Important Topic: Wavefront

Introduction

A time-varying field’s wavefront is the collection of all sites where the wave has the same sinusoid phase. The phrase is only typically applicable to fields that fluctuate sinusoidally in time with a single temporal frequency at each place. Wavefronts frequently move with the passage of time. The wavefronts of waves propagating in a unidimensional medium are normally single points; in a two-dimensional medium, they are curves, and in a three-dimensional one, they are surfaces. A plane wave’s wavefronts are planes. After passing through a lens, wavefronts change shape. The wavefronts of a sinusoidal plane wave are planes perpendicular to the direction of propagation which means “to move” as the wave. The wavefronts of a sinusoidal sphere wave are spherical surfaces.

A brief outline

Refraction can modify the form and/or direction of wavefronts if the propagation speed varies at different points along the wavefront. Lenses, in particular, can transform optical wavefronts between planar to spherical or vice versa. The Huygens–Fresnel principle, which treats each spot in a propagating wavefront as a bundle of discrete spherical wavelets, describes the diffraction phenomenon in classical physics. When a coherent source (such as a laser) finds a slit/aperture that is equivalent in size to its wavelength, the typical bending pattern is most prominent.

Important concepts

Types of Wavefronts

The numerous forms of wavefronts are determined by the path taken by particles originating from a source. Let’s take a closer look at each of these types:

1. Spherical Wavefront

The wavefronts are spheres centred on the source when the point source is an isotropic medium sending out waves in three dimensions. A spherical wavefront is one that has this shape.

Spherical Wavefront Examples

• In a vacuum, electromagnetic waves produce a spherical wavefront.
• When a stone is thrown in the water, it forms concentric circles.
• The invader is positioned with the spherical wavefront symbol by an army man patrolling the opposition on the radar using the camera.

2. Cylindrical Wavefront

We get a cylindrical wavefront when the light source is linear. All locations equidistant from the linear source exist on the surface of the shell in a cylindrical wavefront. The cylindrical wavefront has a cylinder-like appearance. When we draw the wavefront from a single plane, however, we get a concentric circle that looks like a spherical wavefront.

Cylindrical Wavefront Example

When light rays from one lens collide with those from another lens, they converge at a specific spot. It takes the shape of a cylinder as they bend and converge at a point.

3. Plane wavefront

When viewed from a great distance away from any source, the wavefront will look like a plane. A plane wavefront is a name for such a wavefront.

Furthermore, when a little portion of a spherical or cylindrical wavefront starts from a remote source, such as infinity, the plane wavefront is obtained.

Example of a Plane Wavefront

Plane wavefronts are created by a source that is very far away. The rays that come out of the sun are a common illustration of the planar wavefront.

Applications of Wavefront

Wavefront LASIK is a therapy for refractive defects in the human eye that is rapid, straightforward, and effective. It is a medical technique that reshapes the cornea and improves visual clarity by using directed lasers. The negative effects of wavefront-guided LASIK are reduced compared to standard LASIK. Myopia (nearsightedness), astigmatism, and hypermetropia are all conditions that Wavefront Guided LASIK can help with.

Aberrations in the wavefront

Where a single focus distance may not exist due to lens thickness or flaws, methods involving wavefront measurements or forecasts can be regarded as an advanced approach to lens optics. A perfect lens has a sphere surface form for manufacturing reasons, even though the ideal surface would be aspheric. Optical aberrations are the results of flaws like these in an optical system. Spherical aberration and coma are two of the most well-known aberrations.

However, more complex sources of aberrations, such as spatial differences in the index of refraction of the atmosphere in a large telescope, may exist. The wavefront aberration of an optical system is the departure of a wavefront from a desired ideal planar wavefront. A sampling image or a set of two-dimensional polynomial terms are commonly used to describe wavefront aberrations. For many applications in optical systems, minimization of these aberrations is desirable.

A wavefront sensor is a device that detects wavefront aberration in a coherent signal and uses that information to describe the optical quality (or lack thereof) of an optical system. A Shack–Hartmann lenslet array is a popular technique. Adaptive optics, optical metrology, and even the measurement of aberrations in the eye itself are just a few of the uses. A weak laser is fired into the eye, and the reflection of the retina is recorded and processed in this method.

Significance of wavefront in IIT JEE exam

The Oscillations and Waves chapter covers a wide percentage of questions in the exam, at 10%. All you have to do is comprehend each topic’s concepts. If you stick to this course, your Physics preparation will be on point, and you’ll be able to get good grades in this part. According to the distribution of difficulty levels in the previous year’s exams, around 83 per cent of the JEE paper consists of simple and medium-level questions.

FAQ’s

What is Wavefront Aberration, and how does it affect you?

The wavefront aberration of an optical system is the divergence of a wavefront from the perfect planar wavefront. The sampled image and a collection of two-dimensional polynomial terms are commonly used to characterize wavefront aberrations. Many applications in optical systems can benefit from guided treatments such as Wavefront-guided LASIK to reduce these aberrations.

What is Wavefront? Use an instance to support your argument.

A wavefront is a point on which the phase of an optical wave is the same. A wavefront, for example, is a surface where the peak of a sinusoidal water wave has a maximum value and the trough has the lowest value. In addition, these waves have the same phase.

Q. List three Wavefront LASIK benefits.

Ans:

1. Eye refractive defects are precisely corrected.
2. Higher-order aberrations are reduced.
3. Improves contrast sensitivity, which is the ability to see black lettering on a white backdrop.