Abstract
Abstract Lithium niobate (LN), as a nonlinear material with a large nonlinear susceptibility, has been widely employed in second harmonic generation (SHG) up to ultraviolet (UV) frequency range due to its broad low-absorption window. In nanophotonics, it is possible to harness the Mie resonances associated with the single dielectric particles to boost the nonlinear light–matter interactions. Here, we fabricate single Mie-resonant LN nanospheres on a SiO2 substrate via the femtosecond (fs) laser ablation technique. By exploiting the magnetic dipole (MD) Mie resonance, UV SHG from the LN nanosphere is significantly enhanced with a measured conversion efficiency of 4.45 × 10−8 under the excitation of an fs laser at 750 nm. The single LN nanospheres achieved in this work could serve as Mie resonators for building nonlinear nanophotonic devices such as frequency converters and quantum light sources, etc.
Highlights
As a fundamental optical nonlinear effect, second harmonic generation (SHG) is a process that two identical photons convert into a double-frequency photon, which has been widely applied in signal processing, optical spectroscopy, and laser systems [1,2,3]
We demonstrate a strong UV SHG from single Lithium niobate (LN) nanospheres fabricated by the fs laser ablation technique
It can be observed that the intensities of the SHG signals follow the profile of the scattering spectrum, clearly demonstrating that the enhancement of the nonlinear interactions is provided by the magnetic dipole (MD) Mie resonance
Summary
As a fundamental optical nonlinear effect, second harmonic generation (SHG) is a process that two identical photons convert into a double-frequency photon, which has been widely applied in signal processing, optical spectroscopy, and laser systems [1,2,3]. With strong field confinement and great wavelength tunability by the size, geometry, and material composition, Mie resonators recently enable a wide range of applications in nonlinear nanophotonics such as Raman scattering [18, 19] and harmonic generations [19,20,21], as well as photonpair generations [22, 23] For most of these works, high refractive index dielectric materials with large nonlinear susceptibility such as silicon [24], gallium arsenide [25, 26], or germanium [27, 28] are employed, benefiting from their mature fabrication techniques and low loss in the near-infrared region. Our work shows the feasibility of fabricating nanospheres from a bulk LN wafer and extends the Mie-resonance enhanced nanoscale SHG up to the UV frequency range
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