I've been involved with the development of adaptive optics almost from the beginning, and because of that I've been asked to talk about what happened in the development of that field, as I perceived it. In response to that request I have prepared the following—which is an un researched and necessarily somewhat subjective account of what I recall about the development of adaptive optics over the last 30+ years, as seen by an active and deeply involved participant. The work I've been involved with was almost entirely funded by the DoD so it is naturally to be expected that most all of what I'll have to say will have military interests underlying the work—but in fact it couldn't be very different as almost all of the work done to establish the field of adaptive optics was funded with military objectives in mind. Well before there was a field called adaptive optics I published several papers that addressed the matter of what the effects of having to propagate through atmospheric turbulence would be on the performance of various types of optical systems. As a consequence I got drawn into the field of adaptive optics development quite early, both as an analyst and as an advisor to several of the military organizations that were pushing the development of that field. I got to regularly attend government reviews of hardware development programs at various contractors, and then got to go home and analyze technical/pheiiomenology questions that came up during the reviews. As a consequence I've had a great seat from which to watch the story unfold, and now I'm going to try to put words to a bit of that story. I think I was involved in or at least had an overview look at most all of the work that led to the development of the field of adaptive optics, but I'm sure not all of it is still in my memory banks— which is my way of saying that just because I don't mention it doesn't mean it didn't happen. Some of what is missing in this presentation I just don't recall any more, and other parts are missing because they were not, in my opinion, part of the main stream (i. e. the critical path) in the development of the field. In what follows I try to trace the field's development up to about a decade ago.

In the Airborne Laser there are two wavefronts of interest, namely, the inbound wavefront from the beacon and the outbound wavefront of the high-energy laser. The beacon wavefront emanates from the tip of the missile, whereas the high-energy laser wavefront is directed towards the ami point on the missile. Hence, these two wavefronts propagate through different regions of the atmosphere at different time instants, which is the cause of anisoplanatism. In order to account for the anisoplanatic effect, the spatial- temporal correlation between the Zernike polynomials' phase distortion expansion coefficients representing these wavefronts must be determined. Using this correlation information, an underlying linear, stochastic, dynamical system, which represents the atmosphere, is identified. This linear system is the plant. The wavefront sensor and deformable mirror dynamics are also modeled.

A phase reconstructor for an adaptive optics system depends on a model of the response of commands to the deformable mirror in the gradient sensor. Errors in this model may be due to actuator/sensor misregistration. The level of misregistration which produces closed loop instability is calculated for several systems (2 X 2, 4 X 4, and 15 X 15 subapertures). Depending on the servo law, the 15 X 15 system may be stable for misregistration up to 17% of a subaperture but loses 30 degrees of phase margin at 5%. The effects of system size, servo bandwidth, latency, and actuator slaving are illustrated. It is also shown that spatially filtering the reconstructed phase can dramatically reduce the sensitivity to misregistration.

Thermally induced optical distortions severely degrade the quality of high-power/high-energy laser beams, thus reducing the irradiance on target. The purpose of this paper is to present a brief history and a short account of R&D work that culminated in formulating analytical procedures for evaluating the impact of spherical aberrations generated by actively cooled cylindrical components that transmit CW laser radiation. Specifically, the paper deals with edge- and face-cooled optical components and examines how beam shape and cooling strength affect the power-handling performance.

This paper discuses the DELE lethality assessment methodology and explains requirements for experimental data and algorithm development within the laser lethality and vulnerability area. current applications and data sets cover a broad range of laser parameters and materials properties. In addition, new lasers, new materials, and new applications continue to be rapidly added to the area. The purpose of this paper is to introduce the audience to the formalized process/discipline of formulating vulnerability criteria for different High Energy Laser systems by emphasizing the laser/materials phenomenology. Some of the DELE laser facilities and diagnostic capabilities are reviewed.

We begin with a brief review of prior work relating to optical windows for use with high power laser beams. A typical window must provide pressure separation between system segments, ultra-low loss, and small wavefront distortion of the many outgoing laser beams and signal returns despite heating by the high energy laser beam. Historically, two approaches have been examined to improve such windows.

