High Power Laser Science and Engineering, (2016), Vol. 4, e37, 4 pages.
© The Author(s) 2016. This is an Open Access article, distributed under the terms of the Creative Commons Attribution licence (http://creativecommons.org/
licenses/by/4.0/), which permits unrestricted re-use, distribution, and reproduction in any medium, provided the original work is properly cited.
doi:10.1017/hpl.2016.37
Deleterious processes of a diode-pumped cesium vapor
hollow-core photonic-crystal fiber laser
Guofei An, You Wang, Juhong Han, He Cai, Zhigang Jiang, Ming Gao, Shunyan Wang, Wei Zhang,
Hongyuan Wang, Liangping Xue, and Jie Zhou
Southwest Institute of Technical Physics, Chengdu, Sichuan 610041, China
(Received 29 April 2016; revised 21 June 2016; accepted 9 September 2016)
Abstract
A diode-pumped alkali laser (DPAL) provides the significant promise for high-powered performances. In this paper, a
mathematical model is introduced for examination of the kinetic processes of a diode-pumped cesium vapor hollow-core
photonic-crystal fiber (HC-PCF) laser, in which the cesium vapor is filled in the center hole of a photonic-bandgap fiber
instead of a glass cell. The influence of deleterious processes including energy pooling, photo-ionization, and Penning
ionization on the physical features of a fiber DPAL is studied in this report. It has been theoretically demonstrated that
the deleterious processes cannot be ignored in a high-powered fiber-DPAL system.
Keywords: DPAL; hollow core; ionization; photonic bandgap
1. Introduction
In the recent years, a diode-pumped alkali laser (DPAL)
has been extensively studied due to the potential for its
excellent physical features
[1–3]
. The oscillator of a DPAL
usually contains an enclosed glass cell, in which the vapor
of neutral alkali (K, Rb, Cs) and several kinds of buffer
gases (helium and hydrocarbon with small molecular weight)
are sealed with a certain pressure
[4–6]
. In 2006, Payne
et al. proposed a patent describing a new kind of DPAL in
which a hollow-core photonic-crystal fiber (HC-PCF) is used
as the vapor container
[7]
. Unlike a normal DPAL, such an
integrated design is thought to have higher stability. And the
optical coupling efficiency of this system can be improved
significantly comparing with the traditional configuration.
Slepkov et al. also demonstrated the possibility of intro-
ducing alkali vapor into a standard hollow-core fiber with
sufficient gas density
[8]
. Recently, Sintov et al. calculated
the physical features of a rubidium vapor-based fiber laser
using a simple mathematical model, in which the HC-PCF-
DPAL was treated as a three-level laser system
[9]
.
Generally, alkalis are the most easily ionized atomic
species, especially for rubidium and cesium. Figure 1
illustrates the energy level diagram for Cs atoms. The
electrons in cesium atoms are pumped from the 6
2
S
1/2
level to the 6
2
P
3/2
level corresponding to the D
2
line
Correspondence to: Y. Wang, Southwest Institute of Technical Physics,
Renmin South Road 4-7, Chengdu, Sichuan 610041, China. Email:
youwang 2007@aliyun.com
Figure 1. Energy level diagram for a cesium atom.
(852.3 nm). After a rapid relaxation in the fine structure with
the aid of some alkanes with small hydrocarbon molecules,
electrons fall back to the ground state with stimulated
emission corresponding to the D
1
line (894.6 nm). Under
the condition of high-powered pump, the electrons will
be excited to the higher levels (6
2
D
5/2,3/2
and 8
2
S
1/2
) by
energy pooling collisions. Further, ionization processes
including photo-ionization and Penning ionization will occur
on the 6
2
D
5/2,3/2
and 8
2
S
1/2
levels resulting in decrease of
the density of neutral atoms.
To deeply study the kinetics of an HC-PCF-DPAL, we
construct a quasi-five-level model with the cesium vapor as
a gain medium in this report. The deleterious processes
of energy pooling and ionization are taken into account in
1