  The Simons Observatory (SO) is a cosmic microwave background (CMB) experiment
from the Atacama Desert in Chile comprising three small-aperture telescopes
(SATs) and one large-aperture telescope (LAT). In total, SO will field over
60,000 transition-edge sensor (TES) bolometers in six spectral bands centered
between 27 and 280 GHz in order to achieve the sensitivity necessary to measure
or constrain numerous cosmological quantities. In this work, we focus on the
SATs which are optimized to search for primordial gravitational waves that are
detected as parity-odd polarization patterns called a B-modes on degree scales
in the CMB. Each SAT employs a single optics tube with TES arrays operating at
100 mK. The high throughput optics system has a 42 cm aperture and a 35-degree
field of view coupled to a 36 cm diameter focal plane. The optics consist of
three metamaterial anti-re ection coated silicon lenses. Cryogenic ring baffles
with engineered blackbody absorbers are installed in the optics tube to
minimize the stray light. The entire optics tube is cooled to 1 K. A cryogenic
continuously rotating half-wave plate near the sky side of the aperture stop
helps to minimize the effect of atmospheric uctuations. The telescope warm
baffling consists of a forebaffle, an elevation stage mounted co-moving shield,
and a fixed ground shield that together control the far side-lobes and
mitigates ground-synchronous systematics. We present the status of the SAT
development.
