43 research outputs found
Isotopic difference in the heteronuclear loss rate in a two-species surface trap
We have realized a two-species mirror-magneto-optical trap containing a
mixture of Rb (Rb) and Cs atoms. Using this trap, we have
measured the heteronuclear collisional loss rate due to
intra-species cold collisions. We find a distinct difference in the magnitude
and intensity dependence of for the two isotopes Rb and
Rb which we attribute to the different ground-state hyperfine splitting
energies of the two isotopes.Comment: 4 pages, 2 figure
Birth and growth of cavitation bubbles within water under tension confined in a simple synthetic tree
Water under tension, as can be found in several systems including tree
vessels, is metastable. Cavitation can spontaneously occur, nucleating a
bubble. We investigate the dynamics of spon- taneous or triggered cavitation
inside water filled microcavities of a hydrogel. Results show that a stable
bubble is created in only a microsecond timescale, after transient
oscillations. Then, a diffusion driven expansion leads to filling of the
cavity. Analysis reveals that the nucleation of a bubble releases a tension of
several tens of MPa, and a simple model captures the different time scales of
the expansion process
Single-bubble and multi-bubble cavitation in water triggered by laser-driven focusing shock waves
In this study a single laser pulse spatially shaped into a ring is focused
into a thin water layer, creating an annular cavitation bubble and cylindrical
shock waves: an outer shock that diverges away from the excitation laser ring
and an inner shock that focuses towards the center. A few nanoseconds after the
converging shock reaches the focus and diverges away from the center, a single
bubble nucleates at the center. The inner diverging shock then reaches the
surface of the annular laser-induced bubble and reflects at the boundary,
initiating nucleation of a tertiary bubble cloud. In the present experiments,
we have performed time-resolved imaging of shock propagation and bubble wall
motion. Our experimental observations of single-bubble cavitation and collapse
and appearance of ring-shaped bubble clouds are consistent with our numerical
simulations that solve a one dimensional Euler equation in cylindrical
coordinates. The numerical results agree qualitatively with the experimental
observations of the appearance and growth of bubble clouds at the smallest
laser excitation rings. Our technique of shock-driven bubble cavitation opens
novel perspectives for the investigation of shock-induced single-bubble or
multi-bubble cavitation phenomena in thin liquids
Competing mechanisms and scaling laws for carbon nanotube scission by ultrasonication
Dispersion of carbon nanotubes (CNTs) into liquids typically
requires ultrasonication to exfoliate individuals CNTs from bundles.
Experiments show that CNT length drops with sonication time (or
energy) as a power law t?m. Yet the breakage mechanism is not
well understood, and the experimentally reported power law
exponent m ranges from approximately 0.2 to 0.5. Here we simulate
the motion of CNTs around cavitating bubbles by coupling
Brownian dynamics with the Rayleigh-Plesset equation. We observe
that, during bubble growth, CNTs align tangentially to the
bubble surface. Surprisingly, we find two dynamical regimes during
the collapse: shorter CNTs align radially, longer ones buckle.We
compute the phase diagram for CNT collapse dynamics as a function
of CNT length, stiffness, and initial distance from the bubble
nuclei and determine the transition from aligning to buckling. We
conclude that, depending on their length, CNTs can break due to
either buckling or stretching. These two mechanisms yield different
power laws for the length decay (0.25 and 0.5, respectively), reconciling
the apparent discrepancy in the experimental data
Cavitation as a Microfluidic Tool
Cavitation in confined geometries in particular in narrow gaps prevalent in microfluidic geometries allows for novel applications. Here we will give an overview of successful demonstrations of cavitation as a microfluidic tool. Cavitation can pump and mix liquids very rapidly, move objects such as cells, rupture plasma membranes, probe elastic properties in micro-rheology, study coalescence, and even create arbitrary superpositions of shock waves. In all areas, bubbles are created with a focused laser which allows precise temporal and spatial control. With the usage of digital holography arbitrary configurations of bubbles can be created such as bubble clusters, squarish, toroidal, or even linear cavitation bubbles. Interestingly, even in very narrow gaps of a few tens of microns most of the bubble dynamics can be described with potential flow. This presentation will summarize published work and show current research under progress.http://deepblue.lib.umich.edu/bitstream/2027.42/84286/1/CAV2009-final103.pd
An integrated atom-photon junction
Photonic chips that integrate guides, switches, gratings and other
components, process vast amounts of information rapidly on a single device. A
new branch of this technology becomes possible if the light is coupled to cold
atoms in a junction of small enough cross section, so that small numbers of
photons interact appreciably with the atoms. Cold atoms are among the most
sensitive of metrological tools and their quantum nature also provides a basis
for new information processing methods. Here we demonstrate a photonic chip
which provides multiple microscopic junctions between atoms and photons. We use
the absorption of light at a junction to reveal the presence of one atom on
average. Conversely, we use the atoms to probe the intensity and polarisation
of the light. Our device paves the way for a new type of chip with
interconnected circuits of atoms and photons.Comment: 5 pages, 4 figure. Submitted to Nature Photonic
Opto-mechanical measurement of micro-trap via nonlinear cavity enhanced Raman scattering spectrum
High-gain resonant nonlinear Raman scattering on trapped cold atoms within a
high-fineness ring optical cavity is simply explained under a nonlinear
opto-mechanical mechanism, and a proposal using it to detect frequency of
micro-trap on atom chip is presented. The enhancement of scattering spectrum is
due to a coherent Raman conversion between two different cavity modes mediated
by collective vibrations of atoms through nonlinear opto-mechanical couplings.
The physical conditions of this technique are roughly estimated on Rubidium
atoms, and a simple quantum analysis as well as a multi-body semiclassical
simulation on this nonlinear Raman process is conducted.Comment: 7 pages, 2 figure
Generation of laser-induced cavitation bubbles with a digital hologram
We demonstrate a method using a spatial light modulator (SLM) to generate arbitrary 2-D spatial configurations of laser induced cavitation bubbles. The SLM acts as a phase hologram that controls the light distribution in the focal plane of a microscope objective. We generate cavitation bubbles over an area of 380x380 mu m(2) with a 20x microscope objective through absorption of the pulsed laser light in a liquid ink solution. We demonstrate the ability to accurately position up to 34 micrometer sized bubbles using laser energies of 56 mu J. (C) 2008 Optical Society of Americ