Transformation of statistical characteristics of picosecond laser pulses by multiple-scattering media

Higher-order (up to eighth) temporal moments to characterize non-Gaussian picosecond laser pulses were measured in a laboratory-simulation experiment for laser communication through multiple-scattering media. A technique employing deconvolution of higher-order moments (taking into account the impulse response of the detector and sampling system) is described to determine the true moments from the observed sampling scope traces of the pulse shapes. Measuring the broadening of the original pulses (of about 20-ps pulse width) generated with a single spatial mode GaAlAs laser diode by current modulation gain switching method, the temporal moments of order n = 2-8 were analyzed as a function of optical depth, tau of the multiple-scattering medium, consisting of latex, spheres suspended in water, (tau of between 5.5 and 10.31, inclusively) and receiver's field of views (FOV) ranging from 0.503 to 2.1 deg. Higher-order temporal moments curves are presented as a function of both optical depth and FOV showing the general trend of the moments initially to rise quickly and finally to attain saturation or limiting values. A simple empirical relationship of a polynomial function of the order of three is obtained to express the broadened pulse width (n = 2) in the range of optical depth and FOV considered here. The results described in this paper clearly indicate the significance of the contribution of the longer part of the non-Gaussian tails of the broadened pulses to practical design problems in all-weather atmospheric optical communications.