**9.1 Prism**

The prism disperses the light radiation into individual colours or wavelengths. These are found in expensive instruments. The bandpass is lower than that of filters and hence it has better resolution and is depicted in **Figure 9**.

**Figure 9.** *Prism.*

*UV-Visible Spectroscopy for Colorimetric Applications DOI: http://dx.doi.org/10.5772/intechopen.101165*

The two types of the prism are:

1.Refractive

2.Reflective

They undergo dispersion giving wavelengths that do not overlap and the disadvantage is they give non-linear dispersion.

### *9.1.1 Refractive type*

The sources of light, through the entrance slit falls on a collimator. The parallel radiations from the collimator are dispersed into distinctive colorations or wavelength, and through the use of any other collimator, the pix of the front slit is reformed. The reformed ones will be both violet, indigo, blue, green, yellow, orange, or pink. The desired radiation on go-out slit may be decided on with the aid of rotating the prism or by way of preserving the prism stationary and transferring the exit slit which is depicted in **Figure 10**.

#### *9.1.2 Reflective type*

The dispersed radiation gets reflected and can be collected on the same side as the source of light.

#### *9.1.2.1 Grating*

Grating are the most efficient ones in converting a polychromatic to monochromatic light. Two types of the grating are diffraction and transmission.

#### *9.1.2.2 Diffraction grating*

A grating consists of a large number of parallel lines (grooves) ruled on a highly polished surface such as alumina, generally, 15,000–30,000 lines per square inch are drawn. When light rays have impinged on the grating, its grooves act as

**Figure 10.** *Refractive prism.*

scattering centres for light rays. The light is diffracted or reinforcement takes place. Grating are difficult to be prepared. The replica grating is prepared from an original grating. This is done by coating the original grating with a film of an epoxy resin, which after setting is removal to yield a replica (**Figure 11**).

mλ ¼ b Sin i ð Þ � Sin r

λ = wavelength of light produced b = grating spacing i = angle of incidence r = angle of reflection m = order

#### *9.1.2.3 Transmission grating*

Refraction takes place instead of reflection. The wavelength of radiation produced by transmission grating can be expressed by the following equation, the structure is depicted in **Figure 12**.

$$
\lambda = \left(\frac{d\sin\theta}{m}\right)\_{\theta}
$$

**Figure 11.** *Diffraction grating.*

**Figure 12.** *Transmission grating.*

λ = wavelength of radiation d = 1/lines per cm m = order no. (0, 1, 2, 3, … etc.) ϴ = angle of deflection d = 1/2000 = 0.0005 = 5 <sup>10</sup><sup>4</sup> ϴ = 6.89°
