Thermo-optical reshaping of second-harmonic emission from dimer all-dielectric nanoresonators.

All-dielectric nanophotonics offers a wide range of possibilities for thermally induced light manipulation at the nanoscale. High quality resonances allow for efficient light-to-heat conversion supported by various temperature detection approaches based on thermally sensitive intrinsic optical responses. In this work, we study theoretically a phenomenon of the photothermal reshaping of the radiation pattern of second-harmonic generation (SHG) that occurs in resonant all-dielectric systems. In the suggested geometry, a near-IR pulsed laser is used for SHG while a continuous wave visible laser simultaneously heats the structure. The thermo-optical switching of the resonant optical states in the nanostructures governs the reconfiguration of the emission pattern, without significant loss in the magnitude of the SHG. We believe, that our findings will pave the way for subwavelength-size near-IR thermally switchable nonlinear optical devices.

Opto-thermally controlled beam steering in nonlinear all-dielectric metastructures.

Reconfigurable metasurfaces have recently gained a lot of attention in applications such as adaptive meta-lenses, hyperspectral imaging and optical modulation. This kind of metastructure can be obtained by an external control signal, enabling us to dynamically manipulate the electromagnetic radiation. Here, we theoretically propose an AlGaAs device to control the second harmonic generation (SHG) emission at nanoscale upon optimized optical heating. The asymmetric shape of the used meta-atom is selected to guarantee a predominant second harmonic (SH) emission towards the normal direction. The proposed structure is concurrently excited by a pump beam at a fundamental wavelength of 1540 nm and by a continuous wave (CW) control signal above the semiconductor band gap. The optical tuning is achieved by a selective optimization of meta-atoms SH phase, which is modulated by the control signal intensity. We numerically demonstrate that the heating induced in the meta-atoms by the CW pump can be used to dynamically tune the device properties. In particular, we theoretically demonstrate a SH beam steering of 8° with respect to the vertical axis for an optimized device with average temperature increase even below 90° C.

Manipulation Technique for Precise Transfer of Single Perovskite Nanoparticles.

In this article, we present the pick-and-place technique for the manipulation of single nanoparticles on non-conductive substrates using a tungsten tip irradiated by a focused electron beam from a scanning electron microscope. The developed technique allowed us to perform the precise transfer of single BaTiO3 nanoparticles from one substrate to another in order to carry out measurements of elastic light scattering as well as second harmonic generation. Also, we demonstrate a fabricated structure made by finely tuning the position of a BaTiO3 nanoparticle on top of a dielectric nanowaveguide deposited on a glass substrate. The presented technique is based on the electrostatic interaction between the sharp tungsten tip charged by the electron beam and the nanoscale object. A mechanism for nanoparticle transfer to a non-conductive substrate is proposed and the forces involved in the manipulation process are evaluated. The presented technique can be widely utilized for the fabrication of nanoscale structures on optically transparent non-conductive substrates, which presents a wide range of applications for nanophotonics.

Stimulated Raman Scattering from Mie-Resonant Subwavelength Nanoparticles.

Resonant dielectric structures have emerged recently as a new platform for subwavelength nonplasmonic photonics. It was suggested and demonstrated that magnetic and electric Mie resonances can enhance substantially many effects at the nanoscale including spontaneous Raman scattering. Here, we demonstrate stimulated Raman scattering (SRS) for isolated crystalline silicon (c-Si) nanoparticles and observe experimentally a transition from spontaneous to stimulated scattering manifested in a nonlinear growth of the signal intensity above a certain pump threshold. At the Mie resonance, the light gets confined into a low volume of the resonant mode with enhanced electromagnetic fields inside the c-Si nanoparticle due to its high refractive index, which leads to an overall strong SRS signal at low pump intensities. Our finding paves the way for the development of efficient Raman nanolasers for multifunctional photonic metadevices.

Optical cooling of lead halide perovskite nanoparticles enhanced by Mie resonances.

Halide perovskites are a family of semiconductor materials demonstrating prospective properties for optical cooling owing to efficient luminescence at room temperature and strong electron-phonon interaction. Moreover, perovskite based nanophotonic designs would allow for efficient optical cooling at the nanoscale. Here, we propose a novel strategy for the enhancement of optical cooling at the nanoscale based on optical resonance engineering in halide perovskite nanoparticles. Namely, the photoluminescence up-conversion efficiency in a nanoparticle is optimized via excitation of Mie-resonances both at emission and absorption wavelengths. The optimized theoretical photo-induced temperature decrease achieved for a hybrid halide perovskite (CH3NH3PbI3) 530 nm nanoparticle on a glass substrate is more than 100 K under CW illumination at wavelength 980 nm and moderate intensities (∼7 × 106 W cm-2). The optimized regime originates from simultaneous excitation of a magnetic quadrupole and a magnetic octupole at pump and emission wavelengths, respectively. The combination of a thermally sensitive photoluminescence signal and simplicity in the fabrication of a halide perovskite nanocavity will pave the way for implementation of nanoscale optical coolers for advanced applications.

Resonant Nonplasmonic Nanoparticles for Efficient Temperature-Feedback Optical Heating.

We propose a novel photothermal approach based on resonant dielectric nanoparticles, which possess imaginary part of permittivity significantly smaller as compared to metal ones. We show both experimentally and theoretically that a spherical silicon nanoparticle with a magnetic quadrupolar Mie resonance converts light to heat up to 4 times more effectively than similar spherical gold nanoparticle at the same heating conditions. We observe photoinduced temperature raise up to 900 K with the silicon nanoparticle on a glass substrate at moderate intensities (<2 mW/µm2) and typical laser wavelength (633 nm). The advantage of using crystalline silicon is the simplicity of local temperature control by means of Raman spectroscopy working in a broad range of temperatures, that is, up to the melting point of silicon (1690 K) with submicrometer spatial resolution. Our CMOS-compatible heater-thermometer nanoplatform paves the way to novel nonplasmonic photothermal applications, extending the temperature range and simplifying the thermoimaging procedure.

Efficient Second-Harmonic Generation in Nanocrystalline Silicon Nanoparticles.

Recent trends to employ high-index dielectric particles in nanophotonics are motivated by their reduced dissipative losses and large resonant enhancement of nonlinear effects at the nanoscale. Because silicon is a centrosymmetric material, the studies of nonlinear optical properties of silicon nanoparticles have been targeting primarily the third-harmonic generation effects. Here we demonstrate, both experimentally and theoretically, that resonantly excited nanocrystalline silicon nanoparticles fabricated by an optimized laser printing technique can exhibit strong second-harmonic generation (SHG) effects. We attribute an unexpectedly high yield of the nonlinear conversion to a nanocrystalline structure of nanoparticles supporting the Mie resonances. The demonstrated efficient SHG at green light from a single silicon nanoparticle is 2 orders of magnitude higher than that from unstructured silicon films. This efficiency is significantly higher than that of many plasmonic nanostructures and small silicon nanoparticles in the visible range, and it can be useful for a design of nonlinear nanoantennas and silicon-based integrated light sources.