JPH1152111A - Light beam splitter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a light beam splitter which emits a transmitted light in parallel to an incident light and also emits a stray light in the direction different from the optical path of an effective light and which is hardly affected by an internal distortion. SOLUTION: This light beam splutter 1 is constituted so that transparent members 1a, 1b are stuck to form the shape of a parallel flat plate as a whole body. A partial reflection coating 2 is applied on the stuck surface (the light beam splitting surface 1c) of the transparent members 1a, 1b. Moreover, antireflection coatings 3 are applied on the first plane 1d and the second plane 1e of the light beam splitter 1. The light beam splitter 1 forms a minute angle with respect to the first plane 1d and the second plane 1e.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a beam splitter for splitting a light beam into reflected light and transmitted light.

[0002]

2. Description of the Related Art FIGS. 5A and 5B are cross-sectional views along an optical axis showing an example of a conventional beam splitter. The beam splitter shown in FIG. 5A has a first surface 21 a of one parallel flat plate 21.
Is a half mirror type in which a partial reflection coat 22 is provided. The beam splitter shown in FIG. 2B is a half prism type in which two right-angled isosceles triangular prisms 23 are bonded together and a partial reflection coat 22 is applied to the bonding surface. The partial reflection coat 22 applied to these beam splitters has a property of transmitting a part of incident light and reflecting a part of the incident light. Therefore, each of the beam splitters can split the incident light into the transmitted light and the reflected light by the partial reflection coat 22.

When the laser beam is split by using these beam splitters, the following problem occurs. That is, in the light beam splitters shown in FIGS. 5A and 5B, a small amount of reflected light is generated even on the surface on which the partial reflection coating 22 is not applied, as indicated by broken lines in the figure. Stray light. In particular, in the case of the half-mirror type beam splitter shown in FIG. 5A, the stray light 24, 25 is slightly shifted in position parallel to the optical path of the transmitted light and the reflected light, so that the transmitted light And cause unnecessary interference with reflected light. Normally, an anti-reflection coating for preventing stray light is applied to the surface of the beam splitter other than the partial reflection coating, but it is still about 1% in intensity ratio with respect to the incident light.
Reflection occurs.

[0004] For example, in a half mirror type beam splitter shown in FIG.
The partial reflection coat 22 applied to “a” divides incident light into reflected light and transmitted light at an intensity ratio of 50% each. here,
When an anti-reflection coating having an intensity reflectance of 1% is applied to the second surface 21b of the parallel flat plate 21, the transmitted light is reflected by 1% on the second surface 21b and further 50% on the first surface 21a, and then the second light is reflected on the second surface 21b. 2
The stray light 24 generated by transmitting 99% of the surface 21b has an intensity ratio of about 0.5% with respect to the transmitted light. This is converted to an amplitude ratio of 7%. The stray light 24 interferes with the transmitted light to generate interference fringes. The contrast ratio of the interference fringes is 14%, which causes a measurement error. On the other hand, in the case of the half-prism type beam splitter as shown in FIG. 5B, there is a problem that the stray light goes backward in the incident optical path and makes the output of the laser light source unstable.

[0005] A beam splitter proposed to prevent such an adverse effect due to stray light is disclosed in, for example, Japanese Patent Application Laid-Open No. 4-76.
No. 513 is disclosed. As shown in FIG. 6 (a), this beam splitter applies the partial reflection coating 22 on one side of the wedge prism 26, thereby controlling the angle of the stray light generated by reflection on the other side. It is possible to make a certain angle difference with respect to the optical axis of the light and the reflected light. Therefore, by using this beam splitter together with an appropriate optical system, it becomes possible to separate stray light from incident light, transmitted light, and reflected light and remove it, thereby preventing unnecessary interference.

The beam splitter shown in FIG. 6 (b) is disclosed in Japanese Patent Application Laid-Open No. 5-127087. This beam splitter comprises two non-rectangular isosceles triangular prisms 27 bonded together and a partial reflection coat 22
Is a half-prism type. This beam splitter can have a certain angle difference with respect to the optical axes of the incident light, the transmitted light and the reflected light with respect to the angles of the stray light generated on the entrance surface and the reflection surface of the non-rectangular isosceles triangular prism 27. . Therefore, even if this beam splitter is used, by providing an appropriate optical system, it becomes possible to separate stray light from incident light, transmitted light and reflected light and remove it, thereby preventing unnecessary interference.

