One aspect of the propagation-physics challenge associated with airborne, free-space, optical communications
(FSOC), for example, is the characterization and mitigation of link losses due to aero-optic interactions. That
is, air-density gradients due to compressibility effects in turbulent boundary layers, separated flows, and freeshear
flows can disturb the wavefront in the near field of the transceiver. To better understand these aero-optical
mechanisms, a model of a nose-mounted, FSOC transceiver recently was placed in a compressible-flow wind tunnel,
and the resulting wavefront degradations, as a function of flow scenario, were recorded. High-speed, time-resolved
movies of the aero-optic disturbances have been realized, using a Schlieren-imaging technique, and a
very-highframe-rate camera. Discrete, vortical structures (amid otherwise-irregular shedding) were seen to emerge and
convect past the clear aperture. The frequencies of these disturbances have been estimated from the movies, and
these have been compared with high-speed, time-resolved wavefront reconstructions. Losses of -3.5 dB (for the
case of Mach - 0.45 at 10 kft, side view, and λ - 1.55 μm, for example), and disturbance frequencies of - 1200
Hz (and higher) were observed. The system-level impact of the resulting wavefront degradations will be discussed.
We report on a set of measurements made in December 2005 by researchers from the University of Central Florida, SPAWAR's Innovative Science and Technology Experiment Facility (ISTEF), Harris Corporation, NASA Kennedy Space Center, and Northrop Grumman. The experiments were conducted on the Shuttle Landing Facility (SLF) at Kennedy Space Center (KSC) over terrestrial paths of 1, 2, and 5 km. The purpose of the experiments was to determine the atmospheric-induced beam spreading and beam wander at various ranges. Two lasers were used in the experiments. Both were a pulsed 1.06 μm laser; however, one was single-mode and the other was multi-mode. Beam profiles were recorded near the target position. Simultaneous measurements of Cn2, wind speed and direction, humidity, visibility, temperature, and surface temperature profiles were all recorded.
Purpose: The direct comparison of in-vivo OCT images with fixed tissues sections assumes the fixation of tissue has no effect on the size and configuration of final pathology images such as light micrographs. Fixation artifact has been a concern in numerous studies of the pathology of retinal laser lesions. We tested this hypothesis. Methods: The Humphrey OCT model 2000 with a custom mirror and lens assembly was used to scan tissue phantoms and both fresh and fixed ex-vivum tissue samples. The optical configuration was determined by optimization of the contrast and signal strength on tissue phantoms. Fresh porcine retinas were scanned using this optimal configuration, then fixed using either glutaraldehyde or formalin. OCT images were taken of the tissue at various stages during the fixation process. Additionally, we examined fixed retinal tissue containing retinal laser lesions as a part of our study of ultrashort-pulsed laser effects on the macacca mulatta retina. Histologic sections were prepared and evaluated. Results: In this presentation, we describe our optical setup and image optimization process and assess the effects of glutaraldehyde and formalin processing on OCT image quality. The OCT images of glutaraldehyde-fixed laser lesions are compared with similar images of laser lesions in-vivo. Fixation artifacts appeared on OCT at 2 to 24 hours. Opacification of the lumen of large vessels was seen at two hours with both glutaraldehyde and formalin, while fixation induced retinal detachment appeared at 24 hours. Overall, there was a grater delineation of the laser lesions by OCT at 24 hours when compared to at 1 or 2 hours of fixation. Conclusions: Fixations induced changes in OCT scans of retinal tissue are present as early as 2 hours after immersion in fixative. Although both glutaraldehyde and formalin fixation preserve much of the tissue structure, these method of fixation have s significant effect on OCT imaging of both normal retinal tissue and laser lesions.
Researchers and lens designers have established the optical performance benefits of gradient-index (GRIN) optics. Refractive index gradient attributes such as depth, shape, and total index change determine the lens aberrations and in some cases the first-order system properties. Gradient-index designs are usually specified by an index polynomial: however, the most widely used index representations do not correlate with the ion exchange fabrication process used to make GRIN glass. A design-for-manufacture process has been developed which uses ion exchange modeling integrated with optical design software to design manufacturable GRIN lenses. This paper introduces time varying boundary condition (TVBC) diffusion as a useful technique for improving the performance of manufacturable gradient lenses. The implementation of TVBC diffusion in OSLOTM lens design software as a user-defined gradient is detailed and some unique aspects of manufacturable index profiles are pointed out in conjunction with design examples. Both axial and radial gradient designs show significant improvement with an increase in the number of TVBC diffusion steps. Finally, an experimental index profile is shown to reasonably match the TVBC diffusion calculated profile.