40 research outputs found
Attosecond pulse shaping using partial phase matching
Peer ReviewedPostprint (published version
Ultrashort pulse characterization by spectral shearing interferometry with spatially chirped ancillae
We report a new version of spectral phase interferometry for direct electric
field reconstruction (SPIDER), which enables consistency checking through the
simultaneous acquisition of multiple shears and offers a simple and precise
calibration method. By mixing the test pulse with two spatially chirped ancilla
fields we generate a single-shot interferogram which contains multiple shears,
the spectral amplitude of the test pulse, and the reference phase, which is
accurate for broadband pulses. All calibration parameters - shear,
upconversion-frequency and reference phase position - can be accurately
obtained from a single calibration trace.Comment: 11 pages, 7 figure
Three-wave mixing mediated femtosecond pulse compression in BBO
Nonlinear pulse compression mediated by three-wave mixing is demonstrated for ultrashort Ti:sapphire pulses in a type II phase-matched �β-barium borate (BBO) crystal using noncollinear geometry. 170 μJ pulses at 800 nm with a pulse duration of 74 fs are compressed at their sum frequency to 32 fs with 55 μJ of pulse energy. Experiments and computer simulations demonstrate the potential of sum-frequency pulse compression to match the group velocities of the interacting waves to crystals that were initially not considered in the context of nonlinear pulse compression.Peer ReviewedPostprint (author's final draft
Direct characterisation of tuneable few-femtosecond dispersive-wave pulses in the deep UV
Dispersive wave emission (DWE) in gas-filled hollow-core dielectric
waveguides is a promising source of tuneable coherent and broadband radiation,
but so far the generation of few-femtosecond pulses using this technique has
not been demonstrated. Using in-vacuum frequency-resolved optical gating, we
directly characterise tuneable 3fs pulses in the deep ultraviolet generated via
DWE. Through numerical simulations, we identify that the use of a pressure
gradient in the waveguide is critical for the generation of short pulses.Comment: 5 pages, 4 figure
Measuring sub-Planck structural analogues in chronocyclic phase space
The phase space structure of certain quantum states reveals structure on a
scale that is small compared to the Planck area. Using an analog between the
wavefunction of a single photon and the electric field of a classical
ultrashort optical pulse we show that spectral shearing interferometry enables
measurement of such structures directly. Thereby extending the idea of
Praxmeyer et al. In particular, we use multiple-shear spectral interferometry
to fully characterize a pulse consisting of two sub-pulses which are temporally
and spectrally disjoint, without a relative-phase ambiguity. This enables us to
compute the Wigner distribution of the pulse. This spectrographic
representation of the pulse field features fringes that are tilted with respect
to both the time- and frequency axes, showing that in general the shortest
sub-Planck distances may not be in the directions of the canonical (and easily
experimentally accessible) directions. Further, independent of this
orientation, evidence of the sub-Planck scale of the structure maybe extracted
directly from the measured signal.Comment: 7 pages, 7 figures, "Quo vadis Quantum Optics"- special issue of
Optics Communications in memory of Krzysztof Wodkiewic
Space-time coupling of shaped ultrafast ultraviolet pulses from an acousto-optic programmable dispersive filter
A comprehensive experimental analysis of spatio-temporal coupling effects
inherent to the acousto-optic programmable dispersive filter (AOPDF) is
presented. Phase and amplitude measurements of the AOPDF transfer function are
performed using spatially and spectrally resolved interferometry.
Spatio-temporal and spatio-spectral coupling effects are presented for a range
of shaped pulses that are commonly used in quantum control experiments. These
effects are shown to be attributable to a single mechanism: a
group-delay--dependent displacement of the shaped pulse. The physical mechanism
is explained and excellent quantitative agreement between the measured and
calculated coupling speed is obtained. The implications for quantum control
experiments are discussed.Comment: 8 pages, 6 figures; accepted for publication within JOSA
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Strong-field ionization of clusters using two-cycle pulses at 1.8 μm
The interaction of intense laser pulses with nanoscale particles leads to the production of high-energy electrons, ions, neutral atoms, neutrons and photons. Up to now, investigations have focused on near-infrared to X-ray laser pulses consisting of many optical cycles. Here we study strong-field ionization of rare-gas clusters (103 to 105 atoms) using two-cycle 1.8 μm laser pulses to access a new interaction regime in the limit where the electron dynamics are dominated by the laser field and the cluster atoms do not have time to move significantly. The emission of fast electrons with kinetic energies exceeding 3 keV is observed using laser pulses with a wavelength of 1.8 μm and an intensity of 1 × 1015 W/cm2, whereas only electrons below 500 eV are observed at 800 nm using a similar intensity and pulse duration. Fast electrons are preferentially emitted along the laser polarization direction, showing that they are driven out from the cluster by the laser field. In addition to direct electron emission, an electron rescattering plateau is observed. Scaling to even longer wavelengths is expected to result in a highly directional current of energetic electrons on a few-femtosecond timescale
Low-Energy Electron Emission in the Strong-Field Ionization of Rare Gas Clusters
Clusters and nanoparticles have been widely investigated to determine how plasmonic near fields influence the strong-field induced energetic electron emission from finite systems. We focus on the contrary, i.e., the slow electrons, and discuss a hitherto unidentified low-energy structure (LES) in the photoemission spectra of rare gas clusters in intense near-infrared laser pulses. For Ar and Kr clusters we find, besides field-driven fast electrons, a robust and nearly isotropic emission of electrons with <4  eV kinetic energies that dominates the total yield. Molecular dynamics simulations reveal a correlated few-body decay process involving quasifree electrons and multiply excited ions in the nonequilibrium nanoplasma that results in a dominant LES feature. Our results indicate that the LES emission occurs after significant nanoplasma expansion, and that it is a generic phenomenon in intense laser nanoparticle interactions, which is likely to influence the formation of highly charged ions