Diode-pumped 2 μm vibronic (Tm3+, Yb3+): KLu(WO4)2 laser

We report on laser operation in a (6 at. % Tm, 5 at. % Yb): KLu (WO4)(2) codoped crystal. The vibrational frequencies of KLu(WO4)(2) are coupled to the electronic transitions of Tm3+ at 1946 nm, creating virtual final laser levels at higher energy than the ground level H-3(6) of Tm3+. The longest recorded laser wavelength was 2039 nm, which is longer than permitted by a pure electronic transition in Tm3+ ions in KLu(WO4)(2). We show that every laser wavelength can be explained with the electron-phonon coupling effect, where the vibration frequencies were determined through Raman spectroscopy. (C) 2012 Optical Society of America