Pulse Shaping in Intracavity Elements 323
This reflects the fact that the shortest focal length is produced at the inten-
sity maximum leading to the smallest beam size at the position of the aperture.
Obviously, such a lens aperture sequence is just another example of a fast element
whose overall transmission is controlled by the pulse intensity.
Laser pulse induced lensing does take place in nearly all ultrashort pulse
mode-locked lasers. In femtosecond pulse lasers, there is always a pulse shaping
mechanism in the cavity, involving a balance of dispersion and temporal SPM.
The latter effect implies necessarily a spatial modulation of the wavefront, hence
self-lensing. As a result of self-lensing, the size of the cavity modes is modi-
fied, leading ...