18 research outputs found
Digital Holography at Shot Noise Level
By a proper arrangement of a digital holography setup, that combines off-axis
geometry with phase-shifting recording conditions, it is possible to reach the
theoretical shot noise limit, in real-time experiments.We studied this limit,
and we show that it corresponds to 1 photo-electron per pixel within the whole
frame sequence that is used to reconstruct the holographic image. We also show
that Monte Carlo noise synthesis onto holograms measured at high illumination
levels enables accurate representation of the experimental holograms measured
at very weak illumination levels. An experimental validation of these results
is done
Exploring shot noise and Laser Doppler imagery with heterodyne holography
Heterodyne Holography is a variant of Digital Holography, where the optical
frequencies of signal and reference arms can be freely adjusted by
acousto-optic modulators. Heterodyne Holography is an extremely versatile and
reliable holographic technique, which is able the reach the shot noise limit in
sensitivity at very low levels of signal. Frequency tuning enables Heterodyne
Holography to become a Laser Doppler imaging technique that is able to analyze
various kinds of motion.Comment: Information Optics (WIO), 2010 9th Euro-American Workshop on,
Helsinki : Finland (2010
Three dimensional tracking of gold nanoparticles using digital holographic microscopy
In this paper we present a digital holographic microscope to track gold
colloids in three dimensions. We report observations of 100nm gold particles in
motion in water. The expected signal and the chosen method of reconstruction
are described. We also discuss about how to implement the numerical calculation
to reach real-time 3D tracking
Imaging velocities of a vibrating object by stroboscopic sideband holography
We propose here to combine sideband holography with stroboscopic illumination
synchronized with the vibration of an object. By sweeping the optical frequency
of the reference beam such a way the holographic detection is tuned on the
successive sideband harmonic ranks, we are able to image the instantaneous
velocities of the object. Since the stroboscopic illumination is made with an
electronic device, the method is compatible with fast (up to several MHz)
vibration motions. The method is demonstrated with a vibrating clarinet reed
excited sinusoidally at 2 kHz, and a stroboscopic illumination with cyclic
ratio 0.15. Harmonic rank up to n = 100 are detected, and a movie of the
instantaneous velocities is reported
Holographic microscopy for the three-dimensional exploration of light scattering from gold nanomarkers in biological media
The 3D structure of light scattering from dark-field illuminated live 3T3
cells marked with 40 nm gold nanomarkers is explored. For this purpose, we use
a high resolution holographic microscope combining the off-axis heterodyne
geometry and the phase-shifting acquisition of the digital holograms. Images
are obtained using a novel 3D reconstruction method providing longitudinally
undistorted 3D images. A comparative study of the 3D reconstructions of the
scattered fields allows us to locate the gold markers which yield, contrarily
to the cellular structures, well defined bright scattering patterns that are
not angularly titled and clearly located along the optical axis. This
characterization is an unambiguous signature of the presence of the gold
biological nanomarkers, and validates the capability of digital holographic
microscopy to discriminate them from background signals in live cells
Two-step distortion-free reconstruction scheme for holographic microscopy
We propose a three-dimensional holographic reconstruction procedure
applicable with no a priori knowledge about the recording conditions enabling
distortion-free three-dimensional object reconstruction
Coherent microscopy by laser optical feedback imaging (LOFI) technique
The application of the non conventional imaging technique LOFI (Laser Optical
Feedback Imaging) to coherent microscopy is presented. This simple and
efficient technique using frequency-shifted optical feedback needs the sample
to be scanned in order to obtain an image. The effects on magnitude and phase
signals such as vignetting and field curvature occasioned by the scanning with
galvanometric mirrors are discussed. A simple monitoring method based on phase
images is proposed to find the optimal position of the scanner. Finally, some
experimental results illustrating this technique are presented
Vibration motions studied by Heterodyne Holography
Playing with amplitude, phase and frequency of both reference and signal
arms, heterodyne holography is well adapted to vibration analysis. Vibration
sidebands can be imaged and stroboscopic measurement sensitive to mechanical
phase can be mad
Upconversion nanoparticles as intracellular pH messengers
Abstract: Upconversion nanoparticles (UCNPs) should be particularly well suited for measurement inside cells because they can be imaged down to submicrometer dimensions in near real time using fluorescence microscopy, and they overcome problems, such as photobleaching, autofluorescence, and deep tissue penetration, that are commonly encountered in cellular imaging applications. In this study, the performance of an UCNP modified with a pH-sensitive dye (pHAb) is studied. The dye (emission wavelength 580 nm) was attached in a polyethylene imine (PEI) coating on the UCNP and excited via the 540-nm UCNP emission under 980-nm excitation. The UC resonance energy transfer efficiencies at different pHs ranged from 25 to 30% and a Förster distance of 2.56 nm was predicted from these results. Human neuroblastoma SH-SY5Y cells, equilibrated with nigericin H+/K+ ionophore to equalize the intra- and extracellular pH‚ showed uptake of the UCNP-pHAb conjugate particles and, taking the ratio of the intensity collected from the pHAb emission channel (565–630 nm) to that from the UCNP red emission channel (640–680 nm), produced a sigmoidal pH response curve with an apparent pKa for the UCNP-pHAb of ~ 5.1. The UCNP-pHAb were shown to colocalize with LysoBrite dye, a lysosome marker. Drug inhibitors such as chlorpromazine (CPZ) and nystatin (NYS) that interfere with clathrin-mediated endocytosis and caveolae-mediated endocytosis, respectively, were investigated to elucidate the mechanism of nanoparticle uptake into the cell. This preliminary study suggests that pH indicator–modified UCNPs such as UCNP-pHAb can report pH in SH-SY5Y cells and that the incorporation of the nanoparticles into the cell occurs via clathrin-mediated endocytosis. Graphical abstrac