Mitigation of the spectral dependent polarization angle response for
  achromatic half-wave plate
  Polarimetry using a half-wave plate (HWP) modulator provides the strong tools
to avoid a detector 1/f noise and instrument-originated spurious polarization
systematic effects. While the Pancharatnam achromatic HWP (AHWP) is commonly
used for an application that needs a broadband frequency coverage, this
technique introduces a frequency-dependent polarization angle rotation. In this
paper we propose a new technique to mitigate this effect by introducing a
second set of an AHWP. One rotational and one stationary set of AHWPs achieve a
broadband coverage of modulation efficiency without the frequency-dependent
polarization angle rotation. We conducted measurements by using three layers of
sapphire wave plates and demonstrated this technique at millimeter wavelengths
between 72 and 162 GHz. We also discuss a potential application in the CMB
polarization experiment based on numerical simulations.
