The great potential of intense lasers to generate quantum beams for material search is revealed by introducing some instances such as laser electron acceleration for ultrafast electron diffraction / deflectometry and laser terahertz surface wave generation. We have demonstrated that a short electron pulse can be generated by an intense femtosecond laser pulse. Its pulse duration is as short as 100 fs, which is shorter than that obtained a conventional accelerator. This short electron pulse is not only available to material investigation but also the observation of laser-matter interaction phenomena.
We have developed an intense terahertz wave source aiming at in-situ measurement of periodic surface structures induced by terahertz waves on solid materials with high-spatiotemporal resolution. An intense terahertz wave of 119 µJ was generated from a Lithium Niobate crystal induced with an intense laser with fluence of 25 mJ/cm2 by tilted pulse front method. By applying a negative chirp to the laser pulse, the pulse width spread inside the crystal was compensated, and the output of the terahertz wave was maximized.
Feasibility for fabricating meshed pipes was investigated using laser-scan lithography and electrolytic etching onto stainless-steel pipes with an outer diameter of 100 µm. Such meshed pipes will be useful as needles for filtering particles and granules mixed in liquids. The meshed pipes were designed by arraying 30 slits linearly in 8 lines by a circumferential angle pitch of 45º. Each 30-slit array was alternately shifted a half pitch in the axial direction from the neighbored slit-arrays. The target sizes of slits were 50 µm wide and 100 µm long, and the designed distance between slits in the axial direction was also 100 µm. Because the slit widths and lengths were enlarged by the undercut during the etching, slit patterns were delineated by reducing the sizes to 20 µm wide and 75 µm long. As a result, etched slit patterns with mean width and length of 18.5 µm and 74.9 µm, respectively, were obtained. When 6 pipes were etched, all the slits were successfully penetrated in two pipes. Although side walls of slits were inclined and contour edges became twofold caused by the undercut, it was judged that the new fabrication method of meshed pipes is feasible for developing various functional needles.
We developed a vibration measurement system by fiber Bragg gratings (FBGs) with a pulse light. The pulse light is produced by modulating a broadband light with an optical fiber switch at a modulation frequency of 40 kHz. This system enables to separate and detect reflection signals from multiple FBGs like a pulse train. This system achieves multipoint and real-time vibration measurement by FBGs with a time resolution of 25 μs.
The carbon thin film as a target for laser-driven heavy ion acceleration has been developed using the carbonization of polyimide induced by the irradiation of a XeCl excimer laser. The relationship between the depth of the crater produced by the laser irradiation and the laser fluence were measured in order to clear the carbonization mechanisms of polyimide. The melting threshold of polyimide was estimated to 0.058 J/cm2. It is found that the carbonization is induced by the irradiation with the laser fluence around or under the threshold.
Nano/microfabrication experiments on the surface of silicon solar cell are performed by ultraviolet femtosecond laser in the fluence range from 0.10-0.70 J/cm2. The surface morphology change of sample was observed by a laser scanning microscopy and a scanning electron microscope. The crystallinity of surface irradiated by laser pulses was evaluated by Raman spectroscopy. The ablation threshold for silicon was estimated to be 0.10 J/cm2. We successfully produced nano-structures on the surface of silicon solar cell maintaining single-crystalline with the irradiation at the laser fluence of 0.10 J/cm2.
This paper is the fourth report of gas-insulated switchgear (GIS) history (basically after 2000s to present) in Japan from a view point of transitions of the technological developments and practical applications. Firstly, technical progress of 550 kV GIS especially focused on from 1990s to 2010s was summarized referring to an application example of 550 kV mixed technology switchgear (MTS). Application of MTS to 550 kV GIS made it possible to reduce the weight of equipment and SF6 gas. An example of refurbishment of aged 550 kV switchgear to the latest one was also presented. Secondly, deterioration phenomena and their issues for aged GIS were studied regarding gaskets and contacts (e.g. contact wear and grease). Also, a replacement example of aged GCB by using the latest MTS was introduced as one of life extension methods for aged GIS. Finally, transition of GIS developments and the practical applications over a half of century were reviewed by classifying into four terms. Recent trends of SF6 alternative gas and the related international activities in CIGRE and IEC were introduced. Also, features of GIS technologies in Japan were compared with those of overseas GIS in terms of e.g. design, manufacturing, testing techniques and the way to establish and update GIS specifications and standards.
To understand the electrical treeing properties at an interface, treeing breakdown tests are performed using a 1/2 needle polished to half the original thickness. The treeing properties of multilayer samples, which have interfaces similar to Epoxy (EP)/EP-1/2n and Glass/EP-1/2n, are measured. The average tree inception voltage of the EP/EP-1/2n sample is higher than that of the Glass/EP-1/2n sample. The magnitude relationship of the bonding strengths between the EP/EP-1/2n and Glass/EP-1/2n samples is the same as that of the tree inception voltage. The insulation lifetime of the EP/EP-1/2n sample is also higher than that of the Glass/EP-1/2n sample. These results suggest that the interface becomes the weak point for electrical insulation, and the weak bonding of the interface may lower the treeing properties.
Recently, EM wave absorbers are frequently applied to prevent undesired EM waves. In our previous works, EM wave absorbers consisting of a artificially designed material and a ferrite rubber mixture have been proposed. As the newly materials, the authors propose the grid sheets consisting of the conductive material and the metal foil, and evaluate their equivalent relative permittivities. Next, EM wave absorbers consisting of a proposed sheet and a permalloy composite material are designed, and their reflection characteristics are experimentally evaluated.