Optical second-harmonic generation as a probe of electric-field-induced perturbation of centrosymmetric media.

Polarization-selective optical second-harmonic generation (SHG) is applied to monitor nonuniform polarization distributions in centrosymmetric media modulated by an external dc electric field. Two different systems are investigated: first, optical SHG from a Au-Si(100) Schottky Barrier is shown to be a direct probe of the electric field polarity near such a metal-semiconductor interface. Second, a poled polymer exhibits a strong anisotropic SHG signal under normal incidence, indicating a nonuniform field enhancement at the edges of the poling electrode. The results demonstrate the sensitivity of SHG to small symmetry perturbations. Consequences for device applications are discussed.