12 Octave Coherent High Harmonics’ X-ray Supercontinua Enable Ultra-Precise Measurements on a Tabletop.
Published in Phys. Rev. Lett. 120, 093002 March 2018
Coherent X-rays are an
ideal probe of the ultra-fast and ultra-small atomic and molecular world, due
to their nature of having extremely short wavelength, short pulse duration,
unique ability to penetrate thick and opaque objects combined with elemental
specific fingerprints from the atomic absorption edges.
The large synchrotron
and free electron laser facilities are the forefront of science, however
tabletop sources are becoming more and more capable of performing complimentary
invivo studies in the biological and material sciences. The other alternative
source, the high harmonics, originate from a highly nonlinear process of energy
upshift, when a high power laser is focused into a gas with intensities close
to the binding atomic potentials. In this process thousands of photons can add
to create a single photon with X-ray energy.
While Ultrafast
spectroscopies in the visible and infrared (IR) energy regions can probe
non-equilibrium dynamics on the ultrafast time scale, they cannot determine the
chemical nature of the excited state dynamics with elemental selectivity.
Alternatively, coherent X-ray spectroscopies have an important additional
advantage of being able to uncover oxidation state, magnetic state, or charge
localization to specific elements, giving information about the electronic
structures, (i.e., valence, bands and charge), as well as orbital and spin
ordering phenomena.
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Today, atomic
structure can be determined routinely using incoherent X-ray crystallography
techniques. Unlike X-ray crystallography, which requires samples to be
crystalline, XAFS spectroscopy can extract dynamic local structure information
from various phases (i.e crystals, gases, low concentration solutions,
disordered solids etc.), with some prior knowledge. Making it a viable
computational imaging technique at the attosecond - picometer scale on up.
The near- and
extended- X-ray absorption fine structure (XAFS) is a universal response of
matter interacting with X-ray light near an absorption edge. This quantum
phenomenon can be understood in a simple three-step model, where an incident
X-ray is absorbed by an atom, which leads to the ejection of a photoelectron
from a core-shell. Then the photoelectron is scattered from neighboring
non-excited atoms, and the quantum interferences of the outgoing and incoming
scattered electron waves lead to an energy-dependent variation of the X-ray
absorption probability. With some prior knowledge, these techniques can provide
full spatio-temporal and chemical imaging information (4+1D) of the local
atomic structure of materials, including 1) the types of atoms that are
present, coordination numbers (number of neighboring atoms at particular
distances), inter-atomic distances, as well as disorder (using EXAFS), and 2)
the oxidation state, and coordination chemistry (i.e., symmetries, isomerism,
etc.) (using NEXAFS).
Using coherent high
harmonic supercontinua laser-like beams, high quality extended edge coherent
absorption spectroscopy of materials have been observed in the near-keV region
for the first time, to obtain structural and chemical information. Published in
Phys. Rev. Lett. 2018, DOI:
10.1103/PhysRevLett.120.093002
In the near future,
because high harmonic X-ray bursts emerge as an isolated
femtosecond-to-attosecond pulses, it will be possible to perform extensive
spatio-temporal and chemical imaging of the local atomic structure of
materials.
The attosecond -picometer
resolution science is .. a hand away.
cite as:
[1]. Popmintchev, Dimitar, et. al.,
Phys. Rev. Lett. 120, 093002, 1 March 2018 DOI: Phys. Rev. Lett. 2018, DOI:
10.1103/PhysRevLett.120.093002
[2]. Popmintchev, Dimitar, "Quantum
and Extreme Nonlinear Optics Design of Coherent Ultrafast X-ray Light and
Applications" ISBN 9781369490015 2016 https://www.amazon.com/dp/B01N9G9JVZ
[3]. Popmintchev, Tenio, et. al.,
Science Vol. 336, Issue 6086, pp. 1287-1291 08 Jun 2012 DOI: Science, DOI: 10.1126/science.1218497
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