Recently, researchers in Shanghai Institute of Optics and Fine Mechanics (SIOM), Chinese Academy of Sciences (CAS), carried out a systematic investigation on the nonlinear optical properties and ultrafast carrier dynamics of indium selenide (InSe) nanosheets under pulsed excitation with different durations. The related research results have been published in Advanced Optical Materials on Oct. 6, 2021.

InSe is a bandgap adjustable layered semiconductor material with nonlinear optical response in a wide wavelength range. In this work, InSe nanosheets with appropriate thickness and bandgap were obtained via liquid-phase exfoliation technique.

Scientists observed that InSe nanosheets exhibited pulse-duration-dependent saturable absorption and nonlinear scattering responses. The saturable absorption results showed that InSe nanosheets are more easily to be saturated under long-pulse laser excitation than short-pulse laser excitation. At the same time, they found the difference of the scattering phenomena under various pulse durations. Under the excitation of ns pulse light, the scattering of the InSe dispersion was caused by the thermal effect.

However, the scattering phenomenon excited by fs pulse light is caused by the dynamic SSPM, affected by laser streaming. Simultaneously, the continuous wave laser can be modulated with a modulation depth from ~0.2 to –2.5 dB by means of the competition mechanism between saturable absorption and nonlinear scattering in the InSe dispersion under ns pulse excitation. Ultrafast carrier dynamics revealed that the InSe nanosheet has an ultrafast saturation absorption process induced by Pauli blocking of excited electrons, and a photoinduced absorption process may be caused by free carrier absorption or bandgap renormalization.

These detailed characterizations of the linear and NLO properties and ultrafast carrier dynamics is an important step toward the application of InSe in optoelectronic devices.

This work was supported by the Chinese National Natural Science Foundation and the Strategic Priority Research Program of CAS.

Figure 1. Saturable absorption response and carrier relaxation process of InSe nanosheets. (Image by SIOM)

Article website:
https://doi.org/10.1002/adom.202101432