221 research outputs found
Observation of Large Atomic-Recoil Induced Asymmetries in Cold Atom Spectroscopy
The atomic recoil effect leads to large (25 %) asymmetries in simple
spectroscopic investigations of Ca atoms that have been laser-cooled to 10
microkelvin. Starting with spectra from the more familiar Doppler-broadened
domain, we show how the fundamental asymmetry between absorption and stimulated
emission of light manifests itself when shorter spectroscopic pulses lead to
the Fourier transform regime. These effects occur on frequency scales much
larger than the size of the recoil shift itself, and have not been observed
before in saturation spectroscopy. These results are relevant to
state-of-the-art optical atomic clocks based on freely expanding neutral atoms.Comment: 4 pages, 3 figure
A transportable strontium optical lattice clock
We report on a transportable optical clock, based on laser-cooled strontium
atoms trapped in an optical lattice. The experimental apparatus is composed of
a compact source of ultra-cold strontium atoms including a compact cooling
laser set-up and a transportable ultra-stable laser for interrogating the
optical clock transition. The whole setup (excluding electronics) fits within a
volume of less than 2 m. The high degree of operation reliability of both
systems allowed the spectroscopy of the clock transition to be performed with
10 Hz resolution. We estimate an uncertainty of the clock of .Comment: 12 pages, 9 figures, to be published in Appl. Phys.
A compact and efficient strontium oven for laser-cooling experiments
Here we describe a compact and efficient strontium oven well suited for
laser-cooling experiments. Novel design solutions allowed us to produce a
collimated strontium atomic beam with a flux of 1.0\times10^13 s^-1 cm^-2 at
the oven temperature of 450 {\deg}C, reached with an electrical power
consumption of 36 W. The oven is based on a stainless-steel reservoir, filled
with 6 g of metallic strontium, electrically heated in a vacuum environment by
a tantalum wire threaded through an alumina multi-bore tube. The oven can be
hosted in a standard DN40CF cube and has an estimated continuous operation
lifetime of 10 years. This oven can be used for other alkali and alkaline earth
metals with essentially no modifications.Comment: 6 pages, 6 figures, Review of Scientific Instruments, in pres
Interferometer-Type Structures for Guided Atoms
We experimentally demonstrate interferometer-type guiding structures for
neutral atoms based on dipole potentials created by micro-fabricated optical
systems. As a central element we use an array of atom waveguides being formed
by focusing a red-detuned laser beam with an array of cylindrical microlenses.
Combining two of these arrays, we realize X-shaped beam splitters and more
complex systems like the geometries for Mach-Zehnder and Michelson-type
interferometers for atoms.Comment: 4 pages, 6 figure
Multimodal imaging of mild traumatic brain injury and persistent postconcussion syndrome
Background: Persistent postconcussion syndrome (PCS) occurs in around 5– 10% of individuals after mild traumatic brain injury (mTBI), but research into the underlying biology of these ongoing symptoms is limited and inconsistent. One reason for this could be the heterogeneity inherent to mTBI, with individualized injury mechanisms and psychological factors. A multimodal imaging study may be able to characterize the injury better. Aim: To look at the relationship between functional (fMRI), structural (diffusion tensor imaging), and metabolic (magnetic resonance spectroscopy) data in the same participants in the long term (>1 year) after injury. It was hypothesized that only those mTBI participants with persistent PCS would show functional changes, and that these changes would be related to reduced structural integrity and altered metabolite concentrations. Methods: Functional changes associated with persistent PCS after mTBI (>1 year postinjury) were investigated in participants with and without PCS (both n = 8) and non-head injured participants (n = 9) during performance of working memory and attention/processing speed tasks. Correlation analyses were performed to look at the relationship between the functional data and structural and metabolic alterations in the same participants. Results: There were no behavioral differences between the groups, but participants with greater PCS symptoms exhibited greater activation in attention-related areas (anterior cingulate), along with reduced activation in temporal, default mode network, and working memory areas (left prefrontal) as cognitive load was increased from the easiest to the most difficult task. Functional changes in these areas correlated with reduced structural integrity in corpus callosum and anterior white matter, and reduced creatine concentration in right dorsolateral prefrontal cortex. Conclusion: These data suggest that the top-down attentional regulation and deactivation of task-irrelevant areas may be compensating for the reduction in working memory capacity and variation in white matter transmission caused by the structural and metabolic changes after injury. This may in turn be contributing to secondary PCS symptoms such as fatigue and headache. Further research is required using multimodal data to investigate the mechanisms of injury after mTBI, but also to aid individualized diagnosis and prognosis
Crystalline optical cavity at 4 K with thermal noise limited instability and ultralow drift
Crystalline optical cavities are the foundation of today's state-of-the-art
ultrastable lasers. Building on our previous silicon cavity effort, we now
achieve the fundamental thermal noise-limited stability for a 6 cm long silicon
cavity cooled to 4 Kelvin, reaching from 0.8 to 80 seconds.
