Investigation of the nonlinear absorption of [M(Et2timdt)2] (M = Pd, Pt) in the pico- and nanosecond timescales using the Z-scan technique

The nonlinear optical absorption of two neutral metal dithiolenes [M(Et2timdt)2] (M=Pd and Pt) has been investigated at λ = 1064 nm by the open-aperture Z-scan technique using nanosecond and picosecond pulses. For picosecond photoexcitation, both dithiolenes mainly exhibit saturable absorption. Conversely, using nanosecond pulses, a switch from saturable absorption to reverse saturable absorption has been observed depending on the central metal. Based on experimental results, energy-level structures are suggested to explain the nonlinear absorption for both temporal regimes and, in particular, the sign-reversal of nonlinear absorption.