Kazuo Watabe

Optical pump-and-probe test system for thermal characterization of thin metal and phase-change films

A single-shot optical pump-and-probe test system is reported. The system is designed for thermal characterization of thin-film samples that can change their phase state under the influence of a short and intense laser pulse on a subnanosecond time scale. In combination with numerical analysis, the system can be used to estimate thermal constants of thin films, such as specific heat and thermal conductivity. In-plane and out-of plane thermal conductivity can be estimated independently. The system is intended for use in research on optical data storage and material processing with pulsed laser light. The system design issues are discussed. As application examples, we report on using the system to study thermal dynamics in two different thin-film samples: a gold film on a glass substrate (a single-phase system) and the quadrilayer phase-change stack typical in optical data-storage applications.

Simulation study for high- density optical disk system

A newly developed simulator indicates that adopting (1,7)RLL code and PRML method leads to a 29.5GB system.

Behavior of GeSbTeBi phase-change optical recording media under subnanosecond pulsed laser irradiation

We investigated the variations in reflectivity during the phase transition between amorphous and crystalline states of a Bi-doped GeTe-Sb2Te3 pseudobinary compound film with subnanosecond laser pulses, using a pump-and-probe technique. We also used a two-laser static tester to estimate the onset time of crystallization under 2.0-micros pulse excitation. Experimental results indicate that the formation of a melt-quenched amorphous mark is completed in approximately 1 ns, but that crystalline mark formation on an as-deposited amorphous region requires several hundred nanoseconds. Simple arguments based on heat diffusion are used to explain the time scale of amorphization and the threshold for creation of a burned-out hole in the phase-change film.

Assessing Deterioration of an In-field RC Bridge Deck by AE Tomography

Deterioration of aging infrastructures is an important issue in many developing and well-developed countries. For maintenance of the infrastructures in limited budgets, proactive inspections and countermeasures are important before severe structural damage occurs. To assess the deterioration of those structures in a reliable and preferably nondestructive manner is highly demanded. Responding to the demand, acoustic emission (AE) tomography can be regarded as a powerful method since it builds the elastic-wave velocity distribution of the medium that AE waves propagate through while simultaneously locating AE sources. Such a method has been widely tested in laboratories but not yet fully realized in fields. In the present study, the applicability of two-dimensional (2D) and three-dimensional (3D) AE tomography techniques to the evaluation of internal damages in existing RC bridge deck was examined using the data obtained by single-side AE measurement. The overlay of 2D elastic-wave velocity distribution with AE source locations reveals that AE was active in moderate-velocity areas and the boundaries of low-velocity areas, which were regarded as deteriorated areas with progressing defects. Moreover, in the AE measurement, a large number of AE with small amplitudes were observed in the severely deteriorated panel; amazingly, primary AEs were captured, which implied the propagation of an internal crack in the deck.

New Wobble-Address Format for an Optical Disc with a Separated Guide Layer

We propose a physical address format suitable for the separated guide layer of a multilayered optical disc. Since the track format of the guide layer is different from that of conventional multilayered discs, a novel address format is required. The proposed format adopts a land-and-groove-track structure to generate a stable tracking signal. The address information for land and groove tracks is physically premastered by the wobbling and width-modulating of grooves. We fabricated a replicated disc sample with the proposed format and demonstrated a sufficiently low bit error rate by an experiment. Consequently, we considered that the format is a promising solution for the physical format for multilayered discs with a separated guide layer.

Construction of holographic data storage system with dual-reference beam

A novel holographic data storage (HDS) system with dual-reference beam is proposed. Several servo techniques that construct a read and write procedure of the HDS system are introduced and experimentally confirmed.

Behavior of GeSbTeBi phase-change optical recording media under sub-nanosecond pulsed laser irradiation

Reflectivity variations during phase-transition between amorphous and crystalline states of a Bi-doped GeTe-Sb2Te3 pseudo-binary compound film is investigated with sub-nanosecond laser pulses using a pump-and-probe technique. We also use a two-laser static tester to estimate the onset time of crystallization under a 2.0-μs-pulse excitation. Experimental results indicate that the formation of a melt-quenched amorphous mark is completed in about one nanosecond, but crystalline mark formation on an as-deposited amorphous region requires several hundred nanoseconds. Simple arguments based on heat diffusion are used to explain the time scale of amorphization and the threshold for creation of a burned-out hole on the phase-change film.

Experimental study of 30 GB/side rewritable optical disk using a blue-laser diode

The read-write characteristics of a land and groove disk have been examined using a blue-laser diode, high NA objective lens and the PRML method. The wide tilt and defocus margins have been obtained and no deterioration by CW has been observed at a data bit length of 0.0987 /spl mu/m and a track pitch of 0.29 /spl mu/m. These experimental results certify the feasibility of a rewritable optical disk with a capacity of 30 GB/side.

A new write shift compensation method modified for optical systems to which PRML detection is applied

A new write shift compensation method modified for optical disk systems to which PRML detection is applied is developed. The compensation method achieves optimization of all writing pulses adaptively. The compensation parameters are calculated to minimize the probability of detection errors. The experimental results certify that the ch.bER is improved using this method.

30 GB/side rewritable optical disk for HDTV utilizing a blue laser diode

This paper presents a rewritable optical disk with a capacity of 30 GB/side intended for the next generation of rewritable optical disks. The experimental results have shown that this optical disk has wide tilt margin and is a prospective candidate for supplanting VCR in the HDTV era.