Two-dimensional transition metal dichalcogenides are considered promising materials for next-generation photonics and nano-optical devices. Although many previous reports have shown saturable absorption of molybdenum diselenide (MoSe2), these nonlinear optical (NLO) properties of MoSe2 were measured in separate works and under different conditions with their hot-carrier relaxations. Here, we conducted a series of coherent studies on the NLO properties of few-layer MoSe2 via open-aperture Z-scan and degenerate pump-probe techniques. These measurements were taken to test the materials’ capabilities as a slow-saturable absorber. A slow-absorber model was employed to analyze the NLO measurements, and the results show that the NLO modulation depth was modeled to be 7.4% and 15.1% for the linear absorption coefficients of 5.22 cm 1 and 6.51 cm 1, respectively. The corresponding saturated intensities were modeled to be 39.37 MW/cm2 and 234.75 MW/cm2, respectively. The excitation carrier recovery time of few-layer MoSe2 was measured by degenerate pump-probe techniques to be ～220 ps. These nonlinear optical performances make it a promising slow-saturable absorber for passive mode locking in femtosecond lasers.

Two-dimensional (2D) periodical Au and indium tin oxide (ITO) nanocomposite arrays have been fabricated based on a self-assembled nanosphere lithography technique. A button-shaped Au nanoparticle was formed on each hollow hemisphere-shaped ITO shell. Importantly, the underlying formation mechanism during the thermal treatment has been thoroughly explored by comparing structures resulting from different deposition conditions in detail. Compared to the Au nanoparticle arrays without ITO shells, the Au/ITO nanocomposite arrays showed a stronger localized surface plasmon resonance effect and higher absorption in the near-infrared (NIR) region, benefiting from the free-electron interaction enhancement between Au and ITO. The nonlinear optical properties were investigated using a modified femtosecond intensity-scan system, and the results demonstrated Au/ITO nanocomposite arrays with a remarkable two-photon absorption saturation effect for femtosecond pulses at 1030 nm. The versatile NIR optical responses indicate the great potential of the elaborately prepared 2D periodical Au/ITO nanocomposite arrays in many applications such as solar cells, photocatalysis, and novel nano optoelectronic devices.