Research theme

Light possessing orbital angular momenta

Light beams traveling through free space are well described by a paraxial wave equation. Hermite-Gaussian (HG) and Laguerre-Gaussian (LG) beams are solutions of the equation for cartesian and cylindrical coordinates, respectively. Recently the latter have attracted considerable attentions because they possess orbital angular momenta.

1) We have generated a tunable LG beam with large power from a titanium:sapphire laser, and applied it to a control of atomic motions and an optical interference experiment. First, the laser is forced to operate in a high order HG mode by a thin wire in the laser cavity. The HG beam is converted into the LG beam by a mode converter consisting of a pair of cylindrical lenses. Figure shows the output beam patterns of the mode converter for the various angles between the axis of the HG beam and cylindrical lenses. At 45 degree the HG beam is converted to the LG beam. 　

2) We have developed a transverse-mode beam splitter of a light beam.

It is applicable to quantum cryptography.

3) We are going to demonstrate quantum cryptographic communication. A light source is a He-Ne laser, and a spatial phase modulator is used for generating various transverse-mode beams.

HG01 beam LG01 beam LG02 beam

hologram for LG01 interference between LG01 and Gauss

List of Publications

  1. T. Kuga, Y. Torii, N. Shiokawa, T. Hirano, Y. Shimizu, and H. Sasada, "Novel optical trap of atoms with a doughnut beam," Physical Review Letters, 78(25), 4713-4716 (1997).
  2. Y. Torii, N. Shiokawa, T. Hirano, T. Kuga, Y. Shimizu, and H. Sasada, "Pulsed polarization gradient cooling in an optical dipole trap with a Laguerre-Gaussian laser beam," The European Physical Journal, D 1, 239-242 (1998).
  3. H. Sasada and M. Okamoto, "Transverse-mode beam splitter of a light beam and its application to quantum cryptography," Physical Review A 68, 012323 (2003).
  4. H. Okuda and H. Sasada, "Huge transverse deformation in nonspecular reflection of a light beam possessing orbital angular momentum near critical incidence" Optics Express, 14(18), 8393-8402 (2006).
  5. H. Okuda and H. Sasada, "Significant deformations and propagation variations of Laguerre-Gaussian beams reflected and transmitted at a dielectric interface" Journal of the Optical Society of America, A25, 881-890 (2008).
  6. M. Sato and H. Sasada, "Measurements of transverse lateral and longitudinal angular shifts of high-azimuthal-mode Laguerre?Gaussian beams reflected at a dielectric interface near critical incidence" Journal of Optics, 15, 014018 (2013).