Mechanism of recording and erasing of optical information by laser radiation on SiO2-(Co + Si)-SiO2-Si multilayer structure

The optical properties of SiO2-(Co + Si)-SiO2-Si structures studied by treatment with Q-switched YAG:Nd and CO2 lasers are presented. The photo-thermo-chemical reaction of Co with Si has a threshold character. No change in optical properties of (Co + Si) mixture was observed up to 2 MW/cm2 intensities of CO2 laser radiation. A decrease of the reflection coefficient R (at λ = 663 nm) from 70% to 45% is observed as the intensity is increased up to 8 MW/cm2. When this multilayer structure is subject to Q-switched YAG:Nd laser radiation of an intensity from 14 MW/cm2 to 53 MW/cm2, the magnitude of the reflection coefficient returns to its initial value of 70%. It means that information recorded by the CO2 laser is erased. Calculations of the temperature field during irradiation with CO2 and YAG:Nd laser showed that the phase transition from mixture (Co + Si) to CoSi2 caused by CO2 laser irradiation results in recording of information, whereas the thermal impact caused by YAG:Nd laser irradiation results in amorphization of CoSi2 and erasing of information.