2,394 research outputs found
Large Area Crop Inventory Experiment (LACIE). USSR spring and winter wheat models, addendum
There are no author-identified significant results in this report
Characterization of submillimetre quasi-optical twin-slot double-junction SIS mixers
We report on the continuing development of submillimetre quasi-optical slot antenna SIS mixers, which use two-junction tuning circuits. Direct and heterodyne Fourier transform spectrometer measurements have been performed to compare device performance with predictions. Demonstrated double-sideband receiver noise temperatures of better than 540 K at 808 GHz make these SIS mixers substantially better than GaAs Schottky receivers for the astronomically important CI and CO transitions near 810 GHz
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
Frequency shifts of photoassociative spectra of ultracold metastable Helium atoms : a new measurement of the s-wave scattering length
We observe light-induced frequency shifts in one-color photoassociative
spectra of magnetically trapped He atoms in the metastable
state. A pair of ultracold spin-polarized helium atoms is excited into
a molecular bound state in the purely long range potential connected to
the asymptote. The shift arises from the optical coupling of
the molecular excited bound state with the scattering states and the bound
states of two colliding atoms. We measure the frequency-shifts for
several ro-vibrational levels in the potential and find a linear
dependence on the photoassociation laser intensity. Comparison with a
theoretical analysis provides a good indication for the s-wave scattering
length of the quintet () potential, nm, which
is significantly lower than most previous results obtained by non-spectroscopic
methods.Comment: 7 pages, 4 figure
Low-noise slot antenna SIS mixers
We describe quasi-optical SIS mixers operating in the submillimeter band (500-750 GHz) which have very low noise, around 5 h/spl nu//k/sub B/ for the double-sideband receiver noise temperature. The mixers use a twin-slot antenna, Nb/Al-Oxide/Nb tunnel junctions fabricated with optical lithography, a two-junction tuning circuit, and a silicon hyperhemispherical lens with a novel antireflection coating to optimize the optical efficiency. We have flown a submillimeter receiver using these mixers on the Kuiper Airborne Observatory, and have detected a transition of H/sub 2//sup 18/O at 745 GHz. This directly confirms that SIS junctions are capable of low-noise mixing above the gap frequency
Getting the elastic scattering length by observing inelastic collisions in ultracold metastable helium atoms
We report an experiment measuring simultaneously the temperatureand the flux
of ions produced by a cloud of triplet metastablehelium atoms at the
Bose-Einstein critical temperature. The onsetof condensation is revealed by a
sharp increase of the ion fluxduring evaporative cooling. Combining our
measurements withprevious measurements of ionization in a pure BEC,we extract
an improved value of the scattering length nm. The analysis
includes corrections takinginto accountthe effect of atomic interactions on the
criticaltemperature, and thus an independent measurement of the
scatteringlength would allow a new test of these calculations
Development of Lumped Element Kinetic Inductance Detectors for NIKA
Lumped-element kinetic inductance detectors(LEKIDs) have recently shown
considerable promise as direct absorption mm-wavelength detectors for
astronomical applications. One major research thrust within the N\'eel Iram
Kids Array (NIKA) collaboration has been to investigate the suitability of
these detectors for deployment at the 30-meter IRAM telescope located on Pico
Veleta in Spain. Compared to microwave kinetic inductance detectors (MKID),
using quarter wavelength resonators, the resonant circuit of a LEKID consists
of a discrete inductance and capacitance coupled to a feedline. A high and
constant current density distribution in the inductive part of these resonators
makes them very sensitive. Due to only one metal layer on a silicon substrate,
the fabrication is relatively easy. In order to optimize the LEKIDs for this
application, we have recently probed a wide variety of individual resonator and
array parameters through simulation and physical testing. This included
determining the optimal feed-line coupling, pixel geometry, resonator
distribution within an array (in order to minimize pixel cross-talk), and
resonator frequency spacing. Based on these results, a 144-pixel Aluminum array
was fabricated and tested in a dilution fridge with optical access, yielding an
average optical NEP of ~2E-16 W/Hz^1/2 (best pixels showed NEP = 6E-17 W/Hz^1/2
under 4-8 pW loading per pixel). In October 2010 the second prototype of LEKIDs
has been tested at the IRAM 30 m telescope. A new LEKID geometry for 2
polarizations will be presented. Also first optical measurements of a titanium
nitride array will be discussed.Comment: 5 pages, 12 figures; ISSTT 2011 Worksho
Development of Aluminum LEKIDs for Balloon-Borne Far-IR Spectroscopy
We are developing lumped-element kinetic inductance detectors (LEKIDs)
designed to achieve background-limited sensitivity for far-infrared (FIR)
spectroscopy on a stratospheric balloon. The Spectroscopic Terahertz Airborne
Receiver for Far-InfraRed Exploration (STARFIRE) will study the evolution of
dusty galaxies with observations of the [CII] 158 m and other atomic
fine-structure transitions at , both through direct observations of
individual luminous infrared galaxies, and in blind surveys using the technique
of line intensity mapping. The spectrometer will require large format
(1800 detectors) arrays of dual-polarization sensitive detectors with
NEPs of W Hz. The low-volume LEKIDs are fabricated
with a single layer of aluminum (20 nm thick) deposited on a crystalline
silicon wafer, with resonance frequencies of MHz. The inductor is a
single meander with a linewidth of 0.4 m, patterned in a grid to absorb
optical power in both polarizations. The meander is coupled to a circular
waveguide, fed by a conical feedhorn. Initial testing of a small array
prototype has demonstrated good yield, and a median NEP of
W Hz.Comment: accepted for publication in Journal of Low Temperature Physic
Giant Helium Dimers Produced by Photoassociation of Ultracold Metastable Atoms
We produce giant helium dimers by photoassociation of metastable helium atoms
in a magnetically trapped, ultracold cloud. The photoassociation laser is
detuned red of the atomic line and produces strong heating
of the sample when resonant with molecular bound states. The temperature of the
cloud serves as an indicator of the molecular spectrum. We report good
agreement between our spectroscopic measurements and our calculations of the
five bound states belonging to a purely long-range potential well.
These previously unobserved states have classical inner turning points of about
150 and outer turning points as large as 1150 .Comment: 4 pages, 4 figure
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