NONLINEAR RESPONSE AND OPTICAL LIMITING IN INORGANIC METAL CLUSTER MO2AG4S8(PPH3)(4) SOLUTIONS

We describe a series of experiments on acetonitrile solutions of an in organic cluster molecule Mo2Ag4S8(PPh3)(4) and compare them with data on a suspension of carbon particles in liquid (dilute ink). The optica l-limiting behavior is measured by single-picosecond 532-nm pulses and nanosecond-long trains of these picosecond pulses. Nonlinear loss mea surements are also performed with pulse trains at 1064 nm. Both materi als show reduced transmittance for increasing fluence (energy per unit area). We also perform picosecond time-resolved pump-probe measuremen ts at 532 nm, and we find that the observed pump-probe behavior is ide ntical for the metal-cluster solution and the carbon-black suspension. We believe that the nonlinear mechanisms are the same for the two mat erials. Our previous studies of carbon-black suspension indicate that the primary nonlinear losses are due to scattering and absorption by m icroplasmas formed after thermionic emission from heated carbon black augmented by scattering from subsequently created bubbles. The conclus ion of a similar limiting mechanism for the two materials is confirmed by time-resolved shadowgraphic images taken on both samples; however, a definitive conclusion concerning the role of microplasmas versus bu bbles in either material is still under investigation. (C) 1998 Optica l Society of America [S0740-3224(98)00905-9].