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International audience; The structure and crystallization of silver-doped germano-gallate glasses for substitution of potassium for barium ions have been investigated. By means of Raman spectroscopy, a structural study has been carried out revealing a glass network depolymerization with the formation of non-bridging oxygens likely localized on germanium tetrahedra when the barium concentration increases. These structural modifications do not appear to significatively change the silver ion environments or ionic states, as reported on luminescence and optical transmission spectroscopies. A combined differential scanning calorimetry, X-ray diffraction characterization, scanning electron microscopy and micro-luminescence spectroscopy demonstrate that the barium ions introduction tends to stabilize the silver ions and to influence drastically the devitrification and the crystal growth kinetics. Correlations have been established between ionic conductivity, silver distribution and crystal growth mechanisms.

Volume Bragg Gratings (VBG) are inscribed in the bulk of non-conventional photosensitive glasses tailored with silver by means of femtosecond laser irradiation. Thanks to intrinsic features of the spatial distribution of silver-sustained inscribed structures, it is possible to fabricate gratings with sub-wavelength periodic refractive index modulation. As a result, the achieved VBG target first-order Bragg reflection in the VIS - NIR spectral range. This work paves the way to manufacturing more complex optical devices, such as Waveguide Bragg Gratings.

The ability to produce robust fiber-based integrated optical systems operating over a wide spectral domain (UV to mid-infrared), is one of today’s key challenges in photonics. This work reports on the production of crystal-free, light guiding fibers from rich Ga2O3 oxide-based glass compositions. These materials show optical transmission extending from ultraviolet wavelengths (∼0.280 µm) up to 6 µm in the IR for millimeter length scale while exhibiting relatively high vitreous transition temperatures (∼735 °C), nonlinear optical properties and improved surface micro-hardness. This combination of superior thermal, mechanical and optical properties represents a promising alternative for the development of robust fibers operating in the visible up to the 3–5 µm window.

We report on the 3D precipitation, using a direct laser writing approach, of highly fluorescent silver clusters in a Eu3+-doped silver-containing zinc phosphate glass. Micro-spectroscopy of fluorescence emission shows the ability to continuously adjust the local tri-chromatic coordinates in the CIE (Commission Internationale de l’Éclairage) chromaticity diagram between red and white colors, thanks to the laser-deposited dose and resulting tunable combination of emissions from Eu3+ and silver clusters. Moreover, continuous-wave and time-resolved FAST-FLIM spectroscopies showed a significant enhancement of the fluorescence emission of Eu3+ ions while being co-located with UV-excited laser-inscribed silver clusters. These results demonstrate the ability to perform efficient resonant non-radiative energy transfer from excited silver clusters to Eu3+, allowing such energy transfer to be highly localized on demand thanks to laser inscription. Such results open the route to 3D printing of the rare earth ions emission in glass.

We worked on a new scheme of quasi-phase matching (QPM) based on the negative first order of the spatial modulation of the sign of the second-order nonlinearity. Applying this scheme in the case of angular-QPM (AQPM) in a biaxial crystal reveals new directions of propagation for efficient parametric frequency conversion as well as "giant" spectral acceptances. The experimental validation is performed in a periodically poled rubidium-doped

ISBN 978-1-943580-84-2; International audience; We propose a new scheme of quasi-phase matching based on the negative first-order of the spatial modulation of the sign of the second-order optical nonlinearity. The experimental validation is done in a periodically-poled Rubidium-doped KTiOPO4 crystal.

International audience; The generation of silver species has been investigated in silver containing sodo‐gallo‐phosphate glasses subjected to X‐rays irradiations. Radio‐luminescence spectroscopy has evidenced the presence of isolated and paired silver ions. The proportion of silver pairing is found dominant in ortho‐phosphate glass compositions, compared to poly‐phosphate counterparts. The phosphate glass network is reported to have a decisive impact on the X‐Ray photosensitivity and the formation of luminescent silver species, namely Ag2+ hole trap silver ions and Agmx+ silver clusters. The subsistence of femtosecond laser produced silver luminescent structures under X‐Ray irradiation has been demonstrated.

