Toward understanding the mechanism of nonlinear optical characteristics of PbTe thin film for nano-optical memory.

An experimental study is conducted toward understanding the mechanism of nonlinear optical properties of PbTe thin film that were demonstrated potentially usable for nano-optical memory based on super-resolution technology. By way of a real time optical-electrical characterization of a PbTe thin film device, it is found that absorption coefficient decreases with increasing laser power, accompanied by increase in carrier concentration. From z-scan measurements, nonlinear optical coefficient due to a long pulse (1 micros) z-scan is found nearly 3 order of magnitude higher than the one due to a short pulse (30 ps) z-scan when input energy density is relatively comparable. Conceivably, these experimental findings call for a physical model that is able to account for the prevailing role of a thermal contribution within the framework of absorption saturation by band filling. We speculate that the absorption saturation might be enhanced dramatically by making various indirect interband transitions possible via participation of phonons in a photonic excitation process.