OPERATION
Axiolab 5
Illumination and contrast methods in transmitted light
ZEISS
05/2019
430037-7444-001
105
(4) Conclusions
The gray-white color appearing first in the bright
position in the above example (Fig. 4-14/
1
)
corresponds to a path difference of 150 nm
according to the Michel-Lévy color chart
(Fig. 4-15).
When the lambda compensator is brought into the
beam path, the non-birefringent "surroundings"
of the synthetic fiber appear dark red, which
corresponds to the path difference of the
compensator of 550 nm (1st order interference
color for the path difference of 550 nm
corresponds to 1
λ
).
If the polarization direction (n
γ
or n
γ
'
) of the
birefringent sample to be examined is parallel to
the principal polarization direction (n
γ
) of the
lambda compensator, i.e. in the NE-SW direction,
the path difference of the sample (e.g. gray-white:
150 nm) and the path difference of the lambda
compensator (red: 550 nm) add up. This results in
a color change of the sample from grayish white to
greenish-blue (resulting path difference = 700 nm).
If the polarization direction of the birefringence
sample to be examined is perpendicular to the principal polarization direction of the lambda
compensator, i.e. in the NW-SE direction, the path difference of the sample (e.g. gray-white: 150 nm) is
subtracted from the path difference of the compensator (red: 550 nm). In this case, the interference color
of the sample visibly changes from gray-white to orange (resulting path difference = 400 nm).
NOTE
The Michel-Lévy color charts are available in the literature catalog no. 42-312.
4.2.5.4
Measuring path differences with the Axiolab for conoscopy
The measurement compensators are required for exact measurement. 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
(more than 10
λ
or approx. 5500 nm and more) and thus determine the compensator appropriate for the
measurement.
Fig. 4-15
Schematic diagram of the color
charts according to Michel-Lévy
