Submillimeter light carries information about the elusive Galactic magnetic field; the information is encoded in the light's polarization properties.

Our team is now in the process of adding polarization sensitivity to BLAST. The photo at right shows our new cryogenic half-wave plate rotator (recently developed at Northwestern University) installed in the BLAST receiver at U. Penn. Collaborators at Cardiff University are building the half-wave plate itself as well as the photolithographic polarizing grids that will mount in front of the bolometer arrays. The grids have alternating bands of vertical and horizontal polarizers, providing common-mode noise rejection via near-simultaneous detection of orthogonal polarization components. The broadband half-wave plate will have high modulation efficiency for all three frequency bands.

With these new components BLAST will be transformed into BLAST-pol, a new experiment aimed at revealing the large-scale magnetic fields of star forming molecular clouds. Our first flight is scheduled for December 2010, from McMurdo, Antarctica.