Nonlinear absorption and excited state dynamics in Rhodamine B studied using Z-scan and degenerate four wave mixing techniques

We report our experimental results of nonlinear absorption and excited state dynamics in Rhodamine B solutions at 532 nm, on resonance of the absorption band and 600 nm at the absorption edge, studied using the standard Z-scan and degenerate four wave mixing techniques. We observed saturable absorption at 532 nm and a transition from saturable absorption to reverse saturable absorption at 600 nm with increase in either intensity or concentration. Time-resolved degenerate four wave mixing studies using incoherent light from a broadband dye laser also confirmed the presence of excited state absorption through resonant two-photon absorption. Concentration dependent studies indicate a complex behavior of reverse saturable absorption within saturable absorption. Results are explained using an effective five-level model. The value of two-photon absorption coefficient evaluated using the same model was ∼0.58×10−8 cm/W.