In wave optics, the Huygens-Fresnel principle states that:
- The field at the aperture is treated as an ensemble of secondary point sources. Each of them emits spherical waves, the strength and phase of which are defined by the incident wave and the aperture function.
- i.e., each point on a wavefront acts as a source of secondary point sources.
- These aren’t real point sources — they’re mathematical constructs that help us calculate how the wave propagates.
- In a sense, this transforms our understanding from: “how does this complex wavefront propagate?” to “how do many simple spherical waves combine”.
- The field at the screen is the coherent superposition of all contributions from the secondary point sources at the aperture. i.e., the field at the screen is the result of interference of all secondary waves emitted at the aperture.
- The field at any subsequent point is the superposition of all these secondary point sources.