A Graphene-Based Passively Q-Switched Ho:YAG Laser

A 2.09-μm in-band pumped passively Q-switched Ho:YAG laser is demonstrated. Single layer graphene deposited on a quartz substrate is used as the saturable absorber for the Q-switched operation. The minimum pulse width of 2.11 μs is obtained at an average output power of 100 mW, corresponding to a pulse repetition frequency of 57.1 kHz and the pulse energy of 1.75 μJ. The beam quality factors M² of the Q-switched laser are 1.18 and 1.22 in the horizontal and longitudinal direction, respectively. The optical-to-optical conversion efficiency of the passively Q-switched laser is 4.3%, which is the highest conversion efficiency in the 2 μm wavelength, to the best of our knowledge. It shows clearly that the Ho:YAG crystal is a potential gain medium in the 2 μm range for the graphene application.