Stimulated backscattering from the stratosphere: a useful laser guide star?

Summary form only given. Lasers have been employed to create artificial "laser guide stars" (LGS) by exciting various emissions from the upper atmosphere that are bright enough to correct infrared images. Unfortunately, the atmosphere trembles in such a manner that using adaptive optics techniques to correct distortions in blue starlight requires orders-of-magnitude brighter guide stars than any existing LGS. The authors report studies which indicate that stimulated backscattering of a laser focused into the stratosphere, above the atmospheric turbulence, can create such an enormously brighter guide star. There, the atmospheric excitation with the greatest stimulated gain is the S(6) rotational Raman transition of N/sub 2/. Extrapolation to the stratosphere suggests that a one-quarter joule, 352 nm, pulse focused into the stratosphere by the Keck telescope would surpass the S(6) stimulated backscattering threshold.