Monochromator design

Figure 25-6 Types of monochromators (a) grating monochromator (b) prism monochromator. The monochromator design in (a) is a Czemy-Turaer design, while the prism monochromator in (b) is a Bunsen design. In both cases,...

The two most popular monochromator designs are the Littrow and the Ebert-Fastie, shown schematically in Figure 23. The merits of the two systems have been compared for many years for atomic absorption purposes, there seems to be little to choose between them. 

Old design spectrophotometers work similar with those for UV-Vis domain, i.e. are composed of radiation somce, monochromator designed to select a desired wavelength radiation, the sample chamber and the radiation detector. In IR domain, diffuse radiation presents more serious problems then in ultraviolet and visible domain. Thus, in IR domain. 

Figure D.5 Schematic diagram for the doubie monochromator design for PerkinEimer instruments Optima 2000 DV. (Courtesy of PerkinElmer instruments, Norwaik, CT.)...

Reference should be made to Chapters 3 and 4 regarding the theory and performance of spectral isolation devices and monochromator design. The discussion here will be limited to specific applications for atomic absorption... 

A second design (Figure 11.4(b)) is a vacuum monochromator design, which gives measurements in the 160-500 nm wavelength range. The exceptionally low wavelength... 

As shown in Figure 7-20b, the IMirow prism, which permits more compact monochromator designs, is a 30° prism with a mirrored back. Refraction in this type of prism takes place twice at the same interface so that the performance characteristics are similar to those of a 60° prism in a Bunsen mount. 

As the reader will see, the evolution in Raman instrumentation did not follow a linear path. The instrument evolution demonstrates significant interactions among the roles played by the sample properties, the excitation wavelength, evolution of the detectors, monochromator design driven to match the detectors, implementation of FT-Raman (Fourier transform Raman), and the surprising impact of the Raman microprobe. As each development is described, there will be small diversions included in square brackets, almost like a point-counterpoint musical exposition, that explain the interplay of these developments. The selection of topics to be included was motivated to expose the evolution of commercial instrumentation for applications in materials science and analytical spectroscopy. Traditionally, there have been numerous other Raman topics that have been quite interesting but not included here because of our selected focus. 

Monochromators employing prisms for dispersion use a Littrow 60° prism plane mirror mount. Midinfrared instruments employ a sodium ehloride prism for the region from 4000-650 cm (2.5-15.4 pm), a potassium bromide or cesium iodide prism and optics extend the useful speetrum to 400 em (25 pm) or 270 em (37 pm), respectively. Quartz monochromators, designed for the ultraviolet visible region, extend their eoverage into the near infrared to 2500 cm (4 pm). 

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