Leveraging beam deformation to improve the detection of resonances

Decades of work on beam deformation on reflection and especially on lateral shifts have spread the idea that a reflected beam is larger than the incident beam. However, when the right conditions are met, a beam reflected by a multilayered resonant structure can be 10% narrower than the incoming beam. Such an easily measurable change occurs on a very narrow angular range close to a resonance, which can be leveraged to improve the resolution of sensors based on the detection of surface-plasmon resonances by a factor of 3. We provide theoretical tools to deal with this effect and a thorough physical discussion that leads to expect similar phenomena to occur for temporal wave packets and in other domains of physics.