 3rd photodetector 17.When particle when the center of measured zone is passed through, it is very little that this time is focused, can pass through aperture smoothly, along with particle enters the position deviation center of light path, it is big that imaging becomes, and causes part light to be blocked by aperture, the off-center position is many more, the light that is blocked is also just many more, causes the output of the 3rd photodetection 17 and second photodetector 15 to become 1: 1, this moment the particle process the path for measuring the edge of sensitizing range.
The rear flank is identical with the reception principle of forward scattering to scattering, is the optical axis difference, and no longer reuses quality control.The rear flank is collected by scattered light collecting lens 20 through optical window 18, narrow band pass filter 19 to scattered light, and the solid angle scope that these lens are collected light is 128.5-141.5 °, and the rear flank is surveyed by the 4th photodetector 21 to scattered light.
According to the Mie scattering theory, if particle is liquid, its refractive index is 1.33, when particle size one regularly, its pattern to the space scattering energy is fixed, and that is to say that the backward scattered ratio of forward scattering and side fixes.During actual measurement, the output of second photodetector 15 has determined the particle size of surveying, the ratio of second photodetector 15 and the 4th photodetector 21, if the front and back that just in time are Theoretical Calculation are to scattering ratio, at this moment, particle is liquid, otherwise, be designated as solid-state, i.e. ice crystal.