  Adaptive optics (AO) is a key technology for ground-based optical and
infrared astronomy, providing high angular resolution and sensitivity. AO
systems employing laser guide stars (LGS) can achieve high sky coverage, but
their performance is limited by LGS return flux. We examine the potential of
two new approaches that might produce high-intensity atmospheric laser beacons.
Amplified spontaneous emission could potentially boost the intensity of beacons
produced by conventional resonant excitation of atomic or molecular species in
the upper atmosphere. This requires the production of a population inversion in
an electronic transition that is optically-thick to stimulated emission.
Potential excitation mechanisms include continuous wave pumping, pulsed
excitation and plasma generation. Alternatively, a high-power femtosecond
pulsed laser could produce a white-light supercontinuum high in the atmosphere.
The broad-band emission from such a source could also facilitate the sensing of
the tilt component of atmospheric turbulence.
