Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Simultaneous measurement of circular dichroism and Faraday rotation at
  terahertz frequencies using heterodyne detection   A far-infrared system measures the full complex Faraday angle, rotation as
well as ellipticity, with an unprecedented accuracy of 10\,$\mu$rad/T. The
system operates on several far-infrared laser lines in the spectral range from
0.3 to 6 THz and produces results as a continuous function of temperature from
10 to 310K and applied fields between $\pm$ 8\,T. Materials successfully
measured include GaAs 2-DEG heterostructures, various high temperature
superconductors including Bi$_2$Sr$_2$CaCu$_2$O$_{8+x}$, Pr$_{2 -
x}$Ce$_{x}$CuO$_4$, and La$_{2-x}$Sr$_x$CuO$_4$, and single crystals of the
topological insulator Bi$_2$Se$_3$.

2
The categories of this paper are: math
5
The categories of this paper are: gr-qc
9
The categories of this paper are: nlin
34
The categories of this paper are: chem-ph
25
The categories of this paper are: patt-sol
31
The categories of this paper are: ao-sci
13
The categories of this paper are: quant-ph
22
The categories of this paper are: chao-dyn
20
The categories of this paper are: acc-phys
28
The categories of this paper are: alg-geom
1
The categories of this paper are: cs
0
The categories of this paper are: hep-ph
23
The categories of this paper are: solv-int
18
The categories of this paper are: econ
15
The categories of this paper are: nucl-ex
17
The categories of this paper are: q-fin