Direct near-field optical investigation of phase-change medium in blue-ray recordable and erasable disk

The authors report a direct examination of recorded marks in blue-ray recordable and erasable disks with scattering-type scanning near-field optical microscopy. The optical contrasts of the crystalline and amorphous regions of the phase-change layer match with the prediction based on their optical constants. The determined spatial optical variation in the recorded marks reflects the intensity profile of the recording laser beam. The identified nanometer-sized optical features are shown to correspond to 10 nm-sized crystalline domains within the amorphous recorded marks. The revealed near-field signatures show a potential influence on the carrier-to-noise ratio of this optical storage medium.