Comparative study of the spectroscopic and laser properties of Tm3+, Na+(Li+)-codoped Ca3Nb1.5Ga3.5O12 -type disordered garnet crystals for mode-locked lasers

Tm3+,X+-codoped disordered calcium niobium garnet crystals, Ca3Nb2-xGa3+xO12 (CNGG), where X+ is an alkali cation_ Na+ or Li+ (shortly Tm:CNNGG and Tm:CLNGG, respectively), are grown by the Czochralski method. A comparative study of their spectroscopic and laser properties is performed. Raman spectra are also studied. For Tm:CNNGG, the Judd-Ofelt parameters for the Tm3+ dopant ion are Omega(2) = 1.847, Omega(4) = 1.558 and Omega(6) = 0.862 [10(-20)cm(2)] and the radiative lifetime of the F-3(4) state is 4.11 ms. The absorption, stimulated-emission (sigma(SE)) and gain cross-sections are determined for the H-3(6) <--> F-3(4) Tm3+-ion transition. For Tm:CNNGG, the maximum sigma(SE) is 0.49 x 10(-20) cm(2) at 1867 nm. Both crystals exhibit flat and broad gain spectra extending beyond 2 mu m. A compact diodepumped Tm:CNNGG laser has generated 1.05 W at 2007.7 nm with a slope efficiency of 35%. Broadband tuning of Tm:CNNGG and Tm:CLNGG lasers (tuning ranges of 168 nm and 224 nm, respectively), was demonstrated. The Tm3+,X+-codoped CNGG crystals are the promising for sub-100 fs pulse generation at similar to 2 m. (C) 2018 Optical Society of America under the terms of the OSA Open Access Publishing Agreement