3. Single-Slit Fraunhofer Diffraction

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3. Single-Slit Fraunhofer Diffraction 4. Circle
Aperture Fraunhofer Diffraction 5. Resolving
power 6. Grating diffraction
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The Diffraction Grating(????)
Transmission grating
Reflection grating
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Grating Constant (????)
Grating constant
a width of transmission part
b width of reflection part
E.g. A grating ruled with 5000 lines/cm has a
slit spacing of
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Diffraction of Grating (????)
Grating Equation
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Diffraction of Grating Superposition of many
single-slit diffraction
Single-slit
Grating
Bright fringes Principal Maxima
(?????)
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Dark fringes
N is the number of the slits in the grating.
There are N - 1 dark fringes between two neighbor
principal maximum and there is a secondary
bright fringe between two neighbor dark fringes.
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• There are N - 1 dark fringes between two adjacent
  bright fringes
• There is one bright fringe between two dark
  fringes, whose intensity
• is weaker than the above bright fringe.
  This kind of much weaker
• bright fringes are called secondary maxima.
• (3)There are N - 2 weaker bright fringes between
  two adjacent bright fringes.

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Discussions

• The larger the number of the slits N, brighter
  the bright fringes.
• The width of the bright fringes decreases while N
  increases.
• The location of the bright fringes depends on the
  diffraction angle
• for a given certain grating.
• For a fixed k, the angular position of the bright
  fringes varies with
• the wavelength of the incident light.

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Order Missing (??)
If the position of principal maxima is also
the position of dark fringes of the single-slit,
then the principal maxima do actually not exist,
as is called order missing.
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Polarization of Light (????)
Transverse Wave Polarization
Polarization is a characteristic of all
transverse wave. The direction of oscillation and
the direction in which the wave propagates define
a plane, which is called plane of
polarization If the oscillating plane keeps
unchanged, the wave is said to be linearly
polarized. Generally, natural light is not
linearly polarized. And light can be classified
according to its polarization as
linearly polarized, un-polarized,
partially-polarized, etc.
linearly polarized light ????,?????,???? unpolari
zed ????, partially-polarized ?????
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Linearly Polarized Light (?????)
Linearly polarized light the direction
oscillation vector is fixed.
plane of polarization
linearly polarized light, completely polarized
light, planar polarized light
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Unpolarized Light (????)
The light from the ordinary sources is not
polarized, and such light is called unpolarized
light or natural light.
natural light ???
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Polaroid,Polarizer and Analyzer (???,???????)
The polaroid absorbs partly or completely
vibration of incident light in one direction, and
allow another direction pass. So we can get
polarized light by polaroid.
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Maluss Law (?????)
The intensity of the light transmitted
through the analyzer is given by Malus law
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E.g. 10-4One unpolarized light with intensity
I0, falls on two polarizing sheets. The angle
between two polarizing sheets is 450. Find the
transmitted intensity I.
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Polarization by Reflection
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The British scientist D. Brewster discovered
that when the angle of incidence is equal to the
polarizing angle, the reflected ray and the
refracted ray are perpendicular to each other,
from the law of refraction
Brewsters Law