Gold nanorods (GNRs) with two different aspect ratios were successfully utilized as saturable absorbers (SAs) in a passively Q-switched neodymium-doped lutetium lithium fluoride (Nd:LLF) laser emitting at 1.34 μm. Based on the GNRs with an aspect ratio of five, a maximum output power of 1.432 W was achieved, and the narrowest pulse width was 328 ns with a repetition rate of 200 kHz. But, in the case of the GNRs with the aspect ratio of eight, a maximum output power of 1.247 W was achieved, and the narrowest pulse width was 271 ns with a repetition rate of 218 kHz. Our experimental results reveal that the aspect ratios of GNRs have different saturable absorption effects at a specific wavelength. In other words, for passively Q-switched lasers at a given wavelength, we are able to select the most suitable GNRs as an SA by changing their aspect ratio.

In this paper, the fabrication process and characterization of Bi2Te3 topological insulators (TIs) synthesized by the spin-coating-coreduction approach (SCCA) is reported. With this approach, high-uniformity nano-crystalline TI saturable absorbers (TISAs) with large-area uniformity and controllable thickness are prepared. By employing these prepared TIs with different thicknesses as SAs in 2-μm solid-state Q-switched lasers, thickness-dependent output powers and pulse durations of the laser pulses are obtained, and the result also exhibits stability and reliability. The shortest pulse duration is as short as 233 ns, and the corresponding clock amplitude jitter is around 2.1%, which is the shortest pulse duration in TISA-based Q-switched 2-μm lasers to the best of our knowledge. Moreover, in comparison with the TISA synthesized by the ultrasound-assisted liquid phase exfoliation (UALPE) method, the experimental results show that lasers with SCCA synthesized TISAs have higher output powers, shorter pulse durations, and higher pulse peak powers. Our work suggests that the SCCA synthesized TISAs could be used as potential SAs in pulsed lasers.

By simultaneously employing both an electro-optic modulator and carbon nanotube saturable absorber (CNT-SA) in a dual-loss modulator, a subnanosecond single mode-locking pulse underneath a Q-switched envelope with high peak power was generated from a doubly Q-switched and mode-locked (QML) Nd:Lu0.15Y0.85VO4 laser at 1.06 μm for the first time, to our knowledge. CNTs with different wall structures—single-walled CNTs (SWCNTs), double-walled CNTs (DWCNTs), and multi-walled CNTs (MWCNTs)—were used as SAs in the experiment to investigate the single mode-locking pulse characteristics. At pump power of 10.72 W, the maximum peak power of 1.312 MW was obtained with the DWCNT.

Two-dimensional (2D) graphite carbon nitride (g-C3N4) nanosheets have been successfully used as a saturable absorber (SA) in a passively Q-switched Nd:LLF laser at 1.3 μm for the first time, to the best of our knowledge. Under an incident pump power of 9.97 W, the shortest pulse duration of 275 ns was acquired with output power of 0.96 W and pulse repetition rate of 154 kHz, resulting in a pulse energy of 6.2 μJ. In addition, the saturable absorption behaviors of zero-dimensional 12 nm g-C3N4 nanoparticles (g-C3N4-NPs) and three-dimensional ordered mesoporous g-C3N4 (mpg-C3N4) were also observed, although their morphology and structure were quite different from 2D g-C3N4. The experimental results introduce the potential application of g-C3N4 nanomaterials as SAs in Q-switched lasers.

Multilayer black phosphorus (BP) nanoplatelets of different thicknesses were prepared by the liquid phase exfoliation method and deposited onto yttrium aluminum garnet substrates to form saturable absorbers (SAs). These were characterized with respect to their thickness-dependent saturable absorption properties at 3 μm. The BP-SAs were employed in a passively Q-switched Er:Lu2O3 laser at 2.84 μm. By using BP exfoliated in different solvents, stable pulses as short as 359 ns were generated at an average output power of up to 755 mW. The repetition rate in the experiment was 107 kHz, corresponding to a pulse energy of 7.1 μJ. These results prove that BP-SAs have a great potential for optical modulation in the mid-infrared range.