Conquering the timing jitters

Date:
March 3, 2021
Source:
DOE/Argonne National Laboratory
Summary:
A large international team has developed a method that dramatically
improves the time resolution achievable with X-ray free-electron
lasers.

Their method could have a broad impact in the field of ultrafast
science.



FULL STORY ========================================================================== Breakthrough greatly enhances the ultrafast resolution achievable with
X-ray free-electron lasers.


==========================================================================
A large international team of scientists from various research
organizations, including the U.S. Department of Energy's (DOE) Argonne
National Laboratory, has developed a method that dramatically improves
the already ultrafast time resolution achievable with X-ray free-electron lasers (XFELs). It could lead to breakthroughs on how to design new
materials and more efficient chemical processes.

An XFEL device is a powerful combination of particle accelerator and
laser technology producing extremely brilliant and ultrashort pulses of
X-rays for scientific research. "With this technology, scientists can
now track processes that occur within millions of a billionth of a second (femtoseconds) at sizes down to the atomic scale," said Gilles Doumy, a physicist in Argonne's Chemical Sciences and Engineering division. "Our
method makes it possible to do this for even faster times." One of
the most promising applications of XFELs has been in the biological
sciences. In such research, scientists can capture how biological
processes fundamental to life change over time, even before the radiation
from the laser's X-rays destroys the samples. In physics and chemistry,
these X-rays can also shed light on the fastest processes occurring in
nature with a shutter speed lasting only a femtosecond. Such processes
include the making and breaking of chemical bonds and the vibrations of
atoms on thin film surfaces.

For over a decade XFELs have delivered intense, femtosecond X-ray pulses,
with recent forays into the sub-femtosecond regime (attosecond). However,
on these miniscule time scales, it is difficult to synchronize the X-ray
pulse that sparks a reaction in the sample and the laser pulse that
"observes" it. This problem is called timing jitter.

Lead author Dan Haynes, a doctoral student at the Max Planck Institute
for the Structure and Dynamics of Matter, said, "It's like trying to
photograph the end of a race when the camera shutter might activate at
any moment in the final ten seconds." To circumvent the jitter problem,
the research team came up with a pioneering, highly precise approach
dubbed "self-referenced attosecond streaking." The team demonstrated
their method by measuring a fundamental decay process in neon gas at
the Linac Coherent Light Source, a DOE Office of Science User Facility
at SLAC National Accelerator Laboratory.



========================================================================== Doumy and his advisor at the time, Ohio State University Professor Louis DiMauro, had first proposed the measurement in 2012.

In the decay process, called Auger decay, an X-ray pulse catapults
atomic core electrons in the sample out of their place. This leads
to their replacement by electrons in outer atomic shells. As these
outer electrons relax, they release energy. That process can induce
the emission of another electron, known as an Auger electron. Radiation
damage occurs due to both the intense X-rays and the continued emission
of Auger electrons, which can rapidly degrade the sample.

Upon X-ray exposure, the neon atoms also emit electrons, called
photoelectrons.

After exposing both types of electrons to an external "streaking" laser
pulse, the researchers determined their final energy in each of tens of thousands of individual measurements.

"From those measurements, we can follow Auger decay in time with
sub- femtosecond precision, even though the timing jitter was a
hundred-times larger," said Doumy. "The technique relies on the fact
that Auger electrons are emitted slightly later than the photoelectrons
and thus interact with a different part of the streaking laser pulse."
This factor forms the foundation of the technique. By combining so many individual observations, the team was able to construct a detailed
map of the physical decay process. From that information, they could
determine the characteristic time delay between the photoelectron and
Auger electron emission.

The researchers are hopeful that self-referenced streaking will have a
broad impact in the field of ultrafast science. Essentially, the technique enables traditional attosecond streaking spectroscopy to be extended to
XFELs worldwide as they approach the attosecond frontier. In this way, self-referenced streaking may facilitate a new class of experiments
benefitting from the flexibility and extreme intensity of XFELs without compromising on time resolution.

========================================================================== Story Source: Materials provided by
DOE/Argonne_National_Laboratory. Original written by Joseph
E. Harmon. Note: Content may be edited for style and length.


========================================================================== Journal Reference:
1. D. C. Haynes, M. Wurzer, A. Schletter, A. Al-Haddad, C. Blaga, C.

Bostedt, J. Bozek, H. Bromberger, M. Bucher, A. Camper, S. Carron,
R.

Coffee, J. T. Costello, L. F. DiMauro, Y. Ding, K. Ferguson,
I. Grguras, W. Helml, M. C. Hoffmann, M. Ilchen, S. Jalas,
N. M. Kabachnik, A. K.

Kazansky, R. Kienberger, A. R. Maier, T. Maxwell, T. Mazza,
M. Meyer, H.

Park, J. Robinson, C. Roedig, H. Schlarb, R. Singla, F. Tellkamp,
P. A.

Walker, K. Zhang, G. Doumy, C. Behrens, A. L. Cavalieri. Clocking
Auger electrons. Nature Physics, 2021; DOI:
10.1038/s41567-020-01111-0 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2021/03/210303142545.htm

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