KGW, or potassium gadolinium tungstate, is a laser active crystal that is commonly used in solid-state lasers. KGW has a monoclinic crystal structure and is doped with rare earth ions, such as neodymium or chromium, which allow it to amplify light through stimulated emission.

One of the main advantages of KGW as a laser active crystal is its ability to generate laser emissions at a wavelength of 1064 nanometers, which is the same as Nd:YAG lasers. However, KGW has a higher absorption cross-section than Nd:YAG, which means that it can absorb more pump energy and generate higher laser powers.

Cr:KGW, or chromium-doped KGW, is a popular type of KGW laser. Cr:KGW lasers operate at a wavelength of 1.3 microns, which is in the eye-safe region and makes them suitable for military and remote sensing applications. Cr:KGW lasers can also be mode-locked to generate ultra-short pulses in the picosecond or femtosecond range.

Another advantage of KGW as a laser active crystal is its high thermal conductivity, which allows it to dissipate heat efficiently and reduce thermal effects such as thermal lensing. This makes KGW lasers suitable for high-power and high-repetition rate applications.

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

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