Prisms Cornu

FIGURE 7-20 Dispersion by a prism (a) quartz Cornu type and (b) Littrow type. 

The Littrow-mounted quartz prism is a 30°, 60°, 90° prism, being essentially one-half of the Cornu prism. The back surface of the prism has a reflecting surface, either silver or aluminum, such that the light is reflected through the prism as shown in Figure 3-12. The effect thus is the same as... 

Two basic designs of prism spectrometer are commonly used for spectrochemical analytical purposes, the Cornu and the Littrow types. Many of these instruments are presently in use, although grating spectrometers are gradually replacing prism instruments. 

Two types of prisms, namely 60° Cornu quartz prism and 30° Littrow prism are usually employed in commercial instruments. The latter is preferred. Simple glass prisms are used for visible range. For ultraviolet region silica, fused silica or quartz prism are used. Flourlte is used in vacuum ultraviolet range. Ionic crystalline materials are used in the infrared region. Some examples are NaCl, KBr, CsBr, and the mixed crystalline material commonly called KRS-5. 

---