Polarization dependent enhancement of second-harmonic generation by distributed feedback cavity action in a helicoidal ferroelectric liquid crystal cell

A special phase matching for second harmonic (SH) generation was achieved i n 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 experimental ly proved: (1) Two beams with the same circular polarization (e.g., R-R) gi ve the most efficient enhancement. (2) When right- and left-circularly pola rized light (R-L and L-R) beams are used, the SH light intensity is observe d only in one side from which the circular polarization with the same hande dness as that of the helicoid is incident, and is practically zero when obs erving in the opposite side. (3) The polarization of the enhanced SH wave i s the same as the handedness of the helicoid of a ferroelectric liquid crys tal regardless of the polarizations used for fundamental waves.