Intensity of photons

Stimulated emission. The upper state can also decay by stimulated emission controlled by the Einstein B coefficient and the intensity of photons present of the same frequency. 

The rate of the formation of photoexcited electron-hole pairs, Gix), is given as a function of the intensity of photon beam h, the absorption coefiicient of photons a, and the depth of photon-penetration x as shown in Eqn. 10-12 [Butler, 1977] ... 

In the photoresistors and photodiodes use is made of the internal photoelectric phenomenon and of specific properties of semiconducting materials. Photons impinging on the photosensitive element generate an electrical current, which flows through the photoconductor and is amplified by the effect of a small applied voltage. The increase of the current intensity is proportional to the intensity of photons that strike the photosensitive element. 

Photons and phonons do not follow number conservation as do electrons and molecules. However, they do follow energy conservation. An intensity of photons or phonons can be defined as follows... 

To obtain specific values, we measure total energy of emission and the total energy absorbed. It is easier to measure intensity of photons emitted as a function of wavelength. This gives us ... 

We have already briefly discussed luminescence decay times. Reiterating, the decay time of a phosphor has been defined as the time for the steady state luminescence intensity to decay to 1/e, or 0.368, of its original Intensity. It has been found that the intensity of photon emission builds up in the order of microseconds, i.e.- 10 sec. to a specific value, i.e.- the excitation process takes only a few microseconds. Since the intensity also decays in microseconds (if the excitation source is removed), there is an equilibrium value attained in the presence of the excitation source, which is a combination of both excitation time and decay time. This so-called steady state is called Iq, and is promulgated by the population of emitting... 

Excited bound states of atoms are one of the simplest examples of unstable quantum states which decay radiatively into the continuum of possible one-photon states of the electromagnetic field in free space. The search for a satisfactory theoretical explanation of the line frequencies and intensities of photon emission spectra at the beginning of the last century eventually culminated in Heisenberg s "magical paper" from July 1925 [1, 2] and in the development of modern quantum mechanics [3-6]. Although basic aspects of this spontaneous decay process have already been described theoretically in an adequate way in the early days of modem quantum mechanics [7,8], interestingly, some of its time-dependent dynamical aspects are still of topical current interest. 

We initially restrict ourselves to the simplest process the linear intrinsic photogeneration of charge-carrier pairs. Their production rate is proportional to the absorbed intensity of photons of the excitation light in the crystal, and requires neither excitonic processes at the crystal surface nor at the contacts, nor does it involve biexcitonic processes. 

For a piece of material of finite thickness x, such as shown in Fig. 2.10(b), integration of Eq. (2.7) shows that the transmitted intensity of photons that have not suffered interactions in the material is given by... 

Figure 2. The initial trend of increase in absorption and acceptance of photons and electrons as a function of their respective energies, (a) Increase in intensity of photon absorption or emission with photon energy, (b) Increase in intensity of electron acceptance or emission with electron energy.

The near UV spectrum is divided among direct and diffuse sources. The latter cannot be concentrated to a single point, the former can. Consider a flat plate collector cross section (Fig. 13, left). Each point at the surface receives a direct contribution of (photons/cm -s) and a diffuse contribution of Ig (same units). The total intensity of photons collected by the plate is Ip = Ig + I. ... 

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