
404 Femtosecond Pulse Amplification
gain can be reached and thus correspondingly shorter pulses can be amplified.
This was demonstrated by Glownia et al. [11] and Szatmari et al. [12] who
succeeded in amplifying 150–200 fs pulses in XeCl.
7.2.3. Amplified Spontaneous Emission (ASE)
So far we have neglected one severe problem in (fs) pulse amplification,
namely amplified spontaneous emission (ASE), which mainly results from the
pump pulses being much longer than the fs pulses to be amplified. As a conse-
quence of the medium being inverted before (and after) the actual amplification
process, spontaneous emission traveling through the pumped volume can con-