Position errors of three-mirror reflective space optical system will affect the whole system badly,
so we have to calibrate these errors in orbit. This paper proposes a new method for the first time, which
is: we can use Stochastic Parallel Gradient Descent algorithm to calibrate three-mirror reflective remote
sensor, this method don't need wavefront sensor to calibrate position errors. It uses root mean square of
radius of image as system merit, through controlling the six position of second mirror to compensate
system error. This method is suitable for the calibration of three mirror reflective space optical system
for its needless of using wavefront sensor. Results of the simulation show that compared with
traditional sensitive matrix inversion algorithm, this method increases the dynamic range of initial
position errors, and it can improve wavefront error from about 1 wave rms to lower than 0.04 wave rms
in the center field of view.
The space adaptive optics system used for space remote sensing system to improve the image quality will face the
challenge from the wider field of view. In this paper, the SPGD algorithm is present to realize the wavefront sensorless
adaptive optics correction for a wide field of view optics system. Giving the traditional TMA optics system as the example,
the image quality of different field of view is analyzed when there are some different surface errors in the optics system.
The gradient evaluation method and convergence of SPGD is analyzed in detail. The issue of parameter such as the gain
and step selection for SPGD is discussed. Computer simulation of a remote sensing AO system based on SPGD is studied.
And the results show that wavefront sensorless wide field of view adaptive optics correction based SPGD algorithm for the
segmented primary mirror system is acceptable, and the wavefront error is within 1/10λrms.
We develop a fiber optical coherence tomography (OCT) system in the clinical utility of imaging port wine stains (PWS). We use our OCT system on 41 patients with PWS to document the difference between PWS skin and contralateral normal skin. The system, which operates at 4 frames/s with axial and transverse resolutions of 10 and 9 µm, respectively, in the skin tissue, can clearly distinguish the dilated dermal blood vessels from normal tissue. We present OCT images of patients with PWS and normal human skin. We obtain the structural parameters, including epidermal thickness and diameter and depth of dilated blood vessels. We demonstrate that OCT may be a useful tool for the noninvasive imaging of PWS. It may help determine the photosensitizer dose and laser parameters in photodynamic therapy for treating port wine stains.
Large-aperture segmented primary mirror has been widely used in
high-resolution space telescopes. In this paper, we
concentrate on the wavefront sensing and control (WFS&C) methods for a segmented primary mirror comprising a
central octagon and eight surrounding petals. As the wavefront errors have a wide dynamic range in amplitude and
spatial frequency, a multistage wavefront control algorithm is proposed. The control process is divided to five steps to
reduce the wavefront errors gradually. A simulation toolbox integrating multi-disciplinary software has been developed
to verify our WFS&C algorithms. Simulation results give a good demonstration of the feasibility of our algorithms.
A great deal segmented mirror errors consisting of piston and tip-tilt exist when space large aperture segmented optics
system deploys. These errors will result in the departure of segmented mirrors images from the view. For that, proper
scanning function should be adopted to control actuators rotating the segmented mirror, so that the images of segmented
mirror can be put into the view and placed in the ideal position. In my paper, the scanning functions such as screw-type,
rose-type, and helianthus-type and so on are analyzed and discussed. And the optimal scanning function principle based
on capturing images by the fastest velocity is put forward. After capturing, each outer segmented mirror should be
brought back into alignment with the central segment. In my paper, the central and outer segments with surface errors
have the different figure, a new way to control the alignment accuracy is present, which can decrease the bad effects
from mirror surface and position errors effectively. As a sample, a simulation experiment is carried to study the
characteristics of different scanning functions and the effects of mirror surface and position errors on alignment
accuracy. In simulation experiment, the piston and tip-tilt errors scale and the ideal position of segmented mirror are
given, the capture and alignment process is realized by utilizing the improved optics design software ZEMAX, the
optimal scanning function and the alignment accuracy is determined.
