Efficient laser emissions at 1:06μm of swift heavy
ion irradiated Nd:YCOB waveguides
Yingying Ren,1Ningning Dong,1Yuechen Jia,1Lilong Pang,2Zhiguang Wang,2Qingming Lu,3and Feng Chen1,*
1School of Physics, State Key Laboratory of Crystal Materials and Key Laboratory of Particle Physics
and Particle Irradiation (MOE), Shandong University, Jinan 250100, China
2Institute of Modern Physics, Chinese Academy of Sciences, Lanzhou 73000, China
3School of Chemistry and Chemical Engineering, Shandong University, Jinan 250100, China
*Corresponding author: firstname.lastname@example.org
Received September 20, 2011; accepted October 11, 2011;
posted October 19, 2011 (Doc. ID 155033); published November 22, 2011
We report on the fabrication of Nd:YCOB (Nd:YCa4OðBO3Þ3) optical waveguides by using 170MeV Ar8þion irradia-
tion at an ultralow fluence of 2 × 1012ions=cm2. The confocal microphotoluminescence investigation on the pro-
duced waveguides has shown the well-preserved fluorescence features within the guiding layer with respect to
the bulks. Under the optical pump at wavelength of 810nm, continuous wave waveguide lasers at 1061:2nm have
been generated at room temperature with a high slope efficiency of ∼67:9%.
OCIS codes: 230.7390, 140.3390, 130.3120.
© 2011 Optical Society of America
(Nd:YCa4OðBO3Þ3or Nd:YCOB) is an excellent self-
frequency-doubling (SFD) crystal with a combination of
photoluminescence features of the Nd3þions and the
nonlinear properties of YCOB matrix, which makes it
very promising for laser diode directly pumped visible la-
sers [1,2]. By using waveguide technology a unique plat-
form of multifunctional applications could be realized
through highly compact on-chip circuits with small sizes
. Waveguide laser devices are intriguing components
for diverse photonic applications owing to the enhanced
optical gain as well as the excellent performances, such
as low lasing threshold [4,5]. Particularly, based on the
SFD crystals, it is possible to facilitate the integration
of the intracavity visible waveguide lasers that do not
require the additional frequency conversion through a
nonlinear crystal waveguide [6,7]. In addition, the tradi-
tional laser plus nonlinear waveguide configuration (e.g.,
Nd:YVO4þ KTP hybrid system) seems to be quite diffi-
cult to achieve high overlap coupling due to the diverse
properties (e.g., refractive indices, physical densities) of
the laser and nonlinear crystals for waveguide fabrica-
tion . In this sense, the Nd:YCOB waveguide could be
a suitable platform to host the intracavity for the laser
generation of infrared light and synchronously realize
the nonlinear process in the same structure. Neverthe-
less, the first significant step to realize the SFD wave-
guide lasers is to obtain the fundamental frequency
laser generation, e.g., at wavelength of 1:06μm.
A few techniques have been utilized to fabricate wave-
guides in optical crystals, however, only the “physical”
methods, such as ultrafast laser writing  and energetic
ion beam implantation/irradiation [10,11] are applicable
to Nd:YCOB due to its stable chemical properties. As
of yet, there is no report on the Nd:YCOB waveguide la-
sers. The normal ion implantation technique, which has
been widely used to produce waveguiding structures in a
broad range of optical materials, creates negative refrac-
tive index layers (so-called “optical barriers”) at the end
of ion range through the nuclear collision correlated
damages. For the swift heavy ion irradiation (with energy
higher than 1MeV=amu), the refractive index of the
substrates is modified by the electronic excitation in-
duced damages, which mainly happens during most path
of the incident ions’ trajectory via the impact of amor-
phous or highly defective nanotracks from a single ion
or the overlap of a few ions [12–19]. In addition, the re-
quired fluences for swift ions are considerably lower than
those of the normal ion implantation, which saves the
time for the waveguide fabrication . This technique
has been successfully applied to produce waveguides in
a few optical crystals, such as LiNbO3[12,13,19], Nd:YAG
[20,21], KGdðWO4Þ2, and K1−xLixTa1−yNbyO3.
Particularly, the swift heavy ion irradiated Nd:GdCOB
(belongs to same family of Nd:YCOB) waveguides have
shown excellent nonlinear properties for green laser gen-
eration . In this Letter, we report, to our best knowl-
edge for the first time, on the fabrication of Nd:YCOB
waveguides by using swift Ar8þion irradiation, and the
continuous wave (cw) waveguide lasers generation at a
wavelength of 1:06μm.
The Nd:YCOB (doped by Nd3þions with concentration
of 5at:%) wafer was cut along the direction to satisfy the
1061nm fundamental wave to 531nm second harmonic
generation. It was with 5mm × 5mm × 2mm size and op-
tically polished. One sample surface of 5mm × 5mm was
irradiated with Ar8þions by using the facility at the In-
stitute of Modern Physics, Chinese Academy of Sciences.
The accelerating energy was set at 880MeV and the flu-
ence was at 2 × 1012cm−2. In order to slow down the in-
cident ions, a stopper foil of aluminum was placed in
front of the sample. The ion current density was kept less
than 30nA=cm2to avoid additional charging and heating
effect on the sample. According to our calculation by
SRIM (Stopping and Range of Ions in Matter) code ,
the practical irradiation energy reaching on the sample
surface was 170MeV.
