Abstract
Abstract Second harmonic generation (SHG) with a material of large transparency is an attractive way of generating coherent light sources at exotic wavelength range such as VUV, UV and visible light. It is of critical importance to improve nonlinear conversion efficiency in order to find practical applications in quantum light source and high resolution nonlinear microscopy, etc. Here an enhanced SHG with conversion efficiency up to 10−2% at SH wavelength of 282.7 nm under 11 GW/cm2 pump intensity via the excitation of anapole in lithium niobite (LiNbO3, or LN) nanodisk through the dominating d 33 nonlinear coefficient is investigated. The anapole has advantages of strongly suppressing far-field scattering and well-confined internal field which helps to boost the nonlinear conversion. Anapoles in LN nanodisk is facilitated by high index contrast between LN and substrate with properties of near-zero-index via hyperbolic metamaterial structure design. By tailoring the multi-layers structure of hyperbolic metamaterials, the anapole excitation wavelength can be tuned at different wavelengths. It indicates that an enhanced SHG can be achieved at a wide range of pump light wavelengths via different design of the epsilon-near-zero (ENZ) hyperbolic metamaterials substrates. The proposed nanostructure in this work might hold significances for the enhanced light–matter interactions at the nanoscale such as integrated optics.
Highlights
Second harmonic generation (SHG) is a nonlinear optical process which combines two photons at the fundamental frequency (FF) and convert them into one photon at the second harmonic wavelength (SH) [1]
This hyperbolic metamaterials (HMMs) configuration will be employed as a low effective index substrate supporting LN nanodisk whereas the material and thickness of terminating layer i.e. interfacing between HMM and LN nanodisk will be tuned according to its ability of high field enhancement which will be presented
An approach to enhance the near-field effects of nanostructure with higher index contrast between LN and HMM with low losses has been investigated in SHG numerically
Summary
Second harmonic generation (SHG) is a nonlinear optical process which combines two photons at the fundamental frequency (FF) and convert them into one photon at the second harmonic wavelength (SH) [1]. An anapole mode facilitate the generation of SH in LN with aluminum substrate yielding a high conversion efficiency of 1.1528 × 10−3% at VUV regime [15]. These anapoles are generated in nonlinear materials with high refractive index and a relatively narrow transparency range. In order to enhance the index contrast between LN nanostructure and substrate, metamaterials which can be tuned to be as ENZ or even negative refractive index are chosen Among these metamaterials, hyperbolic metamaterials (HMMs), as the topology of the isofrequency surface are hyperbolic curves, have been widely investigated recently [22]. Comparisons of the state of the art in SHG are presented
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