Z-scan investigation of fifth-order optical nonlinearity induced by saturable-absorption from (TBA)2Ni(dmit)2: application for optical limiting

The Z-scan technique has been successfully used to determine the magnitudes and signs of the fifth-order optical nonlinearity induced by two-photon absorption. Here, it was used to investigate the fifth-order optical nonlinearity induced by saturable-absorption (SA) of a charge-transfer salt (TBA)2Ni(dmit)2 (TBA = tetra-n-butylammonium, dmit = 2-thioxo-1,3-dithiole-4,5-dithiolate) with 1064 nm pulses. Under excitation by these 1064 nm pulses, the titled molecule exhibits a typical SA effect at relatively low levels of intensity, while showing strong excited-state absorption (including the first and second excited-state) induced by SA at high intensity levels. Such an excited-state absorption is related to the fifth-order effect. The magnitudes and signs of the fifth- and third-order nonlinearities were estimated. Additionally, the optical limiting effect of this molecule in a dimethyl sulfoxide solution was also studied.