JP2009086392A - Phase-contrast microscope - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a phase-contrast microscope, for detecting a mineral fiber with an extremely small phase difference quantity such as asbestos, which is contained in a sample collected from powder dust in the atmosphere or a building material. <P>SOLUTION: The asbestos phase-contrast microscope 1 comprises a light source 21, a lighting optical system 20 emitting light from the light source 21 to a sample S and an objective lens 30 converging the light transmitted by the sample S to form an image in this order. A ring diaphragm 24 is disposed in the vicinity of a position conjugate with an image-side focusing surface of the objective lens 30 within the lighting optical system 20, and a phase ring 31 having a shape covering an opening part 24a of the ring diaphragm 24 is disposed in a position conjugate with the ring diaphragm 24 on the image side of the objective lens 30. The transmittance μ[%] of the phase ring 21 satisfies 5≤μ≤20. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a phase contrast microscope.

Asbestos was once widely used in building materials because of its heat resistance. In recent years, when disassembling a building using asbestos, a disease considered to be caused by scattered asbestos has become a social problem. Therefore, there is a growing need to investigate the presence or absence of asbestos in the atmosphere. The sample obtained from the atmosphere is first observed with a phase contrast microscope. A phase-contrast microscope is an observation in which the phase shift of light caused by a phase object is changed to contrast of light intensity. A ring-shaped aperture stop (hereinafter referred to as “ring stop”) is provided at a position conjugate with the image side focal plane (pupil) of the objective lens in the illumination optical path of a normal bright field microscope. A special filter called a phase ring (phase plate) in which a ring-shaped phase film is formed at the image side focal position of a certain objective lens or its conjugate position is provided in the optical path of the objective lens. The light that has passed through the phase object has a phase difference with the surrounding light, but can be considered separately from the diffracted light diffracted by the phase object and the transmitted light that has been transmitted. When the phase difference between the diffracted light and the transmitted light is small, the phase is shifted by about a quarter wavelength. Utilizing this, a phase film (phase ring) having an action of shifting the phase of transmitted light by a quarter wavelength is disposed at the conjugate part of the ring stop. As a result, on the image plane, the diffracted light and the direct light interfere with each other and strengthen or weaken each other, resulting in light intensity. When the amount of phase difference generated by the phase object is small, the intensity of the diffracted light is proportional to the amount of phase difference. Since the diffracted light is weaker than the transmitted light, an absorption filter is arranged in the phase film portion so that the direct light is weakened to increase the contrast. An objective lens whose light transmittance by the filter is changed according to the phase difference of the target sample is prepared, and a filter with low transmittance is depicted with high contrast and suitable for observation of an object with a very small phase difference amount. Yes. On the other hand, a filter having a high transmittance has a property that a contrast is drawn low (see, for example, Patent Document 1).
JP 2007-108664 A

  However, the conventional phase contrast microscope has a problem that the transmittance of the filter used is inappropriate, the contrast is low, and mineral fibers such as asbestos having a very small phase difference may be overlooked.

  The present invention has been made in view of such a problem, and is a phase contrast microscope capable of detecting mineral fibers such as asbestos having a very small amount of phase difference contained in a sample collected from atmospheric dust and building materials. The purpose is to provide.

In order to solve the above problems, a phase contrast microscope according to the present invention (for example, the asbestos inspection microscope 1 in the embodiment) includes an illumination optical system that irradiates a sample with light from the light source in order from the light source, and a sample. An objective lens that collects the transmitted light and forms an image, and the illumination optical system has a ring stop disposed in the vicinity of a position conjugate with the image-side focal plane of the objective lens. On the side, a phase ring having a shape that is disposed at a position conjugate with the ring stop and covers the opening of the image of the ring stop is configured. When the transmittance of the phase ring is μ [%], the following formula 5 ≦ μ ≦ 20
It is configured to satisfy More preferably, 11 ≦ μ ≦ 17
It is.

  In such a phase contrast microscope according to the present invention, it is preferable that the magnification of the objective lens is 10 times or 40 times.

  In the phase contrast microscope according to the present invention, the sample is preferably asbestos.

  When the phase-contrast microscope according to the present invention is configured as described above, even if it is a mineral fiber such as asbestos with a very small amount of phase difference, the image has high contrast and is not overlooked.

  Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings. In this embodiment, an asbestos inspection microscope having not only a phase difference objective lens including a phase ring but also a dispersion objective lens including a light shielding ring will be described as an example of the phase difference microscope according to the present invention. First, the configuration of the asbestos inspection microscope 1 will be described with reference to FIG. This asbestos inspection microscope 1 is an upright type, a base 2, an upright base 3, an arm 4, an illumination lens unit 5, a sample stage 6, a stage drive unit 7, a revolver 8, a phase difference objective lens 9, a dispersion objective. A lens 10, an observation lens barrel 11, and an eyepiece lens barrel 12 are provided. An upright base 3 is erected on the base 2, and an arm 4 extends horizontally above the upright base 3. A light source 13 is provided on the rear surface of the base 2 (left side in FIG. 1). An illumination lens unit 5 and a stage driving unit 7 are attached to the front surface of the upright base 3. The stage driving unit 7 moves the sample stage 6 on which the sample S is placed up and down in the direction of the optical axis AX and holds the sample stage 6 so as to be rotatable around the optical axis AX. A revolver 8 for inserting and removing the phase difference objective lens 9 and the dispersion objective lens 10 with respect to the optical path is provided at the lower end of the arm 4, and an observation barrel 11 is provided at the upper end of the arm 3. An eyepiece lens barrel 12 is connected to the distal end portion of the observation barrel 11.

  Hereinafter, the arrangement of the optical system of the asbestos inspection microscope 1 along the optical path will be described. The light source unit 13 houses a light source 21 (for example, a halogen lamp or a tungsten lamp that emits white light). Inside the base 2 are housed a collimator lens 22 and a mirror 23 that reflects the illumination light upward. The illumination lens unit 5 holds a ring diaphragm 24 and a condenser lens 25. A condenser lens 25 includes the illumination optical system 20 from these light sources 21.

  The phase difference objective lens 9 has an objective lens 30 and a phase ring 31. The observation barrel 11 houses an analyzer 32, a depolarizer 33, an imaging lens 34, and a prism 35. Here, the analyzer 32 can rotate around the optical axis AX. The prism 35 is arranged so that the light reaching the prism 35 is separated into two, and one is guided to an eyepiece lens 36 and the other is guided to an imaging device (not shown).

  Now, the operation of the optical system of the asbestos inspection microscope 1 will be described with reference to FIG. The illumination light L 1 emitted from the light source 21 is converted into a parallel light beam by the collimator lens 22 and enters the ring diaphragm 24. Here, the ring aperture 24 has a ring-shaped opening 24a as shown in FIG. The illumination light L1 passes through the opening 24a of the ring diaphragm 24, and is then irradiated on the sample S by the condenser lens 25, and the sample S is Koehler illuminated. When the illumination light L1 illuminates the sample S, transmitted light (also referred to as 0th-order diffracted light) directly transmitted through the sample S and diffracted light diffracted by the sample S are generated. That is, the light L2 from the sample S includes transmitted light and diffracted light. In FIG. 2, the transmitted light is indicated by a solid line and the diffracted light is indicated by a broken line. Note that the symbol AX represents the optical axis of the light L2 from the sample S.

  Light L 2 from the sample S, that is, transmitted light and diffracted light, is incident on the objective lens 30, converted into parallel light, and incident on a phase ring 31 disposed at a position conjugate with the ring diaphragm 24. As shown in FIG. 3B, the phase ring 31 is formed as a ring-shaped phase film on a disk-shaped member 31 that transmits light, and the phase ring (phase film) 31 is formed on the ring diaphragm 24. It is arranged at a position corresponding to the opening 24a (so as to cover the opening 24a). Thus, since the ring diaphragm 24 and the phase ring 31 are arranged at conjugate positions, among the light L2 from the sample S, transmitted light (0th order diffracted light) is incident on the phase ring 31, Diffracted light passes around it. Here, the light diffracted by the sample S (diffracted light) is shifted (delayed) by a quarter wavelength compared to the illumination light L1. On the other hand, the phase ring 31 is configured to shift (advance) the phase of transmitted light by a quarter wavelength and to absorb a part of this light and weaken the light quantity. Accordingly, the transmitted light is advanced by a quarter wavelength, and the amount of light is reduced. Then, the light (transmitted light and diffracted light) L <b> 2 that has passed through the phase ring 31 is imaged on the primary image plane I by the imaging lens 34. At this time, since the diffracted light and the transmitted light are shifted by a half wavelength, the sample images weaken each other and become a dark image, the background becomes bright, and the contrast is formed as a whole. Further, when the phase of light transmitted through the phase ring 31 is delayed by a quarter wavelength, the wavelength shift is eliminated, so that the sample image becomes a bright image and the background becomes dark.

  Although not shown in FIG. 2, the analyzer 32 transmits only light having a specific polarization direction from the light L2 transmitted through the sample S. That is, by rotating the analyzer 32 around the optical axis AX, it is possible to separate and select only light having a specific linear polarization at a specific rotation angle from the light L2 having various polarization directions. That is, it can be confirmed whether the test object has birefringence like asbestos. By observing this sample image with the eyepiece lens 36, it is possible to clearly know the state (color tone, shape, etc.) of the sample S in a specific polarization direction. The analyzer 32 is mainly used together with the dispersion objective lens 10 and can be disposed at any position as long as it is behind the sample S along the optical path. It is desirable to dispose between the lens 9 or the dispersion objective lens 10 and the imaging lens 34.

