  We theoretically investigate the nonlinear optical pulse responses of
excitons in a thin film where the excitonic center-of-mass motion is confined.
A large interaction volume between excitons and radiation yields particular
coupled states with radiative decay times reaching several femto-seconds. By
considering two polarization directions of light, we reveal that these
fast-decay modes dominantly survive in an optical Kerr spectra even under a
massive nonradiative damping $\Gamma=30$ meV. The results clearly show that
there is an optimal combination of the incident pulse width and the film
thickness for maximizing the integrated intensity of nonlinear signals.

Materials Science