The performance of the Cassegrain Adaptive Optics (AO) system of the 8.2 m Subaru Telescope is reported. The system is based on a curvature wavefront sensor with 36 photon-counting avalanche photodiode modules and a bimorph wavefront correcting deformable mirror with 36 driving electrodes. This AO system has been in service since 2002 April for two open-use instruments, an infrared camera and spectrograph (IRCS) and a coronagraph imager with adaptive optics (CIAO). The Strehl ratio in the K-band is around 0.3 when a bright guide star is available under 0".4 seeing condition. High sensitivity of the wavefront sensor allows significant improvement in the image quality, even for faint guide stars down to R=18 mag. The design of the new Nasmyth Adaptive Optics system with 188 control elements under construction is described. This new system with fivefold increase in the number of control elements will provide twice higher Strehl ratio of 0.7. To increase the sky coverage for this new system, a power laser system to produce an artificail guide star in the upper atmosphere is also under construction. The AO system with laser guide capability enables the coverage up to 80% of the entire sky and offers diffraction limited observation for almost any target in the sky. An all solid-state 4W laser to generate the sodium D line emission by summing the two YAG laser frequencies is under development. The generated laser beam is tranmitted through a photonic crystal fiber to the laser launching telescope attached at the backside of the secondary mirror. Expected performance of this laser guide Nasmyth AO system is shown.

The 61-element upgraded adaptive optical system for the 1.2m telescope of Yannan Observatory for astronomical observation had been in operation since May 2004. In this paper, the 61-element upgraded adaptive optical system for 1.2m telescope of Yunnan Observatory will be briefly described. The performance on the 61-element upgraded adaptive optical system is analyzed. Furthermore, the observational results for the stars will be presented.

An adaptive optical system with a 45-channel deformable mirror and a Shack-Hartmann wavefront sensor with 10 x 10 sub-apertures was built for correcting the static and dynamic wavefront aberrations existed in the large-aperture Nd: glass laser for inertial confinement fusion. This paper describes the function and performance of the adaptive optical system. The latest experiment results on the ICF laser system are presented.

In this paper, we report in detail the adaptive optical closed loop system with bimorph deformable mirror as a wavefront corrector and Hartmann-Shack wavefront sensor to compensate the aberrations of the laser beam in the 23TW chirped-pulse amplified Ti:sapphire femtosecond laser system in Shanghai Institute of Optics and Fine Mechanics, CAS. The adaptive system is placed in the vacuum chamber behind the compressor. After the adaptive compensation for the laser beam, we can get the nearly diffraction limited beam.

At the base of the early reported 19 element adaptive optical system for human retina imaging, a new adaptive optical system has been developed. The wavefront correction element is a newly developed 37 element deformable mirror. Some modifications have been adopted for easy operation. Experiments for different imaging wavelengths and axial positions were conducted. Mosaic pictures of photoreceptors and capillaries were obtained. This would be the most detailed image of capillary distribution cover ±3° by ±3° field around the fovea ever reported. Normal and abnormal eyes of different ages have been inspected. Some preliminary very early diagnosis experiment has been tried in laboratory. This system is being planned to move to the hospital for clinic experiments.

We are performing a research on the application of an adaptive optics system to upgrade the beam quality of a laser. We consider the adaptive optics system to consist of a bimorph mirror, a Shack-Hartmann sensor and a control system. Since the laser beam can be circular, annulus or square/rectangle, we predicted the performance of a circular bimorph deformable for each different beam shapes. We selected a bimorph mirror of 120 mm clear aperture with 31 actuators as a design candidate. Firstly we found that the fitting ability of the bimorph mirror for a circular/annulus beam can significantly improve by limiting the correctable area to an annulus of 100mm outer diameter and 20mm inner diameter, which our square laser beam fits into. This study shows that the bimorph mirror, which might be considered as a modal controller, can compensate the square lower order aberrations with fitting abilities larger than 0.95 for tilt, defocus, coma and astigmatism, and 0.82 for spherical aberration. Finally we concluded that the circular bimorph mirror is perfectly okay for square laser beam compensating.

