Engineering Of Focal Field With Space-Variant Polarization Through Reversing Radiation Of Electric-Magnetic Dipole Array

The vector beam with spatially variant polarization has attracted many researchers’ interestsfor its especial properties in focusing. It can provide broad applications in optical data storage,nano-fabrication, particle trapping, high-resolution microscopy and metrology. In this dissertation,we systemically investigate the focal field with spatially variant states of polarization. We alsogive the application of the focal field in trapping particles.Firstly, we propose a discrete complex pupil filter to create focused field in the highnumerical aperture system using cylindrical beams. The radius of this filter is normalized to1.And it consists of six discrete transmitted annular zones with different amplitude and shifted πphase retardation in neighboring zones except for the same retardation in the two outermost zones.The polarization pattern and intensity of the incident azimuthally polarized beam can be modifiedby that and then focused by the high NA lens. An ultra-long (>8λ) diffraction limitedthree-dimensional optical tube with azimuthal polarization spiraling around z-axis can be created.The center of optical tube is null along the axial direction. And the radius of the tube which isdetermined by the transverse full width at half maximum (FWHM) of this focused field is0.31λ inthe focal plane and remains nearly constant throughout the total depth of the tube. This complexpupil filter will meet applications in three dimensional tailoring of focused field and trapping andmanipulating of particles.Secondly, we propose a new method to control of radial polarized vector focusing fielddynamically in a high numerical-aperture imaging system. The intensity and polarization of thisfocused field both can be controlled. The position, amplitude, phase of electric dipoles can beadjusted. Thus the radiation pattern can be changed availably. Through reversing the radiated fieldfrom the electric dipole array situated near the focus of the high-NA lens, the local variation ofintensity and polarization of the focused field is achieved. The optical needle field can be easilychanged to multifocal field and the angle of polarization is rotated in pi/4. This engineered focalfield still maintains a diffraction limited transverse spot size (0.31λ). The multifocal field willmeet potential applications in trapping of multiple particles and optical microscope. Our methodpaved a new way for the regulation of focal field.