Search

Your search keyword '"Aka, Gerard"' showing total 105 results
Start Over Author "Aka, Gerard"
105 results on '"Aka, Gerard"'

9. Acute Bowel Obstructions of the Elderly in a Low African Country

Author

Kouame Bernadin Kouakou, Kouakou Ibrahim Anzoua, Mamadou Traore, Ismael Kalou Leh Bi, Ahou Bernadette N’Dri, Aka Gerard Kakou, Serge Amos Ekra, Blaise Amos Kouakou, Inza Bamba, Djahou Ezechiel Akowendo, Roger Lebeau, and Bamourou Diane

Subjects
General Engineering, Energy Engineering and Power Technology
Published
2022

11. Acute Bowel Obstructions of the Elderly in a Low African Country

Author

Kouakou, Kouame Bernadin, primary, Anzoua, Kouakou Ibrahim, additional, Traore, Mamadou, additional, Leh Bi, Ismael Kalou, additional, N’Dri, Ahou Bernadette, additional, Kakou, Aka Gerard, additional, Ekra, Serge Amos, additional, Kouakou, Blaise Amos, additional, Bamba, Inza, additional, Akowendo, Djahou Ezechiel, additional, Lebeau, Roger, additional, and Diane, Bamourou, additional

Published
2022
Full Text
View/download PDF

14. Crystal Growth and Characterization of Terbium-Based Borate Crystals of Sr$_{3}$Tb(BO$_{3}$)$_{3}$, Li$_{6}$Tb(BO$_{3}$)$_{3}$, and TbCa$_{4}$O(BO$_{3}$)$_{3}$: Color Centers, Spectroscopic Properties, and Optical Gain

Author

Chen, Hengjun, Loiseau, Pascal, Aka, Gerard, Baptiste, Benoît, Veber, Philippe, Ecole Nationale Supérieure de Chimie de Paris - Chimie ParisTech-PSL (ENSCP), Université Paris sciences et lettres (PSL), Institut de minéralogie, de physique des matériaux et de cosmochimie (IMPMC), Muséum national d'Histoire naturelle (MNHN)-Institut de recherche pour le développement [IRD] : UR206-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS), Luminescence (LUMINESCENCE), Institut Lumière Matière [Villeurbanne] (ILM), Université Claude Bernard Lyon 1 (UCBL), Université de Lyon-Université de Lyon-Centre National de la Recherche Scientifique (CNRS)-Université Claude Bernard Lyon 1 (UCBL), and Université de Lyon-Université de Lyon-Centre National de la Recherche Scientifique (CNRS)

Subjects
[PHYS]Physics [physics], [SPI]Engineering Sciences [physics], Lasers, Color, [CHIM]Chemical Sciences, Crystallization, Crystals, Absorption
Abstract

International audience; This work aims to evaluate the prospect for visible laser applications of three terbium-based borate single crystals, viz. Sr$_{3}$Tb(BO$_{3}$)$_{3}$ (STB), Li$_{6}$Tb(BO$_{3}$)$_{3}$ (LTB), and TbCa$_{4}$O(BO$_{3}$)$_{3}$ (TbCOB). Crystals with good optical quality were grown by the Czochralski technique. Formation of color centers was observed in the crystals grown in air atmosphere and was then circumvented by applying a reducing atmosphere during the growth process. The color centers were further studied by absorption and electron paramagnetic resonance spectroscopic characterization. Thermal properties that can impact laser operation, including thermal conductivity, specific heat capacity, and thermal expansion, were characterized using the as-grown crystals. The principal refractive indices of STB and LTB were measured experimentally. Cross sections of the 4f$^{8}$ → 4f$^{8}$ transitions of Tb$^{3+}$ in these crystals were derived from the recorded absorption and emission spectra as well as the Judd–Ofelt calculations. The fluorescence decay curves from the $^{5}$D$_{4}$ excited state were recorded to yield the fluorescence lifetimes. Experimental results and theoretical calculations indicate that these terbium-based crystals have minor nonradiative processes from the $^{5}$D$_{4}$ manifold, and the transition cross sections in the visible spectra range are comparable to those of the previously reported gain media. Lastly, optical gain at 543 nm was measured in these crystals in a pump–probe scheme.

