Huanhuan Shen

Interferometric laser imaging for droplet sizing revisited: elaboration of transfer matrix models for the description of complete systems

We report the development of an interferometric laser imaging for droplet sizing (ILIDS) numerical simulator. It is based on the use of generalized Huygens-Fresnel integrals associated to transfer matrices that describe the whole imaging setup. This simulator allows easy simulation of any kind of ILIDS setup. Simulations are shown to be in good agreement with experimental results. This simulator offers important perspectives in the design, realization, and calibration of ILIDS instruments, as airborne instruments, or in situ measurements in flows.

Cylindrical interferometric out-of-focus imaging for the analysis of droplets in a volume

We propose an original cylindrical interferometric out-of-focus imaging setup to realize the characterization of spherical droplets in a volume. The longitudinal position of the droplets is determined through the orientation of the fringes while the diameter of the droplets is obtained from the frequency of the fringes. The experiments agree with the simulations.

Extended ABCD matrix formalism for the description of femtosecond diffraction patterns; application to femtosecond digital in-line holography with anamorphic optical systems

We present a new model to predict diffraction patterns of femtosecond pulses through complex optical systems. The model is based on the extension of an ABCD matrix formalism combined with generalized Huygens-Fresnel transforms (already used in the CW regime) to the femtosecond regime. The model is tested to describe femtosecond digital in-line holography experiments realized in situ through a cylindrical Plexiglas pipe. The model allows us to establish analytical relations that link the holographic reconstruction process to the experimental parameters of the pipe and of the incident beam itself. Simulations and experimental results are in good concordance. Femtosecond digital in-line holography is shown to allow significant coherent noise reduction, and this model will be particularly efficient to describe a wide range of optical geometries. More generally, the model developed can be easily used in any experiment where the knowledge of the precise evolution of femtosecond transverse patterns is required.

Determination of the Size of Irregular Particles Using Interferometric Out-of-Focus Imaging

We present a mathematical formalism to predict speckle-like interferometric out-of-focus patterns created by irregular scattering objects. We describe the objects by an ensemble of Dirac emitters. We show that it is not necessary to describe rigorously the scattering properties of an elliptical irregular object to predict some physical properties of the interferometric out-of-focus pattern. The fit of the central peak of the 2D autocorrelation of the pattern allows the prediction of the size of the scattering element. The method can be applied to particles in a size range from a tenth of micrometers to the millimeter.