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 period ic light field. With increasing light intensity we observe a liquid-solid f ollowed by a solid-liquid transition which are: known as laser-induced free zing and melting, respectively. Here we report on measurements where, in ad dition to the light intensity, the single particle density was also systema tically varied. As a result, we obtain for the first time the full thermody namic information about the system which allows comparison with numerical p redictions of other authors.