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. In the decoding process, two merged original images were successfully reconstructed by comparing each data storage unit with a fabricated calibration matrix of 16 &times, 16 levels for elliptic orientations and fluorescence intensities. We believe this technique can be applied to semi-permanent high-density data storage device.

International audience; We worked on a new scheme of Quasi-Phase-Matching (QPM) based on the negative first-order of the spatial modulation of the sign of the second-order nonlinearity. Applying this scheme in the case of Angular-Quasi-Phase-Matching (AQPM) in a biaxial crystal reveals new directions of propagation for efficient parametric frequency conversion as well as "giant" spectral acceptances. The experimental validation is performed in a periodically-poled Rubidium-doped KTiOPO4 biaxial crystal. This new approach naturally extends to other periodically-poled uniaxial crystals such as periodically-poled LiNbO3. Phase-matching is the privileged way to optimize the performance of nonlinear optical frequency conversion. Usually, it can be obtained by using the birefringence of anisotropic crystals, which corresponds to birefringence phase-matching (BPM) [1,2]. However, BPM conditions are strongly limited by the refractive indices of the material and they usually forbid the exploitation of the highest coefficient of the second-order electric susceptibility tensor. To overcome this limitation, quasi-phase matching (QPM) is a powerful alternative. It is based on a periodical modulation of the sign of the second-order optical nonlinear coefficient of anisotropic or isotropic non-centrosymmetric crystals [3,4]. We propose here the development and the experimental validation of a new scheme of QPM that allows us to enlarge the spectral range of phase-matched generation and to get access to giant spectral acceptances. For that purpose, we studied Second-Harmonic Generation (SHG) in the ferroelectric periodically-poled Rubidium-doped KTiOPO4 crystal (PPRKTP) [5]. The key parameter of QPM is the periodicity Λ of the spatial modulation of the second-order nonlinearity along the direction of propagation of three interacting waves such as their wavelengths fulfil: 1/λ ! − 1/λ " − 1/λ # = 0. Actually, the goal is to compensate the #% ' , is the grating vector oriented along the propagation direction, and m is the order of the Fourier series. Usually, m is chosen as a positive integer (m ≥ 1), as it is the case for instance while targeting the largest nonlinear coefficient χ !! (#). It is shown in Fig. 1 (left) in the optimal case, i.e. for the lowest QPM positive order m = 1. This is the classical scheme of QPM that we called QPM-A. However, it is also possible to consider propagation directions where m ≤-1. This configuration has been previously theoretically considered, but without any phenomenological interpretation or experimental verification [6]. We called here this new scheme QPM-B. As for the case of positive orders, the lowest QPM-B order (namely m =-1) shown in Fig. 1 (right) leads to the best efficiency compared to higher

Made available in DSpace on 2019-10-06T17:09:21Z (GMT). No. of bitstreams: 0 Previous issue date: 2019-08-01 Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) Agence Nationale de la Recherche Silver-containing glasses are promising candidates for photonic applications, due to the potentiality of spectroscopic properties of silver nanoclusters (NC's)and/or silver metallic nanoparticles. In this framework, silver-containing fluorophosphate glasses are candidates with a strong potential. Indeed, combined with femtosecond laser irradiation, silver NC's may be tailored in three-dimensional fluorescent micro-structures, whose spectroscopic properties have been investigated, revealing the creation of silver NC's but also of NP's during laser irradiation in the studied fluorophosphate glass. Additionally, the photo-inscription of silver NC's is correlatively accompanied by a positive index change, which has led to the demonstration of optical waveguiding behavior. Finally, the management of the reservoir of available silvers for laser inscription is investigated. Unlike previous observations made in standard oxide phosphate glasses, the considered silver-containing fluorophosphate glass exhibes an intriguing ability to be re-written when subjected to successive overlapping laser irradiations. Upon the optimization of compositions with tailored photo-sensitivity, the re-writable ability of fluorophosphate glasses paves the way to the design of advanced photonic devices such as photonic optical circuits, evanescent sensors or 3D high-density optical data storage. Institute of Chemistry São Paulo State University UNESP University of Bordeaux CNRS ICMCB UPR 9048, 87 avenue du Dr. A. Schweitzer University of Bordeaux CNRS CEA CELIA UMR 5107, 351 Cours de la Libération Institute of Chemistry São Paulo State University UNESP FAPESP: 2013/07793-6 FAPESP: 2016/16343-2 FAPESP: 2018/09296-3 Agence Nationale de la Recherche: N°ANR-17-CE08-0042-01

