Role of the cavity field in nonlinear optical response in the condensed phase

Comparison between a rigorous molecular crystal treatment of nonlinear opti cal response and a cavity model approach to third harmonic generation shows that a cavity field should be included at the output frequency. The argume nt for omitting this cavity field, that there is zero macroscopic field at the output frequency, fails to take proper account of polarization at the o utput frequency outside the cavity. (C) 2001 American Institute of Physics.