Visualization of Hermite Gaussian Focal Spot

The longitudinal focal field of a tightly focused light via high NA (1.45 NA) objective lens is imaged via PiFM. The measured PiFM result agrees well (slight mismatch is observed due to the uncorrected nonlinearity of open-loop tip scanner) with the longitudinal field calculated from the dipole-dipole interaction between the polarized tip and the glass substrate.