Adaptive optics celestial body target imaging system based on the picture clearing principle
Technical field
The present invention relates to a kind of adaptive optical imaging system, particularly a kind of Wave-front phase detector that do not need, low cost is based on the adaptive optics celestial body target imaging system of picture clearing principle.
Background technology
The stellar target that the dynamic disturbances of atmospheric turbulence not only makes telescope and observed is constantly shaken, but also constantly changes the shape of imaging facula, and therefore, atmospheric turbulence becomes the key factor of restriction terrestrial telescope resolution characteristic.The optical phase wavefront that is subjected to the atmospheric turbulence disturbance can be measured and proofread and correct to adaptive optical technique in real time, make and receive optical telescope and can obtain target picture near diffraction limit, therefore since the eighties in 20th century, adaptive optical technique is in astronomical sight, and fields such as Laser Transmission just are widely used.An ADAPTIVE OPTICS SYSTEMS that typically is used for the stellar target imaging compensating comprises Wavefront detecting, wavefront reconstruction and wavefront correction three parts composition, wherein wave front detector the most normal utilization be Hartmann wave front sensor, 61 unit celestial body imaging compensating systems as Photoelectric Technology Inst., Chinese Academy of Sciences, the breadboard SWAT of U.S. Lincoln system, and the Come-On system in Europe all adopts Hartmann wave front sensor.But, Hartmann wave front sensor, usually adopt microlens array to cut apart light beam aperture, and incident light is focused on the photosensitive target surface of photodetector (being generally CCD), perhaps lenticular focal plane hot spot image is imaged in the photodetector photosensitive target surface by a relay system.This class Hartmann sensor following shortcoming arranged: the coupling technique more complicated of microlens array and CCD, the focus error of the lenticule unit of microlens array is inconsistent can to influence sensor accuracy, photon utilization factor and quantum efficiency are lower, therefore are difficult to very dark celestial body target is carried out effective imaging; Before the measurement, must calibrate Hartmann wave front sensor with parallel beam, in system, must guarantee that the sub-aperture of Hartmann wave front sensor layout is corresponding according to certain relation with the distorting lens driver layout, otherwise can have influence on the stability of control algolithm and even The whole control system, this has also brought the difficult difficulty of debugging.What more can not ignore is, prices are rather stiff to be used for the high-precision Hartmann wave front sensor of astronomical sight, and the versatility of Hartmann wave front sensor is very poor, and different celestial body imaging self-adaptive optical systems often needs different Hartmann sensors, is difficult to mass production.
In addition, when under the condition of atmospheric turbulence especially severe, using this typical ADAPTIVE OPTICS SYSTEMS to carry out the celestial body imaging, stellar target just can not be considered as point target again, and must treat as the expansion target, therefore, the light that comes from stellar target can not equivalence be from same point, but from different one by one zones.These zonules can be considered as an isoplanatic region respectively, so the light beam that comes from celestial body will experience different atmospheric turbulence zones, therefore the Wave-front phase that is stood will be different with amplitude distortion.Yet what we utilized that Hartmann wave front sensor measures but is these set with light beam of difference spread function, and the controlled deformation mirror produces a Wave-front phase with the Wave-front phase conjugation of these light beams, compensation integral phase distortion.This mode is owing to have directly to carry out the conjugation processing respectively at the light wave from the different isoplanatic regions of stellar target, is difficult to obtain the stellar target picture near diffraction limit.
Summary of the invention
Technology of the present invention is dealt with problems: overcome existing typical stellar target imaging compensating ADAPTIVE OPTICS SYSTEMS and cost an arm and a leg, debug difficulties, influenced seriously by the non-vignetting error that waits, and be difficult under low light condition stellar target is effectively surveyed and the shortcoming of imaging, provide a kind of debugging convenient, low-cost, can effectively eliminate the non-grade of beacon vignetting error, and also can be to the adaptive optics celestial body target imaging system based on the picture clearing principle of effective detection of celestial body and imaging under low light condition.