So-called cone effect or focus anisoplanatism is produced by the limited distance of a laser guide star (LGS) which is created within the Earth atmosphere and consequently located at a finite distance from the observer. We believe this is the first time to investigate the cone effect of the LGS by means of a pure numerical simulation. In this paper, the cone effect of the LGS for different vertical profiles of the refractive index structure constant C²_n is numerically investigated by using a revised computer program of atmospheric propagation of optical wave and an adaptive optics (AO) system including dynamic control process. It is surprisingly found that the effect of altitudes of the LGS on the AO phase compensation effectiveness by using the commonly-available vertical profiles of C²_n and the lateral wind speed in the atmosphere is relatively weak, and the cone effect for some C²_n profiles is even negligible. It is found that the cone effect seems not have obvious relationship with the turbulence strength, however, it depends on the vertical distribution profile of C²_n apparently. On the other hand, the cone effect depends on the vertical distribution of the lateral wind speed as well. The cone effect becomes more obvious as the zenith angle increases. In comparison to a near infrared wavelength, the cone effect becomes larger in the case of the visible wavelength. In all cases concerned in this paper, an AO system by using a sodium guide star has almost same phase compensation effectiveness as that by using the astronomical target itself as a beacon.

The beam spreading, induced by atmospheric turbulence and thermal blooming when a high-energy laser beam propagates through the atmosphere, is numerically calculated and analyzed. The simple scaling relation between the beam quality factor and the characteristic parameters of atmospheric effects is obtained, and can be given by the expression β²_u = 1 + 0.636N^1.558. Moreover, when the distortion parameter N is less than one, the beam spreading is mostly dependent on the linear effects because of the weak thermal blooming effects. However, with the thermal blooming effects strong gradually, the beam spreading induced by the combined effects of turbulence and thermal blooming increases rapidly.

The Shack-Hartmann or Hartmann-Shack wavefront sensors are particular forms of the Hartmann sensor and are the most commonly used in adaptive optics. The traditional Hartmann screen in the pupil is replaced by an array of small lenslets at a conjugate to an image of the pupil or deformable mirror. Each lenslet forms an independent image of the incoming wavefront. Shifts in the positions of these images can be shown by simple geometric optics to be proportional to the mean wavefront gradient over each lenslet. The measurement range or dynamic range of a conventional Shack-Hartmann sensor is normally limited by the sub-aperture size of the detector plane, in which each spot should remain. In order to overcome this restriction, several methods, such as modified unwrapped algorithm or a spatial-light modulator as a shutter, have been proposed. We first simulated the image forming of a conventional Shack-Hartmann wavefront sensor for highly aberrated spherical aberrations through computer simulation, which confirmed that the well-known effect that high aberration shifts the spots outside its conventionally detectable area. We first develop a computer program that simulates Shack-Hartmann’s image forming and we show that simple defocusing the CCD plane can allocate the out-boundary spots to initial or reference positions, which results in the increase of the dynamic range of the Shack-Hartmann sensor.

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.

A new method, named FSI (Fourier Shear Interferometry), is suggested to calculate the phase derivative by Fourier transform of the lateral shear fringes. After filtering intensity spectrum A_F² (f_x, f_y)in the spectrum of the shear fringes, the cross term of the fringe’s intensity, i.e., A(x,y)A(x + s, y)exp[i▵_xφ(x,y)], is obtained by the reverse Fourier transform, and then ▵φ(x, y) can be easily obtained if only |▵φ(x, y)|less than or equal to π. The numerical simulation results demonstrate feasibility and accuracy of the suggested method.

A novel PSD-based Hartmann-Shack wavefront sensor(HSWFS) prototype has been developed. Compared with the conventional CCD-based HSWFS, it can operate at very high sampling rate, and it only has very short readout delaytime. In this paper, the PSD-based HSWFS is described in details, and the performances of the PSD-based HSWFS and the CCD-based HSWFS are compared.

In view of the convenience and effectiveness of a position sensitive detector (PSD) in sensing the local distortion of a light beam wavefront, a high-speed wavefront sensor based on PSD array is proposed, fabricated and characterized. As a prototype of this kind of wavefront sensor it consists of a matrix of 4×4 tetra-lateral PSDs, and each PSD unit measures 500 μm×500 μm with a 300 μm interval between them. Each unit has 4 electrodes, which can be used for photocurrent output. The local distortion of a light beam wavefront can be deduced from those 4 photocurrents. Besides 64 electrodes of 16 element units, the sensor also has another common electrode that can be used in applying a reverse bias. Primary tests of the device show that it has low dark current, high spectral sensitivity, very fast response speed, and quite small crosstalk between its neighbouring units. The dark current of an element unit is less than 1 nA at a reverse bias of 20 V. The peak spectral sensitivity of the sensor is over 0.6 mA / mW at 900 nm wavelength. Its response time is about 10 ns at 45 V reverse bias, and the crosstalk between its neighbouring units is as low as 1.6% at λ= 650 nm and U_r = 5 V.

