OPERATION
ZEISS
Illumination and contrast methods in transmitted light
Axiolab 5
92
430037-7444-001
05/2019
•
Remove the analyzer from the beam path and align the reticle along the split cracks of the sample.
•
Subsequently reinsert the analyzer and remove the Pol adjustment tool sample. The pass directions of
the polarizer and analyzer will now be parallel to the reticle (Polarizer EW, Analyzer NS).
NOTE
It is not necessary to adjust the reticle when working with the intermediate plate and the
binocular photo tube Pol (425520-9100-000).
•
Rotate the Pol rotary stage with the sample, e.g. a synthetic fiber, until the sample appears as dark as
possible. In this position, the fiber extends parallel to one of the two directions of the crossline reticle.
NOTE
Do not change the inter-pupillary distance on the binocular tube, as the angle of the crossline
reticle to the fiber will be changed.
•
Now rotate the stage by 45° so that the longitudinal axis of the fiber is oriented NE-SW (Fig. 4-9). The
sample will display the greatest brightness here (diagonal position). In this position the sample may
have any color.
•
Insert the lambda compensator (possible only if used with screw-in analyzer in tube or intermediate
plate).
Like the sample, the lambda compensator is a birefringent object, albeit with a defined path difference of
550 nm and the principal polarization direction n
γ
definitely oriented in a NE-SW direction.
When the lambda compensator is moved into the beam path, the sample changes its color. The type of
color change depends on the orientation of the sample (NE-SW or NW-SE).
The changes in color are attributable to optical interference. The interference colors (path differences) in
both diagonal positions (NE-SW and NW-SE) of the sample must be compared in this connection.
The path difference results from the superposition (interference) of the polarization direction of the
sample over the polarization direction of the lambda compensator.
The largest path difference occurs when the polarization direction of the sample with the absolutely or
relatively highest refractive index (n
γ
or n
γ
’
) is parallel to the principal polarization direction of the lambda
compensator . The sample will then appear greenish-blue, for example (Fig. 4-8/
2
).
The smallest path difference occurs when the polarization direction of the sample with the absolutely or
relatively lowest refractive index (n
α
or n
α
’
) is perpendicular to the polarization direction of the lambda
compensator . The sample will then appear yellow, for example (Fig. 4-8/
3
).
