Figure 2: n liquid =1.5446.
Rotation of polarizer.
Figure 3: n liquid =1.528
Figure 4: n liquid =1.5394
Figure 5: n liquid =1.5528
Quartz crystals in a range of liquids from n= 1.528 to
Figure 1: liquid index matches ordinary index of quartz.
Central crystal has ordinary index parallel to polarizer and appears thus
with a red -orange halo.
Figure 2: same index of liquid but rotation of the stage by
90°. The central crystal has now extraordinary index (higher) parallel to
polarizer: the halo becomes bright orange.
Figure 3: the lowest liquid refractive index: all crystals
are dark blue with pale yellow halo.
Figure 4: liquid index slightly lower than ordinary quartz
index: all crystals have halo orange to yellow.
Figure 5: the highest liquid refractive index (equal to the
high index of quartz): the central crystal oriented parallel to the optic
axis has a red halo (matching for the D line of sodium), other crystals in
random orientation appear with a dark halo (brown to black) due to their low
index of refraction. With closer
examination, some other crystals are also nearly matching.