Nonlinear spectroscopy of three-level cascade systems in the act of saturable and reverse saturable absorption

Abstract

In the process of nonlinear absorption study using ultra-short laser pulses, it is imperative to know the population dynamics of excited molecules/atoms as a function of time. Using rate equation approach, we have numerically demonstrated the time-dependent population dynamics of three-level cascade systems under single photon resonant excitation by 125 fs single shot laser pulse with central wavelength at 532 nm. We present the effect of life-times, absorption cross-sections and photon flux on population redistribution among the energy levels by considering the saturable absorption (SA) and reverse saturable absorption process (RSA) in the wide range of spectroscopic parameters such as life-times and absorption cross-sections. In cascade energy level systems, ultra-short laser pulses have to be used to investigate higher energy levels absorption cross-section and life-times. Our results can be extended to higher energy levels of cascade systems by incorporating them into the rate equation models.