Published
2020

16. Optical planar and channel waveguides in the new nonlinear crystal [Ca.sub.4]YO[(B[O.sub.3]).sub.3] (YCOB) fabricated by He+ implantation

Author

Boudrioua, Azzedine, Vincent, Brice, Moretti, Paul, Tascu, Sorine, Jacquier, Bernard, and Aka, Gerard

Subjects
Optics, Astronomy, Physics
Abstract

We report the first study of optical planar and channel waveguides fabricated in the new nonlinear crystal [Ca.sub.4]YO[(B[O.sub.3]).sub.3] by use of MeV He+-implantations. The [n.sub.x], [n.sub.y], and [n.sub.z] refractive index modifications are studied. Losses in nonannealed YCOB waveguides measured with a CCD camera are found to be less than 2 dB [cm.sup.-1]. This work is the first step toward the investigation of frequency conversion within the obtained guiding structures. OCIS codes: 230.3120, 230.7380, 230.4320.

Published
2004

18. Efficient and tunable continuous-wave diode-pumped Yb3+:ca4GdO(BO3)3 laser

Author

Auge, Frederika, Balembois, Francois, Georges, Patrick, Brun, Alain, Mougel, Frederic, Aka, Gerard, Kahn-Harari, Andree, and Vivien, Daniel

Subjects
Solid-state lasers -- Research, Diodes, Laser -- Research, Ytterbium -- Research, Astronomy, Physics
Abstract

A demonstration of a diode-pumped, tunable continuous-wave Yb:GdCOB laser was presented. A slope efficiency of 47.5% was obtained at 6 degrees C, producing 191 mW of power at 1050 nm. Temperature did not significantly affect laser performance. Tunability of the laser was achieved from 1035 to 1088 nm with a 1.7% output coupler and 100-nm tunability with a low-transmission output coupling.

Published
1999

28. Optical spectroscopic properties, 0.946 and 1.074 μm laser performances of Nd3+-doped Y2O3 transparent ceramics.

Author

Sattayaporn, Suchinda, Aka, Gerard, Loiseau, Pascal, Ikesue, Akio, and Aung, Yan Lin

Subjects
*OPTICAL spectroscopy, *LASER beams, *NEODYMIUM, *DOPED semiconductors, *YTTRIUM oxides, *TRANSPARENT ceramics
Abstract

0.4% Nd 3+ -doped Y 2 O 3 transparent ceramics have been investigated from their optical absorption and emission properties to the laser performances at two different wavelengths, 0.946 μm and 1.074 μm. Absorption spectra in the range 300–1000 nm was measured to perform Judd-Ofelt analysis: the calculated spectroscopic parameters Ω 2 , Ω 4 and Ω 6 are 7.59 × 10 −20 , 4.04 × 10 −20 and 1.40 × 10 −20 cm 2 respectively. The measured fluorescence and radiative lifetime of 4 F 3/2 manifold are determined to be 283 μs and 328 μs respectively. The branching ratios of 4 F 3/2 → 4 I 9/2 and 4 F 3/2 → 4 I 11/2 transitions are 57% and 38% with corresponding stimulated emission cross sections of 1.02 × 10 −20 and 1.16 × 10 −20 cm 2 respectively. Laser experiments, under 0.808 μm laser diode pumping source, were carried out using a plano-concave resonating cavity. At 1.074 μm, the maximum output power is 3.5 W for an absorbed power of 13.0 W. The optical-to-optical and slope efficiencies reached 26.9 and 31.1%, respectively. For laser operation at 0.946 μm, the maximum output power reached 1.0 W for 13.0 W of absorbed power. The optical-to-optical conversion efficiency and slope efficiency were 7.9 and 12.4%, respectively. [ABSTRACT FROM AUTHOR]

