A broadband air gap polarization prism design based on Hg₂Cl₂, Hg₂Br₂, and Hg₂I₂ crystals is suggested. Spectral ranges of operation extend from visible light up to 40  μm, and strong birefringence of the materials makes it possible to optimize the crystal cut geometry. Results include a large symmetric field of view up to 20 deg wide within the entire mid- and far-infrared transparency range, as well as a power transmittance of more than 80%. The transmittance is determined by the Fresnel reflection at the entrance and exit windows. Furthermore, it can be improved by optional antireflection coatings; losses in the air gap do not exceed 1%. Due to a combination of useful properties, the suggested design significantly outperforms commonly available crystal polarizers.