http://www.launc.tased.edu.au/online/sciences/physics/diffrac.html
What is the difference between
interference & diffraction?
Interference involves the superposition of waves of
(the same / two different) wave fronts, in diffraction
there is a superposition of waves from (the same part
/ different part )of the same wave front.
Diffraction of Light
http://micro.magnet.fsu.edu/primer/lightandcolor/diffractionintro.html
Aperture: Slit, circular and square
http://www.falstad.com/diffraction/index.html
Aperture: Slit, circular and square
http://www.falstad.com/diffractio
n/index.html
http://micro.magnet.fsu.edu/primer/java/diffraction/particlesize/index.html
Diffraction of Light
http://micro.magnet.fsu.edu/primer/java/diffraction/basicdiffraction/index.html
http://hyperphysics.phy-astr.gsu.edu/hbase/phyopt/diffracon.html
Central Maximum
Normal incidence
The secondary sources on the wavefront
between the edges of the barrier sending
waves arriving at the central point are in
phase.
First Maximum
First maximum
The slit is divided into 3 equal parts and the wavelets
from the strips in two adjacent parts cancel, leaving
only wavelets from one part to give a much less
bright band.
First Minimum
2CD=/2 or BE=
At a particular direction , CD=/2 or BE=. A and C and C
and B are out of phase. The points just below A and points
just below C are also out of phase. Consecutively, pairs of
points are out of phase also. It gives destructive interference.
Hence
By
similar
pairing
process, other minima occur
when , where n = 1, 2,
3…..
The maxima occur roughly
half-way
between
the
minima at angles such that
sin  =
3/2a, 5/2a
……
a sin  

CD 
  sin  
2
2
a
n
sin  n 
a
Diffraction Grating
http://hyperphysics.phy-astr.gsu.edu/hbase/phyopt/grating.html#c1
http://hyperphysics.phy-astr.gsu.edu/hbase/phyopt/gratcal.html
http://micro.magnet.fsu.edu/primer/java/diffraction/diffractionorders/index.html
Line Spacing Calculations from Diffraction Gratings
http://www.ppo.ca/gratings.htm
Transmission grating
Reflection grating
For the 1st order Max
What is the path
difference between the
1st slit and 2nd slit?

What is the path
difference between the
1st slit and 3rd slit?
2
Max at:
a sin   
2a sin   2
Angular width of the first maximum
Intensity
Angular position

’
Angular width = 2(’ - )
Angular width of the first maximum
Consider 8 slits, for example
Max at:
(1)
(2)
(3)
a sin   
4a sin   4
(4)
(5)
(6)
(7)
(8)
Min at:
1
4a sin  '  (4  )
2
angular width   '
Pairwise cancellation : 1-5, 2-6, 3-7, 4-8
Angular width of the first maximum
Intensity
Angular position

’
Angular width = 2(’ - )
Explanation of the grating equation
d=a+b
grating



The path difference between the wavelets is d sin  , as it is for all pairs
of wavelets from other corresponding points in these 2 slits and in all pairs
of slits in the grating.
d sin   m
m  0,  1,  2,  3.........
http://micro.magnet.fsu.edu/primer/java/imageformation/gratingdiffraction/index.html
http://lectureonline.cl.msu.edu/~mmp/kap27/Gary-Diffraction/app.htm
http://www.phys.hawaii.edu/~teb/optics/java/slitdiffr/
http://www.schulphysik.de/suren/Applets.html
Example 1
Example 2
Diffraction of electrons ……
http://phys.educ.ksu.edu/vqm/html/doubleslit/
http://micro.magnet.fsu.edu/primer/java/imageformation/airydiskbasics/index.html
END
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