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International audience; We report on the mechanical excitation of a 220 μm thick thermoplastic film in its amorphous state by the radiation pressure of light. By modulating a low power visible laser (from 100 to 600 mW) at low frequencies (below 100 Hz), we observe a deformation of the film interfaces. The phenomenon, that is independent of the laser wavelength, is amplified at a resonant frequency and reaches 0.68 μm. The deformation is reversible and varies linearly with the optical power. Using the damped oscillator model, we show that the resonant frequency depends on the surface tension of the film. The associated free energy is then compared with the energy lost, taking into account the contribution of the damping corresponding to the imaginary part of the Young's modulus.

Generation of subwavelength beam sizes is a fascinating challenge with several implications. The observation of a 120 nm laser spot in the visible part of the spectrum is reported here. It has a size variation of less than 10% in a distance of 50 µ m along the axis of propagation. This so-called Arago spot results from the diffraction of the light from a laser diode by the edges of an absorbing disk. Applications are discussed and hollow beams carrying orbital angular momentum with a 400 nm diameter dark spot in the center are evidenced. This paves the way toward atom lithography via atom guiding or new spectroscopy on forbidden transitions.

International audience; We report on the trapping of micrometer colloids using the evanescent wave from a multimode cylindrical optical waveguide. We show that the particle trapping is a two step process. With a low power visible laser injected in the device, particles are first captured at a radial distance twice greater than the diameter of the waveguide and then drawn near to it. In a second time particles turn around the waveguide and get trapped in a direction corresponding to the TM polarization of the laser. Such a device could be easily implemented in microfluidic systems in order to coat surfaces or to control particles deposition and assembly. Conversely, it could find applications in filtration process to aggregate and remove colloidal pollutants.

International audience; 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 arm 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.

International audience; We present a novel way to generate waves bearing Orbital Angular Momentum (OAM) in a circular waveguide by using two monopole antennas. The OAM mode l = 1 is generated by a combination of the classical TM01 and TE21 modes of the circular waveguide. Two printed monopole antennas are used to create these two modes. The design procedure of this novel "OAM antenna" is presented. The resulting electrical field distribution and the radiation and phase patterns evidence the properties of waves bearing OAM. Index Terms-orbital angular momentum, circular waveguide, monopole antenna.

Most of the vibrating mechanisms of optofluidic systems are based on local heating of membranes that induces liquid flow.We report here a new type of diaphragm pump in a liquid film based on the optical radiation pressure force. We modulate a low power laser that generates, at resonance, a symmetric vibration of a free standing soap film. The film lifetime strongly varies from 56 s at low power (2 mW) to 2 s at higher power (70 mW). Since the laser beam only acts mechanically on the interfaces, such a pump could be easily implemented on delicate microequipment on chips or in biological systems.

International audience; The ability to optically rotate bodies offers new degrees of control of micro-objects with applications in various domains including micro-electromechanical-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.

International audience; The design of two new horn antennas for the generation of radio waves bearing orbital angular momentum (OAM) is presented. The OAM mode = 1 or -1 is generated by combining the guided modes of a circular waveguide with a spiral phase plate. The authors present here two structures to generate OAM wave based on TE11 and TM01 modes. The resulting magnitude and phase patterns of the electrical field and the radiation patterns evidence the presence of waves carrying OAM.

International audience; We present a novel way to generate radio waves bearing Orbital Angular Momentum (OAM) in the horn antenna by using a circular metallic waveguide. The OAM mode ℓ = 1 is generated by combination of two TE21 modes inside a circular metallic waveguide. The resulting electrical field distribution and the radiation patterns evidence the properties of waves carrying OAM. The influences of the horn structure on the properties of the generated OAM waves are also studied. © 2015 IEEE.

International audience; We report on the vibration of a thin soap film based on the optical radiation pressure force. The modulated low power laser induces a counter gravity flow in a vertical free standing draining film. The thickness of the soap film is then higher in the upper region than in the lower region of the film. Moreover, the lifetime of the film is dramatically increased by a factor of 2. Since the laser beam only acts mechanically on the film interfaces, such a film can be implemented in an optofluidic diaphragm pump, the interfaces behaving like a vibrating membrane and the liquid in-between being the fluid to be pumped. Such a pump could then be used in delicate micro-equipment, in chips where temperature variations are detrimental and even in biological systems.

