Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Optical nonlinearity due to intersubband transitions in semiconductor
  quantum wells   We have calculated the contribution of intersubband transitions to the third
order optical nonlinear susceptibility, $\chi^{(3)}(\omega,\omega,\omega)$ for
nonresonant as well as resonant third harmonic generation and
$\chi^{(3)}(\omega,-\omega,\omega)$ for nonlinear refraction and absorption. As
examples, we consider InAs/AlSb and GaAs/GaAlAs quantum wells. The effects of
finite barrier height, energy band nonparabolicity, and high carrier
concentrations are included. It is shown that quantum confinement, rather than
the band nonparabolicity, is responsible for high values of nonresonant
$\chi^{(3)}_{zzzz}$. Very high values of $\chi^{(3)}_{zzzz}$ are obtained for
third harmonic generation and two photon absorption for incident wavelength
near 10.6 $\mu$m. Intensity dependence of refractive index and of absorption
co-efficient is also discussed for intensity well above the saturation
intensity. Effective medium theory is used to incorporate the collective
effects.

26
The categories of this paper are: bayes-an
35
The categories of this paper are: mtrl-th
7
The categories of this paper are: hep-th
3
The categories of this paper are: physics
20
The categories of this paper are: acc-phys
24
The categories of this paper are: dg-ga
9
The categories of this paper are: nlin
16
The categories of this paper are: stat
5
The categories of this paper are: gr-qc
6
The categories of this paper are: astro-ph
23
The categories of this paper are: solv-int
1
The categories of this paper are: cs
22
The categories of this paper are: chao-dyn
15
The categories of this paper are: nucl-ex
13
The categories of this paper are: quant-ph
12
The categories of this paper are: nucl-th