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Neodymium
doped Potassium-Gadolinium Tungstate crystals (Nd:KGd(WO4)2
or Nd:KGW) are low-threshold high effective laser medium exceptionally
suitable for laser rangefinders. The efficiency of such lasers is 3
- 5 times better than that of the Yttrium-Aluminium Garnet (YAG) lasers.
At low pumping energies (0.5 to 1.0 J), KGW crystals are one of the
few materials ensuing an effective generation. KGW single crystals can
also be used for the fabrication of high-efficiency lasers with high
output energy. The single crystals exhibit a high optical quality. KGW
crystals have great value of the bulk strength for laser radiation.
The technology enables the obtaining of KGW single crystals with the
weight of up to 3 kg and fabrication of round active elements with the
diameter from 4 to 12 mm and the length from 50 to 120 mm.
Yb:KGW is one of the most promising laser active
materials. The simple two-level electronic structure of the Yb ion avoids
undesired loss processes such as upconversion, excited state absorption,
and concentration quenching. Compared to the commonly used Nd:YAG crystal,
Yb:KGW crystal has a much larger absorption bandwidth, 3 or 4 times
longer emission lifetime in similar hosts with enhanced storage capacity,
lower quantum defect and is more suitable for diode pumping than the
traditional Nd-doped systems. The smaller Stokes shift reduces heating
and increases the laser efficiency. In comparison with other Yb doped
laser crystals such as Yb:YAG and Yb:YCOB crystals, Yb:KGW has a much
higher (13-17 times) cross-section of absorption, lower quantum defect
(~4%), a cross-section of emission that is 9 times higher than Yb: YCOB,
and an emission band that is broader than Yb:YAG, a high nonlinear coefficient
of refraction, and the highest slope efficiency (87%). With such performance
advantages, Yb:KGW crystals are expected to replace Nd:YAG and Yb:YAG
crystals in high-power diode-pumped laser systems. Yb:KGW also holds
great promise for creating high-power, short pulse duration femtosecond
lasers and their broad applications.
The emission linewidth of KYW:Yb or KGdW:Yb is broader than
in YAG and comparable to that in glasses. This linewidth is interesting
not only for potential tuning but mainly for the generation and amplification
of short (ps or fs) laser pulses. Mode-locking of a diode-pumped KGdW:Yb
laser has been demonstrated and utilization of the crystal anisotropy
for maximum gain bandwidth culminated in the generation of 71 fs pulses
with KYW:Yb in 2001. Also, the first regenerative amplification of fs
pulses in KYW:Yb has been demonstrated in 2001. Whereas fs pulses can
provide ultimate peak powers, much higher average powers and optimum
conditions for frequency conversion to other wavelengths can be realized
with slightly longer pulses (1 ps or more for Raman conversion). The
slope efficiency up to 78% was demonstrated with the Ti:Sapphire-laser
and 66% with the diode laser pumping. This high value of the slope efficiency
opens potentiality for further nonlinear optical conversion of this
radiation with a good overall efficiency. |
PROPERTIES
| Material |
Nd:KGW |
Yb:KGW |
| Crystal structure |
monoclinic
|
monoclinic
|
| Space group |
C62h-C2/c
|
C62h-C2/c
|
| Lattice constant,
Å |
a = 8.10;
b = 10.43; c = 7.60 |
|
| hardness |
5 |
5 |
| density,
g/cm3 |
7.27 |
7.27 |
| Possible
dopant concentrations |
1 - 8 at.
% |
1 - 5 at.
% |
| transmission
range, 10-6m |
0.35-5.5
|
0.35-5.5 |
| optical damage
threshold, GW/cm2 |
20 |
20 |
| emission
cross-section, ñm-2 |
4.3*10-19 |
|
| Thermal conductivity
at 373°K, W x cm-1 x °K-1 |
K[100]
= 0.026; K[010]= 0.038; K[001] = 0.034 |
Ka=2.6 W/mK,
Kb=3.8 W/mK, Kc=3.4 W/mK |
| Young's modulus,
GPa |
E[100]
= 115.8; E[010]= 152.5; E[001] = 92.4 |
|
| Termal expansion
coefficient, at 373°K |
±[100]
= 4 x 10-6 x °K-1; ±[010]=
1.6 x 10-6 x °K-1;
±[001]= 8.5 x 10-6 x °K-1 |
|
| Refraction
index variation |
(0.4 - 1)
x 10-5 |
|
|
Spectroscopic
Properties
|
3% Nd:KGW
|
5% Yb:KYW
|
5% Yb:KGW
|
|
Absorption
peak wavelength, lpump, [nm]
|
810
|
981.2
|
981.2
|
|
Absorption
linewidth, Dlpump, [nm]
|
4.5
|
3.5
|
3.7
|
|
Peak absorption
cross-section, spump, [cm2]
|
1.19x10-19
|
1.33x10-19
|
1.2x10-19
|
| Peak absorption
coefficient, [cm-1] |
20
|
40
|
26
|
| Emission
wavelength, lse, [nm] |
1067
|
1025
|
1023
|
| Emission
linewidth, Dlse, [nm] |
24
|
16
|
20
|
|
Peak emission
cross-section, sse, [cm2]
|
4.3x10-19
|
3x10-20
|
2.8x10-20
|
| Quantum
effect, lpump/lse, [nm] |
0.759
|
0.957
|
0.959
|
| Fluorescence
lifetime, tem, [ms] |
0.1
|
0.6
|
0.6
|
Rods with
round cross-sections are manufactured:
| Diameter
tolerance, mm |
+
0.0 / -0.1 |
| Length
tolerance, mm |
+1.0 /
-0.0 |
| Chamfer |
45 ±
10° x 0.2 ± 0.1 mm |
| Parallelism |
< 30' |
| Perpendicularity |
< 15' |
| Flatness |
< 0.2 |
| Absorption
loss at 1150 nm, cm-1 |
< 0.005 |
We supply rods and
slabs with different cross-sections, dimensions and coatings. Different
dopants compositions with different concentrations are available for
specific customer requirements.
Nd:KGW, Yb-Er:KGW, Yb-Tm:KGW and Yb-Ho:KGW as well as
Nd:KYW compositions are available.
|