Figure 1(a) shows the microscope image of the
170MeV Ar8þion irradiated Nd:YCOB sample. It can be
clearly seen that the ion beam modified region of the Nd:
YCOB is with thickness w ¼ 33:8μm, which is in good
agreement with the mean projected range of the 170MeV
Ar8þions in the Nd:YCOB crystal calculated by the SRIM
2010 code. It should be noted that we did not observe any
December 1, 2011 / Vol. 36, No. 23 / OPTICS LETTERS 4521
0146-9592/11/234521-03$15.00/0 © 2011 Optical Society of America
dark modes by using the m-line technique through the
prism coupler (Metricon 2010). However, by using an
end-face coupling system (at 632:8nm), we found clear
guiding modes [e.g., see TM mode profile in Fig. 1(b)] of
a multimode waveguide structure, which suggests the
configuration of the waveguide structure is a “buried”
layer and must be of positive index changes with respect
with the unmodified bulk. The maximum index alterna-
tion of the waveguide layer was determined to be
∼3 × 10−3, which was estimated from the measurement of
the NA of the planar waveguide . This technique has
been proved to be especially successfully to obtain the
refractive index alternations of multimode waveguides.
We used a fiber-coupled confocal microscope (Olym-
pus BX-41) to investigate the microphotoluminescence
(μ-PL) properties of the Nd:YCOB waveguides. The
488nm excitation laser was focused onto the cross
section by using a 100× microscope objective with NA
N:A: ¼ 0:95. And the backscattered Nd3þfluorescence
emission signals were collected with the same objective,
after passing through a series of filters and a confocal
pinhole, were collected by a fiber-coupled spectrometer
(SPEX500M, USA). The sample was mounted on an XY
motorized stage with a high spatial resolution of 100nm.
Figure 2(a) shows the room-temperature PL emission
spectrum of the Nd3þions in Nd:YCOB crystal correlated
to the4F3=2→4I9=2transition channel. We focused on the
881:6nm emission line in order to obtain the detailed
modification of the Ar8þion beams on the fluorescence
properties of the waveguides. Figures 2(b)–2(d) depict
the spatial dependence of the emitted intensity, peak po-
sition, and line width (FWHM) of the 881:6nm emission
line, respectively. As one can see, the intensity of fluor-
escence signals decreases by only 10% in the waveguide
with respect to the bulk, which means the majority of
the PL active features has been preserved, without clear
quenching. Nevertheless, the peak position shifts by
0:7cm−1, and the emission line is broadened by maxi-
mally 4cm−1, suggesting the obvious modification of the
Nd:YCOB fluorescence emission properties.
The laser operation experiment was performed by
using an end-face coupling system at room temperature.
The end faces of the Nd:YCOB sample were placed clo-
sely between two dielectric mirrors to construct the
Fabry–Perot lasing cavity (the input one with transmis-
sion of 98% at 810nm and reflectivity >99% at 1:06μm
and the output one with reflectivity >99% at 808nm and
∼95% at 1:06μm, respectively). The 810nm pump beam
from a Ti:sapphire cw laser (Coherent 110) was focused
into the cavity by using a convex lens (with focus length
of 25mm), and the emission waveguide laser at ∼1:06μm
was collected with a 20× microscope objective and im-
aged by an infrared CCD camera.
Figure 3 shows the room-temperature laser emission
spectrum of the Nd:YCOB waveguide. The emission line
is centered at 1061:2nm, which corresponds to the main
fluorescence transition of4F3=2→4I11=2channel of Nd3þ
ions. The FWHM of the emission line is ∼1nm, which
clearly demonstrates the realization of waveguide laser
Figure 4 depicts the output 1061:2nm waveguide laser
power as a function of the absorbed pump power at
810nm. Based on this data, one could determine that the
pump threshold (Pth) for laser generation is ∼31:5mW,
irradiated Nd:YCOB sample, and (b) the measured near-field in-
tensity of the TM mode.
(Color online) (a) Microscope image of the Ar8þion
emission spectrum correlated to Nd3þions at4F3=2→4I9=2tran-
sition of the Nd:YCOB crystal, the spatial dependence of the
(b) emitted intensity, (c) spectral shift, and (d) emission width
(at FWHM) of the 881:6nm emission line.
(Color online) (a) Room-temperature luminescence
170MeV Ar8þirradiated Nd:YCOB planar waveguide. The inset
shows the laser modal profile (TE0) at 1061:2nm.
(Color online) Laser emission spectrum from the
4522OPTICS LETTERS / Vol. 36, No. 23 / December 1, 2011
and the slope efficiency (Φ) is as high as 67.9%. The Download full-text
measured maximum output power is ∼35mW at pump
power of 83mW, corresponding to an optical-to-optical
conversion efficiency of 42%. The excellent lasing perfor-
mance of the Nd:YCOB waveguides suggests that the
swift Ar8þion irradiation does not affect the active fea-
tures of material, which opens up an exciting possibility
for further SFD lasing of the waveguides.
In conclusion, we have reported on the fabrication of
an Nd:YCOB planar waveguide by using swift Ar8þion
irradiation. The fluorescence properties of the bulk ma-
terials have been well preserved in the waveguides,
although clear modification happens after the irradiation.
The cw waveguide laser in Nd:YCOB has been realized
for the first time, which exhibits excellent performances
at 1:06μm oscillations. Future work would be performed
on the achievement of the SFD laser from the swift heavy
ion irradiated Nd:YCOB waveguides.
The work is supported by the National Natural Science
Foundation of China (NSFC) (10925524) and the 973 Pro-
ject of China (2010CB832906 and 2010CB832902).
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(Color online) Output laser power at 1061:2nm as a
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