Laser operation can be enhanced either by modifying the laser device itself or by modifying the beam it generates. The distinction is significant in the world of commercial lasers. Modifications to the laser device typically are made by the manufacturer at the factory, or sometimes at customers premises. However, it is the user who normally modifies the laser beam.

Factory modifications come in many forms, including substitution of different power supplies, choice of resonator optics, packaging of the device, and selection of control systems. Many data sheets include long lists of options offered by the manufacturers, which give users a considerable range of choices. However, these options are usually specific to a particular model or laser type, and the user has only limited control over them. The major options for each type of laser are described in Chaps. 7 to 29.

This chapter concentrates on modiflcations the user can make, although often they require hardware purchased from the laser manufacturer. All involve alterations to the laser beam, which can occur within as well as outside the laser cavity. These techniques offer users important flexibility in choice of laser wavelength, pulse length, and (in some cases) output power.