chapter  8
42 Pages

Veselago’s lens is a perfect lens

It was mentioned in Chapter 5 that a slab of negative refractive index material with n = −1 can have a lens-like action: this slab (of infinite transverse width) can form the image of a source located on one its side at two locations, one within itself and another on the opposite side of the source. We call this flat lens a Veselago lens after its original proposer (Veselago 1968). Its imaging action arises as a direct consequence of the negative refraction of a ray across a planar interface between positive and negative index media. An additional condition for a real image to be formed is that the sum of the distances from the source to the slab (d1) and the slab to the external image plane (d2) in the positive medium equals the thickness of the negative index slab (d = d1 + d2) as shown in Fig. 8.1. All this can be deduced with a simple ray analysis. The Veselago lens is a remarkable device: it maps each point on the object plane onto a point in the image plane and thus suffers from no geometrical aberrations. This lens is an example of an Absolute Instrument in geometric optics, preserves distances and angles in the image, and the imaging is projective (Caratheodory 1937). The image does, however, suffer from chromatic aberrations, given that media with negative refractive index are necessarily dispersive. The lens is also short-sighted and can only form images of objects placed within a distance d of the slab. The Veselago lens also accomplishes an image transfer while preserving the transverse translational symmetry, in contrast to conventional lenses, which have curved surfaces that enable them to image.