ABSTRACT
The light-induced change in the refractive index (phase response) of nonlinear medium and
other nonlinear processes are studied by using two, three, four and five-level schemes [2, 4,
5] . The thermal nonlinearly for all channels (principal and excited) are taken into
consideration along with a resonance nonlinearly at a frequency of waves involved in the
nonlinear process due to week spectral selectivity of thermal nonlinearity [4, 5, 7] .
