Light polarized directly generated

Like solid ferroelectrics, the ferroelectric liquid crystals, particularly the FLCPs, show a pyroelectric effect and a piezoelectric effect and are capable of switching polarization direction (dielectric hysteresis). Moreover, they can switch propagating or reflected polarized light. Finally, the polar symmetry of the phase leads to nonlinear optical properties of the FLCPs such as second-harmonic generation, the Pockels effect, and the Kerr effect. These physical properties of the ferroelectric LC polymers are discussed in the following sections. 

The light generated by common sources (sun, lamps) is composed of an ensemble of waves whose polarization planes are randomly oriented around the travelling direction. A radiation of this type is said to be unpolarized. Conversely, if all the waves that constitute the radiation possess the same polarization plane, the wave is linearly polarized (Fig. 6.1). The oscillation direction of the electric field is called polarization direction—or simply polarization—of the wave. 

In SFG spectroscopy, a visible, linearly polarized laser beam (with a fixed frequency yis and polarization direction j) and a linearly polarized IR laser beam (direction k and variable frequency are focused at the interface. An output beam with the sum frequency vis + ir nd polarization direction i is generated from the interface but not from the bulk, because of symmetry-based selection rules.The output light intensity is proportional to the square of the medium second-order nonlinear susceptibility Xijk - a good approximation,... 

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