Abstract
<title>Abstract</title> <p>Young's double-slit experiment, which represents the mystery of quantum physics and the diffraction that goes along with it, has long been used as a fundamental experiment to demonstrate how light is a wave by looking at interference patterns on a distant screen. In conventional diffraction experiments, which normally only show on a far field screen using photons, electrons, atoms, molecules, and other quantum systems. The evolution of the optical field in the Fresnel region is well-established theoretically, but there has not yet been much direct experimental observation of this intermediate field. In this work, we present the first direct experimental visualization of a structured Post-Obstacle Field (POF) immediately beyond a diffracting obstacle. the double-slit assembly consisted of two rectangular transmitting regions separated by a 50 μm diameter human hair acting as the central obstacle. A continuous-wave 632.8 nm He–Ne laser was used to illuminate a diffraction obstacle. Continuous video recordings revealed the emergence of Post obstacle Field (POF) immediately after diffraction captured using an OnePlus 8 Pro smartphone camera. The Post obstacle Field (POF), an operational term that characterizes the optical intensity right after the diffraction barrier, is the name given to the experimentally observed intensity distribution (referred to here as N dominant intensity pathways). To independently verify that these structures represent a physical optical field rather than an imaging artifact, a transparent glass plate was positioned approximately 2 cm behind the obstacle. The same structured intensity pathway pattern was directly observed on the glass, confirming the presence of the post-obstacle field. A study of over twenty paired POF and far-field observations showed that the spatial layout of these prominent channels frequently matched the later observed far-field interference patterns, whereas their absence was associated with the absence of clearly defined interference. The experiment's simplicity of accessibility, affordability, and visual clarity make this work ideal for undergraduate labs and serve as a useful link between theoretical explanations of diffraction and experimental observation.</p>