Spectral properties and 1.55 m laser operation of
Ce3+:Yb3+:Er3+:NaLa(WO4)2 crystal
Xinghong Gong, Yujin Chen, Yanfu Lin, Jianhua Huang, Zundu Luo, and Yidong
Huanga)
Key Laboratory of Optoelectronic Materials Chemistry and Physics, Fujian Institute
of Research on the Structure of Matter, Chinese Academy of Sciences, Fuzhou, Fujian,
350002, China
ABSTRACT: A series of x at.%Ce3+:10 at.%Yb3+:1 at.%Er3+:NaLa(WO4)2 (x=0,
10, …, 50) crystal powders were prepared by high temperature solid phase reaction.
The effect of Ce3+ concentration on the 4I11/24I13/2 transition of Er3+ ions was
analyzed. A single crystal of 48 at.%Ce3+:10.4 at.%Yb3+:1.6 at.%Er3+:NaLa(WO4)2
was grown by the Czochralski method. 1.2 W quasi-continuous-wave laser around
1.55 m was realized when a 2.61 mm thick c-cut slice of the crystal was pumped by
a diode laser at 970 nm. The achieved highest slope efficiency was 12.3% and the
threshold was 3.8 W.
a)
Author to whom correspondence should be addressed; electronic mail: huyd@fjirsm.ac.cn.
1
I. INTRODUCTION
Er3+ is a well-known active ion for solid-state laser in the infrared and visible
ranges due to its intricate energy level structure. In recent years, much attention has
been devoted to the research of Er3+-doped laser material mainly because its emission
around wavelength of 1.55 m via the transition of 4I13/24I15/2 is eye-safe and
matches the so-called third telecommunication window very well1-5. Generally, Yb3+
ions with large absorption cross-section around 970 nm, i.e. the emission wavelength
of InGaAs diode laser, are generally co-doped as sensitizer to improve the
performance of Er3+ laser owing to the resonant energy transfer from Yb3+ (2F5/2) to
Er3+ (4I11/2)5-10. However, for hosts with low phonon energy, efficient 1.55 m laser
can’t be realized due to the up-conversion and back energy transfer caused by the long
fluorescence lifetime of the 4I11/2 multiplet11-13. Since the energy interval between the
4
F7/2 and 4F5/2 multiplets of Ce3+ ions is close to that between the 4I11/2 and 4I13/2 of
Er3+, the Ce3+ ions can be used as the deactivator to shorten the fluorescence lifetime
of the 4I11/2 multiplet and then improve the laser performance14-21.
NaLa(WO4)2 crystal belongs to the tetragonal system with space group I41/a, and
the cell constants are a=5.349 Å, c=6.936 Å, Z=2, and d=6.56 g/cm3
22
. The crystal
melts congruently at 1140 °C and can be grown by the Czochralski method23. Both
Nd3+ and Yb3+ ions singly doped NaLa(WO4)2 crystals have been demonstrated as
excellent gain media for solid-state lasers24-27. However, as many tungstate host
materials, efficient 1.55 m laser is obstructed by the long fluorescence lifetime of the
4
I11/2 multiplet of Er3+ ions due to the low phonon energy of [WO4]2- 11,28.
2
In this work, a series of x at.% Ce3+:10 at.%Yb3+:1 at.%Er3+:NaLa(WO4)2 (x=0,
10, …, 50) crystal powders are prepared by high temperature solid phase reaction and
the effect of Ce3+ concentration on the transition of 4I11/24I13/2 is analyzed. A Ce3+,
Yb3+ and Er3+ co-doped NaLa(WO4)2 crystal is grown by the Czochralski method.
The polarization spectra of the Ce3+:Yb3+:Er3+:NaLa(WO4)2 crystal are analyzed and
the laser operation around 1.55 m of the crystal is realized.
II. EXPERIMENTAL PROCEDURE
A series of crystal powders of x at.%Ce3+:10 at.%Yb3+:1 at.%Er3+: NaLa(WO4)2
with the concentration of Ce3+ ions changing from 0 at.% to 50 at.% with interval of
10 at.% were prepared by high temperature solid phase reaction. The powders were
identified by the X-ray powder diffraction method.
A 48 at.%Ce3+:10.4 at.%Yb3+:1.6 at.%Er3+:NaLa(WO4)2 single crystal was grown
by the Czochralski method and the segregation coefficient of Ce3+, Yb3+, and Er3+ ions
in NaLa(WO4)2 crystal is estimated to be 1.2, 0.52, and 0.8, respectively. The crystal
as grown is yellow, which may be caused by the color centers formed with high
doping of Ce3+. The single crystal was oriented by means of the X-ray diffraction and
polarized microscopy.
For the spectral experiment, a slice with dimensions of 431 mm3 was cut from
the single crystal with the polished face of 43 mm2 parallel to the c axis of the
uniaxial crystal. The absorption spectra of the crystal slice in a range of 400-1700 nm
were recorded using a Perkin-Elmer UV-VIS-NIR spectrometer (Lambda–900). The
3
fluorescence spectra of the powder and crystal samples in a range from 1400 to 1700
nm were recorded using a spectrophotometer (FL920, Edinburgh) when the samples
were excited at 975 nm by a Xe-lamp. The fluorescence signals were detected with an
NIR PMT (R5509, Hamamatsu). Fluorescence decay curves of powder samples at
1010 nm corresponding to the transition from the 2F5/2 multiplet of Yb3+ ions and both
powder and crystal samples at 1535 nm corresponding to the transition from the 4I13/2
multiplet of Er3+ ions were recorded by the same spectrophotometer when the samples
were excited at 975 nm by a microsecond flash lamp (F900, Edinburgh).
Furthermore, the up-conversion fluorescence signals of powder samples past a
monochromator (Triax550, Jobin-Yvon) were detected with a PMT (R928,
Hamamasu) when the samples were excited at 975 nm by a Xe-lamp. The above
fluorescence spectra of powder samples were recorded in the same experimental
condition for comparison between different samples. All the spectral experiments
were carried out at room temperature (RT).
For the laser experiment, an end-pumped linear hemispherical resonator was
adopted. The gain medium was a 2.61 mm thick c-cut crystal slice. The uncoated
