The effect of a scanning flat fold mirror on a CMB B-mode experiment
  We investigate the possibility of using a flat-fold beam steering mirror for a CMB B-mode experiment. An aluminium flat-fold mirror is found to add $\sim$0.075% polarization, which varies in a scan synchronous way. Time-domain simulations of a realistic scanning pattern are performed, and the effect on the power-spectrum illustrated and a possible method of correction applied. 
William F. Grainger, Chris E. North, Peter A. R. Ade
astro-ph.IM astro-ph.CO