SECOND HARMONIC LIGHT GENERATION IN CRYSTALS WITH NATURAL OPTICAL ACTIVITY.
HARVARD UNIV CAMBRIDGE MASS DIV OF ENGINEERING AND APPLIED PHYSICS
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Whenever a circularly polarized laser beam propagates along an axis of three-fold symmetry in a piezoelectric crystal, the second harmonic polarization is circularly polarized in the opposite sense. Rabin and Bey have discussed the theory of second harmonic generation in crystals with natural optical activity. We have observed this circular polarization and also the difference in coherence lengths for opposite senses of circular polarization, with both fundamental and second harmonic beams propagating along the 111 direction in single crystals of NaClO3 and NaBrO3, belonging to the cubic class 23, for which the proper eigenmodes are circularly polarized waves. The nonlinear susceptibility of both NaClO3 and NaBrO3 has been measured and compared with the nonlinear susceptibility of a-quartz. The relative sign of the susceptibilities has been determined in second harmonic interference experiments with the same laser beam traversing two crystals in succession. The interesting question of the sign of the nonlinear susceptibility, piezoelectric constant, optical activity, and the absolute atomic configuration of the antipodes is discussed. The question of conservation of angular momentum is resolved by taking into account the crystalline field potential of three-fold symmetry which gives rise to a torque on the crystal lattice. Author