Gigantic optical nonlinearity in laser-deposited gallium films on the verge of a structural phase transition

Summary form only given. We discuss a means of achieving a large optical nonlinearity in a material on the verge of a transition between structural phases with significantly different optical properties. We have found that films of gallium deposited on fused silica by ultrafast pulsed laser ablation show a fully reversible, surface-assisted metallization when approaching the transition from the /spl alpha/-phase (the normal crystalline form at room temperature and pressure) to the liquid. The nonlinearity has been probed in a quasi cw regime using a Ti:sapphire laser and an optical parametric oscillator (OPO) over a range of infrared wavelengths and is of the order of /spl chi//sup (3)//spl sim/1 esu (estimate for cw excitation).