Three-Dimensional Laser Creation of a Near-IR Laser-Gain Medium Based on Hydride Donor/Acceptor Complexes Made of Coupled Laser-Induced Silver Nanoclusters with Ytterbium Ions.

Femtosecond laser inscription in a ytterbium-doped silver-containing phosphate glass is demonstrated by achieving 3D highly localized laser-induced silver photochemistry. The produced fluorescent silver nanoclusters lead to high optical contrast in the visible range, showing that the coinsertion of Yb ions is not detrimental to the silver-based photochemistry. We demonstrate efficient energy transfer from these silver nanoclusters to the rare-earth Yb ions, leading to near-IR background-free fluorescence emission.

Demonstration of Type A volume Bragg gratings inscribed with a femtosecond Gaussian-Bessel laser beam.

To our knowledge, we report on the first demonstration of Type A VBGs inscribed in silver-containing phosphate glasses by femtosecond laser writing. The gratings are inscribed plane-by-plane by scanning the voxel of a 1030 nm Gaussian-Bessel inscription beam. This results in a refractive-index modification zone, induced by the appearance of silver clusters, extending over a much larger depth than those obtained with standard Gaussian beams.

Individual design of aberration-free intraocular lenses.

An analytical tool capable of easily calculating a new aspheric intraocular lens (IOL) (shape factor, aspherization) chosen to be designed as "aberration free" in terms of spherical aberration and/or coma is reported. In terms of retinal image quality, the theoretical performances given by the new proposed IOLs compare well with commercial IOLs.

Direct-laser-written integrated mid-IR directional couplers in a BGG glass.

The development of coherent sources and other optical components for the mid-infrared has been hampered by the lack of sturdy materials that can withstand high power radiation or exposition to harsh environment. BGG glasses are robust materials transmitting over the 2.5-5 μm region.

Five-Dimensional Optical Data Storage Based on Ellipse Orientation and Fluorescence Intensity in a Silver-Sensitized Commercial Glass.

Five-dimensional (5D) recording and decoding is demonstrated by using femtosecond direct laser writing in a silver-containing commercial glass. In particular, laser intensities and ellipse orientations generated by anamorphic focusing are employed to produce 5D data storage unit (3D for XYZ, 1D for the orientation of the elliptically-shaped data storage unit and 1D for its fluorescence intensity). In the recording process, two different images of a 4-bit bitmap format were simultaneously embedded in the medium by multiplexing the elliptical orientation of the laser focus and its intensity so as to access oriented elliptical patterns with independent fluorescence intensity.

Analytical solution of a personalized intraocular lens design for the correction of spherical aberration and coma of a pseudophakic eye.

This manuscript reports on a closed-form solution determining the personalized required shape of a new intraocular lens able to remove spherical aberration and coma of a pseudophakic eye. The proposed analytical method, within the framework of the Seidel theory of third-order optical aberrations, considers corneal conicities, fourth-order aspheric surface of the intraocular optics, pupil-shift effect and ocular kappa angle.

Femtosecond laser writing of near-surface waveguides for refractive-index sensing.

Femtosecond laser writing of optical waveguides and components in glasses has been a remarkably growing research field during the last two decades. However, such laser- inscribed optical components were mostly written within the volume of the glass due to the unavoidable ablation that arises when the focal spot is approaching the glass surface. This has generally limited the interaction of light with the surrounding medium thus preventing sensing functionality.

Ultrashort laser induced spatial redistribution of silver species and nano-patterning of etching selectivity in silver-containing glasses.

Femtosecond laser-induced spatial redistribution of silver species (ions, clusters, and hole centers) in a silver-containing phosphate glass is investigated by correlative means of near-field scanning optical microscopy (NSOM) images, numerical simulations, chemical micro-probe analysis, and nanoscale spatial profiles after soft etching. In particular, we found that the chemical etching selectivity for nanoscale patterning is strongly dependent upon the irradiation of femtosecond laser due to the spatial redistribution of silver species within the affected area. These results strongly indicate that controlling the distribution of silver species by femtosecond laser irradiation may open new routes for surface nanoscale chemical and/or spatial patterning for the fabrication of 2D surface photonic crystals.

