AlInGaN is most attractive material due to a directive semiconductor materials covering wide band energy ranging 0.8‒6.4 eV. AlInGaN based violet semiconductor laser diodes (LD) is fi rst demonstrated by Nichia Corporation in 1995. Since it, AlInGaN based LDs device characteristics have been improving and its lasing wavelength are expand from UV, blue, to green. In this paper, the technology histories of higher power and longer wavelength GaN based LDs are reviewed. Also, recent high optical power watt class blue and green LDs characteristics are introduced.

View full abstract

Due to high-power fi ber lasers and fi ber-coupled thin disk lasers, the application fi elds of high-power lasers continue to expand, especially for laser processing in automobile, aircraft, and train industries. Based on current applications, laser applications for nuclear technology also show promise because nuclear applications require compact, fl exible, and robust techniques coupled with effi cient real-time monitoring systems with optical techniques in nuclear-contaminated areas with complex structures. We describe how laser-based techniques contribute to nuclear decommissioning which mainly include thick metal underwater laser cutting and cleaning techniques. We also describe how laser techniques can contribute to decommissioning after such serious accidents as the one that occurred in March 2011 at Fukushima Dai-ichi nuclear power plant. Some highly developed laser techniques are expected to contribute successively to new industrial fi elds.

View full abstract

This paper will describe recent work conducted in the UK to highlight the potential of applying high power laser cutting to aspects of decommissioning and dismantling in the nuclear sector. A major driver for this activity is size reduction of metallic structures, vessels and tubing, with the objective of efficient stacking of the cut parts for future long term storage. TWI have used a standard 5 kW multi-mode laser with fibre optic delivery of the beam, to demonstrate techniques for cutting stainless steel tubing, at diameters up to 150 mm and wall thicknesses up to 7 mm, and various thicknesses of plate materials. Using specially developed cutting heads, employing long focal length lenses to form the beam, techniques were developed to allow the cutting of tubes from one side only and without changing the focal position of the laser beam with respect to the diameter of the tube perpendicular to the incident beam. The latter means that remote programming of the cutting path becomes much simpler. For cutting plate materials, special gas nozzle dynamics have produced great tolerance of the cutting process to stand-off distance (the distance between the surface of the material being cut and the exit of the cutting nozzle). One particularly interesting method of remote deployment of these cutting techniques is to use ‘snake arm’ robots. These robots, by nature of their construction, can access areas un-accessible using other techniques. This of course makes them particularly suited to aspects of nuclear decommissioning, particularly in what are termed ‘un-structured environments’, where the exact disposition of items encountered is not known. The paper will also describe the first time a laser cutting head has been installed on the end of a snake arm robot and the combination used in a simulated nuclear cutting application.

View full abstract

A laser Compton gamma-ray beam is unique photon source that can supply polarized, tunable, quasimonochromatic high energy photon beam. This gamma-ray source has possibilities to apply to the maintenances, the conservation, the decommissioning and the security of atomic power plants. Present status of gamma-ray beamline on a synchrotron light facility NewSUBARU are reported. Quasimonochromatic gamma-ray beams from 1 MeV to 73 MeV photon energy are achieved. Photo-nuclear reactions using 17 MeV photon energy were tested. Fast neutrons were measured by a time-of-fl ight technique. A dependence of neutron emission distribution on the polarization of gamma-ray was demonstrated. Nuclear transmutation for a disposal of radioactive nuclear waste and a generation of useful radioactive nuclei are tested.

View full abstract

IAEA verification of the correctness and completeness of State declarations is based on a number of techniques ranging from analysis of open source literature, analysis of commercial satellite imagery, international trade analysis and, of course, field activities conducted by IAEA inspectors and technical staff. A large part of field activities involves instrumentation operated by inspectors or permanently installed at facilities and running in unattended mode. As instrumentation aims at supporting verification of multiple parameters associated with State declarations, multiple techniques are involved, including optical surveillance, sealing and radiation detection, such as neutron coincidence counting or gamma spectrometry. In addition to those techniques considered as traditional for IAEA verification, advanced instrumentation technologies based on lasers have emerged with unique features matching specific safeguards needs, such as the ability to accurately measure distances without physical contact, or extreme sensitivity to trace levels of specific molecules. The paper describes the various safeguards applications based on lasers and focusses on the difficulties that several technologies faced to meet the unique and stringent requirements of IAEA verification.

