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Interferometry and Optics (Ballroom B/C)
Thursday Chair: Simon Barke
16:00 - 16:15 Josep Sanjuan
DLR
The laser ranging instrument on GRACE-Follow onDownload
16:15 - 16:30 Andrew Sutton
NASA JPL
TDI Ranging for the GRACE-FO Laser Ranging InterferometerDownload
16:30 - 16:45 Martin Gohlke
German Aerospace Center - DLR
Optical metrology systems for space applicationsDownload
16:45 - 17:00 Michael Troebs
AEI Hannover
Phase fidelity of a flight-representative optical amplifierDownload
17:00 - 17:15 Thomas Schwarze
Max Planck Institute for Gravitational Physics (Albert Einstein Institute)
High-precision phasemeter for Deep Phase Modulation InterferometryDownload
17:15 - 17:30 Li Yuqiong
Institute of mechanics, Chinese academy of sciences
The performance evaluation of phase-meter prototype with reference signalsDownload
17:30 - 17:45 Aaron Spector
University of Florida
Experimental Investigation of the Back-reflection from an On-axis TelescopeDownload
17:45 - 18:00 Gudrun Wanner
AEI Hannover
Low noise laser interferometer design using IfoCADDownload
The laser ranging instrument on GRACE-Follow on Download
Josep Sanjuan - DLR
Abstract will follow. Topic: Laser ranging instrument (LRI) on-board GRACE-FO: overview and status of the German contribution for the LRI on GRACE-FO, which will be launched in 2017.
TDI Ranging for the GRACE-FO Laser Ranging Interferometer Download
Andrew Sutton - NASA JPL
TDI Ranging for the GRACE-FO Laser Ranging Interferometer Kirk McKenzie, Andrew Sutton, Glenn de Vine, Brent Ware, Robert Spero, William Klipstein, Samuel Francis, and Daniel Shaddock The LISA Experience from the GRACE-­FO Optical Payload (LEGOP) project aims to identify core techniques and technologies from the LISA technology package for testing upon the upcoming Gravity Recovery and Climate Experiment Follow On (GRACE-­FO) mission. GRACE-­FO will place two satellites into a common Low Earth orbit separated by ~200 km and will operate a Laser Ranging Instrument to monitor changes in Earth’s gravitational potential. The GRACE-­FO LRI shares many similarities with LISA, including laser pre-­stabilization, MHz Doppler shifts, ~100 pW receive power and phase measurement based upon a digital phase-­locked loop. These architectural similarities permit an on-­orbit demonstration of a ‘dual one-­way range’ TDI combination that reconstructs the GRACE-­FO measurement, without active phase locking in one satellite. Instead, offline TDI Ranging (TDIR) is applied to suppress the otherwise overwhelming phase noise of the free-­running laser. We present simulation and experimental results demonstrating the application of tone assisted TDIR to suppress free-­running laser frequency noise by ~9 orders of magnitude in a displacement noise limited interferometer with macroscopic optical time-­delays.
Optical metrology systems for space applications Download
Martin Gohlke - German Aerospace Center - DLR
Laser based metrology systems become more and more attractive for space applications and are the core elements of planned missions as LISA (NGO, eLISA) or the GRACE-FO LRI (laser ranging instrument). They can be used for distance measurements between satellites (GRACE-FO-LRI, LISA) or for formation flying mission as DARWIN. Laser based metrology also includes optical clocks/references as needed for laser frequency stabilization in fundamental physics missions. One example is the proposed mSTAR (mini SpaceTime Asymmetry Research) mission, dedicated to perform a Kennedy-Thorndike experiment on a satellite in a low-Earth orbit. By comparing an iodine standard to a cavity-based frequency reference and integration over 2 year mission lifetime, the Kennedy-Thorndike coefficient will be determined with up to two orders of magnitude higher accuracy than the current best ground experiment. To enable the use of existing optical laboratory setups, optimization with respect to power consumption, weight and dimensions is necessary. At the same time the thermal and structural stability must be increased. Over the last few years we investigated adhesive bonding of optical components to thermally highly stable glass ceramics as an easy-to-handle assembly integration technology. Several setups were implemented and tested for later use in space applications. We realized a two-beam heterodyne LISA related interferometer with demonstrated noise levels in the pm-range for translation measurement and nano-radiant range for tilt measurements and two iodine frequency references on EBB and EM level whose frequency stabilities are in the 10^-15 range for longer integration times. The EM setup was thermally cycled and vibration tested. The achieved accuracy and the lessons learned from the performed tests will be represented in the talk and the further steps will be discussed.