[0007]

However, FIG.
A half-mirror type beam splitter using a wedge-shaped prism 26 shown in (a) and a half-mirror type beam splitter using a non-rectangular isosceles triangular prism 27 shown in FIG. However, there are still the following disadvantages. FIG.
In the light beam splitter shown in FIG. 3A, the transmitted light also travels at an angle with respect to the incident light, so that the optical system used with this light beam splitter has a complicated configuration. On the other hand, in the light beam splitter shown in FIG. 6B, internal distortion is likely to occur near the apex angle in the non-rectangular isosceles triangular prism 27 due to its unique structure and processing method. It is difficult. In addition, in the case of the half-prism type beam splitter, since the optical path in the prism is long, the beam is easily affected by the internal distortion of the prism, and the measurement result may include an error.

Accordingly, in view of the above problems, the present invention provides a light beam splitting device that emits transmitted light in parallel to incident light and emits stray light in a direction different from the optical path of effective light, and is hardly affected by internal distortion. The purpose is to provide a vessel.

[0009]

In order to achieve the above object, a beam splitter according to the present invention comprises two or more transparent members bonded so as to form a parallel plate as a whole. One of the bonding surfaces to be formed is configured to make a predetermined angle with respect to the expression of the parallel plate. Furthermore, the beam splitter of the present invention can be used as illumination light introducing means for an optical microscope using a laser beam.In this case, the generated stray light is directed to the outside of the visual field of the optical microscope. The angle between the light splitting surface and the surface of the parallel plate is selected. In addition, the parallel plate is formed using two wedge-shaped transparent members having the same apex angle, and the apex angle of the wedge-shaped transparent member is selected in a range of 0.5 ° or more and 5 ° or less. Is preferred.

[0010]

FIG. 1 is a sectional view taken along the optical axis showing the configuration of a light beam splitter according to the present invention. The light beam splitter 1 of the present invention is configured such that the transparent members 1a and 1b are attached to each other and have a parallel plate shape as a whole. A partial reflection coat 2 is applied to the bonding surfaces (light beam splitting surfaces 1c) of the transparent members 1a and 1b. Also, the first of the beam splitter 1
Surface (light incident surface) 1d and second surface (light emitting surface) 1
Each of e is provided with an anti-reflection coat 3. The light splitting surface 1c has a small angle with respect to the first surface 1d and the second surface 1e.

Since the light beam splitter 1 of the present invention is formed as a parallel plate as a whole, light incident on the first surface 1d and light emitted through the inside of the light beam splitter 1 and emitted from the second surface 1e. And become parallel. Further, since the light beam splitting surface 1c has a small angle with respect to the first surface 1d and the second surface 1e, the stray light 4 generated by reflecting a part of the incident light on the first surface 1d is A certain angle is formed with respect to any of the transmitted light and the reflected light transmitted or reflected by the light or the light beam splitting surface 1c. Therefore, interference between the stray light 4 and the incident light, the transmitted light, and the reflected light can be prevented. Furthermore, if an appropriate optical system is used together with the light beam splitter 1, the stray light 4 can be split and removed from incident light, transmitted light and reflected light. In addition, by using thin transparent members for the transparent members 1a and 1b, the optical path inside the light beam splitter 1 is shortened, and is less affected by internal distortion.

Further, when the light beam splitter 1 of the present invention is used as illumination light introducing means for an optical microscope using a laser light source, the stray light generated by the light beam splitter 1 goes outside the field of view of the optical microscope. Thus, the angles of the light beam splitting surface 1c, the first surface 1d, and the second surface 1e may be selected. By doing so, the light transmitted through the light beam splitting surface 1c is
The stray lights 5 and 6 generated by the light reflected by the surface 1e and the stray lights 7 and 8 generated by the light reflected by the light splitting surface 1c being further reflected by the first surface 1d are converted into angles with the optical axes of the reflected light and the transmitted light. Can be given. Therefore, also in this case, by providing an appropriate optical system, the stray light 5, 6, 7, 8
Can be removed.

It is more preferable to use two wedge-shaped prisms having the same apex angle for the transparent members 1a and 1b constituting the light beam splitter 1 of the present invention. In this case, the wedge-shaped prisms are joined by staggering the direction of the apex angle,
The shape of a parallel plate can be easily formed. FIG. 2 shows an optical path inside the light beam splitter 1 at this time. In FIG. 2, the apex angle of the transparent members 1a and 1b is Δ, and the refractive index is n. Assuming that the incident angle of the incident light on the first surface 1d is θ and the emission angle of the light from the first surface 1d is θ ₁ , the incident angle on the light splitting surface 1c on which the partial reflection coating 2 is applied and Are both θ ₁ + Δ. Then, the light beam reflected by the light beam splitting surface 1c is incident again on the first surface 1d at an incident angle θ ₁ + 2Δ. Also, the emission angle of the light beam from the first surface 1d is assumed to be θ ₂ . Hereinafter, a condition that the incident light and the reflected light are orthogonal to each other will be obtained.