Novel integrated photonics components are highly demanded to develop photonic integrated circuits, or sensing applications with lab-on-chip or lab-on-fiber approaches. Femtosecond laser inscription has demonstrated to be a very attractive approach being highly versatile as well as compatible with laser manufacturing technological transfer. In this framework, some of the innovations to come will result from optimized laser-based processing in prepared materials, namely in specialty glasses with a designed photosensitivity enhancement under laser irradiation. In this framework, we recently demonstrated a new type of waveguides. Here, the positive refractive index modification, labelled type A, is sustained by the laser-induced photochemistry of silver-containing phosphate glasses, with a non-trivial distribution that corresponds to the creation of fluorescent silver clusters. Some of the inner features of the refractive index structures and associated waveguides show mesoscale dimensions of a few hundreds of nanometers, which is of interest for produce sub-wavelength modifications. In this paper, we will present recent results concerning the exploitation of such new waveguides, namely with the investigation of curvature losses and the creation of directional couplers. Additionally, periodically modulated waveguides are considered to address laser-fabricated waveguide Bragg grating functionality. Such development is in progress, especially targeting reflectivity in the visible range.

Direct laser writing in glasses using femtosecond lasers has been extensively studied during the last two decades. It provides a robust and efficient way to directly inscribe 3D photonic structures in the interior of bulk glasses. More specifically, the inscription of 3D embedded waveguides has been well established. However, direct laser writing of waveguides neighboring the glass surface was only demonstrated in few works. This is owed to ablation that arises when approaching the glass surface. This shortcoming was recently overcome using additional processing and/or reinforced glasses. In silver containing glasses, direct laser writing induces the creation of silver clusters around the interaction voxel inducing a Type A refractive index change. It allows the inscription of optical waveguides using very low pulse energy, differing from standard type I waveguides which are inscribed with higher energy pulses. The low energy regime allows for the inscription of waveguides in close proximity to the surface while inhibiting surface ablation. In this work, we demonstrate direct laser writing of near-surface waveguides in a non-reinforced bulk glass sample without resorting to any additional processes, as well as a demonstration of a high-sensitivity refractive index sensor based on such near-surface waveguides. This work highlights the novelty and benefits of type A waveguides inscribed in silver containing glasses and their high potential for sensing applications compatible with laser manufacturing approaches. Finally, our results could be easily transposed to silver containing ribbon shaped glass fibers, thus paving the way towards fiber based sensing applications.

International audience; 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. In this paper, we present the inscription of surface and near-surface silver based waveguides in a silver containing glass with no need for additional processing as it is the case for standard type I waveguides. In addition, an ultra-sensitive refractive index sensor in a 1 cm glass chip is obtained based on near-surface waveguides interacting with liquid droplets acting as top-layer on the glass surface. Remarkably, the device exhibits a novel double-wing feature that sharpens the response and enhances its sensitivity. Our results highlight the advantages of silver based waveguides paving the way towards further surface based sensors in fibers.

