Tm:GGAG disordered garnet crystal for 2 μm diode-pumped solid-state laser

Lasing parameters and wavelength tunability of a new disordered solid-state active medium, Tm3+-doped gadolinium gallium aluminum garnet (Tm3+-doped Gd-3(Ga1-xAlx)(5)O-12, Tm:GGAG), were investigated. Five samples with thulium concentration ranging from 1.4 at.% to 9.2 at.% (Tm/Gd) were designed, grown and investigated. Basic spectroscopic characterization and measurement of a refractive index were performed. Each sample was tested as an active medium of a 2 mu m laser, longitudinally diode-pumped at 786 nm. Tm3+ concentration dependence of laser parameters was investigated. The highest slope efficiency of 43% w.r.t. absorbed power in the pulsed regime and 35% in the CW regime was achieved with the 2.4 at.% (Tm/Gd) sample. All samples produced beams of good quality with estimated M-2 <= 1.6 . Concentration-dependent tunability was investigated and a smooth continuous range of wavelengths, up to 187 nm wide, was recorded.