This application is based upon and claims the benefit of priority from Japanese Patent Application No. 2009-119294, filed on May 15, 2009 and Japanese Patent Application No. 2009-111398 filed on Apr. 30, 2009, the entire contents of which are incorporated herein by reference.
1. Field of the Invention
The present invention relates to a microscope that illuminates a specimen with coaxial incident-light illumination.
2. Description of the Related Art
Conventionally, a microscope is equipped with a plurality of objective lenses of different magnifications mounted on a revolving nosepiece, and makes an observation of a specimen while changing the magnification. However, in an observation with an objective lens of relatively low magnification, there is a problem in that due to the low curvature of the lens, an illumination light is reflected, which results in the occurrence of flare on an observation image. To prevent this, a polarization optical system is used in which a polarizer is placed between a light source and a half mirror, an analyzer is placed between the half mirror and an imaging lens, and a quarter wavelength plate is placed between the objective lens and a specimen, whereby only the reflected light at the face of the objective lens is cut by the analyzer.
Furthermore, there is disclosed a technology for removing flare due to reflection at the face of an objective lens in a polarization optical system in which a prism-type polarizing beam splitter is used instead of a half mirror, and a quarter wavelength plate is placed between the objective lens and a specimen (for example, see Japanese Laid-open Patent Publication No. 2002-311388).
Moreover, in an observation of a specimen that has a hubbly surface with microasperities like a circuit pattern formed on a semiconductor wafer and a substantially uniform reflectance over the whole surface, a differential interference contrast microscope, which uses the interference of light and forms an observation image by converting an optical phase difference corresponding to the microasperities into contrast of light and dark, is used (for example, see Japanese Laid-open Patent Publication No. 2000-275533).
However, in a polarization optical system and a differential interference contrast system using a half mirror and a polarizing element, in addition to a light quantity loss in the half mirror, an attenuation of light quantity occurs in the polarizer and the analyzer, so a light quantity of the light source needs to be increased to obtain the brightness of an observation image, which leads to an increase in size and power consumption.
Furthermore, to meet the field requirement in an observation at low magnification, a light source capable of emitting a luminous flux having a large diameter is required; however, if a prism-type polarizing beam splitter capable of handling a luminous flux having a large diameter is used as a half mirror, the apparatus size is undesirably increased.
A microscope according to an aspect of the present invention includes a wire grid polarizing beam splitter that reflects light emitted from a light source to a direction of an observation optical axis to cause the light to enter an objective lens, and transmits a reflected light from a specimen to cause the reflected light to enter an imaging lens; and a quarter wavelength plate that is placed between the objective lens and the specimen.
The above and other features, advantages and technical and industrial significance of this invention will be better understood by reading the following detailed description of presently preferred embodiments of the invention, when considered in connection with the accompanying drawings.
Embodiments of a microscope according to the present invention are explained in detail below with reference to the accompanying drawings. The present invention is not limited to the embodiments, and various modifications can be made without departing from the scope of the present invention.
An incident-light illumination and imaging unit 5 is mounted on the upper side of the microscope main body 1, and a light source unit 6 is mounted on the side of the back surface of the incident-light illumination and imaging unit 5. The light source unit 6 incorporates a light source 7 that projects emission light toward inside the incident-light illumination and imaging unit 5. A halogen lamp, an LED, or the like is used as the light source 7. The incident-light illumination and imaging unit 5 is equipped with predetermined optical elements, such as illumination lenses 8 and 9, an aperture stop 10, a field stop 11, and a wire grid polarizing beam splitter 12, on an incident-light illumination optical axis L1. The specimen 2 is illuminated by the use of a coaxial incident-light illumination system 19 composed of the light source 7, the illumination lenses 8 and 9, the aperture stop 10, the field stop 11, and the wire grid polarizing beam splitter 12 for optical-path switching.
The wire grid polarizing beam splitter 12 is a polarizing plate that a number of nanometer-level wire-like grids are formed on a substrate, and is placed on the incident-light illumination optical axis L1 at an angle of 45 degrees thereby functioning as a polarizing beam splitter.