Technical solution of the present invention is: based on the adaptive optics celestial body target imaging system of picture clearing principle, mainly comprise: the receiving telescope system, reflection deformable mirror, spectroscope, the high-speed figure processor, high-voltage amplifier, main control computer, snowslide secondary light pipe, image intensifying CCD camera, behind the primary mirror and secondary mirror of the light process receiving telescope system that stellar target comes, become parallel by eyepiece again or approaching parallel light, this bundle light is through after the reflection deformable mirror, incide and be divided into two bundles on the spectroscope, a branch of by lens focus and incide and be placed on the lens focal plane image intensifying CCD camera, the image information of surveying on image intensifying CCD camera through the built-in image capturing system of main control computer is transferred on the main control computer again, for the observation monitoring; Another bundle is focused on the snowslide secondary light pipe that lens converge in its focal plane, the objective function that the photon signal that snowslide secondary light pipe is detected will be optimized as the control algolithm that is built in the high-speed figure processor, principle according to the maximization objective function, the high-speed figure processor is carried out the Genetic Control algorithm, last high-voltage amplifier is applied to the plurality of voltages signal of the optimum that obtains through high-speed figure processor interative computation on each driver on the reflection deformable mirror, the control reflection deformable mirror produces and wavefront from the Beam Wave-Front conjugation of stellar target, proofread and correct the various aberrations of the Beam Wave-Front of stellar target, on the main control computer monitor, just can access stellar target image clearly this moment.
Described Genetic Control algorithm is a kind of genetic algorithm with global optimizing ability, is achieved as follows:
(1) generates the population (individual amount 30-100) that comprises some individualities at first at random, the magnitude of voltage decision that face shape of each individual corresponding respectively distorting lens as resonator end mirrors among the present invention, distoring mirror shape apply on the face driver after by distorting lens;
(2) behind the initialization population, need carry out encoding operation to individuality in the population, coding can pass through binary coding, also can pass through real coding, and the individuality behind the coding is referred to as chromosome.The present invention adopts the coded system of real coding;
(3) behind the coding, calculate the fitness of the correspondence of each minute surface individuality, fitness is to be used for weighing the good degree that each individuality in the population may reach or approach optimum solution, the ideal adaptation degree is big more, just approach optimum solution more, it is selected, and to participate in the later stage interlace operation just big more with the probability of mutation operation, and the light intensity signal that the present invention detects with snowslide secondary light pipe is as the fitness function that will optimize of genetic algorithm;
(4) after each individual fitness is calculated, overall situation genetic algorithm is according to carrying out selection operation with the directly proportional roulette selection mode of fitness, then in the mode that single-point intersects the individuality that is selected in the population is carried out interlace operation in twos according to certain crossover probability (0.5-0.99) again, and then itself carry out mutation operation to the part in the population is individual according to definitive variation probability (0.001-0.9).Selection, intersection and mutation operation are three topmost operations of overall Genetic Control algorithm, and they have determined the global optimizing performance and the convergence capabilities of overall Genetic Control algorithm together;
(5) above 4 steps of the every process of genetic algorithm are carried out once, will produce a new population.The continuous iteration of genetic algorithm is carried out above 4 steps, satisfies predefined termination condition up to algorithm.
Principle of the present invention is: adopt the end mirror of the reflection deformable mirror of plating highly reflecting films system as resonant cavity of solid state laser, reflection deformable mirror is controlled by genetic algorithm, output beam is focused on the focal plane through condenser lens, the objective function that will optimize the signal that detects on the focal plane as genetic algorithm makes distorting lens towards allowing the direction of objective function optimization produce corresponding deflection again.Voltage by each driver on the control reflection deformable mirror, change the surface configuration of distorting lens, produce correspondingly phase compensation amount, compensation fall in the resonator cavity various aberrations, thereby the structure of resonator cavity is changed, suppress higher order mode adaptively and produce, and create the resonator cavity condition that produces basic mode laser that is beneficial to, output beam quality is basic mode laser well.
