Growth of Yb:Y 2 O 3 single crystals by the micro-pulling-down method
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Growth of Yb:Y2O3 single crystals by the micro-pulling-down method A. Novoselov1, J. H. Mun1, A. Yoshikawa1, G. Boulon1,2, and T. Fukuda1 1 Institute of Multidisciplinary Research for Advanced Materials, Tohoku University, Sendai 980-8577, Japan 2 Physical Chemistry of Luminescent Materials, UMR 5620 CNRS, Claude Bernard/Lyon1 University, 69622 Villeurbanne, France
ABSTRACT (YbxY1-x)2O3 (x = 0.0, 0.005, 0.05, 0.08 and 0.15) promising single crystal laser rods of 4.2 mm in diameter and 15–20 mm in length have been grown from the rhenium crucible by the micro-pulling-down method in Ar + H2(3-4%) atmosphere. Linear decrease of lattice constant with the increase of Yb3+-content was observed. High homogeneity of the Yb3+-dopant distribution has been demonstrated. Absorption, emission and Raman spectra have been recorded and decay time was approximated.
INTRODUCTION The rare-earth sesquioxides (RE2O3, RE=Lu, Y and Sc) crystallized in cubic structure are promising host materials for high power solid-state lasers due to a favourable combination of both thermal properties, because of the low phonon energy and high thermal conductivity, and optical properties, because of the wide transparency range [1, 2]. The most promising ion to dope this host is Yb3+ because it has the simplest energy-level diagram involving only two states, 2F7/2 excited state and 2F5/2 ground state associated with spinorbit coupling. Since there is only one 2F5/2 excited state, there is no excited state absorption, no cross-relaxation process and no more up-conversion internal mechanism which otherwise might impede population inversion and reduce the effective laser cross-section in the crystals without any other impurities. It is also easy to convert laser techniques used for the former Nd3+ laser sources to Yb3+-doped ones since their emissions are rather similar: around 1060nm for Nd3+ and between 980 and 1050nm for Yb3+, and works well with high power laser diodes emitting between 920 and 990nm. The low thermal load observed in Yb3+-doped crystals is due to the small quantum defect between infra-red absorption and emission wavelengths. This is another advantage of these types of lasers when the energetic balance allowing compactness of the cavity is considered [3, 4]. However, it should be noted that thermal conductivity of RE2O3 being doped with Yb3+ drops considerably and it is lower than that of Yb3+-doped Y3Al5O12 in the case of scandia [5]. Because sesquioxides are characterized by a high melting point of around 2400 °C, their bulk single crystal growth technology has not been well established yet. A variety of crystal growth techniques such as the Verneuil, Bridgman, Czochralski, flux, floating zone and laser heated pedestal growth (LHPG) methods were applied, but resulted in the crystals being limited in size or optical quality [2, 5-9]. Finally, a diode-pumped femtosecond Yb:Y2O3 ceramic laser was reported recently [10].
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In this paper we show that the growth of Yb3+-doped yttrium oxide crystals is possible by the micr
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