Page 62 - Tunable Lasers Handbook

3 Tunable Excimer Lasers 43

is simplest to have the injected oscillator pulse length equal to or larger than the
amplifier gain time.
In the next subsections we briefly discuss the general techniques that are
used to obtain narrow-linewidth tunable systems, including a discussion of the
gain in the narrowness of the oscillator linewidths as a function of the number of
cavity round-trips. The operation of unstable resonators is also discussed so that
the limitations of an injection seeded regenerative amplifier can be understood.
A brief discussion of avalanche discharge techniques is then given to instill a
feel for the type of devices that are generally available. This includes typically
short-pulse devices (25 ns) as well as techniques that allow stable discharges
resulting in laser pulse lengths of hundreds of nanoseconds. A short review of
electron beam and electron beam sustained discharges will be given as well.

3.1 Tuning and Line-Narrowing Methods

The passive spectral width for a Brewster prism, Littrow prism, and beam
expander chain such as that shown in Fig. 5 is discussed in detail in Chapter 2.
For the case of Brewster prisms. the generalized equation given by Duarte
and Piper [63] reduces to

(1)

For a multiple-prism assembly, or sequence, composed of I- prisms the overall
single-pass dispersion is given by [ 121

FIGURE 5 Dispersive oscillator incorporaring a multiple-prism assembly (from Sze er a[. [~j],.