The illumination light emitted from the light source 7 enters the illumination lens 8, and passes through the aperture stop 10, the field stop 11, and the illumination lens 9, and then is reflected by the wire grid polarizing beam splitter 12, whereby a conjugate image of the light source 7 is formed on the pupil of an objective lens 13. The wire grid polarizing beam splitter 12 polarizes the incident light into linear polarized lights, and reflects only the S-polarized light to a direction of an observation optical axis L2 perpendicular to the incident-light illumination optical axis L1. After that, the illumination light (the S-polarized light) reflected by the wire grid polarizing beam splitter 12 is delivered to the specimen 2 by the objective lens 13.
The aperture stop 10 is placed at the position conjugate to the pupil of the objective lens 13, and the numerical aperture NA is adjusted by adjusting the aperture stop 10. The field stop 11 is placed at the position conjugate to the focal position of the objective lens 13, and a field of view is adjusted by adjusting the field stop 11.
The incident-light illumination and imaging unit 5 is equipped with a revolving nosepiece 14 on the observation optical axis L2 perpendicular to the incident-light illumination optical axis L1 on the underside thereof. A plurality of objective lenses 13 of different magnifications are mounted on the revolving nosepiece 14. The revolving nosepiece 14 can selectively place any one of the objective lenses 13 on the observation optical axis L2 with the rotating operation. Due to the rotation of the focus handle 4, the stage 3 is moved in the up-and-down direction indicated by the arrow A by the focusing mechanism (not shown), whereby focusing on the specimen 2 with respect to the objective lenses 13 is adjusted. A quarter wavelength plate 15 is mounted on a leading end of the objective lens 13, and converts the linear polarized light reflected by the wire grid polarizing beam splitter 12 into a circular polarized light.
By the configuration as shown in
Above the incident-light illumination and imaging unit 5, a tube 17 incorporating the imaging lens 16 is provided on the observation optical axis L2. On the upper part of the tube 17, an eyepiece 18 is mounted. An observation optical system 20 is composed of the quarter wavelength plate 15, the objective lens 13, the wire grid polarizing beam splitter 12, and the imaging lens 16, and imaging of the specimen 2 is observed with the observation optical system 20 and the eyepiece 18. The optical elements composing the observation optical system 20 are placed on the observation optical axis L2.
The wire grid polarizing beam splitter 12 reflects a light, which has been emitted from the light source 7 and transmitted through the illumination lens 8, the aperture stop 10, the field stop 11, and the illumination lens 9, as linear polarized lights, and after the quarter wavelength plate 15 converts the linear polarized light passing through the objective lens 13 into a circular polarized light, the light is delivered to the specimen 2. After the delivered light is reflected by the specimen 2, the light is transmitted through the quarter wavelength plate 15, the objective lens 13, and the wire grid polarizing beam splitter 12, and imaged by the imaging lens 16, and then the imaging is observed through the eyepiece 18.
The light, which has been emitted from the light source 7, passed through the coaxial incident-light illumination system 19, and reflected to the direction of the observation optical axis L2 by the wire grid polarizing beam splitter 12, passes through the objective lens 13; however, if the curvature of the objective lens 13 is low, a portion of the light is reflected by the face of the objective lens 13. Out of the light reflected by the face of the objective lens 13, the light reflected to the direction of the observation optical axis L2 enters the wire grid polarizing beam splitter 12; however, the light remains S-polarized light, so the light is reflected by the wire grid polarizing beam splitter 12, and does not enter the imaging lens 16 on the observation optical axis L2. Therefore, it is possible to suppress the occurrence of flare in the objective lens. Furthermore, the wire grid polarizing beam splitter 12 can keep an attenuation of light quantity lower as compared with a commonly-used half mirror, so the brightness can be ensured without increasing a light quantity of the light source. Moreover, even when the light source 7 capable of emitting a luminous flux having a large diameter enough to meet the field requirement in an observation at low magnification is used, the compact apparatus can be achieved.
