Study of interference between surface plasmon polaritons by leakage radiation microscopy

Interference between two perpendicular surface plasmon polariton (SPP) beams was studied using a leakage radiation microscope, which allows for the observation of SPP propagation without disturbing the two-dimensional interference pattern formed at the region where the beams cross each other. Interference fringes were observed at the image plane of the microscope. Experimental results were discussed using both classical and quantum descriptions of light. Features observed in the Fourier-plane image directly demonstrate that, in correspondence with the widespread quantum description of light, photons do not propagate following the classical lines of electromagnetic energy flow.