Investigation of nonlinear optical properties of exfoliated MoS2 using Photoacoustic Zscan

We studied nonlinear absorption characteristics of exfoliated Molybdenum disulphide (MoS2) dispersion in 1-Methyl-2-pyrrolidinonc and demonstrate a dual absorption characteristic at 532nm nanosecond pulsed laser wavelength. A number of recent reports demonstrate a saturable absorption in MoS2 and other 20 materials at low tlucnces and a deviation from this saturable absorption at higher fluence using open aperture Z scan (OZ scan) technique. It has been suggested that this deviation at higher fluences is due to nonlinear optical scattering. We have recently developed a new technique which combines OZ scan and photoacoustic Z-scan (PAZ scan). It can measure photoacoustic and optical transmission signals simultaneously. The data obtained from both signals are employed to find nonlinear absorption parameters in non-linear optical materials. Our results reveal that non-linear scattering is not the cause of deviation of 20 materials from saturable absorption at higher fluences. We propose that the optical limiting behavior at higher fluence in these 20 materials is dominated by free carrier absorption.