Zero spatial chirp vortices from supercontinuum modulation

Includes bibliographical references (p. 34-35).Seeding a femtosecond pulse into a photonic crystal fiber generates an ultra broad spectrum of light. This supercontinuum light source transmitting through a fork grating will introduce spatial chirp to the optical vortices. An optical setup consisting of a modified 4f-correlator, and two gratings are used to eliminate the spatial dispersion. Here the dispersionless vortex is solved theoretically using the principles of Fraunhofer diffraction. The experimental results are closely examined and strongly agree with numerical simulations. In addition, a simple technique for determining the topological charge of supercontinuum optical vortices is presented. The vortex charge is determined by inspecting the diffraction pattern through a triangular aperture. It is shown that the topological charge is constant, and can be consistently measured, across a wide range of colors