Abstract
We investigate the enhancement of second-harmonic generation in cylindrical GaAs nanowires. Although these nanostructures confine light in two dimensions, power conversion efficiencies on the order of 10 − 5 with a pump peak intensity of ~ 1 GW / cm 2 are possible if the pump and the second-harmonic fields are coupled to the Mie-type resonances of the nanowire. We identify a large range of nanowire radii in which a double-resonance condition, i.e., both the pump and the second-harmonic fields excite normal modes of the nanowire, induces a high-quality-factor peak of conversion efficiency. We show that second-harmonic light can be scattered with large efficiency even if the second-harmonic photon energy is larger than 1.42 eV, i.e., the electronic bandgap of GaAs, above which the material is considered opaque. Finally, we evaluate the efficiency of one-photon absorption of second-harmonic light and find that resonant GaAs nanowires absorb second-harmonic light in the near-field region almost at the same rate at which they radiate second-harmonic light in the far-field region.
Highlights
Optical and electronic properties of semiconductors such as Si and GaAs are suitable for the development of highly-efficient nonlinear and tunable nanophotonic devices
If the pump is slightly detuned from this double resonance condition, the structure turns out to be singly-resonant with the only TM0 mode resonantly excited by the pump and a 4-fold reduction of conversion efficiency—the dotted black circle belongs to this singly-resonant region
We have investigated SH generation from Mie-resonant GaAs nanowires
Summary
Optical and electronic properties of semiconductors such as Si and GaAs are suitable for the development of highly-efficient nonlinear and tunable nanophotonic devices. Sci. 2019, 9, 3381 for the design of nanophotonic devices with enhanced light–matter interactions [17], and they are considered valid alternatives to plasmonic-based systems [18], especially for nonlinear optics which require high light-intensities and, in particular, for applications in the visible and near-infrared, where metals absorb light more efficiently. The key factor to achieve strong nonlinear interactions in semiconductor nanoparticles is to couple light to Mie scattering modes [22]. Nonlinear effects, such as SH and TH generation, have been so far investigated in isolated and arrayed Si- and GaAs-based resonant nanoparticles with three-dimensional (3D) light confinement, such as spheres and finite cylinders (nanodisks or nanopillars). We discuss the role of absorption losses in SH generation, and demonstrate that: (i) Nanowires produce intense SH light even when the SH photon energy is tuned above the electronic bandgap of GaAs, where the material is opaque and it is commonly assumed that harmonic generation is not efficient, and (ii) absorption of SH light is not negligible even when the SH photon energy is tuned below the electronic bandgap of GaAs
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