THE GENERATION OF ULTRASHORT LASER-PULSES

This article is intended to provide an introduction to ultrafast laser development for scientists new to the field, It also aims to provide a snapshot of the state-of-the-art of ultrafast lasers and to indicate how this state evolved over the last thirty years. In the first secti on, the main issues concerning ultrashort pulse generation are discuss ed and the most important ultrafast laser media are briefly reviewed, An extensive historical survey of mode-locking and pulse compression f rom 1964 until 1994 is then presented which covers the most important developments and aims to put recent advances and state-of-the-art femt osecond lasers in context, This review also anticipates future develop ments in practical ultrafast lasers for real-world applications. The b asic techniques of mode-locking are then reviewed at a tutorial level, These include active mode-locking, passive mode-locking with real, re sonant saturable absorbers and passive mode-locking with the optical K err effect. Emphasis is placed on ultrafast solid-state lasers, dye la sers and fibre lasers, Group velocity dispersion and self-phase modula tion are introduced and their interaction discussed in some detail, Fi bre-optic pulse compression is described and the significance of solit on shaping and solitary lasers is highlighted. Some of the phenomena l imiting the minimum achievable duration of laser pulses are identified , The final section describes techniques for measuring ultrashort puls es including electrooptic streak cameras and second harmonic generatio n autocorrelation.