Huygens' Principle (also called the Huygens–Fresnel Principle) is a fundamental concept in wave optics proposed by the Dutch physicist Christiaan Huygens in 1678. It provides a geometric method for understanding wave propagation.
The Principle
Every point on a wavefront can be considered a source of secondary spherical wavelets (called secondary wavelets). The new wavefront at a later time is the envelope of all these secondary wavelets.
Key Concepts
Primary Wavefront – The original advancing wave surface.
Secondary Wavelets – Each point on the primary wavefront acts as a new point source, emitting tiny spherical waves in all directions.
Envelope – The tangent surface (envelope) that touches all secondary wavelets at a given later instant forms the new wavefront.