We have measured the transmittance of 3-kW CO(2) laser light through Ge-coated Ag hollow waveguides. The basic characteristics such as transmissivity, bending loss, and output-beam properties are described. A maximum laser power of 2.6 kW was delivered through a straight hollow waveguide that was 1.7 mm in diameter and 2 m long. Furthermore, 4-m-long waveguides were fabricated by joining two waveguides. Finally, preliminary experiments on welding steel plates were done with the light transmitted through the waveguide. Although the focusing properties of the output beam should be improved for practical laser processing, this type of waveguide is promising for high-power CO(2) laser-light transmission.

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To study the problem of the injected harmonic currents into the overhead line by the modern AC rolling stock, a mini model is presented. A Hybrid Active Power Filter composed of a controlled PWM converter in series with a passive filter is proposed for the compensation of the injected harmonic current. Finally, the results of a two control strategies for the generation of the compensating reference are presented.

Highly selective wet-etching of InGaAs on InAlAs was demonstrated using pH-controlled adipic acid, NH 4 OH and H 2 O 2 solutions. A maximum selectivity of 250 was obtained by controlling the InGaAs and InAlAs etching mechanisms. By identifying the rate-determining steps for the etching of InAlAs and InGaAs, we found that the high selectivity is due to the difference in solubility between the oxide of InAlAs and that of InGaAs in the adipic acid solution. InAlAs/InGaAs HEMTs fabricated in a 3 diameter wafer by using this highly selective etching had a threshold voltage and a transconductance with standard deviations of 38 mV and 11 mS mm −1 , respectively.