Welcome to the website for the Attosecond
Technology project. The
project aims to generate,
diagnose and
use
isolated attosecond duration light pulses in new types of
experiments to probe atomic and molecular systems on the
attosecond timescale - with an emphasis on the development of
the technology required to achieve these goals.
This project was
initially funded by a RCUK
Basic Technology Grant (final report). Since Sept 2008 it
has been funded by an EPSRC Translation Grant "Next Generation
Attosecond Technology".
This website is intended to provide information about the aims and progress of the various parts of the
project.
For information about the project please contact us.
Recent News
Can we freeze time? Laser adventures in the realm of the nano-nanosecond. - John Tisch's Inaugural Lecture
John Tisch (project PI) has professorial Inaugural Lecture at Imperial College, June 22, 2011. Video can be seen
here.
Numerical simulation of attosecond nanoplasmonic streaking
Video abstract: Numerical simulation of attosecond nanoplasmonic streaking
The characterization of the temporal profile of plasmonic fields is important both from the fundamental point
of view and for potential applications in ultrafast nanoplasmonics. It has been proposed by Stockman
et al.
(2007 Nat. Photonics 1 539) that the plasmonic electric field can be directly measured by the attosecond
streaking technique; however, streaking from nanoplasmonic fields differs from streaking in the gas phase because
of the field localization on the nanoscale. To understand streaking in this new regime, we have performed
numerical simulations of attosecond streaking from fields localized in nanoantennas.
In this paper, we present simulated streaked spectra for realistic experimental conditions and
discuss the plasmonic field reconstruction from these spectra. We show that under certain circumstances
when spatial averaging is included, a robust electric field reconstruction is possible.
Lateral Shearing Interferometry of High-Harmonic Wavefronts
LSI: Farfield intensity (left) and phase (right) of the 13th, 19th
and 25th harmonics. Experimental results (blue, shaded represents standard deviation)and simulation (red).
In a collaboration between Prof Ian Walmsley's group at Oxford
(Dane Austin, Tobias Witting and Adam Wyatt) and the Imperial
College attosecond team Lateral Shearing Interferometry (LSI), was demonstrated
for the first time in the Attosecond Laboratory at Imperial college to characterise the wavefront of individual high harmonics. Knowing the space-time structure of high harmonics will shine light on the physical processes involved in the atomic as well
as the macroscopic origin of high harmonic generation (HHG).
LSI for HHG uses two tilted replicas of an IR pulse as the driving field that are generated in a Mach-Zehnder interferometer.
The two resulting foci lead to two HHG sources that are spectrally resolved on a two-dimensional flat-field XUV-spectrometer.
Wavelength is dispersed vertically, and the harmonics propagate freely in the horizontal direction. As a result a two-source
spatial interference pattern is recorded at the detector from which the spatial phase can be extracted.
We measured the 13-25th harmonic generated by a 14fs Ti:Sa laser pulse in krypton. The experimental results
were compared against a simulation. The single atom response is modelled using quantum orbits and the propagation
effects are described with a simplified model, neglecting ionization and dispersion effects on the driving field.
The experimental and theoretical results are shown in the figure on the right.
We demonstrate the generation of a 3.8 fs pulse with energies of up to 250 uJ. An octave spanning spectrum was
produced by coupling 30fs, ~700μJ Ti:Sa laser with a 1kHz repetition rate into a 1 m long hollow fibre.
Compression was achieved with ultrabroadband chirped mirrors.
SPIDER reconstruction of a sub-4 fs pulse.
The pulse was measured with a SEA-SPIDER setup and the reconstructed pulse duration was 3.8 fs, only slightly longer
than the transform limited pulse (3.5 fs) given by the spectrum.
Spectrum and Phase
-
Link to article
Amplification of Impulsively Excited Molecular Rotational Coherence
Molecular phase modulation (MPM) uses the rapid variation of refractive index
in an ensemble of coherently vibrating or rotating molecules to spectrally
modify radiation, allowing broadband radiation to be generated. Typically,
coherent molecular motion is prepared using a rapidly changing pump field, or
fields, which drive the dynamics. A key challenge is to control the phase of the
molecular dynamics with respect to additional ultrafast optical sources. In a
recent Physical Review Letter, researchers at the University of Oxford proposed
and demonstrated a solution to this problem. The scheme involves preparation of
high-coherence molecular dynamics which are phase-stable with respect to
ultrashort pulses.
More Information -
Link to article
Isolated Attosecond Pulses
We have made the first measurements of isolated
attosecond pulses in the UK and are one of only a handful
of groups world-wide with this measurement capability.
These short bursts of xuv light (~280 attoseconds duration,
where 1 attosecond is 10-18s ) were produced
through the process of high harmonic generation and
recorded using an attosecond 'streak' camera. In our
previous work we had already made world-record measurements
of molecular dynamics with attosecond temporal resolution
using the PACER technique [Science312, 424 (2006)], and
we have made ground-breaking measurements of the
carrier-envelope-phase (CEP) dependence of high harmonic
generation that also is also concerned with attosecond
timescale [Nature Physics3, 52 - 57 (2007)].
However, these new results -- which are the fruits of a
focused effort in the last year -- are the first time we
have made a detailed characterisation of an isolated
attosecond xuv pulse generated in our lab. This paves the
way for new dynamic studies on an unprecedented timescale
-- for example, with attosecond pulses at hand one can
trace the motion of electrons in matter, leading to a
deeper understanding of atomic behaviour with applications
in chemistry, biology and materials sciences. Our future
work is focused on the study of ultrafast dyanmics in
nanoplasmonic structures on surfaces.
