Olivier Emile

Characterization of an OAM Flat-Plate Antenna in the Millimeter Frequency Band

Electromagnetic waves bearing orbital angular momentum in the radio frequency range is a growing subject of study. The design of systems able to produce and/or to receive such waves is then of crucial importance. The aim of this letter is to characterize, in an anechoic chamber, a new type of antenna in the millimeter frequency band. The index-varying flat plate generates an electromagnetic wave carrying orbital angular momentum. We then extract the various modes from the radiated field.

Swelling of a foam lamella in a confined channel

We study the dynamics of a foam lamella in a confined channel under the influence of a pushing-pulling pressure. Using optical interferometry we evidence an instantaneous swelling described by a velocity power law for different compositions of the foaming solutions. Based on theoretical considerations we show that the phenomena are mainly dominated by surface forces which also contribute to the kinetics of the drainage. Moreover, the frictional force acting on the lamella during motion depends on the velocity leading to two separate sliding regimes.

Young's double-slit interference pattern from a twisted beam

Abstract A wide range of diffractive elements have been used to evaluate the topological charge of Laguerre–Gaussian beams. Here, we show theoretically and experimentally that this charge can be simply and readily measured from the interference pattern in Young’s double-slit experiment. It can be evaluated from the twisting order of the interference. The results are confronted with previously published studies. The potentialities of the method are then compared with existing techniques.

Dark zone in the centre of the Arago-Poisson diffraction spot of a helical laser beam.

We report on the diffraction of non-zero Laguerre Gaussian laser beams by an opaque disk. We observe a tiny circular dark zone at the centre of the usual Arago-Poisson diffraction bright spot. For such non-diffracting dark hollow beams, we have measured diameters as small as 20 μm on distances of the order of ten metres, without focalization. Diameters depend on the diffracting object size and on the topological charge of the input Laguerre Gaussian beam. These results are in good agreement with theoretical considerations. Potential applications are then discussed.

Rotation of millimeter-sized objects using ordinary light

The ability to optically rotate bodies offers new degrees of control of micro-objects with applications in various domains, including microelectromechanical systems (MEMS), biomanipulations, or optofluidics. Here we demonstrate the optically-induced rotation of simple asymmetric two-dimensional objects using plane waves originating either from ordinary laser sources or from black body radiation. The objects are floating on an air/water interface. We observe a steady-state rotation depending on the light intensity and on the asymmetry of the object. We interpret this rotation in terms of light diffraction by the edges of the object. Such systems could be easily implemented in optofluidic devices to induce liquid flow without the need for special light sources.

Experimental investigation of a moving contact line in a channel

The shape of a moving air–liquid interface in a perfect wetting channel has been investigated over a wide range of capillary numbers. The thickness of the film wetting the channel walls, its shape and the dynamic contact angle are extracted using the total reflection of the laser beam on the wetting film–air interface.

Direct observation of a photon spin-induced constant acceleration in macroscopic systems

The use of a spider silk allows the direct observation of the dynamics induced by the transfer of angular momentum of laser light in a Beth-type experiment. In the optical domain, a uniform angular acceleration of a macroscopic object is demonstrated in agreement with the expected equation of motion. The intrinsic angular momentum exerts a stable torque thats modulus can be continuously adjusted from 0to10−12Nm by changing the optical power. Moreover, a macroscopic no-node mirror is proposed to improve the optical angular momentum transfer in micro-manipulation in the context of optical tweezers.

Naked eye picometer resolution in a Michelson interferometer using conjugated twisted beams

Michelson interferometry is one of the most widely used techniques for accuracy measurements. Its main characteristic feature is to infer a displacement in one of the arms of the interferometer from a phase measurement. Two different twisted beams, also called vortex beams, with opposite twisted rotations in each arm of the interferometer interfere in a daisy flower-like pattern. The number of petals is twice the topological charge. Their position depends on the relative phase of the beams. Naked eye detection of 44 pm displacements is achieved. The sensitivity of such an interferometer together with possible further improvements, and applications are then discussed.

Profile of the liquid film wetting a channel

We have developed a simple optical technique to investigate the characteristics of liquid films wetting solid surfaces. To validate this technique, we have studied the wetting film that separates a train of lamellas moving through a channel. Total reflection of the laser beam on the wetting film/air interface is used to extract the profile and the thickness of the wetting film. For quasistatic movement of lamellas, we show that the thickness is well described by a capillary number power law.

Determination of the topological charge of a twisted beam with a Fresnel bi-prism

The self-interference pattern of a Laguerre Gaussian beam using a Fresnel bi-prism is shown to be very different from what could be expected from a usual laser beam. It resembles the interference pattern that could be obtained using a double slit experiment. The interferences are shifted and the topological charge and its sign can be readily determined considering the shift order of the pattern only. However, since there is no diffraction nor absorption losses unlike in a double slit interference, such a set up could be used even for low power twisted beams or beams with high topological charge. Even fractional topological charges could be determined with an absolute precision of 0.05.