
Nonlinear Refractive Index Effects 409
In amplifier chains operating up to high saturation parameters, saturable
absorbers will generally be used to isolate stages of high gain, reducing the
effect of ASE. In addition the saturable absorber can counteract the broadening
effect of the amplifier because of:
• pulse shaping (steepening of the leading edge) by saturable absorption
and thus elimination of subsequent broadening by the saturable gain
(cf. Fig. 7.4); and
• pulse compression because of the combination of downchirping (if the pulse
has a longer wavelength than that of the peak of the absorption band) by the
absorber and propagation in a gain medium ...