Generation And Propagation Properties Of Anomalous Hollow Beam With Orbital Angular Momentum

As a major invention in the 20th century,laser plays an important role in many fields.With the development of laser technology and the diversification of its application,light-field manipulation has become an important branch.As a typical example,hollow beam,with zero intensity in the center,has a huge application prospect in trapping,medicine,free space optical communication and so on.There are many types of hollow beams,while one of them is very different from others which is named as anomalous hollow beam.The main difference between conventional dark hollow beam and anomalous hollow beam is that there is a solid core at the beam center of anomalous hollow beam.It is discovered by Wu.et al in 2005,and can be used for studying the transverse instability and provide a powerful tool for studying the linear and nonlinear particle dynamics in the storage ring.Based on the theoretical model proposed by Cai in 2007,we derived analytical formulae of anomalous hollow beams passing through the turbulent biological tissues.With the help of these formulae,we investigate the propagation properties of anomalous hollow beams in turbulent biological tissues,the irradiance and spreading properties of anomalous hollow beams in turbulent biological tissues are studied numerically.It is found that the circular and elliptical anomalous hollow beams eventually become Gaussian beams in the far field and the central irradiance of the anomalous hollow beam rises more rapidly as the value ofC_n² grows.We also calculate the formulae of the effective beam size of anomalous hollow beam and find that finallyW_xz becomes equal toW_yz in turbulent biological tissues which can be used to explain the beam spot eventually becomes circular under the influence of turbulence of biological tissues.Although there has been done a lot of research about anomalous hollow beams,only a few experimental results are reported to our knowledge.In this paper,we design the experimental setup for generating the anomalous hollow beam with orbital angular momentum,measure its focal intensity and obtain the FT pattern of this focal intensity.We show both by experiment and simulation calculations that the number of dark rings in the FT is equal to the topological charge.Our experimental results agree well with the theoretical predictions.