9321289 Danchi The Infrared Spatial Interferometer developed at the University of California at Berkeley is at present the world's only multi- aperture stellar interferometer operating in the 9-12 um atmospheric window. This instrument, involving two movable 1.65 m aperture Pfund telescopes, offers unprecedented resolution in the 10 um wavelength region with an ~30 milli-arcsec (mas) resolution at the longest currently available baseline. Support is provided for upgrades to the hardware of the ISI in four areas that would significantly add to its capabilities. The first area is to extend the quantum efficiency and bandwidth with a new type of heterodyne detector. The second area is to upgrade the autoguiding system to use the near-infrared radiation from the stars rather than visible light. This would allow sufficiently short integration times for tip-tilt stabilization of the image for the stars in the present observing program. In addition, this would allow guiding on stars which radiate very weakly at visible wavelengths and yet are intense enough at 11 um to be observed with the ISI, such as some proto-planetary nebulae, OH/IR stars, and proto-stellar sources. The third area involves upgrading the delay line and correlator to match the bandwidth of the present detectors. The effective bandwidth of the correlator and delay line is about 1600 MHz, while the present detectors have bandwidths exceeding 3000 MHz. Thus a significant gain in sensitivity can be achieved through an improvement to this part of the system. The fourth area is to develop the site at Mt. Wilson to increase the baseline length in at least two directions to the maximum allowed by the site, which is about 100 m, increasing the maximum resolution to about 10 mas. ***
