Learning Forum

[Shin-Sung Kim]

This example uses the well-known Young’s double-slit experiment to demonstrate the spatial coherence of sources within an FDTD simulation.nThe simulation uses a TFSF plane wave source traveling in the +x direction that illuminates an opaque screen with two apertures 12 um apart. The fields are observed using a frequency monitor which records the data along y at a distance of 50 um away from the screen.nThe following script runs the simulation for the cases where only the top slit is open, only the bottom slit is open, and the case where both slits are open.nAs the plane wave propagates through the slit, diffraction occurs, making the slit act as a point source. The resulting field profile on the screen is a roughly Gaussian-shaped intensity profile from each slit when only one is open at a time.nWhen both of the slits are open at the same time, the resulting intensity profile recorded by the monitor is not the simple addition of the two intensity profiles shown above. Instead, it is a coherent sum, that includes the interference terms between the two sources.nIt is important to understand that individual FDTD simulations are always coherent. Nevertheless, it is possible to obtain incoherent results by running multiple simulations and adding the results incoherently. nnThe figure below shows the resulting profile for an incoherent system.nNote:nThe example script runs 3 simulations, but you can get both incoherent and coherent results by running only the two simulations where only one slit is open and adding the results incoherently (|E1|^2+|E2|^2) and coherently (|E1+E2|^2).n

[pengrenjuddd]

Hi,

Could you please provide the detailed information about the geometry and the refractive index of "screen"?