Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Ultrafast modulation in a THz graphene-based flat absorber through
  negative photoconductivity   We present the experimental and theoretical study of an ultrafast graphene
based thin film absorption modulator for operation in the THz regime. The flat
modulator is composed of a graphene sheet placed on a dielectric layer backed
by a metallic back reflector. A near IR pulse induces the generation of hot
carriers in the graphene sheet reducing effectively its conductivity. The
system provides a platform with ultrafast modulation capability for flat optics
and graphene based metasurfaces applications.

15
The categories of this paper are: nucl-ex
8
The categories of this paper are: hep-ex
2
The categories of this paper are: math
17
The categories of this paper are: q-fin
11
The categories of this paper are: hep-lat
33
The categories of this paper are: plasm-ph
4
The categories of this paper are: cond-mat
32
The categories of this paper are: atom-ph
21
The categories of this paper are: adap-org
18
The categories of this paper are: econ
6
The categories of this paper are: astro-ph
27
The categories of this paper are: comp-gas
29
The categories of this paper are: funct-an
0
The categories of this paper are: hep-ph
19
The categories of this paper are: eess
25
The categories of this paper are: patt-sol