Electromagnetic analysis of lens coupled LEKID detectors for THz astronomical applications

An EM study of the absorption efficiency of lens coupled LEKID detectors is presented in this contribution. The field at the focal plane of a lens can be expanded in a plane wave spectrum. The incident plane wave can be represented as superposition of TE and TM spectral components. Therefore, the incident and reflected power of each component can be related to the integration of the incident and reflected voltage waves, respectively, obtained from an equivalent circuit, times the incident field plane wave spectrum. The absorption efficiency of lens coupled LEKID can then be related to the ratio between losses and the incident power. Efficiencies above 90% have been obtained in a range of about 2.5 octaves, considering silicon lens and placing air behind the detector and a backing reflector.