10,192 research outputs found
Optomechanical transduction of an integrated silicon cantilever probe using a microdisk resonator
Sensitive transduction of the motion of a microscale cantilever is central to
many applications in mass, force, magnetic resonance, and displacement sensing.
Reducing cantilever size to nanoscale dimensions can improve the bandwidth and
sensitivity of techniques like atomic force microscopy, but current optical
transduction methods suffer when the cantilever is small compared to the
achievable spot size. Here, we demonstrate sensitive optical transduction in a
monolithic cavity-optomechanical system in which a sub-picogram silicon
cantilever with a sharp probe tip is separated from a microdisk optical
resonator by a nanoscale gap. High quality factor (Q ~ 10^5) microdisk optical
modes transduce the cantilever's MHz frequency thermally-driven vibrations with
a displacement sensitivity of ~ 4.4x10^-16 m\sqrt[2]{Hz} and bandwidth > 1 GHz,
and a dynamic range > 10^6 is estimated for a 1 s measurement.
Optically-induced stiffening due to the strong optomechanical interaction is
observed, and engineering of probe dynamics through cantilever design and
electrostatic actuation is illustrated
Condition Monitoring of Power Cables
A National Grid funded research project at Southampton has investigated possible methodologies for data acquisition, transmission and processing that will facilitate on-line continuous monitoring of partial discharges in high voltage polymeric cable systems. A method that only uses passive components at the measuring points has been developed and is outlined in this paper. More recent work, funded through the EPSRC Supergen V, UK Energy Infrastructure (AMPerES) grant in collaboration with UK electricity network operators has concentrated on the development of partial discharge data processing techniques that ultimately may allow continuous assessment of transmission asset health to be reliably determined
Distributed opto-mechanical analysis of liquids outside standard fibers coated with polyimide
The analysis of surrounding media has been a long-standing challenge of
optical fiber sensors. Measurements are difficult due to the confinement of
light to the inner core of standard fibers. Over the last two years, new sensor
concepts have enabled the analysis of liquids outside the cladding boundary,
where light does not reach. Sensing is based on opto-mechanical, forward
stimulated Brillouin scattering interactions between guided light and sound
waves. In most previous works, however, the protective polymer coating of the
fiber had to be removed first. In this work, we report the opto-mechanical
analysis of liquids outside commercially available, standard single-mode fibers
with polyimide coating. The polyimide layer provides mechanical protection but
can also transmit acoustic waves from the fiber cladding towards outside media.
Comprehensive analysis of opto-mechanical coupling in coated fibers that are
immersed in liquid is provided. The model shows that forward stimulated
Brillouin scattering spectra in coated fibers are more complex than those of
bare fibers, and strongly depend on the exact coating diameter and the choice
of acoustic mode. Nevertheless, sensing outside coated fibers is demonstrated
experimentally. Integrated measurements over 100 meters of fiber clearly
distinguish between air, ethanol and water outside polyimide coating. Measured
spectra are in close quantitative agreement with the analytic predictions.
Further, distributed opto-mechanical time-domain reflectometry mapping of water
and ethanol outside coated fiber is reported, with a spatial resolution of 100
meters. The results represent a large step towards practical opto-mechanical
fiber sensors
Optical fibre sensors - applications and potential
Fibre optic sensors have progressed considerably during the past few years and are now establishing their potential as very real contenders in the environmental, structural monitoring and industrial sensing areas. This paper will explore some examples of these emerging applications and analyse the benefits which optical fibre technology offers within these measurement sectors. We shall then continue to explore emerging prospects which offer new opportunities for future research and exploitation
Thermal noise in interferometric gravitational wave detectors due to dielectric optical coatings
We report on thermal noise from the internal friction of dielectric coatings
made from alternating layers of Ta2O5 and SiO2 deposited on fused silica
substrates. We present calculations of the thermal noise in gravitational wave
interferometers due to optical coatings, when the material properties of the
coating are different from those of the substrate and the mechanical loss angle
in the coating is anisotropic. The loss angle in the coatings for strains
parallel to the substrate surface was determined from ringdown experiments. We
measured the mechanical quality factor of three fused silica samples with
coatings deposited on them. The loss angle of the coating material for strains
parallel to the coated surface was found to be (4.2 +- 0.3)*10^(-4) for
coatings deposited on commercially polished slides and (1.0 +- 0.3)*10^{-4} for
a coating deposited on a superpolished disk. Using these numbers, we estimate
the effect of coatings on thermal noise in the initial LIGO and advanced LIGO
interferometers. We also find that the corresponding prediction for thermal
noise in the 40 m LIGO prototype at Caltech is consistent with the noise data.
