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The second-harmonic generation (SHG) in gallium doped ZnO (GZO) nanofilms was studied. The Ga doping in GZO nanofilms influenced the crystal structure of the films, which affected SHG characteristics of the nanofilms. In our experiments, a strong SHG response was obtained in GZO nanofilms, which was excited by 790 nm femtosecond laser. It was observed that the Ga doping concentrations affected, not only the intensity, but also the polarimetric pattern of SHG in GZO nanofilms. For 5.0% doped GZO films, the SHG intensity increased about 70%. The intensity ratio of SHG between the incident light polarization angle of 90° and 0°changed with the Ga doping concentrations. It showed the most significant increase for 7.3% doped GZO films, with an increased ratio of c/a crystal constants. This result was attributed to the differences of the ratios of d33/d31 (the second-order nonlinear susceptibility components) induced by the crystal distortion. The results are helpful to investigate nanofilms doping levels and crystal distortion by SHG microscopy, which is a non-destructive and sensitive method. [ABSTRACT FROM AUTHOR]

Highlights • Our fiber curvature sensor has merits of inline compact, low cost and sensitive. • Highly sensitivity −15.33 dB/m−1 in the range 3.63–4.69 m−1 is experimentally demonstrated. • Low cross sensitivity 0.018 m−1/°C implies it is insensitive to environmental temperature change. Abstract An inline fiber structure formed by a silica tube spliced between single-mode fibers has been developed and tested for curvature measurement based on anti-resonant reflecting waveguide. A Fabry-Perot resonator with leaky modes of guided light in the silica tube is formed based on anti-resonant effect in the resonant wavelengths, which results in lossy dips in the transmission spectrum. Since the transmission power of the resonant dips is sensitive to structure bending, an inline curvature sensor can be realized. Experimental results reveal a high sensitivity up to −15.33 dB/m−1 in the wide curvature range of 3.63–4.69 m−1. The proposed sensor also demonstrates a low temperature sensitivity 0.27 dB/°C implying a small temperature cross sensitivity 0.018 m−1/°C. Our sensor has its merits of compact, low cost and high sensitivity. [ABSTRACT FROM AUTHOR]