Tm 3+ -doped calcium lithium tantalum gallium garnet (Tm:CLTGG): novel laser crystal

Abstract

We report on the development of a novel laser crystal with broadband emission properties at ∼2 µm – a Tm 3+ ,Li + -codoped calcium tantalum gallium garnet (Tm:CLTGG). The crystal is grown by the Czochralski method. Its structure (cubic, sp. gr. I a 3 ¯ d , a = 12.5158(0) Å) is refined by the Rietveld method. Tm:CLTGG exhibits a relatively high thermal conductivity of 4.33 Wm -1 K -1 . Raman spectroscopy confirms a weak concentration of vacancies due to the charge compensation provided by Li + codoping. The transition probabilities of Tm 3+ ions are determined using the modified Judd-Ofelt theory yielding the intensity parameters Ω 2 = 5.185, Ω 4 = 0.650, Ω 6 = 1.068 [10 −20 cm 2 ] and α = 0.171 [10 −4 cm]. The crystal-field splitting of the Tm 3+ multiplets is revealed at 10 K. The first diode-pumped Tm:CLTGG laser generates 1.08 W at ∼2 µm with a slope efficiency of 23.8%. The Tm 3+ ions in CLTGG exhibit significant inhomogeneous spectral broadening due to the structure disorder (a random distribution of Ta 5+ and Ga 3+ cations over octahedral and tetrahedral lattice sites) leading to smooth and broad gain profiles (bandwidth: 130 nm) extending well above 2 µm and rendering Tm:CLTGG suitable for femtosecond pulse generation.