Published
2017
Full Text
View/download PDF

31. Spectroscopy and efficient laser action under diode-pumping of a new broadly tunable crystal : Yb3+:Sr3Y(BO3)3

Author

Chenais, Sébastien, Druon, Frédéric, Balembois, François, Georges, Patrick, Gaume, Romain, Haumesser, P.H., Viana, Bruno, Aka, Gerard, Vivien, Daniel, Edwards, Marie-Laure, Laboratoire Charles Fabry de l'Institut d'Optique / Elsa, Laboratoire Charles Fabry de l'Institut d'Optique (LCFIO), Centre National de la Recherche Scientifique (CNRS)-Institut d'Optique Graduate School (IOGS)-Université Paris-Sud - Paris 11 (UP11)-Centre National de la Recherche Scientifique (CNRS)-Institut d'Optique Graduate School (IOGS)-Université Paris-Sud - Paris 11 (UP11), Laboratoire de Chimie Appliquée de l'État Solide (LCAES), Ecole Nationale Supérieure de Chimie de Paris - Chimie ParisTech-PSL (ENSCP), and Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Centre National de la Recherche Scientifique (CNRS)

Subjects
[PHYS.PHYS.PHYS-OPTICS] Physics [physics]/Physics [physics]/Optics [physics.optics], [PHYS.PHYS.PHYS-OPTICS]Physics [physics]/Physics [physics]/Optics [physics.optics]
Abstract

International audience; The first demonstration of laser action in a Yb31:Sr3Y(BO3)3 crystal is reported. This new material exhibits particularly broad absorption and emission bandwidths (6 and 60 nm, respectively) and hence is of particular interest for diode-pumped femtosecond and tunable laser sources. Efficient operation from diode pumping (1.4 W of cw laser power obtained with 3.6 W of diode pump power and as much as 3.4 W of peak power from high-power quasi-cw pumping) together with smooth tunability (over 50 nm FWHM) is reported. For the comparison, efficiency and thermal limitations of Yb:glass and Yb:Ca4GdO(BO3)3 have been investigated under the same conditions

Published
2002

32. Diode-pumped self-frequency doubling Nd:GdCa4O(BO3)3 lasers : towards green microchip lasers

Author

Lucas-Leclin, Gaëlle, Augé, Frédérica, Auzanneau, Sophie Charlotte, Balembois, François, Georges, Patrick, Brun, Alain, Mougel, Frédéric, Aka, Gerard, Vivien, Daniel, Laboratoire Charles Fabry de l'Institut d'Optique / Elsa, Laboratoire Charles Fabry de l'Institut d'Optique (LCFIO), Centre National de la Recherche Scientifique (CNRS)-Institut d'Optique Graduate School (IOGS)-Université Paris-Sud - Paris 11 (UP11)-Centre National de la Recherche Scientifique (CNRS)-Institut d'Optique Graduate School (IOGS)-Université Paris-Sud - Paris 11 (UP11), Laboratoire de Chimie Appliquée de l'État Solide (LCAES), Ecole Nationale Supérieure de Chimie de Paris - Chimie ParisTech-PSL (ENSCP), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Centre National de la Recherche Scientifique (CNRS), Crismatec, and Edwards, Marie-Laure

Subjects
[PHYS.PHYS.PHYS-OPTICS] Physics [physics]/Physics [physics]/Optics [physics.optics], [PHYS.PHYS.PHYS-OPTICS]Physics [physics]/Physics [physics]/Optics [physics.optics]
Abstract

International audience; An output power of 115 mW at 545 nm has been obtained from a diode-pumped self-frequency doubling Nd:GdCa4O(BO3)3 laser in a stable cavity. The infrared emission of the laser was found to be 1091 nm, not the 1060 nm that was expected when the highest line of the fluorescence spectrum was considered. We have demonstrated that the emission at 1091 nm was caused by the temperature increase at the focus of the pump beam. We demonstrated also, for what we believe was the first time, lasing operation of Nd:GdCOB in a plano-plano cavity and obtained an output power of 22 mW at 545 nm. To our knowledge, this is the highest output power ever reported with a self-frequency-doubling crystal in a plano-plano cavity

Published
2000

33. Efficient, tunable, zero-line-diode-pumped, continuous-wave Yb3+:Ca4LnO(BO3)3 (Ln=Gd,Y) lasers at room temperature, application to miniature lasers