First, the well-known Snell's law, With, Is established. Solving this equation (2) gives Is obtained. In this equation (3), when the value of the apex angle Δ is sufficiently small, Can be approximated.

The stray light 4 generated by the reflection of the incident light on the first surface 1d is emitted at a reflection angle θ. Therefore, the angle between the stray light 4 and the reflected light is Becomes Since this angle is substantially equal to the angle of the stray light generated in another optical path with respect to the transmitted light or the reflected light, as described later, the stray light generated in each optical path is converted into the original optical path at a predetermined angle according to Expression (5). Of the apex angle Δ required to remove the peak angle from the angle .DELTA.

When the beam splitter 1 of the present invention is used as illumination light introducing means for an optical microscope, the transparent member 1a,
It is desirable that the value of the apex angle Δ of 1b be in the range of 0.5 to 5 °. Many optical microscopes on the market today use a so-called infinity optical system in which an objective lens converts a light beam from one point on an object into a parallel light beam and focuses the parallel light beam on a single point on the image plane with an imaging lens. doing. In the case of such an infinite optical system, when an angle formed by a light beam traveling in a region between the objective lens and the imaging lens with the optical axis is α, an image height h on the image plane of the light beam; Between the focal length f of the imaging lens, There is a relationship indicated by Accordingly, in the region between the objective lens and the imaging lens, the conditions of the light beam according to image as the maximum image height h _max of the imaging, Is established.

Generally, a light beam splitter as illumination light introducing means is disposed in a parallel light beam formed between an objective lens and an imaging lens. Therefore, the condition that the stray light generated by the beam splitter 1 of the present invention deviates from the visual field is as follows. From Equation (8), a suitable apex angle Δ can be obtained. Also, the refractive index n of the transparent member used for the illumination light introducing means is usually about 1.5 to 1.8, the maximum image height h _max of the microscope image is 7 to 13.25 mm, Since the focal length f is 160 to 200 mm,
At least the value of Δ needs to be 0.5 ° or more. If the vertex angle Δ is made larger than necessary, the thickness of the entire beam splitter increases, so that the vertex angle Δ exceeding 5 ° is not preferable.

Hereinafter, an embodiment of the present invention will be described with reference to FIG.

[0019] Example beam splitter 11 of this embodiment, the transparent member 1a shown in FIG. 1, in 1b, apex angle 1 ° wedge prism 11a, and 11b using a refractive index of 1.5, these The two sheets are alternately stuck together to form a parallel plate as a whole. Further, a partial reflection coat 2 is applied to a joint surface (light beam dividing surface 11c) of the wedge-shaped prisms 11a and 11b. Further, the first surface (light incident surface) 11 of the light beam splitter 11
The antireflection coat 3 is also applied to d and the second surface (light emission surface) 11e. Hereinafter, the operation of the light beam splitter 11 of this embodiment will be described with reference to FIG. However, the thin line in the figure indicates a normal line at each boundary surface.

The first surface 11d of the beam splitter 11 according to the present embodiment.
Is set to 43.1 °. At each boundary surface of the light beam splitter 11, the exit angle of the light beam is equal to the magnitude of the reflection angle in accordance with Snell's law described above. In the beam splitter 11 of the present embodiment,
First, incident light enters the first surface 11d at an incident angle of 43.1 °, and is emitted from the first surface 11d at an emission angle of 27.1 °. Then, this light is incident on the light beam splitting surface 11c on which the partial reflection coating 2 is applied at an incident angle of 28.1 °. Here, the incident light is split into transmitted light and reflected light at a predetermined intensity ratio determined by the partial reflection coat 2. The transmitted light is emitted from the light splitting surface 11c at an emission angle of 28.1 °, enters the second surface 11e at an incident angle of 27.1 °, and is emitted from the second surface 11e at an emission angle of 43.1 °. Is done. On the other hand, the reflected light from the light beam splitting surface 11c has a reflection angle of 2
After being emitted from the light beam splitting surface 11c at an angle of 8.1 °, it is incident again on the first surface 11d at an incident angle of 29.1 ° and is emitted from the first surface 11d at an angle of 46.9 °. . Therefore, the light transmitted by the beam splitter 11 is emitted in parallel with the incident light, and the reflected light is emitted in a direction perpendicular to the incident light.

