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Irradiance, E, due to an electromagnetic wave is the magnitude of the Poynting vector of that wave (for example, Hecht E 1987, p. 43) which, in a homogeneous medium, can be expressed as follows:
| E | = εv < Ê 2> | |
| = 1 / ( µv ) < Ê 2> | (1) |
where ε is the electric permittivity of the medium, µ is its magnetic permeability, v is the velocity of light in the medium, Ê is the time-dependent magnitude of the electrical vector of the electromagnetic wave, and < x > is the time average of x over a period much longer than that of the electromagnetic wave in question. The transition from the first to the second line of this equation is ensured by the following relationship:
| v = ( εµ )-1/2 | (2) |
In many cases (for example, Mätzler C et al 2006b), µ ~ µ0, where µ0 is the magnetic permeability of vacuum, also referred to as the magnetic constant. In these cases, by using the second line of Eq. 1, one has:
| E | ≈ ( 1 / µ0 ) ( m' / c ) < Ê 2> | |
| = ( 1 / µ0 ) ( m' / c ) ( Ê02 / 2 ) | (3) |
where, m' is the real part of the refractive index (i.e. the refraction index), c is the velocity of light in vacuum, and Ê0 is the amplitude of the electric field of the wave.
| CITATION: Jonasz M. 2006. Radiometry: Irradiance and the Poynting vector (www.tpdsci.com/Tpc/RdmIrdPytg.php). In: Top. Part. Disp. Sci. (www.tpdsci.com). |
HISTORY: Published: 06-Mar-2008 Modified: 06-Mar-2008 Peer-reviewed: PENDING |
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