Page 165 - High Power Laser Handbook

134 Diode Lasers High-Power Diode Laser Arrays 135

Typical Electro-Optical Efficiency
70%

60%

50%

Efficiency 40%

30%

20%

10%

0%
600 800 1000 1200 1400 1600 1800 2000 2200
Wavelength (nm)

Figure 6.1 Typical electro-optical efficiencies of semiconductor material as
a function of wavelength.

Early applications of diode laser arrays, such as pumping of solid-
state laser rods and slabs, took advantage of the narrow wavelength
and the reduced heat load in the laser crystals. With new applications
in the area of materials processing, where diode lasers start to compete
with lamp-pumped solid-state lasers, the brightness of the diode
lasers has become the most important value to be conserved while
scaling up the power to the multikilowatt level. The higher bright-
ness level is also required for new pumping schemes needed for disc
and fiber lasers.
The following sections will describe state-of-the-art high-power
diode lasers and their manufacturing processes. Various forms of diode
laser components, from a diode stack for short pulses (quasi-continuous
wave, or QCW) to high-brightness fiber-coupled modules with con-
tinuous wave (CW) kilowatt output power levels, are introduced.

6.2 Diode Laser Bar Assembly

The performance (maximum power, wavelength, and reliability) of a
diode laser device strongly depends on the temperature of the p-n
junction, as described in Chap. 5. Therefore, all high-power diode