The Acquisition, Tracking and Pointing hardware and software for the Airborne Laser Advanced Concept Testbed (ABL-ACT) Non-Cooperative Dynamic Compensation Experiment (NoDyCE) is described. Five main components make-up the entire ABL-ACT ATP system. These systems are: a 1-meter elevation over azimuth gimbal and gimbal control system with two acquisition sensors, a dome controller, and coarse track system, a fine track system, and a mode logic control system. Each subsystem's unique functionality, hardware choice and top level software architecture will be discussed. The optical, physical and information interfaces between each of the NoDyCE ATP systems is also described, as well as a brie discussion of the NoDyCE experiment goals and the overall NoDyCE architecture.

Techniques for creating accurate scenes of small targets against high clutter cloud backgrounds have been developed. This scene generation capability is a crucial first step in developing acquisition, tracking, and mode logic algorithms for real time implementation. This scene generation capability features multiple targets combined with cloud backgrounds and numerous options for real world sensor effects. The generated frames are radiometrically and spatially accurate to sub-pixel precision.

A Kalman Filter tracker algorithm is developed to increase track accuracy in the presence of scintillation. A simulation is developed which allows comparison of the Kalman Filter tracker to a Centroid tracker. This paper describes the development of the Kalman Filter tracker algorithm and the results of the simulation effort. The Kalman Filter Tracker formulation is described and sensitivity analyses are performed. The Kalman Filter is exercised on MIT Lincoln Lab data for comparison to real data and other algorithms. The results are discussed.

Tracking through a turbulent atmosphere poses several challenging problems. The authors have recently conducted a series of tracking tests at a MIT/Lincoln Laboratories facility where a complete tracking and adaptive optics system is available in a laboratory. The atmosphere is simulated using seven precision rotating phase screens. A great deal has been learned about tracking algorithms and their response under a scintillated atmosphere. Data will be shown to describe a key limitation to high bandwidth tracking. This effect, called the `Optical Frequency', appears to be an upper bound on track bandwidth when using an image based tracking system.

The principal phenomena limiting an accuracy of laser beaming of remote objects in atmosphere is the atmospheric turbulence that induces the laser beam wandering over the object. Recently, a novel algorithm, which is referred as `a bright speckle algorithm', was proposed to compensate for wandering of a repetitively pulsed laser beam, propagating along at the atmosphere range. In the paper we consider the restrictions on the algorithm performance, which are imposed by the atmospheric turbulence. The restrictions are imposed on a distance range of the algorithm as well as on coincidence accuracy of the probe and operation beam wavefront profiles, which are used for the algorithm realization.

Optical turbulence measurements have been performed at North Oscura Peak, White Sands Missile Range using a variety of precision instruments. A commercially available sodar system is used to collect atmospheric profiles, which are calibrated with fine-wire probes to calculate the optical index of refraction structure parameter, C_n², from a height of 15 meters to around 160 meters above the ground.

Cirrus clouds regularly cover approximately 20% of the globe 1 . Understanding laser and other electo-optical transmission in the presence of cirrus clouds is an important consideration for astronomical observations, various lidar systems, and new laser systems like the USAF Airborne Laser. Simulated cirrus cloud data generated by the Regional Atmospheric Modeling System (RAMS) is used as input to a laser propagation code developed at University of California at Los Angeles (UCLA). This code computes realistic laser transmission values through a 1-D cirrus cloud layer. Results are examined for a real data simulation of a thin cirrus case in the FIRE (First ISCCP (International Satellite Cloud Climatology Project) Regional Experiment) Cirrus II field campaign during November 1991.

