7,291 research outputs found
Quantum Mechanical Treatment of Stimulated Raman Cross Sections
Stimulated Raman scattering (SRS) has played an increasingly pivotal role in
chemistry and photonics. Recently, understanding of light-molecule interaction
during SRS was brought to a new quantitative level through the introduction of
stimulated Raman cross section, . Measurements of Raman-active
molecules have revealed interesting insights, and theoretical consideration has
suggested an Einstein-coefficient-like relation between and the
commonly used spontaneous Raman cross sections, . However, the
theoretical underpinning of is not known. Herein we provide a
full quantum mechanical treatment for , via both a semi-classical
method and a quantum electrodynamic (QED) method. The resulting formula
provides a rigorous theory to predict experimental outcome from first
principles, and unveils key physical factors rendering
inherently strong response. Through this formula, we also confirm the validity
of the Einstein-coefficient-like equation connecting and
reported earlier, and discuss the inherent symmetry between all
spontaneous and stimulated optical processes. Hence the present treatment shall
deepen the fundamental understanding of the molecular response during SRS, and
facilitate quantitative applications in various experiments.Comment: 19 pages, 2 figure
Polarized -photon beams produced by collision of two ultrarelativistic electron beams
Many studies have shown that high-energy -photon beams can be
efficiently generated via nonlinear Compton scattering driven by laser pulses
with intensities recently available in laboratories.
Here, we propose a laserless scheme to efficiently generate high-energy
polarized -photon beams by collision of two ultrarelativistic electron
beams. The self-generated field of a dense driving electron beam provides the
strong deflection field for the other ultrarelativistic seeding electron beam.
A QED Monte Carlo code based on the locally constant field approximation is
employed to simulate the collision process, and the polarization properties of
produced photons are investigated. The simulation results and
theoretical analysis indicate that the photon polarization, including both
linear and circular polarizations, can be tuned by changing the initial
polarization of the seeding beam. If an unpolarized seeding beam is used,
linearly polarized photons with an average polarization of 55\% can be
obtained. If the seeding beam is transversely (longitudinally) polarized, the
linear (circular) polarization of photons above 3 GeV can reach 90\% (67\%),
which is favorable for highly polarized, high-energy photon sources.Comment: 12 pages, 8 figure
Theory for charge and orbital density-wave states in manganite LaSrMnO
We investigate the high temperature phase of layered manganites, and
demonstrate that the charge-orbital phase transition without magnetic order in
LaSrMnO can be understood in terms of the density wave
instability. The orbital ordering is found to be induced by the nesting between
segments of Fermi surface with different orbital characters. The simultaneous
charge and orbital orderings are elaborated with a mean field theory. The
ordered orbitals are shown to be .Comment: published versio
Radial Angular Momentum Transfer and Magnetic Barrier for Short-Type Gamma-Ray Burst Central Engine Activity
Soft extended emission (EE) following initial hard spikes up to 100 seconds
was observed with {\em Swift}/BAT for about half of short-type gamma-ray bursts
(SGRBs). This challenges the conversional central engine models of SGRBs, i.e.,
compact star merger models. In the framework of the black hole-neutron star
merger models, we study the roles of the radial angular momentum transfer in
the disk and the magnetic barrier around the black hole for the activity of
SGRB central engines. We show that the radial angular momentum transfer may
significantly prolong the lifetime of the accretion process and multiple
episodes may be switched by the magnetic barrier. Our numerical calculations
based on the models of the neutrino-dominated accretion flows suggest that the
disk mass is critical for producing the observed EE. In case of the mass being
, our model can reproduce the observed timescale and
luminosity of both the main and EE episodes in a reasonable parameter set. The
predicted luminosity of the EE component is lower than the observed EE with
about one order of magnitude and the timescale is shorter than 20 seconds if
the disk mass being . {\em Swift}/BAT-like instruments may
be not sensitive enough to detect the EE component in this case. We argue that
the EE component would be a probe for merger process and disk formation for
compact star mergers.Comment: 9 pages, 3 figures, accepted for publication in Ap
Optical polarization rogue waves in fiber laser
A new kind of optical rogue waves, polarization rogue waves that appear with greatly deviated and unpredictable positions of polarization states, is identified in forming partially mode-locked fiber laser based on parametric frequency conversion
Coherence manipulation of partially mode-locked fiber laser
We find that adjusting the polarization state controls the process of loss of coherence of partially coherent laser,where parametric frequency conversion populates longitudinal modes with a random distribution of position, intensity and polarization
- …