127 research outputs found
Radiation characteristics of corner reflector antennas.
PhDThis thesis presents a study of the radiation characteristics of corner reflector
antennas. The influence of the design parameters on the radiation characteristics are
assessed using an analytical method and the Finite Difference Time Domain (FDTD)
method.
The FDTD method for corner reflector antennas which are electrically small to
medium sized antennas is developed in detail. The important subject of the Absorbing
Boundary Conditions (ABCs) is studied including a study of Mur ABC and Perfectly
Matched Layers. It is shown that both methods reduce the reflections from the
boundaries sufficient so that the far-field radiation pattern can be computed
accurately.
An analytical solution to compute the far-field radiation pattern for infinite comer
reflector antennas is derived and used to understand the radiation mechanisms. Based
on those results, the FDTD method is used to conduct a parametric study on finite
sized comer reflector antennas. Experimental antennas have been built and measured
in order to verify the computational predictions. Very good agreement is reported
The novel idea of a variable beam-width comer reflector antenna is developed and
practical designs of such an antenna are presented. The principle is to design the
comer reflector antenna such that the beam-width of the antenna can be precisely
modified. Data on the gain and beam-width are presented. This has been done both by
computational and by an experimental model.
The influence on the performance of the comer reflector antenna when substituting
the solid reflector plates by rods has been investigated. The computational predictions
have been verified by measurements of an experimental antenna. Very good
agreement has been achieved.
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The possibility of modifying the shape of the comer reflector antenna is investigated.
It is shown that a modified comer reflector antenna with less depth produces the same
far-field pattern as a standard corner reflector antenna. It is also shown that the
performance of small aperture size corner reflector antennas is superior to a
cylindrical parabolic reflector antenna
Collisional losses, decoherence, and frequency shifts in optical lattice clocks with bosons
We have quantified collisional losses, decoherence and the collision shift in
a one-dimensional optical lattice clock with bosonic 88Sr. The lattice clock is
referenced to the highly forbidden transition 1S0 - 3P0 at 698 nm, which
becomes weakly allowed due to state mixing in a homogeneous magnetic field. We
were able to quantify three decoherence coefficients, which are due to
dephasing collisions, inelastic collisions between atoms in the upper and lower
clock state, and atoms in the upper clock state only. Based on the measured
coefficients, we determine the operation parameters at which a 1D-lattice clock
with 88Sr shows no degradation due to collisions on the relative accuracy level
of 10-16.Comment: 4 pages, 3 figure
Observation of Large Atomic-Recoil Induced Asymmetries in Cold Atom Spectroscopy
The atomic recoil effect leads to large (25 %) asymmetries in simple
spectroscopic investigations of Ca atoms that have been laser-cooled to 10
microkelvin. Starting with spectra from the more familiar Doppler-broadened
domain, we show how the fundamental asymmetry between absorption and stimulated
emission of light manifests itself when shorter spectroscopic pulses lead to
the Fourier transform regime. These effects occur on frequency scales much
larger than the size of the recoil shift itself, and have not been observed
before in saturation spectroscopy. These results are relevant to
state-of-the-art optical atomic clocks based on freely expanding neutral atoms.Comment: 4 pages, 3 figure
A transportable strontium optical lattice clock
We report on a transportable optical clock, based on laser-cooled strontium
atoms trapped in an optical lattice. The experimental apparatus is composed of
a compact source of ultra-cold strontium atoms including a compact cooling
laser set-up and a transportable ultra-stable laser for interrogating the
optical clock transition. The whole setup (excluding electronics) fits within a
volume of less than 2 m. The high degree of operation reliability of both
systems allowed the spectroscopy of the clock transition to be performed with
10 Hz resolution. We estimate an uncertainty of the clock of .Comment: 12 pages, 9 figures, to be published in Appl. Phys.
A compact and efficient strontium oven for laser-cooling experiments
Here we describe a compact and efficient strontium oven well suited for
laser-cooling experiments. Novel design solutions allowed us to produce a
collimated strontium atomic beam with a flux of 1.0\times10^13 s^-1 cm^-2 at
the oven temperature of 450 {\deg}C, reached with an electrical power
consumption of 36 W. The oven is based on a stainless-steel reservoir, filled
with 6 g of metallic strontium, electrically heated in a vacuum environment by
a tantalum wire threaded through an alumina multi-bore tube. The oven can be
hosted in a standard DN40CF cube and has an estimated continuous operation
lifetime of 10 years. This oven can be used for other alkali and alkaline earth
metals with essentially no modifications.Comment: 6 pages, 6 figures, Review of Scientific Instruments, in pres
Interferometer-Type Structures for Guided Atoms
We experimentally demonstrate interferometer-type guiding structures for
neutral atoms based on dipole potentials created by micro-fabricated optical
systems. As a central element we use an array of atom waveguides being formed
by focusing a red-detuned laser beam with an array of cylindrical microlenses.
Combining two of these arrays, we realize X-shaped beam splitters and more
complex systems like the geometries for Mach-Zehnder and Michelson-type
interferometers for atoms.Comment: 4 pages, 6 figure
Measurement of the ac Stark shift with a guided matter-wave interferometer
We demonstrate the effectiveness of a guided-wave Bose-Einstein condensate
interferometer for practical measurements. Taking advantage of the large arm
separations obtainable in our interferometer, the energy levels of the 87Rb
atoms in one arm of the interferometer are shifted by a calibrated laser beam.
The resulting phase shifts are used to determine the ac polarizability at a
range of frequencies near and at the atomic resonance. The measured values are
in good agreement with theoretical expectations. However, we observe a
broadening of the transition near the resonance, an indication of collective
light scattering effects. This nonlinearity may prove useful for the production
and control of squeezed quantum states.Comment: 5 pages, three figure
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