Photon radiancy

See also photon flow, photon radiance, spectral radiance, spherical radiance. 

FIGURE 1.7 The geometrical configuration, which express the photonic radiance (HyperPhysics, 2010 Putz, 2010). 

Radiance and luminance L are the flux into a small projected soUd angle dQ. from a small source area dA, divided by the projected solid angle and source area, so that d = L dA dQ.. The nomenclature here does not follow the generic pattern of the first three For the unit of power this is called the radiance with units of W/(cm sr). For photometry it is called the luminance with units of Lylm/(cm sr). For photon units either the photon radiance or the photon luminance is accepted, both with symbol Lp and units ph/(s cm sr). 

Although it is known that the colour of black body radiation is only dependent upon temperature, sparks have colours that are also dependent upon the type of emitting material. However, the form of the radiance curves does not relate exactly with known molecular energy transitions. This suggests that the mechanism of emission in excess of black body radiation is not yet fully established. It is possible that some emission bands only become active when the metal oxide particle is molten, or that the energy is dissipated simply via collisions with other molecules rather than the emission of photons. 

When the atmosphere is assumed to be stratified and plane-parallel, it is common to introduce the radiance hv ] and hv describing upward and downward propagating photons, as was presented previously for the flux (see Eqs. 4.39 and 4.40). In this case, integrating (Eq. 4.51), we obtain ... 

The actinic flux is related but not equal to the irradiance. The relation between the two quantities has been illustrated carefully by Madronich (1987). Consider an atmospheric layer of infinitesimal vertical thickness dz, illuminated from above (Figure 4.8). The quantity of light incident on the top surface of the layer depends on the direction of incidence of the light, as defined by the spherical coordinates 0, <(>. This dependence is specified by the spectral radiance L(X, 0,4>), expressed in units of photons cm-2 s-1 nm 1 sr-1. The number of photons entering the layer (through ds, in time dt, from solid angle dm) is... 

A nondescanned ( direct ) FLIM detection module with two wavelength channels was developed for the Radiance 2000 microscope from Biorad. The detector module contains computer-controlled dichroic beamsplitters and filters, preamplifiers, and overload shutdown of the detectors. The preamplifiers simultaneously deliver photon pulses to a Becker Hickl SPC-830 TCSPC and intensity signals to the standard steady-state recording electronics. Unfortunately all Radiance scanning microscopes were discontinued in 2004. 

This phenomenon of super-radiance is used in the photon-echo technique for high-resolution spectroscopy to measure population and phase decay times, expressed by the longitudinal and transverse relaxation times Ti and T2, see (7.1). This technique is analogous to the spin-echo method in nuclear magnetic resonance (NMR) [904]. Its basic principle may be understood in a simple model, transferred from NMR to the optical region [905]. 

A unit surface element of a source with the spectral radiance [W/(m sr)] emits photons per second within the frequency interval... 

The spectral radiance (p) is defined as the radiant power (or photon flux density) emitted per unit source area per unit sohd angle (conventionally expressed in W/m /sr). 

The spectral radiance is the amoimt of radiation emerging from a small hole in the cavity. Recall from kinetic theory, the number of molecules striking an area is given by u/4, where n is the number density and v is the average velocity. Similarly, the photon flux emerging from a hole in the cavity is nc/4 and the energy flux will be m(i )c/4 and from Equation A.15.23... 

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