1,754 research outputs found
Subtraction of test mass angular noise in the LISA Technology Package interferometer
We present recent sensitivity measurements of the LISA Technology Package
interferometer with articulated mirrors as test masses, actuated by
piezo-electric transducers. The required longitudinal displacement resolution
of 9 pm/sqrt[Hz] above 3 mHz has been demonstrated with an angular noise that
corresponds to the expected in on-orbit operation. The excess noise
contribution of this test mass jitter onto the sensitive displacement readout
was completely subtracted by fitting the angular interferometric data streams
to the longitudinal displacement measurement. Thus, this cross-coupling
constitutes no limitation to the required performance of the LISA Technology
Package interferometry.Comment: Applied Physics B - Lasers and Optics (2008
The end-to-end testbed of the Optical Metrology System on-board LISA Pathfinder
LISA Pathfinder is a technology demonstration mission for the Laser
Interferometer Space Antenna (LISA). The main experiment on-board LISA
Pathfinder is the so-called LISA Technology Package (LTP) which has the aim to
measure the differential acceleration between two free-falling test masses with
an accuracy of 3x10^(-14) ms^(-2)/sqrt[Hz] between 1 mHz and 30 mHz. This
measurement is performed interferometrically by the Optical Metrology System
(OMS) on-board LISA Pathfinder. In this paper we present the development of an
experimental end-to-end testbed of the entire OMS. It includes the
interferometer and its sub-units, the interferometer back-end which is a
phasemeter and the processing of the phasemeter output data. Furthermore,
3-axes piezo actuated mirrors are used instead of the free-falling test masses
for the characterisation of the dynamic behaviour of the system and some parts
of the Drag-free and Attitude Control System (DFACS) which controls the test
masses and the satellite. The end-to-end testbed includes all parts of the LTP
that can reasonably be tested on earth without free-falling test masses. At its
present status it consists mainly of breadboard components. Some of those have
already been replaced by Engineering Models of the LTP experiment. In the next
steps, further Engineering Models and Flight Models will also be inserted in
this testbed and tested against well characterised breadboard components. The
presented testbed is an important reference for the unit tests and can also be
used for validation of the on-board experiment during the mission
In-plane gate single-electron transistor in Ga[Al]As fabricated by scanning probe lithography
A single-electron transistor has been realized in a Ga[Al]As heterostructure
by oxidizing lines in the GaAs cap layer with an atomic force microscope. The
oxide lines define the boundaries of the quantum dot, the in-plane gate
electrodes, and the contacts of the dot to source and drain. Both the number of
electrons in the dot as well as its coupling to the leads can be tuned with an
additional, homogeneous top gate electrode. Pronounced Coulomb blockade
oscillations are observed as a function of voltages applied to different gates.
We find that, for positive top-gate voltages, the lithographic pattern is
transferred with high accuracy to the electron gas. Furthermore, the dot shape
does not change significantly when in-plane voltages are tuned.Comment: 4 pages, 3 figure
Transport properties of quantum dots with hard walls
Quantum dots are fabricated in a Ga[Al]As-heterostructure by local oxidation
with an atomic force microscope. This technique, in combination with top gate
voltages, allows us to generate steep walls at the confining edges and small
lateral depletion lengths. The confinement is characterized by low-temperature
magnetotransport measurements, from which the dots' energy spectrum is
reconstructed. We find that in small dots, the addition spectrum can
qualitatively be described within a Fock-Darwin model. For a quantitative
analysis, however, a hard-wall confinement has to be considered. In large dots,
the energy level spectrum deviates even qualitatively from a Fock-Darwin model.
The maximum wall steepness achieved is of the order of 0.4 meV/nm.Comment: 9 pages, 5 figure
Three-port beam splitters-combiners for interferometer applications
We derive generic phase and amplitude coupling relations for beam
splitters-combiners that couple a single port with three output ports or input
ports, respectively. We apply the coupling relations to a reflection grating
that serves as a coupler to a single-ended Fabry-Perot ring cavity. In the
impedance-matched case such an interferometer can act as an all-reflective ring
mode cleaner. It is further shown that in the highly undercoupled case almost
complete separation of carrier power and phase signal from a cavity strain can
be achieved
Transport properties of quantum dots with hard walls
Quantum dots are fabricated in a Ga[Al]As-heterostructure by local oxidation
with an atomic force microscope. This technique, in combination with top gate
voltages, allows us to generate steep walls at the confining edges and small
lateral depletion lengths. The confinement is characterized by low-temperature
magnetotransport measurements, from which the dots' energy spectrum is
reconstructed. We find that in small dots, the addition spectrum can
qualitatively be described within a Fock-Darwin model. For a quantitative
analysis, however, a hard-wall confinement has to be considered. In large dots,
the energy level spectrum deviates even qualitatively from a Fock-Darwin model.
The maximum wall steepness achieved is of the order of 0.4 meV/nm.Comment: 9 pages, 5 figure
Spin States in Graphene Quantum Dots
We investigate ground and excited state transport through small (d = 70 nm)
graphene quantum dots. The successive spin filling of orbital states is
detected by measuring the ground state energy as a function of a magnetic
field. For a magnetic field in-plane of the quantum dot the Zemann splitting of
spin states is measured. The results are compatible with a g-factor of 2 and we
detect a spin-filling sequence for a series of states which is reasonable given
the strength of exchange interaction effects expected for graphene
Frequency domain interferometer simulation with higher-order spatial modes
FINESSE is a software simulation that allows to compute the optical
properties of laser interferometers as they are used by the interferometric
gravitational-wave detectors today. It provides a fast and versatile tool which
has proven to be very useful during the design and the commissioning of
gravitational-wave detectors. The basic algorithm of FINESSE numerically
computes the light amplitudes inside an interferometer using Hermite-Gauss
modes in the frequency domain. In addition, FINESSE provides a number of
commands to easily generate and plot the most common signals like, for example,
power enhancement, error or control signals, transfer functions and
shot-noise-limited sensitivities.
Among the various simulation tools available to the gravitational wave
community today, FINESSE is the most advanced general optical simulation that
uses the frequency domain. It has been designed to allow general analysis of
user defined optical setups while being easy to install and easy to use.Comment: Added an example for the application of the simulation during the
commisioning of the GEO 600 gravitational-wave detecto
TDI and clock noise removal for the split interferometry configuration of LISA
Laser phase noise is the dominant noise source in the on-board measurements of the space-based gravitational wave detector LISA (Laser Interferometer Space Antenna). A well-known data analysis technique, the so-called time-delay interferometry (TDI), provides synthesized data streams free of laser phase noise. At the same time, TDI also removes the next largest noise source: phase fluctuations of the on-board clocks which distort the sampling process. TDI needs precise information about the spacecraft separations, sampling times and differential clock noise between the three spacecrafts. These are measured using auxiliary modulations on the laser light. Hence, there is a need for algorithms that account for clock noise removal schemes combined with TDI while preserving the gravitational wave signal. In this paper, we will present the mathematical formulation of the LISA-like data streams and discuss a compliant algorithm that corrects for both clock and laser noise in the case of a rotating, non-breathing LISA constellation. In contrast to previous papers, we consider the current optical bench design (split interferometry configuration), i.e. the test mass readout is done by the local oscillators only, instead of reflecting the weak inter-spacecraft light off the test mass. Furthermore, the absolute order of laser frequencies is taken into account and it can be shown that the TDI equations remain invariant. This is a crucial issue and was, up to now, completely neglected in the analysis
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