Subsequently, a second embodiment of the present invention is explained. In the second embodiment, a second polarizing element for generating polarized light in the same direction as a direction of vibration of linear polarized light reflected by the wire grid polarizing beam splitter 12 is placed in a coaxial incident-light illumination system 19A, and a third polarizing element for generating polarized light in the same direction as a direction of vibration of a linear polarized light that the wire grid polarizing beam splitter 12 transmits is placed in an observation optical system 20A, whereby a polarization property of the light used for an observation of a specimen is improved, thereby enabling the further removal of flare.
The polarizer 27 is placed so as to extract linear polarized light (S-polarized light) in the same vibration direction as that of linear polarized light reflected by the wire grid polarizing beam splitter 12 from the illumination light emitted from the light source 7, and the analyzer 28 is placed so as to extract linear polarized light (P-polarized light) in the same vibration direction as that of linear polarized light that the wire grid polarizing beam splitter 12 transmits, thereby increasing an extinction ratio and improving a polarization property of the light used for an observation of imaging of the specimen 2, which enables the further removal of flare.
In the second embodiment, both the polarizer 27 and the analyzer 28 are placed; however, a polarization property of the light used for an observation of a specimen can be improved just by placing any one of the two.
Subsequently, a third embodiment of the present invention is explained. In the third embodiment, a zoom tube 29 is placed between the imaging lens 16 and the wire grid polarizing beam splitter 12; since the coaxial incident-light illumination system 19A is placed between the zoom tube 29 and the objective lens 13, the ray height in a zoom lens is reduced, and even a compact zoom lens makes it possible to ensure a necessary field of view. Furthermore, by the use of the wire grid polarizing beam splitter 12, not only the occurrence of flare is prevented, but also the field requirement for a whole field of view within a zoom range can be met without increasing the size of an illumination device.
The zoom tube 29 is equipped with the variable magnification optical system (not shown), which is composed of a plurality of zoom lenses, and a zoom handle 30, and an observation by varying a zoom/magnification ratio can be made by the zoom/magnification ratio varying operation performed by rotation of the zoom handle 30.
The wire grid polarizing beam splitter 12 reflects light, which has been emitted from the light source 7 and transmitted through the illumination lens 8, the aperture stop 10, the field stop 11, the illumination lens 9, and the polarizer 27, as linear polarized light, and after the quarter wavelength plate 15 converts the linear polarized light passing through the objective lens 13 into circular polarized light, the light is delivered to the specimen 2. After the delivered light is reflected by the specimen 2, the light is again transmitted through the quarter wavelength plate 15, the objective lens 13, the wire grid polarizing beam splitter 12, and the analyzer 28, and enters the variable magnification optical system, and then is imaged by the imaging lens 16.
In the microscope 300 according to the third embodiment, the coaxial incident-light illumination system 19A is placed between the zoom tube 29 and the objective lens 13, whereby the ray height in the zoom lens is reduced, and a bright observation image with a wide field of view can be obtained even with a compact zoom lens. Furthermore, by the placement of the wire grid polarizing beam splitter 12, the polarizer 27, and the analyzer 28, a polarization property of the illumination light is improved, and an attenuation of light quantity is kept low, and the reflected light at the face of the objective lens 13 is prevented from entering the imaging lens 16 thereby preventing the occurrence of flare effectively.
Subsequently, a fourth embodiment of the present invention is explained. A microscope 400 according to the fourth embodiment is equipped with an optical-element switching device 31 for switching the wire grid polarizing beam splitter to be placed on the observation optical axis L2 between wire grid polarizing beam splitters 12 (12A, 12B) with different extinction ratios. By the switching placement of the wire grid polarizing beam splitters 12 (12A, 12B) with different extinction ratios by the optical-element switching device 31, an observation of an image with a degree of halation removal changed can be made.
When the holding member 35 is moved in a direction of the arrow shown in
When a luminance difference of the reflected light from the specimen 2 is large, the wire grid polarizing beam splitter 12A with the high extinction ratio is placed on the observation optical axis L2, which enables an observation of an image with halation reduced; when an amount of reflected light from the specimen 2 is small, the wire grid polarizing beam splitter 12B with the low extinction ratio is placed on the observation optical axis L2, which enables an observation of an image with a light quantity ensured.
Subsequently, a fifth embodiment of the present invention is explained.
