A high stability electron bunch is generated by laser wakefield acceleration with the help of a colliding laser pulse. The wakefield is generated by a laser pulse; the second laser pulse collides with the first pulse at 180 degrees and at 135 degrees realizing optical injection of an electron bunch. The electron bunch has high stability and high reproducibility compared with single pulse electron generation. In the case of 180 degrees collision, special measures have been taken to prevent damage. In the case of 135 degrees collision, since the second pulse is countercrossing, it cannot damage the laser system.
We report on the temperature dependence of electrical resistivity, Seebeck coefficient and Hall coefficient for Fe 2 (V 1-y Ti y )Al with y=0 0.25 and Fe 2 (V 1-z Mo z )Al with z=0 0.20. While the Heusler type Fe 2 VAl ( y=z=0) exhibits a semiconductor like resistivity behavior, a slight substitution of Ti or Mo for V causes a sharp decrease in the low temperature resistivity and a large enhancement in the Seebeck coefficient S: a sign of S is positive for the Ti substitution but negative for the Mo substitution. Substantial enhancements for the Seebeck coefficient are in reasonable accord with changes in the Hall coefficient and can be explained on the basis of the electronic structure of Fe 2 VAl, where the Fermi level is expected to shift slightly from the center of the pseudogap upon the substitution of Ti or Mo for V. In particular, the Mo substitution leads to a large power factor of 4×10 -3 W/mK 2 at room temperature, which is comparable to that of conventional thermoelectric materials.
New type of metal composite material has been developed for the power inductor application. Careful surface treatments of the Fe-based metal powder establish the highly crystallized nano-scale oxide layer on the power surface, and this oxide provides the enough strength and the electronically insulation even without the resin between powders.
We investigated the formation of periodic nanostructures on GaN induced by circularly-polarized femtosecond laser pulses. The structure shape changed from spiral to dots structures with increasing the pulse number. The structure change explained the previous inconsistent results, and we suggest a hypothesis for the formation dynamics. The period of the dots-structures was approximately 150 nm which is almost 1/7 of the laser wavelength, and it kept crystalline comparable to the original substrate. The laser-induced periodic surface structures (LIPSSs) are expected to apply as a new fine processing technology.
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