Law of light reflection: the incident ray, reflected ray and the normal to the reflecting surface all lie on the same plane, and the angles between these rays and the normal are equal, i.e., an angle of incidence is equal to an angle of reflection. Law of independent action of light beams: action produced by one beam doesn't depend on the presence of another beam. Law of rectilinear light propagation: in a uniform medium the light rays are straight lines. However, many very important results from the practical point of view can be obtained more simply with the use of a geometrical optics approach. This rigorous approach is the basis of wave (physical) optics. Typically, light propagation is described by the wave equation, which follows from electromagnetic field theory (Maxwell's equations). Polarization also takes place after light reflection or refraction at a boundary of two dielectrics under the condition of oblique incidence of a light ray on the boundary. After transmittance of natural light through some crystals, it polarizes partially or completely. Partially polarized light is characterized by a predominant vibration direction, but not exclusively. It represents a collection of light waves with all possible vector directions, simultaneously existing and replacing each other at random. At φ = π/2 and E x = E y, an ellipse degenerates to a circumference (circular polarization) at φ = 0 it degenerates to a straight line (linear polarization). Then a vector = rotates in a transversal plane with a rate of angular motion, ω, relative to a center of coordinates and its end describes an ellipse (elliptic polarization, Figure 1). If the Cartesian components of vector have a form: Polarization of monochromatic radiation is characterized by the spatial-temporal behavior of the electric field vector. A value cΔt t is named the coherence length. If a pair of points is chosen along the line of radiation propagation, they are said to be temporarily coherent during time interval Δt t. ![]() If a pair of points is chosen on a wave front surface (which at time instant t = 0 is, by definition, a locus of equiphase points) they are said to be spatially coherent during time interval Δt f. Spatial and temporal coherence should be distinguished. ![]() Usually, the form of wave front varies when the wave transmits through a medium and/or optical system.Īn important concept in optics is radiation coherence, which means a conservation of constant phase difference of electric (or magnetic) field at two different points in the radiation field during a time period Δt. If the phase of monochromatic vibration is the same at each point of a certain surface, then this surface is called a wave surface, or wave front. Nonmonochromatic radiation can be represented as a superposition of monochromatic waves. Near-monochromatic radiation is generated by some types of lasers. Radiation with a single wavelength (λ) which is described by an infinite sinusoid, is called monochromatic. From the point of view of quantum physics, light is a flow of "light quantums," or photons. ![]() The ratio c/v = n is called the refractive index. The velocity of light in a medium, v, is always less than in a vacuum. From the point of view of classical physics, light is transverse electromagnetic waves the propagation velocity of such waves (light velocity) in the vacuum, c, is constant in any coordinate system and represents one of the fundamental constants. By "light," it is usually understood a radiation visible to the human eye (spectra! range 400–700 nm), although the laws of optics are valid for a much larger wavelength range. Optics is a branch of science that deals with light propagation in vacuum and in various media.
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