Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Strong terahertz radiation from relativistic laser interaction with
  solid density plasmas   We report a plasma-based strong THz source generated by using intense
femtosecond laser pulses to irradiate solid targets at relativistic intensity
>10^18W/cm2. Energies up to 50 microJ/sr per THz pulse is observed in the
specular direction when the laser pulses are incident onto a copper foil at
67.5 degree. The source appears to be linearly polarized. The temporal,
spectral properties of the THz are measured by a single shot, electro-optic
sampling method with a chirped laser pulse. The THz radiation is attributed to
the self-organized transient fast electron currents formed along the target
surface. Such a strong THz source allows potential applications in THz
nonlinear physics.

9
The categories of this paper are: nlin
4
The categories of this paper are: cond-mat
32
The categories of this paper are: atom-ph
11
The categories of this paper are: hep-lat
8
The categories of this paper are: hep-ex
18
The categories of this paper are: econ
14
The categories of this paper are: math-ph
30
The categories of this paper are: q-alg
0
The categories of this paper are: hep-ph
27
The categories of this paper are: comp-gas
24
The categories of this paper are: dg-ga
10
The categories of this paper are: q-bio
12
The categories of this paper are: nucl-th
31
The categories of this paper are: ao-sci
7
The categories of this paper are: hep-th
21
The categories of this paper are: adap-org