Properties of Solar and Optical Radiations in the Descriptions of Physical Optics

At researches of properties of solar and optical radiations the basic laws of physical and geometrical optics are used, as well as a quantum theory of interaction of radiations with the matter. The physical properties of solar and optical radiations are analyzing more frequently in the descriptions of physical optics.   

Physical parameters and characteristics of radiations. The continuous spectrum of electromagnetic radiations spreads from γ - rays with a minimum wave-length of 3x10-15m, that arises up at disintegration of radio-active elements to the long radiowaves 3x106 m. In accordance with the change of wave-lengths and frequencies of radiations their properties also are very changing. These properties are determining largely by energy of photon. Middle region of spectrum of electromagnetic radiations, that unites the infra-red radiations with a wave-lengths from 1,0 mm to 0,78 μm, visible radiations – from 0,78 µm to 0,38 µm and ultraviolet radiations - from 0,38 µm to 0,01 µm, is named the optical region of spectrum. The optical radiations of bodies is limited by frequencies from ·1019 Hertzs to 3·1010 Hertzs or by wave-lengths from 10-11 m to 10-2 m. Combination of these radiations in one group is explicated by unique principles of excitation of optical radiations, and also by likeness of methods of their transformation and use.

The region of infra-red radiations is the biggest part of optical region of spectrum. The optical radiations of this area of spectrum own the small values of energy of photon (from 2,0·10-22 J to 2,5·10-9 J), as a result, the infra-red radiations are mainly discovered at their thermal action.

Visible radiations (the light) – radiations that cause the effect of the visual feeling. From all range of optical spectrum that consists of 15 octaves, only one octave corresponds to a visible region.

Unlike infra-red, the ultraviolet radiations have the biggest values of energy of photon (from 5,2·10-19 J to 2,0·10-17 J) between the optical radiations. They interact very actively with the matter (photoluminescence, photo-electric and photo-biological action). Mass of photons of optical radiations is found within the limits of 10-35 - 10- 30 g.

The basic parameters and characteristics of optical radiations are: orientation, spectral composition, polarization, coherence, energy, flux, density of flux, angular divergence and radiant intensity.

An orientation is determined by a wave vector: k = kη0 = (2π/λ)η0 = (νopt/Vopt)η0, where: k = 2π/λ - wave number; η0 - unit vector normal to the wave surface; νopt, λ - angular frequency and wave-length of radiations; Vopt - linear velocity of propagation of wave in a given environment.

In the case of ideal monochromatic radiations the spectral composition of radiations is determined by the value of wave-length. In the case of superposition of certain amount of radiations the spectral composition of radiations is determined by the aggregate of values of wave-lengths. The monochromaticity determines the degree of closeness of electromagnetic oscillations to the ideal oscillations E = Emaxcos(ωt + Ф0), where amplitude Emax, circular frequency ω and phase Ф0 do not rely on time t. The real radiations are not ideally monochromatic. Unmonochromatic oscillations usually appear as a sum of ideal monochromatic oscillations. The higher is the monochromaticity, the narrower is the range of frequencies (wave-lengths), in which monochromatic constituents are grouped. Extraordinarily, the high monochromaticity is characteristic for the radiations of lasers (10-14...10-16 m).

Polarization of radiations characterizes the spacious and time efficiencies of orientation of electrical vector E and magnetic vector H. Waves, in which the directions of vectors E and H are unchangeable in space or are changing in accordance with a certain law, are the polarized waves. The direction of vector of the electric field E defines the direction of polarization. Depending on the direction of motion of end of vector E the polarization of radiations can be linear, circular or elliptic. Only ideal monochromatic oscillations are fully polarized.

The coherence characterizes coordination in the time of flow of a few oscillating or wave processes. At addition of two monochromatic oscillations with identical frequencies, but different amplitudes and phases, the monochromatic oscillation of the same frequency is creating. Amplitude of resulting oscillation relies on amplitudes and phases of composing oscillations. Oscillation in this case is monochromatic. Two unmonochromatic oscillations in a result of their interaction create coherent oscillation, if the difference of phases of these oscillations remains permanent during all time.

It exist the temporal coherence and spatial coherence. The temporal coherence is linked with a degree of monochromaticity of wave. Spatial coherence is linked with coherent properties of wave at the change of amplitudes and phases in a plane, which is perpendicular to the direction of its propagation. All space, that a wave occupies, can be divided onto pieces; in each part a wave saves its coherence. The volume of such part is named the volume of coherence. By means of laser, for example, it is possible to get the radiations, the volume of coherence of which by 1017 times exceeds the volume of coherence of light wave of the same intensity, got with the most monochromatic no-laser radiants.

Energy of radiations We (J) is characterized by energy that is carried by hertzian waves. The energy of radiations, absorbed by a body, more frequently grows into energy of thermal motion of molecules, what is also measured in Joules.

Flux of radiations (power) Фe (W) is the ratio of energy of radiations to the time. For the continuous laser the flux of radiations can exceed of 103...104 W, for pulsed lasers - 1011...1012 W.

Density of flux of radiation (density of power or intensity) Ie [W/m2] is determined by the ratio of flux of radiation to an area Ie = 4Фe/πD2, where D - diameter (linear aperture) of optical beam of the round cross-section. 

Angular divergence of radiation is characterized by a corporal angle of Ω. In this angle the overwhelming part of radiation propagate. In an ideal case the angular divergence is limiting only by the phenomenon of diffraction. Frequently, angular divergence is characterized by the flat angle (by the angular aperture of optical beam). The link between Ω and γ is expressed by the relation: Ω = 2π(1 – cosγ).    

Radiant intensity Ie [W/sr] determines the concentration of flux of radiation of source in space. It is equal to the ratio of flux of radiation to a corporal angle of Ω, within the limits of what the radiations propagate.


Written by Vasil Sidorov on August 04, 2010 in

Technopark QUELTA

Nizhyn Laboratories of Scanning Devices




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