ZEISS
OPERATION
Axio Imager 2
Illumination and contrast methods
176
430000-7544-001
01/2016
4.12.5.3
Measuring path differences
Measuring compensators are required for the accurate measurement of path differences. These
compensators reset or compensate the path difference produced by the specimen to zero (1st order
black).
In the above methods, the addition and subtraction positions are of interest, whereas
only
the
subtraction position is relevant for the measurement.
Path differences in the specimen can have very small (1/50
λ
or 10 nm) and very great values (more than
10
λ
or approx. 5500 nm and more) and thereby determine which compensator is appropriate for the
measurement.
To find the appropriate compensator proceed as follows:
•
Set up the microscope as for transmitted-light polarization (refer to Section 4.12.5.1 (3)).
•
Position the specimen feature to be examined directly under the center of the reticle.
•
Restrict the size of the aperture to a value of about 0.2.
•
Rotate the rotary stage Pol until the specimen is in extinction position, i.e. it appears
entirely dark
.
Once in this position, activate the 45
°
click stop.
•
Rotate the stage
once
(by 45
°
), so that the specimen is diagonal (brighter).
The intensity of the interference or color produced by the specimen allows the following conclusion to be
drawn:
−
If interference colors of varying intensity appear on the object, the path difference ranges between
approximately 1/2
λ
and 5
λ
.
The appropriate compensator is:
Tilting compensator B 0-5
λ
(Accessory 000000-1115-700).
−
If the object-side color changes from light gray/white to a strong interference color when a
compensator
λ
(473704-0000-000) is inserted in the compensator slot, the path difference is
(1/4 ... 1/2)
λ
.
A precondition for the color change effect is evaluation in two specimen positions which are
90
°
apart. Rotate the centered stage (by 2 click stops) to do this.
The appropriate compensator is:
Tilting compensator B 0-5
λ
(Accessory 000000-1115-700).