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OPERATION
Carl Zeiss
Illumination and contrast methods
Axio Imager
160
430000-7344-001
M70-2-0020 e 06/2009
4.9.5.3
Measuring path differences
For the accurate measurement of path differences, measuring compensators are required. These
compensators reset or compensate the path difference produced by the specimen to zero (1
st
order
black).
While for the methods described above, the addition position or additionally also the subtraction position
is of interest, for measurements
exclusively
the subtraction position is relevant.
Path differences in the specimen can assume very small values (1/50
λ
or 10 nm) and very great values
(more than 10
λ
or approx. 5500 nm and more) and with that determine the compensator appropriate
for the measurement.
To find the appropriate compensator follow this procedure:
•
Set the microscope as for transmitted-light polarization (refer to Section 4.9.5.1 (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
. In
this position, activate the 45
°
click stop.
•
Rotate the stage
once
(by 45
°
), so that the specimen is in diagonal position (lightened up).
The intensity of the interference or color produced by the specimen allows the following conclusion to be
drawn:
−
If more or less strong interference colors appear on the object, the path difference ranges
approximately between 1/2
λ
and about 5
λ
.
The suitable 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
.
The occurrence of the color change effect possibly requires the assessment in two specimen
positions lying 90
°
apart. For this purpose, rotate the centered stage (by 2 click stops).
The suitable compensator is:
Tilting compensator B 0-5
λ
(Accessory 000000-1115-700) or the compensation method according
to DE SENARMONT up to 1
λ
using the
Senarmont compensator 546/4 nm
(Accessory 000000-
1115-695).
The compensation method according to DE SENARMONT requires the use of the rotatable
analyzer (000000-1076-680).