Determination of hyperfine structure constants of 5D
5∕2
and 7S
1∕2
states of rubidium in cascade atomic system
Shaohua Li (李少华)
1,2
, Yihong Li (李一鸿)
1,2
, Jinpeng Yuan (元晋鹏)
1,2,
*,
Lirong Wang (汪丽蓉)
1,2,
**, Liantuan Xiao (肖连团)
1,2
, and Suotang Jia (贾锁堂)
1,2
1
State Key Laboratory of Quantum Optics and Quantum Optics Devices, Institute of Laser Spectroscopy,
Shanxi University, Taiyuan 030006, China
2
Collaborative Innovation Center of Extreme Optics, Shanxi University, Taiyuan 030006, China
*Corresponding author: yjp@sxu.edu.cn; **corresponding author: wlr@sxu.edu.cn
Received January 26, 2018; accepted April 3, 2018; posted online May 30, 2018
We present a method to precisely determine the hyperfine structure constants of the rubidium 5D
5∕2
and 7S
1∕2
states in a cascade atomic system. The probe laser is coupled to the 5S
1∕2
→ 5P
3∕2
hyperfine transition, while the
coupling laser is scanned over the 5P
3∕2
→ 5D
5∕2
ð7S
1∕2
Þ transition. The high-resolution double-resonance optical
pumping spectra are obtained with two counter-propagating laser beams acting on rubidium vapor. The
hyperfine splitting structures are accurately measured by an optical frequency ruler based on the acousto-optic
modulator, thus, the magnetic dipole hyperfine coupling constant A and quadrupole coupling constant B are
determined. It is of great significance for the atomic hyperfine structure and fundamental physics research.
OCIS codes: 020.2930, 300.6210.
doi: 10.3788/COL201816.060203.
The measurement of hyperfine splitting structures of
alkali atoms at an excited state is important for electron–
nucleus interaction
[1]
, atomic parity non-conservation
[2]
,
precision measurement of fundamental constants
[3,4]
,high-
resolution laser spectroscopy
[5]
, optical frequency standards,
and optical frequency measurement
[6,7]
.Fortheexcited
states of Rb atoms, the 5D and 7S states have attracted
more and more interest from researchers. For the 5D states,
the small energy difference between the two transitions in-
duces a high-transition probability and a better Doppler-
free background. The relatively narrow natural linewidth
and lower sensitivity to the external environment make
the state a good candidate for establishing optical frequency
standards with high stability
[8]
. For the 7S state, the 5S →
5P → 7S transition is less sensitive to magnetic fields, since
both 5S
1∕2
and 7S
1∕2
states have the same Landé g-factor,
and the linea r Zee man shift is zero
[9]
,whichmakesitwidely
used in precision measurement.
The Doppler-free double-photon spectroscopy
[10]
,optical
double-resonance spectroscopy
[11]
, resonance-enhanced ion-
ization spectroscopy
[12]
, cascade radio-frequency spectros-
copy
[13]
, and electromagnetically induced transparency
spectroscopy
[14]
are used to d etermine the hyperfine structure
constants. Compared with these methods, the double-
resonance optical pumping (DROP ) spectroscopy has a
higher signal-to-noise ratio for detecting the population of
the ground state instead of the excited states. Especially for
Rb atoms, the intermediate 5P
3∕2
state has high spontaneous
emission rate, which will accelerate the DROP process
[15]
.
For the calibration of the spectrum components, the
Fabry–Perot (FP) cavity, electro-optic modulator
(EOM), and acousto-optic modulator (AOM) are often
used as the frequency rulers. The accuracy of the FP
cavity is limited by thermal fluctuations and mechanical
vibrations. The EOM frequency ruler also needs the FP
cavity as the auxiliary tool, which will make the system
complicated. The AOM can be driven by an easily mea-
sured and constructed radio-frequency source, which
has the accuracy of 1 × 10
−6
and an error of less than
1 kHz introduced into the frequency scale
[16]
. It is relatively
free of large systematic effects and leads to a higher pre-
cision in the hyperfine splitting structure measurement.
In this Letter, we determine the hyperfine structure con-
stants of the 5D
5∕2
and 7S
1∕2
states of Rb atoms with
DROP spectroscopy, which is calibrated by the AOM fre-
quency ruler. When the coupling laser is tuned to the
5P
3∕2
→ 5D
5∕2
ð7S
1∕2
Þ transition, and the probe laser is
locked to the 5S
1∕2
→ 5P
3∕2
transition, we obtain high-
resolution DROP spectra. The hyperfine split ting struc-
tures of the 5D
5∕2
and 7S
1∕2
states of the two isotopes
85
Rb and
87
Rb are measured, and thus, the hyperfine
structure constants are determined. This work is impor-
tant for the development of precision measurement.
The relevant hyperfine energy levels of the two isotopes
85
Rb and
87
Rb are illustrated in Fig. 1. The nuclear spin
quantum numbers of
87
Rb and
85
Rb are 3∕2 and 5∕2, re-
spectively. The probe laser operating at 780 nm is reso-
nant on the 5S
1∕2
→ 5P
3∕2
transition, while the coupling
laser is tuned to the upper 5P
3∕2
→ 5D
5∕2
ð7S
1∕2
Þ transition
at 776 nm (741 nm).
The experimental setup is schematically depicted in
Fig.
2. The coupling laser is provided by a Ti:sapphire la-
ser system (SolaTis-SRX-XF, M Squared Lasers), which
can be tuned from 600 to 1000 nm. The wavelength of
the laser can be monitored by a wavelength meter
(WS-7, HighFinesse). The coupling las er is divided into
two beams by the AOM, and then zeroth-order and
first-order laser beams are recombi ned together by the
COL 16(6), 060203(2018) CHINESE OPTICS LETTERS June 10, 2018
1671-7694/2018/060203(4) 060203-1 © 2018 Chinese Optics Letters
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