6-laser

The LASER light source, whose name is based on “Light Amplification by
Stimulated Emission of Radiation”, is the most important device in almost
all photonic applications. First built in 1960 [6.1–6.5] it allows the generation
of light with properties not available from natural light sources. Modern
commercially available laser systems allow output powers of up to 1020W for
short times with good beam quality and of several kW in continuos operation,
usually with less good beam quality. Very short pulses with durations
smaller than 5 · 10?15 s, wavelengths from a few nm in the XUV to the far
IR with several 10 ?m, pulse energies of up to 104 J and frequency stability’s
and resolutions of better 10?13 can be generated. The laser prices range from
$ 1 to many millions of dollars and their size from less than a cubic mm to
the dimensions of large buildings.
The good coherence and beam quality of laser light in combination with
high powers and short pulses are the basis for many nonlinear interactions,
but the laser is a highly nonlinear optical device itself, using nonlinear properties
of materials as described in the previous chapters. Therefore, the fundamental
laws treated in Chap. 2 for the description of light as well as the description
of linear and nonlinear interactions of light with matter in Chaps. 3,
4 and 5 are the basis for the analysis of laser operation and its light properties.
Therefore, the theoretical description of laser devices represents an application
of these laws and can be presented in this chapter in a compact
form. For details the related sections of the previous chapters should be consulted.
The different lasers and their constructions, as well as the resulting
relevant light and operation parameters, are described and the consequences
for photonic applications are discussed. Finally, possible classifications are
given and safety aspects are mentioned. For further reading see [M6, M16,
M17, M23–M25, M27, M28, M30, M33, M43, M44, M49, M50, M58–M65].
6.1 Principle
Lasers are based on the stimulated emission of light in an active material
which has been pre-excited by a pump mechanism. The stimulated emission
can be carried out in laser oscillators which are always the primary source
of laser light. In addition this light can be amplified via stimulated emission