The propagation of high peak-power beams in the atmosphere has been observed in field trials with visible-near infrared (VNIR). Longer infrared (IR) wavelengths beams have some propagation characteristics not tested in the VNIR field experiments. We identify some unique characteristics of IR ultrashort- ulse air propagation: greater transmission, much lower dispersion-induced chirp, lower sensitivity to atmospheric turbulence, and much larger critical power. We summarize the results of self-focusing theory applied to IR ultrashort pulse characteristics, apply the theory to predict the IR self-focusing distance, and show the theory is in close agreement with detailed numerical simulations including extinction and turbulence.
Free-space optical communications systems provide the opportunity to take advantage of higher data transfer
rates and lower probability of intercept compared to radio-frequency communications. However, propagation
through atmospheric turbulence, such as for airborne laser communication over long paths, results in intensity
variations at the receiver and a corresponding degradation in bit error rate (BER) performance. Previous
literature has shown that two transmitters, when separated sufficiently, can effectively average out the intensity
varying effects of the atmospheric turbulence at the receiver. This research explores the impacts of adding more
transmitters and the marginal reduction in the probability of signal fades while minimizing the overall transmitter
footprint, an important design factor when considering an airborne communications system. Analytical results
for the cumulative distribution function are obtained for tilt-only results, while wave-optics simulations are used
to simulate the effects of scintillation. These models show that the probability of signal fade is reduced as the
number of transmitters is increased.
Before fine tracking algorithms can be evaluated for performance at the ABL-ACT facility at North Oscura Peak, the image needs to get onto the fine track sensor. This requires interaction between the gimbal controller, course tracker, and the fine tracker. In order to develop this hardware for North Oscura Peak, and to meet the proposed schedule, a local facility was required. NuSord was developed for this purpose. In addition to supporting the buildup, NuSord will assist in the integration of future hardware and software system that would eventually end up at NOP.
Tracking through a turbulent atmosphere involves many challenges. In the pursuit of better tracking techniques Gemini, a dual tracker was developed. Intended as a research too, Gemini can be used to characterize anisoplanatism, wind, and other atmospheric effects on a frame by frame basis. In addition, one tracker can be converted to a pupil plane or wavefront sensor.