Optics design development of the Simons Observatory Small Aperture Telescopes

The Simons Observatory (SO) will be a cosmic microwave background (CMB) survey experiment with three small-aperture telescopes (SATs) and one large-aperture telescope, which will observe from the Atacama Desert in Chile. In total, SO will field over 60,000 bolometers in six spectral bands centered between 27 and 280 GHz. The SATs are designed to target the primordial B-mode polarization signal. The SATs adopt a three metamaterial anti-reflection coated Silicon lens refractor design each with a 42 cm aperture and 35 degree field-of-view. We discuss the optics design development and optimization process of the SAT refractor system and warm baffling.