Observing the Birth and Splitting of Optical Vortices Through Phase-Stepping Interferometry

ORAL

Abstract

``Twisted" light beams contain photons with Orbital Angular Momentum (OAM), given as $\ell\hbar$ per photon by Allen et al. where $\ell$ is an integer, and are characterized by a helical wavefront. When all of the photons carry the same value of OAM, the beam will have an optical vortex in its center which has a topological charge equal to $\ell$. However, when a light beam carries a superposition of OAM values, there will generally be multiple optical vortices with varying topological charges. We use a near-field imaging system capable of imaging a light beam on the surface of a forked diffraction grating, which imparts OAM onto the first order diffracted beam, to observe the birth and movement of these optical vortices. Additionally, we use a phase-stepping interferometry technique to fully measure the phase of the light beam immediately after passing through the forked grating. In this technique, the transmitted beam through the grating is phase controlled by adjusting its path length through a piece of glass before interfering it with the first order diffracted beam. This is done for at least four different phase steps, and then we use the acquired images to calculate the phase of the light beam, allowing for a full characterization of the beam in the near-field.

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Authors

  • William G. Holtzmann

    Univ of Denver

  • Colin Roberts

    High Precision Devices, Boulder, CO, Raytheon, Tucson, AZ, Seagate Technology, Minneapolis, MN, Ball Aerospace (retired), Bloomfield, CO, New Mexico State University, Brigham Young University, Colorado State University, Heinrich-Heine-Universitat Dusseldorf, National Security Technologies, Universidad de Buenos Aires, Colorado State Univ, Colorado College, Utah State University, Advisor, Material Physics Group, Utah State University, Box Elder Innovations, LLC, JILA and Department of Physics, CU Boulder, JILA and Department of Mathematics, CU Boulder, Colorado State University, Fort Collins, Colorado 80523, USA, JILA, NIST and the University of Colorado, Boulder, NIST, University of Colorado / NIST, University of Colorado/JILA, Colorado Sch of Mines, Colorado School of Mines, Southwestern Indian Polytechnic Institute, UC-Berkeley, Colorado State University, Fort Collins, CO, Wroclaw University of Science and Technology, Wroclaw, Poland, JILA, University of Colorado and NIST, Harvard University and Harvard-MIT Center for Ultracold Atoms, Univ of Colorado - Boulder, USAFA, Univ of Denver, Boyce Research Initiatives and Educational Foundation, Brilliant Sky Observatory, San Diego Mesa College, Utah Valley University, University of Colorado Boulder, Brigham Young Univ - Provo, Oak Ridge National Laboratory, University of Sherbrooke, NIST Boulder, Universidad Complutense de Madrid, Electrical and Computer Engineering Department, Colorado State University, Fort Collins, Co 80525, Lawrence Livermore National Lab. (United States), Physics Department, Colorado State University, Fort Collins, Co 80525, JILA, Department of Physics, University of Colorado Boulder, Los Alamos National Laboratory, University of Alabama, University of Wyoming, University of Guelph, University of Guelph, Canadian Light source

  • Mark E. Siemens

    Univ of Denver