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Abstract
A special phase matching for second harmonic (SH) generation was achieved in the helicoidal structure of a ferroelectric liquid crystal using normally incident two counter propagating waves, when the wavelength of the SH wave was near the selective reflection band edge. Theoretical prediction of the polarization dependence of the phase matched SH intensity was experimentally proved: (1) Two beams with the same circular polarization (e.g., R-R) give the most efficient enhancement. (2) When right- and left-circularly polarized light (R-L and L-R) beams are used, the SH light intensity is observed only in one side from which the circular polarization with the same handedness as that of the helicoid is incident, and is practically zero when observing in the opposite side. (3) The polarization of the enhanced SH wave is the same as the handedness of the helicoid of a ferroelectric liquid crystal regardless of the polarizations used for fundamental waves.