James Kevin Erwin

Information storage and retrieval using macromolecules as storage media

No abstract available.

Magneto‐optical recording on patterned substrates (invited)

Patterning of glass or plastic substrates in the form of shallow square patches is a promising method of increasing the storage density for magneto‐optical disks. The sidewalls of the patches pin the reverse‐magnetized domains that develop in these samples. Confinement of domains within the patch boundaries during thermomagnetic recording has also been demonstrated. We have measured polarization conversion of the incident light on the sidewalls of the patches; a method to reduce the amount of such polarization conversion is proposed in this article.

Measurement of birefringence for optical recording of disk substrates

We experimentally investigate the birefringence of bare and coated substrates for magneto-optical recording, using ellipsometry at wavelengths of 632.8 and 780 nm. The polarization rotation and ellipticity of reflected or transmitted light are measured for different incident angles and for different orientations of the incident linear polarization. The measured data are then fitted by the MULTILAYER computer program, which solves the Maxwell equations for a plane wave propagating in a multilayer structure. This approach makes it possible to determine, with high accuracy, the orientations of the principal axes of the substrate and the corresponding refractive indices. The results show that one of the principal axes is always along the substrates normal direction, but the orientations of the in-plane principal axes can be much different from the radial and track directions. A special feature of the ellipsometers that were used is that a glass hemisphere is placed in contact with the substrate to eliminate refraction of the incident beam. This enables a maximum propagation angle of 70° (with respect to the normal) in the substrate and hence increases the measurement sensitivity. Certain anomalies have been observed, which we believe are associated with the variation of birefringence properties along the thickness direction.

Effect of grooves on magnetization reversal in amorphous TbFeCo thin films

We have investigated the effect of grooves milled by argon ions in soda lime glass substrates on the magnetic behavior of amorphous TbFeCo films deposited onto these substrates. The domains are shown to expand along the grooves when the groove depth exceeds 10 nm. The effect originates from the difference in the coercivities of the film on the land and on the groove, as well as from the pinning of domain walls by the side-walls of the grooves. >

RETROREFLECTING ELLIPSOMETER FOR MEASURING THE BIREFRINGENCE OF OPTICAL DISK SUBSTRATES

A retroreflecting ellipsometer has been constructed for measuring the birefringence of optical disk substrates. In contrast to conventional ellipsometers with two mechanical arms, this system has only one arm along which both the incident and reflected beams travel. This construction eliminates the mechanical limitations of conventional ellipsometers, thereby permitting normal incidence on the sample. In addition, the single arm is adjustable in two dimensions, with the polar incident angle, θ(inc), varying from 0° to 70°, and the azimuthal incident angle, Φ(inc), varying from 0° to 360°. The condition of normal incidence permits accurate measurement of in-plane birefringence. The adjustability of both θ(inc) and Φ(inc) is necessary for the measurement of possible tilts of the index ellipsoid, and also for the variation of birefringence through the substrate thickness. Measurement results showing the useful features of the equipment are presented. The optics of the hemispherical assembly used for retroreflection as well as for the elimination of undesirable refractions are also studied by use of the ZEMAX lens design program.

Thermomagnetic recording in amorphous TbFeCo films on patterned substrates

Magnetization reversal and thermomagnetic recording in amorphous TbFeCo films on patterned glass substrates were studied. Two types of patterns were examined: 1/spl times/1 /spl mu/m/sup 2/ raised and lowered square patches. Pinning of the domain walls at the side-walls of the patches was observed. Thermomagnetic recording experiments confirm the ability of patterned substrates to confine recorded domains within boundaries defined by the side-walls.

Measurements of the magneto-optic Kerr effect and the extraordinary Hall effect on grooved glass substrates coated with amorphous TbFeCo

Kerr loops measured in the 0th, −1st, and −2nd diffraction order beams on deep magneto-optic gratings show constructive and destructive interference of the beams reflected from grooves and lands as a function of effective phase depths and relative widths of grooves and lands. Hall-effect measurements yielded coercivities of grooves, lands, and sidewalls at different angles of the applied field. Sidewall reversals appear clearly in Kerr loops measured in the various diffracted beams, with signal amplitude depending on groove depth and the angle between the sidewall and the diffracted beam.

Differential spot-size focus servo

We describe performance of a differential spot-size (wax-wane) focus servo. Cross talk from the tracks are analyzed in the single detector and differential focus circuits. Magnitude of the cross talk is reduced by a factor of three in the differential circuit. A false FES signal is present when the spot crosses sector marks at na angle.

Micro-optic lens for data storage

We describe a new type of microlens for data storage applications that has improved off-axis performance. The lens consists of a micro-Fresnel pattern on a curved substrate. The radius of the substrate is equal to the focal length of the lens. If the pattern and substrate are thin, the combination satisfies the Abbe sine condition. Therefore, the lens is free of coma. We analyze a 0.5 numerical aperture, 0.50 mm focal length lens in detail. A 0.16 numerical aperture lens was fabricated holographically, and results are presented.

Characterization of photochromic bit-wise volumetric storage media for space applications

We report playback performance results of volumetric optical data storage disks that are made from a new class of light-absorbing (photo-chromic) compounds. The disks are first exposed to a simulated space environment. In order to simulate the space environment, a vacuum oven bakes the disks for certain amount of time at a designated temperature. Test results in this temperature study are fit into an Arrhenius model. Disks are also exposed to radiation doses similar to those found in a space environment. Disks fail in high temperature and large proton-dose conditions. Heavy ions do not cause significant disks failure. The prevention of disk failure due to harsh space environments is also discussed.