Science & Applications: Attoscience

Advances in our understanding of the fundamental processes in nature come in leaps whenever a new technological achievement allows the development of revolutionary diagnostic techniques. In particular those that enable us to see the miniscule or freeze in time the fleeting dynamical processes of the microcosm have contributed to a wealth of findings.

A recent revolution in laser technology has opened the door to the generation of flashes of light that can freeze the ultrafast motion of electrons inside atoms and molecules. Our emerging capability of reproducibly generating and measuring attosecond-duration bursts of light marks the beginning of a new era in exploring motion in the microcosm: the era of attoscience. Attoseconds (10^-18 s) constitute the natural scale for the motion of electrons on the atomic scale. This motion comes now under scrutiny in real-time studies.
These advances begun a decade ago when physicists used intense femtosecond laser pulses to ionize a rare gas (such as neon), and found that new electromagnetic waves were generated in form of "high-order harmonics" at odd multiples of the original optical pulse frequency. It is the interplay between constructive and destructive interference in the superposition of these monochromatic light waves of equally spaced frequencies that gives rise to temporal beating, the underpinning process of attosecond pulse generation.

FIG. 1 The waveform of few-cycle pulse of red laser light (half oscillation period: 1.25 femtosecond = 1250 attoseconds) has been directly sampled by an extreme ultraviolet burst of 250 attosecond duration, providing evidence for the technical capability of controlling and measuring processes on the attosecond scale.

Further innovations in short pulse laser technology gave rise to generation of even single attosecond XUV bursts, which was promptly followed by an upsurge of extraordinary applications. Unfortunately, the low flux of the current attosecond sources limits the scope of applications of attosecond technology to a small fraction of what would potentially be feasible and of interest for advancing a wide range of fields in science and technology. Exploiting the full potential of attosecond technology calls for the feasibility of attosecond pulses being used both as a "starter gun" for triggering microscopic motion and as a "hyperfast-shutter camera" for probing the unfolding processes. To this end, one needs to seek for a new attosecond source exhibiting much higher efficiency.
		FIG. 2 A reflected pulse, rich in harmonic content results by focusing a short laser pulse onto a solid target. Appropriate spectral filtering gives rise to a high-power attosecond pulse.

The AttoSecond Light Source (ASLS) will spark a revolution in exploring the microcosm, by permitting - for the very first time - imaging the position of both basic ingredients of matter - nuclei and electrons - with sub-atomic resolution simultaneously in space and time in any transient state of matter. This technical capability will have far-reaching impact, from physics and chemistry through biology and medicine to future information technologies.

FIG. 3 Three-dimensional computer simulations of solid target interaction with intense laser pulses predict the generation of attosecond pulses with unprecedented duration and intensity.