Research On The Generation Of Twisted Partially Coherent Beams

The twist phase is one type of phase which can only exist in partially coherent beams.It can make the beam present a new statistical characteristic in the aspects of intensity,coherence,polarization and carrying orbital angular momentum.As a result,partially coherent beams with twist phase have wide applications in optical communication,beam shaping,particle capture and improving imaging quality.In this paper,we review the research history and basic theory of twisted partially coherent beams and point out the problems existing in the methods of experimental generation of twisted partially coherent beams.In order to overcome the shortcomings of the current methods for generating twisted partially coherent beams,such as the parameters of coherent width and the twist phase cannot be dynamically regulated or the real-time of beam synthesis is poor,we propose a new experimental method to generate twisted partially coherent beams by incoherent superposition of mutually orthogonal coherent modes.Firstly,the twisted Gaussian Schell-model beam has been represented as the incoherent superposition of eigen-modes.After the cutoff value of the normalized eigenvalues has been determined according to the accuracy of the mode superposition,the approximate expression composed of limited number of eigen-modes and corresponding eigenvalues has been decided to synthesize the beam with high precision.By analyzing and simulating the influence of the number of eigen-modes envolved in the superposition on the synthesis accuracy,the high precision theoretical results are obtained and relevant experiments are carried out.The spectral intensity,the degree of coherence and the rotation angle of the spot are measured and it is proved that this method can effectively and rapidly generate high precision dynamical adjustable twisted partially coherent light.Secondly,we carry out the experiment of pseudo-modes superposition to synthesize twisted Gaussian Schell-model beams.After the twisted Gaussian Schell-model beams has been expressed by the incoherent superposition of pseudo-modes,the number of modes involved in superposition is determined according to the correlation between the modes.The characteristics of both two methods of generation dynamic adjustable beams have been analyzed and compared.It can be found clearly that the former displays better real-time performance with high accuracy while the latter has a wider field of application.Finally,we summarize the paper and look forward to future research work.