Optical studies of low-dimensional phase transitions

Optical techniques such as ellipsometry and Brewster angle and fluorescence microscopy have considerably enhanced our understanding of the physics of thin films. We discuss a few recent results obtained by these techniques. In the domain of wetting phase transitions, ellipsometry experiments have revealed that long range forces can split the classical first order wetting transition into two transitions: a first order transition followed by a second order or critical wetting transition upon increasing the temperature. For Langmuir films, a single molecular layer of an insoluble amphiphilic at the free surface of water, the properties of a number of condensed phases have been studied using Brewster angle and fluorescence microscopy. Unexpected and surprising results have been obtained for both the fracture properties and the melting of two-dimensional crystals.