Modeling and Measuring the Optical Coupling of Lumped Element Kinetic Inductance Detectors at 120–180 GHz

The lumped element kinetic inductance detector (LEKID) is a novel device for high-sensitivity millimeter and submillimeter wave detection. Optimization of this cryogenic device requires the matching of the freespace impedance to the impedance of the absorbing structure defined by an inductance meander. Here we show how this coupling can be modeled and measured using a transmission line model, numerical simulations, and practical quasi-optical room-temperature reflection measurements. Simulations and measurements agree well and allow us to design optimized devices with remarkably high power absorption.