## Physical optics:

In physical optics, we consider light to travel in a form of waves. This model helps us to understand the phenomena of diffraction and interference which the geometric optics are not able to explain. The average speed of light in vacuum or in air is around 3.0 x 108 m/s ((exactly 299,792,458 m/s). the wavelength of the visible light wave varies within a range of 400 to 700 nm, but in many cases, we also use the term “light” to mention the ultraviolet radiation ((10–400 nm) and infrared radiation (0.7–300 μm).

In 1865, the existence of electromagnetic waves was predicted with the help of Maxwell’s equation. These waves travel at a speed of light and have varying magnetic and electric fields which are orthogonal to each other, and also to the direction of propagation of the wave. In today’s life, the light waves are now considered to come under electromagnetic wave type except the case when we talk about the quantum mechanical effects. `

### Optical systems using physical optics

Many approximations are considered in order to design and analyze optical systems. In order to represent the electric field of the light wave, the majority of these use a single scalar quantity, unlike others that use a vector model with orthogonal magnetic and electric vectors. Huygens-Fresnel model is one of those models. Maxwells’ equation was used to derive the equation of Kirchhoff diffraction which puts the Huygens-Fresnel equation on a much strong physical foundation. Many prism manufacturers designs precision optics and custom optical lenses that are used for special purposes.

More complex models involve the modeling of both the magnetic and electric fields of a light wave are needed when dealing with materials whose electrical and magnetic properties affect the interaction of light with the material. The behavior of the light wave, when it interacts with the metal surface, is quite different when it interacts with the dielectric medium. To model a polarised light, we must use a vector model.

Numerical modeling techniques such as the boundary element method, the finite element method, and the transmission-line matrix method are used to model the propagation of light in systems where it is not possible to solve analytically. Such models are computationally demanding and are typically only used to solve small-scale problems that require accuracy that can be achieved with analytical solutions.

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