Attosecond lighthouses may help illuminate the tempestuous sea of electrons
(NCYT/OSA) 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.
|Spatial profile of an attosecond pulse train generated by a usual laser femtosecond laser beam. (Photo: OSA)|
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."
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