New near-infrared optical modulator of Co<sup>2+</sup>:β-Ga<sub>2</sub>O<sub>3</sub> single crystal
Jin Zhang, Yiran Wang, Wenxiang Mu, Zhitai Jia, Baitao Zhang, Jingliang He, Xutang Tao
Abstract
As a binary oxide, β-Ga2O3 is a promising host material with high thermal conductivity compared with the traditional laser materials. In this work, Co2+-doped β-Ga2O3 single crystal was successfully grown by the edge-defined film-fed growth (EFG) method and firstly designed as a near-infrared (NIR) optical modulator by doping with cobalt. The doping concentration of Co2+ ions was determined to be 0.029 at.% by X-ray fluorescence. The thermal conductivity was determined to be 13.0 W·m-1·K-1 along a* direction. There were two typical broadband absorption peaks around 1173 nm and 1588 nm related to the transitions of transitions of 4A2(4F)→4T1(4F). By means of Z-scan technique, the third-order nonlinear refractive index of Co2+:β-Ga2O3 was measured to be 9.14×10−13 (esu), which was much larger than that of Cr4+:YAG crystal. It was further successfully employed as a saturable absorber for passively Q-switched lasers at 1342 nm. In the Q-switched regime, the maximum average output power of 35 mW was obtained with the shortest pulse width of 280 ns and repetition rate of 181 kHz. The results indicated that Co2+:β-Ga2O3 crystals have important potential to be used as optical modulators for passive Q-switching laser generation at the NIR band.