Optical chromatography of ultrasmall particles by Brownian motion in a tilted optical potential induced by bound states in the continuum

We investigate sorting Rayleigh optical particles up to several nanometers in size during Brownian motion in a tilted periodic potential with multiple deep wells. The wells are induced by optical bound states in the continuum within a system of parallel photonic crystal slabs immersed in a liquid. The Brownian dynamics of the particles is significantly altered by resonant optical forces, leading to the complete spatial separation of particles with a size difference of approximately 1% during the diffusion process. In addition, the possibility of creating an integrated platform for continuous optical sorting is discussed.