2,268 research outputs found
Frequency-Domain Coherent Control of Femtosecond Two-Photon Absorption: Intermediate-Field vs. Weak-Field Regime
Coherent control of femtosecond two-photon absorption in the
intermediate-field regime is analyzed in detail in the powerful frequency
domain using an extended 4th-order perturbative description. The corresponding
absorption is coherently induced by the weak-field non-resonant two-photon
transitions as well as by four-photon transitions involving three absorbed
photons and one emitted photons. The interferences between these two groups of
transitions lead to a difference between the intermediate-field and weak-field
absorption dynamics. The corresponding interference nature (constructive or
destructive) strongly depends on the detuning direction of the pulse spectrum
from half the two-photon transition frequency. The model system of the study is
atomic sodium, for which both experimental and theoretical results are
obtained. The detailed understanding obtained here serves as a basis for
coherent control with rationally-shaped femtosecond pulses in a regime of
sizable absorption yields.Comment: 25 pages, 5 figure
Transient dynamics of nonlinear magneto-optical rotation
We analyze nonlinear magneto-optical rotation (NMOR) in rubidium vapor
subjected to continuously-scanned magnetic field. By varying magnetic-field
sweep rate, a transition from traditionally-observed dispersive-like NMOR
signals (low sweep rate) to oscillating signals (higher sweep rates) is
demonstrated. The transient oscillatory behavior is studied versus light and
magnetic-field parameters, revealing a strong dependence of the signals on
magnetic-sweep rate and light intensity. The experimental results are supported
with density-matrix calculations, which enable quantitative analysis of the
effect. Fitting of the signals simulated versus different parameters with a
theoretically-motivated curve reveals presence of oscillatory and static
components in the signals. The components depend differently on the system
parameters, which suggests their distinct nature. The investigations provide
insight into dynamics of ground-state coherence generation and enable
application of NMOR in detection of transient spin couplings.Comment: 9 pages, 7 figures, Submitted to Physical Review
Enhancement of Intermediate-Field Two-Photon Absorption by Rationally-Shaped Femtosecond Pulses
We extend the powerful frequency-domain analysis of femtosecond two-photon
absorption to the intermediate-field regime, which involves both two- and
four-photon transitions. Consequently, we find a broad family of shaped pulses
that enhance the absorption over the transform-limited pulse. It includes any
spectral phase that is anti-symmetric around half the transition frequency. The
spectrum is asymmetric around it. The theoretical framework and results for Na
are verified experimentally. This work opens the door for rational femtosecond
coherent control in a regime of considerable absorption yields
Multi-Channel Selective Femtosecond Coherent Control Based on Symmetry Properties
We present and implement a new scheme for extended multi-channel selective
femtosecond coherent control based on symmetry properties of the excitation
channels. Here, an atomic non-resonant two-photon absorption channel is
coherently incorporated in a resonance-mediated (2+1) three-photon absorption
channel. By proper pulse shaping, utilizing the invariance of the two-photon
absorption to specific phase transformations of the pulse, the three-photon
absorption is tuned independently over order-of-magnitude yield range for any
possible two-photon absorption yield. Noticeable is a set of two-photon dark
pulses inducing widely-tunable three-photon absorption
ALMA imaging of SDP.81 - I. A pixelated reconstruction of the far-infrared continuum emission
We present a sub-50 pc-scale analysis of the gravitational lens system SDP.81
at redshift 3.042 using Atacama Large Millimetre/submillimetre Array (ALMA)
science verification data. We model both the mass distribution of the
gravitational lensing galaxy and the pixelated surface brightness distribution
of the background source using a novel Bayesian technique that fits the data
directly in visibility space. We find the 1 and 1.3 mm dust emission to be
magnified by a factor of u_tot = 17.6+/-0.4, giving an intrinsic total
star-formation rate of 315+/-60 M_sol/yr and a dust mass of 6.4+/-1.5*10^8
M_sol. The reconstructed dust emission is found to be non-uniform, but composed
of multiple regions that are heated by both diffuse and strongly clumped
star-formation. The highest surface brightness region is a ~1.9*0.7 kpc
disk-like structure, whose small extent is consistent with a potential
size-bias in gravitationally lensed starbursts. Although surrounded by extended
star formation, with a density of 20-30+/-10 M_sol/yr/kpc^2, the disk contains
three compact regions with densities that peak between 120-190+/-20
M_sol/yr/kpc^2. Such star-formation rate densities are below what is expected
for Eddington-limited star-formation by a radiation pressure supported
starburst. There is also a tentative variation in the spectral slope of the
different star-forming regions, which is likely due to a change in the dust
temperature and/or opacity across the source.Comment: MNRAS accepted 2015 April 1
ALMA imaging of SDP.81 - II. A pixelated reconstruction of the CO emission lines
We present a sub-100 pc-scale analysis of the CO molecular gas emission and
kinematics of the gravitational lens system SDP.81 at redshift 3.042 using
Atacama Large Millimetre/submillimetre Array (ALMA) science verification data
and a visibility-plane lens reconstruction technique. We find clear evidence
for an excitation dependent structure in the unlensed molecular gas
distribution, with emission in CO (5-4) being significantly more diffuse and
structured than in CO (8-7). The intrinsic line luminosity ratio is r_8-7/5-4 =
0.30 +/- 0.04, which is consistent with other low-excitation starbursts at z ~
3. An analysis of the velocity fields shows evidence for a star-forming disk
with multiple velocity components that is consistent with a
merger/post-coalescence merger scenario, and a dynamical mass of M(< 1.56 kpc)
= 1.6 +/- 0.6 x 10^10 M_sol . Source reconstructions from ALMA and the Hubble
Space Telescope show that the stellar component is offset from the molecular
gas and dust components. Together with Karl G. Jansky Very Large Array CO (1-0)
data, they provide corroborative evidence for a complex ~2 kpc-scale starburst
that is embedded within a larger ~15 kpc structure.Comment: MNRAS accepted, 6th July 201
Pulse-Bandwidth Dependence of Coherent Phase Control of Resonance-Mediated (2+1) Three-Photon Absorption
We study in detail coherent phase control of femtosecond resonance-mediated
(2+1) three-photon absorption and its dependence on the spectral bandwidth of
the excitation pulse. The regime is the weak-field regime of third perturbative
order. The corresponding interference mechanism involves a group of
three-photon excitation pathways that are on resonance with the intermediate
state and a group of three-photon excitation pathways that are near resonant
with it. The model system of the study is atomic sodium (Na), for which
experimental and numerical-theoretical results are obtained. Prominent among
the results is our finding that with simple proper pulse shaping an increase in
the excitation bandwidth leads to a corresponding increase in the enhancement
of the three-photon absorption over the absorption induced by the (unshaped)
transform-limited pulse. For example, here, a 40-nm bandwidth leads to an
order-of-magnitude enhancement over the transform-limited absorption.Comment: 23 pages, 5 figure
THE LECTOTYPE AND TYPE LOCALITY OF CANDOIA CARINATA (REPTILIA, SERPENTES)
The lectotype of Boa carinata Schneider, 1801, has been rediscovered and is now ZMFK35503, having been transferred in 1977 from the Göttingen Museum, its original location. Its typelocality has not been reported previously, but is indicated as “Amboina” on a label with the lectotype.The specimen is redescribed and fi gured, and conforms with expectations for material from the vicinityof the type locality. A brief history of Schneider and of the syntypes of Boa carinata, now Candoiacarinata, is reviewed
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