Femtosecond probing of sodium cluster ionNan+fragmentation

Abstract

We report on the first femtosecond time-resolved experiments in cluster physics. The photofragmentation dynamics of small sodium cluster ions ${\mathrm{Na}}_{\mathit{n}}^{+}$ have been studied with pump-probe techniques. Ultrashort laser pulses of 60-fs duration are employed to photoionize the sodium clusters and to probe the photofragments. We find that the ejection of neutral dimer ${\mathrm{Na}}_2$ and, observed for the first time, neutral trimer ${\mathrm{Na}}_3$ photofragments occur on ultrashort time scales of 2.5 and 0.4 ps, respectively. This and the absence of cluster heating reveals that direct photoinduced fragmentation processes are important at short times rather than the statistical unimolecular decay.