Tomography of irregular rough particles using the error-reduction algorithm with multi-views interferometric particle imaging.

This work reports the 3D reconstruction of a particle from a set of three simulated interferometric images of this particle (from three perpendicular angles of view). The reconstruction of each view from its corresponding interferometric pattern uses the error-reduction (ER) algorithm. The 3D reconstruction enables an estimation of the volume of the particle. The method is tested on a dendrite-like particle. An experimental demonstration of the technique is done using a digital micromirror device (DMD) that generates the interferometric images of "programmable" rough particles.

Beat note stabilization in dual-polarization DFB fiber lasers by an optical phase-locked loop.

A fully fibered microwave-optical source at 1.5 µm is studied experimentally. It is shown that the beat note between two orthogonally polarized modes of a distributed-feedback fiber laser can be efficiently stabilized using an optical phase-locked loop. The pump-power-induced birefringence serves as the actuator. Beat notes at 1 GHz and 10 GHz are successfully stabilized to a reference synthesizer, passing from the 3 kHz free-running linewidth to a stabilized sub-Hz linewidth, with a phase noise as low as -75 dBc/Hz at 100 Hz offset from the carrier. Such dual-frequency stabilized lasers could provide compact integrated components for RF and microwave photonics applications.

Interferometric particle imaging of ice particles using a multi-view optical system.

Interferometric particle imaging enables particle size estimation in a wide range [from 10 µm to a few millimeters] depending on the optical system design. With a multi-view optical system, it is possible to extract more information about the 3D morphology of the particle. In this study, multi-view interferometric out-of-focus imaging of ice particles is performed in a backward-scattering configuration. It is used to estimate ice particle volume and thus to reduce uncertainty concerning particle size estimation. It is further used to better analyze the presence of nearby particles whose images overlap.

Digital micromirror device as programmable rough particle in interferometric particle imaging.

The 2D autocorrelation of the projection of an irregular rough particle can be estimated using the analysis of its interferometric out-of-focus image. We report the development of an experimental setup that creates speckle-like patterns generated by "programmable" rough particles of desired-shape. It should become an important tool for the development of new setups, configurations, and algorithms in interferometric particle imaging.

Interferometric out-of-focus imaging of ice particles with overlapping images.

It is shown that the size and relative positions of two irregular rough particles can be analyzed using interferometric out-of-focus imaging despite the overlapping of their out-of-focus images. Simulations are confirmed by experiments done with ice particles generated in a freezing column.

3D-shape recognition and size measurement of irregular rough particles using multi-views interferometric out-of-focus imaging.

We realize simplified-tomography experiments on irregular rough particles using interferometric out-of-focus imaging. Using two angles of view, we determine the global 3D-shape, the dimensions, and the 3D-orientation of irregular rough particles whose morphologies belong to families such as sticks, plates, and crosses.

Dual-wavelength digital holography for 3D particle image velocimetry: experimental validation.

A multi-exposure digital in-line hologram of a particle field is recorded by two successive pulses of different wavelengths. During the reconstruction step, each recording can be independently analyzed by selecting a given wavelength. This procedure enables avoiding the superimposition of particle images that may be close to each other.

Simultaneous 3D location and size measurement of bubbles and sand particles in a flow using interferometric particle imaging.

We present a system to characterize a triphasic flow in a 3D volume (air bubbles and solid irregular particles in water) using only one CCD sensor. A cylindrical interferometric out-of-focus imaging setup is used to determine simultaneously the 3D position and the size of bubbles and irregular sand particles in a flow. The 3D position of the particles is deduced from the ellipticity of their out-of-focus image. The size of bubbles is deduced from analysis of interference fringes. The characteristics of irregular sand particles are obtained from analysis of their speckle-like pattern. Experiments are confirmed by simulations.

Measuring the universal synchronization properties of driven oscillators across a Hopf instability.

