Investigation of the effect of Cr co-doping on the refractive index, spectroscopic parameters and lasing of Nd:GdVO4 crystals

Cr co-doped (0.5, 1.0, 1.2 and 1.5 at.%) Nd (0.5 at.%):GdVO4 single crystals, used as laser gain medium, were grown by the optical floating zone technique to investigate the effect of Cr on the refractive index and spectroscopic properties. The ordinary (no) and extra-ordinary (ne) refractive index of 0.5 at.% Cr co-doped Nd:GdVO4 crystals was found to be lower than the 1.0 at.% Cr co-doped crystals, and thereafter it becomes almost constant up to 1.5 at.% of Cr co-doping. Further, the thermo-optic coefficient (dn/dT) of Cr co-doped Nd:GdVO4 crystals is positive with values ∼10−5/°C and the value is higher for ne compared to no for all the Cr doping concentrations. Further, the measured fluorescence lifetime of Nd ion decreases from 98 to 85 μs with the increase in Cr concentration. The Judd-Ofelt (JO) analysis revealed that the JO parameters for all the samples are Ω2 ∼9.6–10.6 × 10−20 cm2, Ω4 ∼6.5–7.0 × 10−20 cm2 and Ω6 ∼6.5–7.0 × 10−20 cm2. The radiative lifetime (∼100 μs) and emission cross section (∼3.2–4.1 × 10−19 cm2) are not affected significantly by the Cr co-doping. The investigation suggests that the inclusion of Cr ion in the crystal lattice does not deteriorate the overall spectroscopic properties of the Nd ions, thus Cr may acts as an excellent activator for Q-switching in the Nd:GdVO4 laser gain medium. Further, the self Q-switching in the Cr co-doped Nd:GdVO4 laser element was demonstrated. A stable pulsed laser output at 1066 nm with power ∼105 mW, pulse width ∼477 ns and repetition rate ∼550 kHz was obtained in the 1.0 at.% Cr co-doped crystal.