Introductory remarks

The first day of this Discussion Meeting is mainly devoted to ultra-short laser sources and the methods of measurement of picosecond and subpicosecond pulses of radiation over the electromagnetic spectrum from X-rays to the infrared. The last decade has seen dramatic advances in the understanding of the complex physical and chemical processes occurring in mode-locked lasers and in the interactions, linear and nonlinear, with matter of the ultra-short light pulses so produced. The flashlamp-pumped frequency-tunable dye laser has played a key role in these advances. It provided the shortest and most controllable pulses for the development of time-resolving instruments and, later, was an experimental model for the detailed measurements that eventually led to the elucidation of the mechanisms by which ultra-short pulses evolve in a mode-locked laser from the initial fluorescence intensity fluctuations (see Bradley & New (1974) for references). These new concepts, in turn, were applied to the development of mode-locked continuous wave (c.w.) dye lasers and, more recently, to mode-locked semiconductor diode lasers. Both of these types of c.w. lasers will be discussed in some of the following papers.