The first surface 11d of the beam splitter 11 according to this embodiment
The antireflection coating 3 is also applied to the second surface 11e, and, nevertheless, about 1% of the light is reflected there and becomes stray light. The broken line in FIG. 3 indicates the traveling direction of the main one of the stray light generated by being reflected at each boundary surface of the light beam splitter 11.

The stray light 4 generated when the incident light is reflected by the first surface 11d of the light beam splitter 11 has a reflection angle of 43.1 ° and the first stray light.
Since the light is reflected by the surface 11d, it forms an angle of 3.8 ° with the reflected light. A part of the light transmitted through the first surface 11d and the light splitting surface 11c is reflected at the second surface 11e at an angle of reflection of 27.1 °, and at an incident angle of 26.1 °, the light splitting surface 1c.
1c. Further, this light is emitted from the light splitting surface 11c at an emission angle of 29.1 °, and is incident on the first surface 11d at an incident angle of 29.1 °.
After entering at an angle of 7.1 °, the light is emitted from this at an angle of 43.1 ° to become stray light 5. The stray light 5 is parallel to the stray light 4 and forms an angle of 3.8 ° with the reflected light. On the other hand, a light ray incident from the second surface 11e to the light beam splitting surface 11c at an incident angle of 26.1 ° is reflected at a reflection angle of 26.1 °, and is incident on the second surface 11e at an incident angle of 25.1 °. The light is emitted at an emission angle of 39.5 ° and becomes stray light 6. This stray light 6 is transmitted light and 3.6
Make an angle of °.

Further, a part of the reflected light is reflected at the first surface 11d at a reflection angle of 29.1 °, passes through the light beam splitting surface 11c, enters the second surface 11e at an incident angle of 29.1 °, and exits. The light is emitted at 46.9 ° and becomes stray light 7. The stray light 7 makes an angle of 3.8 ° with the transmitted light. Also, the first surface 11d
A part of the light reflected on the light splitting surface 11c is reflected at a reflection angle 30.1 °, which is equivalent to the incident angle, and then reflected on the first surface 1
The light enters 1d at an incident angle of 31.1 °, is emitted at an emission angle of 50.8 °, and becomes stray light 8. This stray light 8 is 3.9 ° with the reflected light.
At an angle.

As described above, stray light generated by repeated reflection between the light beam splitting surface 11c, the first surface 11d, and the second surface 11e of the light beam splitter 11 is not only incident light but also transmitted light and reflected light. Also, it has an angle of 3.6 ° or more. Therefore, by using an appropriate optical system in combination with the beam splitter 11, the stray light can be separated and removed from incident light, transmitted light and reflected light.

On the other hand, also in the light beam splitter 11 of the present embodiment, the stray light 9 generated when a part of the light beam which causes the stray light 5 is reflected by the first surface 11d.
Some of the light rays that cause the stray light 7 are generated on the second surface 1.
1e is generated by being reflected by 1e
For example, stray light parallel to transmitted light or reflected light also occurs.
However, since each of them is generated by being transmitted or reflected twice or more on the boundary surface where the partial reflection coat 2 or the antireflection coat 3 is applied, the intensity ratio to the effective light is about 0.0025%. It is as follows. If this is converted into an amplitude ratio, it becomes 0.5%. Therefore, the contrast ratio of the interference fringes generated by the stray light and the transmitted light or the reflected light in the light beam splitter 11 of the present embodiment is about 1 which is twice the amplitude ratio.
%, And there is no practical problem.

FIG. 4 shows a light beam splitter 1 according to this embodiment.
1 is a diagram showing an example in which No. 1 is used for a laser polarization microscope. As shown here, the laser light source 12, the light beam splitter 11 of this embodiment, and the objective lens 1 are arranged in this order in the traveling direction of the light beam.
3, an analyzer 14, an imaging lens 15, a stop 16, and an image sensor 17 are arranged and configured.

