Does the leakage radiation profile mirror the intensity profile of surface plasmon polaritons?

Although the leakage radiation (LR) image intensity is considered to be in proportion to the surface plasmon polariton (SPP) intensity at the metal-air interface, it has not been proven experimentally, to the best of our knowledge. Here we investigate the relationship between the measured LR intensity profile of SPP interference fringes, which are produced by two SPP launching gratings, and the simulated SPP intensity. The experimental modulation depths agree well with the simulation result of the in-plane electric field component of SPPs, which demonstrates that the image intensity in LR microscopy provides the intensity profile of the in-plane component.