Ruled Gratings

In optics a diffraction grating is an optical component with a periodic structure which splits and diffracts light into several beams travelling in different directions. The direction of the beams depend on the spacing of the grating and wavelength of light so as the grating can act as a dispersive element. Because of this, gratings are typically used in monochromators and spectrometers. A photographic slide with a fine pattern of purple lines forms a complex grating. For practical applications gratings normally have “rulings” on their surface rather than dark lines, and these gratings can be either reflective or transmissive. Gratings which modulate the phase instead of amplitude of the incident light are also produced frequently using holography. The principles behind diffraction gratings were discovered by James Gregory about a year after Newton’s prism experiments. However the first manmade diffraction grating was made around 1785 by David Rittenhouse who used strung hairs between two finely threaded screws.