Negative refraction and photonic-crystal optics in a cold gas

Abstract

We describe propagation of light in a gas with periodic density modulation, demonstrating photonic-crystal-like refraction with negative refraction angles. We address the role of poorly defined boundaries and damping, and derive an optical analog of the quantum adiabatic theorem. For Cs atoms in an optical lattice, we show that relying on semi-adiabatic propagation one can excite and spatially split positively and negatively refracting modes at experimentally available gas densities.

Limits and possibilities of refractive index in atomic systems

“…For optical wavelengths, this would require a density on the order of 10 14 atoms per cm 3 . The susceptibility could be theoretically increased by increasing the density, but values greater than 10 14 cm -3 are not realistically possible [12,21]. At such high densities, collisions and nonlinear effects become dominant compared to the linear contribution to the dispersion, so this simple model is no longer valid [10,[22][23][24].…”

“…Since then, there have been increasing efforts to modify the index of refraction of a system or to attain a particular value through the design of metamaterials [6][7][8] or control by external fields [9][10][11][12]. Such unusual values for the index have been suggested for use in various applications; for example, a negative index could be used to implement cloaking [13][14][15][16] or to create a "perfect lens" with infinite resolution [17,18], while a medium with a large index decreases the wavelength of light traveling through it, which could be useful in optical imaging [19].…”