With the increase of the laser powers and the decrease of the pulse durations, materials with very large optical nonlinearities are of great interest for the laser community. Indeed, depending on the type of the nonlinearities, they can be used for several applications including frequency conversion and self-focusing. In particular, saturable absorbers are widely studied, as they allow mode-locking of laser systems or super-resolved laser writing. In this work, we have studied the saturable absorption efficiency of Sb2Te3 thin layers. Layers with thicknesses ranging from 2.5 to 30 nm have been deposited using electron beam deposition (Bühler SYRUSpro 710). These films were then annealed in a temperature-controlled furnace at 250°C during 1h to ensure that the layers are completely crystallized. These layers were then thoroughly inspected with X-Ray Diffraction (XRD), Scanning Electron Microscopy (SEM), Backscattered electron detector (BSD) and Transmission Electron Microscopy (TEM). The nonlinear optical properties under nanosecond and femtosecond pulse duration were also studied for each layer using the Z-Scan technique. These studies allowed the determination of the nonlinear absorption and the nonlinear refraction of the samples under two different wavelengths at each pulse duration regime. In this paper we present a correlation between the structure of the Sb2Te3 thin films and the observed nonlinearities.
The diffraction limit is one of the main difficulties in order to achieve nano-resolution. An evolution in this domain can allow a significant advance in the field of photonic circuit fabrication. Surpassing the diffraction limit can be achieved by employing significant optical nonlinearities (nonlinear refraction and/or nonlinear absorption). In this direction we investigate the nonlinear absorption efficiency of annealed Sb2Te3 chalcogenide thin films (20 nm thickness). The studies have been performed using the Z-scan technique, employing 11 ns duration pulses at 1064 nm. The Z-scan technique has been chosen as it allows the simultaneous determination of the nonlinear refraction and the nonlinear absorption of a material, under certain conditions. Our results indicate a significant nonlinear absorption, while the nonlinear refraction is at least one order of magnitude lower. The nonlinear absorption parameter has been found to be in the order of -10-3 m/W under infrared irradiation showing the importance of the prepared materials for laser photoinscription applications. Our values are compared with previous studies, which have been carried out in the visible part of the spectrum. The possibility to perform photonic component fabrication by local modification of the linear or the nonlinear properties of the materials is also discussed.
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