  TolTEC is a new camera being built for the 50-meter Large Millimeter-wave
Telescope (LMT) in Puebla, Mexico to survey distant galaxies and star-forming
regions in the Milky Way. The optical design simultaneously couples the field
of view onto focal planes at 150, 220, and 280 GHz. The optical design and
detector properties, as well as a data-driven model of the atmospheric emission
of the LMT site, inform the sensitivity model of the integrated instrument.
This model is used to optimize the instrument design, and to calculate the
mapping speed as an early forecast of the science reach of the instrument.
