An optical data storage and retrieval system that includes a phase change
storage medium and dual energy sources. The phase change material may
store information by undergoing a transformation from one structural
state to another structural state through application of energy. The
system is equipped with two energy sources, neither of which alone
provides sufficient energy to effect the transformation. The combination
of both energy sources, however, provides sufficient energy to induce the
transformation needed to record information. The energy from either
source may be optical, thermal, electromagnetic, mechanical or magnetic
energy.