Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Spectral engineering with multiple quantum well structures   It is shown that it is possible to significantly modify optical spectra of
Bragg multiple quantum well structures by introducing wells with different
exciton energies. The reflection spectrum of the resulting structures is
characterized by high contrast and tuning possibilities.

22
The categories of this paper are: chao-dyn
6
The categories of this paper are: astro-ph
23
The categories of this paper are: solv-int
37
The categories of this paper are: supr-con
28
The categories of this paper are: alg-geom
19
The categories of this paper are: eess
3
The categories of this paper are: physics
8
The categories of this paper are: hep-ex
35
The categories of this paper are: mtrl-th
16
The categories of this paper are: stat
13
The categories of this paper are: quant-ph
24
The categories of this paper are: dg-ga
14
The categories of this paper are: math-ph
18
The categories of this paper are: econ
17
The categories of this paper are: q-fin
10
The categories of this paper are: q-bio