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Nd or Yb doped Potassium-Gadolinium Tungstate Crystals (KGd(WO4)2 or KGW)
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KGW:Nd
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, m-2 4.3*10-19  
Thermal conductivity at 373K, 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 373K [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.

I N Q U I R Y    F O R M :

Material:
Quantity of elements:
Application:

For example: SHG@1064; SFG@800+267->200; DFG@780-842->10600; OPO@355->460÷560+960÷1150; etc.
polished sites:

BLOCK    or  BLOCK
 a-b b-c a-c
or d  
Dopant conc.:
% ;      Orientation:
Dimensions/Tolerances:
For example:
10.0 +/- 0.1
Coating:

For example: ARC s1/s2 1064 R<0.25%; ARC s1/s2 1064 R<0.25%+532<0.5%;
BBAR s1/s2 1064 R<1%+3÷10<5% etc.
a = mm;
c = mm
b = mm or
dia. = mm;
This field is for additional information such as application,
comments, add. requirements etc.

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