Dr. Jean-Paul Goossens Profile

Dr. Jean-Paul Goossens

at Commissariat à l'Énergie Atomique

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Publications (4)

Proceedings Article | 23 May 2018 Presentation

Laser material Nd:Lu:CaF2 characterization for high-energy and high-repetition rate amplification at 1053 nm (Conference Presentation)

Diane Stoffel, Sébastien Montant, Jean-Paul Goossens, Simone Normani, Alain Braud, Patrice Camy

Proceedings Volume 10683, 106831W (2018) https://doi.org/10.1117/12.2306895

KEYWORDS: Birefringence, Fusion energy, Neodymium, Ions, Thermal effects, Semiconductor lasers, Cameras, Laser-matter interactions, Laser energy, Laser systems engineering

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Laser facility such as Megajoule Laser dedicated to laser-matter interaction including inertial fusion need pre-amplification modules (PAM) which must respect a high beam quality. The actual Nd:Phosphate is used in high energy laser system because of its capacity to be produced in big size. The current PAM work at a repetition rate of 1 shot/5 min limited by a low thermal conductivity of the Phosphate glass. However, it would be interesting to increase the shot rate for alignment and diagnostics purposes. Therefore we propose to change this amplification material by some Nd:crystal in the PAM with a higher thermal conductivity and working at 1053 nm to match the power chain wavelength. For long time Nd: CaF2 has been abandoned because of quenching between Nd ions. The lutetium is “buffer” ion used to break Nd clusters and allow high emission cross section. The Nd Lu:CaF2 thermal conductivity is ten times higher than actual Nd:Phosphate and would permit to achieve a repetition rate at 10 Hz. Nevertheless, this material must fulfil the beam specifications to be integrated in the actual amplification chain. We report a characterization of the thermal induced effects on a parallelepiped rod pumped transversally by laser diodes. The pomp-probe beam configuration contains laser diodes emitting at 797 nm with a fluency of 13 J/cm2 and a probe beam passing through the rod at 1053 nm We study the spatially resolved induced birefringence under a mono-shot pump or variable repetition rates. The experimental setup is composed with a cross-rotating polarizer-analyzer and a camera that measures the intensity signal transmitted by the analyzer. A post numerical analysis consists in fitting the intensity signal transmitted for several polarizer-analyzer angles all over the camera picture. Hence the birefringence can be determined spatially at the end front of the rod. These measures are resolved in time to compare the relaxation behaviour of these two materials. Then we simulate the experiment setup with COMSOL software that includes the thermal and mechanic multiphysics interaction. The objective is to assess physical effects we cannot determine by measures like the mechanical stress induced at the origin of the birefringence pattern. We numerically solve the thermal equation. The thermal source defined must fit the experimental pump geometry and time mono-shot pulse rate or variable repetition rates. We take in account of the Beer-Lambert’s absorption law and supergaussian profile for geometry and time definition. Then we use Hooke’s law in general case for free-elastic material linked to the thermal distribution to deduce the stress and strain induced in the material. The induced birefringence is directly associated to the piezo-optic tensor and the stress material. The stress tensor COMSOL computes allow reconstructing the Jones matrices throughout the rod and thus the spatial birefringence. The numerical spatially and time resolved birefringence is in good agreement with experimental measures. This numerical model allows us to optimize the spatial geometry of cooling in transverse pumping as in longitudinal pumping in thick disk amplifier. CPER#16004205 FEDER#2663710

Proceedings Article | 17 May 2018 Presentation + Paper

Femtosecond and dual-wavelength mode-locked operation in Nd,Lu:CaF2

R. Soulard, S. Normani, J.-L. Doualan, A. Braud, D. Stoffel, S. Montant, J.-P. Goossens, P. Camy

Proceedings Volume 10683, 106831J (2018) https://doi.org/10.1117/12.2314477

KEYWORDS: Mode locking, Femtosecond phenomena, Neodymium, Lutetium, Laser crystals, Pulsed laser operation

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Proceedings Article | 14 March 2018 Presentation

Fluoride crystals for inertial confinement fusion laser drivers (Conference Presentation)

Jean-Paul Goossens

Proceedings Volume 10511, 105110V (2018) https://doi.org/10.1117/12.2291886

KEYWORDS: Laser crystals, Crystals, Ions, Glasses, Absorption, Laser systems engineering, Luminescence, Laser welding, Doping, Laser glasses

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Conventional laser drivers for Inertial Confinement Fusion used phosphate glass as laser medium. The main disadvantage of the glass host is its low thermal conductivity and only one laser shot every 5 minutes can be obtained in the joule range with Laser Megajoule Preamplifier system. Recently, the disordered Nd:CaF2 crystals with co-doping ions has been studied intensely because of wide emission and absorption spectrum, broadband laser operation around 1μm and very good thermal properties. We demonstrate that co-doping Nd:CaF2 single crystals with Lu3+ non-optically active ions significantly improves their absorption, emission, and fluorescence lifetime properties and their laser performance. Laser operation is obtained around 1.055 μm which make these suitable for laser diver for ICF application at 1053 nm. Over the past few years, broadband laser emission has been achieved with Nd-doped fluorite-type crystals, around 1053 nm (4F4I transition Nd3+) by co-doping the host with buffer ions, such as Y3+ and Lu3+. These configurations are very interesting because absorption and emission spectra as wide as with glasses can be obtained. They still being single crystals and having thus among other advantages a high thermal conductivity which makes these materials suitable for high-energy high repetition rate pulsed laser amplifiers applications. However, in the case of CaF2, the 1 μm Nd3+ emission is completely quenched because of clustering of Nd3+ ions. The quenching of the 4F3/2 emitting level starts at low dopant concentration (0.1 at%). To address this drawback, the co-doping of the crystal with non-optically-active ions to form clusters around single Nd3+ ion and then isolated them from each other. In this work, we present the distinct absorption and emission spectra, fluorescence and radiative lifetimes as well as the respective concentrations of the two main emitting centers in CaF2: Nd3+ :Lu3+.Absorption spectra around 800nm (4I9/26>F5/2 transition) for different co-doped samples. Measurements of the thermal conductivity of CaF2 have been realized with a thermal lens technique and a mean value of 4.3 W/m.K has been obtained for a 5%Lu concentration. This value is about ten times higher than the thermal conductivity of glasses, between 0.3 and 0.6 W/mK. For demonstration of lasing performance in our laser ICF driver system, crystals with concentration of 5% Lu have been chosen because it offers the best compromise between spectra wide and thermal conductivity.

Proceedings Article | 14 March 2018 Presentation

Laser material Nd:Lu:CaF2 characterization for amplification application at 1053 nm (Conference Presentation)

Diane Stoffel, Sébastien Montant , Jean-Paul Goossens , Simone Normani, Alain Braud, Jean-Louis Doualan, Patrice Camy

Proceedings Volume 10511, 105111T (2018) https://doi.org/10.1117/12.2287374

KEYWORDS: Birefringence, Thermal effects, Diffusion, Crystals, Diodes, Infrared cameras, Amplifiers, Laser-matter interactions, Diagnostics, Fusion energy

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