The dynamics of a solid-state laser sustaining the oscillation of two orthogonally polarized eigenstates and passively Q switched by a ${\mathrm{Cr}}^{4+}:\mathrm{Y}\mathrm{A}\mathrm{G}$ (YAG denotes yttrium aluminum garnet) saturable absorber is experimentally investigated. A set of rate equations in which the orientation-dependent interactions between the intensities and the saturable absorber have been taken into account is developed to describe theoretically the evolution of such a laser. When a [001]-cut ${\mathrm{Cr}}^{4+}:\mathrm{Y}\mathrm{A}\mathrm{G}$ plate is used, orthogonally polarized pulsed eigenstates are emitted either successively or simultaneously, depending on the orientations of the eigenstates with respect to the crystallographic axes. Namely, in the latter case, beat note carrying pulses are emitted, whose beat frequency is continuously tunable. On the other hand, when a [111]-cut ${\mathrm{Cr}}^{4+}:\mathrm{Y}\mathrm{A}\mathrm{G}$ plate is used, the simultaneity regime is never observed. All experimental results, obtained using a diode pumped Nd:YAG laser, are well confirmed by the theoretical model.

The fundamental linewidth of usual lasers containing linear phase and loss anisotropies is experimentally and theoretically investigated. It is proved that the eigenstates of such lasers are in general nonorthogonal, leading to the prediction of an important excess noise factor. The experiment evidences an enhancement of the Schawlow-Townes linewidth up to a factor of nearly one hundred, in good agreement with theory.

The excess noise factor due to the nonorthogonality of the transverse modes of a geometrically stable cavity subject to large diffraction losses is measured. This transverse excess noise factor is isolated from other sources of modification of the laser linewidth due to a differential measurement method, leading to the experimental evidence of values as large as 13 in cylindrical symmetry. Moreover, it is shown experimentally that the introduction of a well-chosen second diffracting aperture inside the cavity permits one to drastically reduce the overall laser excess noise factor, without altering the laser losses and intracavity power.

Laser light is injected in a free standing horizontal draining soap film through the glass frame sustaining the film. Two propagation regimes are clearly identified depending on the film thickness. At the beginning of the drainage, the soap film behaves as a multimode-one dimensional optofiuidic waveguide. In particular, we observe that the injected light creates a bottleneck in the film and part of the injected light is refracted leading to whiskers. At the end of the drainage where the film thickness is below 1μm, there is a strong selection among the various possible optical modes in the film, and part of the light is defiected. This leads to a self selection of the mode propagation inside the film.

International audience; 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.

The design of an ‘orbital angular momentum (OAM) antenna’ based on an original phase shifter and power divider combination at 2.5 GHz is presented. A prototype is manufactured and characterised based on return loss, radiation and phase patterns. Both simulation and experimental results evidence the properties of waves carrying OAM. This OAM antenna is simple, compact and easy to realise, which makes it suitable for radio communications and radar applications.

International audience; We report on the deformation of an air-water surface with a totally reflected low-power laser beam, inducing a convex mirror effect on the beam propagation. This bending is stronger close to the critical angle and depends on the polarization of the laser light. A model, leading to a simple dependence between the Goos-Hänchen shift and the radius of curvature of the interface, supports these observations. Bendings with radius of curvature as low as 0.10 m are demonstrated.

We predict the existence of a new pulsed-laser operation regime, when the phases and polarizations of the two coupled cold-cavity eigenstates of a monomode solid-state laser are taken into account in the derivation of the Maxwell-Bloch equations. This monomode pulsed regime is experimentally observed, without any normal mode locking or Q switching occurring inside the cavity. We obtain close agreement between experiments and theory, even in the simple case of a Nd:YAG microchip laser, for which sech(2) pulses at nearly megahertz repetition rates are readily observed.

