Diffraction by N-slits

Optical disturbance due to N slits

Irradiance due to N-slits I 0 = I rradiance by single slit at  =0

For principal maxima or

For minima Between consecutive principal maxima, there will be N-1 minima

Subsidiary maxima (N-2) subsidiary maxima between consecutive principle maxima

For large N, irradiance of first subsidiary maxima

Diffraction from multiple slits Slit Diffraction Pattern

Normal incidence Transmission grating

Oblique incidence a

For two wavelengths

Grating in spectroscopy Identification of element

Dispersive power of grating Width of principal maxima

Barely resolved ItIt  s  w

Chromatic resolving power of a grating

Chromatic resolving power of a prism

Reflection grating

Diffraction grating

The nominal track separation on a CD is 1.6 micrometers, corresponding to about 625 tracks per millimeter. This is in the range of ordinary laboratory diffraction gratings. For red light of wavelength 600 nm, this would give a first order diffraction maximum at about 22°.

15  15  0 nm 450 nm Atomic Force Microscope Image of CD

Phase grating Delta function Bessel function

Bragg’s law X-ray diffraction from crystals: 2d Sin θ = n λ

Electron diffraction patterns of a real 3D quasicrystal. The periodic structure of a crystalline solid acts as a diffraction grating, scattering the electrons in a predictable manner. Working back from the observed diffraction pattern, it may be possible to deduce the structure of the crystal producing the diffraction pattern.

1. Optics Author: Eugene Hecht Class no. 535 HEC/O Central library IIT KGP