Jack Drummond (Starfire Optical Range, Air Force Research Laboratory), Steve Novotny (Starfire Optical Range, Air Force Research Laboratory), Craig Denman (Starfire Optical Range, Air Force Research Laboratory), Paul Hillman (Starfire Optical Range, Air Force Research Laboratory), John Telle (Starfire Optical Range, Air Force Research Laboratory), Gerald Moore (Starfire Optical Range, Air Force Research Laboratory), Mark Eickhoff (Boeing LTS), Robert Fugate (New Mexico Institute of Mining and Technology)
Keywords: Lasers
Abstract:
Having upgraded the 20W, 589nm fasor (frequency-addition source of optical radiation) reported at the last AMOS conference to 50W, we have since produced a sodium laser guidestar (LGS) with a V1 magnitude of 5.1 for 30W of fasor power in November 2005, when the annual peak in mesospheric sodium density occurs. This corresponds to a return flux at the top of the telescope of 7000 photons/s/cm2 through one airmass. Late in May 2006, however, a return of only 1340 ph/s/cm2 (V1=6.7) for 30 W of fasor power was obtained at the annual minimum in sodium column density. Earlier in the month, with 49 W of fasor power, the LGS was only as bright as V1=6.3 because of the minimum in column density. By measuring the LGS return flux in circular polarization from various altitudes and azimuths, we have detected the presence of the Earths magnetic field, for the first time ever, as an enhancement in flux from the direction where the field lines are pointing at the SOR. We then give a formulation to predict the brightness of the LGS as a function of direction and time of year. The fasor, itself, is continuously tunable to as fine as 60 femtometers (6×10-6 Angstroms) across the entire sodium D2 line (FWHM ~3 GHz) and is capable of pumping either the D2a or D2b feature with linear or circular polarization. Spectral scans will be shown. While saturation is now being seen for linear polarization, we have seen little, if any, saturation for circular polarization at higher laser powers, and circular produces more than twice the return of linear because of optical pumping. We have succeeded in closing the adaptive optics loop on this very bright LGS, resolving a 0.14 arcsec binary star in June 2006.
Date of Conference: September 10-14, 2006
Track: Lasers