Attosecond Spectroscopy

Attosecond spectroscopy: past, present, and into the future

Once the precision attainable in timing events depended on how fast a human could press the button on a stopwatch. More recently, pulsed laser sources have taken the place of those hand-held devices for measuring the fastest phenomena.

The technology for tracking the time scale of nuclear motion in free molecules and solids was limited by the duration of a single cycle of visible light: approximately 0.000 000 000 000 001 second, or one femtosecond.

Electrons move even faster that that, and for a long time, scientists could only watch their re-arrangements as a blur. During the past several years, laser technology has crossed into the attosecond zone (a thousandth of a femtosecond).

The study of the physical processes of attoscience

Attoscience is the study of the physical processes which occur in less than a fraction of a cycle of visible light, in times less than a quadrillionth of a second.

The motion of electrons inside atoms and molecules which are undergoing photoionization or chemical changes fall within this time scale, as does the plasma motion that causes the reflectivity of metals.

The techniques to study motion on this scale are based on careful control of strong-field laser-atom interactions.

The physical world encompasses enormous ranges of time, from the origin of the universe some fourteen billion years ago (400 quadrillion seconds, or 4 x 10¹⁷ s), to times that are as short compared to a second as a second is short compared to the age of the universe.

These brief instants, a few billionths of a billionth of a second, or 10^-18 s, are called attoseconds or as.

If we use the oscillations of light waves as a clock, the shortest time that we can measure with a beam of visible light depends on how fast we can turn the light on and off. Lasers have been developed over the past two decades which have special features to produce extremely short optical pulses.

Viewing and using attosecond pulses which are creating attoscience

Only a few years ago, the direct measurement of transient phenomena lasting less than an optical cycle seemed a supreme challenge. Now scientists have brought together techniques from atomic and laser physics to make these measurements possible, if not yet routine.

Attoscience is a new field, with the promise of revealing some of the fastest processes of chemistry and atomic physics, or to freeze motion which will allow us to view the structure of matter under extreme conditions.

Lightwave electronics and attosecond control and measurements

Electrons emit light, carry electric current and bind atoms together to form molecules. Insight into and control of their atomic-scale motion is the key to understanding the functioning of biological systems, developing efficient sources of x-ray light, and speeding up electronics.

Capturing and steering this electron motion require attosecond resolution and control, respectively. A recent revolution in technology has made these capabilities possible: that is, controlled light waves can steer electrons inside and around atoms, marking the birth of lightwave electronics.

Isolated attosecond pulses, well reproduced and fully characterized, demonstrate the power of the new technology. Controlled few-cycle light waves and synchronized attosecond pulses constitute its key tools.