Choice of the Miniature Inertial Optomechanical Sensor Geometric Parameters with the Help of Their Mechanical Characteristics Modelling

In this paper, the mechanical characteristics of a miniature optomechanical accelerometer, similar to those proposed for a wide range of applications, have been investigated. With the help of numerical modelling, characteristics such as eigenfrequencies, quality factor, displacement magnitude, normalized translations, normalized rotations versus eigenfrequencies, as well as spatial distributions of the azimuthal and axial displacements and stored energy density in a wide frequency range starting from the stationary case have been obtained. Dependencies of the main mechanical characteristics versus the minimal and maximal system dimensions have been plotted. Geometries of the optomechanical accelerometers with micron size parts providing the low and the high first eigenfrequencies are presented. It is shown that via the choice of the geometrical parameters, the minimal measured acceleration level can be raised substantially

A laser dilatometer setup to characterize dimensionally stable materials from 100 K to 300 K

In our structural dimensional metrology laboratory, we implemented a setup to determine coefficients of thermal expansions (CTE) of ultra-stable materials at temperatures from 300 K down to 100 K. Such low CTE materials are important for dimensionally stable structures in space and terrestrial applications, e. g. to enable precise measurements. This CTE characterization is done in the 10 ppb/K (10·10-9 K-1) range by applying small temperature variation around dedicated absolute temperatures. In order to accommodate arbitrary sample materials, we bounce light off mirrors attached to the sample by custom mounts. The light and therefore the thermal-induced length variations is then analyzed by an interferometer with sub-nanometer sensitivity. Here, we present a more detailed investigation of a process during sample measurements using differential wavefront sensing (DWS)

Optomechanical resonator-enhanced atom interferometry

Matter-wave interferometry and spectroscopy of optomechanical resonators offer complementary advantages. Interferometry with cold atoms is employed for accurate and long-term stable measurements, yet it is challenged by its dynamic range and cyclic acquisition. Spectroscopy of optomechanical resonators features continuous signals with large dynamic range, however it is generally subject to drifts. In this work, we combine the advantages of both devices. Measuring the motion of a mirror and matter waves interferometrically with respect to a joint reference allows us to operate an atomic gravimeter in a seismically noisy environment otherwise inhibiting readout of its phase. Our method is applicable to a variety of quantum sensors and shows large potential for improvements of both elements by quantum engineering. © 2020, The Author(s)

Opto-Mechanical Inertial Sensors (OMIS) for High Temporal Resolution Gravimetry

Gravity field measurement by free-falling atoms has the potential for very high stability over time as the measurement exposes a direct, fundamental relationship between mass and acceleration. However, the measurement rate of the current state-of-the-art limits the performance at short timescales (greater than 1 Hz). Classical inertial sensors operate at much faster response times and are thus natural companions for free-falling atom sensors. Such a hybrid device would gain the ultra-high stability of the free-falling atom sensor while greatly extending the bandwidth to higher frequency using the classical sensor. This requires the stable bandwidth of both devices to overlap sufficiently. We have developed opto-mechanical inertial sensors (OMIS) with good long term stability for just this purpose. The sensors are made of highly stable fused silica material, feature a monolithic optical cavity for displacement readout, and utilize a laser diode stabilized to a molecular reference. With no temperature control and only the thermal shielding provided by the vacuum chamber, this device is stable down to 0.1 Hz which overlaps with the bandwidth of free-falling atom sensors. The OMIS are self-calibrating by converting the fundamental resonances of a molecular gas into length using the free-spectral range of the optical cavity, FSR = c/2nL, and then sampling the OMIS mechanical damping rate and resonance frequency using a nearby piezo. This acceleration calibration is potentially transferable to a companion free-falling atom sensor. Readout is performed by modulating the cavity length of the OMIS with one cavity mirror being the OMIS itself and the other being a high frequency resonator. The high frequency resonator is driven by a nearby piezo well above the response rate of the OMIS and acts like an ultrastable quartz clock. The resulting highly stable tone is demodulated by the readout electronics. For the low finesse optical cavity used here, this yields a displacement resolution of 2x10-13 m/rtHz and a high frequency acceleration resolution of 400 ng /rtHz. At 0.1 Hz the acceleration resolution is 1.5 mug /rtHz limited by the stability of our vibration isolation stage. The OMIS dimensions are about 30 mm x 30 mm x 5 mm and can be fiber coupled to enable co-location with other sensors or as standalone devices for future gravimetry both on Earth and in spac

Stem Cell Derived Phenotypic Human Neuromuscular Junction Model For Dose Response Evaluation Of Therapeutics