When a driven oscillator loses phase-locking to a master oscillator via a Hopf bifurcation, it enters a bounded-phase regime in which its average frequency is still equal to the master frequency, but its phase displays temporal oscillations. Here we characterize these two synchronization regimes in a laser experiment, by measuring the spectrum of the phase fluctuations across the bifurcation. We find experimentally, and confirm numerically, that the low frequency phase noise of the driven oscillator is strongly suppressed in both regimes in the same way. Thus the long-term phase stability of the master oscillator is transferred to the driven one, even in the absence of phase-locking. The numerical study of a generic, minimal model suggests that such behavior is universal for any periodically driven oscillator near a Hopf bifurcation point.

Long time exposure digital in-line holography for 3-D particle trajectography.

One advantage of digital in-line holography is the ability for a user to know the 3-D location of a moving particle recorded at a given time. When the time exposure is much larger than the time required for grabbing the particle image at a given location, the diffraction pattern is spread along the trajectory of this particle. This can be seen as a convolution between the diffraction pattern and a blurring function resulting from the motion of the particle during the camera exposure. This article shows that the reconstruction of holograms recorded under such conditions exhibit traces that could be processed for extracting 3D trajectories.

Lidar-radar velocimetry using a pulse-to-pulse coherent rf-modulated Q-switched laser.

An rf-modulated pulse train from a passively Q-switched Nd:YAG laser has been generated using an extra-cavity acousto-optic modulator. The rf modulation reproduces the spectral quality of the local oscillator. It leads to a high pulse-to-pulse phase coherence, i.e., phase memory, over thousands of pulses. The potentialities of this transmitter for lidar-radar are demonstrated by performing Doppler velocimetry on indoor moving targets. The experimental results are in good agreement with a model based on elementary signal processing theory. In particular, we show experimentally and theoretically that lidar-radar is a promising technique that allows discrimination between translation and rotation movements. Being independent of the laser internal dynamics, this scheme can be applied to any Q-switched laser.

Dual-polarization mode-locked Nd:YAG laser.

A mode-locked solid-state laser containing a birefringent element is shown to emit synchronously two frequency combs associated to the two polarization eigenstates of the cavity. An analytical model predicts the polarization evolution of the pulse train, which is determined by the adjustable intracavity birefringence. Experiments realized with a Nd:YAG laser passively mode locked by a semiconductor saturable absorber mirror are in perfect agreement with the model. Locking between the two combs arises for particular values of their frequency difference, e.g., half the repetition rate, and the pulse train polarization sequence is then governed by the relative overall phase offset of the two combs.

Beat note stabilization of a 10-60 GHz dual-polarization microlaser through optical down conversion.

Down-conversion of a high-frequency beat note to an intermediate frequency is realized by a Mach-Zehnder intensity modulator. Optically-carried microwave signals in the 10-60 GHz range are synthesized by using a two-frequency solid-state microchip laser as a voltage-controlled oscillator inside a digital phase-locked loop. We report an in-loop relative frequency stability better than 2.5×10⁻¹¹. The principle is applicable to beat notes in the millimeter-wave range.

Non-linear optoelectronic phase-locked loop for stabilization of opto-millimeter waves: towards a narrow linewidth tunable THz source.

We propose an optoelectronic phase-locked loop concept which enables to stabilize optical beat notes at high frequencies in the mm-wave domain. It relies on the use of a nonlinear-response Mach-Zehnder modulator. This concept is demonstrated at 100 GHz using a two-axis dual-frequency laser turned into a voltage controlled oscillator by means of an intracavity electrooptic crystal. A relative frequency stability better than 10⁻¹¹ is reported. This approach of optoelectronic down conversion opens the way to the realization of continuously tunable ultra-narrow linewidth THz radiation.

Resonance assisted synchronization of coupled oscillators: frequency locking without phase locking.

Frequency locking without phase locking of two coupled nonlinear oscillators is experimentally demonstrated. This synchronization regime is found for two coupled laser modes, beyond the phase-locking range fixed by Adler's equation, because of a resonance mechanism. Specifically, we show that the amplitudes of the two modes exhibit strong fluctuations that produce average frequency synchronization, even if the instantaneous phases are unlocked. The experimental results are in good agreement with a theoretical model.

