May 29 2014
A wavefront may be described as a surface over which an optical wave presents a constant phase. In other words, a wave front may be the surface over which a wave represents a crest (maximum point), or a trough (minimum point).
A wavefront is essentially a locus of points having the same phase.
The shape of the wave front depends on the shape of the optical source. A point light source exhibits a wavefront that is in the form of spheres that have the center as the point source.
A fluorescent tube source tends to exhibit wavefronts that are cylindrical in shape and concentric with the tube. On the other hand, a large sheet of material, which is uniformly illuminated, would present a wavefront in the form of plane waves aligned parallel to the sheet.
The wave propagates in a direction that is at right angles to the surface of the wavefront at each point. Therefore, sphere-like wavefronts emitted from a point source propagate radially outward, such that the radius of the spheres are perpendicular to their circumferences at each point. The propagation of wavefronts is described by Huygen's principle.
As per Huygen's principle, each point on the wavefront may be considered as a point source, emitting spherical wavelets. The speed at which these wavelets travel is equal to the velocity of the light in that medium.
The wavefront encompasses all the wavelets, such that a tangent line can be drawn to join the front surface of each wavelet.
Wavefront Sensor
A wavefront sensor is a device used to measure the wavefront aberration in a coherent signal. The optical quality of a system can be determined using a wavefront sensor.
Sources and Further Reading
- Topic 14:Wavefronts and Huygens Principle – Colorado University
- Wavefront Sensing Reveals optical coherence – Cornell University