KEYWORDS: Signal to noise ratio, Imaging systems, Space telescopes, Mathematical modeling, Photonics systems, Astronomy, Radiometry, Interference (communication), Signal processing, Detection and tracking algorithms
Photon imaging system (PIS) is widely applied to astronomy observing, deep space exploration. To investigate the
system performance for space application, the process that target radiance converting to photons is presented. In this
processes, radiometry theory and astronomy units are used. Then a mathematical physical model for the imaging system
is used to calculate the system SNR. In the model, the system dark noise and the signal enhancement process are derived
as mathematical equations. The performance of the detection algorithm is also introduced to predict the PIS range
performance of the probability of detection and correct localization and the probability of false alarm based on SNR. At
last, the actual PIS range performance for space application is discussed and valuable data for space telescopes design and
deep space exploration also are provided.
A novel receiving antenna using low precision large aperture nonimaging optical apparatus in free-space optical
(FSO) communication system has been proposed. The receiving optical antenna of FSO communication system is
usually a conventional imaging optical system such as Newton system, Green system or Cassegrain system. It is
ineffective to use a large aperture receiving antenna in FSO communication system because the precision imaging
optical apparatus will be very expensive with aperture increase, so that, in order to reduce the difficulty of pointing
and tracking between transmitter and receiver, the beam divergence has to be increased with the cost of lost part of
the transmitted power. Since in the field of FSO communication system, the receiving optical antenna is used not to
image but to concentrate optical signal as much as possible, the novel concept of using low precision large aperture
nonimaging optical apparatus as receiving optical antenna to replace the conventional imaging optical system was
proposed. Several nonimaging apparatus including spherical reflector, elliptical reflector, compound parabolic
concentrator (CPC) and conical barrel concentrator are analyzed by ray tracing. Their gain and the transmission
rate limitation due to wave-front aberrations are discussed, and their merit used in FSO communication system has
been proved.
The wavefront error and polarization of a side mounted infrared window made of ZnS are studied. The Infrared
windows suffer from temperature gradient and stress during their launch process. Generally, the gradient in temperature
changes the refractive index of the material whereas stress produces deformation and birefringence. In this paper, a
thermal finite element analysis (FEA) of an IR window is presented. For this purpose, we employed an FEA program
Ansys to obtain the time-varying temperature field. The deformation and stress of the window are derived from a
structural FEA with the aerodynamic force and the temperature field previously obtained as being the loads. The
deformation, temperature field, stress field, ray tracing and Jones Calculus are used to calculate the wavefront error and
the change of polarization state.
KEYWORDS: Point spread functions, Image segmentation, Telescopes, James Webb Space Telescope, Space telescopes, Mirrors, Image quality, Imaging systems, Information science, Information technology
For a segmented primary mirror consisting of 7 segments organized in 1 concentric hexagonal band around the
central segment, of which the point spread function (PSF) is represented by the product of the grid function
(GF) and the PSFj of an individual segment. The system PSF and Strehl ratio given for the cases of the
gaps or piston errors are present.
A photon imaging system (PIS), which consists of object lens, micro-channel plate (MCP), photomultiplier tube, relay
lens, CCD camera and image acquisition system is recently constructed. The dark noise of the whole imaging system has
been studied by statistical analysis method. The hypothesis tests method is used to analyze statistical parameters of dark
noise. In this test, the Chi-square goodness-of-fit test method is employed to determine which distribution the acquired
image information is fit for. Subsequently, the section estimation is used to confirm threshold for spatial denoising
process. In order to overcome the effects of the non-uniformity for PIS, we propose a new method to analyze above
processes. In this method the image acquired by PIS was divided into many segments, their statistical characters have
been studied respectively and the statistical parameters of the noise for the different segments are analyzed based on
above method. For the aim of analyzing above acquired statistical parameters and obtaining the relationship in terms of
the different operating conditions of the system, several experiments have been implemented and experiment results also
be presented.
