image: This is a spatial profile of an attosecond pulse train generated by a usual laser femtosecond laser beam. view more
Credit: Fabien Quéré, the French Commissariat à l'Energie Atomique
WASHINGTON, April 30--Physicists have long chased an elusive goal: the ability to "freeze" and then study the motion of electrons in matter. Such experiments could help confirm theories of electron motion and yield insights into how and why chemical reactions take place. Now a collaboration of scientists from France and Canada has developed an elegant new method to study electrons' fleeting antics using isolated, precisely timed, and incredibly fast pulses of light. The team will describe the technique at the Conference on Lasers and Electro-Optics , taking place in San Jose, Calif. May 6-11. (CLEO: 2012 (http://www.cleoconference.org))
The exchanges of electrons during chemical reactions typically occur on time scales less than one femtosecond, or a millionth of a billionth of a second. The only way to freeze electron motion is using pulses of light with durations that are shorter still than the rapid comings and goings of electrons – on the order of quintillionths of a second, or attoseconds. Once they are frozen, "the dynamics of electrons could then be studied by so-called pump-probe experiments" that use a pair of light pulses, explains physicist Fabien Quéré of the French Commissariat à l'Energie Atomique (CEA). The first pulse – dubbed the pump – kick-starts the motion of the electrons at a well-defined starting time, he explains, "and the second one, the probe, looks at the excited system at different times after the pump, to measure its evolution after excitation."
Attosecond pulses have been produced through the interaction of ultra-powerful laser beams with matter. The resulting light bursts, however, come in "trains" – collections of pulses closely spaced in time – that don't work very well in pump-probe experiments. What would work far better are isolated and precisely-timed pulses. That's exactly what Quéré, along with graduate student Henri Vincenti and colleagues at the Applied Optics Laboratory (LOA, France) and the National Research Council of Canada (NRC), have created using a new method, dubbed the "attosecond lighthouse" effect.
In the technique, the initial laser beam is shaped in order to induce an ultrafast rotation of its wavefront, so that its interaction with matter produces a train of individual attosecond pulses that is streaked angularly – like the sweeping beam of a lighthouse. The researchers can thus generate a collection of beamlets, "each one consisting in the time domain, according to theory and simulations, of a single attosecond pulse," Quéré says – which produces an ideal light source for attosecond pump-probe experiments.
According to the researchers, the attosecond lighthouse effect has several major advantages over previous methods for making isolated attosecond pulses. For example, Quéré says, "it is by far the easiest one to implement experimentally. In practice, it only requires a very small rotation of one optical element – a prism or a grating, typically – in existing laser systems."
CLEO: 2012 presentation QTu3H.2, "Attosecond lighthouses," by Fabien Quéré et al. is at 4:45 p.m. on Tuesday, May 8 in the San Jose Convention Center. Quéré's team will also report on the first experimental demonstration of this effect during a CLEO: 2012 post-deadline paper presentation at 9:36 p.m. on Thursday, May 10.
EDITOR'S NOTE: High-resolution images are available upon request. Contact Angela Stark, astark@osa.org.
Press Registration
A Press Room for credentialed press and analysts will be located on-site in the San Jose Convention Center, May 6 – May 11. Media interested in attending the conference should register on the CLEO website (http://www.cleoconference.org/home/news-and-press/press-and-analysts/press-and-analyst-registration-form.aspx) or contact Angela Stark at 202.416.1443, astark@osa.org.
About CLEO
With a distinguished history as the industry's leading event on laser science, the Conference on Lasers and Electro-Optics (CLEO) is where laser technology was first introduced. CLEO unites the field of lasers and electro-optics by bringing together all aspects of laser technology, with content stemming from basic research to industry application. CLEO: Expo showcases the latest products and applications from more than 300 participating companies from around the world, providing hands-on demonstrations of the latest market innovations and applications. The Expo also offers valuable on-floor programming, including Market Focus and the Technology Transfer program.
Sponsored by the American Physical Society's (APS) Laser Science Division, the Institute of Electronic Engineers (IEEE) Photonics Society and the Optical Society (OSA), CLEO provides the full range of critical developments in the field, showcasing the most significant milestones from laboratory to marketplace. With an unparalleled breadth and depth of coverage, CLEO connects all of the critical vertical markets in lasers and electro-optics. For more information, visit the conference's website at www.cleoconference.org.