Interference among the neighboring sub-micron size harmonic particles

In recent times, harmonic nanoparticles (HNPs) have gained considerable interest in many fields like nanophotonics, cell imaging, nanomedicine, etc. Unlike fluorescent particles and quantum dots, HNPs are photo -stable, non -bleaching, bio-compatible, and wavelength -flexible. Here, we explore second harmonic generation (SHG) from sub -micron size BaTiO 3 (BTO) particles. BTO is a well-known perovskite material extensively used for its nonlinear optical properties. Our investigation of out -of -focus diffraction patterns of second harmonic light has helped us know about particle assembly's nature. We have observed interference fringes at the overlapped regions of the out -of -plane SHG patterns that emerged from two, three, and even multiple adjacent particles. Our study may help in the 3D tracking of nonlinear particles in a living cell and deep tissue imaging.