3,518 research outputs found
Monitoring spatially heterogeneous dynamics in a drying colloidal thin film
We report on a new type of experiment that enables us to monitor spatially
and temporally heterogeneous dynamic properties in complex fluids. Our approach
is based on the analysis of near-field speckles produced by light diffusely
reflected from the superficial volume of a strongly scattering medium. By
periodic modulation of an incident speckle beam we obtain pixel-wise ensemble
averages of the structure function coefficient, a measure of the dynamic
activity. To illustrate the application of our approach we follow the different
stages in the drying process of a colloidal thin film. We show that we can
access ensemble averaged dynamic properties on length scales as small as ten
micrometers over the full field of view.Comment: To appear in Soft Material
Simultaneous measurement of the microscopic dynamics and the mesoscopic displacement field in soft systems by speckle imaging
The constituents of soft matter systems such as colloidal suspensions,
emulsions, polymers, and biological tissues undergo microscopic random motion,
due to thermal energy. They may also experience drift motion correlated over
mesoscopic or macroscopic length scales, \textit{e.g.} in response to an
internal or applied stress or during flow. We present a new method for
measuring simultaneously both the microscopic motion and the mesoscopic or
macroscopic drift. The method is based on the analysis of spatio-temporal
cross-correlation functions of speckle patterns taken in an imaging
configuration. The method is tested on a translating Brownian suspension and a
sheared colloidal glass
Simultaneous control of volumetric light distribution through turbid media using real-time three-dimensional optoacoustic feedback
Focusing light through turbid media presents a highly fascinating challenge
in modern biophotonics. The unique capability of optoacoustics for high
resolution imaging of light absorption contrast in deep tissues can provide a
natural and efficient feedback to control light delivery in scattering medium.
While basic feasibility of using optoacoustic readings as a feedback mechanism
for wavefront shaping has been recently reported, the suggested approaches may
require long acquisition times making them challenging to be translated into
realistic tissue environments. In an attempt to significantly accelerate
dynamic wavefront shaping capabilities, we present here a feedback-based
approach using real-time three-dimensional optoacoustic imaging assisted with
genetic-algorithm-based optimization. The new technique offers robust
performance in the presence of noisy measurements and can simultaneously
control the scattered wave field in an entire volumetric region.Comment: 4 pages, 3 figure
Four-dimensional dynamic flow measurement by holographic particle image velocimetry
The ultimate goal of holographic particle image velocimetry (HPIV) is to provide space- and time-resolved measurement of complex flows. Recent new understanding of holographic imaging of small particles, pertaining to intrinsic aberration and noise in particular, has enabled us to elucidate fundamental issues in HPIV and implement a new HPIV system. This system is based on our previously reported off-axis HPIV setup, but the design is optimized by incorporating our new insights of holographic particle imaging characteristics. Furthermore, the new system benefits from advanced data processing algorithms and distributed parallel computing technology. Because of its robustness and efficiency, for the first time to our knowledge, the goal of both temporally and spatially resolved flow measurements becomes tangible. We demonstrate its temporal measurement capability by a series of phase-locked dynamic measurements of instantaneous three-dimensional, three-component velocity fields in a highly three-dimensional vortical flow--the flow past a tab
Towards optical intensity interferometry for high angular resolution stellar astrophysics
Most neighboring stars are still detected as point sources and are beyond the
angular resolution reach of current observatories. Methods to improve our
understanding of stars at high angular resolution are investigated. Air
Cherenkov telescopes (ACTs), primarily used for Gamma-ray astronomy, enable us
to increase our understanding of the circumstellar environment of a particular
system. When used as optical intensity interferometers, future ACT arrays will
allow us to detect stars as extended objects and image their surfaces at high
angular resolution.
Optical stellar intensity interferometry (SII) with ACT arrays, composed of
nearly 100 telescopes, will provide means to measure fundamental stellar
parameters and also open the possibility of model-independent imaging. A data
analysis algorithm is developed and permits the reconstruction of high angular
resolution images from simulated SII data. The capabilities and limitations of
future ACT arrays used for high angular resolution imaging are investigated via
Monte-Carlo simulations. Simple stellar objects as well as stellar surfaces
with localized hot or cool regions can be accurately imaged.
Finally, experimental efforts to measure intensity correlations are
expounded. The functionality of analog and digital correlators is demonstrated.
Intensity correlations have been measured for a simulated star emitting
pseudo-thermal light, resulting in angular diameter measurements. The StarBase
observatory, consisting of a pair of 3 m telescopes separated by 23 m, is
described.Comment: PhD dissertatio
Roadmap on optical security
Postprint (author's final draft
Sensors for ceramic components in advanced propulsion systems: Summary of literature survey and concept analysis, task 3 report
The results of a literature survey and concept analysis related to sensing techniques for measuring of surface temperature, strain, and heat flux for (non-specific) ceramic materials exposed to elevated temperatures (to 2200 K) are summarized. Concepts capable of functioning in a gas turbine hot section environment are favored but others are reviewed also. Recommendation are made for sensor development in each of the three areas
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