The temporal properties of the tilt aberration induced in a plane wave upon propagation through the atmosphere depends upon the statistical characteristics of the optical turbulence encountered along the propagation path. While the Kolmogorov model with infinite outer scale is often employed to describe turbulence, experimental studies indicate that the effective outer scale of atmospheric turbulence, designated L₀, is on the order of 5 m to 100 m. Accounting for the effects of finite outer scale alters the correlative properties of phase aberrations of all orders. Using Taylor's frozen flow hypothesis, we extend the results of spatial correlation studies to model the temporal correlation of wave-front tilt when atmospheric winds are presented. We show that the correlative properties of the wave-front tilt depends upon the quantity v(tau) /D, where v is the wind speed, (tau) is the time delay between tilt measurements, and D is the diameter of the aperture in which the tilt is measured. The outer scale affects the temporal correlation according to the ratio L₀/D. Our results demonstrate that the tilt correlation falls off more rapidly as the relative outer scale is decreased. Correspondingly, the tilt power becomes more concentrated at higher frequencies.

The 3D model of continuous random medium as a chain of phase screens, describing both transverse and longitudinal correlation of wave phase in a wide range of spatial scales have offered. The constructed model essentially removes the lower restriction on thickness of random medium, replaceable by the phase screen. Analysis of phase screens, received through a modified subharmonic method, has been concluded. The statistical research of random walk of a beam in turbulent atmosphere have carried out.

We describe the design and operation of a high speed optical tomography system for measuring 2D images of a dynamic phase object at a rate of 5 kHz. Data from a set of eight Hartmann wavefront sensors is back-projected to produce phase images showing the details of the inner structure of a heated air flow. Series of reconstructions at different downstream locations illustrate the development of flow structure and the effect of acoustic flow forcing.

The development of high performance line-of-sight optical communication links through the turbulent atmosphere is facilitated by laboratory tests of schemes involving adaptive optics, beam tracking, modulation and coding, aperture averaging, fading statistics, and transmitter/receiver diversity. A water-filled turbulence tube has been implemented to simulate, in some respects, the effects produced on a laser beam when it propagates several kilometers through the air. This tube is being used to investigate on a laboratory scale: aperture averaging, fluctuation statistics, optical path difference, high data rate modulation, and various coding schemes. The liquid- filled turbulence tube causes fluctuations on a slower time scale than does the atmosphere. At low turbulence levels it produces log-normal fluctuation statistics, causes tip-tilt errors similar to those previously observed for atmospheric paths, and has already allowed evaluation of aperture averaging and fade statistics. It also allows the testing of various technological schemes to deal with atmospheric turbulence effects without any specific assumptions, such as weak Kolmogorov turbulence, being built into the model.

A turbulence chamber has been designed and built for performing optical propagation experiments. The chamber can produce turbulence 1000 times stronger than that of atmospheric turbulence, and is isotropic and homogeneous. Scintillation measurements for optical propagation inside the chamber are presented and compared with real atmospheric tests. The chamber can be used to perform optical propagation experiments under well-controlled and reproducible conditions. The chamber can be used to develop experiments to test optical communications, lidar, directed energy weapons, electro-optical designers, imaging systems, and air-borne laser systems which have to operate under atmospheric turbulence conditions. The chamber can provide tests results which are much less costly compared to outdoor and field tests.

This paper describes the approach applied at the Technion to investigate the aero-optical effect in supersonic flow conditions. This approach consists of a numerical analysis of the problem (global/local/parametric) accompanied by an experimental effort. The experimental effort ranges from the flow-field structure visualization (shocks, shear and boundary layers, etc.) to optical measurements of gas density gradient distributions along a diagnostic optical beam. Measurements of flow parameters, such as pressure and temperature are being carried for the purpose of validation and calibration of the numerical calculations. The next stage of the experiments will include direct optical distortion measurements. The above mentioned approach aims at supplying concise information for understanding the mechanisms of the aero-optical effects. It and allows future development of prediction and correction methods, in order to modify the acquired optical information.

We discuss an adaptive optical system having a self- organized control channel hierarchy (`adaptive' adaptive imaging system). In this system changes in the quality metric are reflected by corresponding changes to the control algorithm structure. Numerical simulations of an adaptive imaging system with a self-organized control structure demonstrate a property unusual for model-free optimization methods: the algorithm convergence speed did not change, or at times even increased, when the number of control channels N increased.

We discuss the use of Liquid Crystal Phase Modulators (LCPM) as a repeatable disturbance test source for use with adaptive optics systems. LCPMs have the potential to induce controlled, repeatable, dynamic aberrations into optical systems at low cost, low complexity, and high flexibility. Since they are programmable, and can be operated as transmissive elements, they can easily be inserted into the optical path of an adaptive optics system and used to generate a disturbance test source. Laboratory experiments with a Meadowlark LCPM are presented.

