  The Lick Observatory's Shane 3-meter telescope has been upgraded with a new
infrared instrument (ShARCS - Shane Adaptive optics infraRed Camera and
Spectrograph) and dual-deformable mirror adaptive optics (AO) system (ShaneAO).
We present first-light measurements of imaging sensitivity in the Ks band. We
compare measured results to predicted signal-to-noise ratio and magnitude
limits from modeling the emissivity and throughput of ShaneAO and ShARCS. The
model was validated by comparing its results to the Keck telescope adaptive
optics system model and then by estimating the sky background and limiting
magnitudes for IRCAL, the previous infra-red detector on the Shane telescope,
and comparing to measured, published results. We predict that the ShaneAO
system will measure lower sky backgrounds and achieve 20\% higher throughput
across the $JHK$ bands despite having more optical surfaces than the current
system. It will enable imaging of fainter objects (by 1-2 magnitudes) and will
be faster to reach a fiducial signal-to-noise ratio by a factor of 10-13. We
highlight the improvements in performance over the previous AO system and its
camera, IRCAL.
