Light Pulse Speed Record Set

Researchers have set a new record in ultrafast metrology, producing the first light pulses lasting only 80 attoseconds (a billionth of a billionth of a second).

Electrons move at awesome speeds, so any observation of that motion has to also be extremely fast. In just a few attoseconds, the particles in atoms jump between adjacent atoms in a molecule or solid from one place to another. When electrons jump, light is emitted in the visible, ultraviolet or x-ray spectrum; the jumps also can create deformation and malfunctions in biomolecules, or transmit biological information through nerves. The only way to observe such incredibly short flashes is with equally fast light pulses. The faster the light pulse, the sharper the resulting images will be.

Generation of the attosecond pulses: Physicists at the Max Planck Institute for Quantum Optics produced light pulses lasting just 80 attoseconds with ultrashort laser flashes. The laser pulses are focused on a neon gas target streaming out of a thin tube. The intense (ionizing) laser field induces electron oscillations in the neon atoms, which emit attosecond pulses of extreme ultraviolet light. (Photo: Thorsten Naeser)

The 80-attosecond achievement marks the first time scientists have achieved light pulse speeds below 100 attoseconds and was accomplished by a team of physicists led by professor Ferenc Krausz at the Max Planck Institute for Quantum Optics (MPQ) in Garching and professor Ulf Kleineberg at Ludwig Maximilians University Munich, working in cooperation with colleagues at the Advanced Light Source at Berkeley Lab in California.

The achievement will help unlock some of the secrets of ultrafast electron motion inside atoms, molecules and solids, providing insight into electron processes could lead to the development of new light sources, a better understanding of the microscopic origins of serious illnesses, or the creation of superfast electronics.

"Electrons are omnipresent in vital microscopic processes, just as in technology. Their ultrafast motion governs the course of all biological and chemical processes, as well as the speed of the microprocessors constituting the core of computers," said Krausz.

To generate attosecond pulses, the Garching physicists use the strong electric field of flashes in the near-infrared spectrum. In the hypershort laser flashes this field performs hardly more than a single strong oscillation with a period of about 2.5 femtoseconds (a femtosecond is 1000 attoseconds). That is: the light wave now comprises just two high wave peaks and a deep wave valley between them. The force exerted by the electric light field on the electrons is strongest at the summits and the lowest point of the valley; strong enough to liberate electrons which are ejected from rare-gas atoms in the experiment at Garching. This leaves ion rumps.

With the oscillation of the light field the force changes direction and very soon hurls the electrons back to the ion rumps. The recolliding free electrons induce extremely fast electron oscillations which last just attoseconds and emit light flashes of the same duration. These flashes are then in the region of extreme ultraviolet light (XUV, a wavelength of approximately 10 to 20 nm).

The vacuum chamber for attosecond metrology: Attosecond pulses of extreme ultraviolet light (depicted as a blue beam) are focused by a mirror (right) on a jet of neon atoms effusing from a thin valve. At the same time an infrared beam is striking the atoms. Both beams in combination allow real-time observation of the motion of electrons in the neon atoms and measurement of the duration of the attosecond pulse. (Photo: Thorsten Naeser Photo editing: Christian Hackenberger)

Controlled production of this single strong light oscillation within a hypershort flash has now allowed the Garching research team for the first time to release electrons exactly three times during a single laser pulse. On returning to the ion they then emit exactly three attosecond pulses. Each femtosecond laser flash generates three attosecond pulses. One of these pulses has a particularly high intensity, providing more than 100 million photons in a period of just 80 attoseconds.

This pulse is filtered out with special x-ray mirrors from Kleineberg, resulting in a single isolated x-ray pulse lasting 80 attoseconds.

Their experiments, and those of others, are advancing measurement technology to speeds that once seemed impossible.

"Pulses shorter than 100 attoseconds will provide access to hitherto unresolved electron dynamics, particularly electron-electron interactions in real time," said team leader Eleftherios Goulielmakis, PhD, who conducts experiments in Krausz’s research group.

Many of these processes, such as the energy transfer between electrons or the reaction of particles to external influences, can take place within just a few attoseconds.

"By means of attosecond technology we shall one day be able to observe in real time how the microscopic motion of electrons in molecules initiates diseases such as, for example, cancer. We shall likewise be able to switch electric current in atomic circuits with infrared light many trillionth times per second," Krausz said.

A paper on their work, "Single-cycle Nonlinear Optics," appeared in the June 20 edition of Science.

For more information, visit: www.mpg.de/english