Imaging of waveguiding and scattering interferences in individual GaAs nanowires via second-harmonic generation

We use the nonlinear optical property of GaAs to directly visualize the path of the near infrared incident laser light coupled into individual nanowires. We fully illuminate with near infrared pulse laser untapered and tapered GaAs nanowires grown via the Au-assisted vapor-liquid-solid mechanism. We record second-harmonic generation (SHG) signals in the visible spectrum. In some nanowires, an interference pattern is observed and investigated in terms of distances between the maxima of the SHG signal taking into account the effective refractive index in such sub wavelength structures with radius below 90 nm. We propose a model to explain the periodicity of the maxima in the SHG interference pattern. The theoretical model includes the waveguiding and the Mie scattering theories for obtaining the 2π periodicity fitting well the experiments. Moreover, we also measure interferences in tapererd nanowires with a radius down to 76 nm. The possible effect of the gold in non radiative recombination and the presence of the gold particle at the tip of some nanowires are also discussed.