Rowland circle polychromators

Figure 7.13 A Rowland circle polychromator. This configuration is called a Paschen-Runge mount. The source shown is an inductively coupled plasma, hut any of the electrical excitation sources can he substituted. Multiple photomultipler detectors are placed at the appropriate positions on the circumference of the circle to measure dispersed wavelengths. [From Boss and Fredeen, courtesy of PerkinElmer Inc. (www.perkinelmer.com).]...

The glow discharge (GD) is a reduced-pressure gas discharge generated between two electrodes in a tube filled with an inert gas such as argon. The sputtered atom cloud in a GD source consists of excited atoms, neutral atoms, and ions. The emission spectrum can be used for emission spectrometry in the technique of GD-OES, but the GD source can also be used for AAS, AFS, and MS. The source can be used with any of the types of spectrometers discussed for plasma emission sequential monochromator, Rowland circle polychromator, echelle spectrometer, or combination sequential-simultaneous designs. The detectors used are the same as described for plasma emission spectrometry PMTs, CCDs, or CIDs. 

Sketch the components of a Rowland circle polychromator. What is the advantage of this design over a scanning monochromator ... 

FIGURE 3 Schematic representation of the most frequently used grating-based monochromators (A, B, C) and polychromators (D, E, F). A and D are known as Czerny-Turner design. Fastie-Ebert (B) and Littrow (C) have similar designs in that both use a single reflective mirror. A Rowland circle polychromator is depicted in E, and F represents an Echelle spectrograph. 

Figure 15.5—Optical schematics of a polychromator with long focal distance and a concave grating. Reflecting mirrors can be used when lines are too close to one another. Sometimes, several polychromators are combined. To the right, principle of the Rowland circle.

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