Broadband Mie driven random quasi-phase-matching

Abstract

High-quality crystals without inversion symmetry are the conventional platform to achieve optical frequency conversion via three wave-mixing. In bulk crystals, efficient wave-mixing relies on phase-matching configurations, while at the micro-and nanoscale it requires resonant mechanisms that enhance the nonlinear light-matter interaction. These strategies commonly result in wavelength-specific performances and narrowband applications. Disordered photonic materials, made up of a random assembly of optical nonlinear crystals, enable a broadband tunability in the random quasi-phase-matching (RQPM) regime and do not require high-quality materials. Here, we combine resonances and disorder by implementing RQPM in Mie-resonant spheres of a few microns realized by the bottom-up assembly of barium titanate nano-crystals. The measured second harmonic generation (SHG) reveals a combination of broadband and resonant wave mixing, in which Mie resonances drive and enhance the SHG, while the disorder keeps the phase-matching conditions relaxed. This new phase-matching regime can be described by a random walk in the SHG complex plane whose step lengths depend on the local field enhancement within the micro-sphere. Our nano-crystal assemblies provide new opportunities for tailored phase-matching at the micro-scale, beyond the coherence length of the bulk crystal. They can be adapted to achieve frequency conversion from the near-ultraviolet to the infrared ranges, they are low-cost and can cover large surface areas.

Optical Phenomena in Mesoscale Dielectric Particles

“…A separate major direction is associated with the use of mesoscale particles in microscopy [38,39,106,172]. In the authors' opinion, the creation of mesoparticle chains with the required properties using the phase-matching mechanism that relies on the coupling of random quasi-phase-matching with the Mie resonance of the entirely disordered mesostructure is promising [173]. The generation of hot spots, having giant values of the local wavenumber vectors, by use a superoscillation effects [9,10] is extremely promising not only for mesoscale photonics and superresolution imaging, but also for diffractive optics [174], whose research was begun back in 1990 [175].…”

Resonant Scattering Manipulation of Dielectric Nanoparticles

“…[ 144,145 ] New studies have emerged in this area in recent years and revealed that these activated processes in BaTiO 3 and LiNbO 3 nanoparticles are produced through solvothermal processes. [ 146–149 ] For instance, an increase in the size of BaTiO 3 nanoparticles shifted the SHG peak to the red portion (600 nm) due to the influence of the MD mode, whereas LiNbO 3 was demonstrated to operate in the near‐UV region. More materials can be used to explore suitable candidates that feature peculiar optical properties and cover the far‐red and IR region.…”

“…developed 3D disordered microspheres by bottom‐up assembly of BaTiO 3 nanocrystals and demonstrated broadband and simultaneously Mie‐enhanced SHG within a 100 nm wavelength range. [ 149 ]…”

Second Harmonic Generation Enhancement From Plasmonic Toroidal Resonance in Core-Shell Nanodisk

“…Second harmonic generation (SHG) from nanostructures is at the heart of metamaterials and nanooptics since it does not strictly require the macroscale phase-matching condition [1,2]. Especially, the miniaturization and integration trends of metamaterials make it possible to engineer and utilize SHG in many applications, such as characterizations of structural properties and laser beam [1].…”