DIFFRACTION โ Single Slit, Double Slit, N slits
1. In a single slit Fraunhofer diffraction pattern, find the intensities of the first three secondary
maxima, relative to the intensity of central maximum.
2. In a double slit experiment, the wavelength of the light source is 405 nm, the slit separation is 19.44
ยตm and the slit width is 4.05 ยตm.
(a) How many bright fringes are within the central peak of the diffraction envelope?
(b) How many bright fringes are within either of the first side peaks of diffraction envelope?
3. Consider the far field pattern of a double slit. Fifteen bright fringes appear within the central
diffraction peak. If each slit is 0.25 mm wider, by how much are they separated?
4. A set of 15 narrow slits arranged in a line separated by a distance d is illuminated by a
plane wave of wavelength ฮป at normal incidence.
(a) At positions of constructive interference far away from the slits, what is the observed
intensity relative to a single slit?
(b) At what angles, with respect to the incident plane wave, will the constructive
interference occur?
(c) Deduce the approximate intensities for the first three secondary maxima (interference)
relative to the intensity of the primary maxima in the Fraunhofer pattern of a large array
of N slits. You can start from
๐ผ(๐ข,๐ฃ)= ๐2(๐ ๐๐๐๐๐ข
2)2(sinโก(๐ข๐๐
2)
๐ ๐๐(๐ข๐
2))2.
(d) If 5 slits at the center are blocked, explain quantitatively, using convolution theorem, what will
happen to the intensity.
