Optical and thermal analyses on multilayered thin films of a phase-change optical recording disk

Abstract

A computer simulation method to study a laser-induced transient temperature profile of a multilayered phase-change optical recording disk (PCORD) has been developed. The simulation program consists of two parts. One part is an optical analysis program based on the optical characteristic matrix method, and the other is a thermal analysis program based on the finite-element method. A new estimation method for thermal conductivity of recording films was proposed. The estimated thermal conductivity of the thin-film recording media was found to be 50% lower than that of the bulk. Reflectivity, absorbance, and temperature values obtained with this simulation method were compared with those measured by a spectrophotometer and an infrared radiation thermometer when the samples were irradiated in an Ar+ laser beam. The accuracy using this simulator was within 8% for reflectivity and absorbance and within 10% for temperature. A method of optimizing the laser-absorbing layer was studied. With this method simulations showed that the PCORD had a maximum contrast ratio and minimum recording time when thickness, thermal conductivity, and complex refractive index of the laser-absorbing film were 60 nm, 4.2×10−3 W/cm °C, and 2.6−i⋅0.0, respectively. This simulation could provide better film designs for PCORDs and the other optical disks of heat mode recording.