The Cosmology Large Angular Scale Surveyor (CLASS)
Precise observations of the cosmic microwave background have played a leading role in the development of the LCDM model of cosmology, which has been successful in describing the universe’s energy content and evolution using a mere six parameters. With this progress have come hints that the universe underwent an inflationary epoch during its infancy. Cosmic inflation is predicted to produce a background of gravitational waves that would imprint a distinct polarized pattern on the cosmic microwave background (CMB). Measurement of this polarized signal would provide the first direct evidence for inflation and would provide a means to study physics at energy scales around the predicted GUT scale.
The Cosmology Large Angular Scale Surveyor (CLASS) is an array of telescopes located in the Atacama Desert in Chile that is designed to map the large-scale polarization of the cosmic microwave background to test the inflation paradigm. CLASS will measure 70% of the sky at four frequency bands that straddle the Galactic foreground minimum. CLASS’s sensitivity to the large-scale signal is unique to ground-based instruments. It enables CLASS to probe the inflationary signal on angular scales where its magnitude is above contamination due to gravitational lensing and provides a complement to the measurements from current and future high-resolution CMB experiments.
CLASS is enabled by two technology innovations. First, high-sensitivity focal planes have been developed to meet the sensitivity and systematic control requirements of this measurement. Second, measurement of the large-scale polarization requires fast polarization modulation to stabilize the signal. For this, large variable-delay polarization modulators (VPMs) have been developed.
In this talk, I will provide an overview of CLASS, including its targeted science goals, instrument design, and descriptions of its key technologies.