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OPERATION
ZEISS
Illumination and contrast methods in transmitted light …
Axioscope 5/7/Vario
98
430035-7344-001
03/2018
4.2.6
Setting transmitted light polarization
4.2.6.1
Detecting birefringence
(1) Application
The transmitted light polarization method is used for samples which change the polarization of the light.
Such samples are called birefringent. Examples include crystals, minerals or polymers. If such birefringent
substances are observed between crossed polarizers, the birefringent portion of the sample appears
bright while its surroundings remain dark.
A birefringent substance can be recognized by turning the sample by 360° between crossed polarizers.
The sample should show four bright and four dark appearances during the turning procedure. During the
turning procedure, interference colors appear that range from gray (mostly for biological samples)
through white, yellow and red until blue, depending on birefringence, thickness as well as sample
orientation. The interference colors may be of the first or a higher order.
(2) Instrumentation
−
Strain-free objectives
−
Pol rotary stage
−
D Polarizer (rotatable or fixed), if no polarizer is already integrated in the condenser.
−
ACR P&C analyzer module for transmitted light in the reflector turret/slider or D analyzer slider
fixed or with lambda-plate.
−
Depolarizer for avoiding unwanted polarizing effects
A depolarizer (quartz depolarizer) should be incorporated in all microscopes used to examine
mineralogical/geological specimens.
A depolarizer extinguishes undesirable polarization effects possibly (e.g. false or pseudo-pleochroism)
occurring behind the analyzer (e.g. on prism surfaces in the tube), or shifts them to higher orders.
•
Insert the quartz depolarizer with tube lens 115 (428106-9010-000) into the tube
or
•
insert the quartz depolarizer with tube lens 130 in combination with intermediate plate (428106-
9000-000) into the tube.
(3) Setting the microscope
•
Adjust the microscope as described in section
645H
4.2.1 (3) for transmitted light brightfield microscopy
using the KÖHLER method.
•
Center the rotary stage Pol (
1
) (see section 3.1.10.5) and objectives (see section 3.1.10.6).
•
Swing the polarizer (
3
) into the beam path and position it to 0° if you are using a rotatable
polarizer.
•
Put the analyzer (
2
) into the slit for the compensator or swing analyzer module on the
reflector turret/slider. Because of the crossed polarizers the field of view now appears dark.