Two-photon absorption induced optical power limiting behavior of strong femtosecond hyper-Gaussian pulses

摘要

Propagation of strong femtosecond hyper-Gaussian pulses in an organic molecular medium is studied by solving numerically the Maxwell-Bloch equations using an iterative predictor-corrector finite-difference time-domain technique. The carrier-wave frequency of the field is tuned in two-photon resonance with the molecular system simplified by a cascade three-level model. Strong two-photon absorption induced optical power limiting behavior is observed for the hyper-Gaussian pulses of different orders. For the ultrashort hyper-Gaussian pulses, it is found that the "two-photon area" is no further the deciding quantity of the two-photon induced dynamics, and pulses with different temporal profiles will induce different two-photon absorption dynamics and optical limiting processes. With the same pulse duration and field amplitude, pulses of a lower order is found to have a larger input "two-photon area" but a smaller output area, and therefore show a better optical limiting behavior. The population distribution and the generation of new fields during pulse propagation also depend on the shape of the incident field.