We report observation of Bose-Einstein condensation of a trapped, dilute gas
of atomic hydrogen. The condensate and normal gas are studied by two-photon
spectroscopy of the 1S-2S transition. Interactions among the atoms produce a
shift of the resonance frequency proportional to density. The condensate is
clearly distinguished by its large frequency shift. The peak condensate density
is 4.8 +/- 1.1 \times 10^{15} cm^{-3}, corresponding to a condensate population
of 10^9 atoms. The BEC transition occurs at about T=50 uK and n=1.8 \times
10^{14} cm^{-3}.Comment: Accepted for publication in PRL; 9 pages, 4 PostScript figures,
ReVTeX. Updated discussion of degeneracy effect
We have observed the cold collision frequency shift of the 1S-2S transition in trapped spin-polarized atomic hydrogen. We find ∆ν 1S−2S = −3.8 ± 0.8 × 10 −10 n Hz cm 3 , where n is the sample density. From this we derive the 1S-2S s-wave triplet scattering length, a 1S−2S = −1.4 ± 0.3 nm, which is in fair agreement with a recent calculation. The shift provides a valuable probe of the distribution of densities in a trapped sample.
Abstract. Three lidar receiver technologies using the total laser energy required to perform a set of imaging tasks are compared. The tasks are combinations of two collection types (3-D mapping from near and far), two scene types (foliated and unobscured), and three types of data products (geometry only, geometry plus 3-bit intensity, and geometry plus 6-bit intensity). The receiver technologies are based on Geiger mode avalanche photodiodes (GMAPD), linear mode avalanche photodiodes (LMAPD), and optical time-of-flight lidar, which combine rapid polarization rotation of the image and dual low-bandwidth cameras to generate a 3-D image. We choose scenarios to highlight the strengths and weaknesses of various lidars. We consider HgCdTe and InGaAs variations of LMAPD cameras. The InGaAs GMAPD and the HgCdTe LMAPD cameras required the least energy to 3-D map both scenarios for bare earth, with the GMAPD taking slightly less energy. We comment on the strengths and weaknesses of each receiver technology. Six bits of intensity gray levels requires substantial energy using all camera modalities.
In response to the 2010 Haiti earthquake, the ALIRT ladar system was tasked with collecting surveys to support disaster relief efforts. Standard methodologies to classify the ladar data as ground, vegetation, or man-made features failed to produce an accurate representation of the underlying terrain surface. The majority of these methods rely primarily on gradient-based operations that often perform well for areas with low topographic relief, but often fail in areas of high topographic relief or dense urban environments. An alternative approach based on a adaptive lower envelope follower (ALEF) with an adaptive gradient operation for accommodating local slope and roughness was investigated for recovering the ground surface from the ladar data. This technique was successful for classifying terrain in the urban and rural areas of Haiti over which the ALIRT data had been acquired.
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