Simulation of Light Propagation Captured by Photoemission Electron Microscopy (PEEM)

The Photoemission electron microscopes (PEEM) is a powerful tool capable of synchronously imaging wave nature of light manifested by interference patterns as well as its particle nature through the energy exchange between the incident photons and the photoemitted imaging electrons. PEEM offers a non-invasive high-resolution approach for studying light propagation and interaction phenomena within a nanophotonic waveguide [7,8]. The electric field intensity variation of the interference pattern yielded by the interaction between the incident light and the guided mode coupled into the waveguide produces varying photoemission yields creating contrast in PEEM image. The guided modes cannot be excited simply by exposing the waveguide surface to light. A compact efficient coupler such as diffraction gratings is required. In this work an efficient grating coupler is designed using Finite Element Analysis (FEA) to couple a pump beam of 400 nm wavelength from a Ti:sapphire laser source into a 180 nm thick ITO waveguide on a 200nm thick glass substrate. The PEEM image of the electric field distribution yielded by the interference between the guided mode and a probe pulse was simulated and the properties of the interference pattern was studied. The phase delay between the pump and the probe pulse was then increased in steps of π/2 for one optical cycle of the excitation laser causing the interference pattern on the ITO surface to progress in position. By simulating the image of the interference pattern for each delay step and by compiling the images a movie-like documentation of the light propagation in the waveguide is obtained. Simulations show the interference maxima peaks to move away from the coupler with the speed of light for an ITO waveguide