| [Previous
Story] [Next
Story]
ATTOSECOND LIGHT PULSES
DISPLAYED
Extremely short bursts of
light probe ultrafast electronic processes
MITCH JACOBY
How short is short?
When it comes to light pulses, the bar has just been lowered to mere
billionths of a billionth of a second. Researchers have demonstrated
a new laser method that produces attosecond (10–18
second) bursts of light--the shortest duration measured to
date.
 |
| FAST!
Attosecond researchers Kienberger (left) and Hentschel push
the limits of time
resolution. | A number of techniques for probing atomic and molecular
events on very fast time scales have been developed and put to use
in recent years. State-of-the-art femtosecond (10–15
second) lasers and laser procedures provide probes of exceptional
fineness for studying molecular vibrations and chemical reaction
dynamics.
But now the scale of time-dependent measurements has
just passed into the realm of attoseconds. Physicists in Austria
have devised a procedure that produces 650-attosecond bursts of soft
X-rays [Nature, 414, 509 (2001)]. The group has used the record-breaking laser
method to study the dynamics of electronic processes in real
time.
To produce attosecond light pulses, physicists at Vienna
University of Technology's Photonics Institute, including
Reinhard Kienberger, Michael Hentschel, Ferenc Krausz, and their
coworkers, irradiate neon with bursts of red light lasting just 7
femtoseconds. The laser light strips electrons from the gas atoms
and causes them to interact with Ne ions in a process that gives
rise to high-order harmonics--pulses of light (extreme UV and X-ray,
in this case) with much higher frequencies than that of the red
light. The team filters the harmonic light to allow only select
attosecond bursts of X-rays to pass.
Putting the fleeting beams of X-rays to use, the
Vienna scientists train the red light and the X-rays onto a krypton
target in such a way that they can monitor the dynamics of
photoelectrons emitted by the rare gas with attosecond
resolution.
"These are the kinds of exciting developments that
take us into new territory," comments Ahmed H. Zewail, professor of chemistry and physics
at California Institute of Technology. The chemistry Nobel Laureate
notes that by stepping into the realm of attosecond time resolution,
scientists can look forward to studying electron rearrangement
processes in molecules and changes in molecular structures as
molecules undergo electron-transfer reactions. Offering an example,
Zewail suggests that, with further advances in attosecond
techniques, "We may be able to catch a benzene molecule in various
electronic configurations."
Chemical & Engineering News
Copyright ©
2001 American Chemical Society | 
