Power, emitted

Brightness. This is defined as the power emitted per unit area of the output mirror per unit solid angle and is extremely high compared with that of a conventional source. The reason for this is that, although the power may be only modest, as in, for example, a 0.5 mW helium-neon gas laser, the solid angle over which it is distributed is very small. 

Pigure 10 shows the typical commercial performance of LEDs used for optical data communication. Both free-space emission and fiber-coupled devices are shown, the latter exhibiting speeds of <10 ns. Typically there exists a tradeoff between speed and power in these devices, however performance has been plotted as a function of wavelength for purposes of clarity. In communication systems, photodetectors (qv) are employed as receivers rather than the human eye, making radiometric power emitted by the devices, or coupled into an optical fiber, an important figure of merit. 

In this way, ihe emissive power of a grey body is a constant proportion of the power-emitted by the black body, resulting in the curve shown in Figure 9.35 where, for example, e = 0.6. The assumption that the surface behaves as a grey body is valid for most engineering calculations if the value of emissivity is taken as that for the dominant temperature of the radiation. 

From eq. (5.2) we see that the total power emitted by 1 cm2 with e = 1 at 300 K is 45 mW corresponding to an evaporation of 70cm3/h of 4He. At 77 K, a surface of 1 cm2 emits about 0.2 mW, with a 4He consumption of 0.3 cm3/h. Hence the part of the dewar cooled at helium temperature is surrounded by radiation shields or baffles at intermediate temperatures. The latter are either gas cooled or thermally anchored to a LN2 reservoir. 

Radiant intensity can be described as the amount of power (watt) heading in your direction, i.e., per steradian, from a light source. The total amount of power emitted by the source is the radiant flux (watt). If you integrate the radiant intensity over all solid angles, you get the total radiant flux. If it is weighted by the photopic response, then it is the luminous intensity and the luminous flux. 

The remaining variable required for calculation of 3F from Eqs. (7.39) and (7.40) is the collection efficiency Q, which measures the fraction of the total power emitted by a fluorophore that can be gathered as light by the microscope objective. Figure 7.5 shows for both parallel and per-... 

Both p and / are ratios of a power emitted at position z relative to that for an isolated dipole p refers to total power (light plus heat) whereas / refers to radiated power only, derived by integrating the fixed-amplitude dipole radiated intensity 5 [given by Eq. (7.34) without the PT normalization in the denominator] over An steradians. 

A host material is activated with a certain concentration of Ti + ions. The Huang-Rhys parameter for the absorption band of these ions is 5 = 3 and the electronic levels couple with phonons of 150 cm . (a) If the zero-phonon line is at 522 nm, display the 0 K absorption spectrum (optical density versus wavelength) for a sample with an optical density of 0.3 at this wavelength, (b) If this sample is illuminated with the 514 nm line of a 1 mW Ar+ CW laser, estimate the laser power after the beam has crossed the sample, (c) Determine the peak wavelength of the 0 K emission spectrum, (d) If the quantum efficiency is 0.8, determine the power emitted as spontaneons emission. 

In equilibrium the total power emitted by the particle must be equal to that absorbed ... 

The IR intensity is defined as the amount of optical power emitted from a source in to unit solid angle and is expressed in watts per steradian. The IR efficiency is a product of f R intensity and burning time per gram of formulation. 

One of the most interesting uses of emission spectroscopy is the study of the action of lubricants 162,166,167 168,169,170). A loaded steel ball is rotated in a fluid bath and made to slide over a diamond window. A contact region is formed which can be measured by the radiant power emitted. A substraction of the ball surface radiation from the total radiation emitted from the contact region was electronically carried out. A study of the emission spectra of a polyphenyl ether and a naphthenic fluid under dynamic conditions was made. The widths of some of the bands of the ether increased dramatically when a certain load (pressure) was exceeded. These increases were correlated with the changes of chemical composition through decomposition of the fluid 170,171). 

Note that the radiation field is dependent on one angle only, namely the angle 9 subtended by the acceleration r and radius arm vector R the dependence enters Eq. 2.60 as (sin 9)2 which is characteristic of the familiar dipole radiation pattern. It is, therefore, straightforward to integrate Eq. 2.60 over a spherical surface R2 f dQ where dQ = sin 9 d9 dtotal power emitted,... 

For a narrow wavelength range, AX, the value of Mh is nearly constant and the power emitted is simply the product MxAk. 

Optoelectronic—Pertaining to a device that responds to optical power, emits or modifies optical radiation, or utilizes optical radiation for its internal operation. Any device that functions as an electncal-to-optical or oplical-to-electrical transducer. 

Power emitted (watts) Surface area (meter2)... 

Equation 6.44 gives the total power emitted by a black body. However, materials and bodies whose temperatures are measured with radiation-type instruments often deviate considerably from ideal black body behaviour. This deviation is expressed generally in terms of the emissivity e of the measured body (see also Volume 1, Section 9.5.4), and the energy emitted by the body per unit area per unit time is ... 

Planck s radiation law determines the power emitted by a small aperture in a cavity, which is at a given equilibrium temperature. The spectral flux emitted by an isotropic blackbody source into a solid angle 2 = 2rr sin 0r (where 9r is the angular radius of the first optical element of the spectrometer) is ... 

The radiance is a normalized measure of the brightness of a source it is the power emitted per area of source, per solid angle of the beam from each point of the source. 

Radiant power (P) Same as radiant (energy) flux <1>. Power emitted, transferred or received as radiation. The SI unit is J s = W. 

Intensity refers to a property of a source e.g., light intensity designates the rate of light emission for a photometric source (lumens per unit solid angle, or candelas), and radiant intensity is the power emitted per unit solid angle (W steradian-1). 

Radiance is the rate of radiant energy emission (power emitted) per unit sol id angle per unit area (W steradian-1 m-2). 

Figure 24-4 illustrates the processes involved in emission and chemiluminescence spectroscopy. Here, the analyte is stimulated by heat or electrical energy or by a chemical reaction. Emission spectroscopy usually involves methods in which the stimulus is heat or electrical energy, while chemiluminescence spectroscopy refers to excitation of the analyte by a chemical reaction. In both cases, measurement of the radiant power emitted as the analyte returns to the ground state can give information about its identity and concentration. The results of such a measurement are often expressed graphically by a spectrum, which is a plot of the emitted radiation as a function of frequency or wavelength. 

Figure 24-4 Emission or chemiluminescence processes. In (a), the sample is excited by the application of thermal, electrical, or chemical energy. These processes do not involve radiant energy and are hence called nonradia-tive processes. In the energy-level diagram (b), the dashed lines with upward-pointing arrows symbolize these nonradiative excitation processes, while the solid lines with downward pointing arrows indicate that the analyte loses its energy by emission of a photon. In (c), the resulting spectrum is shown as a measurement of the radiant power emitted Pg as a function of wavelength, A.

Sources for fluorescence are usually more powerful than typical absorption sources. In fluorescence, the radiant power emitted is directly proportional to the... 

The total emissive power emitted by a black body is obtained by integration over all wavelengths ... 

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