A great deal segmented mirror errors consisting of piston and tip-tilt exist when space large aperture segmented optics
system deploys. These errors will result in the departure of segmented mirrors images from the view. For that, proper
scanning function should be adopted to control actuators rotating the segmented mirror, so that the images of segmented
mirror can be put into the view and placed in the ideal position. The key of capturing segmented mirror images is
selecting an optimal scanning function. This paper put forward the optimal scanning function principle based on
capturing images by the fastest velocity. The scanning functions, such as screw-type, rose-type, and helianthus-type and
so on, have their own merits and demerits. In my paper, the scanning functions above will be analyzed and discussed. As
a sample, a simulation experiment is carried to study the effects of different scanning functions on three mirror
astigmatism system, whose primary mirror with six segmented mirror. In simulation experiment, the piston and tip-tilt
errors scale and the ideal position of segmented mirror are given, three scanning functions above are used to realize the
capture process by utilizing the improved optics design software ZEMAX, the relationship between scanning functions
and optical system are analyzed and the optimal one is determined.
KEYWORDS: Actuators, Wavefronts, Mirrors, Phase modulation, Spatial frequencies, Space telescopes, Control systems, Wavefront aberrations, James Webb Space Telescope, Telescopes
Segmented primary mirror has been widely used in high-resolution ground-based and space-based telescopes. In this
paper, we mainly discuss the wavefront control issue for a segmented primary mirror with annular-sector subaperture. In
order to balance the requirements of correction in amplitude and spatial frequency, we propose a multistage wavefront
control strategy and allocate the wavefront errors in spatial frequency domain. The power spectral density (PSD) is
calculated to obtain the spatial frequency information of wavefront aberrations. The feasibility of the control strategy is
verified by numerical simulation.
Thermal distortion of the optical elements can greatly reduce the high resolution of the space-borne camera. The
general thermal effect on mirror is analyzed and the optical aberration of the optical surface resulting from 3 kinds of
thermal gradient is discussed. The thermal distortion simulating experiment of a large aperture flat mirror is designed and
the optical aberration is tested on 18" ZYGO with the different axial thermal disturb. The testing results conclude that the
small thermal gradient can greatly affect the wave-front, the aberration of this large aperture flat mirror can be used to
simulate the thermal distortion on space, and MTF is also reduced greatly when this large aperture flat mirror is used in
the real space-borne camera under the same thermal environment. In order to correct the thermal distortion and keep the
high resolution, the 37-units adaptive optics correction close loop experiment is designed and installed in the above
camera. The correction results show that MTF of the testing camera will not reduced greatly under the large thermal
distortion. So employing adaptive optics on a high resolution space camera is the necessary and the valid method to
correct
In multiconjugate Adaptive Optics (MCAO), the phase screens are used to simulate atmospheric turbulence layers to
study the optimal turbulence delamination and the determination of layer boundary position. In this paper, the method of
power spectrum inversion and sub-harmonic compensation were used to simulate atmospheric turbulence layers and
results can be shown by grey map. The simulation results showed that, with the increase of turbulence layers, the RMS
of adaptive system decreased, but the amplitude diminished. So the atmospheric turbulence can be split into 2-3 layers
and be modeled by phase screens. Otherwise, a small simulation atmospheric turbulence delamination system was
realized by JAVA.
This paper concentrates on images formation simulation under low light level condition (10-6-3lx) and photon
limited condition (<10-6lx). In the first part, we introduce the main characteristics and features of low light level images
and system entire noise and simulate a deblurred image intensified by photon imaging system recently constructed under
low light level condition. The influence of scene luminance and photon imaging system optical errors on the simulation
is introduced. Then the system entire noise is appended to low light level images by a novel noise analysis and
generation method based on experimental study method. The second part of this paper deals with simulation of photon
images. Because of randomicity of photon images, roulette wheel selection is utilized to confirm the grey level of
stochastic signal photon image and noise photon image is generated by poissson stochastic process pixel by pixel. The
final photon image is acquired by synthesizing the two images. The simulation presented in this paper provides an
economical and convenient method to investigate the detection ability of photon imaging system and image
reconstruction algorithm under low light level condition and photon limited condition.
