Polarized Microscopy: Principles of Light Polarization and Applications

Polarized Light Production

Polarized Microscopy
Ahmed A. Mirza, PhD200 umHow is polarized light produced?

• A polarization filter
  (polarizer) is set in
  front of the light
  source to select one
  plane of the traveling
  electromagnetic field
  of light

Polarization of Light Waves

Polarization of Light
Unpolarized light
Electric Field
Polarized light
(linear)
Direction
of propagationWITHOUT POLARIZED
WITH POLARIZED
WITHOUT POLARIZED
WITH POLARIZEDPolarizer 1
(Vertical)
Polarizer 2
(Horizontal)
Incident Beam
(Unpolarized)
Vertically
Polarized
Light Wave
Figure 1

Polarized Light Microscopy Setup

Polarizer 2
("Analyzer“)
Objective
Sample
Polarizer 1
("Polarizer“)
Light source

Parallel Polarizers

Polarized light microscopy
Parallel polarizers
Main contrast: light absorption

Crossed Polarizers

Polarizer 2
("Analyzer“)
Objective
Sample
Polarizer 1
("Polarizer“)
Light source
Polarized light microscopy
Crossed polarizers
Main contrasts:
birefringence and light scattering. https://www.wikiwand.com/en/Polarized light microscopy#Media/Fi
le: Polarizing microscope.ogv

Birefringence and Light Scattering

Why does it happen?

• Some material in the sample will have light scattering
  qualities and birefringence (or double refraction)
• Also known as anisotropic
• Usually to different molecular structure holding the
  crystal together
• Example Calcium Carbonate (CaCO3)
• Birefringence is the ability to refract certain polarized
  light
• two polarized light components
• extraordinary (e-ray) and ordinary ray (o-ray).
  a
  ba
  Ca+3
  C+4
  0-2

https://www.youtube.com
watch?v=WdrYRJfiUvo
Ealite

Why Use Polarized Light Microscopy?

Why use polarized light microscopy?
A
B
C
D
62.5 um
1

Birefringence of Fibers Equation

• The equation is simple
  Birefringence of fibers = n | | - nl
• isotropic refractive index of fibers
  = 1/3 (n | | + 2nl)
  Where n | | is refractive index of parallel light and nl is refractive index
  of perpendicular light