Direct laser writing of a new type of waveguides in silver containing glasses.

Direct laser writing in glasses is a growing field of research in photonics since it provides a robust and efficient way to directly address 3D material structuring. Generally, direct laser writing in glasses induces physical modifications such as refractive index changes that have been classified under three different types (Type I, II & III). In a silver-containing zinc phosphate glass, direct laser writing additionally proceeds via the formation of silver clusters at the periphery of the interaction voxel.

Sub-diffraction-limited fluorescent patterns by tightly focusing polarized femtosecond vortex beams in a silver-containing glass.

We report that the shape and size of fluorescent patterns can be controlled by the focused laser intensity distribution, which depends on irradiation conditions as well as on the spin and orbital angular momenta being carried by light, inducing the formation of silver cluster patterns in a silver-containing zinc phosphate glass. In particular, we demonstrate that sub-diffraction-limited inner structures of fluorescent patterns can be generated by direct laser writing (DLW) with tightly focused femtosecond laser vortex beams as Laguerre-Gauss modes (LG0l) with linear and left-handed circular polarizations. We believe this technique, further combined with dual-color DLW, can be useful and powerful for developing structured light enabled nanostructures.

Laser writing of nonlinear optical properties in silver-doped phosphate glass.

The formation of both local second- and third-harmonic generations (SHG and THG) induced by a train of femtosecond laser pulses in silver-doped phosphate glasses is addressed. Based on modeling calculations, including various diffusion and kinetic processes, THG is shown to result from the formation of silver clusters. The latter organize into a ring-shape structure, leading to the emergence of a static electric field.

Dual-color control and inhibition of direct laser writing in silver-containing phosphate glasses.

We report on dual-color control of femtosecond direct laser writing (DLW) in a noncommercial silver-containing zinc phosphate glass, thanks to an additional illumination with a cw (continuous wave) UV laser, either after the femtosecond irradiation or simultaneously. By tuning the cw UV power, we demonstrate the tunable control and inhibition of the production efficiency of laser-induced fluorescent silver clusters, leading up to 100% inhibition for simultaneous co-illumination when the laser writing is performed close enough to the permanent structuring threshold. The role of the cw UV illumination is discussed in terms of inhibition of the silver cluster precursors or of dissolution of the laser-induced silver clusters.

Patterning linear and nonlinear optical properties of photosensitive glasses by femtosecond structured light.

We report on structured light-induced femtosecond direct laser writing (DLW) under tight focusing in non-commercial silver-containing zinc phosphate glass, which leads to original patterns of fluorescent silver clusters. These fluorescence topologies show unique features of frustrated diffusion of charged species, giving rise to distorted silver cluster spatial distributions. Fluorescence and second harmonic generation correlative microscopy demonstrate the realization of structured light-induced direct laser poling, resulting from a laser-induced permanent and stable electric field buried inside the modified glass.

Laser action along and near the optic axis of a holmium-doped KY(WO₄)₂ crystal.

We demonstrate the first (to our knowledge) quasi-three-level conical refraction laser operating at 2 μm, with 1.6 W of output power at 2074 nm, using a holmium-doped KY(WO4)2 crystal. A maximum slope efficiency of 52% has been achieved, along the optic axis with respect to the absorbed pump power.

Chemometrics applied to quantitative analysis of ternary mixtures by terahertz spectroscopy.

Chemometrics was applied to qualitative and quantitative analyses of terahertz spectra obtained in transmission mode. A series of mixtures of three pure analytes, namely, citric acid, D-(-)fructose, and α-lactose monohydrate under various concentrations, was prepared as pressed pellets with polyethylene as binder. Then, terahertz absorbance spectra were recorded by terahertz time domain spectroscopy and analyzed.