These results are complemented by results for a different type of coating,
presented in a companion paper.Comment: Submitted to LSC (internal) review Sept. 20, 2001. To be submitted to
Phys. Lett.
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Electrooptic electric field sensor for dc and extra-low-frequency measurement
This thesis was submitted for the degree of Doctor of Philosophy and awarded by Brunel University.The thesis reports the results of the research carried out towards the development of an electrooptic sensor for DC and extra low frequency electric field measurement. Available cubic electrooptic crystals were compared from the sensor sensitivity point of view. A new figure of merit was used taking into account the attenuation of the electric field in the dielectric crystal and its shape. The effect of optical activity in 23 cubic crystals was analyzed using the concept of Poincare sphere. The cubic crystals were further characterised for the charge relaxation time constant to estimate their performance in DC field measurements. Crystals of Bismuth Germanate and Lithium Niobate were identified as suitable materials for the DC field sensor. The selected crystals were found suitable at extra-low-frequencies. DC field measurements, without the rotation of the crystal, were possible only with Lithium Niobate. However, its performance was influenced to a great extent by the effect of stimulated conductivity. The quarter-wave plate and the crystal of Lithium Niobate were identified as the main sources of temperature instability. A new method of temperature compensation of the quarter-wave plate is proposed. Due to the temperature instability of Lithium Niobate, mainly attributed to the pyroelectric effect and natural birefringence, it is difficult to use the sensor in practical applications. The performance of the sensor is significantly affected by the presence of an external space charge. The proposed method of its elimination using an artificial extension of the sensing element did not reduce the space charge effect adequately. The response of the sensor in a space charge environment was found to be linear and independent of the space charge density. This enabled measurements of static fields in a unipolar environment. The direct field measurements in bipolar environment suffered from a drift which is intolerable in practical measurements. The minimum detectable electric field of this sensor in the frequency range from 1 to 200Hz was 1V/m, with a signal to noise ratio equal to 0dB and a resolution of 1V/m. The static field measurements were limited to measurements of pulses with a duration of 200s, due to a long term drift of photodetectors. The minimum detectable level of DC electric field was 2.4kV/m.EPSR
Design and characterization of 90 GHz feedhorn-coupled TES polarimeter pixels in the SPTpol camera
The SPTpol camera is a two-color, polarization-sensitive bolometer receiver,
and was installed on the 10 meter South Pole Telescope in January 2012. SPTpol
is designed to study the faint polarization signals in the Cosmic Microwave
Background, with two primary scientific goals. One is to constrain the
tensor-to-scalar ratio of perturbations in the primordial plasma, and thus
constrain the space of permissible inflationary models. The other is to measure
the weak lensing effect of large-scale structure on CMB polarization, which can
be used to constrain the sum of neutrino masses as well as other growth-related
parameters. The SPTpol focal plane consists of seven 84-element monolithic
arrays of 150 GHz pixels (588 total) and 180 individual 90 GHz single-pixel
modules. In this paper we present the design and characterization of the 90 GHz
modules
Non-invasive detection of animal nerve impulses with an atomic magnetometer operating near quantum limited sensitivity
Magnetic fields generated by human and animal organs, such as the heart,
brain and nervous system carry information useful for biological and medical
purposes. These magnetic fields are most commonly detected using
cryogenically-cooled superconducting magnetometers. Here we present the frst
detection of action potentials from an animal nerve using an optical atomic
magnetometer. Using an optimal design we are able to achieve the sensitivity
dominated by the quantum shot noise of light and quantum projection noise of
atomic spins. Such sensitivity allows us to measure the nerve impulse with a
miniature room-temperature sensor which is a critical advantage for biomedical
applications. Positioning the sensor at a distance of a few millimeters from
the nerve, corresponding to the distance between the skin and nerves in
biological studies, we detect the magnetic field generated by an action
potential of a frog sciatic nerve. From the magnetic field measurements we
determine the activity of the nerve and the temporal shape of the nerve
impulse. This work opens new ways towards implementing optical magnetometers as
practical devices for medical diagnostics.Comment: Main text with figures, and methods and supplementary informatio
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