Page 182 - High Power Laser Handbook
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150 Diode Lasers High-Power Diode Laser Arrays 151
Output Slow axis Input
Z = 1, 3, 5, ...
Z = 1 Z = 2
Z = 2, 4, 6, ...
Output 6 beams- Fast axis Input 2 × 3 beams-
pitch 0.9 mm pitch 1.8 mm
Z = 1
Z = 2
Z = 3
Z = 4
Z = 5
Z = 6
Figure 6.18 Refractive method of interleaving beams from a diode laser
stack.
the electro-optical efficiency is greater than 55 percent and where
power levels greater than 100 W per diode bar are available. The dif-
ferent wavelengths can be multiplexed with dielectric-edged mirror
into a common beam. Assuming a 12-bar stack with an internal pitch
of 1.8 mm and an average power of 120 W per diode bar, the total
power in a 21 × 10 mm beam size will be 2880 W after interleaving,
and 5742 W after polarization coupling, assuming a 5 percent cou-
pling loss. Multiplexing all seven available wavelengths, the power
will reach more than 35 kW CW from a 2-cm aperture. The full beam
2
parameter product (BPP) can be as low as 80 × 250 mm-mrad for the
two axes, or a combined BPP of 330 mm-mrad. This enables fiber cou-
pling into an 800-mm core diameter fiber with an NA of 0.22, which
has an intrinsic BPP of 352 mm-mrad.
6.6.3 Fiber-Coupled High-Power Diode Laser Devices
Following the above described example of extreme power, fiber-coupled
diode laser stacks have been developed and placed in the market as a
replacement for lamp-pumped solid-state lasers. Because the beam
quality of lamp-pumped solid-state lasers enabled fiber coupling into
a 400- or 600-mm core fiber with an NA of 0.12, the diode laser stacks
had to be designed for the same beam parameter product of less than
120 mm-mrad (full angle). An example of such a design is shown in
Fig. 6.19. The slow-axis beam quality is improved by rearranging
the emitter from the horizontal line in the diode bar to a vertical stack
of emitters, using two stacks of parallel glass plates similar to the
interleaving concept. By choosing the correct number of emitters
for the diode bar, the stack’s beam quality can be made uniform in
both directions and, therefore, most effectively coupled into a fiber.