A microscope 500 is, as shown in
The slider unit 40 is, as shown in
The stage 3 is a movable stage on which the specimen 2, an object to be observed, is put. As shown in
In the coaxial incident-light illumination system 19, as shown in
At this time, the field stop 11 is placed so that the field stop 11 and the face of the specimen 2 are in a conjugate relation. Furthermore, the reflecting surface of the PBS 12 is placed to be located on a point at the intersection of an optical axis of a luminous flux emitted from the light source 7, i.e., the optical axis L1 of the coaxial incident-light illumination system 19 with the optical axis of the objective lens 13, i.e., the optical axis L2 of the observation optical system 20C.
With the microscope 500 configured as above, when the specimen 2 is observed by the differential interference contrast, the slider unit 40 is moved by the operation of the operation knob 40d, and, as shown in
At this time, as shown in
The delivered two linear polarized lights are, as shown in
At this time, if the specimen 2 has the surface with asperities, an optical path difference occurs between reflected lights. Thus, two images based on the two linear polarized lights synthesized by the DIC prism 40b cause interference, and a differential interference image having contrast of light and dark based on a phase difference is generated. Then, when the lights passing through the DIC prism 40b enter the PBS 12, the PBS 12 transmits only the two linear polarized lights synthesized by the DIC prism 40b, and blocks the other light. Consequently, in the microscope 500, a stereoscopic differential interference image having contrast of light and dark can be visually observed through the eyepiece 18.
On the other hand, when a bright-field observation of the specimen 2 is made, the microscope 500 moves the slider unit 40 by the operation of the operation knob 40d, and, as shown in
Consequently, in the microscope 500, when a luminous flux emitted from the light source 7 reaches the PBS 12 as described above, as shown in
The delivered circular polarized light is, as shown in
In this manner, since the microscope 500 uses the PBS 12 instead of a half mirror, a polarizer and an analyzer, which are used in a case of using a half mirror, are not necessary, and switching between the differential interference contrast observation and the bright-field observation can be easily made just by moving the unitized slider unit 40. Furthermore, since the microscope 500 uses the PBS 12 instead of a half mirror, an amount of decrease in light quantity caused by the PBS 12 is smaller than that is caused by the half mirror, so there is an advantage of an increase in brightness of an observation image.
Moreover, in the microscope 500, not only a polarizer and an analyzer are not necessary, but also the DIC prism 40b and the λ/4 plate 40c are unitized. Thus, in the microscope 500, unlike a conventional microscope, there is no need to remove/insert a lot of optical components from/into the microscope main body or the optical path, so it is free from cumbersome storage of the optical components to be removed/inserted, and there is an advantage of no dummy slider required.
Furthermore, since the microscope 500 does not need a polarizer and an analyzer because of using a wire grid polarizing beam splitter as the PBS 12, the weight of the coaxial incident-light illumination system 19 or the observation optical system 20C can be reduced as compared with a case of using a cube polarizing beam splitter.
A conventional optical microscope capable of making a differential interference contrast observation is generally equipped with an insertion/removal hole for inserting or removing a DIC prism. Thus, if the slider unit 40 is formed into a shape responding to such a general insertion/removal hole, the slider unit 40 can be used widely in conventional optical microscopes.
The microscope according to the present invention uses a wire grid polarizing beam splitter thereby effectively preventing the occurrence of flare, and can meet the field requirement in an observation at low magnification without increasing the apparatus size and ensure the brightness.
Furthermore, since the microscope according to the present invention employs the observation optical system including the DIC prism and the λ/4 wavelength plate, which are switchably placed on the optical axis between the polarizing beam splitter and the objective lens, the number of optical components to be removed/inserted at the time of switching the observation method can be reduced, and can be the one that is easy to operate the switching of observation methods.
Additional advantages and modifications will readily occur to those skilled in the art. Therefore, the invention in its broader aspects is not limited to the specific details and representative embodiments shown and described herein. Accordingly, various modifications may be made without departing from the spirit or scope of the general inventive concept as defined by the appended claims and their equivalents.
Number | Date | Country | Kind |
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2009-111398 | Apr 2009 | JP | national |
2009-119294 | May 2009 | JP | national |