Phase behavior of two-dimensional colloidal systems in the presence of periodic light fields

We investigate the phase behavior of a two-dimensional suspension of charge stabilized polystyrene spheres in the presence of a one-dimensional periodic light field. With increasing light intensity we observe a liquid-solid followed by a solid-liquid transition which are: known as laser-induced freezing and melting, respectively. Here we report on measurements where, in addition to the light intensity, the single particle density was also systematically varied. As a result, we obtain for the first time the full thermodynamic information about the system which allows comparison with numerical predictions of other authors.