Free space optical communications (FSO) are beginning to provide attractive alternatives to fiber-based solutions in many situations. Currently, a handful of companies provide fiberless alternatives especially aimed at corporate intranet and sporting event video. These solutions are geared toward solving the 'last mile' connectivity issues. There exists a potential need to extend this pathlength to distances much greater than a 1 km, particularly for government and military applications. For cases of long distance optical propagation, atmospheric turbulence will ultimately limit the maximum achievable data rate. In this paper, we propose a method of improved signal quality through the use of adaptive optics. In particular, we show work in progress toward a high-speed, small footprint Adaptive Optics system for horizontal and slant path laser communications. Such a system relies heavily on recent progress in Micro-Electro-Mechanical Systems (MEMS) deformable mirrors as well as improved communication and computational components.
We discuss the design and implementation of a low-cost, high-resolution adaptive optics test-bed for vision research. It is well known that high-order aberrations in the human eye reduce optical resolution and limit visual acuity. However, the effects of aberration-free eyesight on vision are only now beginning to be studied using adaptive optics to sense and correct the aberrations in the eye. We are developing a high-resolution adaptive optics system for this purpose using a Hamamatsu Parallel Aligned Nematic Liquid Crystal Spatial Light Modulator. Phase-wrapping is used to extend the effective stroke of the device, and the wavefront sensing and wavefront correction are done at different wavelengths. Issues associated with these techniques will be discussed.
While the theory behind design of multiconjugate adaptive optics (MCAO) systems is growing, there is still a paucity of experience building and testing such instruments. We propose using the Lick adaptive optics (AO) system as a basis for demonstrating the feasibility/workability of MCAO systems, testing underlying assumptions, and experimenting with different approaches to solving MCAO system issues.
KEYWORDS: Control systems, Digital signal processing, Resonators, Adaptive optics, Computing systems, Wavefronts, Deformable mirrors, Wavefront sensors, Human-machine interfaces, Control systems design
Sustained operation of high average power solid-state lasers currently requires an adaptive resonator to produce the optimal beam quality. We describe the architecture of a real-time adaptive control system for correcting intra-cavity aberrations in a heat capacity laser. Image data collected from a wavefront sensor are processed and used to control phase with a high-spatial-resolution deformable mirror. Our controller takes advantage of recent developments in low-cost, high-performance processor technology. A desktop-based computational engine and object- oriented software architecture replaces the high-cost rack-mount embedded computers of previous systems.
Thermal wave imaging typically refers to a number of techniques in which a sample to be nondestructively tested is actively heated with either a pulsed or stepped source, and the time dependence of either the heating or cooling of the sample is monitored with an IR camera. Although these techniques have been used in manufacturing applications, the methods used for data analysis have been either too computation intensive for real time implementation, or too qualitative and subjective to be used reliably. Dynamic histogram analysis offers an alternative method for data interpretation that is computationally simple, yet quantitative and repeatable. Features which may be weak or ambiguous in the actual image can be easily identified using a data volume based on the time evolution of the histogram.
This paper describes the performance of a high-speed PtSi infrared charge-coupled device (IRCCD) camera system for recording periodic and transient events in the infrared. Integration times down to 10 microsecond(s) and the ability to record frames based on an external trigger allows this setup to achieve high effective frame rates. The use of a personal computer (PC) as a controller for CCD clocking and video capture results in a flexible camera system design. Examples of the camera system's capacities for short integration time imaging and triggered image capture are presented.
This paper describes the construction of a high-speed PtSi infrared charge-coupled device (IRCCD) camera system funded by the U.S. Army Tank-Automotive Command (TACOM) for recording periodic events in the infrared. A brief discussion of PtSi infrared detection, and an analysis of expected signal contrast and NE(Delta) T of the device are presented. Integration times to less than 1 ms and the ability to record frames based on an external trigger allow this setup to achieve effective frame rates of over 1000 frames per second. The use of a personal computer (PC) as a controller for CCD clocking and video capture results in a flexible camera system design.
This paper discusses the design of an RC network model of the parallel clock registers on a charge coupled device. A model has been developed that takes into account the individual pixel capacitance and resistance of the device the line resistance of the polysilicon clock lines and the line-to-line capacitance between adjacent phases. This RC network forms a lossy transmission line that degrades the clock pulses applied to the device as they travel to its center. In the case of high-speed large area CCDs the deterioration in pulse shape can lead to a significant drop-off in charge transfer efficiency (CTE) as a function of distance from the edge of the device. Using SPICE the parallel clock registers of three different CCDs have been simulated. The first device is a large area scientific imager designed to run at relatively slow clock rates. The second CCD is an upgraded version of that device. It includes Aluminum-strapped clock lines to reduce the RC time constant of the clocking structure. The third device is an infrared PtSi imager. The results of the SPICE simulations are used to find the limiting RC time constant of each device and to project its performance as a high-speed imager. 1 .
This paper discusses the design of a multispectral radiometer and camera implemented using a CCD imager, two Silicon photodiode radiometers and a rotating filter wheel equipped with six bandpass filters spaced throughout the visible and near-IR spectrum. One of the radiometers has a field-of-view matched to that of the camera to measure integrated scene radiance, whereas the other radiometer functions as a spot radiometer to measure small surface radiances. The system is synchronized with the 60 Hz camera video and transfers the 16-bit digitized data from the two radiometers once every video field through a parallel interface to a video data encoder. The encoder incorporates the data into the current video field for VCR recording and later playback and analysis. The system is designed for airborne use mounted underneath the wing of an aircraft. Its main purpose is to analyze the spectral radiances of various surfaces involved in high-speed videography experiments. The data obtained with the radiometer will be used to refine specifications for a high-speed, high-resolution solid state imager. However, applications extend to any field where fast, spectral measurements are required. A data set obtained for a sample application is presented to illustrate the performance of the system.
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