Varying shapes of experimental double-slit interference patterns for light, and a model of particle-modified interference patterns

Abstract

Interference patterns from laser-illuminated double slits were scanned and accumulated for the cases of relatively dim, medium and relatively bright illumination. Detailed analyses were made of the pattern shapes for a large number of data runs. Patterns accumulated from dim light fit the shape of the wave theory patterns well, supporting the quantum concept of gradual accumulation of single photon events. However, the envelope shapes for brighter light did not adequately match those of the wave theory (or those from dim light), in that the bright light patterns had too great an intensity in the bright areas, relative to the dimmer areas in those patterns. These pattern shapes resembled a wave theory pattern squared, or taken to a higher power. The shapes appear to have been the results of the particular method of pulse detection and pulse level discrimination used, which favoured the larger pulse sizes. A model based upon multiple photon detection within each output pulse was developed, using particle statistics combined with wave theory probabilities. The predicted interference patterns from this model fit the experimental results well, providing support for the model. This experiment displays an interesting combination of wave and particle effects, supporting duality for light, in that the transmission of light corresponds to the predictions of probability waves, closely akin to classical optical wave theory, and the detection of light involves particle statistics, supporting the quantum nature of photon detection.