Nonlinear optical absorption of light and efficient luminescence in halide perovskites are important photophysical processes, which can be employed for efficient light conversion from infrared into visible, and result in development of microlasers pumped by infrared light, as well as highly efficient broadband upconverters of light. One of the most critical parameters in these processes is the order of nonlinearity, which allows for prediction of the output emission power for various systems. Herein, we show theoretically and experimentally how the order of nonlinearly excited photoluminescence in halide perovskites is governed by an interplay between contributions from free carriers and excitons. Our generalized theoretical model is confirmed by experiments where we reveal a strong dependence of the nonlinearity order in CsPbBr 3 films and nanocrystals on temperature, excitation wavelength, and thickness and size. By incorporating CsPbBr 3 nanocrystals into optically resonant porous calcium carbonate (CaCO 3 ) microspheres, we demonstrate how the developed approach can be applied in nonlinear nanophotonics, where the information about the order of the nonlinearity is crucial.

No abstract

No abstract

In this study, we investigate the nonlinear optical phenomena emerging from the interaction of vortex beams with achiral nanoparticles, leading to the observation of nonlinear circular dichroism in the high-harmonic generation. Despite the achiral symmetry of the nanoparticles, the interplay between the vector properties of the light, the symmetry of the nanoparticles, and the symmetry of the crystalline lattice of the nanoparticle material leads to circular dichroism in the nonlinear regime. We derive a formula that describes the conditions for the appearance of circular dichroism across all possible scenarios, taking into account all the symmetries. We also show that the absolute value of the incident beam's orbital angular momentum does not play a major role. We believe that this work provides important insights that can help in improvement the design process of chiral sensors, making them more versatile and effective.

Nonlinear harmonic generation in nanostructures is one of the key topics in nanophotonics, as it allows infrared-to-visible light conversion at the nanoscale. Indeed, various nanophotonic designs have been developed to demonstrate high efficiencies for third harmonic generation (THG). However, fabrication approaches for these designs usually involve high-cost lithography-based technological steps. This work reports on the efficient THG in a free-standing Si nanowire array encapsulated into a flexible polymer membrane. High nonlinearity of Si material [Formula: see text] and light coupling with optical resonances in the nanowires yield a strong third-harmonic signal and efficient infrared ([Formula: see text] nm) to visible ([Formula: see text] nm) upconversion. The fabricated membranes demonstrate high flexibility and transparency, which make them convenient to use as infrared light visualizers.