Finite-Size Corrections to Gradient Radiation Forces in High-Q Cylindrical Cavities

We analyze gradient radiation forces in high-Q cylindrical cavities using both the dipole approximation and full Maxwell stress tensor integration. For the TM010 mode, analytic expressions for the optical spring constant on a dielectric sphere are derived. Finite element simulations reveal dipole-model deviations of 50–150% for sphere-to-cavity radius ratios a/R > 0.1, arising from field distortion and multipole scattering. The correction factors provided establish clear boundaries for approximation validity in cavity optomechanical designs, demonstrating that geometric effects dominate force magnitudes in confined electromagnetic systems.