Two-photon laser oscillation by using trapped atoms

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We constructed an extended-cavity diode laser system and a vacuum chamber for the magneto-optical trap (MOT) of rubidium (Rb) atoms. The laser frequency was stabilized and locked to a hyperfine transition of rubidium atom under the computer control.We performed linear and non-linear spectroscopies of Rb atoms in a vapor cell and observed optical transitions between hyperfine sublevels of ^<85>Rb and ^<87>Rb. Spectral resolution was about 6 MHz and was determined by the natural linewidth of the transitions.About 10^8 Rb atoms were trapped in - 1mm^3 by the MOT.The atomic density was almost 100 times as large as that of the atomic beam of Ba which was first used for the two-photon laser oscillation by Mossberg in 1992. We also performed a non-linear spectroscopy with the trapped Rb atoms and many kinds of spectra were observed when we changed the configuration of laser polarizations and strehgth of the external magnetic field. These spectra were well explained by the dressed-atom picture.Ultracold Rb atoms (- 10muK) were obtained when we applyed a polarization gradient cooling to pre-cooled atoms in the MOT.By using a dark MOT,we further increased the atomic density by 50 % form the density obtained by the normal MOT.We developed a novel all-optical trap for neutral atoms by using a doughnut beam. The trap opens the way to a simple technique for atom manipulation, including Bose-Einstein condensation of gaseous atoms.