Agif/Laser.gif Wave refraction in negative index media: always positive and very inhomogeneous.

A Quick Introduction

A laser beam aimed into regular water is bent positively, i.e., on opposite side of the perpendicular to water surface) by refraction.

Prior to our work, researchers thought that a laser beam aimed into left handed water would refract negatively.

However, we have now proved that the inviolable requirements of causality or finite signal speed forbid such negative refraction of any actual waves by any real media.
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The work of Louis Pasteur in 1848 first revealed the importance of the “handedness” of materials (not being identical with its mirror image) in nature and on life itself. Thus, it was not surprising that the announcement in year 2000 of new electromagnetic materials to be called “left-handed” materials(LHMs) was highly publicized and generated widespread interest.

Unfortunately, LHMs are not left handed, the material itself is identical to its mirror image, it does not break chiral symmetry (the mirror image of left handed LHM is not right handed RHM). The real symmetry of interest is time reversal, not spatial or reflection symmetry: it is the temporal propagation of waves that is different in LHM from normal right-handed media (RHM).

Although they are not left-handed, these media do show an interesting topsy-turvy effect: they have a negative index of refraction (because of simultaneously negative e and m) in a narrow range of frequencies.

We therefore give a new name to these media: Negative Index Media (NIM).


To many scientists, starting with Veselago in 1968, this negative index appeared to permit a reversal in the angle of refraction of waves at the boundary between materials with different handedness. In this negative wave refraction a laser beam aimed into a glass of left handed water bends backwards as shown in the animation above.

This possibility stimulated numerous proposals to fabricate Utopian devices; like flat, “perfect” focusing lenses that transmit all incident light. This led to claims that such lenses would make it possible to record over 100 times more movies on a single DVD!

Our research uses the fundamental principle of causality (for example, nothing can arrive before it leaves) and the ultimate speed limit (speed of light) on all physical objects to show that no wave can refract negatively at the boundary between any two materials. All wave refraction is positive.

As history teaches, the discovery of materials with new properties always leads to useful ideas and applications. Our results will right the course of current efforts and keep researchers from becoming disoriented in the Looking Glass World of left handed materials.
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For contact and comments, email to pvalanju@mail.utexas.edu.
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