A steady-state heat conduction solution for optical disk recording using constant or periodically modulated laser irradiation

Abstract

A fast method is presented for accurately calculating just the steady-state temperature in thin-film multilayers heated by continual laser irradiation. The key features are a simple coordinate transformation and a special lattice with which the steady-state portion of the heat conduction solution reported earlier [J. Appl. Phys. 75, 4382 (1994)] may be quickly and efficiently extracted. The earlier solution, expressed in terms of Fourier-transformed Green’s functions, was designed for temperature problems as typically found in optical disk recording situations. In particular, the laser irradiation was assumed to be modulated arbitrarily in time and finite in duration. As the pulse length increases, though, both execution time and memory requirements increase. Thus when long laser pulses are used to model continual laser irradiation, the numerical performance may degrade to unacceptable levels. For the case of periodically modulated laser irradiation (including constant laser irradiation as a special case) which is important for magneto-optical disk recording, the time and memory requirements can be reduced substantially by defining a new coordinate and lattice system in the space spanned by the time and scan directions. In frequency space, the new lattice filters out the frequencies which contribute to the transient part of the solution and retains only the frequencies which contribute to the steady-state part. The temperature formulas themselves remain unchanged; they are merely evaluated over a specially defined lattice which yields just the steady-state temperature more quickly. This paper describes the new coordinate and lattice systems, discusses some numerical issues, and compares the results of the steady-state theory to the results of the earlier original theory which includes the transients.