Nonlinear absorption study in four and five energy level systems

Nonlinear absorption in four and five energy level systems have been studied with the aid of steady-state rate equation approach. We report on the tunability of saturable and reverse saturable absorption as a function of spectroscopic parameters (lifetimes and absorption cross-sections). Detailed information is given on the estimation of spectroscopic parameters in the nonlinear absorption spectroscopy. The advantage of four and five level cascade models over other models is that one can produce simultaneously saturable and reverse saturable absorption. Four and five level models can be potentially used as optical limiters and saturable absorbers due to their merit over two and three level models in terms of long tunability and high power control.