Page 183 - High Power Laser Handbook

152 Diode Lasers High-Power Diode Laser Arrays 153

Figure 6.19 Fiber coupling scheme of stacks. (Courtesy of LaserLine)

Maximum output power 1000 W 2000 W 3000 W 4000 W
Beam quality 20 mm-mrad 30 mm-mrad
Laser light cable 400 μm, NA = 0.1 300 μm, NA = 0.2 or
600 μm, NA = 0.1
Spot at f = 100 mm 0.2 mm 0.3 mm

Table 6.2 Typical Performance Parameters of a Fiber-Coupled Diode Laser System

The power scaling to multikilowatts can be done thereafter by polar-
ization coupling and wavelength multiplexing. Power levels above 4
kW from a 600-mm fiber have been demonstrated with this fiber-cou-
pled approach (see Table 6.2).
Because the power from a single 100-mm fiber of 0.12 NA was
increased from a typical 10 W to more than 100 W for a single wave-
length, an alternate design to actively cooled stacks became available.
By using 19 individual modules, the fibers can be arranged in a close-
packed circle of less than 600 mm and can therefore be coupled into the
same size fiber, thus preserving the low 0.12 NA value. Thus, adding
other wavelengths allows the power to increase by roughly 1.5 kW per
wavelength, providing systems in the multikilowatt range. Figure 6.20
compares the size of a 3-kW lamp-pumped solid-state laser and a diode
laser system of the same output power.
With the initial electro-optical efficiency of diode lasers currently
in the range of 60 to 65 percent, the wall-plug efficiency of diode laser
systems can be above the 40-percent mark, which is well above that
for all diode-pumped solid-state lasers.