Non-diffraction Speckles Generated By Azimuthal Angle Random Phase Modulation

Non-diffracting beams,with some peculiar properties such as non-diffraction and self-reconstruction,whose intensity profile is invariant on propagation,has been researched extensively since it was come up with.In progress,Bessel beam is the classical one of non-diffracting beams.Based on Bessel beam,non-diffracting speckle has been obtained,not only possessing the characters of non-diffracting beams,but also having the characters of the speckles,which owns great application prospect in speckle imaging and ghost imaging with the large depth of field and the character of anti-interference.Afterwards,many ways to generate non-diffracting speckles are studied and applied.It is essential that we usually produce the region,where all plane waves build up a structure like a conic,modulated by arbitrary functions.Consequently,different ways have various merit and demerit in efficiency of intensity utilization,configuration for generating non-diffracting speckles and so on.In this paper,summarizing the study and application presently of the non-diffractive optics,especially for the Bessel beams and non-diffracting speckles,we put forward a method to generate non-diffracting speckles by random phase modulation based on azimuth angle,and make an in-depth discussion theoretically and experimentally.The main achievements are listed as follows.1_Putting forward a method to generate non-diffracting speckles by random phase modulation based on azimuth angle and axicon,and studying the principles of this method and the character of the fields generated by this method.This method roots in axicon method for generating Bessel beam,and we superpose a random phase modulation based on azimuth angle to the axicon to create a new phase mask to modulate plane wave,then non-diffracting speckles can be generated with only-phase spatial light modulator.It is proved that the mutual intension function consists of Bessel function distribution partly,in other words,the non-diffraction character inheriting from the Bessel beam generated by axicon.2.Designing the experimental facility with phase only spatial light modulator,and using a CCD to detect the speckle field,and researching the nature of the non-diffracting speckles field.Compared this method with traditional way,it is obvious that this method is good at the high intensity utilization,meanwhile,the simple device structure and the contollable parameter of the field make the non-diffracting speckles come true easily and practically.3.Making full use of the properties of non-diffracting speckles,especially non-diffraction character,to realize ghost imaging.Its intensity profile is invariant on propagation in the non-diffractive region.And then the object is illuminated by non-diffracting speckles.It is shown that the results of ghost imaging can illustrate a large depth of field.Some relationships between the results and the parameter have been researched slightly.Phase only spatial light modulator is the kernel device in this paper.It is useful in information optics and optical imaging.However,the speckle size and degree of randomness of the field will be influenced by the parameters of this device.So,we should do much of research in the influence generated by this device,when we use this device to generate the non-diffracting speckles field and realize ghost imaging.