Ultrafast solid-state lasers

Abstract

Today's ultrafast all-solid-state lasers continue to demonstrate unsurpassed performances in terms of pulse duration, pulse repetition rates, average power and wavelength range. Optical pulses in the 5-femtosecond range are produced by a variety of methods. Although different in technical detail, each method relies on the same three key components: spectral broadening due to the nonlinear optical Kerr effect, dispersion control, and ultrabroadband amplification. The shortest pulses generated to date all rely on chirped mirrors for dispersion compensation. A major limitation in chirped mirror design arises due to interference between light reflected at different penetration depths inside the minor structure. This results in residual oscillations in the group delay dispersion (GDD) which ultimately limits pulse shortening Unfortunately, there is always a trade-off-between GDD-oscillations and reflection bandwidth. The double-chirped mirror technique (DCM) reduced GDD oscillations and resulted in the sub-6-fs pulses. Novel DCM designs result in a sufficiently large reflection bandwidth that could, in principle, support 4-fs pulses. The technique of Kerr lens mode-locking, successful with Ti:sapphire, has not performed so well in directly diode-pumped lasers. Semiconductor saturable absorber mirrors (SESAMs) were a breakthrough resulting in the first demonstration of self-starting and stable passive mode locking of diode-pumped solid-state lasers with an intracavity saturable absorber. The design freedom of SESAMs has allowed us systematically to investigate the stability regime of passive cw mode-locking with an improved understanding and modeling of Q-switching instabilities. Simple design guidelines allowed us to push the frontiers of ultrafast solid-state lasers.