Mechanism of recording and erasing of optical information by laser radiation on SiO ₂ -(Co + Si)-SiO ₂ -Si multilayer structure

The optical properties of SiO ₂ -(Co + Si)-SiO ₂ -Si structures studied by treatment with Q-switched YAG:Nd and CO ₂ 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/cm ² intensities of CO ₂ 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/cm ² . When this multilayer structure is subject to Q-switched YAG:Nd laser radiation of an intensity from 14 MW/cm ² to 53 MW/cm ² , the magnitude of the reflection coefficient returns to its initial value of 70%. It means that information recorded by the CO ₂ laser is erased. Calculations of the temperature field during irradiation with CO ₂ and YAG:Nd laser showed that the phase transition from mixture (Co + Si) to CoSi ₂ caused by CO ₂ laser irradiation results in recording of information, whereas the thermal impact caused by YAG:Nd laser irradiation results in amorphization of CoSi ₂ and erasing of information.