Principle of the present invention is: the present invention is not needing to utilize under the prerequisite of artificial beacon beam, utilize light that stellar target itself sends as beacon beam, with the avalanche diode on the imaging system focal plane is sensitive detection parts, and the photon information of the beacon beam on the detector is incided in real-time detection; With photon signal as systematic control algorithm, it also is the optimization aim of genetic algorithm, utilize the high-speed figure processor to calculate the needed voltage signal of various wave front aberrations in the distorting lens compensation beacon beam, amplify through high-voltage amplifier again, be applied on each driver of distorting lens, finish closed-loop corrected in real time, wherein main control computer both had been used as the watch-dog of imaging system, for the observation imaging effect, be used for the software of operational management high-speed figure processor again, the calculating of genetic algorithm is then finished in the high-speed figure processor.
The present invention compared with prior art has following advantage:
(1) need be when utilizing Hartmann wave front sensor to carry out wavefront measurement based on the typical stellar target imaging compensating ADAPTIVE OPTICS SYSTEMS of Detection Techniques before the ground wave through Wave-front phase decomposition, wavefront slope calculating, Wave-front phase reconstruct three big processes, computation process is more loaded down with trivial details, as shown in Figure 5, the adaptive optical technique that is based on the picture clearing principle that the present invention adopts, be Detection Techniques before a kind of indirect wave, utilize avalanche diode direct detection photon signal, utilize the strength information of photon signal to carry out closed-loop control again; Thereby the complicated processes of having avoided the measurement wavefront; And the cost of total system also greatly reduces;
(2) existing typical stellar target imaging compensating ADAPTIVE OPTICS SYSTEMS must guarantee in the system that the position of Hartmann wave front sensor becomes the object-image conjugate relation to place with the position of distorting lens as shown in Figure 4.But, in practice, particularly in large-scale optical system, it is difficult even impossible especially will accurately determining these two conjugate positions, the present invention does not need to measure Wave-front phase, thereby there is no need to guarantee conjugate relation between distorting lens and the detector, simplified system's adjustment process greatly;
(3) avalanche diode that adopts of the present invention utilizes in the high-quantum efficiency of silicon and the snowslide gain to amplify, with respect to general be the photodetector of imaging support with the CCD target surface, have efficiency of light energy utilization height, the advantage that can effectively survey low light level grade celestial body; Relative photomultiplier, the avalanche diode that the present invention adopts has the quantum efficiency advantage of higher again;
(4) the present invention does not need to adopt artificial beacon beam, in conjunction with avalanche diode high-quantum efficiency and highly sensitive advantage, can directly utilize imaging stellar target self as beacon, utilize the light that himself sends as beacon beam, this mode can be eliminated the non-vignetting error such as grade that adopts artificial beacon beam to bring, and has reduced difficulty and the cost that adopts artificial beacon to bring;
(5) the present invention front of avalanche diode on focal plane is provided with an aperture diaphragm, again the strength information of the photon signal that avalanche diode detected as the system optimization function, according to certain metric, if the expansion target of observation is relatively large, just select less diaphragm diameter, if instead the expansion target of observation is less relatively, just select bigger diaphragm diameter, select the diameter of diaphragm targetedly by such mode, can cross effectively and eliminate from the non-vignetting error that waits of the beacon that light wave brought of the different isoplanatic regions of stellar target.So just can guarantee correction wavefront and beacon beam wavefront total conjugated that reflection deformable mirror produces, just can accurately proofread and correct the aberration in the beacon beam, make the stellar target can high-resolution imaging;
(6) reflection deformable mirror of the present invention's employing is the piezoelectric type reflection deformable mirror of plating high reflection film system, and this distorting lens resonance frequency is up to 10
4The Hz level, response time is less than 1 millisecond, displacement resolution can reach the 10nm magnitude, and dynamically stroke range reaches several microns, and it not only can proofread and correct low order aberration, also can proofread and correct higher order aberratons, this has just overcome, and initiatively aberration compensation device space resolution is low such as this class of two piezoelectric deforming mirrors, and the shortcoming that is difficult to proofread and correct higher order aberratons has also overcome some other passive aberration compensation element, as the debug difficulties of phase conjugation device, and the shortcoming that increases system complexity.
