Population gratings in degenerate four-wave mixing studies of a nickel dithiolene at 1064 nm

The nickel dithiolene complex Ni(S2C2PhBu)2 has been studied using time-resolved degenerate four-wave mixing (DFWM) at 1064 nm. An analysis of the polarisation and temporal behaviour using the near-counter-propagating geometry shows that population gratings make a substantial contribution to the DFWM signals. These findings contrast with previous DFWM studies using a retro-reflection geometry which suggested that faster processes dominate. Experimental artefacts, inherent to the retro-reflection configuration, can account for this difference. Measurements of the orientational relaxation time in several solvents, and an estimated excited state lifetime in dichloromethane, are presented.