This first part of the experiment employs a laser of a known wavelength to observe diffraction orders from an optical grating. From the incidence and diffraction angles of the laser beam, one can deduce the period of the optical grating from the grating equation. 

 

The second part of the experiment utilizes the optical grating measured in the first experiment to construct a Littrow grating monochrometer. The spectral lines of a mercury lamp are identified in the monochrometer with a specified resolution.