Theoretical study on nonlinear properties of four level systems under nano-second illumination

In this work, we report the theoretical results of the single beam transmittance of an absorber by employing the rate equation approach, utilizing 10 ns laser pulses. With the appropriate choice of lifetimes of the participating levels in the transition and their corresponding absorption cross-section, it is possible to control the onset of different phenomena like saturable absorption, reverse saturable absorption, and double saturable absorption. We discuss how to increase the saturable and optical limiting nature of the system by appropriate changes of spectroscopic parameters. We discuss the estimation of spectroscopic terms from their contribution in the single beam transmittance. (paper)