Broadband Absorption Spectroscopy via Excitation of Lossy Resonance Modes in Thin Films

It is shown that broadband absorption spectroscopy utilizing thin lossy film configurations can be optimally facilitated when applied to metallic and insulating materials. For metallic films, the zero-order highly lossy resonance mode, characterized by ultra wideband absorption behavior under normal incidence, can be shifted, under parallel-polarization oblique incidence, toward a narrow band light-wavelength surface plasmon resonance condition. Higher order low-loss modes, however, occur in thin insulating films, exhibiting Debye relaxation behavior, typical for many aqueous solutions and biological substances. They can be excited in a highly scalable and sensitive manner in various frequency bands, between light and radio frequencies.