The Free Space optical communication (FSO) or wireless optical communication, utilizes the atmospheric medium as transmission channel, where random variety such as fog, atomy and atmosphere flash and the atmospheric turbulence will badly affect the propagation of light, the receiving signal is easily swung and drifted with the change of weather. In this paper, we discussed the attenuation of the atmospheric channel and analyzed the signal characteristics in the condition of the atmospheric overfall, for the OOK modulation, discussed the receiving signal distribution in the atmospheric channel taking account for the noise gain of the light detector, and based on the principle of the Hartman-Shack sensor, we designed a wave-front distortion compensation system with fiber coupler. The signal fading resulted from wave-front phase distortion was compensated effectively by using the compensation system.

A kind of real-time adaptive control (RTAC) algorithm that can be put into practice in the feed-back close loop AO system was introduced in this paper. The RTAC algorithm, doesn't like the traditional control algorithm, considered the effect of atmospheric turbulence and the measurement noise together with the dynamic characteristics of the AO system. The parameters of controller can be modified during iterative calculation through the RTAC algorithm. The RTAC algorithm can adapt to the changes of work conditions to keep achieve optimal control performance. The theory of the RTAC algorithm will be discussed. The computer simulation and the experiment results on a modular adaptive optics experiment system with the RTAC algorithm will be discussed.

Liquid crystal (LC) lens with voltage and azimuth dependent focus is realized by using divided electrode structure. By applying appropriate potentials on the divided electrode, the LC cell behaves like an optical lens having astigmatic properties; the phase retardation of an incident light beam takes an elliptical shape in the cross-section. The axes of the elliptical shape of the phase retardation are electrically controllable.

We have developed a tabletop adaptive optics wavefront control system used to correct dynamic distortions. The system uses a Shack-Hartmann sensor constructed by using a lenslet array and a high-speed CMOS camera to measure distortion, a high-resolution liquid crystal spatial light modulator to correct distortion, and a personal computer to execute feedback control. A correction refresh rate of 50 cycles per second was achieved as the result of the high-speed vision system. The temporal characteristic measurement was based on the response to periodic signals of patterns, and the measured bandwidth was about 7Hz. We also describe the optical configuration and experimental results of a performance evaluation.

In this paper we present and demonstrate a dynamic lens and lens array generation method with programmable focal length based on an Opto-VLSI processor. The Opto-VLSI is driven by computer generated algorithm to generate a discrete Fresnel lens phase hologram. By optimizing the phase hologram, lenses and lens arrays of different focal lengths ranging from 300mm to infinity can be realized. The optical axis of each lens element can be independently addressed to simultaneously focus and steer an optical beam within an angular range of ±0.5°.

A new technology for focus variation with direct electric control without moving part will be presented. The technology relies on an interface between two non-miscible transparent liquids, which can be deformed by electrowetting. This technology has been developed since 10 years in the lab and starts to be available commercially, with the following characteristics: large amplitude of dioptric correction (20 dioptries for a 5mm pupil size), fast response, small power consumption and good transmission in the visible range, clear pupil 1-10mm diameter. This paper will show the basic principle, as well as the physical limitations and optical aberrations due to differential thermal expansion of the two liquids in the cell. Experimental measurements made with a Schack Hartmann wave front analyzer will be presented, as well as numerical simulations of the liquid-liquid interface. Applications will be discussed, mainly in consumer electronics.

Based on the generalized Huygens-Fresnel diffraction integral and the expansion of the hard aperture function into a finite sum of complex Gaussian functions, approximate analytical expressions of standard and elegant Laguerre-Gaussian beams passing through a paraxial ABCD optical system with a hard-edged aperture are derived. On the basis of the truncated second-order moments method in the cylindrical coordinate system and the expansion of the hard aperture function into a finite sum of complex Gaussian functions, an approximate method for calculating the generalized beam propagation factor is proposed. Closed-form expressions for the generalized beam propagation factor of a truncated standard and elegant Laguerre-Gaussian beam are derived that depend on the orders of Laguerre polynomial and the beam truncation parameter. Some typical numerical examples are given and compared. It is shown that the results obtained by using the obtained analytical method accord with those by using the numerical integration method.

Based on the standard electromagnetic boundary condition of aggregate sphere’s theory in plane wave incident case induced by Xu, this paper studied the interactions theory between an arbitrary shaped beam and aggregate spheres. As we set the incident field expansion coefficients as unknown, so it seems easier to solve the scattered field expansion coefficients in the interaction equations. The most challenge task left now for arbitrary shaped beam incident case is to solve the incident field expansion coefficients. Thought out lots of equations derived, we get the same results as Gouesbet but in a totally different way.

