Optical: systems and elements – Compound lens system – Microscope
Reexamination Certificate
1997-09-04
2003-04-15
Nguyen, Thong (Department: 2872)
Optical: systems and elements
Compound lens system
Microscope
C359S368000, C359S371000, C359S385000
Reexamination Certificate
active
06549334
ABSTRACT:
This application claims the benefit of Japanese Patent Application No. 08-25504 filed Sep. 4, 1996.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention concerns a transmission illumination type differential interference microscope.
2. Discussion of the Related Art
One example of the construction of a conventional transmission illumination type differential interference microscope is shown in FIG.
6
.
Illuminating light from a light source
10
is focused by a collector lens
11
, and then illuminates a sample
15
on a slide glass
14
via a condenser lens
13
. Light from the illuminated sample
15
is focused by an objective
16
, so that an enlarged image
18
is formed. The observer observes this enlarged image
18
with eye
20
via an ocular lens
19
. A polarizer
12
and a first Wollaston prism
5
are installed, in that order, in the light path between the collector lens
11
and the condenser lens
13
; furthermore, a second Wollaston prism
6
and an analyzer
17
are installed, in that order, in the light path between the objective
16
and the enlarged image
18
. The first Wollaston prism
5
is positioned at a front-side focal plane of the condenser lens
13
, i.e., at the light-source side focal plane of the condenser lens
13
, while the second Wollaston prism is positioned at the rear-side focal plane of the objective
16
, i.e., at the image-side focal plane of the objective
16
.
The principle of differential interference microscope, in the above-mentioned construction, will be outlined with reference to FIG.
6
. Illuminating light from the light source
10
, which has been focused via the collector lens
11
, is converted into linearly polarized light whose plane of vibration is inclined 45° with respect to the plane of the page by the polarizer
12
. As a result of the birefringent action of the first Wollaston prism
5
, the light from the polarizer
12
is separated into linearly polarized light L
1
, which vibrates in the direction perpendicular to the plane of the page, and linearly polarized light L
2
, which vibrates in a direction parallel to the plane of the page, i.e., into two light beams which are perpendicular to the optical-axis and perpendicular to each other. Both light beams L
1
and L
2
proceed with a small angle of separation after passing through the first Wollaston prism
5
, and reach the sample
15
as substantially parallel light beams as a result of the focusing action of the condenser lens
13
.
After both light beams L
1
and L
2
pass through separate positions on the sample
15
, the light beams are focused on the second Wollaston prism
6
by the focusing action of the objective
16
, and these light beams are again induced to proceed along the same light path by the birefringent action of the second Wollaston prism
6
. Of the two substantially perpendicular linearly polarized light components of the light beams L
1
and L
2
, only the vibrational component, in the direction of the transmission axis of the analyzer
17
, is extracted by the analyzer
17
and induced to interfere, and the interference fringes, corresponding to the phase difference applied to the two light beams L
1
and L
2
inside the sample, are observed.
The constructions of the first and second Wollaston prisms
5
and
6
used as birefringent members, in the above-mentioned conventional example will now be described with reference to FIG.
7
. In a Wollaston prism, such as the prism
5
, a pair of wedge-shaped prisms
5
a
and
5
b
consisting of an optical material, which possesses birefringence, e.g., a crystal such as quartz crystal, calcite, or sapphire, etc., are connected together so that the optic-axis
5
bx
of wedge-shaped prism
5
b
is parallel to the joining surface
5
s
and perpendicular to the optical-axis Z, and so that the optic-axis
5
ax
of wedge-shaped prism
5
a
is perpendicular to both the optic-axis
5
bx
of the first prism
5
b
and the optical-axis Z.
In
FIG. 7
, the optic-axis
5
ax
of the wedge-shaped prism
5
a
, positioned on the side from which the light beams are incident on the Wollaston prism, is oriented parallel to the plane of the page (as indicated by the arrows in the figure), while the optic-axis
5
bx
of the wedge-shaped prism
5
b
, which is also denoted as emission-side prism, is perpendicularly oriented to the plane of the page (as indicated by the + sign in FIG.
7
), and both optic-axes
5
ax
and
5
bx
are oriented so that the directions of these optic-axes are perpendicular to the optical-axis Z. However, this combination of optic-axis orientations could also be arranged so that the orientations on an incident side, wedge-shaped prism
5
a
, and the emission side are reversed, i.e., so that optic-axis
5
ax
of the wedge-shaped prism
5
a
, which is also denoted as the incident-side prism, is perpendicular to the plane of the page, and so that the optic-axis
5
bx
of the emission-side prism
5
b
is parallel to the plane of the page.
The above is an example of the construction of a birefringent optical member in a case where the respective focal planes of the condenser lens
13
and objective
16
lie outside the respective lenses
13
and
16
. However, in cases where lenses
13
and
16
are each constructed of a plurality of lenses, the focal planes are capable of being positioned inside the respective lenses. In this type of configuration, the Wollaston prisms
5
and
6
cannot be positioned at the focal planes of lens
13
and
16
, because the respective focal planes lie within the lenses, therefore, a Nomarski prism
7
, which is modified Wollaston prism such as that depicted in
FIG. 8
, may be utilized.
The Nomarski prism
7
is a prism in which the optic-axis
7
bx
of prism
7
b
is oriented parallel to the joining surface
7
s
and perpendicular to the optical-axis Z, while the optic-axis
7
ax
of the prism
7
a
is oriented perpendicular to the optic-axis
7
bx
of the prism
7
b
and inclined by an angle &thgr; from a plane that is perpendicular to the optical-axis Z. By using such a construction, it is possible to position the separation point SP of the two light beams (which was located inside the prism in the case of the Wollaston prism shown in
FIG. 7
) outside the prism. By positioning the separation point SP of the two beams located outside the prism at the focal planes of the respective lenses
13
and
16
, it is possible to obtain an effect similar to that obtained when Wollaston prisms are positioned at these focal planes.
The Wollaston prisms
5
and
6
or the Nomarski prism
7
used as birefringent optical members, in the above-described conventional examples, are prisms in which two wedge-shaped prisms,
5
a
and
5
b
or
7
a
and
7
b
consisting of an optical material such as quartz crystal, calcite, or sapphire, etc., which possesses birefringence, are joined together so that the orientations of the respective optic axes
5
ax
and
5
bx
or
7
ax
and
7
bx
differ, as shown in
FIG. 7
or FIG.
8
. However, the above-mentioned birefringent materials are generally expensive; accordingly, it is difficult to lower the cost of differential interference microscopes which require such members.
Furthermore, in the birefringent materials, which make up these birefringent optical members, the refractive index to extraordinary ray (linearly polarized light which vibrates parallel to the plane determined by the optic-axis of the crystal and the normal axis of the wavefront) varies with to the above-mentioned angle of incidence. Additionally, the light path of any extraordinary rays passing through the birefringent materials also varies in accordance with the variation in the refractive index. Accordingly, in a conventional example, the phase difference between the separated light beams L
1
and L
2
generated when the light passes through the birefringent optical members
5
and
6
varies according to the angle of incidence of the incident light L with respect to the birefringent optical members
5
and
6
.
Thus, within the field of observat
Otaki Kumiko
Otaki Tatsuro
Morgan & Lewis & Bockius, LLP
Nguyen Thong
Nikon Corporation
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