Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Subwave length light focusing by surface plasmons on a silver film   Two devices for subwave length focusing of light are explored. The first one
is a thin film of a well reflecting metal which the converging beam of surface
plasmons with a wave number $h>>\omega_0/c$ is excited on. The waist of this
beam has a cross section that is much smaller than $\lambda_0^2$. The second
device is a linear nanoantenna with a gap in the middle. A resonance plasmon is
excited in the antenna. The field in the gap concentrates on the spot that is
much smaller than $\lambda_0^2$. In both cases the effect of field enhancement
in the spot of subwave length focusing is greatly decreased because of
propagation losses in the first case and because of a small excitation cross
section in the second case. It is suggested to improve on the effect of
excitation of the film and the nanoantenna by means of interaction with an
adjacent atom or quantum dot.

16
The categories of this paper are: stat
19
The categories of this paper are: eess
27
The categories of this paper are: comp-gas
23
The categories of this paper are: solv-int
37
The categories of this paper are: supr-con
1
The categories of this paper are: cs
24
The categories of this paper are: dg-ga
2
The categories of this paper are: math
5
The categories of this paper are: gr-qc
0
The categories of this paper are: hep-ph
18
The categories of this paper are: econ
35
The categories of this paper are: mtrl-th
4
The categories of this paper are: cond-mat
36
The categories of this paper are: cmp-lg
6
The categories of this paper are: astro-ph
8
The categories of this paper are: hep-ex