2,394 research outputs found

    Large Area Crop Inventory Experiment (LACIE). USSR spring and winter wheat models, addendum

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    There are no author-identified significant results in this report

    Characterization of submillimetre quasi-optical twin-slot double-junction SIS mixers

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    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

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    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 23S1↔23P02^3S_1\leftrightarrow 2^3P_0 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 0u+0_u^+ purely long-range potential well is very good. The results yield a determination of the lifetime of the 23P2^3P atomic state

    Frequency shifts of photoassociative spectra of ultracold metastable Helium atoms : a new measurement of the s-wave scattering length

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    We observe light-induced frequency shifts in one-color photoassociative spectra of magnetically trapped 4^4He∗^* atoms in the metastable 23S12^3S_1 state. A pair of ultracold spin-polarized 23S12^3S_1 helium atoms is excited into a molecular bound state in the purely long range 0u+0_u^+ potential connected to the 23S1−23P02^3S_1 - 2^3P_0 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 23S12^3S_1 atoms. We measure the frequency-shifts for several ro-vibrational levels in the 0u+0^+_u 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 aa of the quintet (5ÎŁg+^5\Sigma_g^+) potential, a=7.2±0.6a=7.2\pm 0.6 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

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    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

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    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 lengtha=11.3−1+2a=11.3^{+2}_{-1} 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

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    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

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    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 ÎŒ\mum and other atomic fine-structure transitions at z=0.5−1.5z=0.5-1.5, 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 (∌\sim1800 detectors) arrays of dual-polarization sensitive detectors with NEPs of 1×10−171 \times 10^{-17} W Hz−1/2^{-1/2}. 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 100−250100-250 MHz. The inductor is a single meander with a linewidth of 0.4 ÎŒ\mum, 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 4×10−184 \times 10^{-18} W Hz−1/2^{-1/2}.Comment: accepted for publication in Journal of Low Temperature Physic

    Giant Helium Dimers Produced by Photoassociation of Ultracold Metastable Atoms

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    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 23S1−23P02^3S_1 - 2^3P_0 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 0u+0_u^+ purely long-range potential well. These previously unobserved states have classical inner turning points of about 150 a0a_0 and outer turning points as large as 1150 a0a_0.Comment: 4 pages, 4 figure
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