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Chapter 5:
Power Scaling Considerations
Several aspects of power scaling have been addressed in previous sections. In this chapter, the basic issues involved with producing higher power from diode-pumped lasers will be covered in some detail. Before proceeding, however, it will be helpful to discuss the factors that are most prominent in the drive for more power. There are three commercial lasers that account for much of the high-power laser sales, and diode-pumped lasers can in general replace them all. These are large frame argon ion lasers producing 20 W or more in the blue-green, Q-switched Nd:YAG lasers producing about 1 J/pulse at 1.06 mm with an average power of 10 W or greater, and cw Nd:YAG lasers producing 50 W or more in the IR. Great strides have been made in producing both commercial and prototype diode-pumped lasers that are competitive with these products. For example, a 10-W cw 532-nm laser is currently available commercially, and higher-power, diffractionlimited TEM00 output is inevitable. Granted that a doubled Nd:YAG laser cannot do everything an argon ion laser can (the multiple-wavelength output of the latter, which includes the UV, is an important property for many end users), but for anyone who has had to deal with installing the utilities for a large-frame ion laser, the advantages of diode pumping are quite compelling. For IR emission, both pulsed and cw diode-pumped lasers have been demonstrated at power levels comparable to commercial lamp-pumped devices. Output energies exceeding 1 J/pulse with repetition rates of hundreds of hertz have already been produced. Continuous-wave operation at 1 mm with output power exceeding 100 W has also been demonstrated, in both Nd- and Yb-doped materials. The problem that commercial manufacturers of diode-pumped lasers face is - and will continue to be - the component cost. Lamps are cheap; diodes are not. An area that shows great promise for diode-pumped lasers is third and fourth harmonic generation of the 1.06-mm output of Nd:YAG. The resulting short-wavelength radiation is useful in semiconductor processing and photolithography. Output is typically TEM00 and may be cw or repetitively Q-switched. Harmonic generation from single-longitudinal-mode lasers has been demonstrated with high conversion efficiency at moderate power levels. Since throughput for industrial processing is dependent on output power, scaling is important for these types of lasers as well.
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