CHARACTERIZATION OF ARTIFICIAL GUIDE STARS GENERATED IN THE MESOSPHERIC SODIUM LAYER WITH A SUM-FREQUENCY LASER

We generated resonant-fluorescent artificial guide stars in the Earth' s mesospheric sodium layer with an 840-Hz, 10-mJ sum-frequency laser o perating at 589 nm and have conducted experiments to characterize the guide stars for use as beacons for atmospheric compensation with adapt ive optics. We made high-resolution images with a 1.5-m telescope and CCD camera with exposures from 0.1 to 10.1 s of spots as small as 1.64 times the diffraction limit. We also used an intensified charge-injec tion-device camera to record live video at frame rates of 30 Hz. Using a photomultiplier tube with both the 1.5-m telescope and a 14-in. tel escope, we collected temporal data and calculated the sodium-layer col umn densities of 2-3 x 10(13)/m(2) from long pulse measurements. We ha ve observed the phenomenon of optical pumping of the sodium layer by p ropagating circularly polarized light at peak power densities incident on the layer of 1.0 mW/cm(2). Propagating circularly polarized light gives a 41-48% increase in fluorescent return signal over linearly pol arized light. Artificial guide stars are suitable for atmospheric comp ensation with the use of adaptive optics.