Random lasing in Nd³⁺ doped potassium gadolinium tungstate crystal powder

Random laser (RL) emission in Nd³⁺ doped potassium gadolinium tungstate - KGd(WO₄)₂:Nd³⁺ - crystal powder is demonstrated. The powder was excited at 813 nm in resonance with the Nd³⁺ transition ⁴I_9/2→⁴F_5/2. RL emission at 1067 nm due to the ⁴F_3/2→⁴I_11/2 transition was observed and characterized. An intensity threshold dependent on the laser spot area and bandwidth narrowing from ≈2.20 nm to ≈0.40 nm were observed and measured. For a beam spot area of 0.4 mm², a RL threshold of 6.5 mJ/mm² (90 MW/cm²) was determined. For excitation intensity smaller than the RL threshold, only spontaneous emission from level ⁴F_3/2 with decay time in the tens microsecond range was observed, but for excitation above the RL threshold, significant shortening of excited level lifetime, characteristic of a stimulated process was found. The overall characteristics measured show that KGd(WO₄)₂:Nd³⁺ is an efficient material for operation of solid state RLs in the near-infrared.