Biomedical Engineering Reference
In-Depth Information
Objective
Analyzer (
−
45º)
WP1(0º)
Condenser
S
pecim
en
WP2 (
Γ,
0º)
Light
source
ε
2
ε
1
Ocular
f
c
f
ob
Polarizer (45º)
Δ
d
Γ+ Δ
Rotatable stage (
σ
)
Nomarski p
rism
f
ob
Figure 2.1
DIC microscope setup. Polarizer at 45
azimuth; WP1: first Wollaston prism at 0
azimuth;
ε
1
:
splitting angle; f
c
: condenser lens focal distance; d: shear amount;
Δ
: optical path difference
introduced by specimen under investigation;
: azimuth of rotatable stage; f
ob
: objective lens focal
distance; WP2: second Wollaston prism at 0
azimuth (the second prism introduces bias
σ
Γ
);
ε
2
:
45
azimuth; Wollaston prism can be replaced by Nomarski prism.
splitting angle; analyzer at
2
“Smith double-refracting interference shearing microscope system.” However, he also gave
credit
[2]
to Lebedeff
[3]
, who constructed the first double-refracting interference shearing
microscope.
In addition, Smith
[1,2]
proposed another DIC microscope with the vertical shear direction,
which he called the “Smith double-focus system.” The system employed lenses made from
birefringent crystals associated with the condenser and objective of the microscope, to
impart a double-focus effect on two beams generated by the birefringence. The two lenses
must be in conjugate positions, preferably at the front focal plane of the condenser and the
back focal plane of the objective, respectively. However, Smith's double-focus DIC system
did not find wide use.
The both Smith's approaches suffered from the same problem. In conventional medium to
high numerical aperture (NA) objective lenses, the back focal plane is located inside the
lens system and therefore not available for insertion of a Wollaston prism or a birefringent
lens. In particular, in the shearing DIC microscope system, if the Wollaston prism is placed
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