Can amplified spontaneous emission produce intense laser guide stars for adaptive optics?

Adaptive optics is a key technology for ground-based optical and infrared astronomy, providing high angular resolution and sensitivity. Systems employing laser guide stars can achieve high sky coverage, but their performance is limited by the available return flux. Amplified spontaneous emission could potentially boost the intensity of beacons produced by 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. Mesospheric metals have insufficient column density for amplified spontaneous emission, but atomic oxygen and nitrogen are potential candidates. They could potentially be excited by a high-energy chirped femtosecond pulsed laser, making visible-wavelength transitions accessible. Such lasers can also generate a white-light supercontinuum in the atmosphere. In addition to providing high intensity, the broadband emission from such a source could facilitate the sensing of the tilt component of atmospheric turbulence.