A robust measuring technique for the wavefront is one of the key parts for a stable adaptive optics system in the practical fields. Also, the measurement resolution of the wavefront is important for improving the performance of an adaptive optics system. In this paper, we propose a robust measuring technique for the wavefront using a Shack-Hartmann wavefront sensor for an adaptive optics system. The proposed measuring technique for the wavefront uses an iterative center of mass algorithm with the hierarchical sizes of a searching window and the hierarchical threshold values. The measurement accuracy and stability are investigated using the proposed hierarchical algorithm and compared with the conventional algorithm of the wavefront in the experiments. Also, we describe the hardware configuration of the adatptive optics system operating in our laboratory.

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.

In this paper, some research results on the geometry characters of laser presented, mainly including that the streamline structure and the spot size of laser beam. A phenomenological model for the streamline structure of laser beam proposed, of which the main point is that a Gaussian beam is divided into two regions in which the streamline structure appears different geometry characters. Also a quantum interpretation on how the beam waist comes into being and the energy shifts between the two regions given. This model meets very well with experimental results. Another work reported in this paper is detecting the laser spot size, for that a new method found. By the approach of the so-called “pre-saturation” in silicon, the novel laser spot size detector with monocrystalline silicon designed and demonstrated right and doable experimentally. This new detector can detect the size of laser beam spot quickly and accurately, with wide response wavelength band and quite small expense.

The voltage-decoupling model for a 37-channel micromachined membrane deformable mirror is established through theoretically and experimentally analyzing the fitting aberration of a continuous-surface deformable mirror. The function between voltage and displacement of an actuator, the linear superposing among the actuators for micromachined membrane deformable mirror are analyzed by means of the measured influence function of actuators. The fitting of the first 36-order Zernike mode is carried out. The analysis shows that micromachined membrane deformable mirror can be applied to correcting low order aberration. This research provides the basis and guideline for designing the adaptive optical system based on micromachined membrane deformable mirror, thus offers a theoretical basis and reference for the application of the deformable mirror.

Latency of wavefront processor is an important factor of closed loop adaptive optical systems. For an adaptive optical system using Shack-Hartmann wave-front sensing and point beam, by ways of task queue, subtask arithmetic decomposition and subtask structure design, a multi-processors structure based on moder parallelism theory is built to realize a pipeline of wavefront gradient, wavefront reconstruction and wavefront control. By traits of field programmable gate array(FPGA) and digital signal processor(DSP), a pipeline wavefront processor based on FPGA+DSP structure is built with highly real-time performance. Clocks of FPGA and DSP, “age” of correctors are primary sources of this wavefront processor’s latency. For a 61-element adaptive optical system whose sampling frequency is 2900HZ, latency of this wavefront processor is less than 100us.

The capability of real time wave-front reconstruction is important for an adaptive optics (AO) system. The bandwidth of system and the real-time processing ability of the wave-front processor is mainly affected by the speed of calculation. The system requires enough number of subapertures and high sampling frequency to compensate atmospheric turbulence. The number of reconstruction operation is increased accordingly. Since the performance of AO system improves with the decrease of calculation latency, it is necessary to study how to increase the speed of wavefront reconstruction. There are two methods to improve the real time of the reconstruction. One is to convert the wavefront reconstruction matrix, such as by wavelet or FFT. The other is enhancing the performance of the processing element. Analysis shows that the latency cutting is performed with the cost of reconstruction precision by the former method. In this article, the latter method is adopted. From the characteristic of the wavefront reconstruction algorithm, a systolic array by FPGA is properly designed to implement real-time wavefront reconstruction. The system delay is reduced greatly by the utilization of pipeline and parallel processing. The minimum latency of reconstruction is the reconstruction calculation of one subaperture.

On the basis of previous formula computing the position of sub-aperture spot image, a universal formula computing the position of sub-aperture spot image for Shack-Hartmann wavefront sensor was developed. The formula is a perfect combination of the coordinates weight algorithm, which times certain coefficient in some coordinates, and the intensity weight algorithm which uses some power of the gray level intensity of the sub-aperture image instead of the gray level intensity itself of the sub-aperture image. The set of concept was introduced, which makes the formula include such factors as noise that influence the accuracy of computing the position of sub-aperture spot image. Some discussion was performed in this paper and it’s proved that the universal formula is well consistent not only with the coordinates weight algorithm and the intensity weight algorithm, but also with the correlation tracking algorithm and the feature tracking algorithm. And some novelty of calculating the position of sub-aperture spot image was presented in this paper.

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 σ²_α 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 σ²_α 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.