First stage of LISA data processing II: Alternative filtering dynamic models for LISA

Space-borne gravitational wave detectors, such as (e)LISA, are designed to operate in the low-frequency band (mHz to Hz), where there is a variety of gravitational wave sources of great scientific value. To achieve the extraordinary sensitivity of these detector, the precise synchronization of the clocks on the separate spacecraft and the accurate determination of the interspacecraft distances are important ingredients. In our previous paper (Phys. Rev. D 90, 064016 [2014]), we have described a hybrid-extend Kalman filter with a full state vector to do this job. In this paper, we explore several different state vectors and their corresponding (phenomenological) dynamic models, to reduce the redundancy in the full state vector, to accelerate the algorithm, and to make the algorithm easily extendable to more complicated scenarios.Comment: 12 page

First stage of LISA data processing: Clock synchronization and arm-length determination via a hybrid-extended Kalman filter

In this paper, we describe a hybrid-extended Kalman filter algorithm to synchronize the clocks and to precisely determine the inter-spacecraft distances for space-based gravitational wave detectors, such as (e)LISA. According to the simulation, the algorithm has significantly improved the ranging accuracy and synchronized the clocks, making the phase-meter raw measurements qualified for time- delay interferometry algorithms.Comment: 14 pages, Phys. Rev. D 90, 064016 (2014

Coherent control of broadband vacuum squeezing

We present the observation of optical fields carrying squeezed vacuum states at sideband frequencies from 10Hz to above 35MHz. The field was generated with type-I optical parametric oscillation below threshold at 1064nm. A coherent, unbalanced classical modulation field at 40MHz enabled the generation of error signals for stable phase control of the squeezed vacuum field with respect to a strong local oscillator. Broadband squeezing of approximately -4dB was measured with balanced homodyne detection. The spectrum of the squeezed field allows a quantum noise reduction of ground-based gravitational wave detectors over their full detection band, regardless of whether homodyne readout or radio-frequency heterodyne readout is used.Comment: 9 pages, 8 figure

Gravitational wave detectors

The existence of gravitational radiation is a prediction of Einstein's general theory of relativity. Gravitational waves are perturbations in the curvature of spacetime caused by accelerated masses. Since the 1960s gravitational wave detectors have been built and constantly improved. The present-day generation of resonant mass antennas and laser interferometers has reached the necessary sensitivity to detect gravitational waves from sources in the Milky Way. Within a few years, the next generation of detectors will open the field of gravitational wave astronomy. © IOP Publishing Ltd and Deutsche Physikalische Gesellschaft

The finite mass beamsplitter in high power interferometers

The beamplitter in high-power interferometers is subject to significant radiation-pressure fluctuations. As a consequence, the phase relations which appear in the beamsplitter coupling equations oscillate and phase modulation fields are generated which add to the reflected fields. In this paper, the transfer function of the various input fields impinging on the beamsplitter from all four ports onto the output field is presented including radiation-pressure effects. We apply the general solution of the coupling equations to evaluate the input-output relations of the dual-recycled laser-interferometer topology of the gravitational-wave detector GEO600 and the power-recycling, signal-extraction topology of advanced LIGO. We show that the input-output relation exhibits a bright-port dark-port coupling. This mechanism is responsible for bright-port contributions to the noise density of the output field and technical laser noise is expected to decrease the interferometer's sensitivity at low frequencies. It is shown quantitatively that the issue of technical laser noise is unimportant in this context if the interferometer contains arm cavities.Comment: 10 pages, 7 figure

Listening to the universe with gravitational waves

Gravitational waves have been predicted by Albert Einstein more than 90 years ago as a consequence of his theory of general relativity. Several km-size gravitational wave detectors have now gone into operation on the ground to observe signals at frequencies from a few Hz to a few kHz. In 2020, LISA, a space-based detector, will open the low-frequency window from 0.1 mHz to 0.1 Hz

Quantum limit of different laser power stabilization schemes involving optical resonators

Three different laser power stabilization schemes are compared: a traditional power stabilization, a traditional one with subsequent optical resonator, and a power stabilization with the novel optical ac coupling technique. The performance of the schemes is evaluated using the theoretical quantum limit and the power stability achieved considering technical limitations. The scheme with optical ac coupling is superior to the other ones especially at high laser power levels that will be used in future interferometric gravitational wave detectors.DFG/EXC/QUES

Sub-pm/Hz\mathrm{\mathbf{\sqrt{\rm Hz}}} non-reciprocal noise in the LISA backlink fiber

The future space-based gravitational wave detector Laser Interferometer Space Antenna (LISA) requires bidirectional exchange of light between its two optical benches on board of each of its three satellites. The current baseline foresees a polarization-maintaining single-mode fiber for this backlink connection. Phase changes which are common in both directions do not enter the science measurement, but differential ("non-reciprocal") phase fluctuations directly do and must thus be guaranteed to be small enough. We have built a setup consisting of a Zerodur$^{\rm TM}$ baseplate with fused silica components attached to it using hydroxide-catalysis bonding and demonstrated the reciprocity of a polarization-maintaining single-mode fiber at the 1 pm/$\sqrt{\textrm{Hz}}$ level as is required for LISA. We used balanced detection to reduce the influence of parasitic optical beams on the reciprocity measurement and a fiber length stabilization to avoid nonlinear effects in our phase measurement system (phase meter). For LISA, a different phase meter is planned to be used that does not show this nonlinearity. We corrected the influence of beam angle changes and temperature changes on the reciprocity measurement in post-processing

Interferometry for LISA and LISA pathfinder

The Laser Interferometer Space Antenna (LISA) is a joint ESA-NASA mission designed to observe gravitational waves in the frequency range between 10 -4 to 1 Hz, where ground-based detectors are limited by terrestrial noise. Sources in this frequency range include supermassive black holes and galactic binary stars. LISA consists of three identical spacecraft separated by 5 million kilometers carrying a total of six free flying proof masses in heliocentric drag-free orbit. The fluctuations in separation between two test masses located in different satellites will be measured by laser interferometry with picometer precision. LISA Pathfinder is a technology demonstration mission for LISA consisting of only two test masses in one single satellite. It will be launched in 2009, five years before LISA. We provide here an overview of the development of LISA and LISA Pathfinder with particular emphasis on the interferometry