Study On Large-scale Sharply Bending Paraxial Beams And Its Application In Particle Manipulation

By employing proper phase modulation,light fields can propagate along a curved path in free space,thus realizing the so-called self-accelerating beam(or bending beam).The concept of “self-accelerating” was originally proposed in the quantum mechanics and was then introduced into the optics domain in 2007.Self-accelerating beams are widely used in particle manipulation,induced plasma channels and discharge control due to their unique properties of self-bending,self-healing and non-diffraction.The prosperity of the self-accelerating beams in optics stimulated the realization of their counterparts in other areas,such as bending matter wave,sound wave and water wave.Conventional self-accelerating beams represented by Airy beams are essentially a caustic surface formed by tangential geometrical rays,so their bending degree depends on the deflection angles of these rays.In this framework,these self-accelerating beams cannot bend at large angle under the paraxial condition.On the other hand,selfaccelerating beam under the non-paraxial condition cannot propagate over a long distance.In order to solve these problems,by altering the formation mechanism of Airy beam,we designed and demonstrated a new-type of light fields that can bend at a large angle even under the paraxial condition.We compared the new beam and the Airy beam in terms of caustic surface and distribution of optical rays,and we gave the physical picture on why the new beam is capable of turning at a sharp angle.We also found that,compared with the conventional self-accelerating beam,the new-designed beam has a better self-healing property.Our theoretical analysis and numerical simulation results have a good agreement with the experimental results.Additionally,this thesis work illustrates the design of a new kind of bending beams with different trajectories.Specifically,we realized large-angle bending beams with trajectories such as circle and ellipse both in simulation and experiment.Furthermore,we have used such self-bending beam to achieve preliminary results of its application in optical tweezer,and the beam successfully trapping and moving the particles along the pre-designed path.These studies will pave the way for our future research via such beams in optical tweezer.In summary,our research has conquered the problem that the conventional self-accelerating beams cannot bend at a large angle under the paraxial condition,and they may bring new prospects for accelerating beams in particle manipulation.