Kazuya Hisada

Multilayer write-once media with Te-O-Pd films utilizing violet laser

Multi-layer write-once optical disks with tellurium suboxide palladium-doped phase-change recording films were designed and adopted to read/write utilizing a violet laser. A dual- layer medium showed carrier to noise ratios (CNRs) of more than 50 dB within a laser power of 7 mW at a linear velocity of 5 m/s in each the condition of numerical aperture (NA) equals 0.65 and NA equals 0.85, which corresponds to a recording capacity of 27 GB and 45 GB on a dual-layer disk of (phi) 120 mm in diameter, respectively. Furthermore, a quadruple-layer medium showed CNRs of more than 48 dB within a laser power of 12 mW at a linear velocity of 5 m/s in the condition of NA equals 0.85, which corresponds to a recording capacity of 90 GB on a quadruple-layer disk of (phi) 120 mm.

One-Head Near-Field Writing/Erasing on a Rewritable Dual-Layer Optical Disk Having High-Index Cover and Separation Layers

Near-field writing and erasing on a rewritable dual-layer optical disk with a single solid immersion lens (SIL) optical head is demonstrated for the first time. A novel beam expander enabled access to both information layers of the disk without exchanging two individual optical heads. A rewritable dual-layer disk having high-index (n=1.8) cover and separation layers was newly developed. By using the SIL optical system and the disk, an effective numerical aperture (NA) of 1.42 is achieved and a recording capacity of 180 Gbyte for the dual-layer rewritable disk is expected.

System of laser pump and synchrotron radiation probe microdiffraction to investigate optical recording process.

We have developed a system of laser-pump and synchrotron radiation probe microdiffraction to investigate the phase-change process on a nanosecond time scale of Ge2Sb2Te5 film embedded in multi-layer structures, which corresponds to real optical recording media. The measurements were achieved by combining (i) the pump-laser system with a pulse width of 300 ps, (ii) a highly brilliant focused microbeam with wide peak-energy width (ΔE∕E ~ 2%) made by focusing helical undulator radiation without monochromatization, and (iii) a precise sample rotation stage to make repetitive measurements. We successfully detected a very weak time-resolved diffraction signal by using this system from 100-nm-thick Ge2Sb2Te5 phase-change layers. This enabled us to find the dependence of the crystal-amorphous phase change process of the Ge2Sb2Te5 layers on laser power.

Crystallization properties of Ge2Bi2Te5 and Ge10Sb90 amorphous nanoparticles subjected to pulsed laser irradiation

Laser-induced crystallization time (Δtc) was studied for Ge2Bi2Te5 and Ge10Sb90 amorphous nanoparticles with diameters of ~20–50 nm and a height of 10 nm, using 10-nm-thick blanket films as references. Δtc of Ge10Sb90 nanoparticles (12 µs) was more than 500 times that of the blanket film (24 ns), whereas that of Ge2Bi2Te5 nanoparticles (80 ns) was close to that of the blanket film (56 ns). These results suggest a significant effect of the characteristic crystallization processes, i.e., the nucleation-dominant (Ge2Bi2Te5) or growth-dominant (Ge10Sb90) crystallization, on Δtc of nanoparticles.