Xiaoxing Feng

Propagation of Gaussian–Schell beam in turbulent atmosphere of three-layer altitude model

We propose a method that is used to derive the moment radius of intensity distribution in a turbulent atmosphere. From this study, we have found that the second moment radius is affected only by the first-order expansion coefficient of the wave structure function. If our attention is directed to a higher moment radius, a higher order approximation of the expansion needs to be used. As an example, the propagation of a Gaussian-Schell beam in a slant path has been studied based on the turbulent atmosphere of a three-layer model. The variation of some beam properties, such as the relative waist width, angular spread, and kurtosis parameter with the initial waist width, wavelength, and zenith angle, has been analyzed and discussed in detail. The study shows that there is little difference between the three-layer model and the Kolmogorov model in studying uplink propagation, and the difference is large for downlink propagation. The intensity profile of the Gaussian beam in turbulence does not keep a Gaussian shape unless the beam spreading due to turbulence is very large or very small.

Effect of atmospheric turbulence on entangled orbital angular momentum three-qubit state

The entangled orbital angular momentum (OAM) three photons propagating in Kolmogorov weak turbulence are investigated. Here, the single phase screen model is used to study the entanglement evolution of OAM photons. The results indicate that the entangled OAM three-qubit state with higher OAM modes will be more robust against turbulence. Furthermore, it is found that the entangled OAM three-qubit state has a higher overall transmission for small OAM values.

Scintillation analysis for multiple uplink Gaussian beams in the presence of beam wander

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.

Experimental investigation of laser transmission at 1.06μm in horizontal atmosphere under fine and haze-fog conditions of summer

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.

Simulation experiment of high energy laser propagation in the atmosphere

Simulation experiment of adaptive optics compensation to thermal blooming phase distortion induced by high energy laser propagation in the atmosphere are carried out. The results of spot pattern and Strehl ratio in the focal plane are obtained when the adaptive optics system is in the open or closed loop shape. The effect of adaptive optics compensation is prominent when the Bradley-Hermann distortion number ND is less than 300, and Strehl ratio is more than 0.4 on the whole. Phase compensation instability appears when the distortion number ND becomes greater than 300, in this case, the compensated beam Strehl ratio goes down rapidly. The experimental Strehl ratio without adaptive optics compensation agrees well with that of the thin lens approximation theory, while the one with adaptive optics compensation has some deviation with that of the ray-optics approximation theory.