MgF2 as a material exhibiting all-angle negative refraction and subwavelength imaging due to the phonon response in the far infrared

We consider the possibility of using MgF2 crystals as a suitable material for achieving all-angle negative refraction at far infrared frequencies. This possibility is associated with the highly anisotropic nature of the phonon response, leading to dielectric tensor components of opposing signs. The results show that this phenomenon should occur at somewhat lower frequencies than that of quartz, which has previously been investigated experimentally, but with relatively high efficiency. We also simulate subwavelength imaging, through canalization, at 247 cm−1, corresponding to the frequency of a transverse optical phonon polarized perpendicular to the extraordinary axis. Our simulations show that the Fabry–Pérot condition (use of a slab of thickness equal to an integral number of half-wavelengths) is not necessarily helpful in achieving subwavelength resolution.