Analysis of plan, circularly and elliptically polarised Optical activity Specific rotation Fresnel theory

1. Polarization

2. Presentation Outline
• Analysis of plan, circularly and elliptically
polarised
• Optical activity
• Specific rotation
• Fresnel theroy
5/9/2020
Dr Arun Upmanyu, Associate Professor
Department of Applied Sciences
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3. Plane Polarised Light
5/9/2020
Dr Arun Upmanyu, Associate Professor
Department of Applied Sciences
35/9/2020
Dr Arun Upmanyu, Associate Professor
Department of Applied Sciences
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Intensity is maximum
when direction of
vibration of light is
perpendicular to principal
section
Rotation of Nicol Prism
Nicol PrismPlane
Polarised light
Analyser
Intensity is zero when
direction of vibration of
light is parallel to
principal section
Principal Section is a plane passing through
the optical axis of a crystal
Principal section

4. Principal section
5/9/2020
Dr Arun Upmanyu, Associate Professor
Department of Applied Sciences
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5. Dr Arun Upmanyu, Associate Professor
Department of Applied Sciences
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Intensity is light is
unaltered
Nicol PrismCircularly
Polarised light
Circulary Polarised Light
Analyser

6. 5/9/2020
Dr Arun Upmanyu, Associate Professor
Department of Applied Sciences
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Intensity is light is
varies in
magnitude but
never zero
Nicol Prism
Elliptically
Polarised light
Analyser
Elliptically Polarised Light

7. 5/9/2020
Dr Arun Upmanyu, Associate Professor
Department of Applied Sciences
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The property of rotating the plane of vibration of polarised light
by certain crystals and other substances is called optical activity.
The substance which rotate the plane of polarisation are said to
be optically active
Optical activity
Polariser
Cross positioned
No light
Analyser
Unpolarised light Polarised light

8. Specific rotation for given wavelength of light at a given
temperature is defined as the rotation(θ) produced by one
decimetre of the solution containing one gram of optically
active material per cubic centimetre of solution.
It depends upon
thickness of the substance
Concentration of the solution or density of the material
the temperature
Mathematically
5/9/2020
Dr Arun Upmanyu, Associate Professor
Department of Applied Sciences
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Specific Rotation
  gm/c.cinionconcentratdecimeterinlenth
degreesinRotation




Cl
St 


9. It is based upon the principle that any single harmonic motion along a straight line
is the resultant of two circular motions of the same frequency.
The plane polarised light entering a crystal along the optic axis CA is split up into
two circularly polarised vibrations rotating in opposite directions with the same
frequency . The tracing point P rotates in the anti clockwise direction and its
rotation is called left-handed. The tracing point rotates in the clockwise direction
and its rotation is called right handed.
5/9/2020
Dr Arun Upmanyu, Associate Professor
Department of Applied Sciences
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Fresnel’s Theory

10. In a crystal like calcite, which is not optically active the two circular motions
have the same velocity. Hence if the tracing points P and Q start
simultaneously from O and travel in their respective, their resultant is always
along CA. thus on coming out of such a crystal the two circular motions will
again combine to produce a linear simple harmonic vibration along CA. This
shows that there will be no rotation in the plane of polarisation.
5/9/2020
Dr Arun Upmanyu, Associate Professor
Department of Applied Sciences
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Fresnel’s Theory

11. •In a crystal like quartz which is optically active, the two circular vibrations move forward with
slightly different velocities in their respective directions. In right handed quartz, the right
handed or clockwise motion will travel faster than the left handed motion or anticlockwise
motion and vice versa.
• In the right handed crystal if the points P and Q start simultaneously from O, then during the
time the tracing point P completes one rotation the tracing point Q will travel a further angle
φ=QCP. The resultant of CP and CQ will act along CA’. Hence the circular motion will combine
to produce s simple harmonic motion along CA’ instead of CA.the plane of polarisation turn
through the an angle
ACA’ = φ/2
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Dr Arun Upmanyu, Associate Professor
Department of Applied Sciences
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φ
O
C
P
A
Q
A
Fresnel’s Theory

12. where φ=(2/)* (μL-μR)d
Or φ/2=(/ )*(μL-μR)d
μL, μR = refractive indices of left handed and
right handed circular components.
d = thickness of the crystal.
 = wavelength of the light.
5/9/2020
Dr Arun Upmanyu, Associate Professor
Department of Applied Sciences
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Fresnel’s Theory