Flashcards in polarising microscopy Deck (53):
What is unique feature of polarising microscope?
1. Standard optics, light source and condenser
2. At least two polarising filters
3. optically active specimen
What can be changed to standard optics and condenser?
May be specially designed and added feature
Give some examples of added feature on standard optics.
1. Filters incorporated into condenser lens
2. a rotating stage
What is two polarising filters?
What system is polariser used in?
What system is analyser used in?
Imaging forming system
Where is polariser ?
In or near the condenser
Where is analyser
In or near the objective
How can polarising microscope used for analysis?
When additional filters are used: quarter wave plate
What are these filters always made of?
Calcite( but inferior)
How to determine whether the light is polarised or unpolarised?
The direction of oscillation of photons determine
What is unpolarised light?
Photon oscillations in any direction
What is polarised light?
Photon oscillations in just one plane
->any single plance
What is the properties of optically active substances?
1. Transparent substance
2. Convert unpolarised light into plane polarised light
What are two beams of plane polarised light emitted called?
What is direction of polarization of E & O rays?
90 degrees to each other
What are alternative terms for "optically active"?
Give examples of optically active substance ?
What should known about optically active substance?
They transmit two separate beams of plane polarised light (called E ray& O ray) with planes of polarisation at 90 degree
How is Polaroid unique in optically active substances?
Only transmits light which is polarised in one plane
Why it is possible Polaroid only transmit one plane polarised light?
O ray is absorbed
Are there always two plan of polarised light?
No, some separation may not be visible without special apparatus
(small angle of separation of E&O rays)
What is the isotrophic substance?
Minority which are not optically active
What do polarising filters made of Polaroid do?
Convert unpolarised light to plane polarised light in the direction similar to optic axis
What determine direction of polarization of unpolarised light transmitted by Polaroid?
Direction of polarization determined by the optic axis
How the transmitted light linked to optic axis?
Transmitted light parallel to the optic axis
What is depends of relationship described ?
--The directing of polarization of the indent light
---directing of the optic axis of the Polaroid
How is relation relevant to the polarising microscope?
->It uses two filters
->Polariser directs plane polarised light onto the specimen
->then passes to the analyser
What happens to incident light parallel to optic axis after transmission thru polaroid?
-no change in plane of polarization
--without change of intensity
what happens to incident light not parallel to optic axis after transmisstion thru polaroid?
-change in direction of polarization
-loss of intensity
what happens to incident light at right angles to optic axis?
no transmission of light
what is three optically actve substance in the polarsing microscope?
How is poloariser and analyser are set up?
with optic axes at 90 degree: crossed polars
what is principle of the polarising microscope?
-background light passed polariser in condenser (same direction as optic ais) but unable to pass analyser in ocular (optic axis is 90degree)
-light repolarised by sepcimen passes through analyser
how to set up the polarsing microscope?
1. add poliarser and analyser
2. set up crossed polars
3. use an opticlaly active specimen
what does "corssed polars? mean?
set up with optic axes of polariser and analyser at 90 degree
How to recognize cross polars?
recognize by dark background called extinction
How does opticlally active specimen work to pproduce dark background?
repolarize the plane polarized background light
how does double refraction happen to optically active substance other than polaroid?
-they produce two transmitted beams of plane polarised light
- light coming from a singel point object splits a and form two images
is double refraction always obvious?
no, as teh separation of the E &O ray is often very small
what is anle of separation dependent?
variable angel of separation depend on the :
-angle of incidence
-relation to the optic axis
what is birefringence?
the sepration of E & O rays
what if angle of incidence parallel to optic axis?
No E&O ray separation
what if angle of incidence at right angles to optic axis?
produce maimum birefringence
three categories of birefringence of specimens?
1. crystaline birefringnece
2. form biferingence
3. stress biferingence
what types of specimens have crystaline birefringence?
crystals except the cubic form
what is cubic form?
have symmetrical arrangement of atoms within srystal lattice
examples of crystaline birefringence specimens?
-picric acid : orthorhomic crystaline form
what types of speicmens have form birefringence?
specimens with a regular or repeating pattern of substructure
what is regular or repeatingi pattern of substructure?
examples of form birefringence specimens？
-striated muscle: parallel rod/ elongated structure
-molecoles in starch grains: radial rod/elongated structure
-myelin (whorled membrane): tagential elongated structures
what types of speicmens have stree birefringence?
specimen with a temporary alighment of their substructure due to stress