  Further, the linearly polarized light that has passed through the analyzer 32 enters the depolarizer 33. The depolarizer 33 rotates the polarization plane of linearly polarized light to make circularly polarized light or elliptically polarized light. By disposing the depolarizer 33, the difference in optical characteristics depending on the polarization direction of linearly polarized light can be eliminated to make it isotropic. For example, although the reflectance at the prism 35 varies depending on the polarization direction, the sample image can be observed without depending on the polarization direction by using linearly polarized light as circularly polarized light. The depolarizer 33 can be disposed at an arbitrary position on the rear side of the analyzer 32 in the traveling direction of the light L2 from the sample S. However, the depolarizer 33 is connected to the rear side of the phase ring 31, or to the phase difference objective lens 9 or the dispersion objective lens 10. It is desirable to dispose it between the image lens 34.

  As described above, the circularly or elliptically polarized light that has passed through the depolarizer 33 forms an image on the primary image plane I by the imaging lens 34. By observing this sample image with the eyepiece 36, the state of the sample S can be known. Of course, the observation image may be captured by an imaging device (for example, a digital camera) and displayed on a display.

  In such an asbestos inspection microscope 1, in order to detect a minute object such as asbestos having a very small phase difference by using such a phase difference objective lens 9, the transmittance μ [% of the phase ring 31 is used. ] Must satisfy the following conditional expression (1).

5 ≦ μ ≦ 20 (1)

  Conditional expression (1) increases the contrast of an image of an extremely small object such as asbestos (for example, a fiber length of 2 to 3 μm or less, a diameter of 0.1 μm or less, a refractive index of about 1.5). Thus, it is a condition for sure detection. If the upper limit value of the conditional expression (1) is exceeded, the contrast of an object with a very small phase difference becomes low, and this object may not be recognized. On the other hand, if the lower limit of conditional expression (1) is not reached, the image becomes too dark and the object cannot be recognized. Here, in order to ensure the effect of the present embodiment, it is preferable to set the lower limit of conditional expression (1) to 11. Moreover, it is preferable to set the upper limit of conditional expression (1) to 17.

  The magnification of the objective lens 30 constituting the phase difference objective lens 9 is set to 10 times or 40 times, so that an image of a minute object such as asbestos can be reliably detected. As described above, since this asbestos inspection microscope 1 is provided with a plurality of objective lenses in the revolver 8 and can be inserted into and removed from the optical path, the 10 × and 40 × phase difference objective lenses, and the 10 × and 40 × By providing the revolver 8 with a double dispersion objective lens, not only observation by a phase difference but also observation by a dispersion staining method is possible.

  4 and 5 show line profiles of the test plate when the transmittance of the phase ring 31 is 14% and 45% in the phase difference objective lens 9 having the 40 × objective lens 30, respectively (transmission). When the rate is 14%, pattern 1 is set, and when the transmittance is 45%, pattern 2 is set.). Here, when the maximum value of the brightness of the image normalized by the average value of the brightness of the image is Max and the minimum value is Min, the maximum contrast C of such a line profile is defined by the following equation (2). Under the above-described conditions, the respective maximum contrasts C are as shown in FIG.

C = (Max−Min) / (Max + Min) (2)

  As can be seen from FIG. 6, by setting the transmittance μ of the phase ring (phase film) 31 so as to satisfy the conditional expression (1) (that is, by setting the pattern 1), the contrast is reduced. A high image can be observed. Note that, as shown in FIG. 7, by satisfying the conditional expression (1), even a very small object such as asbestos having a very small phase difference can be clearly recognized.

It is explanatory drawing which shows the structure of the microscope for asbestos inspection which concerns on this invention. It is explanatory drawing for demonstrating the optical system containing a phase difference objective lens. It is a top view which shows a ring stop and a phase ring, (a) shows a ring stop and (b) shows a phase ring. It is explanatory drawing which shows the line profile in the case of the pattern 1, and its brightness. It is explanatory drawing which shows the line profile in the case of the pattern 2, and its brightness. It is a table | surface which shows the maximum contrast in the case of the patterns 1 and 2. It is an asbestos photographed image, (a) is the case of pattern 1, (b) is the case of pattern 2.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Asbestos inspection microscope (phase contrast microscope) 20 Illumination optical system 24 Ring stop 24a Aperture 30 Objective lens 31 Phase ring S Sample

Claims (3)

In order from the light source, an illumination optical system that irradiates the sample with light from the light source, and an objective lens that collects the light transmitted through the sample and forms an image,
In the illumination optical system, having a ring stop disposed in the vicinity of a position conjugate with the image side focal plane of the objective lens,
The image side of the objective lens is arranged at a position conjugate with the ring diaphragm, and has a phase ring shaped to cover the opening of the image of the ring diaphragm,
When the transmittance of the phase ring is μ [%], the following formula 5 ≦ μ ≦ 20
Satisfactory phase contrast microscope.   The phase contrast microscope according to claim 1, wherein a magnification of the objective lens is 10 times or 40 times.   The phase contrast microscope according to claim 1, wherein the sample is asbestos.