Absorption length

For concentrated or bulk samples a transmission experiment is both the simplest and the most effective. In essence, one measures the X-ray intensities incident and transmitted through a thin and uniform film of the material. Careful analysis of signal-to-noise ratio considerations indicates that optimal results are obtained when the sample thickness is of the order of 2.5 absorption lengths. Since in this case a simple Beer s law applies, the data are usually plotted as In(7//0) versus E. The intensities are measured using ionization chambers in conjunction with high-gain electrometers (see Fig. 11). 

Liu CY, Bard AJ (1989) Effect of excess charge on band energetics (optical absorption length and carrier redox potential) in small semiconductor particles. Phys Chem 93 3232-3237. 

The spectra shown in Fig. 3.1 appear as unstructured, broad absorption bands, with a maximum of absorption around 200 cm-1 for the lightest system and at lower frequencies for the more massive pairs. Absorption is weak, even at the peaks, and amounts to a mean absorption length of more than 1/a 106 cm (that is 10 km) if both gases are present at partial pressures of just one atmosphere. Absorption of rare gas mixtures increases, however, with increasing densities, with a mean absorption length of centimeters as we approach liquid densities. 

Figure 13. Absorption length La and depletion layer width W of an ideally smooth WSe2 electrode in contact with an electrolyte, assuming e = 9 and n,= X 106...

D0 the optical absorption length is the distance the infrared radiation can travel through the sample (cm), equal to 1/p where P is the optical absorption coefficient... 

Blue, chosen because it s absorption was peaked at 620 nm and because it had a deep absorption minimum around 450 nm. In later work, a thiobarbituric acid derivative in PMMA produced an efficiency of 39 % W 1 cm-2 over an estimated 32 pm absorption length [62]. This was followed recently with new tricyanovi-nylaniline doped polymers in which a net efficiency of nearly 250% W 1 cnr2 was demonstrated over 35 pm. [63] An added bonus was that this approach proved to be the stimulus for many materials to be characterized. Materials with p[3 values as large as 3,800x10 48 esu, coupled with good transparency in the 450-470 nm window, were synthesized and optimistically predicted to satisfy criteria for ADPM SHG with target efficiencies of about 2000% W 1 [64] ... 

Surface recombination reduces the luminescence intensity when the excitation light has a very short absorption length. The effect is weak because of the low carrier mobility and diffusion length, so that although there are many defects at the surface of a-Si H, the effect on the luminescence intensity is only 10-20% (Dunstan 1981). A measure of the surface recombination is the product, aLp, of the optical absorption coefficient and the diffusion length. In most situations in a-Si H, and particularly at low temperature, aLp is less than unity, whereas in crystals it is often much greater. 

Source Brightness (particles cm eV steradian ) Elastic Mean 1 Free Path (A) Absorption Length (A) Minimum Probe Size (A)... 

Radiation groups (2) (Ratio of L to radiation absorption length and blackbody radiation flux to enthalpy convection),... 

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