20,492 research outputs found
A Large Atom Number Metastable Helium Bose-Einstein Condensate
We have produced a Bose-Einstein condensate of metastable helium (4He*)
containing over 1.5x10^7 atoms, which is a factor of 25 higher than previously
achieved. The improved starting conditions for evaporative cooling are obtained
by applying one-dimensional Doppler cooling inside a magnetic trap. The same
technique is successfully used to cool the spin-polarized fermionic isotope
(3He*), for which thermalizing collisions are highly suppressed. Our detection
techniques include absorption imaging, time-of-flight measurements on a
microchannel plate detector and ion counting to monitor the formation and decay
of the condensate.Comment: 4 pages, 3 figures (changed content
Multibeam single frequency synthetic aperture radar processor for imaging separate range swaths
A single-frequency multibeam synthetic aperture radar for large swath imaging is disclosed. Each beam illuminates a separate ""footprint'' (i.e., range and azimuth interval). The distinct azimuth intervals for the separate beams produce a distinct Doppler frequency spectrum for each beam. After range correlation of raw data, an optical processor develops image data for the different beams by spatially separating the beams to place each beam of different Doppler frequency spectrum in a different location in the frequency plane as well as the imaging plane of the optical processor. Selection of a beam for imaging may be made in the frequency plane by adjusting the position of an aperture, or in the image plane by adjusting the position of a slit. The raw data may also be processed in digital form in an analogous manner
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Time-of-flight resolved light field fluctuations reveal deep human tissue physiology.
Red blood cells (RBCs) transport oxygen to tissues and remove carbon dioxide. Diffuse optical flowmetry (DOF) assesses deep tissue RBC dynamics by measuring coherent fluctuations of multiply scattered near-infrared light intensity. While classical DOF measurements empirically correlate with blood flow, they remain far-removed from light scattering physics and difficult to interpret in layered media. To advance DOF measurements closer to the physics, here we introduce an interferometric technique, surmounting challenges of bulk motion to apply it in awake humans. We reveal two measurement dimensions: optical phase, and time-of-flight (TOF), the latter with 22 picosecond resolution. With this multidimensional data, we directly confirm the unordered, or Brownian, nature of optically probed RBC dynamics typically assumed in classical DOF. We illustrate how incorrect absorption assumptions, anisotropic RBC scattering, and layered tissues may confound classical DOF. By comparison, our direct method enables accurate and comprehensive assessment of blood flow dynamics in humans
Cardiovascular instrumentation for spaceflight
The observation mechanisms dealing with pressure, flow, morphology, temperature, etc. are discussed. The approach taken in the performance of this study was to (1) review ground and space-flight data on cardiovascular function, including earlier related ground-based and space-flight animal studies, Mercury, Gemini, Apollo, Skylab, and recent bed-rest studies, (2) review cardiovascular measurement parameters required to assess individual performance and physiological alternations during space flight, (3) perform an instrumentation survey including a literature search as well as personal contact with the applicable investigators, (4) assess instrumentation applicability with respect to the established criteria, and (5) recommend future research and development activity. It is concluded that, for the most part, the required instrumentation technology is available but that mission-peculiar criteria will require modifications to adapt the applicable instrumentation to a space-flight configuration
An ytterbium quantum gas microscope with narrow-line laser cooling
We demonstrate site-resolved imaging of individual bosonic
atoms in a Hubbard-regime two-dimensional optical lattice
with a short lattice constant of 266 nm. To suppress the heating by probe light
with the - transition of the wavelength = 399 nm for
high-resolution imaging and preserve atoms at the same lattice sites during the
fluorescence imaging, we simultaneously cool atoms by additionally applying
narrow-line optical molasses with the - transition of the
wavelength = 556 nm. We achieve a low temperature of $T = 7.4(1.3)\
\mu\mathrm{K}$, corresponding to a mean oscillation quantum number along the
horizontal axes of 0.22(4) during imaging process. We detect on average 200
fluorescence photons from a single atom within 400 ms exposure time, and
estimate the detection fidelity of 87(2)%. The realization of a quantum gas
microscope with enough fidelity for Yb atoms in a Hubbard-regime optical
lattice opens up the possibilities for studying various kinds of quantum
many-body systems such as Bose and Fermi gases, and their mixtures, and also
long-range-interacting systems such as Rydberg states.Comment: 14 pages, 6 figure
In-Suit Doppler Technology Assessment
The objective of this program was to perform a technology assessment survey of non-invasive air embolism detection utilizing Doppler ultrasound methodologies. The primary application of this technology will be a continuous monitor for astronauts while performing extravehicular activities (EVA's). The technology assessment was to include: (1) development of a full understanding of all relevant background research; and (2) a survey of the medical ultrasound marketplace for expertise, information, and technical capability relevant to this development. Upon completion of the assessment, LSR was to provide an overview of technological approaches and R&D/manufacturing organizations
Single-particle-sensitive imaging of freely propagating ultracold atoms
We present a novel imaging system for ultracold quantum gases in expansion.
After release from a confining potential, atoms fall through a sheet of
resonant excitation laser light and the emitted fluorescence photons are imaged
onto an amplified CCD camera using a high numerical aperture optical system.
The imaging system reaches an extraordinary dynamic range, not attainable with
conventional absorption imaging. We demonstrate single-atom detection for
dilute atomic clouds with high efficiency where at the same time dense
Bose-Einstein condensates can be imaged without saturation or distortion. The
spatial resolution can reach the sampling limit as given by the 8 \mu m pixel
size in object space. Pulsed operation of the detector allows for slice images,
a first step toward a 3D tomography of the measured object. The scheme can
easily be implemented for any atomic species and all optical components are
situated outside the vacuum system. As a first application we perform
thermometry on rubidium Bose-Einstein condensates created on an atom chip.Comment: 24 pages, 10 figures. v2: as publishe
Optics and lasers: A compilation
A number of innovative devices and techniques in optics and related fields were presented. The following areas were covered: advances in laser and holography technology, articles on spectroscopy and general optics, new information in the area of photography
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