A simple and high precision method to measure the phase modulation characteristics of Liquid Crystal Spatial Light Modulator, namely, the relationship between phase and voltage(gray), is proposed. Using the Digital Wave Front Phase-shifting Interferometer, the phase difference from different voltage (gray) can be obtained directly from the interferometer, so it is easy to get the phase modulating characters of Liquid Crystal Spatial Light Modulator. The wavefront
correction has been realized by using the Liquid Crystal Spatial Light Modulator in adaptive Optics. The distorted wavefront can be tested in the Interferometer and be expressed by Zernike Polynomial, using the phase modulation character of Liquid Crystal Spatial Light Modulator, the corresponding gray picture can be set up. The conjugate wavefront can be obtained, and thus the correcting of the static distorted wavefront is completed and the effect is displayed as proved by the improvement of correlative parameters such as PV value, rms value and strehl ratio.
The optimal turbulence delamination in MCAO for HeFei region are studied. Because of the delamination structure of atmospheric turbulence, the atmospheric can be split into several layers and be modeled by phase screens. It is shown that MCAO system considering 2- layer atmospheric turbulence has a high SR.
The influences of atmospheric turbulence on image resolution of space-borne optical remote sensing system are discussed. The coherence length of wavefront r0 and the variance of angle-of-arrival fluctuation σ2α of sensing system are the main basis to evaluate the atmospheric influence on image resolution. In this paper, different atmospheric turbulence models are chose to calculate r0 and σ2α in order to analyze the influence of atmospheric turbulence, and the results show that the influence of atmospheric turbulence should be weak and in most cases could be ignored for space-borne optical sensing system.
When an adaptive optical system is used in an imaging system observing extended targets, a method of correlation can be used to find the relative movements of the sub-images in its Hartman-Shack waterfront sensor. To get a sub-pixel accuracy, a curve fitting method is presented. This paper describes the method in detail, and presents the simulations and experimental results. These results show an accuracy of 0.1 pixels rms.
It is necessary for an adaptive optics system to be excepted to achieve established signal-noise ratio that enough signal photon fluxes are there in every subaperture. This requests that either the object imaged is bright enough or there is a bright guide star within the field of view. However, it is unfortunately as often as not in the case in nature and the artificial guide stars have need for.
There are two kinds of artificial beacons up to now. They are sodium laser guide star and Rayleigh guide star. The latter among which is generated by the Rayleigh scatter of laser beam from stratosphere. More specially, the laser beam transmitted by ground transmitter propagates upward and undergoes the absorption and the scatter of the atmosphere along the way. It is obvious that only the scattering of the atmosphere within specified altitude range is beneficial. So we always hope that the Rayleigh scattering in this range would be strong and the absorption would be weak to the greatest extent. Under stated altitude, both the scattering and the absorption are the weaker the better.
Either the absorbance or the scatterance is dependents on the wavelength of the laser beam and relates to the atmospheric constitution. In this paper, the optimum wavelength for Rayleigh laser beacons is presented by striving for relative extreme values of the transmissivity and the scattering.
Recently, the progress in adaptive optics makes the cone effect of Rayleigh laser guide stars be solved fairly. So that the applications of this kind of beacon in adaptive optics, especially in multiconjugate adaptive optics (MCAO) presents a bright future once again. The photon flux density required by the wavefront sensor of MCAO with certain performance is proportional to the number of layers. This results in that the laser energy required by guide stars for "classical" MCAO is very high. In the "new concept" MCAO, however, the Rayleigh beacons are formed by light scattered from whole higher atmosphere but not only a selected thin layer. Then the required laser energy degrades greatly.
In this paper, a statistical processing method is performed to process the photon images with the small number of photons. The image intensifier is a necessary tool to get a readable image for the ultraweak luminescence, such as the spontaneous light of sample. The photon image is often interfered by the noise caused by the system and the background. And some signal photons were submerged by the noise. For the sake of getting the useful information from the original image, the collected photon images are summed up to increase the number of the samples. According to the distribution regulations of the signal and the noise, a threshold value T is set up to judge if the photon is the signal or not. The noise photons can be reduced and S/N of the photon image is improved. Compared with the pure accumulation of the images and the integrating processing method, the statistical processing method is more effective to process the limited frames of the images with the small number of photons.
The disadvantage in expanding dynamic range and restraining noise of the traditional H-S (Hartmann-Shack) wavefront sensor centroid computation method is analyzed. Based on the temporal characteristic of atmosphere turbulence, through determining the changing scope of centroid motion between two adjacent sample periods, a new dynamic tracking centroid method of H-S wavefront sensor is proposed. Using this method, the dynamic range of wavefront sensor can be expanded when atmosphere turbulence is strong; the effect of CCD readout noise and shot noise can be reduced.
