1,016 research outputs found
Saturation and alternate pathways in four-wave mixing in rubidium
We have examined the frequency spectrum of the blue light generated via
four-wave mixing in a rubidium vapor cell inside a ring cavity. At high atomic
density and input laser power, two distinct frequency components separated by
MHz are observed, indicating alternate four-wave mixing channels
through the hyperfine states. The dependence of the generated light
on excitation intensity and atomic density are explored, and indicate the
primary process has saturated. This saturation results when the excitation rate
through the 6p state becomes equal to the rate through the 5p state, giving no
further gain with atomic density while a quadratic intensity dependence
remains
A low-cost confocal microscope for the undergraduate lab
We demonstrate a simple and cost-efficient scanning confocal microscope setup
for use in advanced instructional physics laboratories. The setup is
constructed from readily available commercial products, and the implementation
of a 3D-printed flexure stage allows for further cost reduction and pedagogical
opportunity. Experiments exploring the thickness of a microscope slide and the
surface of solid objects with height variation are presented as foundational
components of undergraduate laboratory projects, and demonstrate the
capabilities of a confocal microscope. This system allows observation of key
components of a confocal microscope, including depth perception and data
acquisition via transverse scanning, making it an excellent pedagogical
resource
High Density Mesoscopic Atom Clouds in a Holographic Atom Trap
We demonstrate the production of micron-sized high density atom clouds of
interest for meso- scopic quantum information processing. We evaporate atoms
from 60 microK, 3x10^14 atoms/cm^3 samples contained in a highly anisotropic
optical lattice formed by interfering di racted beams from a holographic phase
plate. After evaporating to 1 microK by lowering the con ning potential, in
less than a second the atom density reduces to 8x10^13 cm^- 3 at a phase space
density approaching unity. Adiabatic recompression of the atoms then increases
the density to levels in excess of 1x10^15 cm^-3. The resulting clouds are
typically 8 microns in the longest dimension. Such samples are small enough to
enable mesoscopic quantum manipulation using Rydberg blockade and have the high
densities required to investigate new collision phenomena.Comment: 4 pages, 4 figures, submitted to PR
Thermal Performance Testing of Cryogenic Insulation Systems
Efficient methods for characterizing thermal performance of materials under cryogenic and vacuum conditions have been developed. These methods provide thermal conductivity data on materials under actual-use conditions and are complementary to established methods. The actual-use environment of full temperature difference in combination with vacuum-pressure is essential for understanding insulation system performance. Test articles include solids, foams, powders, layered blankets, composite panels, and other materials. Test methodology and apparatus design for several insulation test cryostats are discussed. The measurement principle is liquid nitrogen boil-off calorimetry. Heat flux capability ranges from approximately 0.5 to 500 watts per square meter; corresponding apparent thermal conductivity values range from below 0.01 up to about 60 mW/m- K. Example data for different insulation materials are also presented. Upon further standardization work, these patented insulation test cryostats can be available to industry for a wide range of practical applications
Slow magnetoacoustic waves in coronal loops : EIT and TRACE
On May 13, 1998 the EIT (Extreme ultraviolet Imaging Telescope) on board of SoHO (Solar and Heliospheric Observatory) and TRACE (Transition Region And Coronal Explorer) instruments produced simultaneous high cadence image sequences of the same active region (AR 8218). TRACE achieved a 25 s cadence in the FeIX (171 Å) bandpass while EIT achieved a 15 s cadence (operating in "shutterless mode", SoHO JOP 80) in the FeXII (195 Å) bandpass. These high cadence observations in two complementary wavelengths have revealed the existence of weak transient disturbances in an extended coronal loop system. These propagating disturbances (PDs) seem to be a common phenomenon in this part of the active region. The disturbances originate from small scale brightenings at the footpoints of the loops and propagate along the loops. The projected propagation speeds roughly vary between 65 and 150 km s-1 for both instruments which is close to and below the expected sound speed in the coronal loops. The measured slow magnetoacoustic propagation speeds seem to suggest that the transients are sound (or slow) wave disturbances. This work differs from previous studies in the sense that it is based on a multi-wavelength observation of an entire loop bundle at high cadence by two EUV imagers. The observation of sound waves along the same path shows that they propagate along the same loop, suggesting that loops contain sharp temperature gradients and consist of either concentric shells or thin loop threads, at different temperatures
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