Lanthanum hexaboride for Q-switching and mode-locking applications

In this paper, a new saturable absorber (SA) based on Lanthanum Hexaboride (LaB₆) is used to produce Q-switched and mode-locked laser pulses. In constructing the SA, the prepared LaB₆ powder is dispersed in polyvinyl alcohol (PVA) solution before the mixture is dried to form a thin film. A small piece of the film is placed between two fiber ferrules to form a LaB₆ PVA SA and added to a laser cavity of an erbium-doped fiber laser (EDFL) to produce Q-switched and mode-locked pulses. The Q-switched laser operates at 1531 nm. The pulse width of the pulses can be varied between 4.32 to 2.46 μs with a corresponding repetition rate of 62.0 to 89.6 kHz when the pump power is increased from 45.4 to 97.6 mW. At the maximum output power of 4.31 mW, the highest pulse energy of 48.1 nJ was obtained. A passively mode locked EDFL was also successfully realized with LaB₆ SA by adding 100 m long single mode fiber inside the cavity. A stable mode-locked laser operating at 1559.1 nm was achieved at the threshold pump power of 102.8 mW with a pulse rate of 1.88 MHz. The pulse energy of 5.6 nJ and output power of 10.54 mW were obtained at a maximum pump power of 144.6 mW. To the best of our knowledge, this is the first demonstration of utilizing LaB₆ material as SA to produce pulses in the 1.5 μm region.