Wavefront

So far, we have pictured waves by using only an oscillating sine function. This representation is adequate for one-dimensional waves, but for two or higher dimensional waves, this representation becomes difficult, so we introduce the idea of wavefronts.

What is a Wavefront?

A wavefront is an imaginary surface representing corresponding points of a wave that vibrate in unison.

A wavefront is the set of all locations in a medium where the wave is at the same phase. This could be where all the crests are, where all the troughs are, or any phase in between. Wavefronts are useful for showing how waves move in 2 dimensions. The length between two lines on a wavefront is exactly one wavelength.

To summarize, we can say that a wavefront is the set or locus of all the points in the same phase. There are three types of wavefronts as plane wavefront, spherical wavefront, and cylindrical wavefront. In the next few sections, we will understand in brief each of these types of wavefronts.

Wavefront Physics

In this section, we will be discussing some important characteristics of wavefronts:

• Wavefronts proceed with time
• Wavefronts are single points for waves travelling in a one-dimensional medium; curves in a two-dimensional medium, and surfaces in a three-dimensional medium.
• If the propagation speed differs at various points of a wavefront, the orientation and shape of the wavefronts may differ by refraction. Particularly, lenses can alter the wavefront optical shape from spherical to planar, or vice versa.

Wavefront Types

The path followed by the particles emanating from a source determines the different types of wavefronts. Let us understand these different types in detail:

Spherical Wavefront

When the point source is an isotropic medium, sending out waves in three dimensions, the wavefronts are spheres centred on the source, as shown in the figure. Such a wavefront is called a spherical wavefront.

Examples of Spherical Wavefronts

• Electromagnetic waves in a vacuum form a spherical wavefront.
• The concentric circles’ formation when the stone is dropped in a water
• An army man patrolling the opposition on the radar through the camera positions the invader with the spherical wavefront symbol.

Cylindrical Wavefront

When the light source is linear, we obtain a cylindrical wavefront. In a cylindrical wavefront, all the points equidistant from the linear source lie on the surface of a cylinder, as shown in the figure.

The cylindrical wavefront appears like a cylinder. However, if we draw the wavefront from one plane, we obtain a concentric circle like a spherical wavefront.

Example of Cylindrical Wavefront

When rays of light coming out of a lens fall on another lens, they converge at a given point. As they bend and converge at a point, it takes the form of a cylinder.

Plane Wavefront

The wavefront will appear as a plane when viewed from a considerable distance from a source of any kind. Such a wavefront is called a plane wavefront.

Moreover, the plane wavefront is obtained when the small part of the spherical or cylindrical wavefront originates from a distant source, like infinity.

Plane Wavefront Example

Plane wavefronts are generated from a very distant source. A common example of the plane wavefront is the rays coming out of the sun.

Application of Wavefront

Wavefront LASIK is the quick, simplest and effective treatment for refractive errors of the human eye. It is a medical procedure that uses guided lasers to reshape the cornea and improve visual sharpness. Wavefront-guided LASIK lessens the side effects connected with traditional LASIK. Wavefront Guided LASIK is useful in treating the following conditions: Myopia or Nearsightedness, Astigmatism and Hypermetropia.

Watch the video and understand how constructive and destructive interferences are formed.

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