Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Exciton spectroscopy of semiconductors by the method of optical
  harmonics generation   Nonlinear optical phenomena are widely used for the study of semiconductor
materials. The paper presents an overview of experimental and theoretical
studies of excitons by the method of optical second and third harmonics
generation in various bulk semiconductors (GaAs, CdTe, ZnSe, ZnO, Cu$_2$O,
(Cd,Mn)Te, EuTe, EuSe), and low-dimensional heterostructures ZnSe/BeTe.
Particular attention is paid to the role of external electric and magnetic
fields that modify the exciton states and induce new mechanisms of optical
harmonics generation. Microscopic mechanisms of harmonics generation based on
the Stark effect, the spin and orbital Zeeman effects, and on the magneto-Stark
effect specific for excitons moving in an external magnetic field are
considered. This approach makes it possible to study the properties of excitons
and to obtain new information on their energy and spin structure that is not
available when the excitons are investigated by linear optical spectroscopy. As
a result of these studies, a large amount of information was obtained, which
allows us to conclude on the establishing of a new field of research - exciton
spectroscopy by the method of optical harmonics generation.

35
The categories of this paper are: mtrl-th
8
The categories of this paper are: hep-ex
22
The categories of this paper are: chao-dyn
33
The categories of this paper are: plasm-ph
16
The categories of this paper are: stat
32
The categories of this paper are: atom-ph
0
The categories of this paper are: hep-ph
29
The categories of this paper are: funct-an
18
The categories of this paper are: econ
14
The categories of this paper are: math-ph
31
The categories of this paper are: ao-sci
25
The categories of this paper are: patt-sol
3
The categories of this paper are: physics
20
The categories of this paper are: acc-phys
27
The categories of this paper are: comp-gas
34
The categories of this paper are: chem-ph