Grating

Grating is an optical device having many applications.A glass plate on which a large number of equidistant parallel lines are drawn is called a grating. The line portion is opaque and the space between the lines transparent to light. There are two types of grating: Transmission grating and reflection grating.Let ‘a’ be the width of each slit and ‘b’ the width of opaque portion. The total width (a+b) is called grating element and N=1/(a+b) is the number of lines per unit length of grating.
For a grating in a minimum deviation position,
2Sin(D/2) = nNl
where ‘n’ is the order of the spectrum, ‘N’ the number of lines per meter length of the grating, ‘l’ the wavelength of the source and ‘D’ the angle of minimum deviation.