Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Fast Reflective Optic-Based Rotational Anisotropy Nonlinear Harmonic
  Generation Spectrometer   We present a novel Rotational Anisotropy Nonlinear Harmonic Generation
(RA-NHG) apparatus based primarily upon reflective optics. The data acquisition
scheme used here allows for fast accumulation of RA-NHG traces, mitigating low
frequency noise from laser drift, while permitting real-time adjustment of
acquired signals with significantly more data points per unit angle rotation of
the optics than other RA-NHG setups. We discuss the design and construction of
the optical and electronic components of the device and present example data
taken on a GaAs test sample at a variety of wavelengths. The RA-second harmonic
generation data for this sample show the expected four-fold rotational symmetry
across a broad range of wavelengths, while those for RA-third harmonic
generation exhibit evidence of cascaded nonlinear processes possible in
acentric crystal structures.

14
The categories of this paper are: math-ph
7
The categories of this paper are: hep-th
29
The categories of this paper are: funct-an
9
The categories of this paper are: nlin
6
The categories of this paper are: astro-ph
31
The categories of this paper are: ao-sci
36
The categories of this paper are: cmp-lg
10
The categories of this paper are: q-bio
19
The categories of this paper are: eess
13
The categories of this paper are: quant-ph
17
The categories of this paper are: q-fin
4
The categories of this paper are: cond-mat
25
The categories of this paper are: patt-sol
22
The categories of this paper are: chao-dyn
34
The categories of this paper are: chem-ph
15
The categories of this paper are: nucl-ex