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Application to optical data storage of laser-induced synthesis of CuTe

Many optical recording media have been investigated since a few years, but none appears to be fully suitable for WORM optical disk. Te and its alloys have been studied. For alloys, contrast is obtained by crystallization of the amorphous initial film. The constrast is low because it is only due to a difference in structure between the irradiated and non-irradiated zone. We propose a sensitive layer made of thin films of Cu and Te, in 1:1 atomic proportion '. As it is well known, laser annealing of thin sandwich films of that kind allows the synthesis of crystalline compounds. Contrast, in this case, is high due to synthesis of the semiconducting compound CuTe, with optical properties (both in transmission and reflection) quite different from the non-irradiated film ones. A study is made of the irradiation conditions (power density), of the reduction to im scale spots and of the optimization of the contrast. The stability of the layer is also studied by ageing procedure. In particular, we demonstrate the feasibility of a WORM glass disk with this coating. The disk is irradiated with a 830 nm solid state laser diode, pulsed at a frequency of .1 MHz, with instant power within the range 7-10mW. Spots with a diameter in the i.tm range were obtained. Long term stability of the virgin layer makes the technology described here a convincing competitor in the WORM disk market.