OPERATION
Carl Zeiss
Illumination and contrast methods
Axio Imager
178
430000-7344-001
M70-2-0020 e 06/2009
4.9.12
Setting reflected-light polarization – Detection of bireflection and reflection
pleochroism
(1) Use
Incident-light polarization presents another contrasting option for polished sections of ore minerals, coals,
ceramic products, certain metals and metal alloys, as these specimens often show a varied reflection
behavior in linearly polarized light depending on the orientation of the crystals and specimen features.
The illumination light is linearly polarized by the polarizer and directed through the objective onto the
specimen surface, where it is reflected. Here, the light rays experience structure-dependent path
differences or polarization-optical rotations, which on passing the analyzer appear as different gray-scale
values. A compensator with lambda plate enables the conversion from gray to color contrast.
Important!
However, you must not use a 6x20 compensator for this purpose!
With objectives of very low magnification, a rotatable
λ
/4 plate arranged in front of the objective
(Antiflex cap) permits the reflections to be eliminated even with "dark" specimen surfaces, which
otherwise would be unavoidable.
(2) Microscope
configuration
−
Stand with installed and aligned HAL 100 halogen illuminator.
−
Epiplan-Neofluar Pol, EC Epiplan-Neofluar Pol, Epiplan Pol objectives.
−
Reflector module DIC P&C or DIC Rot I P&C in reflector turret;
or reflector module Pol P&C plus analyzer slider;
or analyzer slider plus polarizer slider.
(3) Setting
reflected-light
polarization
•
Set the microscope for reflected-light brightfield as described in Section 4.9.7.
•
If you use the objective position with DIC slider slot, remove the possibly inserted DIC slider.
•
On reflector turret (4-135/
3
), swing the reflector module DIC P&C (4-135/
4
) into the light path. You
may also swing in reflector module Pol P&C and insert the analyzer slider in the corresponding slot.
When using the combination of analyzer slider (4-135/
1
) and polarizer slider (4-135/
2
), you may also
push these into the corresponding slots. If you use the fixed versions of these sliders, the polarizer is
oriented in EAST-WEST direction and the analyzer in NORTH-SOUTH direction.
•
Put specimen onto stage, set the desired magnification, focus and observe the specimen in the now
adjusted polarization contrast while rotating the stage.
If the specimen features show variations in brightness and color, when the stage is rotated, the specimen
is said to have bireflection.
If the specimen has a weak bireflection only, it is advisable to use the analyzer with rotatable lambda
plate.
Pleochroism can be made out by color variations occurring in the specimen while rotating the stage (with
the reflected-light polarizer moved into the light path and the analyzer moved out).