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The domain transfer phenomenon has been applied to light intensity modulated overwrite in order to obtain large power margin. By applying a suitable magnetic field to the multilayer before readout, recorded domains on the memory layer are transferred onto the writing layer. The application of domain transfer before readout improved the read power margin. However, an increase in noise was observed after irradiation of high read power. The reason for the noise increase was found to be an incomplete domain transfer. The incompleteness was successfully explained by introducing a domain nucleation model.

Read/write technologies for the second-generation magneto-optical disk are developed. A large capacity of 1 GB on a 130-mm-diameter disk and high transfer rate of 2∼4 MB/s are attained by mark length recording and the zoned constant angular velocity (zoned CAV) method. Read technologies such as slice level adjustment in the direct slice detection method, the independent edge detection and resync patterns for DC free are combined with the (1-7) run-length limited (RLL) code to provide sufficient edge jitter margin of over 60% of the detection window.

Precise mark-edge recording on a high signal-to-noise ratio (S/N) exchange-coupled direct overwrite magneto-optical (MO) disk provides 2 GB capacity on a 130 mm disk with a sufficient edge jitter margin. Write compensation technology was proven to be effective for both non- and direct-overwrite MO disks.

Write/erase cyclability for mark-edge recording is studied using rare-earth element[RE]-rich TbFeCo media. Mark-edge jitter for the (1-7) random pattern is small enough even after millions of cycles of data writing and erasing.

Exchange-coupled perpendicular anisotropy rare earth-transition metal (RE-TM) double layer films with application as direct overwrite magneto-optical media have been studied employing the Hall effect. An intermediate layer was inserted between a RE-dominated TbDyFeCo layer and a TM-dominated TbFeCo layer in order to modify the exchange interaction. In the case of an in-plane magnetic anisotropy TM-dominated GdCo intermediate layer, the Gd-Co layer was inferred from the Hall effect to be almost fully magnetized in the normal direction at zero applied magnetic field and room temperature. Furthermore, an in-plane domain wall exists inside the TbDyFeCo layer at zero field when the magnetizations of the TbDyFeCo and TbFeCo layers are parallel. It was also found that the in-plane wall moves to the interface between the TbDyFeCo and GdCo layers at a temperature of about 50°C and further into the intermediate layer at higher temperatures.

The extra-ordinary Hall effect has been studied in Ar sputtered Pt(x Å)/Co(5 Å) and Xe sputtered Pt(x Å)/Co(3 Å) multilayers with coercivity ≤8 kA/m and ≥72 kA/m at RT, respectively. The Hall resistivity ρH was found to be larger and have a different Pt layer thickness dependence for the Ar sputtering case as x was varied from 5 Å to 20 Å, although the ohmic resistivity ρR and the saturation magnetization exhibit similar behavior. The estimated values for ρH, ρR, Hall conductivity γHS and extra-ordinary Hall coefficient R 1 for a hypothetical “multilayer” Co film (x=0) are all larger than those for “pure” sputtered Co films. Moreover, it was not possible to explain the observed variation of ρH with the Pt layer thickness with the short-circuiting effect from the non-magnetic Pt layers as predicted by a simple two-layer model. We suggest that the smaller ρH for the Xe sputtered Pt/Co films compared to Ar sputtered films can be attributed to reduced scattering suggesting a beneficial influence of the interface sharpness on the anisotropy of Pt/Co multilayers.

An optical parametric oscillator has been constructed in which a temperature-controlled LiNbO3 crystal in a resonant cavity is pumped by the second harmonic of a mode-locked glass:Nd laser. It produces broadly tunable (λ: 0.62–3.5 µm), intense (peak power \gtrsim 10 MW), ultrashort pulses (pulse width ~ 60 ps) with a narrow spectral width (Δλ~0.1 nm in the red region) and a small beam divergence (Δθ

To achieve high speed overwriting on magneto-optic disks, magnetic field modulation recording using a floating magnetic head has been developed. High reliability for the removable disks can be attributed to the large head-and-disk spacing(2∼4µm), and thick coating(5∼10µm) on the disk. Characteristics of high speed overwriting were investigated at recording frequencies over 10MHz. No residual pre-recorded signal was observed after overwriting.

An autofocusing effect due to wavelength change of diode lasers has been investigated. The following range of an optical spot towards an optical disk widens to maximum of 35 µmp-p as the chromatic aberration of a lens increases to 2.7 µm/nm. This effect occurs at high laser power, and can be used in a focusing servo in an optical pickup to write and/or read data pits.

High linear density magneto-optical recording of 0.3 µm domain length is studied for both laser power modulation and magnetic field modulation methods, through optical observation and numerical simulation of recorded domains on a rotating 5.25 inch TbFeCo disk. In the laser power modulation method, domain length of around 0.3 µm changes largely with fluctuations in recording power. By decreasing the wavelength of the incident laser beam, the amount of change can be reduced. On the other hand, in the magnetic field modulation method, a 0.3 µm domain length can be recorded stably against power deviation even in the case of an 830 nm wavelength at linear velocities of 5∼15 m/sec.

In-Se-Tl-Co compound is found to have short crystallization time of 60ns and high crystallization temperature of 320°C. When recording at a low linear velocity on this material, spiky peaks appear in the readout signals and pre-recorded data can not be completely erased after overwriting with 1 circular laser beam spot. The phase changing process is analysed by a crystallization model and computer simulation of the recording film temperature. Based upon these studies, a new 1-beam-overwriting scheme is proposed, in which a high power laser beam continuously irradiates the recording film, except for short time intervals corresponding to the signals to be recorded. This 1-beam-overwriting is demonstrated to provide high quality overwriting characteristics.

High-density pit-edge recording on magneto-optic disks has been achieved with accurate edge control. Storage density of 0.7 µm/bit is obtained by suppressing timing jitters caused by (1) teardrop-shaped magnetic domains and (2) thermal interaction between magnetic domains.

A compact two-beam optical head using a hybrid two-wavelength laser array is demonstrated for real time verification in a magneto-optic disk. The head height is 10mm. This head uses an aspherical plastic focusing lens and new compound polarized beam splitter ( PBS ) detection optics for detecting spot position signals and magneto-optic signals with the same optics making the head more compact.

Tellurium-based compound thin films which contain arsenic as the second component element are found to have high performance for optical video recording. The required incident argon-ion laser-beam power is about 10 mW for recording in an As–Te system thin film on a polymethyl-methacrylate (PMMA) disk with a cellulose acetate (CA) surface coating rotating at 1800 min-1. Addition of Se to the As–Te system thin film greatly increases film stability. A signal-to-noise ratio of about 45 dB is obtained in reproduced color video signals.