# Negative Refractive index

1. Nov 2, 2004

### saiarun

Negative Refractive index!!!

Is negative refractive index possible(theoretically,in optics). If so what are its implications?

2. Nov 3, 2004

### Galileo

The angle of incidence and the angle of refraction are always between 0 and pi, so their sine is never negative.
If I look at Snell's law:
$$\frac{\sin\theta_i}{\sin\theta_t}=\frac{n_t}{n_i}$$
where $n_i,n_t$ are the refractive indices, the answer is clearly no. It wouldn't make physical sense.

3. Nov 3, 2004

### OldTee

Negative refractive index has been demonstrated in some meta-material recently, it's still a hot topic of research though. Have a look at http://physicsweb.org/articles/news/7/10/10 and http://physics.ucsd.edu/lhmedia/ [Broken]. There're a whole lot more information available by googling.
Snells law still holds, by inserting a negative n you'll get a negative angle, meaning that the refraction angle is actually on the same side as the incident angle.

Last edited by a moderator: May 1, 2017
4. Nov 3, 2004

### Galileo

Pretty cool.

That's why I love physics.

5. Nov 7, 2004

### Claude Bile

The Kramers-Kronig relationships also predict regions of the spectrum where the refractive index of a material is negative, however, these regions also correspond to regions of high absorption (It is argued that because of this, relativity is not violated).

Claude.

6. Dec 9, 2004

### lalbatros

When a material doesn't propagate a wave and doesn't absorb it, it has a negative refractive index.

In that case, the wave impiging on the material doesn't penetrate much inside the material.
Typically over a fraction of wavelength to a few wavelengths. The wave is said "evanescent".

Plasmas offer a good exemple. Below the 'plasma frequency' no wave can propagate. For higher frequency propagation is the rule.
In magnetised plasma things are much more complex.
There are bands of evanescence and bands of propagation. In additions, these bands depend on the direction of the wave and the polarisation.
The refractive index is then a matrix called "dielectric tensor".