crystal slice was held in an aluminum mount and no special care was taken to ensure
the cooling of the slice. In order to reduce the thermal load in the slice, a 970nm diode
laser in pulse mode coupled by a fiber with 800 m diameter core (FAP-980,
Coherent) was used as the pump source. The pulse duration was 2 ms and the duty
cycle was 2%. The pump laser was focused into the gain medium with a waist
diameter of about 290 m. The flat input mirror had 90% transmission at 970nm and
4
99.8% reflectivity at 1.5-1.6 m. Four output couplers with a same 50 mm radius of
curvature and different transmissions of 1.0%, 1.8%, 3.8%, and 5.8% at 1.5-1.6 m
were used. In order to reduce the cavity loss, the length of the hemispherical cavity
was close to 50 mm. Output laser spectra were recorded by a monochromator
(Triax550, Jobin-Yvon) with a thermoelectrically cooled Ge detector (DSS-G025T,
Jobin-Yvon).
III. RESULTS AND DISCUSSION
A. Spectral properties of x at.%Ce3+:10 at.%Yb3+:1 at.%Er3+:NaLa(WO4)2 (x=0,
10, …, 50) crystal powders
For the Yb3+, Er3+, and Ce3+ co-doping powders, several energy transfer
processes would occur when the Yb3+ ions are excited to the 2F5/2 multiplet by 975 nm
pump light. The main energy transfer routes between these ions are shown in Fig. 1.
Firstly, the 4I11/2 multiplet of Er3+ ions will be populated mainly through the resonant
energy
transfer
from
the
2
F5/2
multiplet
of
Yb3+
ions
(2F5/2(Yb3+)+4I15/2(Er3+)2F7/2(Yb3+)+4I11/2(Er3+)). Then, the upper level 4I13/2 of Er3+
ions for the 1.55 m laser is populated mainly through the relaxation from the 4I11/2
multiplet. With co-doping of Ce3+, the energy transfer from Er3+ to Ce3+
(4I11/2(Er3+)+2F7/2(Ce3+)4I13/2 (Er3+)+2F5/2(Ce3+)) will enhance the relaxation of
4
I11/24I13/2.
Due to the low phonon energy of [WO4]2-, strong up-conversion originating from
the 4I11/2 multiplet of Er3+ ions as shown in Fig. 1 has been observed in many
5
tungstates29~31. Fig. 2 shows the up-conversion fluorescence spectra of the 4S3/24I15/2
transition of Er3+ ions when the exciting wavelength is 975 nm. The strong
up-conversion for the sample without doped by Ce3+ ions may originate from the
excited-state absorption (ESA) of the 4I11/2(Er3+) multiplet and the consecutive energy
transfer Yb3+(2F5/2)+Er3+(4I11/2)Yb3+(2F7/2)+Er3+(4F7/2). It can also be found from the
figure that the up-conversion fluorescence of Er3+ ions decreases sharply with the
increase of the Ce3+ concentration, and the up-conversion fluorescence is hardly
detectable for the samples with concentration of Ce3+ higher than 30%.
The energy transfer from Er3+ to Ce3+ not only weakens the up-conversion from
the 4I11/2(Er3+) multiplet, but also improves the energy transfer efficiency  of
2
F5/2(Yb3+)+4I15/2(Er3+)2F7/2(Yb3+)+4I11/2(Er3+). The efficiency  can be estimated by
  1   Yb:Er /  Yb 20,32, where  Yb:Er and  Yb are the fluorescence lifetimes of the
2
F5/2 multiplet of Yb3+ ions in the samples co-doped with Er3+ ions and not,
respectively, and which can be obtained by fitting the measured single exponential
fluorescence decay curves of the 2F5/2 multiplet. As shown in Fig. 3, the energy
transfer efficiency is improved from 34% to 85% with the increment of the Ce3+
concentration from 0 to 40 at.%. The results can be confirmed by the enhanced
fluorescence around 1.55 m as shown in Fig. 4 when the samples are excited at 975
nm.
The single exponential fluorescence decay curves at 1535 nm corresponding to
the transition from the 4I13/2 multiplet of Er3+ ions were also measured when the
samples were excited at 975 nm. The fitted fluorescence lifetimes of the 4I13/2
6
multiplet for all the samples as a function of Ce3+ concentration are shown in Fig. 5.
The lifetime is shortened from 4.1 to 2.9 ms for the sample with x=0 to x=50, which
may be caused mainly by the increase of crystal defects with the Ce3+ concentration.
B. Spectral properties of Ce3+:Yb3+:Er3+:NaLa(WO4)2 single crystal
The RT polarized absorption spectra of the 48 at.%Ce3+:10.4 at.%Yb3+:1.6
at.%Er3+:NaLa(WO4)2 single crystal are shown in Fig. 6. The absorption spectra
related to the Er3+ ions were analyzed by the Judd-Ofelt (J-O) theory32,33. The detailed
calculation procedure is similar to that reported in Ref. 34. The values of the
refractive indices for  and  polarizations were taken from Ref. 26 and the reduced
matrix elements of unit tensor operators used in the calculation could be found in Ref.
35. The measured and calculated oscillator strength, denoted as fexp and fcal,
respectively, and the root mean square deviations RMS f are listed in Table I. For the
Er3+ ions, the magnetic dipole transition of 4I15/24I13/2 cannot be ignored35 and the
values of fmd are also listed in Table I. The calculated intensity parameters Ωtq and the
effective intensity parameters are listed in Table II. The effective intensity parameters
were calculated from  teff  (2 t   t ) / 3 36. The intensity parameters of some
other Er3+-doped crystals reported are also listed in Table 2 for comparison. On the
basis of the calculated intensity parameters, the values of spontaneous emission
probability AJJ’, fluorescence branching ratio , and radiative lifetime  r for the
main fluorescence levels of Er3+ ions in the crystal could be calculated and the results
are listed in Table III.
7
For the important 4I13/24I15/2 transition of Er3+ ions, the emission cross section
at wavelength  can be obtained from the measured fluorescence spectra by the
Fuchtbauer-Landenburg (F-L) formula42 or from the absorption spectra by the
reciprocity method43. Fig. 7 shows the polarized emission cross section spectra
