Resonantly enhanced second-and third-harmonic generation in dielectric nonlinear metasurfaces

Nonlinear dielectric metasurfaces provide a promising approach to control and manipulate frequency conversion optical processes at the nanoscale,thus facilitating both advances in fundamental research and the development of new practical applications in photonics,lasing,and sensing.Here,we employ symmetry-broken metasurfaces made of centrosymmetric amorphous silicon for resonantly enhanced second-and third-order nonlinear optical response.Exploiting the rich physics of optical quasi-bound states in the continuum and guided mode resonances,we comprehensively study through rigorous numerical calculations the relative contribution of surface and bulk effects to second-harmonic generation(SHG)and the bulk contribution to third-harmonic generation(THG) from the meta-atoms.Next,we experimentally achieve optical resonances with high quality factors,which greatly boosts light-matter interaction,resulting in about 550 times SHG enhancement and nearly 5000-fold increase of THG.A good agreement between theoretical predictions and experimental measurements is observed.To gain deeper insights into the physics of the investigated nonlinear optical processes,we further numerically study the relation between nonlinear emission and the structural asymmetry of the metasurface and reveal that the generated harmonic signals arising from linear sharp resonances are highly dependent on the asymmetry of the meta-atoms.Our work suggests a fruitful strategy to enhance the harmonic generation and effectively control different orders of harmonics in all-dielectric metasurfaces,enabling the development of efficient active photonic nanodevices.

Nonlinear chiral metaphotonics:a perspective

We review the physics and some applications of photonic structures designed for the realization of strong nonlinear chiroptical response.We pay much attention to the recent strategy of utilizing different types of optical resonances in metallic and dielectric subwavelength structures and metasurfaces,including surface plasmon resonances,Mie resonances,lattice-guided modes,and bound states in the continuum.We summarize earlier results and discuss more recent developments for achieving large circular dichroism combined with the high efficiency of nonlinear harmonic generation.

Modifying light–matter interactions with perovskite nanocrystals inside antiresonant photonic crystal fiber

Structured environments are employed in a plethora of applications to tailor dynamics of light–matter interaction processes by modifying the structure of electromagnetic fields.The promising example of such a system is antiresonant photonic crystal fibers(AR-PCFs),which allow light–analyte interactions in a very long channel.Here we probe contribution of microstructuring and nontrivial mode hierarchy on light–matter interactions in AR-PCFs by investigating lifetime shortening of perovskite(CsPbBr3)nanocrystals grown to fiber capillaries.The crystals have been deposited using a wet chemistry approach and then excited by a supercontinuum source in the 450–500 nm range.Emission spectra have been measured and analyzed via the time-correlated single photon counting(TCSPC)technique,unravelling contributions of core and cladding modes.Fluorescence lifetime imaging inside an AR-PCF enables mapping input of various electromagnetic channels into light–matter interaction processes.Our results pave the way for tailoring the dynamics of high-order quantum processes,promoting the concept of AR-PCF as a light-driven reactor.