Multimodal Broadband Plasmonic Absorber With Densely Packed Metallic Nanostars

A nanoplasmonic absorber consisting of a metal-dielectric-metal stack with a top layer of densely packed nanostars is designed and numerically investigated. The multimodal absorber can achieve 91% average absorption efficiency in the wavelength range of 450-700 nm. Remarkably, super absorption exhibits desirable insensitivity to both incident angles and polarization states. Electric field intensity was significantly enhanced in a nanogap region between adjacent nanostars, corresponding to an electric field enhancement factor of up to 300. Broadband absorption is attributed to the excitation of multiple resonance modes. Underlying mechanisms of individual modes were well revealed by a thorough physical analysis. The proposed absorber shows great potentials to enhance performances of various optical or optoelectronic devices.