Visible nonlinear optical properties of tellurium and application as saturable absorber.

• The nonlinear optical properties of Te nanosheets in the visible band is investigated by Z-scan technology. • The Q-switched laser is achieved with the Te SA at the wavelength at 605 nm, 639 nm, and 721 nm. • The Q-switched mode-locked laser is achieved with the Te SA at the wavelength at 639 nm. Tellurium, a novel two-dimensional (2D) Group-VI material, has attracted much attention benefitting from its excellent electrical and optical properties. In this contribution, tellurium nanosheets were directly dispersed in toluene in the existence of polymer and were easily fabricated into flexible thin films. The nonlinear optical absorption properties of tellurium film at the visible band were studied by the open-aperture Z-scan method. For the application of laser modulation, we realized the passively Q-switched Pr: YLF laser over the spectrum of orange (605 nm), red (639 nm), deep red (721 nm) with tellurium film as the saturable absorber (SA). Furthermore, we also realized the passively Q-switched mode-locked laser at 639 nm with the tellurium SA. The research results indicate the tellurium thin film has remarkable nonlinear optical absorption properties and could be a promising optical modulator in the visible domain. [ABSTRACT FROM AUTHOR]