The Airborne Laser Concepts Testbed is located on White Sands Missile Range, NM and is used to explore and develop new methods for tracking, pointing, and compensation of laser beams. All of these efforts require a knowledge of the optical turbulence along the propagation path. The site utilizes a 52.6 km propagation path over a desert basin between two mountain peaks (North Oscuro Peak (NOP) and Salinas Peak). Characterization of the optical turbulence at ABL ACT is challenging due to the long path length int he atmospheric boundary layer and the complex terrain of the site. A suite of instrumentation is being used to approach the problem; a sodar, fine wire probes, a pupil plane imager, a differential image motion monitor, and a scintillometer. In addition, a weather station senses ambient temperature, humidity, pressure, wind speed and direction, and solar radiation-received both horizontally and parallel to the mountain west-facing slope at NOP.

A comparison of CO2 Doppler lidar and GPS rawinsonde measurements of horizontal wind velocity was conducted during May 2000 at Hanscom AFB, Massachusetts. Seven days of side-by-side measurements using both lidar and GPS sondes were achieved comparing wind velocity as a function of altitude up to 6 km. The horizontal wind velocity was determined by the CO2 Doppler lidar using the Velocity Azimuth Display (VAD) method. Horizontal winds were also determined simultaneously using a differential GPS-tracked rawinsonde which provides GPS position coordinates once per second. Both lidar VAD wind speed Root Mean Squared Difference (RMS) and lidar vs. GPS sonde RMS were calculated and compared as a function of altitude, time, and stability regime. On average, significant increases in both the lidar VAD RMS and lidar vs. GPS RMS were observed during unstable conditions compared to stable conditions. Analyses of lidar VAD RMS show the smallest typical values average near 0.5 m/s over a single profile.

Optical fields propagation through the Earth's turbulent atmosphere are subject to time varying phase distortions. These phase distortions place severe limitations on electro- optical systems, such as imaging, tracking and vibrometry sensors. The generation of artificial beacons by laser backscatter (guide stars) for wavefront sensing may not be acceptable and natural beacons for wavefront sensing may not be available. Diversity techniques, however, allow passive wavefront measurement of the aberrated wavefront. This paper reports a phase diversity method based upon the transport- of-intensity equation for recovering phase from irradiance measurements. Digitized intensity data over a rectangular array of data is expanded into Zernike polynomials and a matrix method used to solve the transport-of-intensity equation. The phase diversity technique is evaluated in the pupil as well as the focal plane. Simulation and experimental data is provided.

A new lidar system for measuring near simultaneously aerosol extinction, size distribution and turbulence profiles up to 20 km altitude has been developed. On the basis of measurements and a Monte Carlo beam propagation model, the atmospheric aerosol contributions to laser beam widening for a horizontal propagation path at various elevations is estimated and compared with beam widening caused by turbulence.

It is well known that data obtained from measurements of turbulence intensity, wind velocity profiles, and temperature at the altitudes of 10 - 15 km signify the zones of sharp changes near the tropopause. In this context it is essential to distinguish the footprint of the aircraft from characteristic of nondisturbed turbulence. So this work is still continue in the following directions: atmospheric characteristic at altitudes of 10 - 15 km, turbulence characteristic at altitudes of 10 - 15 km, characteristic of aircraft foot prints under conditions of real flight. And direct measurements of turbulence and refraction are performing in a plane footprint at the ground level. We are assuming to construct the model of atmospheric turbulence on the high-elevated paths along the long distance propagation.

The method which defines the space spectrum parameters of the turbulent medium is presented. The experiment laser beams distribution with various diameters and at different wavelengths are used to define the spectrum parameters. The relation between the value of dispersion of gravity center wandering of the laser beam and the function of correlation of intensity in the observation plane is used. The method consists in estimating the correlation function of intensity distribution and the value of dispersion of gravity center wandering of the laser beam in the observation plane using the experimental data and the solution of the system of equations. The system of equation is made on the basis of an analytical relation between this dispersion and this correlation function. This method has been used to process the data of numerical experiment. These results proved to be good. From the data about the intensity distribution of two laser beams with various diameters obtained in physical experiment, the structural characteristic of refractive index and the outer scale Lo are obtained. The method is universal in that it allows one to use the beams with an arbitrary distribution of intensity at the input of turbulent. The comparison between the results of physical experiment and numerical experiment for which the spectrum parameters have been recovered by the described method is performed. The characteristics of intensity distribution are shown to be close.