Abstract: An optical recording medium comprising adjacent thin layers of two different materials, which, upon marking with an energy beam, form a marked area comprising an alloy or mixture of the two materials. The optical properties of the marked area has contrast sufficiently different from the optical properties of the unmarked area so that the marked area can be reliably sensed. One of the first of the thin layers comprises a metal and the other of the thin layers comprises a metal or a semiconductor. The metals are taken from the group comprising Al, Au, Pb and Sn and the semiconductors are chosen from the group comprising Ge and Si.

Abstract: An improved photoconductor for GaAs laser addressed devices sensitive to illumination at about 1.5 eV is an amorphous material containing silicon, hydrogen and a material taken from the group consisting of Ge, Sn and Pb. A preferred embodiment of this invention is amorphous Si.sub.x Ge.sub.1-x H.sub.y where x equals 0.78 to 0.93 and y equals 14-20 atomic percent.