Diffraction grating definition

DIFFRACTION GRATING. A series of very fine, closely spaced parallel slits, or of very narrow, parallel reflecting surfaces, which, when light is incident upon it at a definite angle, produces a succession of spectra. The complete optical theory is somewhat complicated, but the action of a plane transmission grating may he explained approximately as follows. 

To each colour belongs a definite refrangibility. That had first to be proved, and it was NEWTON who proved it [2]. Until FRAUNHOFER, a hundred and fifty years later [3], made a diffraction grating, what spectroscopy there was rested upon the dispersion of light by glass prisms. 

Fig. 1 (a) Definition of parameters (angles, mode numbers, layers, and indices) for a porous silicon (in-plane) diffraction grating and (b) comparison with Bragg gratings... 

The following definitions are required 6g is the angle between a ray parallel to the collimator axis and the grating normal, the angle of incidence 8 = 0g + Si9 and the diffraction angle 9d = 9g — 5d. In the symmetrical Littrow case 5 = — <5d, and Eq. (3) follows from the general grating equation... 

Fig. 5.7.2 Definitions of angles of incidence, 9, and diffraction, 6, at a reflection grating.

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