Wavelength-selectivity

Infrared instruments using a monochromator for wavelength selection are constructed using double-beam optics similar to that shown in Figure 10.26. Doublebeam optics are preferred over single-beam optics because the sources and detectors for infrared radiation are less stable than that for UV/Vis radiation. In addition, it is easier to correct for the absorption of infrared radiation by atmospheric CO2 and 1420 vapor when using double-beam optics. Resolutions of 1-3 cm are typical for most instruments. 

Laser Photochemistry. Photochemical appHcations of lasers generally employ tunable lasers which can be tuned to a specific absorption resonance of an atom or molecule (see Photochemical technology). Examples include the tunable dye laser in the ultraviolet, visible, and near-infrared portions of the spectmm the titanium-doped sapphire, Tfsapphire, laser in the visible and near infrared optical parametric oscillators in the visible and infrared and Line-tunable carbon dioxide lasers, which can be tuned with a wavelength-selective element to any of a large number of closely spaced lines in the infrared near 10 ]lni. 

In an attempt to shed some light on the wavelength selection Datye and Langer [139] considered finite amplitude perturbations of the local wavelength. This type of approach was used in a somewhat refined version by... 

Prepare a benzene-toluene mixture by placing 0.05 mL of each liquid in a 25 mL graduated flask and making up to the mark with methanol. Take 1.5 mL of this solution, place in a lOmL graduated flask and dilute to the mark with methanol this solution contains benzene at the same concentration as solution 5, and toluene at the same concentration as solution 5. Measure the absorbances of this solution at the two wavelengths selected for the Beer s Law plots of both benzene and toluene. Then use the procedure detailed in Section 17.48 to evaluate the composition of the solution and compare the result with that calculated from the amounts of benzene and toluene taken. 

It is important to note that there are many publications which discuss optimal ways of selecting individual spectral wavelengths for use with ILS. Much of this work comes from the near infrared (NIR) community. It provides many examples of the power of intellegent wavelength selection. Unfortunately these methods often require more computional time and power than is convenient. 

Mark, H. "A Monte Carlo Study of the Effect of Noise on Wavelength Selection during Computerized Wavelength Searches", Appl. Spec. 1988 (8) 1427-1440. 

The presentation in this paper concentrates on the use of large-scale numerical simulation in unraveling these questions for models of two-dimensional directional solidification in an imposed temperature gradient. The simplest models for transport and interfacial physics in these processes are presented in Section 2 along with a summary of the analytical results for the onset of the cellular instability. The finite-element analyses used in the numerical calculations are described in Section 3. Steady-state and time-dependent results for shallow cell near the onset of the instability are presented in Section 4. The issue of the presence of a fundamental mechanism for wavelength selection for deep cells is discussed in Section 5 in the context of calculations with varying spatial wavelength. 

Figure 2. UV light-induced deposition of silver nanoparticles (al-a3) and wavelength-selective visible light-induced dissolution of silver nanoparticles (bl-b3).

W.R. Hruschka, Data analysis wavelength selection methods, pp. 35-55 in P.C. Williams and K. Norris, eds. Near-infrared Reflectance Spectroscopy. Am. Cereal Assoc., St. Paul MI, 1987. P. Geladi, D. McDougall and H. Martens, Linearization and scatter-correction for near-infrared reflectance spectra of meat. Appl. Spectrosc., 39 (1985) 491-500. 

D. Jouan-Rimbaud, D.L. Massart, R. Leardi, et al.. Genetic algorithms as a tool for wavelength selection in multivariate calibration. Anal. Chem., 67 (1995) 4295 301. 

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