27 research outputs found
Field strength scaling in quasi-phase-matching of high-order harmonic generation by low-intensity assisting fields
High-order harmonic generation in gas targets is a widespread scheme used to
produce extreme ultraviolet radiation, however, it has a limited microscopic
efficiency. Macroscopic enhancement of the produced radiation relies on
phase-matching, often only achievable in quasi-phase-matching arrangements. In
the present work we numerically study quasi-phase-matching induced by
low-intensity assisting fields. We investigate the required assisting field
strength dependence on the wavelength and intensity of the driving field,
harmonic order, trajectory class and period of the assisting field. We comment
on the optimal spatial beam profile of the assisting field
Quasi-phase-matching high-harmonic radiation using chirped THz pulses
High-order harmonic generation in the presence of a chirped THz pulse is investigated numerically with
a complete 3D nonadiabatic model. The assisting THz pulse illuminates the high-order harmonic
generation gas cell laterally inducing quasi-phase-matching. We demonstrate that it is possible to
compensate the phase mismatch during propagation and extend the macroscopic cutoff of a propagated
strong IR pulse to the single-dipole cutoff. We obtain 2 orders of magnitude increase in the harmonic
efficiency of cutoff harmonics (170 eV) using a THz pulse of constant wavelength, and a further factor
of 3 enhancement when a chirped THz pulse is use
Genetic optimization of attosecond-pulse generation in light-field synthesizers
We demonstrate control over attosecond pulse generation and shaping by
numerically optimizing the synthesis of few-cycle to sub-cycle driver
waveforms. The optical waveform synthesis takes place in an ultrabroad spectral
band covering the ultraviolet-infrared domain. These optimized driver waves are
used for ultrashort single and double attosecond pulse production (with tunable
separation) revealing the potentials of the light wave synthesizer device
demonstrated by Wirth et al. [Science 334, 195 (2011)]. The results are also
analyzed with respect to attosecond pulse propagation phenomena
Viral epidemics in a cell culture: novel high resolution data and their interpretation by a percolation theory based model
Because of its relevance to everyday life, the spreading of viral infections
has been of central interest in a variety of scientific communities involved in
fighting, preventing and theoretically interpreting epidemic processes. Recent
large scale observations have resulted in major discoveries concerning the
overall features of the spreading process in systems with highly mobile
susceptible units, but virtually no data are available about observations of
infection spreading for a very large number of immobile units. Here we present
the first detailed quantitative documentation of percolation-type viral
epidemics in a highly reproducible in vitro system consisting of tens of
thousands of virtually motionless cells. We use a confluent astroglial
monolayer in a Petri dish and induce productive infection in a limited number
of cells with a genetically modified herpesvirus strain. This approach allows
extreme high resolution tracking of the spatio-temporal development of the
epidemic. We show that a simple model is capable of reproducing the basic
features of our observations, i.e., the observed behaviour is likely to be
applicable to many different kinds of systems. Statistical physics inspired
approaches to our data, such as fractal dimension of the infected clusters as
well as their size distribution, seem to fit into a percolation theory based
interpretation. We suggest that our observations may be used to model epidemics
in more complex systems, which are difficult to study in isolation.Comment: To appear in PLoS ONE. Supporting material can be downloaded from
http://amur.elte.hu/BDGVirus