331 research outputs found
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
Phase-matching gating for isolated attosecond pulse generation
We investigate the production of an isolated attosecond pulse~(IAP) via the
phase-matching gating of high-harmonic generation by intense laser pulses. Our
study is based on the integration of the propagation equation for the
fundamental and generated fields with nonlinear polarisation found via the
numerical solution of the time-dependent Schr\"odinger equation. We study the
XUV energy as a function of the propagation distance (or the medium density)
and find that the onset of the IAP production corresponds to the change from
linear to quadratic dependence of this energy on the propagation distance (or
density). Finally, we show that the upper limit of the fundamental pulse
duration for which the IAP generation is feasible is defined by the temporal
spreading of the fundamental pulse during the propagation. This nonlinear
spreading is defined by the difference of the group velocities for the neutral
and photoionised medium
14C dating to study the development of soils in the forest-steppe of the central russian upland as a result of bioclimatic changes and long-term cultivation
Temporal changes in soils of forest landscapes of the forest-steppe zone - Haplic Luvisols and Greyzemic Phaeozems - under the impact of Holocene climate changes (natural factor) and long-term cultivation (anthropogenic factor) were studied on level interfluves of the Central Russian Upland. To study soil evolution under the impact of climate changes, soil chronosequences of archaeological sites - paleosols buried under ramparts of ancient settlements and background surface soils of adjacent areas - were analyze
ΦCrAss001 represents the most abundant bacteriophage family in the human gut and infects Bacteroides intestinalis
peer-reviewedCrAssphages are an extensive and ubiquitous family of tailed bacteriophages, predicted to infect bacteria of the order Bacteroidales. Despite being found in ~50% of individuals and representing up to 90% of human gut viromes, members of this viral family have never been isolated in culture and remain understudied. Here, we report the isolation of a CrAssphage (ΦCrAss001) from human faecal material. This bacteriophage infects the human gut symbiont Bacteroides intestinalis, confirming previous in silico predictions of the likely host. DNA sequencing demonstrates that the bacteriophage genome is circular, 102 kb in size, and has unusual structural traits. In addition, electron microscopy confirms that ΦcrAss001 has a podovirus-like morphology. Despite the absence of obvious lysogeny genes, ΦcrAss001 replicates in a way that does not disrupt proliferation of the host bacterium, and is able to maintain itself in continuous host culture during several weeks
Effect of biochar on soil co2 fluxes from agricultural field experiments in russian far east
Agricultural soils are a major source of greenhouse gases. Biochar is a soil improver and, when applied to the soil, sequesters carbon. However, a different combination of soil and climatic conditions and biochar leads to different research results. In this research, the effects of 1 kg/m2 and 3 kg/m2 biochar application to clay soils on the CO2 flow in field experiments along two cropping seasons in the Russian Far East were investigated. Data showed that biochar significantly reduces the cumulative flow of soil CO2, compared with untreated field plots. In 2018, the greatest reduction in soil CO2 emissions (28.2%) with 3 kg/m2 of biochar was obtained, while in 2019, the greatest decrease in the cumulative CO2 flow at the application dose of 1 kg/m2 (57.7%) was recorded. A correlation between a decrease in the value of the cumulative CO2 flux and an increase in the biomass grown in the studied areas of agricultural crops during the season of 2018 was found
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