There are currently no functional neuromuscular junction (hNMJ) systems composed of human cells that could be used for drug evaluations or toxicity testing in vitro. These systems are needed to evaluate NMJs for diseases such as amyotrophic lateral sclerosis, spinal muscular atrophy or other neurodegenerative diseases or injury states. There are certainly no model systems, animal or human, that allows for isolated treatment of motoneurons or muscle capable of generating dose response curves to evaluate pharmacological activity of these highly specialized functional units. A system was developed in which human myotubes and motoneurons derived from stem cells were cultured in a serum-free medium in a BioMEMS construct. The system is composed of two chambers linked by microtunnels to enable axonal outgrowth to the muscle chamber that allows separate stimulation of each component and physiological NMJ function and MN stimulated tetanus. The muscle\u27s contractions, induced by motoneuron activation or direct electrical stimulation, were monitored by image subtraction video recording for both frequency and amplitude. Bungarotoxin, BOTOX® and curare dose response curves were generated to demonstrate pharmacological relevance of the phenotypic screening device. This quantifiable functional hNMJ system establishes a platform for generating patient-specific NMJ models by including patient-derived iPSCs

TOWARDS HYBRID INERTIAL NAVIGATION BASED ON ATOM INTERFEROMETRY FOR SPACE APPLICATIONS

Inertial sensors, which often employ a mass-spring system, typically perform a relative measurement of the local acceleration field and therefore require calibration to establish scale and to remove offset bias. However, these parameters are not stable and eventually drift leading to errors in navigation systems. This is particularly problematic for the offset bias since it will generate a positioning error which grows quadratic in time. Inertial sensing by atom interferometry in contrast, yields an absolute measurement of the local acceleration field which eliminates the offset bias. Despite these advantages, atom interferometer-based inertial sensors have two major drawbacks, namely the low sample rate (in the order of some Hz) and the limited dynamic range, leading to phase wrapping and an ambiguous measurement output. The combination of an atom interferometer with a opto-mechanical sensors is a promising approach to overcome the beforementioned problems. We are planning to combine an atom interferometer based on stimulated Raman transitions in a Mach-Zehnder configuration using Rubidium-87 with opto-mechanical sensors. The atom interferometer shall be capable measuring the linear acceleration sequentially along three independent axes. The opto-mechanical sensors will be directly attached to the retro-reflectors of the atom interferometer and built by cavities that are read out by optical means through a common laser system also utilized for the atom interferometer. Our work focusses on the technology maturation and miniaturization of the system with the final goal to utilizes such a sensor in space on a satellite. Therefore, a first prototype is under development for terrestrial use. Moreover, we are planning to launch such a sensor system onboard a TEXUS (Technology experiments under zero gravity) rocket within the next five years, pathing the way for a CubeSat mission in the next eight years and a technology demonstration on a satellite within the next eleven years. This talk gives an overview on mission specific requirements for the different use cases and the top level size, weight and power budgets as well as the current status of these activitie

HYBRID INERTIAL SENSORS - FUTURE PROSPECTS OF INERTIAL SENSORS BASED ON ATOM INTERFEROMETRY

Positioning currently relies heavily on Global Navigation Satellite Systems (GNSS). Combined with classical accelerometers and gyroscopes, precise determination of orientation and position at any given time become available. However, but the availability of GNSS (e.g. GPS) is limited and not guaranteed at all times. In this paper we present an alternative based on atom interferometry using cold atom ensembles. An inertial sensor based on cold atoms allows, in theory, for nearly drift-free measurements of inertial forces with accuracies unreached by classical sensors, but the technology is still locked away in large physics laboratories [Nyman 2006]. This paper introduces a compact device called SECAMP, which is capable of cooling atoms down to µ-Kelvin. SECAMP has the potential to measure inertial acceleration in three degrees of freedom. In the following, we present the current experimental setup of the apparatus and outline the next steps for the inertial sensor

Opto-mechanical resonator-enhanced atom interferometry

We combine an optical-mechanical resonator with an atom interferometer. A classical cantilever and matter waves sense their acceleration with respect to a joint reference. Apart from research on macroscopic quantum objects, applications are in the realm of quantum sensing. We demonstrate its robustness by operating an atom-interferometric gravimeter beyond its reciprocal response in a highly dynamic environment, exploiting the common mode signal. As a proof of concept, we have demonstrated post correction using the OMIS by instigating single frequency strong motion for a T=10 ms interferometer. An improvement factor of 16 was achieved yielding 5x10^(-4)ms^(-2)/rtHz in the short term stability of gravitational acceleration measurements with our atom interferometer. We discuss the potential of an advanced OMIS set-up for field gravimeters