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This paper proposes a modification of the Hufnagel-Andrews-Phillips (HAP) Refractive Index Structure Parameter model that will better characterize the HAP profile against experimental data using the turbulent intensity, which is the ratio of wind speed variance to the average wind speed-squared, and Korean Refractive Index Parameter yearly statistics, Comparisons between this modified HAP model, the Critical Laser Enhancing Atmospheric Research 1 (CLEAR 1) profile model and several of the data sets are made. These comparisons highlight that this new model offers a more consistent representation of the averaged experimental data profiles than the CLEAR 1 model did. In addition, comparisons between this model and various experimental data set reported in the literature will show good agreement between the model and averaged data, and reasonable agreement with non-averaged data sets. This improved model should prove useful in system link budget estimates and atmospheric research.

Atmospheric propagation experiments have been conducted over the 1km TISTEF laser range to examine the effects of turbulence, absorption and scattering on a supercontinuum laser beam. This supercontinuum laser beam has been band limited to transmit only visible wavelengths (400-850 nm). In this work, the effects of atmospheric turbulence on the supercontinuum laser will be examined.

Over the years, there has been much interest in the use of optical wavelengths for communication because of the potential for high data rates. However, the performance of these systems can become significantly degraded due to turbulence-induced signal fluctuations. These fluctuations can be minimized by enlarging the receiving aperture, thereby averaging the fluctuations. There is extensive interest in developing probability density functions (PDFs) describing these intensity fluctuations so as to accurately predict system performance. This work examines several PDF models that have been suggested to represent fluctuations by comparing them to simulations of realistic propagation scenarios of a collimated Gaussian beam with centroid wander. Unlike with an infinite plane or spherical wave, the empirical PDF shape in these simulations changed significantly with increased aperture, going from a positively skewed to a negatively skewed distribution; therefore, the PDF model that describes it also must change. This change in skew can have serious consequences on the metrics of an optical communication system, e.g., number of fades and bit-error rate. In this work, we examine the evolution of the empirical PDF with aperture size and the fit of potential PDF models under various strengths of turbulence. We show that the change in skew with increasing aperture size occurred for all strengths of turbulence and that the currently used PDF models do not adequately characterize this for realistically sized apertures where beam wander is present.

Beam wander associated with a propagating beam in the atmosphere has impact on the short-term and long-term spot size, and the scintillation index. New theoretical models are presented here for beam wander and beam-wander-induced scintillation index. These models are then compared with computer simulation results.

Free-space optical communications (FSOC) is becoming an important option for both atmospheric and space-based high data rate networks. Long-range, mobile FSOC links in the former environments must mitigate the effects of turbulence if they are to provide reliable, high link availability under cloud-free atmospheric conditions. Adaptive optics (AO) has been proposed as one means of reducing link degradation in turbulence, but field validated AO performance models are few and not definitive. These models are important if credible FSOC high performance links are expected to be deployed using AO systems. This paper reviews the Strehl ratio for the Andrews AO model and provides comparisons between predicted AO-based FSOC link budgets and measured link performance derived from several field trials. These results suggest that AO systems perform well under weak turbulence or short range under 10 km, but only offer limited tip/tilt gain in moderate turbulence and no gain under high/saturation regime turbulence at longer ranges. Long range links close to the ground in high moderate turbulence may degrade AO performance further.

Probability Density Functions (PDFs) describing intensity fluctuations of a propagated beam are necessary to reliably predict operation of Free-Space-Optical (FSO) systems. This becomes especially important when considering the tails of the distribution. For example, accuracy in the low-intensity tail is necessary in the design of FSO communication systems as it determines the probability of fade. Accuracy in the high-intensity portion of the tail is necessary for eye safety calculations and to prevent equipment damage. In this work, we evaluate PDF models considering the statistics of the fit to empirical data for point and distributed apertures for several values of Rytov variance. Based on p-values and level of significance, we compare the quality of the fit of common PDF models to empirical data. As part of this, we evaluate the transition of the best fit PDF as the aperture area is increased. Both simulated and measured data will be included in this analysis.