Interference fringes caused by beams narrower than the fringe spacing

Abstract

The interference of light has not only contributed to our understanding of natural laws, but it has also been used as a crucial foundational technology supporting modern industry. Both fundamental and applied aspects are being actively researched on interference. We've made an optical element that consists of a half-mirror and a mirror with an adjustable relative angle, and we're studying the fundamental characteristics of interference fringes. The fringe spacing can be altered by adjusting their relative angle. When light is incident on this device, numerous bright and dark lines appear, similar to thin-film interference or interference fringes of equal thickness. This report describes how the interference pattern and light intensity change as the width of the incident light beam is narrowed below the fringe spacing.