KEYWORDS: Digital signal processing, Adaptive optics, Deformable mirrors, Mirrors, Sensors, Control systems, Image quality, Reflectivity, Control systems design, Image sensors
A mini adaptive optics system is developed in which a micro-machined membrane deformable mirror and the technique of cross-folded optical path are employed. The system has a volume of 30x20x10cm3, a weight of 4kg, while its bandwidth is 17Hz, and the accuracy of its wave-front sensor is ?/15 mis. The system is aimed at improving the image quality of space-based optical systems, but it is versatile. The control host is a PC computer, and various functions are realized, such as, real time display of image or wave-front, testing of the response matrix of the deformable mirror, and closed-loop control. An experimental system is also setup to test the performance ofthe AO system. The results of the experiments show that the AO system is very effective in compensation for thermal deformations and dynamic disturbances.
In order to examine the performance of adaptive optics system in the laboratory environment, a new simple laboratory atmosphere turbulence simulator (ATS) is developed which uses the hot resistance coil to generate the hot air turbulence and the fan to control the intensity of the turbulence. The spatial and temporal characteristics of the turbulence generated by the ATS are tested in different experimental conditions by the test system and then compared with the theoretical Kolmogorov spectrum atmosphere turbulence. The results show that the spatial and temporal characteristics of the turbulence generated by ATS have definite similarity with the Kolmogorov atmosphere turbulence under certain experimental conditions. Finally the reason of the difference with theory Kolmogorov atmosphere turbulence is analyzed.
In this paper, we analyse the principle of fiber Bragg grating anay as en-/de-coder and its realizing method. Then, an improved scheme, which can heighten data rate of single channel in this OCDMA system, is put forward by us. Furthermore, this scheme additionally possesses the convenience ofvariable bit rate service.
One of principle difficulties in zonal wavefront reconstruction is computationally intensive. In this paper the method of wavelet decomposition is applied to the reconstruction matrix, then a threshold is added to the wavelet-coefficients matrix to remove the high resolution wavelet coefficients which can be ignored. The resulting matrix is sparse, leading the computational cost decreases greatly, so the computational speed increases. Theoretical analysis and computer simulation are made and expected result is got.
The paper describes the necessity of employing AO on space camera to overcome the thermal and gravitational influences in order to improve its image quality. Simulative computation of six cases are made to the thermal distortion of primary mirror of a typical Ritchey-Chretien space optical system by using finite element method. The P-V and RMS values, the Zernike coefficients of the mirror's surface are given. An AO correcting experiment system was designed and completed, both open-loop and close-loop experiments were made. A (Phi) 100 mm K9 glass reflective plane mirror was used as a proportional model of the primary mirror to simulate its thermal distortion. Three typical cases -- axial thermal gradient, radial gradient and the local thermal gradient were selected to simulate the on-orbit environment influences. This experiment results prove that AO can correct the low frequency thermal distortion of primary mirror on space camera and decrease the difficulty of temperature control of space optical system.
When a laser beam is used to produce a sodium guide star, a Rayleigh guide star can be got as a 'by-product' with the temporal-gating method. In the case of the atmospheric phase distortion is confined to two thin turbulent layers, the sodium guide star is used to measure both the low-altitude and the high-altitude phase distortion (phi) b while the Rayleigh guide star provides a suitable probe signal for the contribution (phi) l of low-altitude turbulence layer. The wavefront distortion (phi) l of low-altitude turbulence layer. The wavefront distortion (phi) h causing by the high-altitude turbulence layer alone is then easy obtainable from (phi) l and (phi) b. The multiconjugate correction system could be founded upon these.
