Study On Self-focusing And Propagation Characteristics Of Airy-like Pin Beam

Airy beam is one of the most investigated novel beams for the reason that it remains shape-preserving during propagation.Besides,when it comes to propagating in free space,Airy beam also presents some other characteristics such as self-accelerating,self-bending and self-healing,which make Airy beam a perfect candidate for laser processing and particle manipulation.Moreover,radially symmetric Airy beam,also known as abruptly autofocusing beam,bends toward the optical axis during propagation,which can be seen as selffocusing phenomenon,then the intensity of the focal spot suddenly surges with the maximum value becomes hundreds time of the initial position and a spot taken form of zero-order Bessel beam.In addition,abruptly auto-focusing beam is not able to preserve its shape even in free space,it would suddenly oscillate right after the foci and then morph into zero-order Bessel-like beam.Optical pin-like beam,a recently proposed Airy-like beam,whose trajectory takes the form of power-law,tends to focus on the axis and then remains shapeinvariant.In this thesis,the theoretical mode and propagation characteristics analysis of Airy-like pin beam are studied based on the principle of Airy beam.The main studied contents and results of this thesis are as follows:1.The approximate analytical expression of the Airy-like pin beam light field in the free space is derived based on the stationary-phase method and argument asymptotic equation,and the calculation method of the light field propagation is given.The propagation characteristics of Airy-like pin beam firstly take the form of abruptly auto-focusing beams until each filament meets on the axis,suddenly the beam morphs into zero-order Bessel beam while its amplitude profile is irrelevant to the propagation distance z.2.The numerical solution of the beam propagation mode of Airy-like pin beam is carried out with using the split-step Fourier iterative algorithm.The simulation results show that by changing the decay factor and the initial radius,the properties of the beam could be strongly affected.3.Based on the first-and second-order stationary of the phase,the equations for the optical beam and caustics can be derived.By inversely solving the equations of stationary method,the trajectory of the Airy-like pin beam could be pre-designed by calculating the phase function on the initial plane.Eventually,the phase holograms are generated by solving the phase function.4.Experiments to verify the theoretical and the simulation results that proposed by encoding the phase hologram into spatial light modulator is conducted.Firstly,by analysing the experimental results of the self-focusing case,it turns out that decay factor induces dramatic effects on the focal intensity contrast and the initial radius size exerts strong influence to the focal length.And then the experiments of long-range propagation charateristic show that Airy-like pin beam presents steady intensity profile and preserving shape during propagation with a rather small initial radius value and a small decay factor.It turns out that the simulation results and the experiment results come in good agreement.In this thesis,the self-focusing and propagation characteristics of Airy-like pin beam are studied in free space,which provides a certain theoretical and experimental guidance for the applications of Airy-like pin beam that achieve both great propagation quality and highpower output.The Airy-like pin beam has potentials applications in the fields of high-power laser propagation in atmosphere and laser-based communication.