International audience; The femtosecond direct laser writing technique in glasses has been widely used and extensively studied during the last two decades. This technique provides a robust and efficient way to directly inscribe embedded 3D photonic devices in bulk glasses. Following direct laser writing, a local refractive index change (Δn) is induced that is generally classified under three distinguished types (type I, type II & type III). Each type allows for the fabrication of its own variety of 3D photonic components. However, in silver containing glasses, direct laser writing induces the creation of a new type of refractive index change, called type Argentum (type A). It is based on the creation of silver clusters that allow for the creation of optical waveguides. In this paper, we report that both type I and type Argentum modifications could be triggered in silver containing glasses by finely choosing the inscription parameters. A comparative study between both types of single mode waveguides is presented taking into account the morphology, Δn profile and the guided mode profile. Finally, we highlight the originality of type Argentum waveguides paving the way for promising applications not accessible by type I waveguides.

Made available in DSpace on 2019-10-06T15:44:27Z (GMT). No. of bitstreams: 0 Previous issue date: 2019-01-01 Here, we report the luminescence properties of Yb3+/Pr3+ dual-doped fluorophosphate glasses containing silver clusters. Through the solubility of silver into the glass system as function of its initial concentration, charged species characterized as Ag+ and Agmn+ were formed and identified according to their absorption and emission spectral responses. By changing the transition metal concentration, multi-energy transfer mechanisms were observed between silver and Yb3+/Pr3+ co-doped glasses. The stabilization of silver species seems to be detrimental to the radiative processes of the rare earth ions under excitation at 444 nm (Pr3+3H4 → 3P0 absorption line). In other words, the main visible emissions of Pr3+ and the NIR emission of Yb3+ decrease with increment of Ag concentration. However, energy transfer occurs for large spectral range by the excitation of the silver species. In consequence, the visible and NIR emission could be activate in a broadband from ultraviolet to the blue part of the spectral region. These two observations highlight the competitive absorption processes and probabilities between the cationic elements and the interest to use the transition metal species as sensitizers to excite the rare earth elements. Institute of Chemistry - São Paulo State University - UNESP, CP 355 University of Bordeaux CNRS ICMCB UPR 9048, 87 Avenue du Dr. A. Schweitzer University of Bordeaux CNRS CEA CELIA UMR 5107, 351 Cours de la Liberation Institute of Chemistry - São Paulo State University - UNESP, CP 355

International audience; 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

We study the angular dependence in polarized light of the optical absorption for the Er 3 + transition 4 I 15 ∕ 2 → 4 I 13 ∕ 2 in Y 2 SiO5, revealing thus the associated anisotropy and the orientation of the related absorption principal directions in the dielectric plan perpendicular to the monoclinic axis b. The measurements are performed at low temperature. This allows us to isolate the lowest crystal field levels in the ground and excited states. We spectrally resolve and independently characterize the two yttrium substitution sites in the Y 2 SiO5 matrix. The absorption tensor components cannot be unambiguously determined yet while only considering the investigated dielectric plane. Still, measurements remarkably demonstrate that this transition of interest well resolved at low temperature is not only a magnetic-dipole allowed transition but indeed a hybrid electric–magnetic transition.

We experimentally and numerically characterize multiple filamentation of laser pulses with incident intensities of a few TW/cm2. Propagating 100 TW laser pulses over 42 m in air, we observe a new propagation regime where the filament density saturates. As also evidenced by numerical simulations in the same intensity range, the total number of filaments is governed by geometric constraints and mutual interactions among filaments rather than by the available power in the beam.

We measured broad tunable spectra between 1.4 and 4.7 μm in the nonlinear crystal La3Ga5.5Ta0.5O14 (LGT). They were generated in the femtosecond regime from phase-matched difference frequency generation and optical parametric amplification.