View full abstract

In a sodium-cooled fast reactor (SFR), liquid sodium is used as a heat transfer fluid because of its excellent heat transport capability. On the other hand, it has strong chemical reactivity with water vapor. One of the design basis accidents of the SFR is the water leakage into the liquid sodium flow by a breach of heat transfer tubes in a steam generator. Therefore the study on sodium-water chemical reactions is of paramount importance for safety reasons. This study aims to clarify the sodium-water reaction mechanisms using laser diagnostics. The sodium-water counter-flow reactions were measured using laser diagnostics such as laser induced fluorescence, CARS, Raman scattering and photo-fragmentation. The measurement results show that the sodium-water reaction proceeds mainly by the reaction Na + H2O → NaOH + H and the main product is NaOH in this reaction. Its forward and backward reaction rates tend to balance with each other and the whole reaction rate reduces as temperature increases.

View full abstract

Accelerator Mass Spectrometry (AMS) is used for the trace determination of long-lived radioisotopes at natural isotopic abundances or less. This paper shows some recent trends and developments for improving AMS using a laser photodetachment technique, including a specific application for trace 129I determination. Advanced AMS for 129I was designed based on the development of a negative pulsed ion source for iodine by laser ablation and intracavity second-harmonic generation of a pulsed injectionlocked Ti:Sapphire laser for I-photodetachment.

View full abstract

lasers were developed, available wavelengths of diode lasers have been extended. External cavity diode laser systems consisting of a diode laser, a collimator, and a grating enables one to obtain a single frequency for high resolution spectroscopy. Laser techniques such as laser cooling have made much progress in recent years. The progress in the fields of atomic and molecular sciences, quantum electronics and so on has spread to trace isotope analysis. In this review, we introduce spectroscopic methods of isotope analyses utilizing laser resonant photoexcitation with single frequency diode lasers.

View full abstract

We investigated the effects of laser incident angle variation on the hardening of metal in laser peening experiments. We used full annealed SUS316L stainless steels as test samples. A 2nd harmonic of Nd:YAG laser light was used to produce laser-peened samples. We used Vickers microhardness tests to estimate the work hardening due to the plastic deformation caused by laser peening. The hardness of the laser-peened samples varied with the numerical aperture of the optics corresponding to the angle of incidence of the laser radiation. The hardness measurements revealed the desirable numerical aperture for laser peening experiments.

View full abstract

A laser-induced liquid jet system for surgery and other medical applications is fabricated by using a hollow optical fiber that transmits Er:YAG laser light for liquid jet generation. Since water has an extremely high absorption coefficient at the wavelength of Er:YAG laser light (λ = 2.94 μm),highpressure liquid jet is produced by a relatively low laser power. To evaluate the system performance for medical applications, we experimentally investigated the mechanism of bubble generation in the water and improved the system to obtain high jet pressure. In addition, we tried to produce shock wave and examined the relations between shock wave pressure and system configuration. We showed the feasibility of the system for both of soft and hard tissue processing.

View full abstract

For spatiotemporal characterization and control of local plasmons at nanostructures excited by femtosecond laser pulses, we developed an electrical-field cross-correlation imaging method using a dark-fi eld microscope. Bandwidth-limited plasmon response functions are obtained simultaneously for various gold nanocrosses distributed on a quartz substrate from a series of cross-correlation image shots using an 800-nm femtosecond laser pulse. Based on the plasmon response functions we can deterministically shape the plasmon pulse at a specifi c nantostructures.

View full abstract