Laser Interactions with Optical Recording Materials
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LASER INTERACTIONS WITH OPTICAL RECORDING MATERIALS Ernesto E. Marinero IBM Research, Almaden Research Center, 650 Harry Rd., San Jose, CA 95120-6099
ABSTRACT Laser-material interactions are pivotal to optical storage technology. Laser quenching and thermomagnetic processes form the memory basis for approaches based on "phase-change" materials and magneto-optical alloys respectively. Recent progress in phase-change materials indicates that compound semiconductors as well as single element materials are characterized by fast crystallization times. In this work we review, utilizing time-resolved optical and conductivity probes, the melt-kinetics and glass formation processes in Te thin films and the laser-induced crystallization of amorphous GeTe. The latter studies are complemented by x-ray diffraction and TEM analysis. Results are also presented on time-resolved Kerr rotation studies to investigate the magnetic domain formation kinetics in thermo-magnetic recording. Material research problems facing laser interactions with optical recording materials will be discussed.
INTRODUCTION A new technology based on laser-induced material transformations has emerged in recent years that promises to dramatically impact information storage. Optical Storage Recording takes advantage of micron and submicron laser heating to alter the phase of the absorbing layer or to change the magnetic properties of the irradiated region. Because the information storage is achieved by a laser source, several advantages over conventional magnetic recording are offered, the most salient of which are the large head-disk spacings, environmental stability can be more readily attained by utilizing protective overcoats and the possibility of very high-density recording. Search for improved materials as well as a more comprehensive study of the physics of the recording process provides a challenging field in laser-materials research. In this paper, a brief description of the basic aspects of optical storage recording is first given. This is followed by a discussion of results from the author's lab pertaining to time-resolved studies in chalcogenide semiconductors and amorphous magneto-optical (M-O) alloys. The paper also discusses key material -iroblems facing this technology.
MATERIAL INTERACTIONS The most promising candidates as materials for optical storage recording to-date are "phase-change" semiconductors (alloys and compounds) and amorphous magneto-optical (M-O) materials. Phase change materials were first studied in the early 1970's (1) and the storage of information is based on their structural-dependent optical properties. Data is recorded by generating amorphous spots utilizing a short-pulse laser and erasing is accomplished by recrystallizing the material with long laser pulses. The reflectivity difference at visible and near-IR wavelengths between these two phases can exceed 20%, permitting easy distinction between recorded and erased bits. A substantial amount of work has been
Mat. Res. Soc. Syrp. Proc. Vo .74.
1987 Materials Resea
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