Benefits of differential detection for nanoplasmonics

Here we describe a differential intensity interrogation method, where two measurements of the DTF are made simultaneously at unequal incident angles, and their difference is constructed. The zero crossing of the difference signal can be tracked with a tunable light source in a closed-loop system, similarly to the way in which beam position is tracked using quadrant detectors, resulting in an accurate and robust measurement. Our device also utilizes a metal film perforated with a 2-D array of nanoholes, as in Tetz et al. With this technique, SPP resonance can be achieved at normal or near-normal incidence, permitting measurement over a large area not limited by the focal depth of the imaging optics. The area can then be segmented into independent measurement channels, boosting device throughput.