Y. Uchiyama

Efficient ultraviolet-light (345-nm) generation in a bulk LiIO 3 crystal by frequency doubling of a self-seeded gain-switched AlGaInP Fabry–Perot semiconductor laser

A self-seeded gain-switched semiconductor laser is applied as a fundamental optical source to second-harmonic generation, and improvement of frequency-conversion efficiency is demonstrated. 345-nm ultraviolet light of 0.12-muW average power is generated in a bulk LiIO(3) crystal for 690-nm fundamental light of 10.5-mW average power, which is composed of 500-MHz pulse trains emitted from an AlGaInP diode laser with a 68-ps temporal width and a 0.11-nm spectral bandwidth. It is clearly shown that the narrowing of the spectral bandwidth by the self-seeding technique gives rise to a normalized conversion efficiency of 0.218%/Wcm , which is fourtimes larger than that for pulses without seeding.

Verification of the Astro-E Hard X-ray Detector based on newly developed ground support equipment

We report the first results of the ground test of the Hard X-ray Detector (HXD) on board the Astro-E mission, by means of the newly developed Ground Support Equipment (GSE). Astro-E will be launched in 2000 by a Japanese M-V rocket. In order to verify the detector system during the limited time before launch, fast and versatile GSE is necessary. For this, we have developed a flexible test system based on nine VME I/O boards for a SUN workstation. These boards carry reconfigurable Field Programmable Gate Arrays with 50,000 gates, together with 1 Mbyte SRAM devices tightly coupled to each FPGA device. As an application of using this GSE, we have tested the performance of a phoswitch unit of the Flight Model of the HXD. In this paper, we present a schematic view of the GSE highlighting the functional design,and the result of our ground test of the HXD-sensor under the high count rate environment expected in orbit.

Generation of ultraviolet (335-nm) light by intracavity frequency doubling from active mode-locking action of an external-cavity AlGaInP diode laser.

An intracavity frequency-doubling scheme was merged with an actively mode-locked AlGaInP laser diode with an external cavity to provide efficient generation of 335-nm ultraviolet light. Intense pulses of <16ps were successfully generated inside the cavity at subgigahertz repetition frequencies. We applied those pulses to intracavity second-harmonic generation from a 5-mm-long LiIO(3) crystal, which resulted in average ultraviolet power of 70muW for an average fundamental power of 73 mW.

Spectrally Narrowed Operation of a Gain-Switched 690 nm GaInP/AlGaInP Fabry-Perot Laser by Self-Seeding Technique

Spectrally narrowed pulses from a gain-switched 690 nm GaInP/AlGaInP Fabry-Perot laser are successfully obtained by the self-seeding technique. A commercially available laser diode emits 48 ps pulses with a spectral width of 0.10 nm or less. This scheme will provide a compact and efficient light source for generation of ultraviolet light by nonlinear optical methods such as second-harmonic generation.

Chandra observations of the HII complex G5.89-0.39 and TeV source HESSJ1800-240B

Several TeV gamma-ray sources have been found towards star forming HII regions, opening up the possibility that such star formation regions may accelerate particles. We have analysed an 80ks Chandra observation of the G5.89-0.39 HII complex and surrounding area towards the W28 SNR. Our preliminary results give us 325 sources in the full Chandra image and establish that the two HII regions in G5.89-0.39 contain B type stars. This is a step towards establishing the energetics of the clusters and the potential for multi-TeV particle acceleration. Previous preliminary results of the Chandra observations were published in [1].

Intracavity ultraviolet second-harmonic generation scheme (335-nm) combined with an actively mode-locked AlGaInP laser diode fundamental light source

We propose an advanced LD-based UV-SHG scheme, where the external cavity active mode-locking and the intracavity SHG configurations are combined to increase the averaged fundamental power (P/sub av//sup /spl omega// and to shorten the pulses, both of which are expected to lead to higher UV output. We used a 670 nm AlGaInP LD. The laser was driven by an RF sinusoidal signal with a DC bias current. The external cavity was set by a mirror with its reflectivity of 0.97. The length of the external cavity was approximately 69-cm-long, which corresponds to the roundtrip frequency of 217 MHz. In order to increase (P/sub av//sup /spl omega//, the pulse repetition frequency was set around second or fourth harmonics of the roundtrip frequencies (434 or 870 MHz). A 5-mm-long LiIO/sub 3/ crystal, which was cut for type-I phase-matching at 690 nm, was inserted between the laser and the mirror. The generated UV light was taken out of the cavity by a dichroic mirror inside the cavity.