Contributions in nearly non-diffracting beams' propagation

Abstract

Due to their unique properties, non-diffracting beams, such as Bessel beams, are increasingly used in various biomedical, imaging, research, and industrial applications. In this thesis, I present designs for two types of optical systems that generate nearly non-diffracting beams. The first system produces a quasi-nondiffracting light sheet, while the second explores different methods for generating constant intensity, constant DOF, tunable range, Bessel beams. The motivations behind this work, potential applications of the developed systems, and a review of the relevant literature and background theory are discussed. The main proposed ideas to achieve these goals are also presented and analyzed. The research includes mathematical descriptions and numerical simulations of the developed systems. An experimental realization of the light sheet system is described, with the results presented and discussed. To generate the light sheet, we propose a setup comprising a laser, a telescope to expand and collimate the laser beam, a Powell lens to expand the beam in the spanwise direction, and a mask on a cylindrical lens. The mask, formed by a pair of double slits, works with the cylindrical lens to produce a thin, nearly non-diffracting light sheet. For generating constant intensity, constant DOF, tunable range, Bessel beams, we propose three optical systems. The first system consists of three refractive axicons: the first two axicons create a nearly constant-diameter annular beam, and the third, a logarithmic axicon, generates a nearly constant intensity segment of light. The tunability is achieved by adjusting the distance between the first two axicons. The second system employs a newly designed optical lens to transform an annular beam into a Bessel beam with a constant intensity, constant DOF, and tunable range. The third system involves placing a ring aperture in front of a logarithmic axicon. The tunability is achieved by varying the mean radius of the ring aperture.