Polarized Microscopy . For anisotropic studies

Polarized microscopy utilizes polarized light to enhance contrast, resolve detail, and analyze the optical properties of samples.


_Principles:_

1. Polarized light: Vibrations confined to specific planes
2. Birefringence: Double refraction in anisotropic materials
3. Dichroism: Selective absorption of polarized light


_Components:_

1. Polarizer: Produces polarized light
2. Analyzer: Filters polarized light
3. Compensator: Enhances contrast
4. Objective lens: Transmits polarized light


_Techniques:_

1. Cross-polarized light microscopy
2. Plane-polarized light microscopy
3. Circularly polarized light microscopy
4. Differential interference contrast (DIC) microscopy


_Applications:_

1. Geology: Mineral identification
2. Materials science: Fiber and texture analysis
3. Biomedical research: Tissue and cellular structure analysis
4. Quality control: Material inspection


_Benefits:_

1. Enhanced contrast and resolution
2. Reduced glare and artifacts
3. Non-destructive testing

1. POLARIZED
MICROSCOPY
FUNDAMENTALS OF MICROBIOLOGY

2. The polarizing microscope is like a light microscope except that the
condenser and ocular are equipped with polarising optics,each of
which transmits only plane-polarized light.
The polarizing microscope differs from a compound microscope
(used in life science laboratory) in its basic principle of working.
However, both of them have similar basic function that is to yield
an enlarged image of an object placed on the stage.
You can convert a compound microscope to a polarising or
petrological microscope by introducing two special devices
analyser and polariser.
INTRODUCTION

3. P M
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4. COMPONENTS
Light source
Polarizer
Condensing lens
Substage diaphragm(s)
Graduated Rotating Stage
Objective lens
Microscope tube / barrel
Accessory slot
Analyser
Ocular/Eye piece
Bertrand lens

5. The light source can be natural like sunlight; a concave
mirror is present near the base of the polarising microscope
which reflects the ordinary light upwards .
In case of an artificial light, it is an electric device.
The lamp is present which is built into the microscope base
The bulb with tungsten filament or halogen bulb is used. It
gives yellowish tint to the field view.
Therefore, a blue filter is inserted above the light source to
change the colour of light to that of daylight.
LIGHT SOURCE

7. The light consisting of electromagnetic vibrations moves
outward in every direction from a point source of white
light, such as a microscope bulb or natural sunlight.
The initially unpolarised ordinary light becomes polarised
after passing through the polariser and vibrates in a single
plane.
The polariser is usually inserted in the path of light and is
present below the graduated rotating stage.
The light is polarised on passing through the polariser.
POLARISER

8. It is also called as condenser or convergent lens.
It is a small hemispherical lens attached to a swivel bar.
Condenser can be inserted into the optical train when
required.
It serves to direct a cone of light on the thin section and
give optimum resolution for the objectives used.
The entire lens system below the microscope stage,
including polariser, aperture diaphragm and condenser, can
often be racked upwards or downward in order to optimise
the quality of illumination.
CONDENSING LENS

9. One or two diaphragms may be located below the stage.
They are used to reduce the area of light entering the thin
section.
They should be in focus at the same position as the thin
section.
The aperture diaphragm is closed to increase resolution
SUBSTAGE DIAPHRAGM(S)

10. The graduated rotatable stage lies in between the two Nicols
(polariser and analyser).
Thin section of the mineral or rock is placed over this stage. The
microscopic stage or disc is flat.
It is capable of rotation and can be locked at any point.
The vernier scale is attached to the stage.
The rotation can be accurately measured with the help of vernier
scale.
It is employed for precise angular measurement.
The mineral/rock thin section is attached to the centre of the
stage by metal spring clips.
GRADUATED ROTATING STAGE

11. It is placed at lower end of microscope tube / barrel.
The function of objective lens is to produce an image which is sharp and
clear.
The objectives of three power for image magnification are used for
mineralogical work: low, medium and high.
These objectives are mounted on nose piece and can be successively
rotated into position.
The important properties of the objectives are magnification, numerical
aperture and the degree of aberration correction.
The quality of the intermediate image is determined by numerical aperture
and the degree of aberration correction.
The accessory plates can be inserted in the slot in the microscopic barrel
just above the objective lens.
OBJECTIVE LENS

