Spectroscopy Using Sum- and Difference-Frequency Generation in Molecular Solids

Both sum- and difference-frequency generation in organic materials are demonstrated and explored under conditions where all three waves (${\omega }_1$ and ${\omega }_2$ ingoing and ${\omega }_1\pm {\omega }_2$ outgoing) are resonant with molecular transitions. The experiments are carried out in centrosymmetric media in which a small electric field is used to distinguish the polar sublattices. Unique electric field dependences of the parametric signals were discovered. The spectroscopic line narrowing and dephasing-induced coherent-emission resonances of these ${\chi }^{\mathrm{}\left(2\right)\mathrm{}}$ processes make them useful new spectroscopic methods.