An adaptive optics system with the adaptive ability to different detected objects and seeing conditions is being investigated in Beijing Institute of Technology. When seeing conditions are good, and the Shack-Hartmann wave front sensor of adaptive optics system is working under very low light level, the subaperture of Shack-Hartmann sensor need to be adjusted larger than that when it is working under higher light level and the seeing condition is not good enough. By setting a motorized zoom lens in front of the Shack-Hartmann WFS of a conventional adaptive optics system, the subaperture array of the WFS can be adjusted from 8 X 8 to 2 X 2 in the pupil of the telescope with step by step if necessary. With this method, the overall performance of adaptive optics system can be boosted. Based on an adaptive optics system of the 1.2 meter telescope, a discussion on the noise analysis of Shack-Hartmann WFS associated with subaperture optimization is presented in this paper.
The application of image fusion in biomedical image analysis has led to a new concept about the nature of disease and to new diagnostic capabilities. However, the algorithm research of fusion is still an open research topic because the algorithm is often changed with different original images, different detectors and different research objects. This paper focuses on comparison of four image fusion algorithms based on wavelet transform to select the suitable methods for biomedical image fusion. The algorithms include: (1) weighted algorithm, (2) maximum selection algorithm, (3) stressing one image and (4) logic OR algorithm. For the sake of selecting the suitable image fusion methods for biomedical images, we propose six quantitative performance measure criterion linked with the characters of the biomedical image: standard deviation ((sigma) ), peak signal-to-noise ratio (PSNR), mean deviation ((Delta) (mu) ), the difference in entropy ((Delta) H), coefficient of correlation between the fusion image and ideal image (Correlation) and the difference in contrast between the fusion image and ideal image ((Delta) Contrast). Using the four algorithms to process biomedical images, such as fluorescence image and the corresponding transmission image, the visual investigation and the six quantitative performance measure criterion indicate that the weighted algorithm is the most suitable method for biomedical images among the four algorithms.
A high gain fluorescence microscope is developed to meet the needs in medical and biological research. By the help of an image intensifier with luminance gain of 4 by 104 the sensitivity of the system can achieve 10-6 1x level and be 104 times higher than ordinary fluorescence microscope. Ultra-weak fluorescence image can be detected by it. The concentration of fluorescent label and emitting light intensity of the system are decreased as much as possible, therefore, the natural environment of the detected call can be kept. The CCD image acquisition set-up controlled by computer obtains the quantitative data of each point according to the gray scale. The relation between luminous intensity and output of CCD is obtained by using a wide range weak photometry. So the system not only shows the image of ultra-weak fluorescence distribution but also gives the intensity of fluorescence of each point. Using this system, we obtained the images of distribution of hypocrellin A (HA) in Hela cell, the images of Hela cell being protected by antioxidant reagent Vit. E, SF and BHT. The images show that the digitized ultra-sensitive fluorescence microscope is a useful tool for medical and biological research.
The designs of existing Adaptive Optical System are "unadaptive" themselves, it means the parameters of the systems, such as subaperture diameter d, dynamic range of wavefront distortion correction, frequency bandwidth, etc., are fixed. Since these parameters were mainly decided according to some statistic values of atmospheric disturbance and detected objects, those systems don't have the ability to adapt the variation of observation conditions to obtain optimized operating parameters in real time though it is necessary in many cases. In this paper, a concept of an Adaptation of Adaptive Optical System(AAOS) is proposed. The AAOS has certain real time optimization ability against the variation of the brightness of detected objects m, atmospheric coherence length r0 and atmospheric time constant ? by means of changing subaperture number and diameter, dynamic range, and systems' temporal response. The necessity of AAOS using a Hartmann-Shack wavefront sensor and some technical approaches are discussed. Scheme and simulation of an AAOS with variable subaperture ability by use of both hardware and software are presented as an example of the system.
The relationship between the performance of a partial correction adaptive telescope using laser guide stars and the star brightness is discussed. The laser energy requirements for Rayleigh guide star as well as sodium guide star are presented in cases where the diameter d of a subaperture of the telescope is larger than the atmospheric coherence length r0 and the residual rms phase error across the subaperture is larger than 0.63.
