Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Flat lens without optical axis: Theory of imaging   We derive a general theory for imaging by a flat lens without optical axis.
We show that the condition for imaging requires a material having elliptic
dispersion relations with negative group refraction, equivalent to an effective
anisotropic refractive index n(theta). Imaging can be achieved with both
negative (n<0) and positive (n>0) refractive indices. The Veselago-Pendry lens
is a special case with isotropic negative refractive index of n(theta)=-1.
Realizations of the imaging conditions using anisotropic media and
inhomogeneous media, particularly photonic crystals, are discussed. Numerical
examples of imaging and requirements for sub-wavelength imaging are also
presented.

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The categories of this paper are: nucl-ex
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The categories of this paper are: patt-sol
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The categories of this paper are: astro-ph
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The categories of this paper are: quant-ph
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The categories of this paper are: gr-qc
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The categories of this paper are: adap-org
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The categories of this paper are: acc-phys
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The categories of this paper are: cs
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The categories of this paper are: stat
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The categories of this paper are: eess
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The categories of this paper are: math
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The categories of this paper are: q-fin
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The categories of this paper are: physics
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The categories of this paper are: chao-dyn
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The categories of this paper are: bayes-an
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The categories of this paper are: funct-an