We also report for the first time a clear linear dependence of the cavity
frequency drift on the incident optical power. The lowest fractional frequency
drift of /s is attained at a transmitted power of 40 nW, with
an extrapolated drift approaching zero in the absence of optical power. These
demonstrations provide a promising direction to reach a new performance domain
for stable lasers, with stability better than and fractional
linear drift below /s
Long range transport of ultra cold atoms in a far-detuned 1D optical lattice
We present a novel method to transport ultra cold atoms in a focused optical
lattice over macroscopic distances of many Rayleigh ranges. With this method
ultra cold atoms were transported over 5 cm in 250 ms without significant atom
loss or heating. By translating the interference pattern together with the beam
geometry the trap parameters are maintained over the full transport range.
Thus, the presented method is well suited for tightly focused optical lattices
that have sufficient trap depth only close to the focus. Tight focusing is
usually required for far-detuned optical traps or traps that require high laser
intensity for other reasons. The transport time is short and thus compatible
with the operation of an optical lattice clock in which atoms are probed in a
well designed environment spatially separated from the preparation and
detection region.Comment: 14 pages, 6 figure
An ultrastable silicon cavity in a continuously operating closed-cycle cryostat at 4 K
We report on a laser locked to a silicon cavity operating continuously at 4 K
with instability and a median linewidth of 17 mHz at 1542
nm. This is a ten-fold improvement in short-term instability, and a
improvement in linewidth, over previous sub-10 K systems. Operating at low
temperatures reduces the thermal noise floor, and thus is advantageous toward
reaching an instability of , a long-sought goal of the optical clock
community. The performance of this system demonstrates the technical readiness
for the development of the next generation of ultrastable lasers that operate
with ultranarrow linewidth and long-term stability without user intervention.Comment: 5 pages, 4 figure
Wavelength dependent ac-Stark shift of the 1S0 - 3P1 transition at 657 nm in Ca
We have measured the ac-Stark shift of the 4s2 1S0 - 4s4p 3P1 line in 40Ca
for perturbing laser wavelengths between 780 nm and 1064 nm with a time domain
Ramsey-Borde atom interferometer. We found a zero crossing of the shift for the
mS = 0 - mP = 0 transition and \sigma polarized perturbation at 800.8(22) nm.
The data was analyzed by a model deriving the energy shift from known
transition wavelengths and strengths. To fit our data, we adjusted the Einstein
A coefficients of the 4s3d 3D - 4s4p 3P and 4s5s 3S - 4s4p 3P fine structure
multiplets. With these we can predict vanishing ac-Stark shifts for the 1S0 m =
0 - 3P1 m = 1 transition and \sigma- light at 983(12) nm and at 735.5(20) nm
for the transition to the 3P0 level.Comment: 8 pages, 5 figures, 2 table
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