Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Microwave emission by nonlinear crystals irradiated with a
  high-intensity, mode-locked laser   We report on the experimental investigation of the efficiency of some
nonlinear crystals to generate microwave (RF) radiation as a result of optical
rectification (OR) when irradiated with intense pulse trains delivered by a
mode-locked laser at $1064\,$nm. We have investigated lithium triborate (LBO),
lithium niobate (LiNbO$_3$), zinc selenide (ZnSe), and also potassium titanyl
orthophosphate (KTP) for comparison with previous measurements. The results are
in good agreement with the theoretical predictions based on the form of the
second-order nonlinear susceptibility tensor. For some crystals we investigated
also the second harmonic generation (SHG) to cross check the theoretical model.
We confirm the theoretical prediction that OR leads to the production of higher
order RF harmonics that are overtones of the laser repetition rate.

7
The categories of this paper are: hep-th
34
The categories of this paper are: chem-ph
26
The categories of this paper are: bayes-an
18
The categories of this paper are: econ
31
The categories of this paper are: ao-sci
0
The categories of this paper are: hep-ph
12
The categories of this paper are: nucl-th
32
The categories of this paper are: atom-ph
13
The categories of this paper are: quant-ph
6
The categories of this paper are: astro-ph
33
The categories of this paper are: plasm-ph
22
The categories of this paper are: chao-dyn
23
The categories of this paper are: solv-int
5
The categories of this paper are: gr-qc
27
The categories of this paper are: comp-gas
11
The categories of this paper are: hep-lat