obtained by these two methods. Here, the Stark level data of Er3+ ions in NaGd(WO4)2
crystal34 were adopted in the reciprocity method since both the NaLa(WO4)2 and
NaGd(WO4)2 crystals are similar in structure and composition. It can be seen that, due
to the re-absorption of the emission from the 4I13/24I15/2 transition44, the emission
cross sections calculated by the F-L formula are smaller in the shorter wavelength
region but larger in longer wavelength region compared with those calculated by
reciprocity method. The peak emission cross sections calculated by the reciprocity
method are about 0.8310-20cm2 (-polarized) and 0.7710-20cm2 (-polarized),
which are comparable to those of some other Er3+-doped materials, such as
0.9510-20cm2
(-polarized)
0.8610-20cm2
and
(-polarized)
for
Ce3+:Er3+:NaLa(MoO4)216, and 1.1310-20cm2 (-polarized) and 0.6410-20cm2
(-polarized) for Er3+:YAl3(BO3)445, but smaller than 1.8710-20 (E//Ng), 1.7910-20
(E//Np), and 2.8510-20 (E//Nm) for KLu(WO4)211. The fluorescence lifetime of the
4
I13/2 multiplet of the crystal was measured to be 3.6 ms, which is longer than the
radiative lifetime calculated by the J-O method. This discrepancy, on the one hand,
may originate from the uncertainty of the J-O calculation; on the other hand, may be
caused by the re-absorption effect. Considering the long fluorescence lifetime of the
4
I13/2 multiplet in the crystal and the high fluorescence quantum efficiency of the
8
multiplet in the tungstates29,34, a low threshold laser around 1.55 m can be expected
in the Ce3+:Yb3+:Er3+:NaLa(WO4)2 crystal.
Since the Er3+ laser around 1.55 m via the 4I13/24I15/2 transition operates in
three-level scheme, the possible laser wavelength can be estimated by the gain cross
section46
q
q
Gq ( )  P em
( )  (1  P) abs
( )
where P is the population inversion ratio of Er3+ ions. The wavelength dependences of
polarized gain cross section for different P values (P=0.3, 0.4, …, 0.7) are shown in
Fig.
8.
The
smooth
and
broad
gain
curves
indicate
that
the
Ce3+:Yb3+:Er3+:NaLa(WO4)2 is a good candidate for gain medium of tunable and
ultra-short lasers.
IV. QUASI-CW LASER PERFORMANCE AROUND 1.55 μm
In the laser experiment, as expected, only weak upconversion green fluorescence
was observed and the laser oscillation around 1.55 m was realized. Fig. 9 shows the
laser output power versus the absorbed pump power for the four output couplers.
Because the duty cycle of the quasi-cw pulse laser was 2%, the values in the figure
are the measured ones multiplied by 50. For the output coupler with 1.8%
transmission, the achieved maximum output power is 1.2 W with slope efficiency of
12.3%, and the absorbed pump threshold power is 3.8 W. The output power and slope
efficiency for the Er3+:Yb3+:Ce3+:NaLa(WO4)2 crystal are obviously higher than those
of Er3+:Yb3+:KYW (80 mW and 1.6%) and Er3+:Yb3+:KLu(WO4)2 (152 mW and 1.2%)
9
crystals without Ce3+ ions11.
Fig. 10 shows the output laser spectra for the four output couplers when the
absorbed power is 13.6 W. It can be found that the laser wavelength shifts from 1590
to 1555 nm when the output-coupler transmission increases from 1.0% to 5.8%. The
shift of the laser wavelength with the increment of output coupler transmission can be
explained by the -polarized gain curves shown in Fig. 8.9
V. CONCLUSION
Ce3+ ions as the deactivator have been introduced to Er3+:Yb3+:NaLa(WO4)2
crystal to enhance the 4I11/24I13/2 relaxation of Er3+ ions by the energy transfer
4
I11/2(Er3+)+2F7/2(Ce3+)4I13/2(Er3+)+2F5/2(Ce3+)
and
then
improve
the
laser
performance around 1.55 m via the 4I13/24I15/2 transition of Er3+ ions. The
experiment results obtained from a series of x at.%Ce3+:10 at.%Yb3+:1
at.%Er3+:NaLa(WO4)2 (x=0, 10, …, 50) crystal powders indicate that the
up-conversion fluorescence originating from the 4I11/2 multiplet of Er3+ ions is
restrained significantly for the samples with concentration of Ce3+ higher than 30%
and the energy transfer efficiency of Yb3+Er3+ is improved from 34% to 85% with
the increment of the Ce3+ concentration from 0 to 40 at.%. However, the fluorescence
lifetime of the 4I13/2 multiplet of Er3+ ions is shortened from 4.1 to 2.9 ms with the
increment of the Ce3+ concentration from 0 to 50 at.%, which may be caused mainly
by the increase of crystal defects with the Ce3+ concentration. A 48 at.%Ce3+:10.4
at.%Yb3+:1.6 at.%Er3+:NaLa(WO4)2 single crystal was obtained by the Czochralski
10
method. The spectral properties of the crystal were analyzed and the results show that
the Ce3+:Yb3+:Er3+:NaLa(WO4)2 is a good candidate for 1.55 m laser.
Quasi-continuous wave laser oscillation around 1.55 m was realized when this
crystal was pumped by diode laser at 970 nm. The achieved highest output powder
and slope efficiency were 1.2 W and 12.3%, respectively, and the threshold was 3.8 W.
More efficient laser operation around 1.55 m may be expected when the
concentrations of Yb3+ and Er3+ are also optimized and the quality of the crystal is
further improved, and this work is in progress.
ACKNOWLEDGMENTS
This work has been supported by the National Natural Science Foundation of China
(grants 50802094 and 50972142), the Major Programs of the Chinese Academy of
Sciences (grant SZD08001-1), and the Chinese National Engineering Research Center
for Optoelectronic Crystalline Materials.
11
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TABLE I. Mean wavelength and polarized experimental and calculated oscillator
strengths for Er3+ in Ce3+:Yb3+:Er3+:NaLa(WO4)2 crystal.
f (10-6 cm2)
J  -multiplet

