Page 113 - An Introduction to Analytical Atomic Spectrometry - L. Ebdon

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Figure 4.11
Schematic diagram of a blazed reflection grating.

blaze wavelength, l where
b

Energy is concentrated in the first order at l , in the second order at half l , and so on.
b
b
Light striking the surface of the grating will be diffracted to a larger or lesser degree depending on its
wavelength, hence a spatial separation of wavelengths is achieved. The diffracted light is collimated
and focused, using mirrors, on to an exit slit, and the diffraction grating can be scanned so that
different wavelengths are focused on to the slit in turn. A grating may be mounted in a monochromator
in several ways. One method, the Ebert mounting (Fig. 4.12a) uses a large spherical mirror to collimate
and focus the beam. Czerny and Turner suggested replacing the large, expensive Ebert mirror with two
small, spherical mirrors mounted symmetrically, as shown in Fig. 4.12b.

In order to differentiate between wavelengths, a spectrometer with high resolution (ca 0.01 nm) is
advantageous. Apart from using an echelle grating, there are two ways of achieving this, either by
increasing the number of lines per millimetre on the grating or by increasing the focal length of the
monochromator. A typical 0.5 or 0.25 m monochromator of