Description of drawings
Fig. 1 is a structural representation of the present invention;
Fig. 2 is the structural drawing of the used distorting lens of the present invention;
Fig. 3 is the process flow diagram of genetic algorithm for control algolithm of the present invention;
Fig. 4 is the synoptic diagram of existing celestial body imaging compensating ADAPTIVE OPTICS SYSTEMS;
Fig. 5 is the process that Wave-front phase was measured and restored to existing Hartmann wave front sensor.
Embodiment
As shown in Figure 1, the present invention is made up of receiving telescope system 13, reflection deformable mirror 4, spectroscope 5, high-speed figure processor 8, high-voltage amplifier 9, main control computer 12, snowslide secondary light pipe 7, image intensifying CCD camera 11, from the light of waiting to observe celestial body, primary mirror 2 by telescopic system 13 receives, secondary mirror 1 with light-ray condensing before primary mirror 2 focuses of telescopic system 13; Light passes 2 one circular holes of primary mirror and focuses on after the primary mirror 2 then, the eyepiece 3 of telescopic system 13 of being reflected again becomes parallel or near parallel light again, light is through after the reflection deformable mirror 4, incide and be divided into two bundles on the spectroscope 5, a branch of focused on and incide by lens 10 be placed on the lens 10 focal plane image intensifying CCD cameras 11, the image information of surveying on image intensifying CCD camera through the built-in image capturing system of main control computer 12 is transferred on the main control computer 12 again, for the observation monitoring, another bundle is focused on the avalanche diode that lens 6 converge in its focal plane 7, the aperture diaphragm 14 that can adjust bore has been placed in avalanche diode 7 fronts, the strength information of the photon signal that aperture diaphragm 14 back avalanche diodes 7 detect is as the fitness function of genetic algorithm, the also objective function that will optimize as genetic algorithm, according to the principle of maximization objective function, high-speed figure processor 8 is used for carrying out the program that control algolithm is a genetic algorithm.Because adopt the high-speed figure processor specially as the performer of algorithm, system bandwidth can be caught up with the speed that aberration changes, so the real-time performance of this system accesses assurance.Last high-voltage amplifier 9 is applied to the plurality of voltages signal of the optimum that obtains through high-speed figure processors 8 interative computations on each driver on the reflection deformable mirror 4, control reflection deformable mirror 4 produces and wavefront from the Beam Wave-Front conjugation of stellar target, proofreaies and correct the various aberrations of the Beam Wave-Front of stellar target.On main control computer 12 monitors, just can access stellar target image clearly this moment.
Main control computer 12 usefulness among the present invention not only are used for the software of operational management high-speed figure processor also as the display device of image supervisory control.Snowslide secondary light pipe 7 has the advantage of low noise, fast-response, high sensitivity, high bandwidth, low cost, can both respond visible light and near infrared light, can effectively survey low light level grade celestial body; The front of avalanche diode 7 is provided with an aperture diaphragm 14 on focal plane, and the strength information of the photon signal that avalanche diode 7 is detected is as the system optimization function again.According to certain metric, if the expansion target of observation is relatively large, just select less diaphragm diameter, if instead the expansion target of observation is less relatively, just select bigger diaphragm diameter, select the diameter of diaphragm targetedly by such mode, can cross effectively and eliminate from the non-vignetting error that waits of the beacon that light wave brought of the different isoplanatic regions of stellar target.Wherein, diaphragm 14 diameter ranges are between tens microns to several millimeters usually.
