859 research outputs found
Fermat's principle with complex refractive indices and local light-ray rotation
We describe local light-ray rotation in terms of complex refractive indices.
We show that Fermat's principle holds, and we derive an extended Snell's law.
The change in the angle of a light ray with respect to the normal to a
refractive-index interface is described by the modulus of the refractive-index
ratio, the rotation around the interface normal is described by the argument of
the refractive-index ratio.Comment: 3 pages, 2 figure
Perfect imaging with planar interfaces
We describe the most general homogenous, planar, light-ray-direction-changing sheet that performs one-to-one imaging between object space and image space. This is a nontrivial special case (of the sheet being homogenous) of an earlier result [Opt. Commun. 282, 2480 (2009)]. Such a sheet can be realized, approximately, with generalized confocal lenslet arrays
Quantifying metarefraction with confocal lenslet arrays
METATOYs can change the direction of light in ways that appear to, but do not
actually, contravene the laws of wave optics. This direction change applies
only to part of the transmitted light beam; the remainder gets re-directed
differently. For a specific example, namely confocal pairs of rectangular
lenslet arrays with no dead area between lenslets, we calculate here the
fractions of power of a uniform-intensity light beam incident from a specific
(but arbitrary) direction that get re-directed in different ways, and we derive
an equation describing this redirection. This will facilitate assessment of the
suitability of METATOYs for applications such as solar concentration. Finally,
we discuss similarities between the multiple refraction of light at the lenslet
arrays and multiple refraction and reflection of cold atoms at a barrier in the
presence of the light fields.Comment: 24 pages, 15 figure
Geometric limits to geometric optical imaging with infinite, planar, non-absorbing sheets
New ray-optical elements allow generalized refraction of light rays, but
geometry imposes limitations on possible mappings between the positions of an
object and its geometric image. Here I study the case of an infinite, planar,
non-absorbing sheet that images the entire three-dimensional space. The most
general case of such a sheet is equivalent to a thin lens with different
object- and image-sided focal lengths. Special cases include ordinary thin
lenses, confocal lenslet arrays, and negative refraction with n_2 = -n_1.Comment: 10 pages, 1 figur
Experimental demonstration of holographic three-dimensional light shaping using a Gerchberg-Saxton algorithm
We use a three-dimensional Gerchberg–Saxton algorithm (Shabtay (2003) Opt. Commun. 226 33) to calculate the Fourier-space representation of physically realizable light beams with arbitrarily shaped three-dimensional intensity distributions. From this representation we extract a phase-hologram pattern that allows us to create such light beams experimentally. We show several examples of experimentally shaped light beams
Metamaterials for light rays: ray optics without wave-optical analog in the ray-optics limit
Volumes of sub-wavelength electromagnetic elements can act like homogeneous
materials: metamaterials. In analogy, sheets of optical elements such as prisms
can act ray-optically like homogeneous sheet materials. In this sense, such
sheets can be considered to be metamaterials for light rays (METATOYs).
METATOYs realize new and unusual transformations of the directions of
transmitted light rays. We study here, in the ray-optics and scalar-wave
limits, the wave-optical analog of such transformations, and we show that such
an analog does not always exist. Perhaps, this is the reason why many of the
ray-optical possibilities offered by METATOYs have never before been
considered.Comment: 10 pages, 3 figures, references update
Co-word maps of biotechnology: an example of cognitive scientometrics
To analyse developments of scientific fields, scientometrics provides useful tools, provided one is prepared to take the content of scientific articles into account. Such cognitive scientometrics is illustrated by using as data a ten-year period of articles from a biotechnology core journal. After coding with key-words, the relations between articles are brought out by co-word analysis. Maps of the field are given, showing connections between areas and their change over time, and with respect to the institutions in which research is performed. In addition, other approaches are explored, including an indicator of lsquotheoretical levelrsquo of bodies of articles
Imaging with parallel ray-rotation sheets
A ray-rotation sheet consists of miniaturized optical components that
function - ray optically - as a homogeneous medium that rotates the local
direction of transmitted light rays around the sheet normal by an arbitrary
angle [A. C. Hamilton et al., arXiv:0809.2646 (2008)]. Here we show that two or
more parallel ray-rotation sheets perform imaging between two planes. The image
is unscaled and un-rotated. No other planes are imaged. When seen through
parallel ray-rotation sheets, planes that are not imaged appear rotated,
whereby the rotation angle changes with the ratio between the observer's and
the object plane's distance from the sheets.Comment: 8 pages, 6 figure
Ray-optical refraction with confocal lenslet arrays
Two parallel lenslet arrays with focal lengths f1 and f2 that share a common focal plane (that is, which are separated by a distance f1+f2) can refract transmitted light rays according to Snell's law, but with the 'sin's replaced with 'tan's. This is the case for a limited range of input angles and other conditions. Such confocal lenslet arrays can therefore simulate the interface between optical media with different refractive indices, n1 and n2, whereby the ratio η=-f2/f1 plays the role of the refractive-index ratio n2/n1. Suitable choices of focal lengths enable positive and negative refraction. In contrast to Snell's law, which leads to nontrivial geometric imaging by a planar refractive-index interface only for the special case of n1=±n2, the modified refraction law leads to geometric imaging by planar confocal lenslet arrays for any value of η. We illustrate some of the properties of confocal lenslet arrays with images rendered using ray-tracing software
Local light-ray rotation
We present a sheet structure that rotates the local ray direction through an
arbitrary angle around the sheet normal. The sheet structure consists of two
parallel Dove-prism sheets, each of which flips one component of the local
direction of transmitted light rays. Together, the two sheets rotate
transmitted light rays around the sheet normal. We show that the direction
under which a point light source is seen is given by a Mobius transform. We
illustrate some of the properties with movies calculated by ray-tracing
software.Comment: 9 pages, 6 figure
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