Hafnium Diboride as a saturable absorber for Q-switched lasers

Abstract

ABSTRACTHafnium diboride (HfB2) is used in hypervelocity re-entry vehicles (such as intercontinental ballistic missile (ICBM) or ICBM heat shields), nuclear reactors and aerodynamic leading edges because of its strong tensile strength and high thermal resistance. HfB2 is an ultra-high-temperature ceramic (UHTC) with a melting point of 3250°C. In this paper, we study the performance of HfB2 as a saturable absorber in Q-switched lasers. HfB2 has a non-saturable absorptance of 2.5 dB/µm, a saturable absorptance of 0.8 dB/µm and a saturation fluence of 12 µJ/cm2. In addition, the saturation lifetime is estimated as 989.3 ps, while the recovery lifetimes are estimated as 254.9 and 22.1 ps. As a saturable absorber in our Q-switched laser, we observed pulses with durations between 880 and 2000 ns. With the addition of an acousto-optic modulator, we have observed Q-switching mode-locking, with pulses as low as 250 ns. HfB2 can potentially work at very high power, since its damage fluence is no less than 361 mJ/cm2.