In this paper, we investigate power scalability of ytterbium-doped ultra large core photonic crystal fiber laser operating on the zero-line transition. We first report on an 80 microm core diameter ytterbium-doped rod-type photonic crystal fiber laser emitting up to 94 W in continuous wave regime when operating at 977 nm, which is to our knowledge the highest output power ever achieved from a single-mode solid-state laser operating at this wavelength. Key parameters of ytterbium-doped three-level laser, such as transparency pump intensity, pump absorption saturation, and gain competition between three and four-level laser operation are then discussed in the particular context of high power fiber laser operating at 977 nm.

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It is demonstrated that the form birefringence related to the so-called nanogratings is quantitatively correlated to the porosity-filling factor of these nanostructures. We reveal that matters surrounding the nanopores exhibit significant refractive index decrease which is likely due to the fictive temperature increase and/or the presence of a significant amount of interstitial O 2 . The control of the porosity was achieved by adjusting the laser pulse energy and the number of pulses/micron i.e. the overlapping rate. Applications can be numerous in fast material processing by the production of nanoporous matter, and photonics by changing the optical properties.

The harsh environment associated with the next generation of nuclear reactors is a great challenge facing all new sensing technologies to be deployed for on-line monitoring purposes and for the implantation of SHM methods. Sensors able to resist sustained periods at very high temperatures continuously as is the case within sodium-cooled fast reactors require specific developments and evaluations. Among the diversity of optical fiber sensing technologies, temperature resistant fiber Bragg gratings are increasingly being considered for the instrumentation of future nuclear power plants, especially for components exposed to high temperature and high radiation levels. Research programs are supporting the developments of optical fiber sensors under mixed high temperature and radiative environments leading to significant increase in term of maturity. This paper details the development of temperature-resistant wavelength-multiplexed fiber Bragg gratings for temperature and strain measurements and their characterization for on-line monitoring into the liquid sodium used as a coolant for the next generation of fast reactors.

We review the question on the origin of the differences observed on various properties when we scan the femtosecond laser beam in an isotropic media (i.e. a glass) in two orientations of a given direction. Publications on refractive index changes, birefringence, nanogratings, stress, bubbles formation and on quill writing effects are analyzed. A new interpretation based on space-charge built from ponderomotive force and stored in the dielectric inducing an asymmetric stress field is proposed.

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kW fiber lasers, long-term optical data storage such as Microsoft's "project silica", [1] etc.) and optical sensing (structural health monitoring of engines, deep drilling). [2] In most applications operating in a HT environment, refractory crystalline oxide materials such as alumina (Al 2 O 3 ) or zirconia (ZrO 2 ) are candidates of choice, due to their high melting points and good resistance to oxidation and abrasion. Furthermore, directionally solidified eutectic ceramics (e.g., unidirectionally solidified Al 2 O 3 /oxide eutectic composite made of perovskite or garnet phase) also can improve thermal stability, [3] as demonstrated for instance in aircraft gas turbines and thermal power generation systems (e.g., operation for 1000 h at 1700 °C).However, other HT applications, such as long-lived data storage for the zettabyte era [1] or optical sensors (down-hole oil/gas exploration, monitoring of structure health, temperature regulation of engines, etc.) require using glass materials that can be functionalized and shaped into chips, disks, planar waveguides or optical fibers. Both the materials and geometric designs need be considered due to practical demands, such as compactness and lightness, flexibility, high-transparency, fast and complex manufacturing shaping, chemical/radioactive/ electromagnetic resistance, and low cost. For these reasons, Aluminosilicate glasses offer wide-ranging potential as enabling materials for a new generation of optical devices operating in harsh environments.In this work, a nonconventional manufacturing process, the molten core method, is employed to fabricate and study sapphire (Al 2 O 3 ) and YAG (yttrium aluminum garnet) derived all-glass silicate optical fibers in which a femtosecond (fs) laser is used to imprint oriented nanostructures inside the fiber cores. Both writing kinetics and thermal stability of the laser-modified regions are investigated over a wide temperature range (20-1200 °C). The laser-imprinted modifications in these high alumina-content fibers exhibit improved thermal stability with respect to commercial pure silica and GeO 2doped silica analogs. Furthermore, optical devices in the form of Rayleigh backscattering and fiber Bragg grating sensors are fabricated to demonstrate the high-temperature sensitivity and stability of these nonconventional fibers. This functionalization of aluminosilicate fibers by fs-laser direct writing opens the door to a new generation of optical devices suitable for high-temperature operation.

The paper addresses the creation of circular optical properties from a femtosecond laser light beam with a linear polarization in an achiral material (glass) under an orthogonal incidence. In this situation, all aspects of the experiment are achiral and therefore should not give rise to chiral property creation. From that observation, we propose an interpretation that involves the action of a light-induced torque on the matter carrying a light-induced dielectric moment. We found that a direct current (DC) electric field could be produced in the lattice by the femtosecond laser in our conditions and that a non-collinear dielectric moment is created by a nonlinear effect between the DC electric field and the stress field due to the transformation of the material. We reveal that it is possible to break the chiral symmetry of glass using an intense, ultrashort laser light pulse.