The investigation of the photo-inscription of waveguides in Barium Gallo-Germanate glass (BGG: BaO, GeO2, Ga2O3) is presented. This type of glass has been chosen because of its robustness, its chemical stability and its transmission throughout the whole visible region up to 5 µm. Irradiation with a focused femtosecond laser pulse train of different BGG samples leads to relatively high positive refractive index changes over a wide range of exposure conditions. Waveguides with a controllable diameter ranging from 4 to 35 µm and index change up to 10-2 were inscribed. A glass sample with custom molecular composition, adding a halogen component to remove hydroxyl ions and reduce the absorption band near 3 µm, was fabricated. Inscription of low-loss waveguides was performed, supporting only two transverse modes at the wavelength of 2.78 µm, and matching well with single-mode fluoro-zirconate fibres at this wavelength. An upper bound for the propagation losses of 0.5±0.1 dB/cm was determined along the waveguides, mainly due to absorption of hydroxyl ions in the glass, which can further be reduced by improving the purification process. The results presented show the great potential of the BGG glass family for the fabrication of core waveguides operating in the 2-5 µm spectral range and open a pathway towards the integration of mid-IR photonic devices based on BGG glasses.

Direct laser writing in glasses using femtosecond lasers has been widely used and extensively studied during the last two decades. This technique provides a robust and efficient way to directly inscribe 3D photonic devices in the volume of bulk glasses. Following direct laser writing, a local refractive index change is induced, that is generally classified under three different types (Type I, II and III). Each type allows the fabrication of its own variety of embedded 3D photonic components. More specifically, type I refractive index change is usually preferred for the formation of photo-inscribed waveguides [1]. However, in silver containing glasses, direct laser writing induces a novel type of refractive index change, called type A [2]. It is based on the creation of fluorescent silver clusters distributed on the vicinity of the laser-glass interaction voxel [3] allowing for the inscription of a novel type of waveguides [2] exhibiting numerous interesting properties. In this paper, a comparative study between Type A and Type I waveguides in silver containing zinc phosphate glasses is presented. The morphology of waveguides, guided mode profile, refractive index profile and propagation losses as well as a thermal stability study are presented. Finally, this study shows the similar functionality of Type A waveguides compared to type I, thus exhibiting some significant advantages leading the way for promising applications based on type A waveguides’. 1. Davis, K.M., et al., Writing waveguides in glass with a femtosecond laser. Optics Letters, 1996. 21(21): p. 1729-1731. 2. Abou Khalil, Alain., et al., DLW of new type of waveguides in silver containing glasses. Scientific Reports, Submitted. 3. Bellec, M., et al., Beat the diffraction limit in 3D direct laser writing in photosensitive glass. Optics Express, 2009. 17(12): p. 10304-10318.

Calcium Fluoride (CaF2) was identified among the first host crystals for active laser media. However, due to the need of charge compensation of Nd3+-doped fluorite crystal structures, other host materials like YAG, oxide and fluorite glasses were preferred over the years. Recent developments made on ytterbium-doped alkaline-earth fluorides have shown that it is possible to have better scalability of crystal growth, very high thermal conductivity, high laser-induced damage threshold, longer emission lifetime, lower nonlinear refractive index and large emission wavelength tuning range. Due to these reasons, Yb-doped CaF2 has once again proved to be a competitive material for high-energy and high-power operations. Waveguides confine light propagation resulting in reduced lasing thresholds and enhanced laser efficiencies. By properly managing the three-dimensional translation of the focal volume of pulsed lasers, it is possible to create waveguides and other 3D structures inside crystals. Recently, depressed cladding waveguides written inside CaF2 were reported. In this work, we will present the first, to the best of our knowledge, double track waveguides inscribed inside doped and undoped CaF2 crystal with different pulse energies. Waveguide characterization, determination of mode-field diameter, analysis of polarization dependent guiding and also direct refractive index change measurements of the waveguides were performed and will be presented. Additionally, single pass gain and lasing experiments will be demonstrated both theoretically and experimentally.

