We are working to develop a comprehensive, integrated software framework and toolset to support model-based engineering (MBE) of laser weapons systems. MBE has been identified by the Office of the Director, Defense Science and Engineering as one of four potentially “game-changing” technologies that could bring about revolutionary advances across the entire DoD research and development and procurement cycle. To be effective, however, MBE requires robust underlying modeling and simulation technologies capable of modeling all the pertinent systems, subsystems, components, effects, and interactions at any level of fidelity that may be required in order to support crucial design decisions at any point in the system development lifecycle. Very often the greatest technical challenges are posed by systems involving interactions that cut across two or more distinct scientific or engineering domains; even in cases where there are excellent tools available for modeling each individual domain, generally none of these domain-specific tools can be used to model the cross-domain interactions. In the case of laser weapons systems R&D these tools need to be able to support modeling of systems involving combined interactions among structures, thermal, and optical effects, including both ray optics and wave optics, controls, atmospheric effects, target interaction, computational fluid dynamics, and spatiotemporal interactions between lasing light and the laser gain medium. To address this problem we are working to extend Comet™, to add the addition modeling and simulation capabilities required for this particular application area. In this paper we will describe our progress to date.
The Comet Performance Engineering Workspace is an environment that enables integrated, multidisciplinary
modeling and design/simulation process automation. One of the many multi-disciplinary
applications of the Comet Workspace is for the integrated Structural, Thermal, Optical Performance
(STOP) analysis of complex, multi-disciplinary space systems containing Electro-Optical (EO) sensors
such as those which are designed and developed by and for NASA and the Department of Defense. The
CometTM software is currently able to integrate performance simulation data and processes from a wide
range of 3-D CAD and analysis software programs including CODE VTM from Optical Research
Associates and SigFitTM from Sigmadyne Inc. which are used to simulate the optics performance of EO
sensor systems in space-borne applications.
Over the past year, Comet Solutions has been working with MZA Associates of Albuquerque, NM, under
a contract with the Air Force Research Laboratories. This funded effort is a "risk reduction effort", to help
determine whether the combination of Comet and WaveTrainTM, a wave optics systems engineering
analysis environment developed and maintained by MZA Associates and used by the Air Force Research
Laboratory, will result in an effective Model-Based Engineering (MBE) environment for the analysis and
design of laser weapons systems.
This paper will review the results of this effort and future steps.
The application of adaptive optics has been hindered by the cost, size, and complexity of the systems. We describe here
progress we have made toward creating low-cost compact turn-key adaptive optics systems. We describe our new low-cost
deformable mirror technology developed using polymer membranes, the associated USB interface drive
electronics, and different ways that this technology can be configured into a low-cost compact adaptive optics system.
We also present results of a parametric study of the stochastic parallel gradient descent (SPGD) control algorithm.
In prior work we introduced a method of choosing mesh parameters for a single wave-optics propagation between two
effective apertures. Unfortunately, most systems that require wave-optics modeling, like modeling laser resonators with
gain media, propagations through the atmosphere, and imaging systems with internal limiting apertures, have multiple
apertures and phase screens that induce diffraction. We begin here by augmenting the single propagation theory to
include diffraction from both apertures and phase aberrations. We then introduce a technique for analyzing complex
systems of simple optics to determine the appropriate wave-optics mesh parameters.
In prior work we described a 5x5 ray matrix formalism and how to integrate the effects that are not modeled in wave-optics
with the ray matrix model. In this paper we describe how to complete the integration of the two techniques by
modifying the Siegman ABCD ray matrix decomposition. After removing the separable effects like image rotation and
image inversion, we break the 5x5 ray matrix into two 2x2 sections (a.k.a. the ABCD matrices) that correspond to the
two axes orthogonal to the propagation. We then present a general algorithm that breaks any arbitrary ABCD matrix
into four simple wave-optics steps. The algorithm presented has sufficient generality to handle image planes and focal
planes. This technique allows for rapid and accurate wave-optics modeling of the propagation of light through complex
optical systems comprised of simple optics.
One of the most common and important tasks in wave optics simulation is choosing what mesh spacings and mesh dimensions to use for a given problem. To obtain correct results, it is crucial that the mesh spacings are sufficiently small and the mesh dimensions sufficiently large, but if one makes the spacings too small, or the dimensions too large, that can greatly increase the simulation run time, and that may be unaffordable. It is therefore important to understand exactly what the applicable constraints are, so that one may choose mesh spacings and dimensions that will yield correct results without being over-conservative. However this problem can be nontrivial, especially when modeling propagation through aberrating media, or when there is potentially useful a priori information available which might allow us to relax the modeling constraints. For example, if the light source is known to be well-collimated, we know that all of the light to be modeled will be concentrated along one axis, allowing us to use smaller meshes than we would if the light were uncollimated. Similarly, if the receiver has a limited field of view, we need not model any light incident upon it from angles outside its field of view. In this paper we present a simple general method to determine what mesh spacings and dimensions will work for any given wave optics propagation problem, including problems involving propagation through aberrating media and/or a priori information about the source and/or receiver.
ABLSim is a software tool for high fidelity modeling of advanced optical systems such as a laser weapons systems and compensated imaging syste. It makes use of a well established modeling approach known as 'wave optics', in which optical wavefronts are modeled using 2D meshes of complex numbers. Wave optics is the most powerful approach known for predicting the performance of optical systems in the presence of strong turbulence. ABLSim differs from previous wave optics modeling tools primarily in that it is much easier to use. Historically, wave optics codes been notoriously difficult to use with the result that only a very small number of people - the code authors and a few others -could use the codes effectively. ABLSim is designed to make wave optics accessible to a much broader user community. In ABLSim, the user assembles system models in a 'connect-the-blocks' visual programming environment, where each block represents a system component such as an optical sensor, a laser source, a mirror or a lens. Each connection represents a specific type of interaction: for example, connections between optical components represent optical interfaces. ABLSim provides a GUI for setting up parameter studies and a Matlab interface for postprocessing.
The ABLE ACE pupil plane imaging experiment (PPI) measured the irradiance distributions of individual pulses originating from two laser sources on the ABLE ACE transmitter aircraft and incident upon the aperture of the receiver aircraft. The laser pulses were very short, and PPI has high spatial resolution but very low temporal sampling, so the PPI data is simply a series of uncorrelated snapshots of the illuminated aperture.Form the PPI data we can compute the irradiance variance, the probability density function of irradiance, the irradiance covariance function, and the amplitude correlation function, and other irradiance statistics. These statistics can be used for comparison with theory, simulation, and other measurements, and also to estimate the strength of turbulence. The amplitude correlation function is a direct measure of the Strehl ration and optical transfer function that would be achieved with perfect phase correction; this gives us an upper bound on the performance of an actual ABL system. We have PPI data from all ABLE ACE flights, over almost all of the time the science lasers were firing. We have compared PPI results with theory, simulation, simultaneous measurements, and a previous experiment. We see good agreement on all counts.