In General > s.a. dispersion; electricity; light.
* Idea: The bending of light when propagating in a medium in which the speed of lightvp varies with position; When it occurs at the boundary between two homogeneous media with different values of n, it is described by Snell's Law.
* Index of refraction: Defined by n(ω):= c/vp = k/kvacuum; For light, k = ω/c and n = c/v.
* Complex index of refraction: The imaginary part of the index of refraction gives the absorption length in a material.
@ References: Champenois et al PRA(08)-a0711 [matter waves in gases].
> Related topics: see Fermat's Principle; Snell's Law.
> Online resources: see Wikipedia page.

Negative Index of Refraction > s.a. meta-materials / electromagnetism in curved spacetime; Kramers-Kronig Relations.
* History: 1968, Existence of materials which bend light in the opposite direction to conventional materials (also known as left-handed materials) first proposed; 2000, Demonstrated for the first time in experiments; 2003, Several experiments and simulations demonstrated that negative refraction is real and that causality is not violated; 2005, New material discovered made from layers of superconducting and ferromagnetic thin films (until now, negative refraction had only been achieved in metamaterials and photonic crystals); Associated phenomena are a reverse Doppler shift and backward Cerenkov radiation and pressure.
@ General references: Veselago SPU(68); Smith et al PRL(00); Smith & Kroll PRL(00); Smith pw(03)may; Zhang et al PRL(03) + pw(03)oct; Pendry CP(04) [rev]; Pendry & Smith PT(04)jun; Lakhtakia & Mackay JPA(04) [vacuum, gravitationally assisted]; Lakhtakia & McCall NJP(05) [focus issue]; Ward et al NJP(05) [physical origin]; news pw(05)dec, SFN(06)may; McCall PRL(07) [not with gravity]; Ramm PLA(08)-a0710 [in acoustics], PLA(08) [no perfect lenses]; Plum et al PRB(09), Zhang et al PRL(09) + Wegener & Linden Phy(09); Guney & Meyer PRA(09)-a0907 [and Klein paradox]; Mackay & Lakhtakia PLA(09) [not a covariant notion]; Forcella et al PRL(17)-a1611 [and spatial non-locality]; Nguyen a1803 [mathematical results and applications].
@ Experiments, realizations: Shelby et al Sci(01)apr [experiment]; news pw(07)may [natural material]; Velázquez-Ahumada et al AJP(11)apr [for microwaves]; Amariti et al JHEP(13)-a1107 [in hydrodynamics, and applications to quark-gluon plasma], JHEP(11)-a1107 [and superconductivity].

Other Special Situations > s.a. Rainbow.
* Schlieren / shadowgraph imaging: A method that allows for visualizing transparent gas density variations.
@ General references: Gekelman et al AJP(11)sep [complex index of refraction, and plasma experiments].
@ Fluctuations in the medium: Kovadlo & Kochetkova a1101-conf [in Earth's atmosphere]; Gearhart & MacIsaac TPT(20) [classroom demo of Schlieren imaging].
@ Other variations: Jääskeläinen et al AJP(11)jun-a1012, Nazari & Nouri-Zonoz PRD(12)-a1110 [spacetime index of refraction].
> Gravity and curved-spacetime-related topics: see modified versions of QED [spacetime index of refraction]; photon phenomenology [curved spacetime].

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