Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Second-harmonic generation in germanium-on-insulator from visible to
  telecom wavelengths   The second-order $\chi^{2}$ process underpins many important nonlinear
optical applications in the field of classical and quantum optics. Generally,
the $\chi^{2}$ process manifests itself only in a non-centrosymmetric
dielectric medium via an anharmonic electron oscillation when driven by an
intense optical field. Due to inversion symmetry, group-IV semiconductors like
silicon (Si) and germanium (Ge) are traditionally not considered as ideal
candidates for second-order nonlinear optics applications. Here, we report the
experimental observation of the second-harmonic generation (SHG) in a
Ge-on-insulator (GOI) sample under femtosecond optical pumping. Specially, we
report the first-time measurement of the SHG signal from a GOI sample in the
telecom S-band by pumping at $\sim$$3000$ nm.

12
The categories of this paper are: nucl-th
16
The categories of this paper are: stat
36
The categories of this paper are: cmp-lg
26
The categories of this paper are: bayes-an
9
The categories of this paper are: nlin
2
The categories of this paper are: math
34
The categories of this paper are: chem-ph
29
The categories of this paper are: funct-an
23
The categories of this paper are: solv-int
10
The categories of this paper are: q-bio
20
The categories of this paper are: acc-phys
1
The categories of this paper are: cs
13
The categories of this paper are: quant-ph
19
The categories of this paper are: eess
35
The categories of this paper are: mtrl-th
8
The categories of this paper are: hep-ex