Optical pumping of gaseous atoms in the ground states and in the excited states is reviewed. We present at first important phenomena observed in optical pumping experiments with a circularly or linearly polarized light, classifying the various perturbations on the Zeeman substates, such as perturbations of resonant or nonresonant light, static magnetic field, radio-frequency fields and atomic collisions. Recent studies on the applications to the frequency standard and to the measurements of extremely weak magnetic fields are also shown. We present finally on optical pumping with lasers, which has been extensively studied in recent years.
Oxide growth kinetics of SiO2 films grown on silicon in an O2/N2 mixture is empirically studied. It is found that a parabolic law is obtained at 10-2 atm of oxygen partial pressure PO., and an inverse-logarithmic law at 10-3 atm. The Mott-Cabrera oxidation rate equation is adapted to the thermal oxidation of silicon in the case of P02≥10-2 atm, and the Mott-Cabrera's rate constants are determined. Finally, a value of 1. 90 eV is derived as the activation energy of silicon atoms entering into the oxide.
Laser Doppler velocimetry is applied to the measurement of sedimentation velocity of solid particles and details of sedimentation phenomenon are investigated. Every crossing of a particle through the probe volume of the velocimeter generates a burst signal which contains the Doppler beat frequency corresponding to its velocity. A histogram of the sedimentation velocity is obtained by counting the number of burst signals after selecting the frequency. By the use of the formulae for terminal sedimentation velocity, conversion of the measured histogram into the distribution of particle diameter is attempted. One difficulty, namely, an interference effect among the particles, is found. Decrease of the particle number within a unit volume can suppress this interference effect, however, it is attended by a long measuring time for the ordinary differential heterodyne method. A new Doppler method is thus adopted in which two incident beams cross each other from opposite directions. The feasibility of the present method is verified by comparing the particle-diameter distribution obtained experi-mentally with those from microscope inspection.