JP2000028519A - Illuminating optical system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an illuminating optical system having small size and advantageous cost, and capable of changing continuously from a loop-belt illumination to a circular illumination. SOLUTION: In this illuminating optical system for converting a laser beam into a loop-belt illumination luminous flux, a variable loop-belt mask 30 having a polarizer 32 in the region of a parallel plane-shaped glass pane 31, corresponding to the central region of the laser beam is installed, and a transmittance at the polarizer 32 is enabled to change continuously by rotating the variable loop-belt mask 30 relative to the optical axis of the laser beam.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an illumination optical system used for a confocal laser scanning microscope (hereinafter, abbreviated as CLSM).

[0002]

2. Description of the Related Art Recently, CLSMs tend to be widely used because they can achieve high resolution as compared with general optical microscopes. In other words, the theory of such a CLSM is detailed in CONFOCAL MICROSCOPY by T. Wilson Ed., Etc., but the point spread function (P
SF) is the product of the PSF of the illumination optical system (condenser lens) and the PSF of the detection optical system (objective lens), so that it is a basic principle that high resolution can be achieved.

[0003] By the way, at present, CL which is widely used
Many SMs are epi-illuminated CLSMs.
As an LSM optical system, there is an optical system configured as shown in FIG. In this case, the laser light emitted from the laser light source 1 is applied to the lens systems 101 and 1 constituting the beam expander.
The light passes through a half mirror 4, a galvanometer mirror 5, and a relay lens system 6, passes through an objective lens 7, and irradiates a specimen 8. The reflected light from the sample 8 travels in the opposite direction as described above, passes through the half mirror 4, the confocal lens 9, and the pinhole 10, and is photoelectrically converted by the photodetector 11.

FIG. 5 shows a one-dimensional scanning optical system for simplicity, but two-dimensional scanning becomes possible by adding another galvanomirror. In such an epi-illumination type CLSM, the objective lens 7 also serves as a condenser lens. Thus, the PSF obtained by the CLSM is the square of the PSF of the objective lens 7. Figure 6 shows the objective lens
7 and the squared PSF are shown. As is clear from the figure, the half-width is narrowed by the square effect, while the diameter of the first dark ring does not change. Further, the primary maximum is further reduced by the square effect, and both resolution and contrast can be improved as compared with a general optical microscope.

However, recently, there has been a demand for more accurate detection of the CLSM, such as an increase in the depth of focus and an improvement in the resolution. One using a ring-shaped illumination optical system has been considered. In other words, those using such an annular illumination optical system can improve the resolution in the horizontal direction by using a diffractive optical element, an axicon prism, a ring filter, etc. to convert the illumination light beam into an annular illumination. ,
This allows for an increase in the depth of focus.

FIG. 7 shows a schematic configuration of a CLSM using such an annular illumination optical system, and the same parts as those in FIG. 5 are denoted by the same reference numerals. In this case, the laser light emitted from the laser light source 1 is divided into two axicon prisms 20 and 21 which are arranged to face each other to generate annular illumination.
Through the beam reducers 22 and 23, and converts the light into annular illumination light of a desired size. The annular illumination passes through the half mirror 4, the galvanometer mirror 5, and the relay lens system 6, passes through the objective lens 7, and passes through the objective lens 7. 8. Others are the same as FIG.

When such an annular illumination optical system is used,
Comparing the PSF with the objective lens 7 of the normal illumination (the illumination without any voids, hereinafter referred to as circular illumination) described with reference to FIG. 6, as shown in FIG. In comparison, the width of the PSF is reduced, the resolution in the horizontal direction is improved, and the depth of focus (not shown) can be increased.

[0008]

By using the annular illumination optical system in this way, it is possible to increase the resolution in the horizontal direction and the depth of focus. That is, according to the CLSM using such an annular illumination optical system, the resolution in the horizontal direction can be improved by about several% as compared with the ordinary optical microscope.
However, on the other hand, the so-called sectioning effect in the optical axis direction is inferior to circular illumination. This sectioning effect is more remarkable as the depth of focus becomes shallower, and it may be desired to take advantage of this advantage depending on the purpose of observation.

Therefore, in reality, it is ideal if an illumination optical system capable of continuously changing the intensity distribution in the central region of laser light from annular illumination to circular illumination can be realized at low cost without increasing the size. It is.

Therefore, conventionally, it has been considered that both annular illumination light and circular illumination using the above-described axicon prism can be used as necessary, and an annular illumination optical system and a circular illumination optical system are used. There is a type in which the two optical systems can be switched. However, if these annular illumination optical system and circular illumination optical system are alternately put in and out of the optical path,
The entire optical system becomes extremely large, which is disadvantageous in terms of cost.

