With two sets of experimental instruments, laser transmission was investigated through horizontal atmosphere at 1.06 m under fine and haze-fog events. One set of the instruments is an indirect transmission meter used to measure visibility and the other one is a direct transmission meter used to measure the attenuation of laser power. Results show that the variation of transmittance got from laser power (Tp) and that obtained by visibility (Tvis) are highly correlated. For relative humidity (RH) below 85%, the curve of Tvis fits that of Tp very well. While the RH is above 85%, the Tvis is more likely smaller than Tp under fine meteorological condition, but under haze-fog condition Tvis is larger than Tp on the contrary. For different weather condition, the relation efficient between extinction coefficient and visibility is different. Even for similar visibility, the extinction coefficient of haze-fog event is larger than that of fine event.
Proc. SPIE. 9142, Selected Papers from Conferences of the Photoelectronic Technology Committee of the Chinese Society of Astronautics: Optical Imaging, Remote Sensing, and Laser-Matter Interaction 2013
For a beam from ground to space, the main optical turbulence effects are scintillation and beam wander. Multiple incoherent beams can reduce the scintillation. The scintillation is determined by the number of the beams, the beam separation and the size of the beam wander variance. A wave optics simulation was applied to study the scintillation index of 1-, 3, 6 collimated uplink Gaussian beams, where a hexagonal close-pack spacing is used. Based on the results of simulations, we propose an approximation to average spatial correlation in terms of the beam separation in the tracked and untracked cases. The relation between scintillation index and beam separation is different in the weak and moderately-strong fluctuation regimes when the number of beams is the same. And the average spatial correlation is determined by the beam waist radius, beam separation and beam wander variance.
Numerical experiments are carried out about the temporal and spatial variation of branch points by four-dimension code of laser propagating in atmosphere. The theory of branch-point detection and phase reconstruction is introduced. The act of branch points' creating and annihilating is emulated when the light wave propagating in atmosphere. The evolvement of branch points in some propagating range with time is emulated, too. The behavior of branch points in the distorted optical field is simulated when the main laser and beacon laser propagate in the atmosphere with opposite direction at the same time. The work could provide a reference for further study of laser propagation through atmosphere and adaptive optics system.