Broadband saturable absorption and exciton-exciton annihilation in MoSe 2 composite thin films

Polyvinyl alcohol (PVA) was utilized as a matrix to host two-dimensional (2D) liquid-phase-exfoliated MoSe2 nanosheets. These 2D MoSe2/PVA composite thin films were experimentally proven to be preferable for efficient nonlinear optical devices. Our nonlinear optical study shows that these composite thin films possess strong saturable absorption (SA) over a wide wavelength range from 400 nm to 800 nm under the irradiation of femtosecond and nanosecond lasers. The SA property of our films was measured for various laser pulse durations, wavelength and linear absorption. Moreover, employing pump-probe, exciton-exciton annihilation was experimentally observed and studied at 800 nm. Our research gives clear insight into the photophysical properties of MoSe2/PVA thin films and shows the material’s potential as a photonic device.