125 research outputs found
Operating LISA as a Sagnac interferometer
A phase-locking configuration for LISA is proposed that provides a
significantly simpler mode of operation. The scheme provides one Sagnac signal
readout inherently insensitive to laser frequency noise and optical bench
motion for a non-rotating LISA array. This Sagnac output is also insensitive to
clock noise, requires no time shifting of data, nor absolute arm length
knowledge. As all measurements are made at one spacecraft, neither clock
synchronization nor exchange of phase information between spacecraft is
required. The phase-locking configuration provides these advantages for only
one Sagnac variable yet retains compatibility with the baseline approach for
obtaining the other TDI variables. The orbital motion of the LISA constellation
is shown to produce a 14 km path length difference between the
counter-propagating beams in the Sagnac interferometer. With this length
difference a laser frequency noise spectral density of 1 Hz/
would consume the entire optical path noise budget of the Sagnac variables. A
significant improvement of laser frequency stability (currently at 30
Hz/) would be needed for full-sensitivity LISA operation in the
Sagnac mode. Alternatively, an additional level of time-delay processing could
be applied to remove the laser frequency noise. The new time-delayed
combinations of the phase measurements are presented.Comment: 8 pages, 2 figure
The performance of arm locking in LISA
For the laser interferometer space antenna (LISA) to reach it's design
sensitivity, the coupling of the free running laser frequency noise to the
signal readout must be reduced by more than 14 orders of magnitude. One
technique employed to reduce the laser frequency noise will be arm locking,
where the laser frequency is locked to the LISA arm length. This paper details
an implementation of arm locking, studies orbital effects, the impact of errors
in the Doppler knowledge, and noise limits. The noise performance of arm
locking is calculated with the inclusion of the dominant expected noise
sources: ultra stable oscillator (clock) noise, spacecraft motion, and shot
noise. Studying these issues reveals that although dual arm locking [A. Sutton
& D. A Shaddock, Phys. Rev. D 78, 082001 (2008).] has advantages over single
(or common) arm locking in terms of allowing high gain, it has disadvantages in
both laser frequency pulling and noise performance. We address this by
proposing a hybrid sensor, retaining the benefits of common and dual arm
locking sensors. We present a detailed design of an arm locking controller and
perform an analysis of the expected performance when used with and without
laser pre-stabilization. We observe that the sensor phase changes beneficially
near unity-gain frequencies of the arm-locking controller, allowing a factor of
10 more gain than previously believed, without degrading stability. We show
that the LISA frequency noise goal can be realized with arm locking and
Time-Delay Interferometry only, without any form of pre-stabilization.Comment: 28 pages, 36 figure
Experimental Demonstration of Time-Delay Interferometry for the Laser Interferometer Space Antenna
We report on the first demonstration of time-delay interferometry (TDI) for
LISA, the Laser Interferometer Space Antenna. TDI was implemented in a
laboratory experiment designed to mimic the noise couplings that will occur in
LISA. TDI suppressed laser frequency noise by approximately 10^9 and clock
phase noise by 6x10^4, recovering the intrinsic displacement noise floor of our
laboratory test bed. This removal of laser frequency noise and clock phase
noise in post-processing marks the first experimental validation of the LISA
measurement scheme.Comment: 4 pages, 4 figures, to appear in Physical Review Letters end of May
201
Laser interferometry for the Big Bang Observer
The Big Bang Observer is a proposed space-based gravitational-wave detector intended as a follow on mission to the Laser Interferometer Space Antenna (LISA). It is designed to detect the stochastic background of gravitational waves from the early universe. We discuss how the interferometry can be arranged between three spacecraft for this mission and what research and development on key technologies are necessary to realize this scheme
Suppression of Classical and Quantum Radiation Pressure Noise via Electro-Optic Feedback
We present theoretical results that demonstrate a new technique to be used to
improve the sensitivity of thermal noise measurements: intra-cavity intensity
stabilisation. It is demonstrated that electro-optic feedback can be used to
reduce intra-cavity intensity fluctuations, and the consequent radiation
pressure fluctuations, by a factor of two below the quantum noise limit. We
show that this is achievable in the presence of large classical intensity
fluctuations on the incident laser beam. The benefits of this scheme are a
consequence of the sub-Poissonian intensity statistics of the field inside a
feedback loop, and the quantum non-demolition nature of radiation pressure
noise as a readout system for the intra-cavity intensity fluctuations.Comment: 4 pages, 1 figur
Control and tuning of a suspended Fabry-Perot cavity using digitally-enhanced heterodyne interferometry
We present the first demonstration of real-time closed-loop control and
deterministic tuning of an independently suspended Fabry-Perot optical cavity
using digitally-enhanced heterodyne interferometry, realising a peak
sensitivity of 10 pm over the 10-1000 Hz frequency
band. The methods presented are readily extensible to multiple coupled
cavities. As such, we anticipate that refinements of this technique may find
application in future interferometric gravitational-wave detectors
Arm-length stabilisation for interferometric gravitational-wave detectors using frequency-doubled auxiliary lasers
Residual motion of the arm cavity mirrors is expected to prove one of the
principal impediments to systematic lock acquisition in advanced
gravitational-wave interferometers. We present a technique which overcomes this
problem by employing auxiliary lasers at twice the fundamental measurement
frequency to pre-stabilise the arm cavities' lengths. Applying this approach,
we reduce the apparent length noise of a 1.3 m long, independently suspended
Fabry-Perot cavity to 30 pm rms and successfully transfer longitudinal control
of the system from the auxiliary laser to the measurement laser
Phase measurement device using inphase and quadrature components for phase estimation
A phasemeter for estimating the phase of a signal. For multi-tone signals, multiple phase estimates may be provided. An embodiment includes components operating in the digital domain, where a sampled input signal is multiplied by cosine and sine terms to provide estimates of the inphase and quadrature components. The quadrature component provides an error signal that is provided to a feedback loop, the feedback loop providing a model phase that tends to track the phase of a tone in the input signal. The cosine and sine terms are generated from the model phase. The inphase and quadrature components are used to form a residual phase, which is added to the model phase to provide an estimate of the phase of the input signal. Other embodiments are described and claimed
The Big Bang Observer: High Laser Power for Gravitational Wave Astrophysics
The Big Bang Observer is a proposed space-based gravitational-wave detector which will utilize two 300 W, 355 nm wavelength lasers on each of three spacecraft. This wavelength will be achieved by frequency tripling Nd:YAG lasers
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