A recently developed scheme for closed loop stable control of two deformable mirrors (DMs) for compensation of both amplitude and phase fluctuations is examined. An approximate model describing the two DM system is developed using the Rytov theory. This model is used to evaluate the impact of measurement noise on the performance of the two DM system. The model is also used to evaluate the impact of misregistration on the stability of the two DM system. Wave optical simulation results are used to validate the predictions obtained from the Rytov theory based model.
Many adaptive optics systems rely on a Shack-Hartmann wave front sensor (WFS) coupled with a traditional least squares reconstructor to estimate the aberrations in the incident wave front. Unfortunately, the performance of this approach degrades in the presence of strong scintillation because, when there are intensity fluctuations in the wave front, the WFS does not measure the average phase gradient within each subaperture as assumed by the reconstruction algorithm. As scintillation increases, branch points in the wave front increase the disparity between what the WFS measures and what the reconstruction algorithm expects. A reconstruction algorithm is presented that attempts to mitigate the branch point problem by using a more realistic model for the Shack-Hartmann WFS measurements. Wave optics simulations over a variety of atmospheric conditions are used to compare the performance of this algorithm against a least squares reconstructor and a complex exponential reconstructor.
A high frame rate (120 Hz), multi-target, video tracker has been developed and used in an operational environment. The tracker is able to track multiple targets simultaneously, while providing fine-track track errors on a user selected target. The system is able to accommodate real-world issues such as sensor bad pixels and natural background clutter. Several fine track modes are available, including centroid, leading edge, and correlation. The tracker provides sub- pixel track accuracy against both resolved and unresolved targets. The system has been extensively tested against radiometrically correct cloud scenes and has been successfully integrated in a tracking system to provide multi-target tracking of real targets viewed against terrain and cloud backgrounds.
In last years proceedings, the above authors reported a basic limitation on the maximum effective bandwidth when tracking through atmospheric turbulence. This limitation, called the optical frequency, was shown to be an upper limit on tilt detection. This paper will further expand on this fundamental limitation. Further testing at the MIT/Lincoln Laboratory has provided more insight into the optical frequency as well as other tracking limitations. It will be shown in this paper that scintillation appears to be dominant above the optical frequency and that by wisely selecting the bandwidth of the tracking system, one can exclude some of the noise of scintillation, while still performing the best possible tracking.
In developing High Energy Laser (HEL) weapons, it is necessary to understand the absolute radiometry associated with propagating the beam to the target. This is important for setting filter attenuation levels for the tracker, laser beacons, and battle damage assessment sensors, along with more traditional calculations of laser fluence on the target. In this paper, we will present the theory and experimental validation for laser beams propagating over large distances through atmospheric turbulence. We conducted several experiments at Starfire Optical Range (SOR) in Albuquerque during 1997 to prove that we can accurately predict the uplink irradiance, the target signature, and the power levels or signal received from laser propagation. Specifically, using the Lageos satellite, we were able to predict the absolute signal to within 20% of the measured values. Subsequent experiments verify that the models we developed continue to accurately predict the absolute radiometry associated with laser beam propagation. The results should be useful for laser sensing, modeling and simulation, and exploitation and target recognition.
Boeing-SVS Inc. has developed a small, inexpensive inertial measurement system that provides a two-axis optical inertial reference for a variety of optical pointing and tracking system applications. The design combines two distinct innovations. The first is the realization of a fully functional commercial off-the-shelf (COTS) system, and the second is the miniaturization of the sensing assembly and support electronics.
Simulation development for Laser Weapon Systems design and system trade analyses has progressed to new levels with the advent of object-oriented software development tools and PC processor capabilities. These tools allow rapid visualization of upcoming laser weapon system architectures and the ability to rapidly respond to what-if scenario questions from potential user commands. These simulations can solve very intensive problems in short time periods to investigate the parameter space of a newly emerging weapon system concept, or can address user mission performance for many different scenario engagements. Equally important to the rapid solution of complex numerical problems is the ability to rapidly visualize the results of the simulation, and to effectively interact with visualized output to glean new insights into the complex interactions of a scenario. Boeing has applied these ideas to develop a tool called the Satellite Visualization and Signature Tool (SVST). This Windows application is based upon a series of C++ coded modules that have evolved from several programs at Boeing-SVS. The SVST structure, extensibility, and some recent results of applying the simulation to weapon system concepts and designs will be discussed in this paper.
