We describe a compact, tunable, optical time-delay module that functions by means of total internal reflection within two glass prisms. The delay is controlled by small mechanical motions of the prisms. The device is inherently extremely broad band, unlike time delay modules based on "slow light" methods. In the prototype device that we fabricated, we obtain time delays as large as 1.45 ns in a...

We report new observations of the H 2 O megamaser in the Seyfert 2 galaxy Mrk 348. Following our initial detection in 2000 March using the Effelsberg 100 m telescope, re-analysis of previous data on this source indicates that the maser was present but only marginally detectable in late 1997. Monitoring through late 2000 shows that the maser has again decreased to its original level. The H 2 O l...

We have been successful in developing light and durable mirrors made of CFRP (Carbon Fiber Reinforced Plastic) laminates for the reflector of the new CANGAROO-II 7 m telescope. The reflector has a parabolic shape (F/1.1) with a 30 m effective area which consists of 60 small spherical mirrors of CFRP laminates. The orientation of each mirror can be remotely adjusted by stepping motors. After the...

We address the question: what is the smallest spot size to which an x-ray beam can be focused? We show that confinement of the beam within a narrowly tapered waveguide leads to a theoretical minimum beam size of the order of 10 nm (FWHM), the exact value depending only on the electron density of the confining material. This limit appears to apply to all x-ray focusing devices. Mode mixing and i...

By selecting short exposure images taken using a CCD with negligible readout noise we obtained essentially diffraction-limited 810 nm images of faint objects using nearby reference stars brighter than I = 16 at a 2.56 m telescope. The FWHM of the isoplanatic patch for the technique is found to be 50 arcseconds, providing ∼20% sky coverage around suitable reference stars.

By excitation of cadmium vapor with a high-peak-power KrF excimer laser pulse, fluorescence of an atomic transition at lambda = 508 nm is induced by a two-photon ionization process followed by fast recombination. The nonlinear response of the medium is used to develop a simple single-shot autocorrelator for subpicosecond KrF excimer laser pulses operating down to intensities of less than 10(9)W...

We describe time-resolved measurements of the evolution of the spectrum of radiation emitted by an optically-pumped continuous-wave InGaAs-GaAs quantum well laser, recorded as lasing builds up from noise to steady state. We extract a fitting parameter corresponding to the gain dispersion of the parabolic spectrum equal to -79 ± 30 fs2 and -36 ± 6 fs2 for a resonant and anti-resonant structure, ...

High-quality PbS nanocrystals were produced in multigram-scale quantities through a solventless, heterogeneous, and relatively green route. The heterogeneous nature of this reaction allows one to limit the diffusion in the system, allowing for unprecedented monodispersity and quality of the product demonstrated by a full-width at half-maximum of the photoluminescence peak (PL fwhm) as low as 52...