NONLINEAR REFRACTION AND ABSORPTION IN METAL CLUSTER COMPOUND (N-BU(4)N)(4)[MO8CU12O8S24] - THE DISPERSION BEHAVIOR AND OPTICAL LIMITING EFFECT

We report the observation of time resolved self-defocusing effects in metal cluster compound (n-Bu(4)N)(4)[Mo8Cu12O8S24]. We also present th e dispersion of the nonlinear refractive index, n(2), of the compound measured over a spectral range below the resonance 2.45 eV. The time r esolved self-defocusing effects clearly indicate that the observed non linear refraction should be of electronic origin. The dispersion can b e fit by a two-level model. Away from the resonance, n(2) = -2 x 10(-1 1) cm(2) W-1 M(-1), while at 532 nm, just below the resonance, n(2) = -(2.3 +/- 0.5) x 10(-9) cm(2) W-1 M(-1). In addition, the measurements reveal the involvement of excited state absorption. Based on these ob served nonlinearities, optical limiting of the compound has been demon strated with nanosecond laser pulses of 532 nm wavelength.