Second-harmonic generation spectroscopy: A technique for selectively probing excitons - art. no. 085111

We show that second-harmonic generation (SHG) and sum-frequency generation (SFG) are selective tools for probing excitons. In SHG and SFG measurements performed on C-60 and CuCl films we observe Frenkel and Wannier excitons, respectively. On the other hand, no second-harmonic (sum-frequency) intensi ty enhancement was observed at energies above the conductivity gap. This is in strong contrast to, for instance, one-photon and two-photon absorption experiments. The selectivity of SHG and SFG for excitons compared to interb and transitions can be explained in terms of coherence of the respective ex citation processes.