Disordered Tm3+,Ho3+-codoped CNGG garnet crystal: Towards efficient laser materials for ultrashort pulse generation at ∼2 μm

Identifier:  imarina:8680383

Handle: https://hdl.handle.net/20.500.11797/imarina8680383

Authors:  Pan, ZB; Loiko, P; Wang, YC; Zhao, YG; Yuan, HL; Tang, KY; Dai, XJ; Cai, HQ; Serres, JM; Slimi, S; Ben Salem, E; Dunina, E; Kornienko, A; Fomicheva, L; Doualan, JL; Camy, P; Chen, WD; Griebner, U; Petrov, V; Aguiló, M; Díaz, F; Solé, RM; Mateos, X

Abstract:
© 2020 Elsevier B.V. We report on the growth, structure refinement, optical spectroscopy, continuous wave and femtosecond mode-locked laser operation of a Tm3+,Ho3+-codoped disordered calcium niobium gallium garnet (CNGG) crystal. The 2.64 at.% Tm, 0.55 at.% Ho:CNGG is grown by the Czochralski method. Its cubic structure, sp. gr. Ia3¯d - O10h, a = 12.4952(1) Å, is refined by the Rietveld method revealing a random distribution of Ga3+ and Nb5+ cations over octahedral and tetrahedral sites. The Ho3+ transition probabilities are determined within the Judd-Ofelt theory accounting for an intermediate configuration interaction (ICI). For the 5I7 → 5I8 Ho3+ transition, the maximum stimulated-emission cross-section σSE is 0.47 × 10−20 cm2 at 2080.7 nm. The gain bandwidth of Tm,Ho:CNGG at ∼2 μm is > 150 nm and the thermal equilibrium decay time - 6.80 ms. The Tm3+ ↔ Ho3+ energy transfer parameters are determined. A diode-pumped Tm,Ho:CNGG microchip laser generated 413 mW at 2088.4 nm with a slope efficiency of 15.9%. A continuous wavelength tuning between 1940.3 and 2144.6 nm is demonstrated. Ultrashort pulses as short as 73 fs are achieved at 2061 nm from a Tm,Ho:CNGG laser mode-locked by a GaSb semiconductor saturable absorber mirror at a repetition rate of 89.3 MHz.