In an optomechanical cavity the optical and mechanical degree of freedom are strongly coupled by the radiation pressure of the light. This field of research has been gathering a lot of momentum during the last couple of years, driven by the technological advances in microfabrication and the first observation of quantum phenomena. These results open new perspectives in a wide range of applications, including high sensitivity measurements of position, acceleration, force, mass, and for fundamental research. We are working on low frequency pondero-motive light squeezing as a tool for improving the sensitivity of audio frequency measuring devices such as magnetic resonance force microscopes and gravitational-wave detectors. It is well known that experiments aiming to produce and manipulate non-classical (squeezed) light by effect of optomechanical interaction need a mechanical oscillator with low optical and mechanical losses. These technological requirements permit to maximize the force per incoming photon exerted by the cavity field on the mechanical element and to improve the element’s response to the radiation pressure force and, at the same time, to decrease the influence of the thermal bath. In this contribution we describe a class of mechanical devices for which we measured a mechanical quality factor up to 1.2 × 106 and with which it was possible to build a Fabry-Perot cavity with optical finesse up to 9 × 104. From our estimations, these characteristics meet the requirements for the generation of radiation squeezing and quantum correlations in the ∼ 100kHz region. Moreover our devices are characterized by high reproducibility to allow inclusion in integrated systems. We show the results of the characterization realized with a Michelson interferometer down to 4.2K and measurements in optical cavities performed at cryogenic temperature with input optical powers up to a few mW. We also report on the dynamical stability and the thermal response of the system.
The interaction of the radiation pressure with micro-mechanical oscillators is earning a growing interest for its
wide-range applications (including high sensitivity measurements of force and position) and for fundamental
research (entanglement, ponderomotive squeezing, quantum non-demolition measurements). In this contribution
we describe the fabrication of a family of opto-mechanical devices specifically designed to ease the detection of
ponderomotive squeezing and of entanglement between macroscopic objects and light. These phenomena are not
easily observed, due to the overwhelming effects of classical noise sources of thermal origin with respect to the
weak quantum fluctuations of the radiation pressure. Therefore, a low thermal noise background is required,
together with a weak interaction between the micro-mirror and this background (i.e. high mechanical quality
factors). The device should also be capable to manage a relatively large amount of dissipated power at cryogenic
temperatures, as the use of a laser with power up to a ten of mW can be useful to enhance radiation pressure
effects. In the development of our opto-mechanical devices, we are exploring an approach focused on relatively
thick silicon oscillators with high reflectivity coating. The relatively high mass is compensated by the capability
to manage high power at low temperatures, owing to a favourable geometric factor (thicker connectors) and
the excellent thermal conductivity of silicon crystals at cryogenic temperature. We have measured at cryogenic
temperatures mechanical quality factors up to 105 in a micro-oscillator designed to reduce as much as possible
the strain in the coating layer and the consequent energy dissipation. This design improves an approach applied
in micro-mirror and micro-cantilevers, where the coated surface is reduced as much as possible to improve the
quality factor. The deposition of the highly reflective coating layer has been carefully integrated in the micromachining
process to preserve its low optical losses: an optical finesse of F = 6×104 has been measured in a
Fabry-Perot cavity with the micro-resonator used as end mirror.
The aim of this contribution is to report and discuss a preliminary study and rough optimization of a novel concept of
MEMS device for vibration energy harvesting, based on a multi-modal dynamic behavior. The circular-shaped device
features Four-Leaf Clover-like (FLC) double spring-mass cascaded systems, kept constrained to the surrounding frame
by means of four straight beams. The combination of flexural bending behavior of the slender beams plus deformable
parts of the petals enable to populate the desired vibration frequency range with a number of resonant modes, and
improve the energy conversion capability of the micro-transducer. The harvester device, conceived for piezoelectric
mechanical into electric energy conversion, is intended to sense environmental vibrations and, thereby, its geometry is
optimized to have a large concentration of resonant modes in a frequency range below 5-10 kHz. The results of FEM
(Finite Element Method) based analysis performed in ANSYSTM Workbench are reported, both concerning modal and
harmonic response, providing important indications related to the device geometry optimization. The analysis reported in
this work is limited to the sole mechanical modeling of the proposed MEMS harvester device concept. Future
developments of the study will encompass the inclusion of piezoelectric conversion in the FEM simulations, in order to
have indications of the actual power levels achievable with the proposed harvester concept. Furthermore, the results of
the FEM studies here discussed, will be validated against experimental data, as soon as the MEMS resonator specimens,
currently under fabrication, are ready for testing.
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