Laser-induced glass processing has led to huge progress and applications over the last two decades. Here, we review recent advances in femtosecond laser-induced photochemistry in isotropic transparent oxide glasses specifically tailored with silver photoactive agents. The understanding of the influence of the considered glass matrix on the nature and properties of the created silver species is of prime importance. After presenting the key material properties, the formation mechanisms of laser-induced silver-based species are discussed, and potential technological applications are highlighted. Laser-induced processing of silver-containing oxide glasses paved the way for the fabrication of complex integrated waveguides and optical circuits with innovative fluorescent, nonlinear optical, and plasmonic properties. The universality of the method is expected to extend in any glass material that shows a similar laser-induced behavior in terms of silver cluster production.

We report on the absorption profile of the monoclinic holmium-doped $$\hbox {KY}(\hbox {WO}_4)_2$$ crystal near the optic axis for the maximal absorption wavelength at 1960 nm. The full angular distribution of the absorption coefficient at the vicinity of such optical singularity has been experimentally and numerically investigated. Furthermore, laser experiments along the optic axis have been carried out. So-called conical refraction laser and classical Gaussian laser operation are compared near the optic axis, taking into account the complex absorption profile.

International audience; We have developed laser grade and highly Yb3+-doped cubic rare-earth sesquioxides (RE2O3, RE = Y, Gd, Lu) single crystals by means of a newly designed high-temperature solution growth method which gives them spectroscopic properties different from those obtained by high-temperature solidification methods. Absorption and emission cross sections, visible anti-Stokes emission, fluorescence decays of the new cubic Gd2O3:Yb3+ single crystals are presented and compared to those of Y2O3:Yb3+ and Lu2O3:Yb3+ crystals. The case of cubic Gd2O3:Yb3+ is particularly interesting since its basic spectroscopic properties have never been detailed and we were capable of achieving Yb-doping level as high as 20%.

Optical parametric generation in nonlinear crystals across the atmosphere transmission band II (3–5 μm) is of interest for various applications such as infrared spectroscopy or countermeasures. For an efficient parametric generation in this spectral range with well-developed ultrashort laser sources, we identified Langatate La 3 Ga 5.5 Ta 0.5 O 14 (LGT) [1]. LGT is transparent from 0.25 up to 6.5 μm and can be grown in large sizes using the Czochralski method. Its unique nonlinear coefficient d 11 =2.4 ± 0.4 pm/V at λ=0.67 μm as well as the refinement of the Sellmeier equations are reported in ref [1]. The study highlights the potential for LGT to generate broadband spectrum between 1.5 and 5 μm if pumped around 0.97 μm available from a Ti:Sapphire (Ti:Sa) laser.

Femtosecond laser writing in glasses is a growing field of research and development in photonics, since it provides a versatile, robust and efficient approach to directly address 3D material structuring. Laser-glass interaction process has been studied for many years, especially the local changes of the refractive index that have been classified by three distinct types (types I, II and III, respectively). These refractive index modifications are widely used for the creation of photonics devices such as waveguides [1], couplers, photonic crystals to fabricate integrated optical functions in glasses for photonic applications as optical circuits or integrated sensors. Femtosecond laser writing in a home-developed silver containing zinc phosphate glasses induces the creation of fluorescent silver clusters distributed around the laser-glass interaction voxel [2]. In this paper, we introduce a new type of refractive index modification in glasses. It is based on the creation of these photo-induced silver clusters allowing a local change in the refractive index Δn = 5×10-3, which is sufficient for the creation of waveguides and photonics devices. The wave guiding process in our glasses along these structures with original geometry is demonstrated for wavelengths from visible to NIR [3], giving a promising access to integrated optical circuits in these silver containing glasses. Moreover, the characterization of the waveguides is presented, including their original geometry, the refractive index change, the mode profile, the estimation of propagation losses and a comparison with simulation results. 1. K. M. Davis, K. Miura, N. Sugimoto, and K. Hirao, Opt. Lett. 21, 1729-1731 (1996). 2. M. Bellec, A. Royon, K. Bourhis, J. Choi, B. Bousquet, M. Treguer, T. Cardinal, J.-J. Videau, M. Richardson, and L. Canioni, The Journal of Physical Chemistry C 114, 15584-15588 (2010). 3. S. Danto, F. Desevedavy, Y. Petit, J.-C. Desmoulin, A. Abou Khalil, C. Strutynski, M. Dussauze, F. Smektala, T. Cardinal, and L. Canioni, Advanced Optical Materials 4, 162-168 (2016).

