Propagation Characteristics Of Conical Circular Airy Beams And Their Applications

In recent years,the tight focusing of beams is one of the research hotspots in the field of optics.It has been found that cylindrical vector beams(CVBs)can obtain a focused light field with novel characteristics after focusing through a high numerical aperture(NA)lens.Since then,the research on the tight focusing of CVBs has attracted the attention of many scientific research teams.In particular,radially polarization beams(RPBs)can produce a longitudinal light field with narrow distribution along the optical axis after they are tightly focused.On this basis,by modulating the incident RPB,an optical needle with strong longitudinal light field component was generated.This phenomenon has broad application prospects in many fields such as particle acceleration and particle capture,high resolution optical imaging and super-resolution optical imaging,nano-lithography and optical data storage.At present,the research of optical needle mainly focuses on the selection and phase modulation of radially polarized CVBs.Most research teams use circular pupil or other binary optical devices with a high NA lens to tightly focus the incident beam and produce optical needles with ultra-long focal depth.In the selection of incident light field,there are many CVBs,such as Gaussian beam,Laguerre-Gaussian beam,BesselGaussian beam,etc.As far as we know,no one has ever produced an optical needle by changing the conical angle of a circular Airy beam(CAB).CABs can be regarded as one-dimensional Airy beams in radial distribution,and CABs have some novel propagation characteristics such as non-diffraction,self-healing and self-focusing.In recent years,it has been a hot research topic in the field of optics.Due to the transverse self-acceleration characteristic of Airy beam,CABs can self-bend in the propagation process.When propagating a certain distance,the beams meet on the optical axis and appear interference phenomenon,form a sharply enhanced focusing field,which is the unique self-focusing phenomenon of CABs.This propagation characteristic makes CABs have a good research prospect in the field of tight focusing beams.This thesis mainly studies the propagation characteristics of CABs and CCABs,and the adjustment effect of different parameters on CABs and CCABs.This thesis focuses on the novel phenomenon that the radially polarized CCAB can produce an ultra-long longitudinal light field,namely the optical needle,after self-focusing.The optical needle can be obtained without the use of circular pupil or other binary optical devices,and high NA lens.And the optical needle can be adjusted by changing the conical angle and the radius of the main ring of the CCAB.The results show that when the radius of the main ring is 30 times the wavelength and the conical angle is-65 degrees,the length of the optical needle generated by the radially polarized CCAB can reach 20 times the wavelength and the transverse half peak width can reach 0.38 times the wavelength,breaking the optical diffraction limit.In addition,we find that optical needles with transverse width breaking the diffraction limit can be generated at different primary ring radius when the conical angle is kept large.Meanwhile,the length of optical needles increases with the increase of main ring radius,while the transverse half-peak width almost remains unchanged,which provides a new idea for generating optical needles.