On the other hand, as disclosed in Japanese Patent Application Laid-Open No. 7-63508, there is a filter using a ring filter having an annular slit. By switching the ring filter in and out of the illumination optical system, it is possible to switch between annular illumination and circular illumination. In this case, only one illumination optical system may be used, and a plurality of ring filters having different transmittances in the central region of the laser beam may be prepared. It is possible to discretely change from illumination to circular illumination. However,
In order to continuously change the intensity distribution in the central region of the laser beam from annular illumination to circular illumination, that is, to approach the variable from annular illumination to circular illumination continuously, a large number of ring filters are prepared. Therefore, there is a problem that the size and cost of the apparatus are increased as a result.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide an illumination optical system which can be continuously varied from annular illumination to circular illumination, and which is compact and advantageous in cost.

[0013]

According to the first aspect of the present invention,
An illumination optical system for converting a laser beam into an annular illumination light beam includes annular illumination generating means for continuously changing the transmittance of an area corresponding to a central area of the laser light.

According to a second aspect of the present invention, in the first aspect, the annular illumination generating means includes an annular mask having a polarizer in a region corresponding to a central region of the laser beam. The band mask is rotatable with respect to the optical axis of the laser beam.

According to a third aspect of the present invention, in the first aspect of the present invention, the annular illumination generating means includes an annular mask having a wave plate in a region corresponding to a central region of the laser beam, and the annular mask. And a polarizer through which the laser light emitted is transmitted, and the annular mask is rotatable with respect to the optical axis of the laser light.

As a result, according to the first aspect of the present invention,
Since the transmittance of the central region of the annular mask can be continuously varied, it is possible to continuously change from annular illumination to circular illumination.

According to the second or third aspect of the present invention, the continuous change from the annular illumination to the circular illumination is performed by rotating the annular mask with respect to the optical axis of the laser beam and by controlling the central area of the variable annular mask. Is realized by continuously varying the transmittance of the optical system, the configuration is simple, the entire optical system can be reduced in size, and the cost can be reduced.

[0018]

Embodiments of the present invention will be described below with reference to the drawings. (First Embodiment) FIG. 1 shows a schematic configuration of a confocal laser scanning microscope to which the illumination optical system of the present invention is applied, and the same parts as those in FIG. ing.

In this case, a variable annular mask 30 is provided in the optical path between the lens systems 101 and 102 constituting the beam expander and the half mirror 4, and the laser light emitted from the laser light source 1 is transmitted to the lens systems 101 and 102. The laser beam is incident on the variable annular mask 30 through the variable annular mask 30, and the laser beam passing through the variable annular mask 30 is incident on the half mirror 4.

As shown in FIG. 2A, the variable annular mask 30 has a polarizer 32 in a central area corresponding to a central area of a laser beam on a parallel flat glass plate 31. By being installed in the optical path and being rotatable with respect to the optical axis, the transmittance of the central region having the polarizer 32 can be continuously varied. That is, in such a variable annular mask 30, if the angle of the direction of the polarizer 32 with respect to the direction of the linearly polarized light of the incident laser beam is θ, the transmittance of the central region of the variable annular mask 30 is COS.
² (θ), the transmittance of the central region can be continuously varied from 0 to 100% by rotating the angle θ of the direction of the polarizer 32 from 0 to 90 degrees.

The glass plate 31 of the variable annular mask 30
Is provided with a polarizing plate 33. This polarizing plate 33
Is the polarizer 3 of the laser beam passing through the variable annular mask 30.
This is for aligning the directions of polarized light different by θ between the central region having 2 and the peripheral region. This polarizing plate 33
Is preferably the same as the polarization direction of the laser light in the peripheral region. However, the polarizing plate 3
When 3 is installed, the transmittance in the central region becomes COS ⁴ (θ).

The half mirror 4 may be replaced by a polarizing beam splitter instead of the polarizing plate 33. In this case, since the reflected light from the sample 8 does not return to the photodetector 11, the distance between the objective lens 7 and the polarization beam splitter is one.
A quarter wave plate is required.

Next, the operation of the embodiment configured as described above will be described. First, the observer selects a desired illumination state depending on the state of the specimen to be observed and the purpose of the observation. In this case, the angle θ of the polarizer 32 in the central region of the variable orbicular zone mask 30 is rotated from 0 to 90 degrees, and the transmittance of the region corresponding to the central region of the laser beam is continuously adjusted from 0 to 100%. I do. In this case, the intensity distribution of the orbicular zone illumination light after passing through the variable orbicular zone mask 30 is as shown in FIG. In other words, FIG. 2B shows a case where the incident laser light is a generally used Gaussian beam, and the intensity distribution in the central region having the polarizer 32 according to the rotation angle of the variable annular mask 30 is It can be continuously hyperpolarized from 0 to 100% as indicated by the dotted line, and when the transmittance is 0%, it becomes a hollow annular illumination light flux and is obtained as complete annular illumination. Is 100%, normal circular illumination is obtained.

