Numerical analyses on optical limiting performances of chloroindium phthalocyanines with different substituent positions

Optical limiting properties of two soluble chloroindium phthalocyanines with α- and β-alkoxyl substituents in nanosecond laser field have been studied by solving numerically the coupled singlet–triplet rate equation together with the paraxial wave field equation under the Crank–Nicholson scheme. Both transverse and longitudinal effects of the laser field on photophysical properties of the compounds are considered. Effective transfer time between the ground state and the lowest triplet state is defined in reformulated rate equations to characterize dynamics of singlet–triplet state population transfer. It is found that both phthalocyanines exhibit good nonlinear optical absorption abilities, while the compound withα-substituent shows enhanced optical limiting performance. Our ab-initio calculations reveal that the phthalocyanine withα-substituent has more obvious electron delocalization and lower frontier orbital transfer energies, which are responsible for its preferable photophysical properties.     

Optical power limiting of ultrashort hyper-Gaussian pulses in cascade three-level system

Propagation of strong femtosecond hyper-Gaussian pulses in a cascade three-level molecular system is studied by solving numerically the Maxwell–Bloch equations by the iterative predictor-corrector finite-difference time-domain method.Optical power limiting behavior induced by strong nonlinear two-photon absorption is observed for different orders of the femtosecond hyper-Gaussian pulses. Pulses of a higher order temporal profile are found to have a wider power range of optical limiting but a larger output saturation intensity. Both the output saturation value and the damage threshold of optical power limiting decrease with pulse duration increasing. The decrease of the pulse area along the pulse propagation is much slower than that obtained from the two-photon area theorem due to invalidity of the slowly varying amplitude approximation and the monochromatic field hypothesis.