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International audience; 16.1 Introduction 383 16.2 Physical Issues 384 16.2.1 The Laser Mean Power 385 16.2.2 The Wavelength 385 16.2.3 Pulse Duration and Repetition Rate 385 16.2.4 Spatial Concentration and Beam Shaping 385 16.2.5 Material Response 386 16.3 Recent Technological Advances 387 16.3.1 Femtosecond Laser 387 16.3.2 Nondivergent Subwavelength Beams 388 16.3.3 Subwavelength Focusing of Light with Photonic Nanojet 389 16.3.4 Subwavelength Deposition by LIFT Technique 389 16.4 Laser Microprocesses 392 16.4.1 Material Deposition and Thin-Layer Control 392 16.4.2 Nanoparticle Fabrication 392 16.4.3 Microdrilling 393 16.4.4 Microcutting 393 16.4.5 Laser Microwelding 395 16.4.6 Surface Texturing 396 16.4.7 Additive Manufacturing 397 16.4.8 Waveguide Writing 399 16.5 Conclusions 399 References 40

A nanoscale layer of amorphized silicon is obtained by implantations with silicon ions through a P-doped FZ-silicon wafer material few nanometers below the wafer surface. After a controlled annealing, the amorphized silicon material is sandwiched between two layers of recrystallized silicon. Defects remain at the interface c-Si/a-Si/c-Si. Photoluminescence at very low temperature is experimented to determine the energy levels generated by this design. TEM pictures show that some nanocrystalline elements are located close to the interface surrounded by a-Si. However, the photoluminescence spectra do not present any signal of luminescence from them. This could be due to random sizes of nanocrystals. Then, a scan from energies below the silicon bandgap has been realized at 8 K. The spectrum is composed of multiple narrow peaks close to the conduction band and a broadband from 0.78 eV to 1.05 eV. In order to determine the origin of these signals, spectra of three distinct peaks were collected at different temperatures from 8 K to 120 K. The broadband collapses more rapidly by increasing the temperature than the narrow lines and theirs maxima of intensity differ.

The determination of the physical state of the lubricant materials in complex mechanical systems is highly critical from different points of view: operative, economical, environmental, etc. Furthermore, there are several parameters that a lubricant oil must meet for a proper performance inside a machine. The monitoring of these lubricants can represent a serious issue depending on the analytical approach applied. The molecular change of aging lubricant oils have been analyzed using an all-standard-components and self-designed FT-Raman spectrometer. This analytical tool allows the direct and clean study of the vibrational changes in the molecular structure of the oils without having direct contact with the samples and without extracting the sample from the machine in operation. The FT-Raman spectrometer prototype used in the analysis of the oil samples consist of a Michelson interferometer and a self-designed photon counter cooled down on a Peltier element arrangement. The light coupling has been accomplished by using a conventional 62.5/125μm multi-mode fiber coupler. The FT-Raman arrangement has been able to extract high resolution and frequency precise Raman spectra, comparable to those obtained with commercial FT-Raman systems, from the lubricant oil samples analyzed. The spectral information has helped to determine certain molecular changes in the initial phases of wearing of the oil samples. The proposed instrument prototype has no additional complex hardware components or costly software modules. The mechanical and thermal irregularities influencing the FT-Raman spectrometer have been removed mathematically by accurately evaluating the optical path difference of the Michelson interferometer. This has been achieved by producing an additional interference pattern signal with a λ= 632.8 nm helium-neon laser, which differs from the conventional zero-crossing sampling (also known as Connes advantage) commonly used by FT-devices. It enables the FT-Raman system to perform reliable and clean spectral measurements from the analyzed oil samples.

International audience; We demonstrate that non-paraxial Fourier elements can be designed by an iterative Fourier transform algorithm with the help of a simple projection step. The element designed by this model shows better reconstruction in both spots position and power distribution than the one of the paraxial design and very close to the desired pattern.

The rigorous vector-based simulation methods for subwavelength diffractive lenses are methods of growing importance. In this paper, we introduce a rigorous vector-based method to compute the electromagnetic propagation. It includes the Finite-Difference Time-Domain (FDTD) for the near field simulation, and the Radiation Spectrum Method (RSM) for the far field propagation. This approach is then proposed to design effective medium cylindrical diffractive lenses. This kind of component, made up of binary features that behave as an effective medium, can achieve an higher diffraction efficiency than conventional diffractive optical elements. The layout design of the component is realised thanks to the FDTD simulation by estimating the phase difference introduced by subwavelength binary gratings. Then, the whole modeling of the component, whose minimum feature size can be smaller than 100 nm, is done with the RSM algorithm. Because of their subwavelength, aperiodic, finite and high spatial frequencies characteristics, these devices conception methods prevent the use of scalar modeling or coupled wave theory. The proposed method overcomes these limitations. First, the principle of the rigorous vector-based method is introduced. Then, we present the design of the subwavelength structures by means of the FDTD method, followed by the design of the subwavelength element. Finally, the simulation method of the subwavelength lens by use of the FDTD method for the near field propagation and the RSM for the far field calculation is also presented. Finally, we discuss the comparison between a subwavelength lens and its multilevel counterpart.

International audience; We propose an iterative algorithm based on our scalar non-paraxial propagator for the design of Fourier Diffractive Optical Elements (DOEs) having features on the order of the illumination wavelength. The simulation results show that our algorithm using iterative Fourier transform and iterative projection obtains higher performance DOEs than a purely scalar paraxial design with the same order of calculation time. Upon verification with the experimental results, we find that our scalar-based design method is valid for DOEs with surprisingly small feature sizes (about half the wavelength) and diffraction angles up to about 37°.

International audience; We present a scalar model to overcome the computation time and sampling interval limitations of the traditional Rayleigh-Sommerfeld formula and Angular Spectrum Method in computing wide-angle diffraction in the far-field. Numerical and experimental results show that our proposed method based on an accurate non-paraxial diffraction step onto a hemisphere and a projection onto a plane accurately predicts the observed non-paraxial far-field diffraction pattern, while its calculation time is much lower than the more rigorous Rayleigh-Sommerfeld integral. The results enable a fast and efficient way to compute far-field non-paraxial diffraction where the conventional Fraunhofer pattern fails to predict correctly.