Partially Coherent Beams With Special Correlation Functions And Their Propagation Properties In Atmospheric Turbulence

The propagation and control of laser beams play an important role in laser applications.With the development of laser application,more and more studies have found that laser beams with lower coherence are more useful than general laser beams in free-space optical communications,remote sensing,laser radar and laser processing.Therefore,the study of partially coherent beams have been catched the most attention.Due to the constraint of nonnegative definiteness of the spatial correlation functions,most studies on partially coherent fields are based on conventional Gaussian correlated Schell-model beams in the early days,whose degrees of coherence have position-independent Gaussian profiles.However,the spatial correlation function of partially coherent beams is not only limited to the form of Gaussian distribution.Recently,various partially coherent beams with non-conventional correlation functions have been proposed based on the sufficient conditions for devising the special correlation functions.These beams can generate prescribed far-field intensity distributions without modulation by optical element,and have potential applications in optical communications,beam shaping,laser weapon and optical trapping.More and more attention is being paid to partially coherent beams with special correlation functions in atmospheric turbulence.In this dissertation,we focus on devising novel partially coherent beams with special correlation functions and studying the propagation properties of partially coherent beams with special correlation functions in non-Kolmogorov turbulence.The main works are listed as follows.We introduce a new theoretical model for partially coherent beams with special correlation functions,which is referred as non-uniformly Hermite-Gaussian(NUHG)correlated beams.Compared to the non-uniformly correlated(NUC)beam,the spectral degree of coherence of NUHG beams is modulated by Hermite function.By utilizing the extended Huygens-Fresnel principle,we study the propagation properties of NUHG beams in free space.Numerical results demonstrate that NUHG correlated beams exhibit selffocusing and laterally shifted intensity maxima.The focal area is sharper than NUC beams.In addition,the focal profile can be controlled by the order of Hermite function.The influence of turbulence on the beam quality are also analyzed.Our results will have potential application in beam shaping and optical trapping.The propagation properties of multi-sinc Schell-model(MSSM)beams in non-Kolmogorov turbulence have been studied.In free space,MSSM beams demonstrate flattopped far-fields,dark-hollow far-fields and multi-rings far-fields for suitable values of beam parameters.We derive several analytical expressions for the root-mean-square angular width and the propagation factor of MSSM beams propagating in non-Kolmogorov turbulence with the extended Huygens-Fresnel principle and the second-order moments of the Wigner distribution function.The beam quality of MSSM beams with different far-fields are analyzed comparatively.Results show that MSSM beams with dark-hollow far-fields is less affected by the turbulence than the cases of flat-topped far-fields and multi-rings far-fields.And such advantage will become more obvious with larger darkhollow size.Besides,MSSM beams are less affected by the turbulence than GSM beams.Our results may be used in optical communications.The propagation properties of Gaussian Schell-model array(GSMA)beams in free space and non-Kolmogorov turbulence have been studied.Array beams are usually used in high-power and high-intensity laser system.And most of array beams are constituted by correlated or uncorrelated superposition of off-axis beam.Although these beams demonstrate lattice patterns in the initial plane,it will be quickly destroyed along with the propagation.For the case of GSMA beams,the lattice patterns will be formed in the far field by the modulation of special correlation function.And it will keep invariant for further propagation.By employing the second-order moments of the Wigner distribution function,we derive the analytical expressions for propagation factor of GSMA beams.The effects of beam parameters and non-Kolmogorov turbulence on beam quality are analyzed in detail.Compared to the Gaussian Schell-model beam and array beams constituted by superposition of off-axis beam,GSMA beams have significant advantage in the robustness of the destructive effect of non-Kolmogorov turbulence,especially for the GSMA beam with more lattice elements and bigger relative separation distance of each lattice element.The propagation factor of electromagnetic concentric rings Schell-model(EM CRSM)beams in non-Kolmogorov turbulence have been studied.The intensity profile of this beam demonstrates adjustable multi-rings far-fields by the modulating of the special correlation function.By employing the second-order moments od Wigner distribution function,we derive the analytical expression for propagation factor of EM CRSM beams in non-Kolmogorov turbulence.Our results show that an EM CRSM beam has advantage over a scalar CRSM beam for reducing the turbulence-induced degradation under suitable conditions,especially in the strong turbulence.Compared to the electromagnetic Gaussian Schell-model(EGSM)beam and MSSM beams,the EM CRSM beam is less affected by the turbulence.