Nano-sized Laser Beams without Diffraction Spreading

Whereas exciting progress has been made to beat diffraction in optical spectroscopy [1-8], making a nano-sized laser beam remains challenging due to diffraction spread [9,10]. Using Bethe’s expression for the optical transmission coefficient of a circular hole in a perfect conductor screen of zero thickness [9,11]. T=1024π3a6/27λ4, we found that the transmission of light with a wavelength λ=800 nm through such a circular hole of a radius of 1 nm is about ~2.3 × 10-6. So a decent nanosized laser beam for miniaturization of optical elements is not available. Here we show that coupling Surface Plasmon-Polaritons (SPPs) to appropriate dielectric material can result in fundamentally diffraction-free down-sized, especially nano-sized laser beams. For example, the composite structure Si3N4/Au(44.5nm)/SiO2 (456nm)/(SiO2, Si3N4, SiO2) can achieve a nano-sized laser beam of about half the incoming light intensity. This approach, by transforming the macroscopic laser beams into multiple nano-sized laser beams, holds promise for ultrafast laser imprinting of nanopores for DNA sequencing and other miniature photonic devices in optical signal processing industries.