In this contribution we detail the full characterization of the anisotropy of the absorption properties of two different Yb-doped monoclinic borate compounds under polarized light. The studied crystals are Li 6 (Gd) 0.75 Yb 0.25 (BO 3 ) 3 and Li 6 Y 0.75 Yb 0.25 (BO 3 ) 3 , respectively, grown by the Czochralski method. We focused on the study of their absorption at the zero line transition as a function of the polarization direction of the incident light for two different crystal cuts of each compound. We discuss the different Eigen frames that must be considered in these materials due to their monoclinic character, as well as the optimal crystal orientation for the considered absorption and the potential influences when used as laser materials.

We measured continuously tunable beams between 1.4 and 4.7 µm in the nonlinear crystal La3Ga5.5Ta0.5O14 (LGT) as predicted theoretically. They were generated in the femtosecond regime from difference frequency generation and optical parametric amplification.

International audience; A detailed investigation of the photo-inscription of waveguides in barium gallo-germanate (BGG, BaO, GeO2, Ga2O3) glass is presented. Upon irradiation of BGG glass samples of different contents of germanium dioxide with a femtosecond laser pulse train, positive refractive index changes are produced over a wide range of exposure conditions. Waveguides with a controllable diameter ranging from 4 to 35 µm and a maximum index change up to 10−2 were inscribed. A glass sample with custom molecular composition was purified to remove hydroxyl ions and reduce the strong absorption band near 3 µm. A careful tailoring of the writing conditions allowed for the inscription of low-loss waveguides supporting only two transverse modes at the wavelength of 2.78 µm. An upper bound for the propagation losses of 0.5 ± 0.1 dB/cm was determined, showing the great potential of the BGG glass family for the fabrication of core waveguides operating in the 2-4 µm spectral range. Our results actually open a pathway towards the integration of mid-IR photonic devices based on the BGG glass family.

International audience; We detail the full characterization of the anisotropy of the absorption properties of two different Yb-doped monoclinic borate compounds under polarized light. The studied crystals are Li6(Gd)0.75Yb0.25(BO3)3 and Li6Y0.75Yb0.25(BO3)3, respectively, and were grown by the Czochralski method. We focused on the study of their absorption at the zero line transition as a function of the polarization direction of the incident light for two different crystal cuts of each compound. We discuss the different eigenframes that must be considered in these materials, due to their monoclinic character, as well as the optimum crystal orientation for the considered absorption and show the potential influences when used as laser materials.

International audience; The investigation of nonlinear optical (NLO) properties is closely linked to the discovery of Lasers (Light Amplification by Stimulated Emission of Radiation) by Theodore Harold Maiman in 1960. The area of research has been devoted first naturally to non centrosymmetric crystals (LiNbO3, KDP, BBO, etc.). In 1961, Franken revealed for the first time on a quartz crystal the second harmonic generation [1037]. This discovery opened a new pathway for numerous innovative applications such as frequency conversion (second and third harmonic or sum and difference of frequency) starting from the interaction of monochromatic light sources and high fluence laser interaction with material. In the specific case of glasses, due to their isotropic nature, they do not provide second order nonlinearity such as a second harmonic signal, which forms the base of optical effect such as electro-optical effect (Pockels).

International audience; 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. By breaking the glass centro-symmetry, this field gives rise to a local effective second-order susceptibility, inducing SHG. Both theoretically predicted SHG and THG evolutions with respect to the number of pulses in the train are in good agreement with experimental observations. In particular, the observed reaching of a maximum in the nonlinear optical responses after a few thousands of pulses is explained by the competition of various physical processes. A cooling of the glass is shown to improve the process efficiency of the laser writing of second-order nonlinearity.