Optical patterns generated in a nonlinear optical ring resonator composed of spatial light modulator and 2D optical feedback have two series of the spatial frequencies. The spatial frequency filtering technique allows us to select the desired spatial frequencies. The pattern generations with a single slit, a band-cut filter, and a low-cut filter are experimentally demonstrated.

Adaptive optics can be used to improve the performance of a near-ground laser communication link by reducing intensity scintillation of an optical carrier collected by a down- range receiver. Such an adaptive optics system may include a Shack-Hartmann wavefront sensor to measure the wavefront of a beacon laser, and a deformable mirror to apply the appropriate conjugate wavefront to a transmitted communication beam. In this paper, we investigate the performance of such an adaptive optics system using multiple phase screen Monte Carlo computer simulations. Specifically, we consider the effects of intensity dynamic range of the wavefront sensor and of the aperture size of the adaptive optics on the mean and variance of the received intensity.

Laser beam propagation through atmospheric turbulence may result in strong intensity fluctuations at the receiver plane of a free-space communication link. To minimize intensity fluctuations, we consider an approach based on the use of a dynamic random phase diffuser placed in the transmitter plane. To create a phase diffuser having controlled statistical properties, a nonlinear optical system with 2D feedback (artificial optical turbulence generator) is used. This system can provide real-time laser beam spatial coherence control for a laser transmitter in order to optimize laser communication link performance.

Given are the results of experimental study on the quasi real time holographic correction for the lens distortions in the passive observational telescope in the visible range of spectrum, using the liquid crystal optically addressed spatial light modulator.

Space-based inflatable technology is of current interest to NASA, DOD, and in particular to the Air Force Research Laboratory. Potentially large gains in lowering launch costs, through reductions in structural mass and volume are driving this activity. Diverse groups are researching and developing this technology for radio and radar antennae, optical telescopes, and solar power and propulsion applications. Regardless of the use, one common requirement for successful application is the accuracy of the inflated surface figure. This paper gives a very cursory description of the research being performed at the Air Force Research Laboratory in the fields of membrane mirrors and real time holography. First, the article will show a shape modification method for the membrane mirror, achieved through enforced boundary displacements. The membrane mirror shape modification, resulted in moving the inflated membrane shape towards a desired optical profile. Minimization of the optical figure error is further discussed. Next, the optical requirements levied from the membrane mirror to an optically addressed spatial light modulator performing real time holographic correction are discussed. A proposed optical configuration in which a real time holographic optical element could be combined with the membrane mirror to achieve near diffraction limited optical performance is discussed.

The next generation optical space telescopes with apertures > 10 m for imaging, lidar, communications and directed energy focusing will be unable to use conventional technologies which are impractical or too costly. Our solution is to construct a telescope from a lightweight, low-quality primary, which is holographically corrected for surface distortions, in situ. This scheme makes it possible to correct for apertures of virtually unlimited size, over a narrow bandwidth, at optical and UV wavelengths. In this talk we present the first holographically corrected telescope ever constructed for astronomical imaging. We present evidence that a distant beacon, combined with a static holographic recording may be the most inexpensive and simplest approach. The design of the telescope also makes it possible to incorporate an adaptive optics correction system for compensation of longer-term mirror deformation/sag and thermal distortions.

Real-time holography compensates for severely aberrated primary mirrors in large aperture telescope systems. A prototype optically addressed liquid-crystal spatial light modulator device developed for this application is demonstrated with short response times, approximately 600 microsecond(s), and high diffraction efficiencies approaching 40%.

The basic characteristics of the optically addressed spatial light modulators are presented based on ferroelectric liquid crystal (FLC) as a light modulating media and amorphous hydrogenated silicon carbide a-SiC:H and dye-doped polyimide films as photoconducting layers. The parameters of the constituent parts are described, among them: photoconductivity of photosensitive layers, data about newly developed light blocking layers, characteristics of the FLC materials, utilizing the deformed helix ferroelectric effect. The dynamics of the response in hundreds Hz region, the diffraction efficiency of 20% at spatial resolution better than 501 p/mm, and sensitivity in range of microWatt/cm² are obtained.

Large numerical aperture telescope with nonlinear optical correction for distortions, designed for the remote self- luminous object imaging, was realized in experiment and investigated. Dynamic hologram, recorded in optically addressed liquid crystal spatial light modulator, was used as the corrector. Nearly diffraction limited performance of the system was demonstrated.

Proposed is the novel method of dynamic nonlinear-optical correction for distortions in wide spectral band. The method is based on combining of the negative optical feedback correction and dynamic holography correction in the system, using optically addressed phase modulators. State-of-the-art of key technologies is evaluated.