What happens when light meets two parallel slits? The answer depends entirely on how deeply you dare to look. This lecture invites undergraduate physicists to re-examine the iconic double-slit experiment through four distinct epochs of optical physics. We begin with Sir Isaac Newton’s corpuscular theory, analyzing why a classical stream of localized particle "bullets" fails to explain the complex fringes of reality. To decode these patterns, we introduce Fourier optics, transforming the slits into spatial frequencies and revealing how a lens mathematically calculates the field's far-field diffraction pattern. However, real-world light is messy; using statistical optics, we strip away the idealized assumption of perfectly coherent sources to explore how fluctuating wave-fields and phase degradation blur our interference fringes. We will try to understand these blurring effects in the context of synchrotron sources and try to understand the importance of coherence in next generation coherence based imaging techniques. We will end the lecture by venturing into quantum optics, where the classical wave completely dissolves. We will confront the ultimate paradox: the observer effect. We will discover how tracking which-way a photon travels collapses the wave function, instantly erasing the interference pattern. By tracing this evolution through a single experimental geometry, this lecture bridges the gap between Newtonian mechanics and quantum reality. Ultimately, you will see that the double-slit is not just a textbook demonstration, but a profound playground where the act of measurement defines the nature of light itself.
Dr. Venkata Sree Charan Kuppili is a Beamline Scientist for the SpectroMicroscopy beamline at the Canadian Light Source (CLS) and an Adjunct Professor at the University of Saskatchewan. With nearly seven years at the CLS, he specializes in cutting-edge spectro-microscopy to advance condensed matter physics. Throughout his career, Dr. Kuppili has designed novel imaging methodologies at large-scale facilities worldwide. His achievements include setting up a 3D ptycho-tomography system at Diamond Light Source (UK), analyzing ancient magnetic signatures at the University of Cambridge, and developing soft X-ray ptycho-tomography systems at the CLS.