379 research outputs found
A simple analytical alignment model for laser-kicked molecular rotors
We develop a mathematically simple yet accurate model for the single-pulse
non-resonant impulsive alignment of thermal ensembles of linear molecules. We
find that our molecular alignment model, which is based on the 2D rotor, not
only provides a simplification for analytical and numerical calculations, but
also establishes intuitive connections between system parameters, such as
temperature and pulse intensity, and the resulting shape of the temporal
molecular alignment
Phase distortions of attosecond pulses produced by resonance-enhanced high harmonic generation
Resonant enhancement of high harmonic generation can be obtained in plasmas
containing ions with strong radiative transitions resonant with harmonic
orders. The mechanism for this enhancement is still debated. We perform the
first temporal characterization of the attosecond emission from a tin plasma
under near-resonant conditions for two different resonance detunings. We show
that the resonance considerably changes the relative phase of neighbouring
harmonics. For very small detunings, their phase locking may even be lost,
evidencing strong phase distortions in the emission process and a modified
attosecond structure. These features are well reproduced by our simulations,
allowing their interpretation in terms of the phase of the recombination dipole
moment
Generation of Attosecond Pulses with Controllable Carrier-Envelope Phase via High-order Frequency Mixing
Advancing table-top attosecond sources in brightness and pulse duration is of
immense interest and importance for an expanding sphere of applications. Recent
theoretical studies [New J. Phys., 22 093030 (2020)] have found that high-order
frequency mixing (HFM) in a two-color laser field can be much more efficient
than high-order harmonic generation (HHG). Here we study the attosecond
properties of the coherent XUV generated via HFM analytically and numerically,
focusing on the practically important case when one of the fields has much
lower frequency and much lower intensity than the other one. We derive simple
analytical equations describing intensities and phase locking of the HFM
spectral components. We show that the duration of attosecond pulses generated
via HFM, while being very similar to that obtained via HHG in the plateau, is
shortened for the cut-off region. Moreover, our study demonstrates that the
carrier-envelope phase of the attopulses produced via HFM, in contrast to HHG,
can be easily controlled by the phases of the generating fields
Macroscopic effects in generation of attosecond XUV pulses via high-order frequency mixing in gases and plasma
We study the generation of attosecond XUV pulses via high-order frequency
mixing (HFM) of two intense generating fields, and compare this process with
the more common high-order harmonic generation (HHG) process. We calculate the
macroscopic XUV signal by numerically integrating the 1D propagation equation
coupled with the 3D time-dependent Schr\"odinger equation. We analytically find
the length scales which limit the quadratic growth of the HFM macroscopic
signal with propagation length. Compared to HHG these length scales are much
longer for a group of HFM components, with orders defined by the frequencies of
the generating fields. This results in a higher HFM macroscopic signal despite
the microscopic response being lower than for HHG. In our numerical
simulations, the intensity of the HFM signal is several times higher than that
for HHG in a gas, and it is up to three orders of magnitude higher for
generation in plasma; it is also higher for longer generating pulses. The HFM
provides very narrow XUV lines ()
with well-defined frequencies, thus allowing for a simple extension of optical
frequency standards to the XUV range. Finally, we show that the group of HFM
components effectively generated due to macroscopic effects provides a train of
attosecond pulses such that the carrier-envelope phase of an individual
attosecond pulse can be easily controlled by tuning the phase of one of the
generating fields.Comment: 14 pages, 7 figure
Interatomic coulombic decay rate in endohedral complexes
Interatomic coulombic decay (ICD) in van der Waals endohedral complexes was predicted to be anomalously fast. However, the available theoretical calculations of the ICD rates in endohedral complexes only consider the equilibrium geometry, in which the encapsulated atom is located at the centre of the fullerene cage. Here we show analytically that the dominant contribution of the dipole plasmon resonance to ICD does not deviate from its equilibrium geometry value, while contributions of higher multipole plasmons to the ICD can be neglected for most atomic displacements possible for an endohedral complex at room temperature. This is in contrast to the behaviour predicted for ionic endohedral compounds. Our results show that the conclusion of the earlier works on the ultrafast character of the ICD in endohedral complexes holds generally for a wide range of geometries possible under a thermal distribution, rather than only for the equilibrium geometry
Authentic Films as a Tool for the Development of Sociocultural Competence
The article is devoted to the problem of foreign language teaching with the help of authentic films and TV series. Some effective ways of using such tools are discussed in the article
Authentic Films as a Tool for the Development of Sociocultural Competence
The article is devoted to the problem of foreign language teaching with the help of authentic films and TV series. Some effective ways of using such tools are discussed in the article
Molecular Auger Interferometry
We propose a theory of interferometric measurement of a normal Auger decay width in molecules. Molecular Auger interferometry is based on the coherent phase control of Auger dynamics in a two-colour (ω/2ω) laser field. We show that, in contrast to atoms, in oriented molecules of certain point groups (e.g. CH3F) the relative ω/2ω phase modulates the total ionisation yield. A simple analytical formula is derived for the extraction of the widths of Auger-active states from a molecular Auger interferogram, avoiding the need of either attosecond or high-resolution spectroscopy
- …