COL 9(7), 072701(2011) CHINESE OPTICS LETTERS July 10, 2011
Polarization enhancement and suppression of four-wave
mixing in multi-Zeeman levels
Zhiguo Wang (王王王志志志国国国), Yuxin Fu (付付付雨雨雨欣欣欣), Yue Song (宋宋宋 悦悦悦), Guoxian Dai (代代代国国国宪宪宪),
Feng Wen (问问问 峰峰峰), Jinyan Zhao (赵赵赵金金金燕燕燕), and Yanpeng Zhang (张张张彦彦彦鹏鹏鹏)
∗
Key Laboratory for Physical Electronics and Devices, Ministry of Education, Shanxi Key Laboratory of
Information Photonic Technique, Xi’an Jiaotong University, Xi’an 710049, China
∗
Corresp onding author: ypzhang@mail.xjtu.edu.cn.
Received September 26, 2010; accepted January 28, 2011; posted online May 26, 2011
Polarization dependence of the enhancement and suppression of four-wave mixing (FWM) in a multi-
Zeeman level atomic system is investigated b oth theoretically and experimentally. A dressing field applied
to the adjacent transition can cause energy level splitting. Therefore, it can control the enhancement
and suppression of the FWM processes in the system due to the effect of electromagnetically induced
transparency. The results show that the pumping beams with different polarizations select the transitions
b etween different Zeeman levels that, in turn, affect the enhancement and suppression efficiencies of FWM.
OCIS codes: 270.1670, 190.4180, 190.4223.
doi: 10.3788/COL201109.072701.
In the past few decades, various studies on multi-wave
mixing (MWM) processes have been carried out
[1−9]
.
Given that weak generated signals can be transmitted
through the resonant atomic medium, effects related to
electromagnetically induced transparency (EIT)
[10]
are
considered excellent to ols in investigating MWM pro-
cesses. Furthermore, when multi-Zeeman energy levels
are involved in the atomic systems
[11,12]
of EIT and four-
wave mixing (FWM) processes
[3,7,13,14]
, polarizations of
the involved laser beams are expected to play a impor-
tant role in these processes. EIT and FWM processes
can be effectively controlled by selecting different tran-
sitions between various Zeeman sublevels through the
adjustment of the polarization states of the involved
laser beams
[3,7,11−14]
. Moreover, the FWM efficiencies
in multi-level atomic systems can be modified by adding
dressing laser beams.
In this letter, we aim to demonstrate experimen-
tally that degenerate FWM (DFWM) is enhanced or
suppressed by the combined polarization and dressing
effects. The polarizations of pumping beams are changed
to select the transitions between different Zeeman levels
that usually have different transition strengths resulting
from distinct Clebsch–Gordan (CG) coefficients
[11,12]
. In
this process, the dressing beam determines the effective
frequency detuning of the probe beam from multi-
Zeeman levels. Compared with previous research
[7]
, we
have observed the different rules of enhancement and
suppression of FWM as a result of selecting different
transition passages. The experimental observations are
explained by the interplay among multi-dressing fields
and multi-transition passages.
We considered the FWM process in a ladder-type
three-level atomic system (Fig. 1(a)). There are four
laser beams applied to the system, including two pump-
ing laser beams E
c
(ω
c
, k
c
, and Rabi frequency G
c,M
)
and E
0
c
(ω
c
, k
0
c
, G
0
c,M
), a weak probe field E
p
(ω
p
, k
p
,
G
p,M
), and a dressing field E
d
(ω
d
, k
d
, G
d,M
), where
subscript M represent the magnetic quantum number of
the lower states in transitions in which these fields were
radiated. These pulse laser beams are aligned in the spa-
tial configuration shown in Fig. 1(b). The two beams, E
c
and E
0
c
, have a small angle of 0.3
◦
and are tuned to drive
the transition |ai (3S
1/2
) to |bi (3P
3/2
). Generally, E
c
propagates in the opposite direction of the probe field E
p
.
A population grating between states |ai and |bi induced
by E
c
and E
0
c
(both with frequency ω
c
) is probed by
beam E
p
with the same frequency (ω
c
). This interaction
generates a DFWM signal E
f
(Fig. 1(a)), which satisfies
the phase-matching condition
[14]
: k
f
= k
p
+ k
c
− k
0
c
.
The experiment was carried out in sodium atoms
placed in a heat pipe oven and involved three energy
levels. The two pumping laser beams, E
c
and E
0
c
, and the
Fig. 1. (a) Zeeman structure of the three-level ladder-type
atomic system generating the FWM signal E
f
. Solid line:
dressing field E
d
; Short-dashed lines: the linearly polarized
pumping fields E
c
and E
0
c
; long-dashed lines: the circular-
p olarized pumping fields; dotted line: the probe field E
p
; (b)
schematic diagram of the experimental configuration.
1671-7694/2011/072701(4) 072701-1
c
° 2011 Chinese Optics Letters