Size characterization of neutral rare-gas clusters based on time-resolved polarization anisotropy measurements

Abstract

The size determination of neutral clusters is experimentally challenging. In particular, weakly-bound rare-gas clusters tend to fragment upon ionization, resulting in systematic errors in cluster size studies. In contrast, characterization of the temporal polarization anisotropy dephasing provides a soft detection scheme for cluster size estimation, which avoids fragmentation of the clusters. Here, we present a systematic experimental study of argon and neon clusters in the size range of 50 to 10.000 atoms using this technique. In order to extract the mean cluster sizes from the data, we present an efficient analytical model of the polarization anisotropy dephasing of an ensemble of doped clusters. The approach shows remarkable sensitivity to small changes in the mean cluster size of just a few tens of atoms and allows us to refine the widely used Hagena scaling law for the estimation of rare-gas cluster sizes.