Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: An optical phase-locking with large and tunable frequency difference
  based on vertical-cavity surface-emitting laser   We present a novel technique to phase-lock two lasers with controllable
frequency difference. In our setup, one sideband of a current modulated
Vertical-Cavity Surface-Emitting Laser (VCSEL) is phase locked to the master
laser by injection seeding, while another sideband of the VCSEL is used to
phase lock the slave laser. The slave laser is therefore locked in phase with
the master laser, with a frequency difference tunable up to about 35 GHz. The
sideband suppression rate of the slave laser is more than 30dB at 30 uW seed
power. The heterodyne spectrum between master and slave has a linewidth of less
than 1 Hz. A coherent population trapping resonance of rubidium is achieved
using such beams.

37
The categories of this paper are: supr-con
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The categories of this paper are: funct-an
12
The categories of this paper are: nucl-th
0
The categories of this paper are: hep-ph
36
The categories of this paper are: cmp-lg
33
The categories of this paper are: plasm-ph
1
The categories of this paper are: cs
24
The categories of this paper are: dg-ga
5
The categories of this paper are: gr-qc
22
The categories of this paper are: chao-dyn
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The categories of this paper are: bayes-an
23
The categories of this paper are: solv-int
13
The categories of this paper are: quant-ph
10
The categories of this paper are: q-bio
4
The categories of this paper are: cond-mat
18
The categories of this paper are: econ