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
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