An extended application of β-Ga2O3 single crystals to the laser field: Cr4+:β-Ga2O3 utilized as a new promising saturable absorber

Abstract

Considering their easy growth and doping in bulk crystal growth, and good crystalline quality, β-Ga₂O₃ single crystals, a very important wide-bandgap semiconductor, are now also considered to be a promising optical crystal candidate. In this work, a Cr⁴⁺:β-Ga₂O₃ single crystal has been grown successfully by the edge-defined film-fed growth method. The thermal conductivity of Cr⁴⁺:β-Ga₂O₃ has been measured along the a* direction at room temperature obtaining 16.2 W m⁻¹ K⁻¹, and it was much larger than that of the usually used Cr⁴⁺-doped crystals, such as Y₃Al₅O₁₂ (YAG) or YVO₄. The Raman spectrum indicated that the cutoff phonon energy of the β-Ga₂O₃ crystal was 767.8 cm⁻¹. A passively Q-switched nanosecond pulsed Nd:YAG laser based on a Cr⁴⁺:β-Ga₂O₃ saturable absorber was experimentally demonstrated for the first time to our knowledge and its mechanism is explained by first-principles calculations. By inserting the Cr⁴⁺:β-Ga₂O₃ crystal into the Nd:YAG laser cavity, a Q-switched laser operation was obtained with a maximum average output power of 50 mW. The corresponding pulse repetition rate, pulse width, and pulse energy were determined to be of 421.5 kHz, 235.2 ns and 0.12 μJ, respectively.