Short electron pulses are, however, difficult to generate, because electrons carry a charge and move more slowly than the speed of light.
Electron microscopy and electron diffraction can provide the spatial resolution to image atoms, but filming atomic motions requires ultrashort shutter speeds —
the shorter the electron pulses, the sharper the images from the microcosmos.
Not exact matches
Impact of pre-plasma on fast
electron generation and transport from
short pulse, high intensity lasers
Ideally, the
electron gains so much energy in the laser field that upon impact with the atom, a much
shorter flash of light with very high energy is emitted — an attosecond laser
pulse, with a frequency in the ultraviolet - or x-ray regime.
Recording the energy of the
electrons that passed through the
pulse generates a crisp side - profile of the
short laser beam, not unlike a sporting photo - finish image (see right).
The
shorter the
pulse duration, the faster the
electron oscillation can be observed.
Dr. Hiroki Mashiko, a NTT scientist of the team, said, «We contrived the robust pump - probe system with an extremely
short isolated attosecond
pulse, which led to the observation of the fastest
electron oscillation in solid - state material in recorded history.
The high voltage is delivered only in very
short bursts, using just enough energy to accelerate the tiny
electrons without heating up the heavy gas particles
pulses; thus, plasma is generated.
The extremely brief
electron pulses ensure that the image remains sharp, much like a
short - exposure photograph of a speeding object.
This
pulse also has to be
short to catch the direction of
electron motion and have enough photon energy to knock the excited
electrons out of the molecule.
However, generating
short pulses is much more difficult to do with
electrons than with light.
In the experiments,
electrons are set in motion by a very strong electric field which is provided for the very
short time interval of 50 fs (1 fs = 10 - 15 s) by a strong optical
pulse interacting with the LiH material.
Pulse duration of 45 femtoseconds for monochromatized harmonics is 300 times shorter than the typical pulse duration of synchrotron radiation (15 picoseconds) and is comparable to the pulse length of a free - electron laser (
Pulse duration of 45 femtoseconds for monochromatized harmonics is 300 times
shorter than the typical
pulse duration of synchrotron radiation (15 picoseconds) and is comparable to the pulse length of a free - electron laser (
pulse duration of synchrotron radiation (15 picoseconds) and is comparable to the
pulse length of a free - electron laser (
pulse length of a free -
electron laser (FEL).
Researchers use a similar trick to study atomic
electrons — by pinging atoms with exceedingly
short light
pulses, they can watch
electrons» quantum states evolve in unprecedented detail.
In order to observe the ultrafast
electron motion in the inner shells of atoms with
short light
pulses, the
pulses must not only be ultrashort, but very bright, and the photons delivered must have sufficiently high energy.
Electrons within a target atom are first excited by a photon contained within the pump
pulse, which is then followed after a
short delay by a second photon in a probe
pulse.
The sharp acceleration turns the traveling
electron wave into a plane wave, like a nice regular
pulse of an
electron beam with an extremely
short wavelength — exactly the kind of beam useful for imaging.
Under the effect of powerful and very
short laser
pulses, the molecule's
electron shell configuration changed: a «hole» appeared — a shell vacancy which then began to oscillate moving from one end of the molecule to the other.
Varga's research focuses on the interaction of lasers and matter at the atomic scale and is part of the new field of attosecond science — an attosecond is a billion billionths of a second — that is allowing scientists to study extremely
short - lived phenomena such as the making and breaking of chemical bonds and tracking the real - time motion of
electrons within semiconductors by probing them with attosecond
pulses of laser light.
The Nitrogen - Vacancy defect (NV centre) in diamonds and diamond nanocrystals (nanodiamonds) provides a unique alternative for DNP as the NV centre
electron spin can be optically polarized to over 90 % polarization at room temperature by
short laser
pulses.
These opportunities include the use of
short -
pulsed X-ray sources for extracting time - dependent structural information from proteins; and the revolutionary new possibilities created by X-ray Free
Electron Lasers, which combine ultrafast X-ray
pulses with high brilliance focussing capabilities to create an entirely new regime of pre-damage time - resolved serial femtosecond crystallography on unprecedented time - scales.