The Application Of Optical Vortex In Imaging

Optical vortices have some special characters, such as spiral phase, zero intensity in their center, orbital angular momentum of each photon. Therefore, Optical vortices have been widely used in many fields. We focus on the application of the optical vortices in imaging.Firstly, Laguerre-Gauss vortex beam and Airy vortex beam are introduced in this paper. The diffraction characters of these two special kinds of the vortex beams are analyzed in the theory. They are combined with dark field microscopy and the corresponding dark field microscopy system is built. The polystyrene spheres with the size of 960nm are utilized as samples to carry out this experiment. We use Gauss beam, Laguerre-Gauss vortex beam, Airy beam and Airy vortex beam as the illumination lights of this microscopy system,respectively. Through analyzing the corresponding output images, it is shown that the imaging quality based on the dark field microscopy system under Airy vortex illumination.Secondly, the basic principle of the Hilbert transform and the spiral phase filter is analyzed. Airy spiral phase filter is designed. The transmittance function of this filter and the coherent spread function of the image system are derived. Through changing the radius of the main ring po and the scaled parameter wo in the transmittance functions, the distributions of the coherent spread function is controlled. It is found that the width of the main lobe which determines the resolution decreases with the increased ?0 and the amplitudes of the side lobes which connect with the contrast fluctuate with w0. Compared with Laguerre-Gauss spatial filter and Bessel-like spiral phase filter which have been existing, higher contrast and resolution can be achieved by using Airy spiral phase filter. At the same time, to implement edge enhancement with any intensity at any direction, the off-axis Airy spiral phase filter is proposed. By controlling the center position of this filter, anisotropic edge enhancement can be implemented. In the experiment, the amplitude-contrast and phase-contrast objects are used as samples to verify our theories.Finally, the principle of the spiral zone plate is studied. Fractional phase spiral zone plate and off-axis phase spiral zone plate are proposed. The transmission functions of these two kinds of the phase spiral zone plates are deduced and simulated.The light diffraction after passing through them is theoretically analyzed. For fractional phase spiral zone plate, by setting the fractional topological charge p and the orientation angle ? , the intensity and the direction of the anisotropic edge enhancement can be controlled. For the off-axis SZP, the intensity and the direction of anisotropic edge enhancement are controlled by the displacement distance ro and the azimuthal angle ?0, respectively. The experiments which respectively use phase object and living biological cells are carried out to demonstrate these two phase spiral zone plates in the system. Both of them show the similar abilities in the anisotropic edge enhancement under femtosecond laser illumination.