Attosecond Analysis

INTERVIEW | TECHNOLOGY FOCUS Attosecond analysis

Attosecond spectroscopy promises real-time observation of the motion of electrons inside atoms. Nadya Anscombe talks to Ferenc Krausz from the Max-Planck Institute of Quantum Optics and the Ludwig-Maximilians-University of Munich in Germany about the technology.

Why is attosecond off with the electric field of light. To advance spectroscopy important? electronics to its ultimate limits we will have If you want to capture a fast-moving object, to draw on attosecond technology. you need a fast shutter speed on your camera. Until recently, no experimental In spectroscopy, ultrashort light pulses act as technique existed that can directly probe that shutter and can take pictures of ultrafast electron–electron interactions in matter on microscopic dynamics. The development of the atomic scale. The accurate theoretical femtosecond pulses allowed the motion of description of these interactions and resultant atoms in molecules to be recorded and led to dynamics becomes very difficult for an the birth of femtochemistry. Now, attosecond increasing number of electrons. Even for pulses are required to capture the atomic- systems with just two electrons, no accurate scale motion of electrons in atoms, molecules ab initio calculations exist for the dynamical or solids. Unlike conventional techniques, behaviour. Attosecond spectroscopy can, for such as X-ray crystallography, attosecond the first time, offer a method of investigating ienna spectroscopy gives real-time, direct, dynamic V these interactions experimentally and help

information about the motion of electrons. of y theorists to develop simplified but reasonably Indirect ways of accessing such dynamics, t accurate models for describing multi-electron such as frequency-domain measurements, systems for addressing realistic situations. work in simple situations (such as in the case There are so many applications for of quantum transitions between well isolated this technology that no one group can states), but if there is interference as a result Universi Technical investigate them all. That is why it is of the many possible pathways or if many important that many groups around the quantum states are involved, the data can be Ferenc Krausz, one of the pioneers of attosecond science. world are developing attosecond technology, hard to decipher. Attosecond spectroscopy and I am pleased to see that research in the is the only way of getting real-time access field is proliferating rapidly. to dynamics occurring on the electronic What are the applications for timescale, that is, to processes clocked in the attosecond spectroscopy? What needs to be done before atomic unit of time of 24 as. Because attosecond spectroscopy can be the technology becomes used to look at the dynamic behaviour of commercially available? What can be achieved with the electrons, the list of applications is endless. More than half of an attosecond technology today? For example, in life sciences attosecond measurement system is already The shortest pulses demonstrated so far spectroscopy may ultimately create ways commercially available. Few-cycle phase- have a duration of 80 as. These pulses, of understanding the microscopic origins controlled near-infrared laser systems, thanks to the order-of-magnitude increase of how a disease, such as cancer, emerges which serve as a driver of the attosecond in their photon flux as compared with their and develops at the most fundamental pulses, are available off-the-shelf. The rest predecessors, enable measurements with a level: in terms of the motion of electrons. is simple and complicated at the same time. dramatically improved signal-to-noise ratio, In biology, structure determines function The attosecond source, a gas jet, is extremely offering a temporal resolution close to the or malfunction. Although a change in simple, whereas the part needed for atomic unit of time. Attosecond spectroscopy structure can take a long time, the initial performing the attosecond measurements is was previously used to study isolated atoms event that triggered the change is always more complex. The design of a measurement in the gas phase, but the technique has now an electronic motion. To understand why system very much depends on what you been extended to observe electron motion in a molecule decides to change its structure want to investigate. There are no major condensed-matter systems and on surfaces or composition, you have to understand hurdles to be overcome with the technology in real time. Attosecond photoemission what happens at the instant when that itself: it is ready to be used. However, the spectroscopy presents a clear path towards change begins. Attosecond spectroscopy can equipment used today is complex and it is ultimately uncovering the intermediate observe these events in real time. important to make it reliable and easy to use, processes involved in the ejection of a Advancement of modern electronics as researchers do not want to go through photoelectron from condensed matter. This towards its ultimate frontier — the atomic years of training before they can use the is a basic process analysed by Einstein more scale, in both space and time — means that technology to do important research. than a hundred years ago, but with many one day we will want to be able to make important details remaining hidden to the electronic circuits from atomic structures and Nadya Anscombe is a freelance science and present day. to switch currents in these circuits on and technology journalist based in the UK.