Demonstration experiment for observing Haidinger’s interference rings using microparticles deposited on reflective surfaces

Abstract

Abstract

Abstract A demonstration experiment for observing Haidinger’s interference rings (fringes of equal inclination) is proposed and experimentally implemented. The method uses microparticles deposited on the reflective surfaces of plane-parallel glass plates or flat mirrors. These particles act as localised secondary sources, converting the angular interference structure into a directly observable ring pattern on a screen in the far field. While similar observations have been reported for dusty mirrors, this work extends the technique to glass plates. We demonstrate that microparticles on both surfaces introduce additional coherent scattering paths exhibiting a similar angular phase dependence, leading to a pronounced enhancement of fringe visibility without altering the geometric arrangement of the rings. The experiment employs inexpensive and readily available equipment, such as a low-power semiconductor laser pointer, a glass plate, and a mirror, enabling stable interference patterns with high fringe visibility to be observed under standard classroom lighting. Quantitative analysis of the interference patterns is presented, including measurements of ring radii and determination of the glass plate thickness. The shifts of selected ring radii provide a direct and intuitive demonstration of the wavelength dependence of interference, allowing students to explore optical dispersion without the need for spectrometers. By combining classical interferometry with accessible experimental techniques and digital data processing, this approach makes Haidinger’s fringes readily observable and pedagogically effective for both secondary school and university laboratory exercises.