Phase fidelity of a flight-representative optical amplifier Download
Michael Troebs - AEI Hannover
The Laser Interferometer Space Antenna (LISA) needs to transmit clock information between spacecraft to correct for phase noise between the clocks on the different spacecraft. For this purpose phase modulation sidebands at GHz frequencies will be imprinted on the laser beams between spacecraft. Differential phase noise between the carrier and a sideband introduced within the optical chain must be low. One possible laser source for LISA consists of an Ytterbium-doped fiber amplifier originally developed for inter-satellite communication, seeded by the laser used for the technology demonstrator mission LISA Pathfinder. We report on a transportable setup to measure the phase fidelity of optical amplifiers and results from a flight-representative optical amplifier.
High-precision phasemeter for Deep Phase Modulation Interferometry Download
Thomas Schwarze - Max Planck Institute for Gravitational Physics (Albert Einstein Institute)
We present the development of dedicated hardware for modulation signal synthesis and phase measurement for the Deep Phase Modulation Interferometry (DPMI) technique. This technique can be used for the tracking of (free floating) test masses in multiple degrees of freedom utilizing a compact optical setup and a high dynamic range. In our implementation, a sinusoidal modulation is applied through a ring piezo-electric actuator to one arm of a Mach-Zehnder interferometer to reach large modulation depths in the order of 10 rad. The interferometer phase is extracted from the photodetector signal by a complex fit to the harmonic amplitudes of the modulation frequency. We use a Field Programmable Gate Array (FPGA) that hosts a Direct Digital Synthesizer (DDS) and a Digital Signal Processing (DSP) core. The former allows generation and control of the modulation signal to drive the ring piezo-electric actuator. The latter computes the harmonic amplitudes by performing multiple single-bin discrete Fourier transforms. These amplitudes are subsequently transmitted to a PC via Ethernet to conduct the complex fit computations. The results obtained from a zero measurement with an optical signal revealed a phasemeter precision of 2.3 pm/rtHz below and 0.1 pm/rtHz above 10 Hz with a dynamic range over multiple fringes.
The performance evaluation of phase-meter prototype with reference signals Download
Li Yuqiong - Institute of mechanics, Chinese academy of sciences
Heterodyne laser interferometry is considered as the most promising readout scheme for future space gravitational wave detection missions, in which the gravitational wave signals disguise as small phase variances within the heterodyne beat note. This makes the phase-meter, which extracts the phase information from the beat note, the key device to this system. In this presentation, a prototype of phase-meter based on digital phase-locked loop technology is developed, and the major noise sources which may contribute to the noise spectra density are analyzed. Two experiments are also carried out to evaluate the performance of the phase-meter prototype. The results show that the sensitivity is achieved 2 rad/Hz in the frequency range of 0.04 Hz-10 Hz. Due to the effect of thermal drift, the noise obviously increases with the frequencies down to 0.1 mHz.
Experimental Investigation of the Back-reflection from an On-axis Telescope Download
Aaron Spector - University of Florida
The current generation of proposed space based interferometric gravitational wave detectors all use a reflecting telescope to transfer the laser signals between the spacecraft. One of the proposed telescope designs is an on-axis classical Cassegrain with the secondary mirror axially aligned to the primary mirror. Since the outgoing beam will be incident normal to the secondary some of the light will be reflected directly back to the optical bench. Length changes between the telescope structure and the optical bench will cause this back-reflected light to introduce phase noise to the measurement signal. The phase noise from this process must be suppressed below 0.1 rad/rtHz to meet the LISA requirements. We derived a set of requirements for the mode-matched power in the back-reflected field that scale with the stability of the optical pathlength between the telescope and the optical bench. Simulations have demonstrated that the back-reflected power can be sufficiently attenuated by using a specifically patterned anti-reflective (AR) region at the center of the secondary mirror. After pursuing a wide variety of shapes for the AR region we settled on several candidates to further investigate and optimize. Several prototype secondaries have been manufactured by etching a patterned AR region into a metallic reflective coating using photolithography. An experimental testbed was built to measure that back-reflection from these prototypes and the preliminary results indicate that we are close to meeting the requirements for attenuating the back-reflection.
Low noise laser interferometer design using IfoCAD Download
Gudrun Wanner - AEI Hannover
Laser interferometers in gravitational physics are typically designed to achieve very low phase noise. The standard optical design tools (ZEMAX, CodeV, etc.), however, do not provide all needed functions, like the computation of signals on quadrant photodiodes or automatic placement of components. For this reason, we have written and used in the past years dedicated algorithms that are now combined in our publicly available interferometer design software IfoCAD. This software now allows to design and optimize 3D laser interferometer layouts, compute readout signals like the interferometric phase, differential wavefront sensing signal (DWS), contrast and heterodyne efficiency. We will discuss the properties and functions of IfoCAD on examples relevant for (e)LISA, like the impact of the chosen phase definition to resulting phase noise, top hat beams and fiber modes, their propagation with diffraction, and imaging optics design for low tilt to length coupling.