Atmospheric turbulence over long horizontal paths perturbs phase and can also cause severe intensity scintillation in the pupil of an optical communications receiver, which limits the data rate over which intensity-based modulation schemes can operate. The feasibility of using low-order adaptive optics by applying phase-only corrections over horizontal propagation paths is investigated. A Shack-Hartmann wave-front sensor was built and data were gathered on paths 1 m above ground and between a 1- and 2.5-km range. Both intensity fluctuations and optical path fluctuation statistics were gathered within a single frame, and the wave-front reconstructor was modified to allow for scintillated data. The temporal power spectral density for various Zernike polynomial modes was used to determine the effects of the expected corrections by adaptive optics. The slopes of the inertial subrange of turbulence were found to be less than predicted by Kolmogorov theory with an infinite outer scale, and the distribution of variance explained by increasing order was also found to be different. Statistical analysis of these data in the 1-km range indicates that at communications wavelengths of 1.3 mum, a significant improvement in transmitted beam quality could be expected most of the time, to a performance of 10% Strehl ratio or better.

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A small, low-cost sensor capable of autonomous detection of a wide variety of chemical agents in either vapor, particulate or liquid phase is urgently needed. It now appears that this need also extends to homeland defense and the vast network of civilian security forces including police, fire, public health and emergency medical personnel. We are developing a low-cost, compact infrared Chemical Threat Monitor (CTM) that could meet this need. This palm-sized handheld instrument combines Foster-Miller's unique optical "wedge" technology with novel, disposable infrared fiber optic sensors for sample collection. These technologies will be coupled to emerging high sensitivity, low-cost uncooled linear array infrared detectors optimized for this application. This combination will provide the individual user with most of the capability of today's expensive FTIR units in a miniature robust unit that has no moving parts. In this paper we will describe the CTM device, its operation, and present preliminary results on liquid chemical agent simulants.

Atmospheric turbulence over long horizontal paths perturbs phase and also can cause severe intensity scintillation in the pupil of an optical communications receiver. This limits the bit error rate over which intensity based modulation schemes can operate. To quantifi the extent ofthe problem, we built a high speed and high resolution wavefront sensor capable of measuring both the amplitude and phase over a horizontal turbulent path. We present resulting measurements of the probability distributions ofboth amplitude and phase as well as Zernike polynomial decomposition ofthe temporal power spectra of phase fluctuations. These results are compared to existing turbulence models, and are used to determine requirements for a wavefront correction scheme using adaptive optics. SPIE Vol. 3125. 0277-786X/971$lO.OO Downloaded From: http://proceedings.spiedigitallibrary.org/ on 05/27/2015 Terms of Use: http://spiedl.org/terms