  PULSE is a new concept to augment the currently operating 5.1-m Hale
PALM-3000 exoplanet adaptive optics system with an ultraviolet Rayleigh laser
and associated wavefront sensor. By using an ultraviolet laser to measure the
high spatial and temporal order turbulence near the telescope aperture, where
it dominates, one can extend the faintness limit of natural guide stars needed
by PALM-3000. Initial simulations indicate that very-high infrared contrast
ratios and good visible-light adaptive optics performance will be achieved by
such an upgraded system on stars as faint as mV = 16-17 using an optimized
low-order NGS sensor. This will enable direct imaging searches for, and
subsequent characterization of, companions around cool, low-mass stars for the
first time, as well as routine visible-light imaging twice as sharp as HST for
fainter targets. PULSE will reuse the laser and wavefront sensor technologies
developed for the automated Robo-AO laser system currently operating at the
Palomar 60-inch telescope, as well as take advantage of pending optimization of
low-order NGS wavefront sensing and planned new interfaces to the PALM-3000
real-time reconstruction computer. The laser measurements will drive the 3,388
active element high-order deformable mirror in open-loop, while an adaptive
optics sharpened faint natural source will be measured by the current PALM-3000
wavefront sensor in its lowest spatial sampling mode, with commands sent in
closed-loop to the 241 active element low-order deformable mirror. The natural
guide star loop corrects for both the relatively weak low-order high-altitude
turbulence as well as functioning as both the tip-tilt and low-bandwidth
`truth' sensor loops in a traditional laser adaptive optics system.