Examination of femtosecond laser matter interaction in multipulse regime for surface nanopatterning of vitreous substrates.

The paper presents our results on laser micro- and nanostructuring of sodium aluminosilicate glass for the permanent storage purposes and photonics applications. Surface structuring is realized by fs laser irradiation followed by the subsequent etching in a potassium hydroxide (10M@80 °C) for 1 to 10 minutes. As the energy deposited is lower than the damage and/or ablation threshold, the chemical etching permits to produce small craters in the laser modified region.

Two-photon excited fluorescence in the LYB:Eu monoclinic crystal: towards a new scheme of single-beam dual-voxel direct laser writing in crystals.

We report on two-photon excited fluorescence in the oriented Eu(3+)doped LYB monoclinic crystal under femtosecond laser tight focusing. Due to spatial walk-off, the two polarization modes of the incident femtosecond beam simultaneously provide the independent excitation of two distinct focuses, leading to a single-beam dual-voxel nonlinear excitation of fluorescence below material modification threshold. These observations emphasize on the anisotropy of both two-photon absorption as well as fluorescence emission.

Three-dimensional direct femtosecond laser writing of second-order nonlinearities in glass.

We demonstrate that direct femtosecond laser writing in silver-containing zinc and gallium phosphate glass enables generation of three-dimensional (3D) optical second-order nonlinear microstructures having an χ(2) value about 2.5 times that of quartz. The proposed physical model involves photo-reduction, photo-dissociation, and migration of silver species within the glass matrix.

Propagation beam consideration for 3D THz computed tomography.

In this paper, a model of the beam propagation is developed according to the physical properties of THz waves used in THz computed tomography (CT) scan imaging. This model is first included in an acquisition simulator to observe and estimate the impact of the Gaussian beam intensity profile on the projection sets. Second, the model is introduced in several inversion methods as a convolution filter to perform efficient tomographic reconstructions of simulated and real acquired objects.

In situ semi-quantitative analysis of polluted soils by laser-induced breakdown spectroscopy (LIBS).

Time-saving, low-cost analyses of soil contamination are required to ensure fast and efficient pollution removal and remedial operations. In this work, laser-induced breakdown spectroscopy (LIBS) has been successfully applied to in situ analyses of polluted soils, providing direct semi-quantitative information about the extent of pollution. A field campaign has been carried out in Brittany (France) on a site presenting high levels of heavy metal concentrations.

Cross-correlation technique for dispersion characterization of chirped volume Bragg gratings.

We propose using cross-correlation frequency-resolved optical gating for dispersion characterization of optical elements with high dispersion, such as ultrashort pulse stretchers and compressors. The technique is based on spectrally resolved second-order cross correlation (sum frequency generation) of a stretched pulse with a reference short pulse. Dispersion of optical elements with a high pulse stretching ratio can be completely characterized using this method, even with moderate resolution of spectral measurements of the cross-correlation signal.

Ultrashort laser pulse diffraction by transmitting volume Bragg gratings in photo-thermo-refractive glass.

We report on the characteristics of ultrashort laser pulse diffraction by transmitting volume Bragg gratings recorded in photo-thermo-refractive glass. The angular and spectral selectivity properties of these phase volume gratings are shown to obey the predictions of a modified Kogelnik's coupled wave analysis that accounts for polychromatic beams. Spatio-temporal distortions such as angular dispersion and pulse front tilt that occur after diffraction by a single volume grating are studied and corrected by using a volume grating pair.

Beat the diffraction limit in 3D direct laser writing in photosensitive glass.

Three-dimensional (3D) femtosecond laser direct structuring in transparent materials is widely used for photonic applications. However, the structure size is limited by the optical diffraction. Here we report on a direct laser writing technique that produces subwavelength nanostructures independently of the experimental limiting factors.