102 research outputs found
Singular value demodulation of phase-shifted holograms
We report on phase-shifted holographic interferogram demodulation by singular
value decomposition. Numerical processing of optically-acquired interferograms
over several modulation periods was performed in two steps : 1- rendering of
off-axis complex-valued holograms by Fresnel transformation of the
interferograms; 2- eigenvalue spectrum assessment of the lag-covariance matrix
of hologram pixels. Experimental results in low-light recording conditions were
compared with demodulation by Fourier analysis, in the presence of random phase
drifts.Comment: 4 pages, 3 figure
Spatiotemporal heterodyne detection
We describe a scheme into which a camera is turned into an efficient tunable
frequency filter of a few Hertz bandwidth in an off-axis, heterodyne optical
mixing configuration, enabling to perform parallel, high-resolution coherent
spectral imaging. This approach is made possible through the combination of a
spatial and temporal modulation of the signal to reject noise contributions.
Experimental data obtained with dynamically scattered light by a suspension of
particles in brownian motion is interpreted
Short-time Fourier transform laser Doppler holography
We report a demonstration of laser Doppler holography at a sustained
acquisition rate of 250 Hz on a 1 Megapixel complementary
metal-oxide-semiconductor (CMOS) sensor array and image display at 10 Hz frame
rate. The holograms are optically acquired in off-axis configuration, with a
frequency-shifted reference beam. Wide-field imaging of optical fluctuations in
a 250 Hz frequency band is achieved by turning time-domain samplings to the
dual domain via short-time temporal Fourier transformation. The measurement
band can be positioned freely within the low radio-frequency spectrum by tuning
the frequency of the reference beam in real-time. Video-rate image rendering is
achieved by streamline image processing with commodity computer graphics
hardware. This experimental scheme is validated by a non-contact vibrometry
experiment
Phase-resolved heterodyne holographic vibrometry with a strobe local oscillator
We report a demonstration of phase-resolved vibrometry, in which out-of-plane
sinusoidal motion is assessed by heterodyne holography. In heterodyne
holography, the beam in the reference channel is an optical local oscillator
(LO). It is frequency-shifted with respect to the illumination beam to enable
frequency conversion within the sensor bandwidth. The proposed scheme
introduces a strobe LO, where the reference beam is frequency-shifted and
modulated in amplitude, to alleviate the issue of phase retrieval. The strobe
LO is both tuned around the first optical modulation side band at the vibration
frequency, and modulated in amplitude to freeze selected mechanical vibration
states sequentially. The phase map of the vibration can then be derived from
the demodulation of successive vibration states
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
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
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
Holographic laser Doppler imaging of pulsatile blood flow
We report on wide-field imaging of pulsatile motion induced by blood flow
using heterodyne holographic interferometry on the thumb of a healthy
volunteer, in real-time. Optical Doppler images were measured with green laser
light by a frequency-shifted Mach-Zehnder interferometer in off-axis
configuration. The recorded optical signal was linked to local instantaneous
out-of-plane motion of the skin at velocities of a few hundreds of microns per
second, and compared to blood pulse monitored by plethysmoraphy during an
occlusion-reperfusion experiment.Comment: 5 pages, 5 figure
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