Article,
Toward Waveguide-Based Optical Chromatography
FRONTIERS IN PHYSICS, (2021)
DOI: 10.3389/fphy.2020.603641
Abstract
We report analytical expressions for optical forces acting on particles
inside waveguides. The analysis builds on our previously reported
Fourier Transform method to obtain Beam Shape Coefficients for any beam.
Here we develop analytical expressions for the Beam Shape Coefficients
in cylindrical and rectangular metallic waveguides. The theory is valid
for particle radius a ranging from the Rayleigh regime to large
microparticles, such as aerosols like virus loaded droplets. The theory
is used to investigate how optical forces within hollow waveguides can
be used to sort particles in ``optical chromatography'' experiments in
which particles are optically propelled along a hollow-core waveguide.
For Rayleigh particles, the axial force is found to scale with a (6),
while the radial force, which prevents particles from crashing into the
waveguide walls, scales with a (3). For microparticles, narrow Mie
resonances create a strong wavelength dependence of the optical force,
enabling more selective sorting. Several beam parameters, such as power,
wavelength, polarization state and waveguide modes can be tuned to
optimize the sorting performance. The analysis focuses on cylindrical
waveguides, where meter-long liquid waveguides in the form of
hollow-core photonic crystal fibers are readily available. The modes of
such fibers are well-approximated by the cylindrical waveguide modes
considered in the theory.
