Coherent beam combining with an ultrafast multicore Yb-doped fiber amplifier

International audienceActive coherent beam combination using a 7-non-coupled core,polarization maintaining, air-clad, Yb-doped fiber is demonstrated as amonolithic and compact power-scaling concept for ultrafast fiber lasers. Amicrolens array matched to the multicore fiber and an active phasecontroller composed of a spatial light modulator applying a stochasticparallel gradient descent algorithm are utilized to perform coherentcombining in the tiled aperture geometry. The mitigation of nonlineareffects at a pulse energy of 8.9 μJ and duration of 860 fs is experimentallyverified at a repetition rate of 100 kHz. The experimental combiningefficiency results in a far field central lobe carrying 49% of the total power,compared to an ideal value of 76%. This efficiency is primarily limited bygroup delay differences between cores which is identified as the maindrawback of the system. Minimizing these group delay issues, e.g. by usingshort and straight rod-type multicore fibers, should allow a practical powerscaling solution for femtosecond fiber systems

A new efficient front-tracking numerical framework to simulate recrystallization and grain growth mechanisms in presence of complex second phase particle populations

International audienceSecond phase particles (SPP) play an essential role in controlling grain size and properties of polycrystalline nickel-base superalloys. The full-field methods are of great interest as they can reproduce microstructure evolutions and heterogeneities. Several methods have been developed to reproduce the Smith-Zener pinning (SZP) mechanism at the polycrystalline scale, considering the presence of SPP in the microstructure. In this context, complex deterministic numerical frameworks have been developed in the last decades, such as the vertex methods, and different front-capturing approaches, including the multi phase-field (MPF) and level-set (LS) frameworks. The LS approach is an advanced formalism where the physics of the interaction between the GB and SPP can be captured in 2D or 3D and for static or dynamic SPP populations. However, when SPP become very small compared to the mean grain size, the cost of such calculations can become prohibitive even in 2D. In this context, a new 2D front-tracking methodology was recently developed to model ReX and GG with the same precision that the LS method but with drastically reduced calculation times. This presentation will be dedicated to the enhancement of this front-tracking approach to consider the SZP with the same precision that the LS approach but with a much more appreciable efficiency

Top-hat beam output of a single-mode microstructured optical fiber: Impact of core index depression

International audienceNot Availabl

Top-hat beam output with 100 μJ temporally shaped narrow-bandwidth nanosecond pulses from a linearly polarized all-fiber system

International audienceWe report on an all-fiber system delivering more than 100 μJ pulses with a top-hat beam output in the few nanoseconds regime at 10 kHz. The linearly polarized flattened beam is obtained thanks to a 3-mm-long single-mode microstructured fiber spliced to the amplifier’s output

Investigation of the Incorporation of Cerium Ions in MCVD-Silica Glass Preforms for Remote Optical Fiber Radiation Dosimetry

International audienceThe incorporation of Ce3+ ions in silicate glasses is a crucial issue for luminescence-based sensing applications. In this article, we report on silica glass preforms doped with cerium ions fabricated by modified chemical vapor deposition (MCVD) under different atmospheres in order to favor the Ce3+ oxidation state. Structural analysis and photophysical investigations are performed on the obtained glass rods. The preform fabricated under reducing atmosphere presents the highest photoluminescence (PL) quantum yield (QY). This preform drawn into a 125 µm-optical fiber, with a Ce-doped core diameter of about 40 µm, is characterized to confirm the presence of Ce3+ ions inside this optical fiber core. The fiber is then tested in an all-fibered X-ray dosimeter configuration. We demonstrate that this fiber allows the remote monitoring of the X-ray dose rate (flux) through a radioluminescence (RL) signal generated around 460 nm. The response dependence of RL versus dose rate exhibits a linear behavior over five decades, at least from 330 µGy(SiO2)/s up to 22.6 Gy(SiO2)/s. These results attest the potentialities of the MCVD-made Ce-doped material, obtained under reducing atmosphere, for real-time remote ionizing radiation dosimetry

Ultrafast multicore Yb-doped fiber amplifier (Oral)

International audienc