Does Nature Allow Negative Refraction with Low Losses in Optical Region?

TL;DR

This paper derives a causality-based criterion for negative refraction that sets fundamental limits on material losses, indicating that reducing losses may eliminate negative refraction in optical materials.

Contribution

It provides a rigorous causality-based criterion for negative refraction, linking material losses to the fundamental feasibility of negative refraction in optical media.

Findings

Lower limits on electric and magnetic losses are established by causality.

Reducing or compensating losses can eliminate negative refraction.

The criterion aids in designing and testing new left-handed materials.

Abstract

From the fundamental requirement of causality, we derive a rigorous criterion of negative refraction (left-handedness). This criterion imposes the lower limits on the electric and magnetic losses in the region of the negative refraction. If these losses are eliminated or significantly reduced by any means, including the compensation by active (gain) media, then the negative refraction will disappear. This theory can be particularly useful in designing new left-handed materials: testing the expected polarizabilities of a medium against this criterion would check the compliance with the causality and verify the design feasibility.