 abs (nm)

fexp
fcal
4
1525
2.05
4
806
655
547
522
490
0.61
2.52
0.59
14.61
1.81
I13/2
I9/2
F9/2
4
S3/2
2H
11/2
4F
7/2
4
RMS f (10-7 cm2)
RMS error (%)
1.41 (ed)
0.58 (md)
0.44
2.52
0.52
14.61
2.27
2.89
4.7
16
fexp
fcal
1.52
0.94 (ed)
0.58 (md)
0.22
2.33
0.39
16.54
0.96
0.45
2.16
0.27
16.55
1.51
3.61
5.3
TABLE
II.
Comparison
of
the
J-O
parameters
for
Er3+
Ce3+:Yb3+:Er3+:NaLa(WO4)2 and in some other laser crystals
Crystal
NaLa(WO4)2
NaY(WO4)2
NaGd(WO4)2
KY(WO4)2
KGd(WO4)2
YVO4
YAG
Ω
Ω
Ωeff
Ω210-20 cm2
Ω410-20 cm2
Ω610-20 cm2
Reference
13.87
16.03
15.31
8.93
14.91
7.96
8.90
13.45
0.79
3.00
3.10
3.07
2.48
2.19
2.31
0.96
2.23
1.19
1.91
1.00
1.30
1.53
1.30
1.40
0.82
1.67
1.08
This work
17
[37]
[34]
[38]
[39]
[40]
[41]
in
TABLE III. Spontaneous emission probabilities AJJ’, fluorescence branching ratios β,
and radiative lifetime r for Er3+ in Ce3+:Yb3+:Er3+:NaLa(WO4)2 crystal

