Mid-infrared optical force chromatography using evanescent waves for sorting particles by molecular species

The optical force exerted on micro- and nanoparticles can be significantly enhanced through molecular vibrational resonance. When a mid-infrared laser excites a particle’s vibrational modes, light momentum is transferred to the particle via absorption, resulting in a resonant enhancement of the optical force. This scheme enables the sorting of particles according to chemical species by tuning the laser wavenumber, as various molecular vibrational modes exist in the midinfrared spectral region. Herein, we present the experimental results of mid-infrared optical force chromatography, in which particles composed of siloxane and carbonyl bonds (such as silica and PMMA) are separated and sorted depending on their absorbance values.