702 research outputs found
Feedback Enhanced Sensitivity in Optomechanics: Surpassing the Parametric Instability Barrier
The intracavity power, and hence sensitivity, of optomechanical sensors is
commonly limited by parametric instability. Here we characterize the parametric
instability induced sensitivity degradation in a micron scale cavity
optomechanical system. Feedback via optomechanical transduction and electrical
gradient force actuation is applied to suppress the parametric instability. As
a result a 5.4 fold increase in mechanical motion transduction sensitivity is
achieved to a final value of .Comment: 4 pages, 4 figure
On the transduction of various noise sources in optical microtoroids
Optical microresonators constitute the basic building block for numerous precision measurements including single-particle detection, magnetometry, force and position sensing. The ability to resolve a signal of interest is limited however by various noise sources. In this tutorial style paper we provide a matrix formalism to analyze the effect of various modulations upon the optical cavity. The technique can in principle be used to estimate the sensitivity of microresonator based sensors and potentially to identify the optimal detection basis and cavity parameters to optimise the signal to noise ratio
Cavity optoelectromechanical regenerative amplification
Cavity optoelectromechanical regenerative amplification is demonstrated. An
optical cavity enhances mechanical transduction, allowing sensitive measurement
even for heavy oscillators. A 27.3 MHz mechanical mode of a microtoroid was
linewidth narrowed to 6.6\pm1.4 mHz, 30 times smaller than previously achieved
with radiation pressure driving in such a system. These results may have
applications in areas such as ultrasensitive optomechanical mass spectroscopy
Model of a microtoroidal magnetometer
We present a model of a cavity optomechanical magnetic field sensor based on a microtoroidal resonator. The magnetic field induced expansion of a magnetostrictive material is transduced onto the physical structure of a highly compliant optical microresonator. The resulting motion is read out optically with ultra-high sensitivity. According to our theoretical model sensitivities of up to 750 fT/√ Hz may be possible. The simultaneous presence of high-quality mechanical and optical resonances in microtoroids greatly enhances both the response to the magnetic field and the measurement sensitivity
Cavity Optomechanical Magnetometer
A cavity optomechanical magnetometer is demonstrated where the magnetic field
induced expansion of a magnetostrictive material is transduced onto the
physical structure of a highly compliant optical microresonator. The resulting
motion is read out optically with ultra-high sensitivity. Detecting the
magnetostrictive deformation of Terfenol-D with a toroidal whispering gallery
mode (TWGM) resonator a peak sensitivity of 400 nT/Hz^.5 was achieved with
theoretical modelling predicting that sensitivities of up to 500 fT/Hz^.5 may
be possible. This chip-based magnetometer combines high-sensitivity and large
dynamic range with small size and room temperature operation
Expression of ECM proteins fibulin-1 and -2 in acute and chronic liver disease and in cultured rat liver cells
Fibulin-2 has previously been considered as a marker to distinguish rat liver myofibroblasts from hepatic stellate cells. The function of other fibulins in acute or chronic liver damage has not yet been investigated. The aim of this study has been to evaluate the expression of fibulin-1 and -2 in models of rat liver injury and in human liver cirrhosis. Their cellular sources have also been investigated. In normal rat liver, fibulin-1 and -2 were both mainly present in the portal field. Fibulin-1-coding transcripts were detected in total RNA of normal rat liver, whereas fibulin-2 mRNA was only detected by sensitive, real-time quantitative polymerase chain reaction. In acute liver injury, the expression of fibulin-1 was significantly increased (17.23-fold after 48 h), whereas that of fibulin-2 was not modified. The expression of both fibulin-1 and -2 was increased in experimental rat liver cirrhosis (19.16- and 26.47-fold, respectively). At the cellular level, fibulin-1 was detectable in hepatocytes, “activated” hepatic stellate cells, and liver myofibroblasts (2.71-, 122.65-, and 469.48-fold over the expression in normal rat liver), whereas fibulin-2 was restricted to liver myofibroblasts and was regulated by transforming growth factor beta-1 (TGF-β1) in 2-day-old hepatocyte cultures and in liver myofibroblasts. Thus, fibulin-1 and -2 respond differentially to single and repeated damaging noxae, and their expression is differently present in liver cells. Expression of the fibulin-2 gene is regulated by TGF-β1 in liver myofibroblasts
Interferometric detection of mode splitting for whispering gallery mode biosensors
Sensors based on whispering gallery mode resonators can detect single
nanoparticles and even single molecules. Particles attaching to the resonator
induce a doublet in the transmission spectrum which provides a self-referenced
detection signal. However, in practice this spectral feature is often obscured
by the width of the resonance line which hides the doublet structure. This
happens particularly in liquid environments that reduce the effective Q factor
of the resonator. In this paper we demonstrate an interferometric set-up that
allows the direct detection of the hidden doublet and thus provides a pathway
for developing practical sensor applications.Comment: 9 page
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