3D-reconstructions for the estimation of ice particle's volume using a two-views interferometric out-of-focus imaging set-up.

The characterization of ice crystals has important applications in airborne research and civil aviation. Interferometric out-of-focus imaging is a promising technique. We investigate in this study the impact of the 3D shape reconstruction of the particles from a pair of interferometric images on the estimation of the ice particle's volume. An interferometric image gives indeed the 2D autocorrelation of the particle's shape. As different shapes can exhibit a similar 2D autocorrelation, particles of different shapes can have similar interferometric images. In this study, the volume of ice particles is estimated from a pair of interferometric images (with two perpendicular angles of view). The relative error in the particle's volume estimation is shown to be around ΔV V≈30% depending on the choice of the initial 3D particle's shape. It appears that the choice of the shape of the particle for both angles of view has a lower impact on the estimation of the particle's volume than the other sources of errors due to image acquisitions themselves.

Management of colorectal peritoneal metastases: Expert opinion.

When peritoneal metastases are diagnosed (strong agreement of experts): (i) seek advice from a multidisciplinary coordination meeting (MCM) with large experience in peritoneal disease (e.g. BIG RENAPE network); (ii) transfer (or not) the patient to a referral center with experience in hyperthermic intraperitoneal chemotherapy (HIPEC), according to the advice of the MCM. With regard to systemic chemotherapy (strong agreement of experts): (i) it should be performed both before and after surgery, (ii) for no longer than 6 months; (iii) without postoperative anti-angiogenetic drugs. With regard to cytoreductive surgery (strong agreement of experts): (i) Radical surgery requires a xiphopubic midline incision; (ii) no cytoreductive surgery via laparoscopy. With regard to HIPEC: HIPEC can be proposed for trials outside an HIPEC referral center (weak agreement between experts): (i) if surgery is radical; (ii) if the expected morbidity is "reasonable"; (iii) if the indication for HIPEC was suggested by a MCM, and; (iv) mitomycin is preferred to oxaliplatin (which cannot be recommended) for this indication.

Suppression of the Moiré effect in sub-picosecond digital in-line holography.

Digital in-line holography is widely used in flow studies where the 3D position, size and velocity of particles or fibers have to be known at a given time. When holograms are recorded by using a sub-picosecond laser the enlargement of the spectral distribution acts as a spatial low-pass filter over the intensity distribution of the diffraction pattern. This is not a disadvantage as regards to the spatial sampling. Indeed, the Moiré effect, due to the sub-sampling of the fringe pattern is naturally reduced. Experimental results are provided.

Growth kinetics and morphology of snowflakes in supersaturated atmosphere using a three-dimensional phase-field model.

Simulating ice crystal growth is a major issue for meteorology and aircraft safety. Yet, very few models currently succeed in reproducing correctly the diversity of snow crystal forms, and link the model parameters to thermodynamic quantities. Here, we demonstrate that the new three-dimensional phase-field model developed in Demange et al. [npj Comput. Mater. 3, 1 (2017)2057-396010.1038/s41524-017-0015-1] is capable of reproducing properly the morphology and growth kinetics of snowflakes in supersaturated atmosphere. Aside from that, we show that the growth dynamics of snow crystals satisfies the selection theory, consistently with previous experimental observations. Finally, we link the parameters of the phase-field model to atmospheric parameters.

Instrumentation for ice crystal characterization in laboratory using interferometric out-of-focus imaging.

Airborne characterization of ice crystals has important applications. The extreme difficulty of realizing in situ tests requires the development of a complete instrumentation in the laboratory. Such an installation should enable design, development, test, and calibration of instruments in conditions as close as possible to real ones. We present a set of numerical and experimental tools that have been developed to realize ice crystal sensors based on interferometric particle imaging. The set of tools covers the development of complementary simulators for crystal growth and interferometric particle imaging predictions, experimental generation of "programmable" ice crystals, and instrumentation of a freezing column where different techniques as in-focus imaging, out-of-focus imaging, and digital in-line holography can be combined simultaneously for test and calibration.