Old Research theme

Laser cooling

Recently laser cooling and trapping have been the most active fields in physics. Atoms have been cooled below a few hundreds nK, and Bose-Einstein condensation has been realized by several groups. Three physicists won the 1997 Nobel Prize for their pioneering works of the fields, and the other three physicist won the 2001 Nobel Prize.

We have demonstrated a novel optical trap of cooled atoms using the Laguerre-Gauss optical beam in a joint research with Kuga group of University of Tokyo. Figures show an optical potential and its cross section provided by an LG03-mode optical beam. The horizontal axes represent the distance from the optical axis, and the vertical axis shows the potential height. Because the atoms are trapped in the dark core of the beam without any external fields, the trap provides ideal circumstances for precise measurements and other applications. 　

We have built a laser cooling apparatus in our lab, and finally trapped Rb atoms in a magnetopical trap at 3 PM on December 10, 1998.

At present, we have started laser cooling of metastable helium atoms in corporation with Shirahama group. Metastable helium atoms generated in discharge of helium gas in room temperature have large initial velocity more than 1000 m/s. Therefore, they travel a long distance before they are deccelerated by laser cooling and captured in MOT. As a result, the apparatus is huge, and efficiency for collecting atoms is low.

We have develop a novel appartus in which metastable atoms are provided by discharge of very cold helium gas just above the liquid helium surgface. The initial velocity is much smaller than that in the conventional apparatus, hence the size is very small as shown in the following pictures.

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. Y. Shimizu and H. Sasada, "Mechanical force in laser cooling and trapping," American Journal of Physics, 66(11), 960-966 (1998).
  4. M. Haraguchi, Y. Shibayama, K. Kikuchi, M. Okamoto, H. Sasada, and K. Shiraham, "Production of cold metastable helium atoms in a cryostat" Physica B, 329-333, 34-35 (2003).