Study On Propagation Characteristics Of RAiGV Beams Modulated By Cotangent And Cosine Functions

Optical tweezers technology has great application prospects in emerging fields such as biological genetic engineering,super-resolution imaging,and material molecules,due to its non-contact,high-precision,and non-destructive manipulation characteristics.The traditional optical tweezers technology based on Gaussian Beam can only transport a single particle in a straight line due to its small and narrow control range.Ring Airy Gaussian Vortex Beams(RAiGV Beams)is a new type of beam.The characteristics of non-diffraction,self-bending,self-healing,self-focusing and vortex can realize efficient optical micro-manipulation of multiple particle capture,rotation and curved transportation.At the same time,the change of the amplitude and frequency of RAiGV beams or the mathematical function modulation of its polarization and phase provide more possibilities for particle manipulation diversity.In this thesis,a dual-modulation function based on vortex phase is designed for the RAiGV beams,and the simulation and experimental verification of the propagation,self-focusing and self-healing characteristics of the modulated beam are carried out.The main research contents and results are as follows:1.The propagation characteristics of the RAiGV beams modulated by the cotangent functions in free space are studied by the step Fourier method.The results show that the modulated beams have self-bending and self-focusing effects,and the annular initial beam field will be split into multiple beam lobes consisting of a main lobe and several side lobes during propagation,and the number,rotation angle and rotation direction of the optical lobes depend on the modulation parameters n and φ1.In addition,the peak beam intensity ratio and its trajectory in the process of beam propagation are studied,and the modulation effects of topological charge,wavelength and main modulation parameters on the trajectory are analyzed,and it is found that the trajectory of the peak beam intensity point is a spiral curve that shrinks toward the center.2.A dual-modulation RAiGV beam is proposed with a cotangent function as the main modulation function(the main modulation parameter n controls the beam splitting,φ1 controls the beam rotation),and the cosine function is the sub-modulation function(m andφ2 are the secondary modulation parameters).The propagation characteristics of the beam under the dual-modulation of cotangent+cosine function are also studied.The results show that:when φ1 changes by Δφ1,the beam will rotate by an angle of Δφ1/n,while the change of φ2 does not affect the rotation of the beam;when the main modulation parameter n is greater than or equal to 1/2 of the secondary modulation parameter m,the secondary modulation parameter will not affect the main modulation type.The propagation characteristics of the beam have a significant impact,and only the peak beam intensity of the beam lobes under the main modulation and the symmetry of the propagation trajectory are fine-tuned;when the main modulation parameter n is less than 1/2 of the secondary modulation parameter m,the beam propagation process will produce(m-2|n|)additional lobes with different beam intensity distributions,and the propagation trajectory has a large deviation.3.The self-healing properties of dual-modulated beams were studied by adding shading to the beam.Five different types of occlusion are given at a certain distance of beam propagation,and the beam field and phase distribution of the corresponding occlusion beam increase with the propagation distance are obtained,and the peak beam intensity and propagation trajectory are combined with the comparative analysis of the unobstructed situation.The results are as follows:when one of the lobes(one main lobe and its side lobes)is completely blocked or when blocking all the side lobes of the beam,the beam does not have the self-healing ability;when all the main lobes of the beam are blocked,blocking the innermost ring of the beam,or blocking all the outer rings of the beam,the beam has the self-healing ability.The above results show the self-healing properties of the dual-modulated beam similar to the RAiGV beam.4.The experimental device for studying the dual-modulated RAiGV beams propagation characteristics is based on the spatial light modulator.The beam is modulated by the calculated phase hologram,and the self-focusing,splitting,and rotation of the beams are carried out.The results of the experiment and the simulation results are in good agreement.The results show that:the number of main lobes of the dual-modulated RAiGV beams and the beam intensity distribution are related to n and m,and the number of beam lobes is Max{2|n|,m}.In this thesis,the propagation characteristics of self-focusing and self-healing of cotangent and cosine functions modulated RAiGV beams are studied,which has high flexibility and operability and can be used in the field of holographic optical tweezers.