Far-infrared nonlinear optics. I.χ(2)near ionic resonance

Abstract

Frequency doubling is used to determine absolutely ${\chi }^{\mathrm{}\left(2\right)\mathrm{}}$(2ω,ω,ω) of GaAs and ${\mathrm{LiTaO}}_3$ at far-infrared frequencies, 20≤ω≤57 ${\mathrm{cm}}^{\mathrm{-}1}$. Resonant enhancement is observed in ${\mathrm{LiTaO}}_3$ as an ionic resonance is approached. The technique employed in this study is extendable to the 200-${\mathrm{cm}}^{\mathrm{-}1}$ range, where it appears feasible to experimentally distinguish between mixed electronic-ionic contributions such as the third-order lattice potential and second-order dipole moment.