Controlled phase separation of polymer-liquid crystal mixtures for reversible optical data storage

A system for reversible optical data storage has been studied, using mixtures of polymers with liquid crystal molecules. A thin coating of a polymer-liquid crystal mixture with a laser absorbing dye would be spin coated onto a substrate and recording would be done with two types of write laser pulses. One laser pulse would be of high intensity and focused to small diameter, giving large temperature gradients and relatively fast cooling rates. The other write pulse would have lower intensity and larger diameter, resulting in smaller temperature gradients and slower cooling. A third pulse, reserved for reading, would not have sufficient intensity at the wavelength absorbed by the system to heat significantly. It would be scattered at different intensities into a photodetector depending on the cooling history of the spot being read. The feasibility of the principle was demonstrated through an experiment in which a 4-8-microm sample coating is applied to clear resistor coated glass. Energy was put into the system by a pulse generator whose power and pulse duration can be controlled. Low intensity laser light scattering patterns were observed during and after the resistive pulse to monitor the sample morphology during the experiment. A short heating pulse resulted in more intense light scattering at small angles than longer, lower power pulses.