Photon absoiption

A more complex analysis of the effect of laser phase diffusion has been appli fS the case of one-photon vs. three-photon absoiption (i.e., simultaneous absorption 3a)j and third-harmonic generation frqnt>t coi laser. As discussed in Section 3.3.2, current experiments vary the relative ph of two laser beams by passing co3 and co, through a gas. If the laser frequcnc somewhat unstable, then the relative phase of the two beams will acquire a fhtct y ing phase that is a source of phase loss in the system. The phase fluctuations q ... 

Two-photon absoiption cross-sections have been calculated, selected examples of which are listed in Table 11. The cr, values increase upon increase in dendrimer size and TT-system, with the value for tire dendrimer depicted in Figure 15 amongst the largest for organometallic compounds. 

FIGURE 4.2. BL lamp axial radiative flux distiibiilion measured at two radial positions (A) 3.1-cm and (o) 4..S-cm. Solid lines represent the ESSDE model predictions evaluated at set radial positions (Reprinted from Chem. Eng. Joum., 90, M. Salaices, B. Serrano and H.I. de Lasa, Experimental evaluation of photon absoiption in an aqueous Ti02 sluiTy reactor, 219-229, Copyright 2002, with pemiission from Elsevier). 

The symmetry of the polymer and sidechains for materials such as poly(di-n-hexylsilane) dictate that is identically zero for these polymers. However, recent publications have described measurements of for poly silanes to be on the order of 10" - 10 12 esu for third harmonic generation [28] and four wave mixing processes [29], Two-photon absoiption cross section, being proportional to Imx ), should therefore be strong as well for this class of polymers. We have observed this to be the case, with x(3)=3.2x10 esu at 560 nm, and the primary excitation decay paths of energy transfer, polymer chain scission, and UV fluorescence very similar to those observed with single photon exposure [21,30]. 

Figure 13 Calculated lower bound values for n2 in poly(di-n-hexylsilane), generated from the fit to the two-photon absoiption data in figure 8.

The evaluation of absorption photon rates in slurry reactors is a rather challenging task since light can experience a combination of reflection, scattering and absoiption in the Ti02 particle suspension. 

The primary quantum yield (Primary Q.Y.) establishes the number of molecules degraded from a primary process or event that involves direct absoiption of radiation over the number of photons absorbed (Cassano et al., 1995 and Davydov et al., 1999). Cassano et al., (1995) argue that according to the second law of photochemistry, the absorption of light by a molecule is a one-quantum process. Therefore a quantum yield factor involving the sum of all primary processes must be less than or equal to unity and this as a result that the energy absorbed by the molecule is partially lost by re-emission, collision or other processes (Alfano and Cassano, 1988). 

The level of input signal to the detector cell is determined by the integrated absoiption of photons... 

FIGURE 52 Plot of the optical absoiption coefficient (a) as a function of photon energy ( ) for three samples (a H, top a-C H, middle and a-Sic H, bottom) along with the theoretical curves [134]. 

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