Ultrafast solid-state laser oscillators: a success story for the last 20 years with no end in sight

Ultrashort lasers provide an important tool to probe the dynamics of physical systems at very short time-scales, allowing for improved understanding of the performance of many devices and phenomena used in science, technology, and medicine. In addition ultrashort pulses also provide a high peak intensity and a broad optical spectrum, which opens even more applications such as material processing, nonlinear optics, attosecond science, and metrology. There has been a long-standing, ongoing effort in the field to reduce the pulse duration and increase the power of these lasers to continue to empower existing and new applications. After 1990, new techniques such as semiconductor saturable absorber mirrors (SESAMs) and Kerr-lens mode locking (KLM) allowed for the generation of stable pulse trains from diode-pumped solid-state lasers for the first time, and enabled the performance of such lasers to improve by several orders of magnitude with regards to pulse duration, pulse energy and pulse repetition rates. This invited review article gives a broad overview and includes some personal accounts of the key events during the last 20 years, which made ultrafast solid-state lasers a success story. Ultrafast Ti:sapphire, diode-pumped solid-state, and novel semiconductor laser oscillators will be reviewed. The perspective for the near future indicates continued significant progress in the field.