Excited-state population distributions of alkaline-earth
metal in a hollow cathode lamp
Pengyuan Chang (常鹏媛), Bo Pang (逄 博), Yisheng Wu (吴一胜),
and Jingbiao Chen (陈景标)*
State Key Laboratory of Advanced Optical Communication System and Network, School of Electronics
Engineering and Computer Science, Peking University, Beijing 100871, China
*Corresponding author: jbchen@pku.edu.cn
Received October 22, 2017; accepted January 4, 2018; posted online March 7, 2018
The intensities of fluorescence spectral lines of Ca atoms and Sr atoms in two different hollow cathode lamps
(HCLs) are measured by element-balance-detection technology. In the wavelength range of 350–750 nm in
the visible spectral region, using the individual strongest line (Ca 422.67 nm, Sr 460.73 nm) as the bench mark,
the population ratios between the excited states of Ca atoms and Sr atoms are calculated by rate equations
and the spontaneous transition probabilities. The HCLs with populations at excited states can be used to realize
the frequency stabilization reference of the laser frequency standard.
OCIS codes: 300.6210, 020.1335, 260.2510.
doi: 10.3788/COL201816.033001.
Hollow cathode lamps (HCLs) with alkaline-earth
metal are attracting growing attention nowadays as
sources of intense atomic spectral lines in various physical
devices applied in atomic absorption and emission spec-
troscopy
[1–3]
. Furthermore, the atom unit most frequently
employed in a traditional Faraday anomalous dispersion
optical filter (FADOF)
[4]
is a vapor cell with atomic den-
sity determined by thermal equilibrium
[5–8]
. Hence, the
samples of atomic filters have to be heated to high temper-
atures to get an atomic density high enough to guara ntee
the transmittance
[9,10]
. To overcome this limitation , an
innovative method of utilizing an HCL to realize a Sr
element FADOF was proposed, as the HCLs can provide
the high atomic density at room temperature
[11]
. Moreover,
since the state-of-the-art HCLs cover about 70 kinds of
high melting point metal elements, we believe that, due
to its rich spectral lines, without heating, scalability,
low fabrication cost, and potential applications in various
atomic spectra
[12–16]
they can be used in submarine commu-
nication systems as well as excited-state FADOFs without
the use of a pump laser
[5,6]
.
Basic knowledge about HCLs is meaningful for
the exploration of further applications
[17,18]
. The HCLs
have rich atomic spectral lines; nevertheless, the spectral
measurements are often contaminated by buffer gas-line
interference
[14–23]
. A new method of measurement, as shown
in Fig.
1, element-balance-detection technology, is intro-
duced by us, whi ch can remove the effect of the buffer
gas-line via the subtraction relation between two spectral
signals of Ca HCL and Sr HCL, as shown in Figs.
2 and 3.
This method is simply described as follows: two spectral
signals of Ca HCL and Sr HCL both include the buffer
gas-line; in order to distinguish the atom lines between
the spectral signals, we conduct a subtraction operation
of two signals to make the buffer gas-lines offset each
other. Although the components of the buffer gas may
be different, the results imply that the subtraction pro-
cedure is coping better with this problem. Hence, the
element-balance-detection technology is applicable for
similar situations in atomic spectroscopy measurement,
which exists in the interference of impurity lines.
In this Letter, we measured the intensities of fluores-
cence spectral lines of Ca and Sr atoms in two different
HCLs, respectively. In the wavelength range of 350–
750 nm in the visible spectral region, using the individual
strongest line (Ca 422.67 nm, Sr 460.73 nm) as the bench
mark, we calculated the population ratios between the ex-
cited states by rate equations and spontaneous transition
probabilities. The measured results showed that the inten-
sities of the spectral lines of Ca and Sr atoms are signifi-
cantly different.
The measurement setup is schematically shown in Fig.
1.
Figure
2 shows the energy diagrams of the transitions re-
lated to the Ca and Sr atoms’ spectral signal. The Sr HCL
and Ca HCL are powered by Power1 and Power2 (gener-
ating a current range of 0 to 20 mA), respectively, which
are placed across the cathode and anode terminals. The
intensities of the fluorescence spectral lines of Ca and
Sr atoms were strikingly different along with the current
increase. The USB2000+ spectrometer in connection with
Fig. 1. Experimental schemes of Ca HCL and Sr HCL in the con-
figuration of element-balance-detection technology for spectrum
research.
COL 16(3), 033001(2018) CHINESE OPTICS LETTERS March 10, 2018
1671-7694/2018/033001(5) 033001-1 © 2018 Chinese Optics Letters
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