OPERATION
ZEISS
Illumination and contrast methods in transmitted light
Axiolab 5
94
430037-7444-001
05/2019
4.2.4.3
Measuring path differences
The measurement compensators are required for the exact measurement of path differences. These
return, i.e. compensate, the path difference created by the specimen to zero (black of the first order).
Whereas in the above-described methods the addition or subtraction position was of interest,
only
the
subtraction position is of interest in the measurement.
Path differences in the specimen can assume very small values (1/50
λ
or 10 nm) and very large values
(greater than 10
λ
or approx. 5500 nm and higher) and thus determine the compensator appropriate for
the measurement.
The suitable compensator is determined as follows:
•
Configure the microscope as for transmitted light brightfield microscopy (see section 4.2.1), taking
care to ensure the correct inter-pupillary distance in the binocular tube (see section 4.1.1).
•
Accurately position the specimen to be examined on the center of the reticle.
•
Limit the aperture to a value of about 0.2.
•
Turn the Pol rotary stage until the specimen is almost extinguished, i.e.
completely dark
, and set the
45° locking position.
•
Rotate the stage
once
(by 45°) so that the specimen is in a diagonal position (sample becomes bright).
The interference intensity or color leads to the following conclusion:
−
If more or less strong interference colors appear on the specimen, the path difference ranges
approximately between 1/2
λ
and 5
λ
.
The suitable compensator is:
B 0-5
λ
.
tilting compensator
−
If the specimen-side color changes from light gray/white to a strong interference color, when a
lambda compensator (473704-0000-000) is inserted in the compensator slot, the path difference is
(1/4 - 1/2)
λ
.
NOTE
A prerequisite for the occurrence of the color change effect may be the evaluation in two
specimen positions rotated at an angle of 90° from one another, plus a centered stage.
The suitable compensator is:
B 0-5
λ
tilting compensator
or the DE SENARMONT compensation method up to 1
λ
using the
546/4 nm Senarmont compensator
.
NOTE
The DE SENARMONT compensation method requires the use of the rotatable analyzer.
−
After insertion of the lambda compensator and rotation of the specimen by 90°, the interference color
remains white; in this case, however, it is a "higher-order white" and thus the path difference is > 5
λ
.
