Frequency difference lock-in phenomenon’s weakening
by transverse magnetic field in Y-shaped cavity
dual-frequency laser
Guangzong Xiao (肖光宗)*, Bin Zhang (张 斌), Zhiguo Wang (汪之国),
Yangying Fu (傅杨颖), and Mengfan Gong (龚梦帆)
College of Optoelectronic Science and Engineering, National University of Defense Technology, Changsha 410073, China
*Corresponding author: xiaoguangzong@nudt.edu.cn
Received July 3, 2015; accepted September 29, 2015; posted online October 16, 2015
We report experimental progress in weakening the frequency difference lock-in phenomenon in a Y-shaped cavity
dual-frequency laser. A cube coil pair is chosen to provide a uniform magnetic field for tunability and uniformity
of magnetic field strength. When the transverse magnetic field intensity is 9 mT, the frequency difference lock-in
phenomenon is evidently weakened and the frequency difference can be continuously tuned in the range of
0.12 MHz to 1.15 GHz. Moreover, the relationship between the minimal frequency difference and magnetic field
intensity are investigated and discussed. Then a Y-shaped cavity dual-frequency laser is expected to be utilized
as an optimum light source for heterodyne interferometric sensing and precise laser measurement.
OCIS codes: 140.0140, 140.1340, 140.3460.
doi: 10.3788/COL201513.111405.
Orthogonally polarized dual-frequency lasers are widely
applied in two-frequency interferometers, ellipsometers,
displacement measurement, wave plate measurement, and
other measuring systems
[1–5]
. However, for the He-Ne laser
transitions there exists a lock-in frequency difference
below which one of the polarized waves dies because of the
strong competition among waves
[6,7]
.
Doyle and White pointed out that t he mode competi-
tion could be overcome by the presence of a small
magnetic field that is normal to the laser axis
[8]
. Gudelev
and Yasinskiı˘ experimentally investigated the lasing char-
acteristics of the two-frequency He-Ne laser with an active
medium located in a homogeneous transverse magnetic
field
[9]
. They confirmed that the transverse magnetic field
is an effective means of weakening the interaction of the
orthogonally polarized waves.
Zhang et al. studied the Zeeman birefringence-type
dual-frequency laser based on both the Zeeman effect
and intracavity birefringence
[10,11]
. They applied a trans-
verse magnetic field to decrease the mode competition
and obtained the full frequency difference output from
approximately 1 MHz to hundreds of MHz
[12]
.
In 2011, our group developed a novel dual-frequency
laser based on the Y-shaped cavity; this laser was called
a Y-shaped cavity dual-frequency laser, and we studied its
characteristics
[13–15]
. Subsequently, the progress of research
on its applications has been rapid. Micro-force measure-
ments achieved a resolution of 10
−5
N using the Y-shaped
cavity dual-frequency laser
[16]
. A novel approach for accel-
eration measurement has been demonstrated based on this
type of laser. The investigation indicated that an acceler-
ation measurement resolution of 10
−5
–10
−6
g in the range
of 5 g can be expected
[17]
. A new displacement measure-
ment configuration has been patented
[18]
.
Compared with other dual-frequency lasers with large
frequency differences based on the birefringence effect,
better frequency difference stability is expected in the
developed laser because no birefringent element is in its
cavity. Meanwhile, the frequency difference can be tuned
to a certain value for adjusting to different applications for
the abovementioned superiorities. The Y-shaped cavity
dual-frequency laser is expected to bring about a revolu-
tion in precision measurement. However, the frequency
difference lock-in phenomenon still exists, thereby affect-
ing its performance in the measurement field.
In this Letter, we report the experimental progress in
weakening the frequency difference lock-in phenomenon
in a Y-shaped cavity dual-frequency laser. We developed
a tunable and convenient transverse magnetic field setup
and tested its magnetic field intensity distribution. Then,
the basic principle of weakening the frequency difference
lock-in phenomenon by a transverse magnetic field was
analyzed. Moreover, we report the preliminary experimen-
tal results and discuss the minimal frequency difference
variations with the transverse magnetic field intensity.
Conclusions are given last.
Figure
1 shows the configuration of the weakening
frequency difference lock-in phenomenon in a Y-shaped
cavity dual-frequency laser and its accessorial experimen-
tal setup.
First, the two terms used in this Letter are defined as
follows. P-light indicates that the electric field vector is
perpendicular to the plane of incidence, whereas S-light
indicates that the electric field vector is parallel to the
plane of incidence. The Y-shaped cavity dual-frequency
laser in Fig.
1 generates two orthogonal polarized lights
with a frequency difference called P-light and S-light,
respectively.
COL 13(11), 111405(2015) CHINESE OPTICS LETTERS November 10, 2015
1671-7694/2015/111405(4) 111405-1 © 2015 Chinese Optics Letters