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Optical limiting properties of neutral nickel dithiolenes

Wide applications of lasers have stimulated a great interest in development of optical limiting devices. These devices can be used to protect optical sensor form laser-induced damage because their transmission is high when they are exposed to low-power laser light, and their transmission becomes low when irradiated by intense laser beams. Here we report such a device based on nonlinear optical effects in two neutral nickel complexes with multi-sulfur 1,2 dithiolene ligands, 1 and 2. The limiting device consisted of a focusing setup and a 1-mm-thick cell, which contained a benzene solution of one of the complexes. THe limiting properties were investigated by both nanosecond and picosecond laser pulses. At 532 nm, the limiting thresholds of complexes 1 and 2 measured by the picosecond laser pulses. At 532 nm, the limiting threshold of complexes 1 and 2 measured by the picosecond laser pluses with a focusing geometry were determined to be approximately 0.3 J/cm2. The linear absorption spectra of the to complexes also indicated that their limiting response should cover the visible and near-IR region. All these result show their limiting performance is superior to the limiting effecting C60. Picosecond time-resolved pump-probe and Z-scan experiments revealed that the observed limiting effects should originate from excited-state absorption and refraction.