The observation of interference effects definitively indicates the presence of overlapping waves. Thomas Young postulated that light is a wave and is subject to the superposition principle; How to simulate and set up it, this article will help.
When monochromatic light passing through a single slit illuminates a screen, a characteristic diffraction pattern is observed. Diffraction is a product of the superposition of waves—i.e., it is an interference effect. The detailed pattern of constructive and destructive interference fringes can be derived by treating every point on the wave front passing through the slit as a secondary source of spherical waves. The paths from three representative secondary sources to the viewing screen are shown here. The central bright fringe in a single-slit diffraction pattern is produced by the constructive interference of all of the secondary sources. The width of the central fringe is inversely proportional to the width of the slit. Diffraction effects become pronounced only when the width of the slit is an appreciable fraction of the wavelength of the light.
The key is to make very efficient use of the rays so that a high-fidelity fringe pattern is formed without tracing rays that don’t contribute to the interference process. This is done with a straightforward Non-Sequential layout as shown in the figure below. The two pinholes are circular disks of radius 5 µm separated by 100 µm (the disk centers are displaced along the x-axis by +/- 50 µm). The distance from the source plane to the pinhole plane is 10 mm as is the distance from the pinhole plane to the observation plane. The wavelength is taken to be 0.632 µm.
In OpticStudio, such fringe patterns are found by using coherent detection of rays with a Detector Rectangle. A collection of elementary fringe patterns (from sample points taken across the whole source) is then summed on an intensity basis to yield a resultant fringe pattern. The visibility of the resultant fringe pattern is a measure of the partial coherence of the light at the pinholes. The angular distribution of the rays propagating from each pinhole is set by the scattering model. In reality, the light will exhibit diffraction, so at the observation plane it is the overlap of two diffracted beams that is ultimately detected.
The corresponding entries are shown below.
After propagating a short distance from light source, taken here to be 10 um, the source ray encounters a Standard Surface. The purpose of this surface is to convert the incoming on-axis ray into two scattered rays directed at the two pinholes. And then the two scattered rays are directed at the two pinholes. When the rays arrive at the pinholes, Scattering and Importance Sampling are used once again. Regarding to Importance Sampling, please refer to the article: How To Improve The Scattering Analysis Efficiency In An Astronomical Telescope Design
The resulting fringe pattern is found by viewing the coherent irradiance distribution as shown below.
We conclude by noting that ray tracing has been used to model interference of light emanating from two small pinholes.
Reference Source:
- https://www.zemax.com/
- Zemax Optical Design Program User’s Guide, Zemax Development Corporation
- https://www.britannica.com/science/light/Thin-film-interference
- https://www.olympus-lifescience.com/en/microscope-resource/primer/java/doubleslitwavefronts/
