279 research outputs found
Magnetic field control of elastic scattering in a cold gas of fermionic lithium atoms
We study elastic collisions in an optically trapped spin mixture of fermionic
lithium atoms in the presence of magnetic fields up to 1.5kG by measuring
evaporative loss. Our experiments confirm the expected magnetic tunability of
the scattering length by showing the main features of elastic scattering
according to recent calculations. We measure the zero crossing of the
scattering length that is associated with a predicted Feshbach resonance at
530(3)G. Beyond the resonance we observe the expected large cross section in
the triplet scattering regime
Characterization of a Quantum Light Source Based on Spontaneous Parametric Down-Conversion
We have built a quantum light source capable of producing different types of
quantum states. The quantum light source is based on entangled state
preparation in the process of spontaneous parametric down-conversion. The
single-photon detection rate of eight-hundred thousand per second demonstrates
that we have created a bright state-of-the-art quantum light source. As a part
of the characterization we measured two-photon quantum interference in a
Hong-Ou-Mandel interferometer.Comment: 33 page
Nanophotonic hybridization of narrow atomic cesium resonances and photonic stop gaps of opaline nanostructures
We study a hybrid system consisting of a narrowband atomic optical resonance
and the long-range periodic order of an opaline photonic nanostructure. To this
end, we have infiltrated atomic cesium vapor in a thin silica opal photonic
crystal. With increasing temperature, the frequencies of the opal's
reflectivity peaks shift down by >20% due to chemical reduction of the silica.
Simultaneously, the photonic bands and gaps shift relative to the fixed
near-infrared cesium D1 transitions. As a result the narrow atomic resonances
with high finesse (f/df=8E5) dramatically change shape from a usual dispersive
shape at the blue edge of a stop gap, to an inverted dispersion lineshape at
the red edge of a stop gap. The lineshape, amplitude, and off-resonance
reflectivity are well modeled with a transfer-matrix model that includes the
dispersion and absorption of Cs hyperfine transitions and the
chemically-reduced opal. An ensemble of atoms in a photonic crystal is an
intriguing hybrid system that features narrow defect-like resonances with a
strong dispersion, with potential applications in slow light, sensing and
optical memory.Comment: 8 pages, 6 figure
Superpixel-based spatial amplitude and phase modulation using a digital micromirror device.
This is the final version of the article. Available via open access from Optical Society of America via the DOI in this record.We present a superpixel method for full spatial phase and amplitude control of a light beam using a digital micromirror device (DMD) combined with a spatial filter. We combine square regions of nearby micromirrors into superpixels by low pass filtering in a Fourier plane of the DMD. At each superpixel we are able to independently modulate the phase and the amplitude of light, while retaining a high resolution and the very high speed of a DMD. The method achieves a measured fidelity F = 0.98 for a target field with fully independent phase and amplitude at a resolution of 8 à 8 pixels per diffraction limited spot. For the LG10 orbital angular momentum mode the calculated fidelity is F = 0.99993, using 768 à 768 DMD pixels. The superpixel method reduces the errors when compared to the state of the art Lee holography method for these test fields by 50% and 18%, with a comparable light efficiency of around 5%. Our control software is publicly available.We thank Duygu Akbulut, Hasan Yılmaz, Henri Thyrrestrup, Michael J. Van De Graaff, Pepijn W.H. Pinkse, Ad Lagendijk and Willem L. Vos for discussions. This work is part of the research program of the Stichting voor Fundamenteel Onderzoek der Materie (FOM). A.P.M. acknowledges European Research Council grant no. 279248
Scattering Lens Resolves sub-100 nm Structures with Visible Light
The smallest structures that conventional lenses are able to optically
resolve are of the order of 200 nm. We introduce a new type of lens that
exploits multiple scattering of light to generate a scanning nano-sized optical
focus. With an experimental realization of this lens in gallium phosphide we
have succeeded to image gold nanoparticles at 97 nm optical resolution. Our
work is the first lens that provides a resolution in the nanometer regime at
visible wavelengths.Comment: 4 pages, 3 figure
Focusing Light through Random Photonic Media by Binary Amplitude Modulation
We study the focusing of light through random photonic materials using
wavefront shaping. We explore a novel approach namely binary amplitude
modulation. To this end, the light incident to a random photonic medium is
spatially divided into a number of segments. We identify the segments that give
rise to fields that are out of phase with the total field at the intended focus
and assign these a zero amplitude, whereas the remaining segments maintain
their original amplitude. Using 812 independently controlled segments of light,
we find the intensity at the target to be 75 +/- 6 times enhanced over the
average intensity behind the sample. We experimentally demonstrate focusing of
light through random photonic media using both an amplitude only mode liquid
crystal spatial light modulator and a MEMS-based spatial light modulator. Our
use of Micro Electro-Mechanical System (MEMS)-based digital micromirror devices
for the control of the incident light field opens an avenue to high speed
implementations of wavefront shaping
Analysis of Photoassociation Spectra for Giant Helium Dimers
We perform a theoretical analysis to interpret the spectra of purely
long-range helium dimers produced by photoassociation (PA) in an ultra-cold gas
of metastable helium atoms. The experimental spectrum obtained with the PA
laser tuned closed to the atomic line has been
reported in a previous Letter. Here, we first focus on the corrections to be
applied to the measured resonance frequencies in order to infer the molecular
binding energies. We then present a calculation of the vibrational spectra for
the purely long-range molecular states, using adiabatic potentials obtained
from perturbation theory. With retardation effects taken into account, the
agreement between experimental and theoretical determinations of the spectrum
for the purely long-range potential well is very good. The results
yield a determination of the lifetime of the atomic state
Control of light transmission through opaque scattering media in space and time
We report the first experimental demonstration of combined spatial and
temporal control of light trajectories through opaque media. This control is
achieved by solely manipulating spatial degrees of freedom of the incident
wavefront. As an application, we demonstrate that the present approach is
capable to form bandwidth-limited ultrashort pulses from the otherwise randomly
transmitted light with a controllable interaction time of the pulses with the
medium. Our approach provides a new tool for fundamental studies of light
propagation in complex media and has potential for applications for coherent
control, sensing and imaging in nano- and biophotonics
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