Self-assembled gold nanoparticles as saturable absorber for low-threshold all-solid-state pulsed 2 μm laser

In order to overcome the shortcomings of un-uniformity of two-dimension (2D) material based saturable absorbers (SAs) and improve the performance of consequently generated laser pulses, a kind of gold nanoparticles (GNPs) based SAs was synthesized and employed to form 2 μm low-threshold pulsed laser. Two SA samples with different density of GNPs were fabricated and their modulation performance was compared under similar condition. Using Tm:YAP as gain medium, the constructed passively Q-switched 2 μm all-solid-state laser could deliver the shortest laser pulses with duration of 580 ns, repetition rate of 129 kHz and an average output power of 601 mW by using the first SA sample (with high GNPs density), corresponding to a pulse energy of 4.37 μJ and a peak power of 6 W. Laser pulses with a high pulse energy of 6.1 μJ and a peak power of 7.5 W were obtained with the second sample (with low GNPs density). Besides, the formed Q-switched lasers showed very low thresholds because of the large third-order nonlinear coefficient of GNPs. These results showed that the GNPs could be a promising SA for 2 μm wavelength band.