S. Debrus et al., Z-scan determination of the third-order optical nonlinearity of gold : silica nanocomposites, J APPL PHYS, 88(8), 2000, pp. 4469-4475
Third-order nonlinear optical properties of Au:SiO2 thin films were studied
at the surface plasmon resonance wavelength by the z-scan technique using
a nanosecond laser. Films were prepared by a multilayer deposition sputteri
ng technique. They were composed of 2 nm mean diam gold particles, with a m
etal volume fraction of 20%. Z-scan measurements performed both with and wi
thout aperture showed a very large nonlinear absorption masking the nonline
ar refraction. The nonlinear absorption coefficient beta was found to be ne
gative and equal to -1.1x10(-2) cm/W. The different mechanisms contributing
to this absorption are discussed and the large value of beta is correlated
to the duration of the laser pulses. Moreover, it is shown that a mean fie
ld theory is not appropriate to evaluate the effective susceptibility at hi
gh metal concentrations. (C) 2000 American Institute of Physics. [S0021- 89
79(00)10519-5].