622 research outputs found
Imaging trapped quantum gases by off-axis holography
We present a dispersive imaging method for trapped quantum gases based on
digital off-axis holography. Both phase delay and intensity of the probe field
are determined from the same image. Due to the heterodyne gain inherent to the
holographic method it is possible to retrieve the phase delay induced by the
atoms at probe beam doses two orders of magnitude lower than phase-contrast
imaging methods. Using the full field of the probe beam we numerically correct
for image defocusing.Comment: 4 pages, 5 figure
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
Optical collisions of cold, metastable helium atoms
We have studied the optical collisions of cold, metastable
helium atoms in a magneto-optical trap. We have detected
the rate of Penning and associative ionization of two
metastable helium atoms at a temperature of 1 mK with and
without nearly resonant light. We find that the associative
ionization rate is increased with more than a factor 20 due to
the presence of the light field. The absolute ionization rate
near resonance of (1.9±0.8)×10^(-9) cm3/s for the optical collision
differs two orders of magnitude with the rate reported
by Bardou et al. (Europhys. Lett. 20, 681 (1992)). Our experimental
findings are in good agreement with theory. We
present a simple, semi-classical model, which accounts for all
the observed features
Atom lithography without laser cooling
Using direct-write atom lithography, Fe nanolines are deposited with a pitch
of 186 nm, a full width at half maximum (FWHM) of 50 nm, and a height of up to
6 nm. These values are achieved by relying on geometrical collimation of the
atomic beam, thus without using laser collimation techniques. This opens the
way for applying direct-write atom lithography to a wide variety of elements.Comment: 7 pages, 11 figure
Cost-effectiveness of Guided Internet-Delivered Cognitive Behavioral Therapy in Comparison with Care-as-Usual for Patients with Insomnia in General Practice
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