73 research outputs found
Precise determination of h/m_Rb using Bloch oscillations and atomic interferometry: a mean to deduce the fine structure constant
We use Bloch oscillations to transfer coherently many photon momenta to
atoms. Then we can measure accurately the ratio h/m_Rb and deduce the fine
structure constant alpha. The velocity variation due to the Bloch oscillations
is measured thanks to Raman transitions. In a first experiment, two Raman
pulses are used to select and measure a very narrow velocity class. This method
yields to a value of the fine structure constant alpha^{-1}= 137.035 998 84
(91) with a relative uncertainty of about 6.6 ppb. More recently we use an
atomic interferometer consisting in two pairs of pi/2 pulses. We present here
the first results obtained with this method
Light management in highly-textured perovskite solar cells: From full-device ellipsometry characterization to optical modelling for quantum efficiency optimization
While perovskite solar cells (PSCs) are now reaching high power conversion
efficiencies (PCEs), further performance improvement requires a fine management
and an optimization of the light pathway and harvesting in the cells. These go
through an accurate understanding, characterization and modelling of the
optical processes occurring in these complex, often textured, multi-layered
systems. In the present work, we have considered a typical methylammonium lead
iodide (MAPI) solar cell built on a fluorine-doped tin oxide (FTO) electrode of
high roughness (43 nm RMS). By variable-angle spectroscopic ellipsometry (VASE)
of the full PSC device, we have been able to determine the optical constants of
all the device layers. We have designed a one-dimensional (1D) optical model of
the stacked layers where the rough texture is described as layers of
effective-medium index. We have supported the model using data extracted from
scanning electron microscopy, diffuse spectroscopy and photovoltaic efficiency
measurements. We show that the 1D model, while insufficient to describe
scattering by the FTO plate alone, gives an accurate description of the full
device optical properties. By comparison with the experimental external quantum
efficiency (EQE), we estimate the internal quantum efficiency (IQE) and the
effect of the losses related to electron transfer. Based on this work, we
finally discuss the optical losses mechanisms and the possible strategies that
can be implemented to improve light management within PSC devices and further
increase their performances.Comment: 14 pages, 5 figure
An achiral magnetic photonic antenna as a tunable nanosource of superchiral light
Sensitivity to molecular chirality is crucial for many fields, from biology
and chemistry to the pharmaceutical industry. By generating superchiral light,
nanophotonics has brought innovative solutions to reduce the detection volume
and increase sensitivity at the cost of a non-selectivity of light chirality or
a strong contribution to the background. Here, we theoretically propose an
achiral plasmonic resonator, based on a rectangular nanoslit in a thin gold
layer behaving as a magnetic dipole, to generate a tunable nanosource of purely
superchiral light. This nanosource is free of any background, and the sign of
its chirality is externally tunable in wavelength and polarization. These
properties result from the coupling between the incident wave and the magnetic
dipolar character of our nano-antenna. Thus, our results propose a platform
with deep subwavelength detection volumes for chiral molecules in particular,
in the visible, and a roadmap for optimizing the signal-to-noise ratios in
circular dichroism measurements to reach single-molecule sensitivity
Bloch oscillations of ultracold atoms: a tool for a metrological determination of
We use Bloch oscillations in a horizontal moving standing wave to transfer a
large number of photon recoils to atoms with a high efficiency (99.5% per
cycle). By measuring the photon recoil of , using velocity selective
Raman transitions to select a subrecoil velocity class and to measure the final
accelerated velocity class, we have determined with a relative
precision of 0.4 ppm. To exploit the high momentum transfer efficiency of our
method, we are developing a vertical standing wave set-up. This will allow us
to measure better than and hence the fine structure
constant with an uncertainty close to the most accurate value coming
from the () determination
Combination of Bloch oscillations with a Ramsey-Bord\'e interferometer : new determination of the fine structure constant
We report a new experimental scheme which combines atom interferometry with
Bloch oscillations to provide a new measurement of the ratio
. By using Bloch oscillations, we impart to the atoms up to
1600 recoil momenta and thus we improve the accuracy on the recoil velocity
measurement. The deduced value of leads to a new
determination of the fine structure constant
with a relative uncertainty of . The comparison of this
result with the value deduced from the measurement of the electron anomaly
provides the most stringent test of QED
The Lamb shift in muonic hydrogen and the proton radius
By means of pulsed laser spectroscopy applied to muonic hydrogen (μ− p) we have measured the 2S F = 1 1/2 − 2PF = 2 3/2 transition frequency to be 49881.88(76) GHz. By comparing this measurement with its theoretical prediction based on bound-state QED we have determined a proton radius value of rp = 0.84184 (67) fm. This new value is an order of magnitude preciser than previous results but disagrees by 5 standard deviations from the CODATA and the electronproton scattering values. An overview of the present effort attempting to solve the observed discrepancy is given. Using the measured isotope shift of the 1S-2S transition in regular hydrogen and deuterium also the rms charge radius of the deuteron rd = 2.12809 (31) fm has been determined. Moreover we present here the motivations for the measurements of the μ 4He + and μ 3He + 2S-2P splittings. The alpha and triton charge radii are extracted from these measurements with relative accuracies of few 10 − 4. Measurements could help to solve the observed discrepancy, lead to the best test of hydrogen-like energy levels and provide crucial tests for few-nucleon ab-initio theories and potentials
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