High-speed figure processor 8 is by the image acquisition part, the control arithmetic section, the D/A conversion portion is formed, image capture module is gathered the photonic data that snowslide secondary light pipe 7 measures in real time, the objective function that will optimize as control algolithm with the strength information of the photon signal that collects, the operation of control arithmetic section high speed iteration can obtain making the digital voltage signal of objective function optimum in real time based on the control algolithm of genetic algorithm; The D/A conversion portion is converted to simulating signal with digital voltage signal again, amplifies through high-voltage amplifier 9, is applied on reflection deformable mirror 1 each driver behind as correcting device before the primary waves.The image intensifying CCD camera 11 that is used for the picture element diagnosis is to have added image intensifier before the CCD target surface, with being coupled to after the figure image intensifying on the CCD target surface, can survey the low light level again, and can both respond visible light and near infrared light.
As shown in Figure 2, reflection deformable mirror of the present invention 4 is the reflective distorting lens of reflection deformable mirror of the continuous mirror surface formula of plating highly reflecting films, and it is mainly by thin mirror surface 41, piezoelectric ceramic actuator 42, substrate 43 and contact conductor 44 compositions.The surface deformation of reflection deformable mirror 4 is to lean on the promotion of minute surface piezoelectric ceramic actuator 43 behind to produce, the displacement resolution of the piezoelectric ceramic actuator 43 that adopts is very high, control is very convenient: apply voltage for piezoelectric ceramic actuator 43, utilize inverse piezoelectric effect just can produce displacement.Because the monolithic piezoelectric ceramic sheet also can only produce 0.1~0.2 little next distortion under the voltage of hundreds of volts, so, piezoelectric ceramic actuator 43 is formed by stacking by a lot of piezoelectric ceramic pieces, each potsherd is in parallel and deflection superposes on circuit, so just can increase the deflection of distorting lens 4.Substrate 44 is mainly used to support piezoelectric ceramic actuator 43, one end of a plurality of piezoelectric ceramic actuators links to each other with rigid substrates 44, and the other end links to each other with thin mirror surface 42, and contact conductor 45 is connected on each driver, draw by the through hole on the substrate 44, link to each other with high-voltage amplifier 9.
Principle as the sharpening adaptive optical technique used in the present invention is: do not need to adopt expensive Wavefront sensor to measure the wavefront error of celestial body target, but utilize the picture sharpening index that can reflect wavefront error information as the quality factor of weighing the imaging system imaging capability, control reflection deformable mirror 4 is proofreaied and correct wavefront error, quality factor is reached or near optimum value.If the light beam phase place from stellar target is that (r, θ), the preceding phase place of compensated wave that produces through reflection deformable mirror 4 is that (r, θ), r, θ are the polar coordinates on condenser lens 6 object planes to W2, in order to handle problems conveniently, the object plane radius are normalized to 1 to W1.According to the Fourier diffraction theory, the light intensity signal on the photodetector can be expressed as:
Wherein, I
0The amount that is directly proportional from the beacon beam power of stellar target,
If A=is (a
1, a
2... a
k... a
n), be each the rank zernike polynomial coefficient that is used for explaining from the beacon beam Beam Wave-Front of stellar target, B=(b
1, b
2... b
k... b
n) be the zernike polynomial coefficient of the Wave-front phase of reflection deformable mirror 4 generations, the mode of being expressed Wave-front phase by zernike polynomial has:
W1(r,θ)=A.Zk(r,θ) (2)
W2(r,θ)=B.Zk(r,θ) (3)
Make C=(c
1, c
2... c
k... c
n)=A-B (4)
Then (1) can be written as:
Because zernike polynomial has orthogonality, when | when C| is smaller, have by the Taylor expansion theorem:
F≈I
OX?exp(j(|C|)≈I
O?X(1-|C|
2) (6)
By (6) formula as can be known, photodetector is that the photon number that detects on the avalanche diode 7 is many more, and light intensity signal F is big more, just shows that aberration correction must be good more.Optimal situation is | C|=O, at this moment, reflection deformable mirror 4 just can produce accurately one with wavefront from the Beam Wave-Front conjugation of stellar target, proofread and correct the various aberrations of introducing because of factors such as atmospheric turbulences fully, fuzzy stellar target can be imaged on the monitor of main control computer 12 clearly.