The laser light source 12 emits linearly polarized coherent illumination light. The beam splitter 11 is a laser light source 1
The illumination light emitted from 2 is reflected and directed to the objective lens 13. The objective lens 13 focuses the illumination light incident from the light beam splitter 11 on the sample 18, and converts the imaging light diffracted by the sample 18 and returned to parallel light into the original optical path in the opposite direction. Dodge. Then, the beam splitter 11 transmits the image forming light from the objective lens 13. Further, the analyzer 14 transmits only light having a polarization component orthogonal to the illumination light out of the imaging light transmitted through the light beam splitter 11, and the imaging lens 15 transmits the analyzer 1.
The parallel imaging light transmitted through 4 is focused on the imaging element 17. The stop 16 is disposed on the front surface of the image sensor 17 to remove a light beam that passes through a position deviated from the optical path of the image forming light. Here, the focal length of the imaging lens 12 is 1
80 mm, and the maximum image height on the image sensor 17 is 11 mm
It is. Therefore, in the region between the objective lens 13 and the imaging lens 15, only light rays whose angle with the optical axis is 3.5 ° or less contribute to image formation, and the angle with the optical axis is 3.5 °.
Are removed by the stop 16.

By the way, in the laser polarization microscope shown in FIG. 4, when the illumination light is reflected by the light beam splitter 11, stray lights 4 to 8 are generated along the path shown in FIG. However, since all of these stray lights travel at an angle of 3.8 ° or more with respect to the optical axis, they are condensed outside the field of view on the specimen 18 and do not directly affect observation. Also, when the imaging light passes through the beam splitter 11, stray light is generated in the same manner as described above. However, since this travels at an angle of 3.6 ° or more with the imaging light, it is removed by the stop 16. It does not affect the observation.

Further, in this laser polarization microscope, by using the light beam splitter 11 of the present embodiment, which is made of a parallel plate as a whole, the optical axis of the transmitted light does not bend with respect to the optical axis of the incident light, but is straightened. A simple observation system can be configured. Furthermore, this beam splitter 11 is a thin wedge prism 11
a, 11b, the light beam splitter 11
It is itself a thin parallel plate. Therefore, even if this beam splitter 11 is used for a laser polarization microscope as shown in FIG.
Polarization observation with high sensitivity can be performed.

[0030]

As described above, according to the beam splitter of the present invention, the stray light travels at a certain angle with the incident light, transmitted light and reflected light, so that the stray light is removed by an appropriate optical system configuration. It becomes possible to do. Further, according to this beam splitter, the optical axis of the incident light and the optical axis of the transmitted light can be made parallel, and there is no problem due to internal distortion.

[Brief description of the drawings]

FIG. 1 is a sectional view along an optical axis showing a configuration of a light beam splitter according to the present invention.

FIG. 2 is a diagram for explaining an optical path inside a light beam splitter according to the present invention.

FIG. 3 is a diagram showing an embodiment of the present invention.

FIG. 4 is a diagram showing an example in which the beam splitter shown in FIG. 4 is used in a laser polarization microscope.

FIG. 5A is a cross-sectional view along the optical axis showing a configuration of a conventional half mirror type beam splitter. (B) is a cross-sectional view along the optical axis showing the configuration of a conventional half-prism beam splitter.

FIG. 6A is a cross-sectional view along the optical axis showing a configuration of a half-mirror type beam splitter using a conventional wedge-shaped prism. (B) is a cross-sectional view along the optical axis showing a configuration of a conventional half-prism type beam splitter using a non-rectangular isosceles triangular prism.

[Explanation of symbols]

 1,11 Light beam splitter 1a, 1b Transparent member 1c, 11c Light beam splitting surface 1d, 11d, 21a First surface 1e, 11e, 21b Second surface 2,22 Partial reflection coating 3 Antireflection coating 4,5,6,7 , 8, 9, 10, 24, 25 Stray light 11a, 11b, 26 Wedge prism 12 Laser light source 13 Objective lens 14 Analyzer 15 Imaging lens 16 Aperture 17 Image sensor 18 Sample 21 Parallel plate 23 Right-angled isosceles triangular prism 27 Non Right angle isosceles triangular prism

Claims (4)

[Claims] 1. An image forming apparatus comprising: two or more transparent members bonded together so as to form a parallel plate as a whole; one of the bonding surfaces forming a light beam splitting surface having a predetermined angle with respect to the surface of the parallel plate; A beam splitter configured to form 2. An angle between the light splitting surface and the surface of the parallel plate is selected so as to be used as illumination light introducing means of an optical microscope using a laser light source and to generate generated stray light to the outside of the visual field of the optical microscope. The beam splitter according to claim 1, wherein 3. The beam splitter according to claim 1, wherein the parallel plate is formed of two wedge-shaped transparent members having the same apex angle. 4. The beam splitter according to claim 3, wherein a vertex angle of the wedge-shaped transparent member is 0.5 ° or more and 5 ° or less.