Characteristics of sodium guidestars created by the 50-watt FASOR and first closed-loop AO results at the Starfire Optical Range
2006
A computer-automated cw sodium guidestar FASOR (Frequency Addition Source of Optical Radiation) producing a
single frequency 589-nm beam with up to 50 W for mesospheric beacon generation has been integrated with the 3.5-m
telescope at the Starfire Optical Range, Kirtland AFB, New Mexico. Radiance tests have produced a peak guidestar V 1
magnitude = 5.1 (~7000 photons/s/cm 2 at zenith) for 30 W of circularly polarized pump power in November 2005. Estimated
theoretical maximum guidestar radiance is about 3 times greater than measured values indicating saturation due
to atoms possibly becoming trapped in F'=1 and/or atomic recoil. From sky tests over 3.5 years, we have tracked the
annual variation of the sodium column density by measuring the return flux as a function of fasor power and determining
the slope at zero power. The maximum occurs on October 30 and the minimum on May 30, with corresponding predicted
returns of 8000 (V 1 = 4.8) and 3000 (V 1 = 5.8) ph/s/cm 2 with 50 W of fasor power and circular polarization. The
effect of the Earth's magnetic field on the radiance of the sodium laser guidestar (LGS) from various azimuths and elevations
has been measured. The peak return flux over our observatory occurs at [az=198 o ; el=+71 o ], compared with the
direction of the magnetic field lines at [190 o ; +62 o ], and it can vary by a factor of 3 over the sky above el = 30 o . First
results for non-optimized sodium LGS adaptive optics (AO) closed-loop operation have been obtained using binary
stars. Strehl ratios of 0.03 have been measured at 850 nm and a 0.14 arc second binary star has been resolved during
first closed loop observations. Guidestar characteristics, including radiance, size, and Rayleigh backscatter, the sodium
LGS wavefront sensor (WFS) AO system, and recent closed-loop results on binary stars are presented.
Keywords:
- Correction
- Source
- Cite
- Save
- Machine Reading By IdeaReader
6
References
21
Citations
NaN
KQI