  The first time simultaneous measurements of sodium column density and the
absolute flux from a sodium laser guide star, created by a monochromatic 3 W cw
laser, tuned to the peak of the sodium D2 hyperfine structure, were conducted
at the MMT and CFA 60 inch telescope in 1997. The results show that linearly
and circularly polarized laser returns are proportional to the simultaneous
sodium column density. Moreover, circularly polarized laser provides about 30%
increase in fluorescent return over linearly polarized laser. A laser guide
star with R = 10.3 mag. or absolute flux of 8.4x10^5 photons/s/m^2, could be
formed from a 1 watt projected circularly polarized sodium laser beam when
sodium layer abundance N(Na) = 3.7x10^9 /cm^2. Together with the distributed
column density measurements (e.g. seasonal and diurnal variations), we can
project laser power requirements for any specified guide star brightness.
  The mesosphere sodium column density variation was measured above Tucson sky
throughout the year, through sodium absorption line measurements in stellar and
solar spectra. Previous measurements, e.g. Papen et al, 1996, have not been
made at this latitude (32 degrees). Further, our absorption method is more
direct and may be more accurate than the lidar methods normally used. The
seasonal variation amplitude is smaller than that at higher latitudes. While
the annual mean sodium column density tends to be lower than at higher
latitudes. Diurnal sodium column density tends to vary by as much as a factor
of two within an hour.
