Fundamental limits to near-field optical response, over any bandwidth

Understand

We develop an analytical framework to derive upper bounds to light--matter interactions in the optical near field, where applications ranging from spontaneous-emission amplification to greater-than-blackbody heat transfer show transformative potential.

• Our framework connects the classic complex-analytic properties of causal fields with newly developed energy-conservation principles, resulting in a new class of power--bandwidth limits.
• These limits demonstrate the possibility of orders-of-magnitude enhancement in near-field optical response with the right combination of material and geometry.
• At specific frequency and bandwidth combinations, the bounds can be closely approached by canonical plasmonic geometries, with the opportunity for new designs to emerge away from those frequency ranges.