Generationandpropagationoftwistedpartiallycoherentbeams

Twist phase is a fully new form of phase which can only exist in partially coherent beams.The introduction of twist phase pioneers a new research direction for the phase-based regulation of partially coherent beams.Under the action of twist phase,partially coherent beams can display novel optical properties which have some potential applications in many fields,such as beam shaping,particle capture,optical imaging,free-space communication,and so on.In this thesis,we present an overview on the development history and the fundamental theory of the twisted partially coherent beams,then focus on its theoretical models,experimental generations and propagation characteristics by taking twisted Gaussian Schell-model beam and twisted elliptical multi-Gaussian Schell-model beam as examples.Firstly,a theoretical and experimental generation method of twisted Gaussian Schell-model beam is proposed,which fills the gap of experimental generation of this beam for many years.With the help of Wigner distribution functions,we use a three-cylindrical-lens system to transform an anisotropic Gaussian Schell-model beam to a twisted Gaussian Schell-model beam.An experimental setup was established for generating the anisotropic Gaussian Schell-model beam with precisely controlled beam widths and coherence widths along two orthogonal directions,and then,using the three-cylindrical-lens optical system,the genuine twisted Gaussian Schell-model beam was generated and demonstrated in experiment.Secondly,we introduce a new kind of partially coherent sources whose cross spectral density function is described as the incoherent superposition of elliptical twisted Gaussian Schell-model sources with different beam widths and transverse coherence widths,named as twisted elliptical multi-Gaussian Schell-model beam.Analytical expression for the cross spectral density function propagating through a paraxial ABCD optical system is derived with the help of generalized Collins formula.Our results show that the twisted elliptical multi-Gaussian Schell-model beam is capable of generating flat-topped elliptical beam profile in the far field,and the beam spot during propagation exhibits the clockwise or anti-clockwise rotation with respect to its propagation axis,and the rotation direction is determined by the sign of the twist factor.In addition,the analytical expressions for the orbital angular momentum and the propagation factor are also derived by means of Wigner distribution function.The influences of the twisted factor and the beam index on the orbital angular momentum and the propagation factor are studied and discussed in detail.Finally,we summarize this thesis and propose the further research work.