The laser light from the laser light source 1 is transmitted through beam expander systems 101 and 102 to the variable annular mask 3.
It is incident on zero. In this case, the variable annular mask 30
It is assumed that the laser light incident on the laser beam is linearly polarized light or has been converted to linearly polarized light immediately before being incident on the variable orbicular zone mask 30.

Assuming that the transmittance in the central area of the variable annular mask 30 is 0% and the light is a hollow annular illumination light beam, the laser light from this annular illumination is converted into a half mirror 4, a galvano mirror 5, and a relay lens system. The sample 8 passes through the objective lens 7 and irradiates the sample 8. Next, the reflected light from the sample 8 is reflected by the half mirror 4, the confocal lens 9, and the pinhole 10.
, Photoelectrically converted by the photodetector 11 and data on the specimen 8 is detected.

On the other hand, when the transmittance in the central region of the variable orbicular zone mask 30 is 100% and the illumination is a perfect circular illumination, data on the specimen 8 is detected in the same manner as described above. Therefore, according to this configuration, the parallel flat glass plate 3 is provided in the illumination optical system that converts the laser light into the annular illumination light flux.
By providing a variable annular mask 30 having a polarizer 32 in a region corresponding to the central region of one laser beam, and rotating the variable annular mask 30 with respect to the optical axis of the laser beam,
Since the transmittance of the polarizer 32 can be continuously varied, it can be further continuously varied from annular illumination to circular illumination. Based on the above, the depth of focus is reduced and CLSM
If you want to emphasize the sectioning effect of
When emphasis is placed on improving the horizontal resolution, the observer can easily select a desired illumination state depending on the state of the sample or the purpose of observation, such as annular illumination. Further, since the continuous change from the annular illumination to the circular illumination is realized by rotating the variable annular mask 30 around the optical axis, the configuration is simple and the entire optical system can be miniaturized. It can be inexpensive. (Second Embodiment) First Embodiment
In the embodiment, the one having the polarizer in the central region of the variable orbicular zone mask has been described. However, in the second embodiment,
A に wavelength plate is used instead of the polarizer.

Further, in the second embodiment, the schematic configuration of the illumination optical system is the same as that of FIG. 1, so that FIG. FIG. 3A shows a variable orbicular zone mask used in the second embodiment. in this case,
As shown in FIG. 3A, the variable annular mask 40 has a half-wave plate 42 in a central area corresponding to the central area of the laser beam of the parallel flat glass plate 41. 4
1, a polarizing plate 43 is provided.

In such a configuration, when a linearly polarized laser beam is incident on the variable annular mask 40, the central portion of the laser beam passes through the half-wave plate 42. In this case, if the angle between the direction of the linearly polarized light of the incident laser light and the fast axis or slow axis of the half-wave plate 42 is α, the center of the variable annular mask 40 having the half-wave plate 42 The laser light in the region keeps a state of linear polarization, but its direction rotates by 2α with respect to the laser light in the peripheral region. When the laser light transmitted through the variable orbicular zone mask 40 is passed through a polarizing plate 43 having the same polarization direction as the linearly polarized light of the laser light in the peripheral region,
The transmittance in the central region is COS ² (2α).

Therefore, even in this case, when the variable annular mask 40 is rotated with respect to the optical axis depending on the state of the sample to be observed and the purpose of observation, as shown in FIG. The transmittance in the central region of the mask 40 can be continuously varied, and the same effect as in the above-described first embodiment can be expected.

In the second embodiment as well, the function of the polarizing plate 43 can be replaced by using the half mirror 4 as a polarizing beam splitter. (Third Embodiment) In the first embodiment described above, the variable annular mask having a polarizer in the central region has been described. However, in the third embodiment, a polarizer is used instead of a polarizer. , A Fabry-Perot interferometer.

Note that, also in the third embodiment, the schematic configuration of the illumination optical system is the same as that of FIG. 1, so that FIG. FIG. 4 shows a variable orbicular zone mask used in the third embodiment. In this case, the variable annular mask 50 using the Fabry-Perot interferometer is shown in FIG.
As shown in (a), two mirrors 52 are provided in a central area corresponding to the central area of the laser beam on a parallel flat glass plate 51.
1, 522 are arranged so as to face each other.

In such a configuration, the mirror 5
The distance between the mirrors 21 and 522 is d, the refractive index of the medium (glass plate 51) between the mirrors 521 and 522 is n,
Assuming that the inclination with respect to the optical axis of 0 is θ, the wavelength of the laser beam is λ, and an integer m, n · d · COS θ = (λ / 2) m holds. Is θ or the distance d between the mirrors 521 and 522
By adjusting (or the optical path length n · d), the transmittance of the laser light having the wavelength λ in the central region of the variable annular mask 50 can be continuously varied.

