Femtosecond laser propagation through aerosol clouds for improved communications and remote sensing applications

Optical communications and remote sensing applications have been limited by ability of the laser beam to penetrate aerosol clouds. Ultra short femtosecond laser pulses are now available for these applications. The fundamental question that must be answered is whether there is increased transmission through aerosols when a very short pulse is used. The basic idea is that there should be increased transmission because the electrons in matter can not respond to an instantaneous applied electromagnetic field and because the physical "bullet" of light is so short that the usual constructive and destructive interference will not add coherently. In this paper, results of research carried out with 9 fs pulses propagating through aerosol clouds of 1-4 mum in size are reported. The interaction of ultra short pulses with matter is starting to approach the time domain where the electrons in matter do not have time to interact with an instantaneously applied electromagnetic field. Experiments were carried out for transmission, through aerosol clouds contained in a tube, for 9 fs pulses and compared with those of continuous wave case. Results indicated that there was about a 0.5 % increase in the transmission. The magnitude of the increase was to be expected given that the phenomenon is just starting to turn on. Theoretical calculations indicate that for a free electron the time for the electron to follow an applied field is about 2.5-3 fs. In order to better understand the phenomena, additional experiments were conducted on fused silica glass, and on water contained in a cell