This paper present new methodology to address critical refractivity turbulence issues for laser propagation using a new measurement system-a portable balloon-ring platform with multiple fine wire sensors at several separations. All raw data is transmitted to a ground station-allowing spectra to be calculated. The new platform is discussed and preliminary examples of observations, including artifacts, are shown and discussed. This new platform provides capabilities during the daytime as well as nighttime-unlike conventional thermosondes that are used only at night. Such all time observations are important due to the pronounced diurnal variation in the planetary boundary layer where many laser systems are operated. Plans to address the longstanding concern of wake contamination on systems suspended below a balloon quantitatively will be presented. The objective of this effort is to develop the capability that can address several questions related to laser propagation such as: 1) Is the atmospheric isotropic for the scales of interest? 2) Is the turbulence Kolmogorov under various atmospheric conditions, or how often is the structure function represendted by the r2/3 law? 3) what are the profiles of inner and outer scale? 4) To what degree does wake contamination affect conventional thermosonde measurements? 5) Does fine structure within the scattering volume sensed by radar affect refractive index structure parameter (Cn2) and eddy dissipation rate (epsilon) estimates? These questions and concerns will be addressed by making the appropriate observations using the balloon-ring platform. Many of the measurements will be taken at Vandenberg AFB since the Western Test Range operates a ground receiving station, balloon launch facility, VHF radar, boundary layer radars, sodars, and instrumented towers that will enhance this effort. This effort provides an observation platform that will ultimately lead to the development and validation of conceptual/statistical/physical models.
The purpose of this investigation is the study of the process of the optical vortices pair arising from the nonzero intensity minimum. We propose and analyze a local polynomial model of optical vortex pair creation. The optical vortices arise around zero points of intensity, which lie on the zero-crossing lines of real and imaginary parts of wave field on real-plane. The appearance of the optical vortices is an indication of transition of wave into a new more complex state. Numerous theoretical and experimental papers are devoted to the investigation of such objects; the structure of isolated vortex and its statistical properties are studied there usually. The coordinates of real-plane zero points are located in the recovery problems of optical wave fields. However, the location of real-plane points is impossible for experimental data because of discretization and quantization of signals. Therefore an analytical model is necessary to study the creation and annihilation of the optical vortex pair and other spatial points at wave propagation.
The Department of Defense has an increasing number of high-energy laser weapons programs with the potential to mature in the not too distant future. However, as laser systems with increasingly higher energies are developed, the difficulty of the laser safety problem increases proportionally, and presents unique safety challenges. The hazard distance for the direct beam can be in the order of thousands of miles, and radiation reflected from the target may also be hazardous over long distances. This paper details the Air Force Research Laboratory/Optical Radiation Branch (AFRL/HEDO) High-Energy Laser (HEL) safety program, which has been developed to support DOD HEL programs by providing critical capability and knowledge with respect to laser safety. The overall aim of the program is to develop and demonstrate technologies that permit safe testing, deployment and use of high-energy laser weapons. The program spans the range of applicable technologies, including evaluation of the biological effects of high-energy laser systems, development and validation of laser hazard assessment tools, and development of appropriate eye protection for those at risk.
A new material for optics is being developed that promises to be far more robust than alternative materials. It is a photo-thermo-refractive (PTR) glass in which Bragg gratings (holograms) can be written in the interior (not the surface) of the glass. The gratings are permanent as they are not removed by illuminating them with light at other wavelengths or by heating unless the temperature exceeds 400 degree(s)C. This technology can be used to make diffractive elements such as spatial filters, attenuators, switches, modulators, beam splitters, beam samplers, beam deflectors, selectors of particular wavelengths (notch filters, add/drop elements), spectral shape formers (gain equalizers), spectral sensors, angular sensors, Bragg spectrometers, and transverse and longitudinal mode selectors in a laser resonator. The PTR Bragg grating has been exposed to a 100 W, 1096 nm beam focused to 100 kW/cm2 spot for 10 minutes without exhibiting any temperature rise. The pulsed laser damage threshold has been measured to be within 30% of that of the best silica glass used in high power 1064 nm systems. The useful spectral range of this glass is from 350 nm to 2.8 microns.
EAGLE (Evolutionary Air & Space Global Laser Engagement) is the proposed high power weapon system with a high power laser source, a relay mirror constellation, and the necessary ground and communications links. The relay mirror itself will be a satellite composed of two optically-coupled telescopes/mirrors used to redirect laser energy from ground, air, or space based laser sources to distant points on the earth or space. The receiver telescope captures the incoming energy, relays it through an optical system that cleans up the beam, then a separate transmitter telescope/mirror redirects the laser energy at the desired target. Not only is it a key component in extending the range of DoD's current laser weapon systems, it also enables ancillary missions. Furthermore, if the vacuum of space is utilized, then the atmospheric effects on the laser beam propagation will be greatly attenuated. Finally, several critical technologies are being developed to make the EAGLE/Relay Mirror concept a reality, and the Relay Mirror Technology Development Program was set up to address them. This paper will discuss each critical technology, the current state of the work, and the future implications of this program.