Ultrafast science: from femtoseconds to attoseconds

Summary form only given. The evolution of ultrafast optics has now arrived at a point where the laser pulse duration approaches the oscillation cycle of the visible/near-infrared carrier waves (T/sub OSC//spl ap/2-3 fs). For significant further progress towards pulse durations of around 1 femtosecond or less one has to resort to shorter carrier wavelengths in the UV/VUV/XUV spectral range. In the absence of laser media with sufficient bandwidth in these spectral regions, new generation techniques (other than laser mode locking) need to be developed. In addition, depending on the carrier wavelength, either the undistorted transport of sub-femtosecond pulses (e.g., through the interaction medium) or their temporal characterization issues an enormous challenge to the experimentalist. This tutorial reviews proposals and recent experimental progress towards the generation and measurement of short-wavelength pulses with sub-femtosecond or attosecond duration. Particular emphasis is placed on few-cycle-driven high-order XUV harmonics. This radiation holds promise for becoming capable of probing processes such as optical field ionization and inner-shell relaxation for the first time in the time domain. This experimental capability is expected to have significant impacts, among others, on laser-produced plasma control and X-ray laser research.