A ray is a geometrical representation of light that is idealised by picking a curve that is perpendicular to the wavefronts of actual light and points in the direction of energy flow in optics. By separating the real light field into discrete rays that can be computationally carried through the system using ray tracing techniques, rays are used to represent the propagation of light via an optical system. This enables even the most complicated optical systems to be mathematically investigated or computer-simulated. Ray tracing is based on approximate solutions to Maxwell’s equations that are valid as long as light waves pass through and around objects with dimensions substantially larger than the wavelength of the light. Diffraction, for example, requires wave optics theory, which is not covered by ray optics or geometrical optics. In some cases, adding phase to the ray model can be used to describe wave phenomena like interference.
A light ray seems to be a perpendicular to light wavefronts, curved or straight line having a tangent which is collinear only with wave vector. In a homogenous medium, light beams are straight. They bend at the interface of two different media and can also be bent in a medium with a changing refractive index. The propagation of rays across an optical system is described by ray optics. The imaged objects are considered as a collection of separate point sources, each of which produces spherical wavefronts and outward rays. To find the equivalent point on the picture, rays from each object point can be mathematically propagated. Fermat’s principle, that states that its shortest path for a beam of light connecting two points is the path that takes the shortest amount of time, leading to a somewhat stricter description of a light ray.
In optical modelling, a variety of unique rays are employed to examine an optical system. These are defined and discussed in the following sections, which are organised by the sort of system they are used to mimic. A light beam that impacts a surface is called an incident ray. The angle of incidence is the angle formed by this beam and the perpendicular or normal to the surface. This reflected ray which corresponds to a certain incident ray illustrates the reflecting light by the surface. This angle produced by the surface normal as well as the reflected beam is known as the angle of reflection. According to the Law of Reflection, the angle of reflection for a specular (non-scattering) surface is always equal to the angle of incidence.
The light that is transmitted through the surface is represented by the refracted ray or transmitted ray that corresponds to a specific incident beam. The angle of refraction is the angle formed between this beam and the normal, and it is determined by Snell’s Law. The power in the incident beam must equal the total of the power in the refracted ray, the power in the reflected ray, and any power absorbed at the surface, according to the law of conservation of energy. If the substance is birefringent, the refracted ray may divide into ordinary and exceptional rays, each of which has a distinct index of refraction when passing through it.
A meridional ray, also known as a tangential ray, is a ray that is constrained to the plane containing the optical axis of the system and the object point from which it originated. A skew ray is one that does not propagate in the same plane as the object point and optical axis. The optical axis is not crossed by such rays, and they are not parallel to it. In an optical system, the marginal ray (also known as a ray or a marginal axial ray) is the meridional ray that begins at the point where the object crosses the optical axis and ends at the system’s aperture stop. The meridional beam that originates at the border of the object and travels through the centre of the aperture stop is the primary ray or chief ray (also known as the b ray) in an optical system. At the pupil sites, this ray crosses the optical axis. As a result, main rays are analogous to rays in a pinhole camera.
The size of an image is determined by the distance between the principal ray and the optical axis at a given place. The Lagrange invariant, which describes the optical system’s throughput or etendue, is defined by the marginal and chief rays combined. For each object point, some writers define a “primary ray.” For each object point, some writers define a “primary ray.” The marginal principal ray is the primary ray that originates at a location on the object’s edge.
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