12. This sits above the microscopic stage.
The microscope is focused either by moving the microscope
stage up or down (newer models) or by moving the upper
microscope tube up or down (older models) using focusing
screws.
Both coarse and fine adjusting knobs are present.
MICROSCOPIC TUBE/BARREL

13. There is accessory slot below the analyser into which accessory
plates, e.g. quartz wedge, or gypsum plate, can be inserted.
The slot is oriented so that accessory plates are inserted at 45o
to the cross wires.
ACCESSORY SLOT

14. It is the second polariser called analyser mounted within the microscope
tube.
It can be pushed in and out so that it can be in the light path (inserted
position) or out of the light path (analyser out position).
The analyser is similar to the polariser; it is also made of polarising film but
oriented in a North-South direction, i.e. at right angles to the polariser.
When the analyser is inserted into the optical train, it receives light
vibrating in an East-West direction from the polariser and cannot transmit
it; thus, the field of view is dark and the microscope is said to have crossed
polars (CP or XP).
With the analyser out, the polariser only is in position; plane polarised light
is being used and the field of view appears bright.
ANALYSER

15. It is placed at upper end of microscope tube.
The eye piece merely enlarges the image including any imperfection
resulting from poor quality objective.
Ocular (or eyepiece) contains microscope cross wires which can be
independently focused by rotating its uppermost lens.
Eyepieces of different magnification are available.
Monocular heads are standard on student microscopes whereas Binocular
heads are used in advanced microscopes.
OCULAR/EYE PIECE

16. It is used for studying minerals in convergent light.
It is inserted into the upper microscope tube.
This lens is used to produce and examine interference figures which
fills the field of view, provided that the convergent lens (condenser) is
also inserted into the optical path train.
If the microscope does not possess a Bertrand Lens the entire eye piece
should be removed to examine the interference figures.
BERTRAND LENS

17. Quartz wedge is used for the determination of interference colour,
optical sign and the nature of vibration-direction of the mineral.
Mica plate is also known as quarter-wave plate.
It which gives a pale neutral gray interference colour, when it is put
into the slot of the tube.
It is used for determining the optical sign of a mineral.
Gypsum plate also known as sensitive-tint plate because it produces
sensitive violet red interference colour of first order.
It is used for determining the optical sign of a mineral.
Bereck compensator is an optical device made of calcite mineral.
OPTICAL ACCESSORIES

18. A polariser allows the light to vibrate in one single
direction .
When the polarised light passes through the object
(anisotropic material),light vibrates in different directions.
Polarised light ,which has undergone some modifications
after passing through anisotropic material ,is allowed to
pass through the analyser ,which depolarizes it by
changing the angle of refraction .Interfering waves are
cancelled or reinforced.
WORKING PRINCIPLE

19. When interfering waves get cancelled the object is dark
,and when interfering waves get reinforced, the object
appears bright.
The polariser and analyser remain adjusted in such a
fashion that when the analyser is rotated at 360° the
visual field alternates between bright and dark and every
180° turn.
The two positions of maximum light transmission are
obtained when the analyser is set parallel to the polariser.
WORKING PRINCIPLE

20. The birefringence of some biological materials such as
muscle fibres, hair and plant fibres is large enough to permit
them to be conveniently studied by the orthoscopic technique
and the retardation may be determined by quartz or gypsum
sensitive tin plates
1.
Very useful to observe the contents of anisotropic materials
in fresh preparations.
2.
Polarized light technique may be used in biological research
not only to identify particular features, but also to conduct
analysis as in determining the lipid content of lipoprotein.
3.
APPLICATIONS

21. In certain cells accumulation of salts in the form of crystals is seen
To observe the nature of such crystals this microscope is used.
Polarization microscope is used to observe the sections of insect
cuticle and certain egg shells of insects with heavy mineral
deposition.
The greatest value of polarized light microscopy remains in the
field of examination of more or less transparent crystalline
materials by transmitted light. It is thus applicable for the
identification of rocks ,refractories and ceramics.
Metals and minerals may also be examined by reflected polarized
light.
APPLICATIONS