A photon counting imaging system which can detect emission down to the order of 1 counts cm-2 sec-1 (at the photocathode) has been developed, and it has been used to obtain the ultraweak bioluminescence images of a living Kunming mouse. In this paper, we give statistical analysis for calculation of the photon distribution in images obtained, and we use Chi-square ((chi) 2) statistic to get signal and noise distribution to process these images. It has been proved that the imaging system has the ability in detecting ultraweak bioluminescence of animals, and the statistical method for image processing can effectively increase the signal/noise ratio and improve the image quality.
The problem of correlation wavefront sensing using an extended arbitrarily structured target as a light source is studied. The principle of extended target correlation wavefront sensing employing an intensity-transmittance type of mask is analyzed. The problems of simulation and selection of a target in laboratory experiments are discussed. The methods of generating the mask images from the target structure and of preparing the experimental masks from the mask images are presented. Typical results of the mask images generated by processing the target image are given. The preliminary experiment on the extended target wavefront sensing using the intensity-transmittance type mask are made. The effects of two different intensity-type masks on wavefront sensing are compared. Experimental results that are in agreement with the theory are obtained.
An experimental setup of photon counting real-time image acquisition system is introduced, wherein a photon image head (an image intensifier with high radiant emittance gain) is coupled with a high frame rate CCD camera by a super powerful relay lens. The restrictions on luminous emittance of object are analyzed for multiphoton and single photon imaging modes. The methods of determining readout noise are introduced. The application examples of system in adaptive optics wavefront sensor operated with a faint object, and in experimental study on the optical wave-particle duality and the uncertainty relation are presented.
Multiconjugate adaptive optics is an attractive tentative plan for increasing the isoplanatic patch of turbulent atmosphere. Some basic problems relating to this plan have been discussed and corresponding formulas have been given.
The bandwidth requirements for an adaptive optics system with R-C filter as servo response has been derived. The relationship of this bandwidth to Strehl Ratio has been presented in two cases of the constant wind speed and the constant pseudo-wind speed which predominates over the natural winds at all altitudes. It has been found that a bandwidth of hundreds hertz is more than enough for the former while thousands of hertz may be needed for the latter.
A detailed analysis of the characteristics, regularities, and relationships of the centroiding errors of image spots caused by discrete and limited sampling, photon noise, and readout noise of the detector in a Hartmann-Shack wavefront sensor, wherein an image intensified charge-coupled device used as a photon detector is presented. The theoretical analysis and experimental results herein prove useful for optimum design and application of the sensor.
Atmospheric disturbed wavefront with Kolmogoroff spectrum is represented by the Zernike polynomials suggested by R. Noll in 1976. From the irradiance distribution in two defocal planes, one is in the front of focal plane and the other is in the behind focal plane, the response elements for each term of Zernike polynomials with a given detector array and successively the whole response matrix R have been obtained. For an incoming atmospheric disturbed random wavefront WR, with its irradiance distribution detected and the matrix R, it is easy to solve the corresponding coefficients for each term of Zernike polynomials and reconstruct the detected wavefront.
By taking the atmosphere as an N-layer model and keeping the isoplanatic angle invariable for all the layers, the gain of the isoplanatic patch compared to the conventional adaptive optical system has been derived.
An experimental set-up of H-S (Hartmann-Shack) wavefront sensor using an ICCD (intensified charge coupled device) as a photon detector is introduced. The centroiding errors of image spots caused by discrete and limited sampling, photon noise, and read-out noise are analyzed theoretically and experimentally.
The gains of an isoplanatic patch, both in diameter and in area, are presently derived for a Multiconjugate Adaptive Optics system through comparison with a conventional system for height-dependent refractive index structure coefficient. By treating the atmosphere as an N-layer model and keeping the isoplanatic patch size invariable for all layers, the patch gain is obtained.
The limitations of a Hartmann type wavefront sensor are theoretically and experimentally
studied based on photon counting technique. An experimental set-up for
simulation of single subaperture adaptive astronomical telescope is described. The
results of experiments and analyses show that a star of the 8th magnitude can be
dealt with by this kind of wavefront sensors within 1 ms of time and with A/1O of
wavefront distortion detection sensitivity. As for calibration of experiments, an
algorithm related to luminous flux at entrance pupil of telescope and its corresponding
photo-electron rate detected by the wavefront sensor is presented and yenfied
by experiments.
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