Effect of nonlinear absorption in estimation of order of nonlinear optical process by fluorescence intensity

We report the effect of nonlinear absorption on the fluorescence signal. Attenuation of the incident beam intensity (I) in the medium due to nonlinear absorption reduces the fluorescence signal. We show that fluorescence signal proportional to I2 is not always indicative of two-photon absorption process but such a dependence can be obtained for three or four-photon absorption process due to attenuation of the pump beam by nonlinear absorption. This reduction in the fluorescence signal due to nonlinear absorption is found to be more sensitive in the higher order nonlinear optical processes.

► Effect of nonlinear absorption on the fluorescence signal is studied.
► I2 dependence of fluorescence can be obtained for three-photon absorption process.
► Reduction of fluorescence is more sensitive to higher order nonlinear optical processes.
► Attempt is made to analyze intensity dependence of fluorescence signal in Rubrene.
► Analysis would be useful in fluorescence based nonlinear absorption measurements.