Optical penetration

Sample requirements Magnetic material of interest must be within optical penetration depth of the probing light... 

Many inorganic solids lend themselves to study by PL, to probe their intrinsic properties and to look at impurities and defects. Such materials include alkali-halides, semiconductors, crystalline ceramics, and glasses. In opaque materials PL is particularly surface sensitive, being restricted by the optical penetration depth and carrier diffusion length to a region of 0.05 to several pm beneath the surface. 

Optical penetration depth the distance into the semiconductor at which the transmitted light intensity reaches 1/e of the incident light intensity at the surface of the semiconductor... 

A related, useful quantify for characterizing the absorption of light by semiconductors is the optical penetration depth (Figme 5). This quantity is defined as the inverse of the absorption coefficient that is, penetration depth s. From equation (4), it can be seen that the penetration depth is the distance into the semiconductor at which the transmitted light intensity reaches 1/e of the incident light intensity at the smface of the solid. In general, when compared to direct... 

Regarding sample concentration, c, solid-state measurements are preferable to solution-based data, particularly to avoid solvent effects. Although experimentally more difficult, UV/vis measurements, taken while the compound is in its photo-activated state, are also important as the absorption of the photo-activated state might differ from that of the ground state, thence effecting a varied depth of optical penetration. 

The important point is that is proportional to the optical penetration depth, 5, but depends only logarithmically on the photosensitizer concentration, light fluence and threshold value. Hence, doubling any one of the latter factors does not double the effective treatment depth a 7-fold increase is required. This is a limitation, in that it makes it more difficult to extend the treatment depth, but conversely it means that these factors do not have to be known as accurately as they would if depended linearly on them. (Note that Equation (7) must be modified to include effects like photobleaching and oxygen depletion, but the essential conclusions remain valid.)... 

The fundamental process of SLA is the solidification process of a liquid photopolymer, for example an epoxy resin. It is interspersed with suitable photoinitiators and exposed to ultraviolet (laser-) radiation, which initiates polymerization in those areas where the resin is heated by the laser beam according to the cross-sections. The beam deflection is realized by a scanner system consisting of two movable mirrors [102]. The curing is limited in the horizontal direction by the diameter of the laser beam and in the vertical direction by the optical penetration depth of the used resin. After completion of a layer the platform moves down according to the layer thickness and new resin is coated. After finishing the build process the model requires post-processing, in which the model is cleaned, the support removed and post-cured in a UV-hght chamber. 

Ipatova et al. (1981) first pointed out, in the context of intervalley electronic Raman scattering in doped semiconductors such as Ge and Si (Chandrasekliar et al. 1977, Contreras et al. 1985), that the electronic mean free path is often shorter than the optical penetration depth in the presence of strong electronic scattering i.e., l<6 = q K In this case, the intraband electronic Raman scattering cross section is more appropriately described by a collision-dominated response (Ipatova et al. 1981, Zawadowski and Cardona 1990),... 

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