Absorption and emission cross section

The absorption and emission cross sections of Eu3+ are relatively small. The Dq- F lasing transition is also a hypersensitive transition (66) and therefore very host dependent. No systematic effort appears to have been made to exploit this feature to improve lasing performance. 

Figure 3. Absorption and emission cross section spectra of Rhodamine 101 perchlorate in bulk PMMA.

Fig. 3.26. (a) Schematic level diagram illustrating radiative and radiationless transitions, (b) Absorption and emission cross section of rhodamine 6G dissolved in ethanol... 

High gain and high power organic dye-doped polymer optical fiber amplifiers absorption and emission cross sections and gain characteristics. Jap. Journal of Appl. Phys., 36, 2705-2708. 

Quimby, R.S., 2002. Range of validity of McCumber theory in relating absorption and emission cross sections. 1. Appl. Phys. 92 (1), 180-187. 

The amount of fluorescence emitted by a fluorophore is determined by the efficiencies of absorption and emission of photons, processes that are described by the extinction coefficient and the quantum yield. The extinction coefficient (e/M-1 cm-1) is a measure of the probability for a fluorophore to absorb light. It is unique for every molecule under certain environmental conditions, and depends, among other factors, on the molecule cross section. In general, the bigger the 7c-system of the fluorophore, the greater is the probability that the photon hitting the fluorophore is absorbed. Common extinction coefficient values of fluorophores range from 25,000 to 200,000 M 1 cm-1 [4],... 

Let N(j,Ni,N2, and Nj, be the equilibrium population densities of the states 0, 1,2, and 3, respectively (reached under continuous wave excitation intensity Iq), and let N = NQ + Ni+N2 + N3he the total density of optical absorbing centers. The up-converted luminescence intensity ho (corresponding to the transition 2 0) depends on both N2 and on the radiative emission probability of level 2, A2. This magnitude, which is dehned below, is proportional to the cross section a20 (called the emission cross section and equal to the absorption cross section ao2, as shown in Chapter 5). Thus we can write... 

Since the fluorescence band usually is a mirror image of the absorption band, the maximum values of the cross-sections in absorption and emission are found to be equal ... 

As the light collection capacity of a dispersive monochromator is frequently low, the use of filters can lead to more precise measurements of emission signals if the bandwidth is suflBciently narrow to avoid spectral interference. Interference filters with a bandwidth of 5 nm are available, and for maximum selectivity these should be used with near parallel light (L7). In atomic absorption the light collection capacity of the monochromator is frequently unimportant as the source intensity is high and the cross section of the optimum absorption zone of the flame is small. 

Here (Tabs,i is the cross-section for an absorption from the Si -level to higher lying states, Nt is the density of triplet excitations and (Tt is the corresponding cross-section for absorption into higher lying triplet levels. Since the first two terms on the right hand side both depend linearly on the density N xc of excited Si-states an effective stimulated emission cross-section iVsc,cn = sc- ahs,i can be defined. A quantitative treatment of the triplet absorption is more complicated since the density of molecules in the 7 -stale has to be known. 

In Eq. (3), 039 and 023 are the cross sections for stimulated emission and absorption. For narrow-line absorption and emission spectra, these two cross sections are equal. For broadband spectra with emission bandwidth greater than kT, the cross sections are connected by a generalized Einstein relation (6J. The final term in Eq. (3) accounts for possible excited-state absorption from the upper laser level to higher excited-states indicated by the dashed level in Fig. 1. If aesa > a32> absorption from level 3 dominates stimulated emission and laser action is not possible. 

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