97 research outputs found
Deployable Optics for CubeSats
Since the beginning of the space age, many structures with different levels of complexity have been proposed for the deployment of equipment such as solar arrays, antennae, and scientific instruments. By increasing the packaging efficiency, stowing during launch and then deploying in orbit provides an opportunity for the improvement of the capabilities of small satellites payloads while maintaining a contained launch volume. The latter is particularly important when considering the launch of future constellations and, in particular, CubeSats where the volume is significantly constrained by the size of the pod. The focus of this work is the development of a camera/telescope barrel ideally suited for a Cassegrain configured space instrument, hosting the primary mirror at one (satellite side) end and the secondary mirror supported by a cruciform element at the other end (aperture). The barrel is stowed and deployed using a telescopic approach with three coaxial large diameter hollow cylinders making up the segments of the barrel. For an optical telescope, one of the most important challenges is in maintaining a highly accurate distance between the optical elements (in this case, primary and secondary mirrors which are positioned with an accuracy of a few micron). Thermo-mechanical distortions due to on orbit temperature variations and any micro-vibration excitation from sources on the spacecraft can cause significant degradation of the optical performance. To maintain the required shape stability, the main structural parts are made in a thermally invariable material and incorporate features to provide alignment and locking out. The large diameter of the structure, and low coefficient of thermal expansion, give the assembly excellent resilience to thermal and micro-vibration disturbances whilst keeping mass to a minimum. This “tube” arrangement also naturally fulfils the light baffling requirements of the telescope. Another significant challenge is the apparatus to drive the sequential deployment of the cylinders. Systems that use lead screws and gears have been proposed, however they present significant complexities and their mass has a substantial impact on the mass budget of the overall assembly. Here, a novel robust and simple wire-driven system is proposed to operate the deployment. The main advantages being the simplicity, light weight, and robustness with respect to severe vibration environments. This article will describe the development of the device and the testing of the proof of concept/qualification model
Broad Feshbach resonance in the 6Li-40K mixture
We study the widths of interspecies Feshbach resonances in a mixture of the
fermionic quantum gases 6Li and 40K. We develop a model to calculate the width
and position of all available Feshbach resonances for a system. Using the model
we select the optimal resonance to study the 6Li/40K mixture. Experimentally,
we obtain the asymmetric Fano lineshape of the interspecies elastic cross
section by measuring the distillation rate of 6Li atoms from a potassium-rich
6Li/40K mixture as a function of magnetic field. This provides us with the
first experimental determination of the width of a resonance in this mixture,
Delta B=1.5(5) G. Our results offer good perspectives for the observation of
universal crossover physics using this mass-imbalanced fermionic mixture.Comment: 4 pages, 2 figure
Photoassociative Production and Trapping of Ultracold KRb Molecules
We have produced ultracold heteronuclear KRb molecules by the process of
photoassociation in a two-species magneto-optical trap. Following decay of the
photoassociated KRb*, the molecules are detected using two-photon ionization
and time-of-flight mass spectroscopy of KRb. A portion of the metastable
triplet molecules thus formed are magnetically trapped. Photoassociative
spectra down to 91 cm below the K(4) + Rb (5) asymptote have
been obtained. We have made assignments to all eight of the attractive Hund's
case (c) KRb* potential curves in this spectral region.Comment: 4 pages, 4 figure
A high-flux 2D MOT source for cold lithium atoms
We demonstrate a novel 2D MOT beam source for cold 6Li atoms. The source is
side-loaded from an oven operated at temperatures in the range 600<T<700 K. The
performance is analyzed by loading the atoms into a 3D MOT located 220 mm
downstream from the source. The maximum recapture rate of ~10^9 /s is obtained
for T=700 K and results in a total of up to 10^10 trapped atoms. The recaptured
fraction is estimated to be 30(10)% and limited by beam divergence. The
most-probable velocity in the beam (alpha_z) is varied from 18 to 70 m/s by
increasing the intensity of a push beam. The source is quite monochromatic with
a full-width at half maximum velocity spread of 11 m/s at alpha_z=36 m/s,
demonstrating that side-loading completely eliminates beam contamination by hot
vapor from the oven. We identify depletion of the low-velocity tail of the oven
flux as the limiting loss mechanism. Our approach is suitable for other atomic
species.Comment: 13 pages,9 figures, submitted to Phys.Rev.
Transition from Collisionless to Hydrodynamic Behaviour in an Ultracold Atomic Gas
Relative motion in a two-component, trapped atomic gas provides a sensitive
probe of interactions. By studying the lowest frequency excitations of a two
spin-state gas confined in a magnetic trap, we have explored the transition
from the collisionless to the hydrodynamic regime. As a function of collision
rate, we observe frequency shifts as large as 6% as well as a dramatic,
non-monotonic dependence of the damping rate. The measurements agree
qualitatively with expectations for behavior in the collisionless and
hydrodynamic limits and are quantitatively compared to a classical kinetic
model.Comment: 5 pages, 4 figure
Spin Excitations in a Fermi Gas of Atoms
We have experimentally investigated a spin excitation in a quantum degenerate
Fermi gas of atoms. In the hydrodynamic regime the damping time of the
collective excitation is used to probe the quantum behavior of the gas. At
temperatures below the Fermi temperature we measure up to a factor of 2
reduction in the excitation damping time. In addition we observe a strong
excitation energy dependence for this quantum statistical effect.Comment: 4 pages, 3 figure
Resonant control of elastic collisions in an optically trapped Fermi gas of atoms
We have loaded an ultracold gas of fermionic atoms into a far off resonance
optical dipole trap and precisely controlled the spin composition of the
trapped gas. We have measured a magnetic-field Feshbach resonance between atoms
in the two lowest energy spin-states, |9/2, -9/2> and |9/2, -7/2>. The
resonance peaks at a magnetic field of 201.5 plus or minus 1.4 G and has a
width of 8.0 plus or minus 1.1 G. Using this resonance we have changed the
elastic collision cross section in the gas by nearly 3 orders of magnitude.Comment: 4 pages, 3 figure
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