Author

Druon, Frédéric, Auge-Rochereau, Frederika, Balembois, François, Georges, Patrick, Brun, Alain, Aron, Astrid, Mougel, Frédéric, Aka, Gerard, Vivien, Daniel, Laboratoire Charles Fabry de l'Institut d'Optique / Elsa, Laboratoire Charles Fabry de l'Institut d'Optique (LCFIO), Centre National de la Recherche Scientifique (CNRS)-Institut d'Optique Graduate School (IOGS)-Université Paris-Sud - Paris 11 (UP11)-Centre National de la Recherche Scientifique (CNRS)-Institut d'Optique Graduate School (IOGS)-Université Paris-Sud - Paris 11 (UP11), Laboratoire de Chimie Appliquée de l'État Solide (LCAES), Ecole Nationale Supérieure de Chimie de Paris - Chimie ParisTech-PSL (ENSCP), and Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Centre National de la Recherche Scientifique (CNRS)

Subjects
[PHYS.PHYS.PHYS-OPTICS]Physics [physics]/Physics [physics]/Optics [physics.optics]
Abstract

International audience; We demonstrate an efficient cw 976-nm-diode-pumped Yb31:Ca4GdO(BO3)3 laser. At room temperature we obtained 814 mW of power with a slope efficiency of 77% and a small-signal gain per round trip of 1.67. We also demonstrate that the Yb31:Ca4LnO(BO3)3 (Ln 5 Gd, Y) crystals are suitable for a plano-plano microchiptype cavity. With this microlaser we have obtained an average power of 300 mW, which corresponds to an optical-optical conversion efficiency of 27%

Published
2000

34. New-green self-frequency doubling diode-pumped Nd:Ca4GdO (BO3)3 laser

Author

Mougel, Frédéric, Augé, Frédérica, Aka, Gerard, Kahn-Harari, Andrée, Vivien, Daniel, Balembois, François, Georges, Patrick, Brun, Alain, Laboratoire de Chimie Appliquée de l'État Solide (LCAES), Ecole Nationale Supérieure de Chimie de Paris - Chimie ParisTech-PSL (ENSCP), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Centre National de la Recherche Scientifique (CNRS), Crismatec, Laboratoire Charles Fabry de l'Institut d'Optique / Elsa, Laboratoire Charles Fabry de l'Institut d'Optique (LCFIO), and Centre National de la Recherche Scientifique (CNRS)-Institut d'Optique Graduate School (IOGS)-Université Paris-Sud - Paris 11 (UP11)-Centre National de la Recherche Scientifique (CNRS)-Institut d'Optique Graduate School (IOGS)-Université Paris-Sud - Paris 11 (UP11)

Subjects
[PHYS.PHYS.PHYS-OPTICS]Physics [physics]/Physics [physics]/Optics [physics.optics], ComputingMilieux_MISCELLANEOUS
Abstract

International audience

Published
1998

38. First measurement of the nonlinear coefficient for Gd1-xLux Ca4O(BO3)3 and Gd1-xScxCa4O(BO3)3 crystals

Author

Andersen, Martin Thalbitzer, Mortensen, Jesper Liltorp, Germershausen, Sven, Tidemand-Lichtenberg, Peter, Buchhave, Preben, Gheorghe, Lucian, Lupei, Voicu, Loiseau, Pascal, Aka, Gerard, Andersen, Martin Thalbitzer, Mortensen, Jesper Liltorp, Germershausen, Sven, Tidemand-Lichtenberg, Peter, Buchhave, Preben, Gheorghe, Lucian, Lupei, Voicu, Loiseau, Pascal, and Aka, Gerard

Abstract

The effective nonlinear coefficient and temperature acceptance bandwidth of three Lu and Sc co-doped GdCa4O(B03)3 type nonlinear crystals were measured. NCPM for SHG in to the blue-UV spectral region can be obtained by controlling the co-dopant concentration. Measurements were based on intra-cavity SHG of a CW Ti:Sapphire laser, and the effective nonlinear coefficients were found to be in the range of 0.5 to 0.6 pm/V for the three crystals used. The FWHM temperature acceptance bandwidth was measured to be more than 35 °C using a 6 mm long Gd0.871Lu0.129Ca4O(BO3)3 crystal. A maximum of 115 mW at 407.3 nm in a single direction was measured using a 6.5 mm long Gd0.96Sc 0.04CaO(BO3)3 crystal.

Published
2007

Catalog

Books, media, physical & digital resources
See catalog results