Control Of Airy Beams And Abruptly Autofocusing Beams In The Direct-space

Since Airy beams have been realized,they have attracted intense attentions due to their exotic behaviors,that not only are they diffraction-free and self-healing as other nondiffracting beams,but more interestingly they self-accelerate or known as self-bend transversely without interaction,and they have associated with a number of applications including particle manipulation,super-resolution imaging,laser filamentation,laser micromaching and plasmon generation.Besides,abruptly autofocusing(AAF)beams,relied on radially symmetric interference of Airy beams,can remain the intensity almost constant along the curve trajectory up until the focal point where beam suddenly focuses its energy right and the intensity abruptly increases.Due to this novel autofocusing characteristic,AAF beams can be utilized in many fields such as laser ablation,multiphoton polymerization,generation of light bullet and microparticles manipulation.However,most generation methods of Airy beam or AAF beam are in the Fourier space,which will introduce an additional Fourier lens.This thesis mainly focuses on the realization and the manipulation of Airy beams and AAF beams in the direct space.The main contents of this dissertation are list as follows:First,we discuss the phenomena of Airy apodization,and design an Airy beam along parabolic trajectory for apodization.In addition,we get the critical radial wavevector and critical radial slope by the contrast of experiment results and simulation data using apodized Airy beam.On this basis we display six non-apodized Airy beams with different trajectories both in experiment and simulation.Then,we propose a technique to scale the AAF beams in the direct space by introducing a scaling factor in the phase.Analytical formulas are deduced based on optical caustics,explicitly revealing how the scaling factor can affect the peak intensity and the size of the focal spot.Meanwhile we demonstrate that the multiplication of a scaling factor in the phase is equivalent to the axial-scaling transformation under the paraxial approximation.Further numerical and experimental results confirm the fidelity of our theoretical predictions.In addition,the peak intensity level of the focal spots can be maintained by amplitude shaping with a phase-only hologram.