Keck Array
Keck Array is a ground based polarimeter located at the South Pole. It consists of five receivers, which are aimed to measure primordial B-mode polarization imprinted on the CMB. Each receiver consists of orthogonal pairs of antenna-coupled transition edge sensor (TES) bolometers. Together with BICEP3, the BICEP/Keck program of telescopes observe the polarization of the CMB from 95GHz to 270GHz.
![Keck Array telescope (1 of 5)](https://caltechsites-prod.s3.amazonaws.com/cosmology/images/b2_instrument_fig4.original.png)
Keck Array observes from the South Pole, where the atmospheric loading is consistently very low. Optics are cryogenically cooled for very low internal loading. Sub-kelvin bolometers are photon-noise limited, while low optical loading keeps photon noise low. Systematics are minimized due to using a small, on-axis refracting telescope, while the detectors can be characterized the optical far field.
![Keck Array field team](https://caltechsites-prod.s3.amazonaws.com/cosmology/images/_81497976_jamiebock-thekeckarrayfittedwithnewre.original.jpg)
Here is a nice video showing our observing strategy.