Presentation on polarized light microscope

1. Submission date 27/03/2021
ADAMA SCIENCE AND TECHNOLOGY UNIVERSITY
School of Mechanical, Chemical & Materials Engineering
Department of Mechanical Design & Manufacturing Engineering
Material characterization Technique
Presentation on polarized light microscope
by: 1. Binyam Getye
2. Kebebe Urgie

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Polarized Light Microscopes – Overview
Polarized light microscopes are a type of optical microscopes that involve polarized
light for better understanding and visualization of materials that are anisotropic and
birefringent.
The polarized light microscope is primarily designed for observing and
photographing visible specimens due to their optically anisotropic character.
To accomplish this task, the microscope must be equipped with both a polarizer
positioned in the light path at a location before the sample and an analyzer placed in
the optical path between the objective rear opening, and there are observation tubes
or camera port.

3. Polarized light microscope
 Designed to observe optically
anisotropic specimen (birefringence
specimen)
 Equipped with polarizer and analyzer
 Works on the principle of interference
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4. Components of polarized light microscope & their function
Eyepiece
Observation tube
Bertrand lens
Analyzer
Retardation plate (compensator)
Graduated circular rotating stage
Light source
Polarizer
 Basic Components
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5.  EYEPIECE
 Eyepieces are fitted with a cross wire reticle to mark the center of the field of
view.
 Orientation of the eyepiece with respect to the polarizer and analyzer is
guaranteed by a point that slides into the observation tube sleeve
 BERTRAND LENS
 It is a specialized lens mounted within the observation tube.
 Projects an interference pattern formed at objective rear focal plane in
focus at the microscope image plane.
 Is designed to allow accurate adjustment of the illuminating aperture
diaphragm and to see interference figures.
Functions of polarized light microscope parts
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6. RETARDATION PLATE (COMPENSATOR)
 These are inserted between the cross polarizers.
 Enhances the optical path difference in the specimen.
GRADUATED CIRCULAR ROTATING STAGE
 It is a 360 degree rotating specimen stage.
 Facilitates the orientation studies with centration of the objective and stage
with microscope optical axis.
 It contains the Vernier scale to measure the degree of rotation of the
specimen with accuracy of 0.1 degree.
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7. FUNCTION OF MAJOR COMPONENTS
 BIREFRINGENT SPECIMEN
 Birefringence is an optical property of a
material having a refractive index that
depends on the polarization and
propagation direction of light.
 Birefringent materials have different
indices of refraction for light polarized
parallel or perpendicular to the optical
axis.
 Two beams with orthogonal polarization
are produced if illumination is at an
angle to optical axis
 Depending upon the orientation of the
specimen, colour of the image changes
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8. POLARIZER AND ANALYZER
I. POLARIZER confines white light to
vibrate in one plane when light
passes through it .
II. The birefringent specimen breaks
the polarized light into two
components viz. ordinary and extra
ordinary light.
III.These two components of light
when passes through ANALYZER,
INTERFERENCE occurs by virtue of
which image obtained is colourful .
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9.  SIMPLE LIGHT MICROSCOPE
 POLARISED LIGHT
MICROSCOPE
 It has polarizer and analyzer.
 An optically anisotropic
specimen called birefringent
specimen is used.
 Works on the principle of
interference.
 Colourful image is obtained
due to interference.
 It does not have these two
components.
 Any specimen can be
used.
 Works on the principle of
reflection and refraction.
 Color of the image
obtained is same as that of
the specimen.
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10. Plane light
Polarized light
High relief
Low relief
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11. FACTORS AFFECTING THE COLOR OF IMAGE
Orientation of the specimen.
Thickness of the specimen.
Path difference between the ordinary and extra
ordinary light rays.
Orientation of the polarizer and analyzer with
respect to each other.
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Important Applications
Polarizing microscope has a wide range of applications in the field of
visual mineralogy and geology to inspect, analyze and understand tiny
particles like minerals and crystals. Considering their advantages in
visualizing anisotropic and birefringent particles, these microscopes are
also widely used in medical and biological fields today.

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It is mostly used in the field of geology to study rocks and minerals.
Besides that, can also be used in medicine, chemistry, biology and
sometimes in metallurgy. it is the best choice to study materials like
minerals, polymers, ceramics, wood, urea, substances of natural and
synthetic fibers with those birefringent properties, cellophane, and also
botanical and insect specimens and fish scales. With polarizing
microscopy, it is possible to determine the color absorption, structure,
composition and refraction of light in isotropic (gases and liquids – one
refractive index) and anisotropic substances.

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Figure: Some biological samples observed in polarizing light microscope:
A- wheat stem cross section, B- potato starch, C- wool, D- human hair.

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Advantage of polarized light microscope
Polarized light microscopes are the default choices for study of tiny particles
in the field of visual mineralogy. Materials like crystals and fibers are
anisotropic and birefringent in nature and using other high-end techniques
like X-ray diffraction and scanning electron microscopy to analyze these
materials wouldn’t give promising results.
• Geology, Pathology and recently even Biology, Asbestos Testing and
Forensic Sciences use polarized light microscopes. In fact, in routine asbestos
pathology, these polarized microscopes are mainly preferred for their high-
precision and cost-effective qualities.

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Fibers, crystals and minerals are the most commonly examined materials in visual
mineralogy and medical specimens like bone, teeth, striated muscle, urine crystals, gout
crystals and amyloids also need polarized light microscopes to be examined. Using any
other microscopes for analyzing these specimens can produce varying results.
These microscopes are especially known for their anti-reflective and anti-scratch properties.
In earth and material science applications, analysis of birefringent and anisotropic particles
requires high integrity of light transmission and involves critical aspects such as internal
reflections that can be only addressed by polarized light microscopes.
These microscopes provides crucial information regarding refractive index, birefringence,
sign of elongation, pleochroism, and angle of extinction of the crystals under study. No
other microscope can provide information on this depth and importance in the field of
crystallography.

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Disadvantage of polarized light microscope
•The method requires a great degree of sophistication on the part of the microscope.
•Even using phase polar illumination, not all the fibers present may be seen.
The method uses only a tiny amount of materials for analysis. This may lead to sampling
bias and false result
Polarized lenses make it difficult to view LCD screens
When you are wearing glasses that have polarized lenses, then the chemical agents added
to the product to create the filtering mechanism reduce the amount of light your eyes
process from an LCD screen. Although you can still see them when you have a direct
line-of-sight, moving to different angles can make the screen disappear completely. It
may also impact the amount of color that some people can perceive when looking at
information or watching a show.

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Figure 1:- Light path way in polarized light microscope

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In summary, polarized microscopy provides a great deal of
information about the composition and three-dimensional structure
of various samples. The technique, which is virtually unlimited in
its scope, can provide information about the thermal history and the
stresses and strains a sample is subjected to during formation.
Polarized microscopy, useful in manufacturing and research, is a
relatively inexpensive and accessible research and quality control
tool that can provide information not found by any other technique.

20. THANK YOU
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