Broad-angle coherent perfect absorption-lasing and collimation in two-dimensional non-Hermitian phononic crystals

Abstract Coherent perfect absorption-lasing and collimation have been extensively studied primarily for normal incidence, leaving broad-angle scenarios relatively unexplored. In this work, we investigate a two-dimensional non-Hermitian phononic crystal, aiming to achieve broad-angle coherent perfect absorption-lasing and collimation. Our approach involves orchestrating a parity-time phase transition in the band structure through a combination of non-symmorphic glide symmetry in the lattice, gain-loss modulation, and engineering of the band structure. In both the real and imaginary parts of the band structure, exceptional points form a slab-like contour with nearly zero dispersion along the boundary of the Brillouin zone. As a result, the range of incidence angles for coherent perfect absorption-lasing and collimation is significantly expanded at the frequency of the exceptional points.