Page 181 - High Power Laser Handbook
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150 Diode Lasers High-Power Diode Laser Arrays 151
Figure 6.16
Beam shaping with
tilted cylindrical
lens array.
P-polarized
P-polarized
P-polarized
P-polarized
Figure 6.17 Polarization coupling scheme with half-wave plate and
polarization cube.
6.6.2 Power Scaling
Multikilowatt power levels can be reached by using multiple diode
laser bars. As shown in Sec. 6.4, the diodes can be arranged on mini-
channel heat sinks in a stacked format. The fill factor in such stacks
only reaches values of up to 50 percent due to the pitch of the heat
sinks and the beam size created by the fast-axis collimation lens. This
fill factor can be increased by interleaving the beams of a second stack
between the beams of the first stack (Fig. 6.18). In general, two meth-
ods are available for interleaving two stacks without power loss:
using a stack of glass plates (refractive; Spectra Physics) or a slotted/
striped mirror (reflective) (Fraunhofer Institute for Laser Technology)
to interleave two stacks without power loss. Both techniques double
the power and brightness of a stack. To further increase the power
and brightness, the beams from two interleaved sets of stacks can be
combined by polarization coupling, as described in Fig. 6.17.
If the wavelength is of minor importance for the application,
the power and brightness can be further increased by adding multi-
ple wavelengths to the beam. More than seven narrow-band diode
wavelengths have been developed between 800 and 1030 nm, where