Two-color cesium magneto-optical trap with 6S
1/2
-6P
3/2
-
7S
1/2
(852 nm + 1470 nm) ladder-type system
Jie Wang (王 杰)
1,2
, Guang Yang (杨 光)
1,2
, Jun He (何 军)
1,2,3
, and
Junmin Wang (王军民)
1,2,3,
*
1
State Key Laboratory of Quantum Optics and Quantum Optics Devices, Shanxi University, Taiyuan 030006, China
2
Institute of Opto-Electronics, Shanxi University, Taiyuan 030006, China
3
Collaborative Innovation Center of Extreme Optics, Shanxi University, Taiyuan 030006, China
*Corresponding author: wwjjmm@sxu.edu.cn
Received November 17, 2016; accepted February 17, 2017; posted online March 13, 2017
A 1470 nm þ 852 nm two-color (TC) cesium (Cs) magneto-optical trap (MOT) with a 6S
1∕2
-6P
3∕2
-7S
1∕2
ladder-
type system is proposed and experimentally investigated. To the best of our knowledge, it is the first report about
the 1470 nm þ 852 nm Cs TC-MOT. One of the three pairs of the 852 nm cooling and trapping beams (CTBs) in
a conventional Cs MOT is replaced with a pair of the 1470 nm CTBs. Thus, the TC-MOT partially employs the
optical radiation forces from photon scattering of the 6P
3∕2
(F
0
¼ 5) −7S
1∕2
(F
00
¼ 4) excited-state transition
(1470 nm). This TC-MOT can cool and trap Cs atoms on both the red- and blue-detuning sides of the two-
photon resonance. This work may have applications in cooling and trapping of atoms using inconvenient wave-
lengths and background-free detection of cold and trapped Cs atoms.
OCIS codes: 020.3320, 270.4180, 300.6210.
doi: 10.3788/COL201715.050203.
Laser cooling and trapping of neutral atoms in a conven-
tional magneto-optical trap (MOT) plays an important
role and has a profound impact in many fields, such as pre-
cision measurements, optical atomic clocks, quantum de-
generate gases, and quantum information processing
[1–3]
.
To date, most laser cooling schemes have used the optical
radiation forces caused by photon scattering from the sin-
gle-photon transition between atomic ground state and
excited state. This approach has been extremely success-
ful, leading to a range of techniques including Doppler
cooling
[4]
, polarization gradient cooling
[5]
, and velocity-
selective coherent population trapping
[6]
. However, there
are few theoretical and experimental investigations of
two-photon laser cooling in a ladder-type atomic system.
Furthermore, these studies have mostly focused on the
cooling of alkaline-earth-metal atoms as a second stage
using the narrow
1
S
0
-
3
P
1
inter-combination transition
after the initial precooling with a strong
1
S
0
-
1
P
1
dipole
transition
[7–9]
. Most recently, with the development of
excited-states spectroscopy
[10,11]
, a two-color (TC) MOT
based on the cesium (Cs) 6S
1∕2
-6P
3∕2
-8S
1∕2
(852 nm þ
795 nm) ladder-type system, which partially uses the op-
tical radiation forces from photon scattering between two
excited states (6P
3∕2
and 8S
1∕2
states), has been experi-
mentally demonstrated
[12–14]
. The TC-MOT can cool and
trap atoms on both the red- and blue-detuning sides of
the two-photon resonance. This approach has been ap-
plied to background-free detection of trapped atoms from
the related transitions driven without a laser beam with
the help of narrow-bandwidth high-contrast interference
filters in our previous work
[13]
. Also, this approach has ap-
plications in assisted cooling of certain atomic or molecu-
lar species that require lasers at inconvenient wavelengths.
For instance, a laser cooling technique to cool hydrogen or
anti-hydrogen atoms using the cooling transition between
excited states has been proposed
[15]
.
The primary motivation of this work is to better
understand the cooling and trapping mechanism from
multi-photon transitions. Figure
1(a) shows the decay
channels from the Cs 8S
1∕2
state with a decay rate of Γ
0
¼
2π × 1.52 MHz and the 7S
1∕2
state with a decay rate of
Γ ¼ 2π × 3.30 MHz. Compared with the Cs 6S
1∕2
-6P
3∕2
-
8S
1∕2
TC-MOT
[12–14]
, the Cs 6S
1∕2
-6P
3∕2
-7S
1∕2
TC-MOT
is significantly simpler because there are fewer decay chan-
nels. Actually, the behaviors of these TC-MOTs are differ-
ent in the conditions of low cooling and trapping laser
intensity, which is illustrated and analyzed in the text. Con-
sequently, it can aid in understanding the cooling and trap-
ping mechanism in this simple ladder-type system. Another
advantage of having fewer decay channels is that the
Fig. 1. Relevant energy-level and fine transitions of Cs atoms
for (a) a 6S
1∕2
-6P
3∕2
-8S
1∕2
(852 nm þ 795 nm) ladder-type
system (not to scale) and for (b) a 6S
1∕2
-6P
3∕2
-7S
1∕2
(852 nm þ 1470 nm) ladder-type system (not to scale). There
are fewer decay channels from the Cs 7S
1∕2
state than that from
the Cs 8S
1∕2
state, which may aid in the analysis of the cooling
mechanism.
COL 15(5), 050203(2017) CHINESE OPTICS LETTERS May 10, 2017
1671-7694/2017/050203(5) 050203-1 © 2017 Chinese Optics Letters