The evolution of hot spot and nanojet by engineering the local modes of microcylinder

Hot spot and photonic nanojet (PNJ) are subwavelength focused beams generated from the microsphere or microcylinder. In this paper, we proposed a method of excitation of high-order resonant modes in microcylinder with a high-refractive index cladding and modulation of local modes at the exit end to generate the hot spot. A hot spot with a full width at half maximum waist of 66.70nm(2/8.47) on the surface is obtained and explained by the wave superposition theory modulated by local modes. The influence of local structures and refractive index on the waist, effective length and exit direction of the hot spot is discussed. The focal position of the hot spot can be gradually moved out and converted to the nanojet by engineering the local modes of the microcylinder. Also, a cubic array chip is suggested for decreasing the difficulty of manufacture. And it shows that number and position of the hot spot can be controlled by adjusting the refractive index and height of the local structure. This work provides a possibility for potential applications in the fields of high-throughput super-resolution near-field imaging, localized excitation and imaging of single-molecule fluorescence.