13 research outputs found
Excitation of atoms in an optical lattice driven by polychromatic amplitude modulation
We investigate the mutiphoton process between different Bloch states in an
amplitude modulated optical lattice. In the experiment, we perform the
modulation with more than one frequency components, which includes a high
degree of freedom and provides a flexible way to coherently control quantum
states. Based on the study of single frequency modulation, we investigate the
collaborative effect of different frequency components in two aspects. Through
double frequency modulations, the spectrums of excitation rates for different
lattice depths are measured. Moreover, interference between two separated
excitation paths is shown, emphasizing the influence of modulation phases when
two modulation frequencies are commensurate. Finally, we demonstrate the
application of the double frequency modulation to design a
large-momentum-transfer beam splitter. The beam splitter is easy in practice
and would not introduce phase shift between two arms.Comment: 11pages, 7 figure
Asymmetric superradiant scattering and abnormal mode amplification induced by atomic density distortion
The superradiant Rayleigh scattering using a pump laser incident along the
short axis of a Bose-Einstein condensate with a density distortion is studied,
where the distortion is formed by shocking the condensate utilizing the
residual magnetic force after the switching-off of the trapping potential. We
find that very small variation of the atomic density distribution would induce
remarkable asymmetrically populated scattering modes by the matter-wave
superradiance with long time pulse. The optical field in the diluter region of
the atomic cloud is more greatly amplified, which is not an ordinary mode
amplification with the previous cognition. Our numerical simulations with the
density envelop distortion are consistent with the experimental results. This
supplies a useful method to reflect the geometric symmetries of the atomic
density profile by the superradiance scattering.Comment: 7pages,4 figures, Optical Express 21,(2013)1437
Long-time nonlinear dynamical evolution for P-band ultracold atoms in an optical lattice
We report the long-time nonlinear dynamical evolution of ultracold atomic
gases in the P-band of an optical lattice. A Bose-Einstein condensate (BEC) is
fast and efficiently loaded into the Pband at zero quasi-momentum with a
non-adiabatic shortcut method. For the first one and half milliseconds, these
momentum states undergo oscillations due to coherent superposition of different
bands, which are followed by oscillations up to 60ms of a much longer period.
Our analysis shows the dephasing from the nonlinear interaction is very
conducive to the long-period oscillations induced by the variable force due to
the harmonic confinement.Comment: 8 pages, 7 figure
Asymmetric superradiant scattering and abnormal mode amplification induced by atomic density distortion
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Research data supporting "High carrier mobility along the [111] orientation in Cu2O photoelectrodes"
Included in the dataset are detailed information into the crystallography, morphology, electronic properties, (photo)electrochemical and carrier dynamics of both single-crystal Cu2O thin films and polycrystalline Cu2O with favored crystal orientations. Multiple intruments, including Empyrean X-ray Diffractometer, Zeiss Merlin Scanning Electron Microscope, Tecnai Osiris Transmission Electron Micrisocope, Newport LCS-100 Solar Simulator, Biologic SP-200, GC9790plus Gas Chromatograph, Keithley 2450 SourceMeter, Shimadzu UV-3600 Plus Double-beam Spectrophotometer, were applied to collect the data.
Abstract of associated publication:
Solar fuels offer a promising approach to provide sustainable fuels by harnessing
sunlight. Following a decade of advancement, Cu2O photocathodes are capable of
delivering a performance comparable to that of photoelectrodes with established
photovoltaic materials. However, considerable bulk charge carrier recombination
that is poorly understood still limits further advances in performance. Here we
demonstrate performance of Cu2O photocathodes beyond the state-of-the-art by
exploiting a new conceptual understanding of carrier recombination and transport
in single-crystal Cu2O thin films. Using ambient liquid-phase epitaxy, we present a
new method to grow single-crystal Cu2O samples with three crystal orientations.
Broadband femtosecond transient reflection spectroscopy measurements were used
to quantify anisotropic optoelectronic properties, through which the carrier mobility
along the [111] orientation was found to be an order of magnitude higher than those
along other orientations. Driven by these findings, we developed a polycrystalline
Cu2O photocathode with an extraordinarily pure (111) orientation and (111) terminating
facets using a simple and low-cost method, which delivers 7 mA cm−2 current density
(more than 70% improvement compared to that of state-of-the-art electrodeposited
devices) at 0.5 V versus a reversible hydrogen electrode under air mass 1.5 G
illumination, and stable operation over at least 120 h.European Research Council (HYPERION, grant 756962)
Engineering and Physical Sciences Research Council (grant H2CAT, EP/V012932/1)
Swiss National Science Foundation (P2ELP2_195109)
Engineering and Physical Sciences Research Council (EP/
T001038/1)
UK Research and Innovation (EP/X022986/1)
St John’s College Cambridge (Title A)
European Research Council (MatEnSAP, 682833)
UK Research and Innovation (EP/X030563/1)
National Natural Science Foundation of China (52072187, 22122903)
National Key Research and Development Program of China (019YFE0123400)
Royal Society and Tata Group (UF150033
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