Development of Spin Polazized Atomic Beam of Cesium by Means of the Laser Optical Pumping for Probing the Spin State at the Topmost Layr of Magnetic Surfaces

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For the purpose of probing the surface magnetism, we have developped the spin polarized atomic beam of Cesium by means of laser optical pumping. The spin polarized atomic beam is very attractive because of nearly perfect polarization, high sensitivity to the spin state of the topmost layr of the surface and plausibility of observing muptipole interactions with the surface state since the probe total spin of the probe is larger than one. In principle, the final state of the atom is expected to have the perfect spin polarization or special allignment by cyclic transition of the resonant absorption and the spontaneous emission of circularly polarized photons between the atomic ground state |6^2S_<1/2>, F=4> and the excited state |6^2P_<3/2>, F=5> (Zeeman pumping), following the cyclic transition between the ground state |6^2S_<1/2>, F=3> and the excited state |6^2P_<3/2>, F=4> (hyperfine pumping).By the support of this grant-in-aid, we have prepared the experimental apparatus with extreme … More ly high vacuum which is evacuated to 2X10^<-9> Pa by a set of the tandem turbo-molecular pump system. The well collimatied thermal-energy atomic beam of Cesium is produced into the vacuum by using a multi-channel array at the exit of the atomic source through a low-temperature collimator with an aparture of 1mm in diameter. The divergent angle of the beam was 0.6ﾟ and the number density of atoms was 10^6 Cs/cm^3 at 436 K, while they increased to 5ﾟ and 10^7 Cs/cm^3 respectively at 536 K.For the optical pumping, we need three sets of semiconducter laser systems whose frequency must be stabilized within several MHz at the resonace frequency of 3.5X10^8 MHz. In order to fullfill the requirement of the stabilization and spectral narrowing of laser oscillation, we established a new method of frequency-locking by the technique of frequency-selective optical feedbak to a Fabry-perot type semiconductive lasers. Finally, the single-path optical feedback system under an existence of an inversion mechanism of feedback laser was found to induce a spontaneous symmetry breaking in polarization of photons as a result of circular dichroism of atoms in a cell. The range of self-frequency-locking has attained up to 740 MHz when 2% of laser intensity was returned to the laser.In the case of the thermal-energy atomic beam of Cesium, occupation probability of the ground state F=4 was about 80% after hyperfine pumping by the laser of 3mW in intensity and 3mm in diameter. The polarization after Zeeman pumping is estimated by the following equation ; <m_F>/F=5/12・DELTAI^+-DELTAI^-/DELTAI^<(e)>. The polarization of about 60% was currently achieved.In order to optimize the energy of atomic beam to minimize the trapping of Cs atoms at the surfaces, the energy-tunable atomic source below 10 keV is under development. The present progress of the spin polarized atomic beam promoted by the grant-in-aid stimulates us to continue the the systematic study about the interaciotn of spin polarized atomic beam with the magnetic sruface from now on. Results of an application of this method to the surface magnetism will be reported in the near future. Less