Radiation force on a nonlinear microsphere by a tightly focused Gaussian beam

Area of Science:

• Optics
• Nanotechnology
• Materials Science

Background:

• Nonlinear optical phenomena in microspheres are crucial for advanced optical applications.
• Understanding radiation forces is key for optical trapping and manipulation.
• Kerr-effect microspheres exhibit intensity-dependent refractive indices, influencing light-matter interactions.

Purpose of the Study:

• To characterize radiation forces on nonlinear Kerr microspheres under focused Gaussian beams.
• To investigate the impact of diffraction and interference on these forces.
• To compare force characteristics between Kerr and linear (dielectric) microspheres.

Main Methods:

• Calculating average force using the surface integral of the energy-momentum tensor.
• Employing multipole spherical-wave expansions for electromagnetic field vectors.
• Iteratively computing the nonlinear refractive index using the Rytov approximation.

Main Results:

• Radiation force on Kerr microspheres is larger and increases faster with sphere size and numerical aperture compared to linear microspheres.
• Force magnitude on Kerr microspheres increases nonlinearly with beam power.
• Kerr nonlinearity can induce reversals in the radiation force direction.

Conclusions:

• The study provides a method for analyzing radiation forces on nonlinear microspheres.
• Kerr nonlinearity significantly alters radiation force characteristics, enabling novel optical manipulation strategies.
• The technique is adaptable for analyzing other weak optical nonlinearities.