Unusual absorption and emission characteristics of Cr co−doped Nd:GdVO4 laser gain crystal

Abstract

Single crystals of Cr co-doped Nd (0.5 at%):GdVO4 with varied Cr concentrations of 1.0, 1.2 and 1.5 at% were grown in ambience having 10%, 20% and 25% oxygen by optical floating zone technique for the first time to the best of our knowledge. Lattice parameters were found to be unchanged with Cr doping concentration. The etch pit dislocation density was in the range of 103–104/cm2. The observed fringes of nearly uniform thickness and spacing in birefringence interferometry indicate the optical uniformity of the crystal across the cross-section. Further, the effect of the doping concentration and the growth atmosphere on the optical absorption, particularly for the 2A1→2B2 transition (at ~1100 nm) due to Cr5+ ion, was investigated using polarized lights (i.e., E ǁ [001] or π-polarized) and E ⊥ [001] or σ-polarized) and found to be polarization sensitive. The transition peak of Cr at 1100 nm are allowed only for π- polarization of light whereas the transitions at 650 nm are allowed only for σ- polarization of light. The absorption of Cr5+ ion increases at 1100 nm with the increase of oxygen ambience for the Cr concentration 1.2 and 1.5 at% and for the crystals with Cr concentrations of 1.0 at%, a reverse effect in the absorption of Cr5+ ion was observed. The broad absorption transition at ~1100 nm is important as it results in saturable absorption that is used for self-Q-switching application. In accordance with the absorption data the photo luminescence intensity increases for 1.0 at% Cr doping and decreases for the 1.2 and 1.5 at% Cr doping with the increase of oxygen percentage in the growth ambience respectively. The observation has important technical implication in context to saturable absorption application. It suggests that to attain the desired level of saturable absorption, the growth ambience and the concentration of Cr should be chosen in line with the result presented here.