Therefore, even in this case, depending on the state of the sample to be observed and the purpose of observation, the variable annular mask 50 can be tilted with respect to the optical axis or the distance d between the mirrors 521 and 522 can be adjusted. As shown in FIG. 4B, the transmittance in the central region of the variable orbicular zone mask 50 can be continuously varied, and the same effect as in the first embodiment can be expected.

The present invention is not limited to the above-described embodiment, but can be variously modified without departing from the present invention. For example, according to the first and second embodiments, since the transmittance can be continuously varied only in the region corresponding to the central region of the laser beam, only the portion corresponding to the central region of the laser beam can be changed. What is necessary is just to make the transmittance continuously variable. Here, instead of the polarizing plate 33 (43) used in the first and second embodiments, a polarizer is provided in a region corresponding to the central region of the glass plate as in the variable annular mask 30 (40). By arranging so as to face the variable annular mask 30 (40),
As in the first and second embodiments, the illumination light required for the annular illumination is transmitted through the glass plate, so that the illumination light is compared with the illumination light obtained through the polarizing plate 33 (43). Light amount attenuation can be reduced.

Although the variable annular mask is used in the first to third embodiments, a liquid crystal filter having a variable transmittance in the central region may be used instead. In addition,
The present invention includes the following inventions.

(1) In the illumination optical system according to the first aspect, the annular illumination generating means has an interference filter having a pair of mirrors arranged in a region corresponding to the central region of the laser beam so as to face each other. The annular zone mask is tilted with respect to the optical axis of the laser beam, or the optical path length between the pair of mirrors is made variable. (2) In the illumination optical system according to the first aspect, the annular illumination generating means comprises an annular mask in which a region corresponding to the central region of the laser beam is a liquid crystal filter.

[0037]

As described above, according to the present invention, it is possible to continuously vary from annular illumination to circular illumination. When importance is placed on improving the resolution in the horizontal direction, a desired illumination state can be easily selected by the observer according to the state of the sample or the purpose of observation, such as annular illumination when importance is placed on improving the resolution in the horizontal direction. In addition, since continuous variation from annular illumination to circular illumination is realized by continuously varying the transmittance of the central area of the variable annular mask, the configuration is simple and the entire optical system is small. And cost reduction.

[Brief description of the drawings]

FIG. 1 is a diagram showing a schematic configuration of a first embodiment of the present invention.

FIG. 2 is a diagram showing a schematic configuration of a variable annular mask used in the first embodiment and an intensity distribution of annular illumination light.

FIG. 3 is a diagram showing a schematic configuration of a variable annular mask used in a second embodiment of the present invention and an intensity distribution of annular illumination light.

FIG. 4 is a diagram showing a schematic configuration of a variable annular mask and an intensity distribution of annular illumination light used in a third embodiment of the present invention.

FIG. 5 is a diagram showing a schematic configuration of an example of an optical system of a conventional epi-illumination type CLSM.

FIG. 6 is a diagram showing a relationship between a PSF of an objective lens of an optical system of a conventional epi-illumination type CLSM and a PSF of the square thereof.

FIG. 7 is a diagram showing a schematic configuration of a CLSM using a conventional annular illumination optical system.

FIG. 8 is a diagram showing a comparison between a PSF of an objective lens and a PSF of an objective lens for normal illumination when a conventional annular illumination optical system is used.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Laser light source, 101, 102 ... Lens system, 4 ... Half mirror, 5 ... Galvano mirror, 6 ... Relay lens system, 7 ... Objective lens, 8 ... Specimen, 9 ... Confocal lens, 10 ... Pinhole, 11 ... 30, 40, 50: Variable annular mask; 31, 41, 51: Glass plate; 32: Polarizer; 33, 43: Polarizer; 42: 1/2 wavelength plate; 521, 522: Mirror.

Continued on front page F term (reference) 2G043 AA03 EA13 FA01 FA02 HA02 HA05 HA07 HA15 2G059 AA05 EE01 EE09 FF01 FF03 GG01 JJ13 JJ17 JJ19 JJ20 JJ30 LL01 2H052 AA08 AC04 AC15 AC17 AC28 AC34

Claims (3)

[Claims] 1. An illumination optical system for converting a laser beam into an annular illumination beam, comprising an annular illumination generating means capable of continuously changing the transmittance of a region corresponding to a central region of the laser beam. An illumination optical system characterized by the above. 2. The annular illumination generating means includes an annular mask having a polarizer in a region corresponding to a central region of the laser light, and the annular mask can be rotated with respect to an optical axis of the laser light. 2. The illumination optical system according to claim 1, wherein: 3. The annular illumination generating means includes: an annular mask having a wave plate in a region corresponding to a central region of the laser light; and a polarizer through which the laser light emitted from the annular mask passes. The illumination optical system according to claim 1, wherein the annular mask is rotatable with respect to an optical axis of the laser beam.