Phasemeter core for intersatellite laser heterodyne interferometry: modelling, simulations and experiments

Inter satellite laser interferometry is a central component of future space-borne gravity instruments like LISA, eLISA, NGO and future geodesy missions. The inherently small laser wavelength allows to measure distance variations with extremely high precision by interfering a reference beam with a measurement beam. The readout of such interferometers is often based on tracking phasemeters, able to measure the phase of an incoming beatnote with high precision over a wide range of frequencies. The implementation of such phasemeters is based on all digital phase-locked loops, hosted in FPGAs. Here we present a precise model of an all digital phase locked loop that allows to design such a readout algorithm and we support our analysis by numerical performance measurements and experiments with analog signals.Comment: 17 pages, 6 figures, accepted for publication in CQ

Real-time phasefront detector for heterodyne interferometers

We present a real-time differential phasefront detector sensitive to better than 3 mrad rms, which corresponds to a precision of about 500 pm. This detector performs a spatially resolving measurement of the phasefront of a heterodyne interferometer, with heterodyne frequencies up to approximately 10 kHz. This instrument was developed as part of the research for the LISA Technology Package (LTP) interferometer, and will assist in the manufacture of its flight model. Due to the advantages this instrument offers, it also has general applications in optical metrology

Planet Formation Imager (PFI): Introduction and Technical Considerations

Complex non-linear and dynamic processes lie at the heart of the planet formation process. Through numerical simulation and basic observational constraints, the basics of planet formation are now coming into focus. High resolution imaging at a range of wavelengths will give us a glimpse into the past of our own solar system and enable a robust theoretical framework for predicting planetary system architectures around a range of stars surrounded by disks with a diversity of initial conditions. Only long-baseline interferometry can provide the needed angular resolution and wavelength coverage to reach these goals and from here we launch our planning efforts. The aim of the "Planet Formation Imager" (PFI) project is to develop the roadmap for the construction of a new near-/mid-infrared interferometric facility that will be optimized to unmask all the major stages of planet formation, from initial dust coagulation, gap formation, evolution of transition disks, mass accretion onto planetary embryos, and eventual disk dispersal. PFI will be able to detect the emission of the cooling, newly-formed planets themselves over the first 100 Myrs, opening up both spectral investigations and also providing a vibrant look into the early dynamical histories of planetary architectures. Here we introduce the Planet Formation Imager (PFI) Project (www.planetformationimager.org) and give initial thoughts on possible facility architectures and technical advances that will be needed to meet the challenging top-level science requirements.Comment: SPIE Astronomical Telescopes and Instrumentation conference, June 2014, Paper ID 9146-35, 10 pages, 2 Figure

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 $\sim$10 pm$/\sqrt{\mathrm{Hz}}$ 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

Spatiotemporal heterodyne detection

We describe a scheme into which a camera is turned into an efficient tunable frequency filter of a few Hertz bandwidth in an off-axis, heterodyne optical mixing configuration, enabling to perform parallel, high-resolution coherent spectral imaging. This approach is made possible through the combination of a spatial and temporal modulation of the signal to reject noise contributions. Experimental data obtained with dynamically scattered light by a suspension of particles in brownian motion is interpreted

Deep phase modulation interferometry

We have developed a method to equip homodyne interferometers with the capability to operate with constant high sensitivity over many fringes for continuous real-time tracking. The method can be considered as an extension of the "J_1...J_4" methods, and its enhancement to deliver very sensitive angular measurements through Differential Wavefront Sensing is straightforward. Beam generation requires a sinusoidal phase modulation of several radians in one interferometer arm. On a stable optical bench, we have demonstrated a long-term sensitivity over thousands of seconds of 0.1 mrad/sqrt[Hz] that correspond to 20 pm/sqrt[Hz] in length, and 10 nrad/sqrt[Hz] in angle at millihertz frequencies

Path-Length-Resolved Dynamic Light Scattering: Modeling the Transition From Single to Diffusive Scattering

Dynamic light-scattering spectroscopy is used to study Brownian motion within highly scattering samples. The fluctuations of the light field that is backscattered by a suspension of polystyrene microspheres are measured as power spectra by use of low-coherence interferometry to obtain path-length resolution. The data are modeled as the sum of contributions to the detected light weighted by a Poisson probability for the number of events that each component has experienced. By analyzing the broadening of the power spectra as a function of the path length for various sizes of particles, we determine the contribution of multiple scattering to the detected signal as a function of scattering anisotropy