Nonlinear absorption spectra of transparent organic crystals for optical limiting applications at visible wavelengths

We have studied nonlinear absorption spectra and optical limiting properties of transparent molecular organic crystals. ements performed in the 450–650 nm range, using nanosecond pulses, show that these materials have large and broadband nonlinear absorptions. Efficient optical limiting properties are obtained due to crystal packing effects: high active molecule concentration, specific orientation, and enhanced local field factor. nanosecond regime, the nonlinear absorption is a two-step process: two-photon absorption followed by an excited-state absorption. At resonance, the nonlinear response of studied crystals spans over two orders of magnitude in agreement with quantum chemistry calculations.