  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 exhaustive graphical analysis of this
article can provide the brief idea about transmittance curves of the nonlinear
absorption to the experimentalists. In four and five level cascade models,
simultaneously saturable and reverse saturable absorption can be generated.
