Negative index of refraction

Apart from SNOM (or NSOM), two new, highly resolving techniques are emerging that deserve brief mention here. These are stimulated emission depletion (STED) using focal and doughnut-focal beam shapes, and the microscopy with super lenses out of negative index of refraction materials (NIMs). 

In the theoretically analyzed NIM technique, objects are imaged with a resolution much smaller than the illuminating wavelength, because NIMs, unlike conventional materials, make light to refract inward rather than outward, due to the negative index of refraction." Flat nanolenses of this kind can be used as light couplers in nanooptics. This does, however, not signify a behavior of the surface material, but is rather a particular super lens effects. Practical applications are to be expected. 

NIM Negative index of refraction material used for the construction of superlenses. 

Figure 7.1. Paired metallic nanorods that exhibits negative index of refraction in the visible spectrum.

R.B. Greegor, C.G. Parazzoli, K. Li, and M.H. Tanielian, Origin of dissipative losses in negative index of refraction materials. Applied Physics Letters, Vol. 82, pp. 2356-2358,2003. 

With the recommended procedure well-developed, clear hexagonal dipyramidal crystals of hydroxyapatite, ranging up to 0.3 mm. in length, have been obtained. The crystals are uniaxial negative with index of refraction e = 1.643 0.002 and Atomic parameters and unit cell dimensions as measured by x-ray diffraction are published elsewhere.6... 

Across real surfaces and interfaces, the dielectric response varies smoothly with location. For a planar interface normal to a direction z, we can speak of a continuously changing s(z). More pertinent to the interaction of bodies in solutions, solutes will distribute nonuniformly in the vicinity of a material interface. If that interface is charged and the medium is a salt solution, then positive and negative ions will be pushed and pulled into the different distributions of an electrostatic double layer. We know that solutes visibly change the index of refraction that determines the optical-frequency contribution to the charge-fluctuation force. The nonuniform distribution of solutes thereby creates a non-uniform e(z) near the interfaces of a solution with suspended colloids or macromolecules. Conversely, the distribution of solutes can be expected to be perturbed by the very charge-fluctuation forces that they perturb through an e(z).5... 

Fig. 6.2. A general multilayer structure with m layers between a semi-finite transparent ambient and a semi-infinite substrate. Each layer j (j = 1,2,..., m) has thickness dj and its optical properties are described by its complex index of refraction. The optical electric field at any point in layer j is n represented by two components one propagating in the positive x direction and one propagating in the negative x direction...

The direction of the principal axes of the index of refraction tensor n can be described by the indicatrix. For isotropic crystals the indicatrix is a sphere. For positive uniaxial crystals it is a prolate spheroid (ns > n0j) for negative uniaxial crystals it is an oblate spheroid (nol > n,). For orientations away from the principal axis orientations, the extraordinary ray will have a refractive index h - intermediate between nm and ne. 

Index of Refraction Magnesite is uniaxial negative and when pure has refractive indices, for sodium light of r]0 = 1.700 and rje = 1.509. It fluoresces on irradiation with X rays. 

The difference between index of refraction in two directions, measured with polarized light. The birefringence originates in the molecular orientation in either a glassy or crystalline phase. Positive birefringence occurs when the principal optic axis lies along the chain and negative when it is perpendicular. See also Dichroism. ... 

In the previous section we showed (Equation 24.12) that the index of refraction was simply the square root of the dielectric constant and, since the dielectric constant is a function of frequency and can become negative, the index of refraction is a function of frequency and may be complex. Summarizing,... 

Khoo, I. C., D. H. Werner, X. Liang, A. Diaz, andB. Weiner. 2006. Nano-sphere dispersed liquid crystals for tunable negative-zero-positive index of refraction in the optical and terahertz regimes. Optics Letts. 31 2592. 

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