4a-E-2 Light Modulation in Optical Pumping Experiment

滋 安東, 清人 大川, 高啓 久保

H. Gilles, Bernard Cheron, J. Hamel

Harald Klepel, Dieter Suter

Krystyna Kolwas, M. Kolwas

George William Series

The absorption of light by optically pumped atoms undergoing magnetic resonance is calculated from expressions based on a simplification of Barrat and Cohen-Tannoudji's theory of optical pumping. The density matrix for the system is first derived in orders of approximation which correspond to successive cycles of pumping. The off-diagonal elements of the matrix, and consequently the absorption of light, are modulated. The amplitudes of modulation are resonance functions which are, in general, more complicated than solutions of the Bloch equations. The selection rules for electric dipole radiation limit the possible frequencies of modulation to ω0 and 2ω0 for primary interactions (ω0 is the applied frequency), but modulation at higher frequencies can arise through the circulation of coherence in optical pumping cycles. The functions which represent the amplitude of modulation at 4ω0 are derived in first and second order, for comparison with experiment.

Robert B. Partridge, George William Series

Optical pumping experiments have been performed on helium 4 atoms in the metastable level 2 3 S 1 with the object of studying the modulation of light in absorption in the longitudinal and transverse beams. Magnetic resonance curves were obtained similar to those found in emission in double-resonance experiments. With a particular geometrical arrangement employing circular polarizers, the Bloch magnetic resonance curves were obtained. Modulation at four times the applied frequency was obtained with a linear polarizer in the pumping beam. This modulation is ascribed to the circulation of coherence in the optical pumping cycle. From the behaviour of the resonance signals as a function of the frequency and amplitude of the stimulating field, it is inferred that a substantial part of the signal arises from coherence which has survived two complete cycles. The observations are satisfactorily explained by the theory developed in the previous paper.