Shown in Figure 3, genetic algorithm of the present invention is as follows:
(1) genetic algorithm produces an initial population at first at random, and population comprises the initial population of face shape individuality of the reflection deformable mirror 4 of some (general 15-100), each individual face shape of corresponding distorting lens respectively;
(2) behind the initialization population individuality is encoded.Because the method for real coding can improve the operation efficiency of genetic algorithm, improves the complicacy of genetic algorithm, so take the mode of real coding to encode to each face type is individual.Each individual available following form is represented:
V
i=[v
1v
2,...,v
n] (i=1,2,...,M) (7)
Wherein, V
iA minute surface face type individuality in the expression population, corresponding to a chromosome of genetic algorithm, M represents the scale of population; v
j(j=1,2 ... n) be real number, representative be the magnitude of voltage that is applied on the reflection deformable mirror 1, on the mathematics implication, they distinguish a gene position of corresponding genetic algorithm again, value is at [v
Minv
Max] between, v
MinRepresent minimum voltage, v
MaxRepresent maximum voltage, n is the number of driver on the distorting lens;
(3) behind the coding, calculate the fitness of the correspondence of each minute surface individuality, the photon signal that detects with avalanche diode 7 is as the fitness function of genetic algorithm, the objective function that will optimize as genetic algorithm with this fitness function simultaneously;
(4) after each individual fitness is calculated, according to carrying out selection operation with the directly proportional roulette selection mode of fitness, behind the selection operation, in the mode that single-point intersects the individuality that is selected in the population is carried out the main mode that the interlace operation interlace operation is the new individuality of genetic algorithm generation in twos according to certain crossover probability (being generally 0.5-0.99) again, the mode that the present invention adopts single-point arithmetic to intersect, it produces new individuality by the individual mode that the exchange portion gene takes place of two minute surface face shapes to parent, and two face type individualities establishing the reflection deformable mirror 4 that will intersect are respectively V
1, V
2, then two indicating panel individualities that produce through intersection are:
V
1’=λ1.V
1+λ2.V
2 (8)
V
2’=λ1.V
2+λ2.V
1 (9)
(8), in (9), parameter lambda 1+ λ 2=2 and 0<λ, 1,0<λ 2;
The laggard row variation of interlace operation is operated, and mutation operation is the mode of operation of decision genetic algorithm local search ability, and it is to produce new individual supplementary mode, and the present invention adopts the mode of single-point intersection non-uniform mutation.Specific implementation is as follows: establish the individual V of being of a face type that certain generation makes a variation
i=[v
1v
2..., v
n], the variation position is V
k(k=1,2 ... n), and the new individuality in process variation back is V
i'=[v
1v
2..., v
n], then new gene position V
k' be:
V
k’=V
k-Δ(t,V
k-V
min) (10)
(10) in, V
MinBe V
kDesirable lower limit, the function Δ (t y) returns one in [0, y] interval interior value, and available following formula is described:
Δ(t,y)=y.r(1-t/T)
a (11)
(11) in, r is individual random number in [0,1], and T is the total iterations of genetic algorithm, and on behalf of algorithm, t carry out algebraically, and a is a weight factor, and by (11) as can be known, (t y) levels off to zero to Δ when t levels off to T.
(5) genetic algorithm is every through judging whether an algorithm reaches end condition behind fitness calculating, 4 genetic manipulations of selecting, intersect, make a variation, if do not satisfy end condition, then enter into iteration of future generation and calculate, carry out various genetic manipulations again; If satisfy end condition then finish algorithm.