J'  J
4
I13/2
4
I11/2
4
I9/2
4
F9/2
4S
3/2
2H
11/2
4F
7/2
4
I15/2
I13/2
4
I15/2
4
I11/2
4
I13/2
4
I15/2
4
I9/2
4I
11/2
4I
13/2
4I
15/2
4F
9/2
4I
9/2
4I
11/2
4I
13/2
4I
15/2
4S
3/2
4F
9/2
4I
9/2
4I
11/2
4I
13/2
4
I15/2
2H
11/2
4S
3/2
4F
9/2
4I
9/2
4I
11/2
4I
13/2
4I
15/2
4

AJJ’ (s-1)
β (%)
AJJ’ (s-1)
β (%)
391.20
70.63
483.22
6.19
128.08
491.71
29.59
232.64
231.70
4400
1.97
196.67
104.82
1365
3427
0.75
128.85
807.22
527.22
507.14
35030
1.15
0.06
17.66
200.11
449.89
1185
3769
100
12.8
87.2
0.9
20.5
78.6
0.6
4.8
4.7
89.9
0
3.9
2.0
26.8
67.3
0
0.3
2.2
1.4
1.4
94.7
0
0
0.3
3.6
8
21.1
67
273.20
54.39
359.97
5.72
69.54
501.85
32.42
171.33
224.41
3766
1.06
136.9
59.84
721.22
1803
0.74
149.12
836.04
546.31
516.08
39650
0.93
0.04
12.68
201.75
387.34
928
4368
100
13.1
86.9
1
12
87
0.7
4.1
5.4
89.8
0
5.1
2.2
26.5
66.2
0
0.4
2
1.3
1.2
95.1
0
0
0.2
3.5
6.6
15.7
74
18
τr (ms)
3.20
2.17
1.69
0.19
0.28
0.025
0.18
FIGURE CAPTIONS
FIG. 1. Energy level diagram of Ce3+, Er3+ and Yb3+ multiplets involved in 1.55 μm
laser emission processes.
FIG.
2.
Up-conversion
fluorescence
spectra
Er3+
of
ions
in
the
Ce3+:Yb3+:Er3+:NaLa(WO4)2 powder samples with different concentration of Ce3+
ions under excitation at 975 nm.
FIG.
3.
Energy
transfer
efficiency

