Study On The Propagation Properties Of Near-Infrared Laser

The propagation of near-infrared beam in atmospheric turbulence has been expensively study for a long time, which has extensive applications in free space optical communications, satellite remote sensing, laser ranging and mapping. In the past decades, Kolmogorov model has been widely accepted and used. However, recent research has indicated great deviation from the Kolmogorov model in some portions of the atmosphere. Toselli et al. proposed a non-Kolmogorov spectrum, which has wide applicability. Much work has been carried out concerning the properties of various beams through Kolmogorov and non-Kolmogorov turbulence. In this paper, we investigated the propagation properties of special beam elegant Hermite-cosh-Gaussian beam through non-Kolmogorov turbulence, and we also studied the evaluation method of near-infrared laser illumination uniformity.(1) Based on the extended Huygens-Fresnel theory and the second moments of the Wigner distribution function, an analytical expression for the propagation factor of partially coherent elegant Hermite-cosh-Gaussian beam in non-Kolmogorov turbulence is derived. The results show that:the propagation factor (M2factor) is no longer propagation invariants in atmosphere; the turbulent atmosphere makes the propagation factor greater. Partially coherent EHChGB with higher beam order, longer wavelength, shorter coherent length, smaller beam width, greater Ω has smaller M2factor, which means the beam is less affected by the Non-Kolmogorov turbulence. The M2factor increases with increasing of outer scale Lo and decreasing of inner scale l0.(2) On the basis of second moments of the Wigner distribution function, the analytical expressions for the root mean square (rms) beam width and spreading angular of partially coherent EHChGB have been derived. We used the relative beam width and relative spreading angular to describe the effect of non-Kolmogorov turbulence on the beam spreading. The spreading of EHChGB has been investigated by numerical calculation, and the results show that:the EHChGB through non-Kolmogorov turbulence experiences greater spreading with stronger turbulence. Beam with higher beam order, longer wavelength, shorter coherent length, smaller beam width, greater Ω has smaller beam spreading. Under same turbulence condition, EHChGB is less affected by atmospheric turbulence than EHGB. (3) Based on the effective radius of curvature theory proposed by H.Weber, an analytical expression of partially coherent EHChGB is derived. The affection of atmospheric turbulence and beam parameters on the effective radius of curvature is studied quantitatively. The results show that the effective radiuses of curvature of EHChGB propagation in free space and turbulent atmosphere are significantly different.(4) The area surrounded by normalized PSD (power spectral density) is adopted to evaluate the near infrared laser illumination intensity uniformity. Using this method, the evaluation parameters of different near-infrared laser illuminator’s uniformity are studied. The results verify the reasonableness of the laser power spectrum as an evaluation parameter.