Adaptive Optics for Extremely Large Telescopes 4 – Conference Proceedings

To date, modeling of sodium guidestar mesospheric excitation has assumed that the distribution within the sodium ground states (F = 1 or F = 2) and the distribution between the two ground states was well modeled by a Maxwell-Boltzmann distribution. Recent experimental evidence from Starfire Optical Range and the modeling results of Bhamre et al., show that the Maxwell-Boltzmann distribution is not a good approximation for the velocity distribution within ground states after optical excitation by a narrowband laser (linewidth < 1 MHz). A model is presented to account for the non-Boltzmann effects on the velocity groups of the Doppler profile of the mesospheric sodium atoms. The model is shown to agree fairly well with data provided from the 3.5m telescope and narrowband laser guidestar at Starfire Optical Range. These results challenge the efficacy of reducing the linewidth of sodium laser guidestars below 1 MHz.