An overview of optics design and beam characterization of the TolTEC camera

The TolTEC camera is an imaging polarimeter installed at the Large Millimeter Telescope (LMT) in Mexico. Coupled with the 50m LMT, this camera uses polarization-sensitive Kinetic Inductance Detectors (KIDs) to simultaneously create high resolution images at 1.1, 1.4, and 2.0 mm wavelengths. Light collected by the telescope is directed through the window of the cryostat using three large, room temperature mirrors. Then a series of 4K optics splits the light into three frequency bands and guides them to the three detector arrays. We describe the alignment procedure for the room temperature optics used during the first commissioning run in December 2022 which determines how well the light is coupled between the telescope and the camera. A liquid nitrogen source was used to determine the location of the beam center at each of the three mirrors. The angular positions were adjusted using a tip-tilt mechanism attached to the back of each mirror until the beams were correctly positioned. We then characterized the beam at two points along the optics path using a scannable, chopped IR source to create beam maps. We present the resulting diffraction-limited beam maps and focus curves for mm-wave calibration sources observed by the Toltec camera coupled to the LMT.

Toltec is completing commissioning now and beginning to acquire data for a set of legacy science surveys. TolTEC’s images in three mm-wave bands are especially suited for studying CMB anisotropies such as the Sunyaev-Zel’dovich effect and dust emission. As an example of the unique capability of the Toltec survey data, we estimate the capability of the initial legacy survey data to distinguish between models of energy deposition from AGN feedback by stacking a selection of high redshift, quiescent galaxies and measuring the SZ and dust profiles at cosmic noon.