Intensity light reflection equation4/23/2024 ![]() For example, it may be possible to use a model taking into account the directional emission by considering reflectivity as the sum of diffuse and specular components. In a case where the contribution of radiation directed at big angles to the surface normal is rather large it is possible to employ approximate methods of radiation transfer calculations. Generally in this case the more simple model of diffuse (not dependent on angle) reflection and emission of the rough surface is used. If we are dealing with rough surfaces, taking into account the dependence of reflection (and emission) characteristics on direction is very difficult in most cases even for very simple shapes of radiating surfaces. The two directional reflectivities are used in radiation transfer calculations as a rule only for specular reflection. Play with prisms of different shapes and make rainbows. See how changing from air to water to glass changes the bending angle. In this case many experimental points need to be measured. Explore bending of light between two media with different indices of refraction. The study of two directional reflectivity is very laborious. Basically there are the data on normal-hemispherical reflectivity at room temperature. At present the quantity of experimental data is insufficient. ![]() In this case, theoretical calculations of directional reflection characteristics cannot be acheived and the characteristics have to be determined experimentally. The case is widely encountered where the microroughness sizes are comparible with the wavelength. The directional reflection characteristics depend on the optical properties of the substance, temperature, wavelength, sizes, and the geometric shape of the surface microroughness. The expressions for the reflectivity components in spectral region of nontransparency of the second medium will have a form: In the more general case the medium 2 may have both a transparency region of the spectrum (χ 2 = 0) and a nontransparency one (χ 2 > 0). In radiation transfer the case is often found when the medium 1 is nonabsorbing (χ 1 = 0) and medium 2 is absorbing. In the case of incidence of radiation from an optically more dense medium onto an interface with an optically less dense one (n 21 θ c the full internal reflection takes place, i.e., ρ - ρ || = 1 ( Figure 1b). The parallel component is equal to zero at the Bruster angle θ Br ( Figure 1a). At n 21 > 1 the perpendicular component is increased monotonically to unity with increasing angle θ, and the parallel component first decreases to zero and then increases to unity. Curve 1 is related to reflectance of natural nonpolarizated radiation, curve 2 is related to ρ and curve 3 - to ρ ||. ![]() The angular dependence of reflectivity in this case has the form shown in Figure 1. In spectral range of transparency of two adjacent media (1 and 2), when the absorption indexes x 1 and x 2 are small in comparison with refractive indexes n 1 and n 2, the following expressions are applied for the perpendicular ( ) and parallel (||) polarized components of incident radiation: The value of reflectivity as a function of an incident angle may be calculated using Fresnel's formulas if refractive index n and absorption index χ of sample material are known. The methods for calculation and measurement of reflectivity are well developed.įor optically smooth sample surface (if its mean square microroughness is at least 100 times less than the wavelength of the radiation) the reflection is specular and the angle of reflection is equal to the angle of incidence. In this case the reflection depends on sample thickness and instead of "reflectivity" we may recommend the use of the term "reflection coefficient". The oscillations in one rope are in a vertical plane and are said to be vertically polarized.Sometimes the term "reflectivity" is understood as the ratio of the mentioned fluxes when the sample reflects volumetrically including its interior if it is semitransparent to thermal radiation. ![]()
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