Thomas Young's double slit experiment beautifully demonstrates the wave nature of light. The interference pattern observed in that experiment fundamentally depends on the statistical fluctuations of the waves that are emitted by the slits. Here, the statistical correlation between these fluctuations, also known as the spectral degree of spatial coherence, is studied in a new type of double slit interferometer. It is found that this correlation can be controlled by surface plasmon polaritons (SPPs) that travel between the slits. Specifically, the correlation can be tuned by the slit separation distance, which allows for both an increase or a decrease in the spatial coherence of the emerging fields relative to that of the incoming fields. Two case studies are presented, one regarding the spatial coherence of sunlight and the other regarding the spatial coherence of light used in optical tweezers, as examples of areas in which spatial coherence modulation is of considerable interest. Other areas of interest include free-space and fiber-optic communications. In general, the ability to modulate the coherence of light by dynamic SPP control can enable integrated spatial coherence switching at high rates and on the nanoscale.
For further information please contact amit.agrawal [at] nist.gov (Amit Agrawal), 301-975-4633.