Temporal and angular analysis of nonlinear scattering in carbon-black suspensions in water and ethanol

The physical origin of the nonlinear scattering of light induced by the focusing of intense laser pulses onto carbon-black suspensions (CBS's) is discussed through the interpretation of pump-probe experiments and angular analyses. Pump-probe experiments are carried out with a time delay ranging from picoseconds to the milliseconds, and angular analyses are performed in both the picosecond and the nanosecond regimes. The comparison between pump-probe experimental results obtained from solutions of CBS in water, CBS in ethanol, and indoaniline in ethanol shows that the scattering phenomenon is associated with the carbon particles within the first nanoseconds, the influence of the solvent being significant only at much longer times through thermal relaxation processes. Thermodynamical considerations confirm these experiments and clearly show that a vaporized or land) ionized carbon particle may be an efficient scattering center for visible wavelengths. The measurements of time-integrated angular scattering intensities for 10-ns-duration pulses demonstrate the influence of multiple scattering at high laser fluences. Time-resolved angular scattering experiments show the existence of a shock wave during the growth of scattering centers created by the percussive picosecond-duration pump pulse. (C) 1999 Optical Society of America [S0740-3224(99)02009-3].