of
Yb3+
to
Er3+
for
the
Ce3+:Yb3+:Er3+:NaLa(WO4)2 powder samples versus the concentration of Ce3+ ions.
FIG.
4.
Room
temperature
fluorescence
spectra
of
Er3+
ions
in
the
Ce3+:Yb3+:Er3+:NaLa(WO4)2 powder samples with different concentration of Ce3+
ions under excitation at 975 nm.
FIG. 5. Room temperature fluorescence lifetime of the 4I13/2 multiplet for Er3+ ions in
the Ce3+:Yb3+:Er3+:NaLa(WO4)2 powder samples versus the concentration of Ce3+
ions under excitation at 975 nm.
FIG. 6. Room temperature polarized absorption spectra of the 48 at.%Ce3+:10.4
at.%Yb3+:1.6 at.%Er3+:NaLa(WO4)2 single crystal.
FIG. 7. Comparison of emission cross section around 1.55m for Er3+ ions in the 48
at.%Ce3+:10.4 at.%Yb3+:1.6 at.%Er3+:NaLa(WO4)2 single crystal as a function of
wavelength. The solid lines are calculated by the reciprocity method and the dashed
lines are calculated by the F-L formula.
FIG. 8. Polarized gain cross section around 1.55m for Er3+ ions in the 48
at.%Ce3+:10.4 at.%Yb3+:1.6 at.%Er3+:NaLa(WO4)2 single crystal as a function of
wavelength.
FIG. 9. Output power of laser around 1.55 m versus absorbed pump power at 970
nm for 48 at.%Ce3+:10.4 at.%Yb3+:1.6 at.%Er3+:NaLa(WO4)2 single crystal.
FIG. 10. Laser spectra of the 48 at.%Ce3+:10.4 at.%Yb3+:1.6 at.%Er3+:NaLa(WO4)2
single crystal with different transmissions of output mirror.
19
FIG. 1.
Xinghong GONG, et al. J. Appl. Phys.
20
FIG. 2.
Xinghong GONG, et al. J. Appl. Phys.
21
FIG. 3.
Xinghong GONG, et al. J. Appl. Phys.
22
FIG. 4.
Xinghong GONG, et al. J. Appl. Phys.
23
FIG. 5.
Xinghong GONG, et al. J. Appl. Phys.
24
15

12
-1
Absorption coefficient (cm )
9
6
3
0
15

12
9
6
3
0
400
600
800
1000
1200
1400
1600
Wavelength (nm)
FIG. 6.
Xinghong GONG, et al. J. Appl. Phys.
25
1.0

0.8
FL
RM
0.4
2
cm )
0.6
Cross section (10
-20
0.2
0.0
1.0
0.8
FL
RM

0.6
0.4
0.2
0.0
1450
1500
1550
1600
1650
Wavelength (nm)
FIG. 7.
Xinghong GONG, et al. J. Appl. Phys.
26
1.0
P=0.3
P=0.4
P=0.5

P=0.6
0.5
P=0.7
0.0
-20
2
cm )
P=0.8
Gain cross section (10
-0.5
-1.0
1.0
P=0.3
P=0.4

P=0.5
0.5
P=0.6
P=0.7
P=0.8
0.0
-0.5
-1.0
1450
1500
1550
1600
1650
Wavelength (nm)
FIG. 8.
Xinghong GONG, et al. J. Appl. Phys.
27
1.4
=10.3%
T=1%
1.2
T=1.8% =12.3%
T=3.8% =11.5%
T=5.8% =11.2%
Output power (W)
1.0
0.8
0.6
0.4
0.2
0.0
2
4
6
8
10
12
14
Absorbed pumb power (W)
FIG. 9.
Xinghong GONG, et al. J. Appl. Phys.
28
T=1.0%
Intensity (a.u.)
T=1.8%
T=3.8%
T=5.8%
1550
1560
1570
1580
1590
1600
Wavelength (nm)
FIG. 10.
Xinghong GONG, et al. J. Appl. Phys.
29