2,307 research outputs found
Performance analysis of spatial laser speckle contrast implementations
This work presents an analysis of the performances for four different implementations used to compute laser speckle contrast on images. Laser speckle contrast is a widely used imaging technique for biomedical applications. These implementations were tested using synthetic laser speckle patters with different resolutions, speckle sizes, and contrasts. From the applied methods, three implementations are already known in the literature. A new alternative is proposed herein, which relies on two-dimensional convolutions, in order to improve the image processing time without compromising the contrast assessment. The proposed implementation achieves a processing time two orders of magnitude lower than the analytical evaluation. The goal of this technical manuscript is to help the developers and researchers in computing laser speckle contrast images
Imaging With Nature: Compressive Imaging Using a Multiply Scattering Medium
The recent theory of compressive sensing leverages upon the structure of
signals to acquire them with much fewer measurements than was previously
thought necessary, and certainly well below the traditional Nyquist-Shannon
sampling rate. However, most implementations developed to take advantage of
this framework revolve around controlling the measurements with carefully
engineered material or acquisition sequences. Instead, we use the natural
randomness of wave propagation through multiply scattering media as an optimal
and instantaneous compressive imaging mechanism. Waves reflected from an object
are detected after propagation through a well-characterized complex medium.
Each local measurement thus contains global information about the object,
yielding a purely analog compressive sensing method. We experimentally
demonstrate the effectiveness of the proposed approach for optical imaging by
using a 300-micrometer thick layer of white paint as the compressive imaging
device. Scattering media are thus promising candidates for designing efficient
and compact compressive imagers.Comment: 17 pages, 8 figure
Molecular Contrast Optical Coherence Tomography: A Review
This article reviews the current state of research on the use of molecular contrast agents in optical coherence tomography (OCT) imaging techniques. After a brief discussion of the basic principle of OCT and the importance of incorporating molecular contrast agent usage into this imaging modality, we shall present an overview of the different molecular contrast OCT (MCOCT) methods that have been developed thus far. We will then discuss several important practical issues that define the possible range of contrast agent choice, the design criteria for engineered molecular contrast agent and the implementability of a given MCOCT method for clinical or biological applications. We will conclude by outlining a few areas of pursuit that deserve a greater degree of research and development
SLM-based Digital Adaptive Coronagraphy: Current Status and Capabilities
Active coronagraphy is deemed to play a key role for the next generation of
high-contrast instruments, notably in order to deal with large segmented
mirrors that might exhibit time-dependent pupil merit function, caused by
missing or defective segments. To this purpose, we recently introduced a new
technological framework called digital adaptive coronagraphy (DAC), making use
of liquid-crystal spatial light modulators (SLMs) display panels operating as
active focal-plane phase mask coronagraphs. Here, we first review the latest
contrast performance, measured in laboratory conditions with monochromatic
visible light, and describe a few potential pathways to improve SLM
coronagraphic nulling in the future. We then unveil a few unique capabilities
of SLM-based DAC that were recently, or are currently in the process of being,
demonstrated in our laboratory, including NCPA wavefront sensing,
aperture-matched adaptive phase masks, coronagraphic nulling of multiple star
systems, and coherent differential imaging (CDI).Comment: 14 pages, 9 figures, to appear in Proceedings of the SPIE, paper
10706-9
Better 3D Inspection with Structured Illumination Part I: Signal Formation and Precision
For quality control in the factory, 3D-metrology faces increasing demands for
high precision and for more space-bandwidth-speed-product SBSP (number of
3D-points/sec). As a potential solution, we will discuss
Structured-Illumination Microscopy (SIM). We distinguish optically smooth and
rough surfaces and develop a theoretical model of the signal formation for both
surface species. This model is exploited to investigate the physical limits of
the precision and to give rules to optimize the sensor parameters for best
precision or high speed. This knowledge can profitably be combined with fast
scanning strategies, to maximize the SBSP, which will be discussed in paper
part II.Comment: 7 pages, 5 figures, submitted to Applied Optics on April 17, 201
A Demonstration of Wavefront Sensing and Mirror Phasing from the Image Domain
In astronomy and microscopy, distortions in the wavefront affect the dynamic
range of a high contrast imaging system. These aberrations are either imposed
by a turbulent medium such as the atmosphere, by static or thermal aberrations
in the optical path, or by imperfectly phased subapertures in a segmented
mirror. Active and adaptive optics (AO), consisting of a wavefront sensor and a
deformable mirror, are employed to address this problem. Nevertheless, the
non-common-path between the wavefront sensor and the science camera leads to
persistent quasi-static speckles that are difficult to calibrate and which
impose a floor on the image contrast. In this paper we present the first
experimental demonstration of a novel wavefront sensor requiring only a minor
asymmetric obscuration of the pupil, using the science camera itself to detect
high order wavefront errors from the speckle pattern produced. We apply this to
correct errors imposed on a deformable microelectromechanical (MEMS) segmented
mirror in a closed loop, restoring a high quality point spread function (PSF)
and residual wavefront errors of order nm using 1600 nm light, from a
starting point of nm in piston and mrad in tip-tilt. We
recommend this as a method for measuring the non-common-path error in
AO-equipped ground based telescopes, as well as as an approach to phasing
difficult segmented mirrors such as on the \emph{James Webb Space Telescope}
primary and as a future direction for extreme adaptive optics.Comment: 9 pages, 6 figure
SAVI: Synthetic apertures for long-range, subdiffraction-limited visible imaging using Fourier ptychography
Synthetic aperture radar is a well-known technique for improving resolution in radio imaging. Extending these synthetic aperture techniques to the visible light domain is not straightforward because optical receivers cannot measure phase information. We propose to use macroscopic Fourier ptychography (FP) as a practical means of creating a synthetic aperture for visible imaging to achieve subdiffraction-limited resolution. We demonstrate the first working prototype for macroscopic FP in a reflection imaging geometry that is capable of imaging optically rough objects. In addition, a novel image space denoising regularization is introduced during phase retrieval to reduce the effects of speckle and improve perceptual quality of the recovered high-resolution image. Our approach is validated experimentally where the resolution of various diffuse objects is improved sixfold
Interferometric speckle visibility spectroscopy (ISVS) for human cerebral blood flow monitoring
Infrared light scattering methods have been developed and employed to
non-invasively monitor human cerebral blood flow (CBF). However, the number of
reflected photons that interact with the brain is low when detecting blood flow
in deep tissue. To tackle this photon-starved problem, we present and
demonstrate the idea of interferometric speckle visibility spectroscopy (ISVS).
In ISVS, an interferometric detection scheme is used to boost the weak signal
light. The blood flow dynamics are inferred from the speckle statistics of a
single frame speckle pattern. We experimentally demonstrated the improvement of
measurement fidelity by introducing interferometric detection when the signal
photon number is insufficient. We apply the ISVS system to monitor the human
CBF in situations where the light intensity is 100-fold less than that in
common diffuse correlation spectroscopy (DCS) implementations. Due to the large
number of pixels () used to capture light in the ISVS
system, we are able to collect a similar number of photons within one exposure
time as in normal DCS implementations. Our system operates at a sampling rate
of 100 Hz. At the exposure time of 2 ms, the average signal photon electron
number is 0.95 count/pixel, yielding a single pixel interferometric
measurement signal-to-noise ratio (SNR) of 0.97. The total pixels provide an expected overall SNR of 436. We successfully
demonstrate that the ISVS system is able to monitor the human brain pulsatile
blood flow, as well as the blood flow change when a human subject is doing a
breath holding task
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