The 3.51 μm 3He–136Xe laser shows promise for applications to mean field magnetometry. A careful analysis of the locking mechanisms is performed and experimentally verified. The high gain of the transition and the high mass of the 136Xe atom permits one to increase the magnetometer scale factor by a factor of 3 compared with 20Ne. Moreover, in the general case, the width of the locking region is divided by the same factor.

We built a compact two-tunable-frequency longitudinally pumped solid-state laser specially designed to measure atomic lifetimes. Weak coupling between the laser eigenstates permits the obtaining of a continuously tunable frequency difference between 0 and 10 GHz. Such a source provides either a linear polarization rotating at such frequencies, or a sinusoidally modulated intensity with a 100% modulation amplitude. As an example, the fluorescence lifetime of the first excited state of Cr4+ in YAG is measured in the zero-fluence limit using a two-frequency Nd:YAG laser at 1064 nm.

Two-frequency solid-state lasers are shown to provide beat notes at microwave frequencies with continuous tunability, high spectral purity and 100% modulation depth. Owing to an intra-cavity birefringent crystal providing both electro- and thermo-optic properties, the laser delivers a beat frequency that is both voltage- and temperature-controlled. First, a dual phase-locked loop is experimentally demonstrated to stabilize a two-frequency solid-state laser against a RF synthesizer, resulting in a linewidth of 25 mHz. Second, we show that pump-power modulation can lead to a new two-frequency pulsed operation with pulse-to-pulse RF coherence. Third, a specially designed two-frequency composite Er-Yb:glass-LiTaO/sub 3/ microchip laser is shown to provide a beat note up to 100 GHz with continuous tunability. Applications of these lasers to local oscillators in microwave-photonic systems and to lidar-radars are discussed.

Summary form only given.These results show that the use of forked eigenstates permits to continuously control the behavior of passively Q-switched Nd:YAG lasers, passing from a short pulse behavior to longer pulse operation and finally to cw regime.

Two-frequency solid-state lasers are shown to provide beat notes at frequencies from dc to the THz range with continuous tunability, high spectral purity and 100% modulation depth. Depending on the desired range, one- and two-axis cavities are built. Applications of such lasers as a local oscillator in radio-over-fiber communication systems or as a quasi-absolute tunable frequency source for highly-dense wavelength division multiplexed networks are emphasized.

The continuous-wave oscillation of a tunnel ring fiber laser is demonstrated. The high losses encountered in tunneling systems are compensated for by a high-gain amplifying medium from barrier widths for 0 to lambda/2. The experimental observations are in good agreement with a simple theoretical model. This near-field probe system allows one to detect small displacements in the picometer range.

The relaxation of a geometrically unstable Fabry-Perot cavity is theoretically and experimentally investigated. It is observed that the usual sum of the exponential decays of the intensities in the different transverse modes of the cavity is replaced by a more complex behavior. In particular, light couplings into the fundamental mode of the cavity with initial wave excitation factors larger than unity, i.e., larger than in the case of mode-matched injection, are directly observed. The influence of the cavity Fresnel number and of transverse mode crossings and anticrossings on these cavity decays is isolated.

It is shown experimentally that one can image an object embedded in a turbid medium by probing the medium with light with a rotating linear polarization. This method permits the ballistic photons to be isolated from the large background of photons that have been multiply scattered by optically dense anisotropic scatterers. This technique achieves a good signal-to-noise ratio even with a low-power continuous laser, leading to images with a diffraction-limited resolution comparable with that obtained in optically homogeneous media.

Summary form only given. Radio-on-fiber applications require the use of local oscillators in the GHz range carried by an optical frequency. Such a GHz modulation can be directly created by the beat note of the two eigenstates of the laser. Usually lasers are designed to oscillate in a single state of polarization. However, in the general case, a laser exhibits two polarization eigenstates. Here we make use of these two eigenstates to build lasers emitting two frequencies. The generated beat note lies in the GHz range in the case of single-axis lasers and can reach THz frequencies by using two-axis cavities.