Valence state manipulation of Sm
3+
ions
via a phase-shaped femtosecond laser field
YE ZHENG,
1
YUNHUA YAO,
1
LIANZHONG DENG,
1,
*WENJING CHENG,
2
JIANPING LI,
1
TIANQING JIA,
1
JIANRONG QIU,
3
ZHENRONG SUN,
1
AND SHIAN ZHANG
1,4,5
1
State Key Laboratory of Precision Spectroscopy, East China Normal University, Shanghai 200062, China
2
School of Electronic & Electrical Engineering, Shangqiu Normal University, Shangqiu 476000, China
3
State Key Laboratory of Silicon Materials, Zhejiang University, Hangzhou 310027, China
4
Collaborative Innovation Center of Extreme Optics, Shanxi University, Taiyuan 030006, China
5
e-mail: sazhang@phy.ecnu.edu.cn
*Corresponding author: lzdeng@phy.ecnu.edu.cn
Received 24 October 2017; revised 11 December 2017; accepted 12 December 2017; posted 19 December 2017 (Doc. ID 309766);
published 30 January 2018
The ability to manipulate the valence state conversion of rare-earth ions is crucial for their applications in color
displays, optoelectronic devices, laser sources, and optical memory. The conventional femtosecond laser pulse has
been shown to be a well-established tool for realizing the valence state conversion of rare-earth ions, although the
valence state conversion efficiency is relatively low. Here, we first propose a femtosecond laser pulse shaping tech-
nique for improving the valence state conversion efficiency of rare-earth ions. Our experimental results demonstrate
that the photoreduction efficiency from Sm
3
to Sm
2
in Sm
3
-doped sodium aluminoborate glass using a π phase
step modulation can be comparable to that using a transform-limited femtosecond laser field, while the peak laser
intensity is decreased by about 63%, which is very beneficial for improving the valence state conversion efficiency
under the laser-induced damage threshold of the glass sample. Furthermore, we also theoretically develop a (2 1)
resonance-mediated three-photon absorption model to explain the modulation of the photoreduction efficiency
from Sm
3
to Sm
2
under the π-shaped femtosecond laser field. © 2018 Chinese Laser Press
OCIS codes: (320.5540) Pulse shaping; (320.2250) Femtosecond phenomena; (190.4400) Nonlinear optics, materials; (160.4670)
Optical materials.
https://doi.org/10.1364/PRJ.6.000144
1. INTRODUCTION
Over the past few decades, the valence state conversion of rare-
earth-ion-doped luminescent materials has attracted great at-
tention due to their potential applications in ultrahigh-density
3D optical memories [1,2], broadly tunable lasers [3,4], and so
on. In the studies of these rare-earth ions, samarium (Sm) ions
were those most studied. For example, Qiu et al. observed
permanent photoreduction from Sm
3
to Sm
2
inside a so-
dium aluminoborate glass irradiated by an infrared (800 nm)
femtosecond pulsed laser [5,6], and also demonstrated the re-
cording, readout, and erasure of a 3D optical memory using
the valence-state conversion of Sm ions [2]. Jiao et al. showed
that Sm ions can be selectively incorporated into the precipi-
tated nanophases, which can enhance the photoreduction of
Sm
3
ions under even lower laser power [7]. Recently, the
photoreduction of Sm ions doped in other matrix materials
has also aroused considerable interest, such as crystals [8,9],
phosphors [10], glass films [11], and glass-ceramics [12,13].
Moreover, the valence state conversion of other rare-earth ions,
like europium (Eu) [14–20] and manganese (Mn) ions [21,22],
has also been extensively studied. For example, Lim et al. dem-
onstrated that the photoreduction efficiency from Eu
3
to
Eu
2
depends on the initial ion concentration, irradiation laser
intensity, and exposure time [16]. Similar phenomena were also
observed in the photo-oxidation from Mn
2
to Mn
3
[22].
Previous studies showed that femtosecond laser pulse exci-
tation provides a very useful strategy for obtaining the valence
state conversion of rare-earth ions due to the high laser inten-
sity. In these studies, the researchers usually employed a con-
ventional femtosecond laser pulse with a Gaussian shape, but
the valence state conversion efficiency by a Gaussian-shaped
femtosecond laser pulse was relatively low. In this work, we first
develop a phase-shaped femtosecond laser field to improve the
valence state conversion efficiency of rare-earth ions. Our ex-
perimental study indicates that the photoreduction efficiency
from Sm
3
to Sm
2
in Sm
3
-doped sodium aluminoborate
glass using a π-shaped femtosecond laser field can be compa-
rable to that using a transform-limited (TL) laser field, but the
144
Vol. 6, No. 2 / February 2018 / Photonics Research
Research Article
2327-9125/18/020144-05 Journal © 2018 Chinese Laser Press