These gratings are called long-period fiber grating. A diffraction grating is a structure with a repeating pattern. The recorded light pattern is a diffraction grating. The diffraction grating used is usually a single crystal. Historically, spectrophotometers use a monochromator containing a diffraction grating to produce the analytical spectrum. It is similar to what occurs when waves are scattered from a diffraction grating. However, this model and approximation is a reasonable one to illustrate a diffraction grating conceptually. American astronomer David Rittenhouse made the first engineered diffraction grating. The multilayers serve as a diffractive grating for the incident light. Here, the laser has a narrow beam that is equal to the grating period. This was similar to notable German physicist Joseph von Fraunhofer's wire diffraction grating in 1821. Decorative patterned plastic films based on reflective grating patches are very inexpensive and commonplace. A new grille with vertical grating was the primary change. Denoted by "R" the radius of a spherical grating. The first in-fiber Bragg grating was demonstrated by Ken Hill in 1978.