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Much insight into the behaviour of electrons comes from studying highly excited atoms known commonly as Rydberg atoms. In these atoms one or more electrons are excited to a very high-energy orbit. Rydberg electrons spend most of their time moving very slowly compared to electrons in the atomic core. The period of a Rydberg electron in a 100 nm radius orbit is five picoseconds, some 200,000 times longer than the 25 attosecond period of a ground state electron of a hydrogen atom. Such slow moving electrons can be “filmed” in pump-probe experiments using commercially available femtosecond lasers.

Studies of Rydberg atoms and molecules have provided enormous insight into the motion of electrons as the results can be extrapolated for the behaviour of core electrons. Such correlated electron motion drives many of the important processes in chemistry and biology and is often a key factor determining the character of novel complex materials.

But, the electrons in most atoms and molecules do not move in such convenient timescales as Rydberg electrons; nevertheless, there is still much to be learned from this motion. When sunlight reacts in our skin to help us manufacture vitamin D, how exactly do the electrons permit the carbon ring to open? Where do the electrons move during this process? Or in chemical physics can we learn how to make organic solar cells for energy applications?

To answer questions like these we must find ways to see electron motion directly. Currently when we peer at an atom or molecule using a femtosecond pulse the motion of the rapidly moving electrons is lost in a blur and so we must shorten the time duration of the strobe. If we could develop sufficiently short pulses to allow us to strobe the motion of electrons themselves we would truly enter a new and astonishing realm of science. This has led to the birth of attoscience: the creation and use of laser pulses less than one femtosecond long – attosecond pulses in the ultraviolet or X-ray region.

This Special Issue of Lasers in Engineering is devoted to attodynamics and analysis with ultra-short laser pulses. It consists of eight papers written by European and American physicists and engineers, and provides a unique and valuable exploration of both theoretical and experimental attoscience.

Prof. Janina Marciak-Kozlowska
Institute of Electron Technology

Poland Prof. Miroslaw Kozlowski
Warsaw University, Poland

Prof. Jonathan Lawrence
University of Lincoln, UK

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