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.