Abnormal elemental redistribution in oxyfluoride glasses
induced by high repetition rate femtosecond laser
Shengzhi Sun (孙盛芝)
1
, Song Ye (叶 松)
2
, Zhenyan Wang (王振彦)
1
, Juan Song (宋 娟)
3
,
Bin Qian (钱 滨)
4,
*, and Jianrong Qiu (邱建荣)
4,
**
1
Ningbo University of Finance and Economics, Ningbo 315175, China
2
School of Materials Science and Engineering, Tongji University, Shanghai 201804, China
3
School of Material Science and Engineering, Jiangsu University, Zhenjiang 212013, China
4
State Key Laboratory of Modern Optical Instrumentation, College of Optical Science and Engineering,
Zhejiang University, Hangzhou 310027, China
*Corresponding author: binqian1984@163.com; **corresponding author: qjr@zju.edu.cn
Received January 15, 2019; accepted March 28, 2019; posted online June 11, 2019
We report on the elemental redistribution behavior in oxyfluoride glasses with a high repetition rate near-
infrared femtosecond laser. Elemental analysis by an electro-probe microanalyzer demonstrates that the redis-
tributions of Ca
2+
and Yb
3+
ions change dramatically with pulse energy, which are quite different compared with
previous reported results. Confocal fluorescence spectra of Yb
3+
ions demonstrate that the luminescence intensity
changes obviously with the elemental redistribution. The mechanism of the observed phenomenon is discussed.
This observation may have potential applications in the fabrication of micro-optical devices.
OCIS codes: 160.5690, 160.2750, 160.4760, 350.3390.
doi: 10.3788/COL201917.061601.
Femtosecond (fs)–laser-induced micro-modifications in
transparent materials have attracted considerable interest
and been extensively studied for several decades
[1–3]
. Owing
to its unique advantages (high accuracy, low thermal ef-
fect, and minimum collateral damage), fs laser microma-
chining is considered and confirmed as one of the most
promising ways to modify the micro-properties of trans-
parent materials, such as glasses
[2,4–6]
, crystals
[3,7]
, and
polymers
[8]
. With fs lasers, various micro-properties of
materials can be modified, for instance, conversion of sin-
gle crystal, polycrystal, and amorphous
[9,10]
, modification
of refractive index
[11]
, change of valence state
[12,13]
, precipi-
tation of nanoparticles
[14,15]
, and selective migration of
ions
[16]
. All these changes induced by a fs laser can be
used for fabrication of functional micro-optical devices,
such as optical waveguides
[17]
, directional couplers
[18]
,
three-dimensional (3D) optical data storage media
[19]
,
and 3D micro-fluidic devices
[20,21]
.
Recently, space-selective manipulation of elements in
glass by a fs laser has been an advanced research
hotspot
[16,22]
, since most optical properties of materials
such as absorption, luminescence, refractive index, and
optical nonlinearity are highly related to element distribu-
tion. Numerous interesting phenomena as well as potential
applications have been reported by several research
groups
[16,23–30]
. Microscopic control of the intensity distribu-
tion of luminescence
[23]
and simultaneous control over the
precipitation of multiple crystalline phases and active ion
migration
[27]
have been realized in some materials.
Furthermore, a method for controlling the shape of the
elemental distribution with a spatial light modulator has
been reported
[28]
. According to previous observation
[2,23–25]
,
the relative concentration of glass network modifying ions
is usually higher at the periphery and lower in the
central area of the laser-affected region, indicating that
the network modifying ions tend to diffuse from the
vicinity of the focal point to the boundary of the laser
modified area. Meanwhile, the relative concentration of
glass network forming ions is opposite to that of network
modifying ions, migrating from the periphery of the
modified region to the center. Generally, diffusion coeffi-
cients of different elements and temperature gradients
are considered to be the key factors for the formation
mechanism of element migration
[16,29]
. However, a few
experiment results that do not conform with the previous
proposition mentioned above have also been reported
[31,32]
,
demonstrating that the mechanism of element migration
might be more complicated than what was previously
proposed.
In this Letter, we report on an abnormal phenomenon of
element migration in oxyfluoride glasses after the irradia-
tion of a 250 kHz fs laser at 800 nm. Electron microprobe
analysis shows that the distributions of elements (Ca
2þ
,
Yb
3þ
, and Si
4þ
) are highly dependent on laser pulse energy.
The glass network modifying ions (Ca
2þ
and Yb
3þ
) migrate
to the center area at lower pulse energy, while they diffuse
to the periphery of the modified region at higher pulse en-
ergy. The possible mechanism for this diversified migration
of elements has been discussed, including the influences of
temperature gradient, diffusion coefficient, and laser-in-
duced crystallization. Moreover, the relationship between
element distribution and fluorescence intensity of Yb
3þ
has
been investigated with the confocal fluorescence spectrum,
indicating that space-selective manipulation of element dis-
tribution is a promising way to fabricate multifunctional
optical devices in glasses.
COL 17(6), 061601(2019) CHINESE OPTICS LETTERS June 2019
1671-7694/2019/061601(5) 061601-1 © 2019 Chinese Optics Letters