Page 270 - High Power Laser Handbook
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238 So l i d - S t at e La s e r s Thin-Disc Lasers 239
120
Azimuthal stress (MPa) 80
40
0
0 1 2 3 4 5 6 7 8 Classical design,
2
Pump power density (kW/cm ) soldered on CuW
Composite disk,
directly cooled
40
20
Radial stress (MPa) −20 0
−40
−60
−80
0 1 2 3 4 5 6 7 8 9
2
Pump power density (kW/cm )
Figure 10.10 Comparison of the maximum radial and azimuthal stress
inside the disc for two different mounting designs.
The transparent layer on top of the disc has nearly no axial tempera-
ture gradient and the directly cooled design shows a significantly
smaller deformation. This results in a reduced refractive power of the
thin-disc as can be seen in Fig. 10.11. But the remaining aspherical
contributions of the OPD are stronger, as there is more hot material
inside the resonator.
10.5.6 Numerical Modeling of Gain and Excitation
Yb:YAG shows a significant temperature-dependent reabsorption of
the laser radiation. In the thin-disc design it is operated at a compa-
rable high inversion level, resulting in a significant reduction of the
pump absorption. Consequently, the coupling between the differen-
tial equations of pump absorption, laser amplification, inversion, and
