High-contrast optical storage in VO₂ films

When vanadium dioxide, VO₂, undergoes its semiconductor-to-metal transition at 68 °C its reflectivity decreases by about a factor of 2 throughout the visible range. By using a thin VO₂ film on a vanadium substrate we were able to achieve a much higher contrast between the reflectivities of the two VO₂ phases. The VO₂ film was grown as an antireflecting coating for one of the phases and thus the film thickness was used to determine the light wavelength at which the contrast will reach its maximum value. For example, with an 800-Å-thick film a contrast of 16 (rather than 2) was obtained at a light wavelength of 7000 Å. In utilizing the present system for optical storage the high contrast obtained yielded an order of magnitude higher read-out efficiency than the efficiency reported for VO₂ films sputtered on glass. To demonstrate information recording in the present system, both a pulsed laser and a cw laser were used for spatially selective"writing" in the film. It was found that the present system has high "write sensitivity" with a threshold, easy erasability, and high-resolution capability. Cyclic operation without fatique and the convenience of using the same cw laser for both writing and reading, are other advantages of the system described.