112 research outputs found
Ultra-sensitive surface absorption spectroscopy using sub-wavelength diameter optical fibers
The guided modes of sub-wavelength diameter air-clad optical fibers exhibit a
pronounced evanescent field. The absorption of particles on the fiber surface
is therefore readily detected via the fiber transmission. We show that the
resulting absorption for a given surface coverage can be orders of magnitude
higher than for conventional surface spectroscopy. As a demonstration, we
present measurements on sub-monolayers of 3,4,9,10-perylene-tetracarboxylic
dianhydride (PTCDA) molecules at ambient conditions, revealing the
agglomeration dynamics on a second to minutes timescale.Comment: 4 pages, Fig.1a corrected y-axis, p.2 minor text changes to
facilitate the understanding of eq. 4 and
Cold Atom Physics Using Ultra-Thin Optical Fibers: Light-Induced Dipole Forces and Surface Interactions
The strong evanescent field around ultra-thin unclad optical fibers bears a
high potential for detecting, trapping, and manipulating cold atoms.
Introducing such a fiber into a cold atom cloud, we investigate the interaction
of a small number of cold Caesium atoms with the guided fiber mode and with the
fiber surface. Using high resolution spectroscopy, we observe and analyze
light-induced dipole forces, van der Waals interaction, and a significant
enhancement of the spontaneous emission rate of the atoms. The latter can be
assigned to the modification of the vacuum modes by the fiber.Comment: 4 pages, 4 figure
Dispersive Optical Interface Based on Nanofiber-Trapped Atoms
We dispersively interface an ensemble of one thousand atoms trapped in the
evanescent field surrounding a tapered optical nanofiber. This method relies on
the azimuthally-asymmetric coupling of the ensemble with the evanescent field
of an off-resonant probe beam, transmitted through the nanofiber. The resulting
birefringence and dispersion are significant; we observe a phase shift per atom
of \,1\,mrad at a detuning of six times the natural linewidth,
corresponding to an effective resonant optical density per atom of 0.027.
Moreover, we utilize this strong dispersion to non-destructively determine the
number of atoms.Comment: 4 pages, 4 figure
Optical interface created by laser-cooled atoms trapped in the evanescent field surrounding an optical nanofiber
Trapping and optically interfacing laser-cooled neutral atoms is an essential
requirement for their use in advanced quantum technologies. Here we
simultaneously realize both of these tasks with cesium atoms interacting with a
multi-color evanescent field surrounding an optical nanofiber. The atoms are
localized in a one-dimensional optical lattice about 200 nm above the nanofiber
surface and can be efficiently interrogated with a resonant light field sent
through the nanofiber. Our technique opens the route towards the direct
integration of laser-cooled atomic ensembles within fiber networks, an
important prerequisite for large scale quantum communication schemes. Moreover,
it is ideally suited to the realization of hybrid quantum systems that combine
atoms with, e.g., solid state quantum devices
Daily entropy of dissolved oxygen reveals different energetic regimes and drivers among high‐mountain stream types
High‐resolution time series of dissolved oxygen (DO) have revealed different ecosystem energetics regimes across various stream types. Ecosystem energetic regimes are relevant to better understand the transformation and retention of nutrients and carbon in stream ecosystems. However, the patterns and controls of stream energetics in high‐mountain landscapes remain largely unknown. Here we monitored percent DO saturation (every 10 min) over 2 years in a glacier‐fed, krenal (groundwater‐fed) and a nival (snowmelt‐fed) stream as they are typical for the high mountains. We used daily Shannon entropy to explore the temporal dynamics of stream water DO and to infer information on the ecosystem energetics and on the potential drivers. We found that discharge modulated the drivers of DO variations at daily and seasonal scales. Elevated bed movement along with high turbidity and very high gas exchange rates drove the daily DO patterns in the glacier‐fed stream during snow and ice melt, whereas light seemed to drive DO dynamics in the krenal and nival streams. We found a window of favorable conditions for potential gross primary production (GPP) during the onset of the snowmelt in the glacier‐fed stream, whereas potential GPP seemed to extend over longer periods in the krenal and nival streams. Our findings suggest how the energetic regimes of these high‐mountain streams may change in the future as their biological and physical drivers change owing to climate warming
A Nanofiber-Based Optical Conveyor Belt for Cold Atoms
We demonstrate optical transport of cold cesium atoms over millimeter-scale
distances along an optical nanofiber. The atoms are trapped in a
one-dimensional optical lattice formed by a two-color evanescent field
surrounding the nanofiber, far red- and blue-detuned with respect to the atomic
transition. The blue-detuned field is a propagating nanofiber-guided mode while
the red-detuned field is a standing-wave mode which leads to the periodic axial
confinement of the atoms. Here, this standing wave is used for transporting the
atoms along the nanofiber by mutually detuning the two counter-propagating
fields which form the standing wave. The performance and limitations of the
nanofiber-based transport are evaluated and possible applications are
discussed
Optical Properties of Collective Excitations for Finite Chains of Trapped Atoms
Resonant dipole-dipole interaction modifies the energy and decay rate of
electronic excitations for finite one dimensional chains of ultracold atoms in
an optical lattice. We show that collective excited states of the atomic chain
can be divided into dark and bright modes, where a superradiant mode with an
enhanced collective effective dipole dominates the optical scattering. Studying
the generic case of two chain segments of different length and position
exhibits an interaction blockade and spatially structured light emission.
Ultimately, an extended system of several interfering segments models a long
chain with randomly distributed defects of vacant sites. The corresponding
emission pattern provides a sensitive tool to study structural and dynamical
properties of the system.Comment: 8 pages, 12 figure
Background-free detection of trapped ions
We demonstrate a Doppler cooling and detection scheme for ions with low-lying
D levels which almost entirely suppresses scattered laser light background,
while retaining a high fluorescence signal and efficient cooling. We cool a
single ion with a laser on the 2S1/2 to 2P1/2 transition as usual, but repump
via the 2P3/2 level. By filtering out light on the cooling transition and
detecting only the fluorescence from the 2P_3/2 to 2S1/2 decays, we suppress
the scattered laser light background count rate to 1 per second while
maintaining a signal of 29000 per second with moderate saturation of the
cooling transition. This scheme will be particularly useful for experiments
where ions are trapped in close proximity to surfaces, such as the trap
electrodes in microfabricated ion traps, which leads to high background scatter
from the cooling beam
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