Abstract
Herein, pure ZnO, Ag-doped ZnO, and Cu-doped ZnO films with excellent ultrafast (femtosecond) nonlinear absorption/limiting behavior were deposited on quartz substrates by magnetron sputtering. From the open-aperture Z-scan result, under femtosecond pulses, the strong two-photon absorption (TPA) behavior of metal-doped ZnO was found, and the absorption coefficient was found to be several times that of pure ZnO, which will expand the design and application strategies of metal-doped wide-gap semiconductor materials in the field of nonlinear devices. Moreover, the samples exhibited superior optical limiting behavior with respect to the optical modulation characteristics of the input–output laser. The mechanism of optical limiting effects is induced by the TPA-induced reverse saturable absorption of the deep level and low excited state processes.
Highlights
Among semiconductor nanomaterials, wurtzite zinc oxide (ZnO) is one of the most important II–VI group elements.1 Based on a wide range of physical chemistry and biomedical applications, it can be said that ZnO films have a lot of realizable research value and potential prospects.2–6 Nowadays, as a representative of renewable energy, solar energy provides much convenience for production and life
The doped metal nanoparticles interact with the semiconductor nanostructures, which will cause internal stress and donor impurity levels, thereby modulating the linear and nonlinear optical (NLO) properties of the original semiconductor material, including second/third harmonic generation and extremely large third-order nonlinear refractive index/reflectance modulations related to the dielectric constant
We demonstrated that the optical limiting (OL) mechanism of Ag-doped ZnO (AZO) films is two-photon absorption (TPA) induced reverse saturable absorption (RSA),11 while Cu-doped ZnO (CZO) films show saturable absorption (SA) and RSA under different laser intensities
Summary
Wurtzite zinc oxide (ZnO) is one of the most important II–VI group elements. Based on a wide range of physical chemistry and biomedical applications, it can be said that ZnO films have a lot of realizable research value and potential prospects. Nowadays, as a representative of renewable energy, solar energy provides much convenience for production and life. The doped metal nanoparticles interact with the semiconductor nanostructures, which will cause internal stress and donor (acceptor) impurity levels, thereby modulating the linear and nonlinear optical (NLO) properties of the original semiconductor material, including second/third harmonic generation and extremely large third-order nonlinear refractive index/reflectance modulations related to the dielectric constant. Pure ZnO and noble metal-doped ZnO films have unique NLO behavior, such as a higher NLO absorption/refraction coefficient and OL characteristics, especially in the case of femtosecond pulse laser excitation, which means it is of research value to fabricate better metal-doped systems. Under nano/femtosecond pulses, the stronger two-photon absorption induced RSA characteristics realize the NLO behavior of absorbing intense light and transmitting weak light, which means that AZO and CZO films may have potential application in the field of optical limiting devices and all-optical switches
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