Study Of Vectorial Diffraction Theory In High Intensity Focusing System

The shape and size of focal spot are determinant factors of imaging resolution or fabrication precision in optical system,which are bound up with lens numerical aperture(NA).NA is a dimensionless parameter to describe the light collecting angle range of lens,and lens achieve better spatial resolution and focus beam easier with higher NA value.Normally,people define high numerical aperture lens system whose NA are greater than 0.7 as high intensity focusing system.At present,there are two common theories based on wave optics utilizes to solve problems relating optical hyperfine lithography and super-resolution imaging diffraction,which are scalar diffraction theory and vector diffraction theory.The former applies to focusing issues ignoring the polarization of incident beam when NA<0.7,while the latter is considering the influence of the component of the electric field component in the spatial direction on the sub-micron focusing spot,so it appropriate for vector incident beam when NA>0.7.The shape and size of focus spot are affected by the vector characteristics,polarization,amplitude and phase of incident beam to a great extent,aside from the influence of aberration and depolarization in the high NA optical system.Therefore,vector diffraction theory that contains whole information of incident beam is prerequisite to study vector beam and focusing diffraction in high NA lens.In this thesis,vector beams with different polarizations(radially and azimuthal polarized beam)and amplitude distributions(Bessel-Gaussian and Laguerre-Gaussian beam)have been studied based on vector diffraction theory as well as focusing diffraction issues in high NA lens,and it has been found that the shape and size of focal spot are greatly affected by the polarization and amplitude distribution of vector beam through analog computation.Among them,the azimuthal polarized light and the first-order Laguerre-Gaussian radially polarized light can obtain the focal spots beyond the super-diffraction limit spot(200nm)in the high NA optical system,and the first-order Laguerre-Gaussian azimuthal polarized light can obtain the double annular spot under the high NA optical system.These consequences provide researchers with referential significance in light field modulation and special spots application.Moreover,the influence of the dielectric interface on the diffraction spot of the intense focusing system is studied,taking the Stimulated Emission Depletion Microscopy(STED)as an example.We studied how the aberration and refractivity difference between specimen and other medium affect the resolution of STED system in details.The simulation study found that the resolution of the STED system is very sensitive to the existence of aberrations.When there is coma and astigmatism and no aberration,the spatial resolution of the STED system is reduced by 1.87 and 1.95 times,respectively.Therefore,this research which are valuable to improve the resolution of STED system.