Patent Application
20080094710
The present invention relates to a Fresnel's zone plate having a complex illumination function in which opaque bands and transparent bands are arranged alternately in the radial direction from the center of a transparent substrate, and to an X-ray microscope with no objective lens, using such a Fresnel's zone plate as a complex illumination lens.
In X-ray microscopes of the type that obtains a high-resolution transmission image of an object using X-ray source, there is known one that uses a Fresnel's zone plate as an objective lens (see Patent Document 1, for example).
The Fresnel's zone plate is produced by forming a group of a plurality of concentric circles so that the diameter Rn of an n-th circle counted from the center is proportional to the square root of n on a transparent substrate that transmits X-ray, and arranging opaque bands (black circles) and transparent bands (white circles) alternately in the radial direction from the center, as shown in
In such a Fresnel's zone plate, it is possible to increase the resolution by decreasing the width of the outermost opaque band (the outermost zone width), and a Fresnel's zone plate having resolution in the order of 1 μm is available at present as a result of development in fine processing technique.
Patent Document 1: Japanese Laid-Open Patent Publication No. 10-104400
However, because of the limitation of fine processing technique in production of a Fresnel's zone plate, it was still difficult to obtain an image of such high resolution as exceeding 1 μm only by decreasing the width of the outermost opaque band of the Fresnel's zone plate.
In an optical system of an X-ray microscope using a conventional Fresnel's zone plate, since a Fresnel's zone plate for focusing is arranged directly before a sample and an observation area of the sample is covered, a plane wave emitted from the Fresnel's zone plate is used as a sample illumination wave for illuminating the sample. In other words, conventional Fresnel's zone plates lack the function of illuminating a sample with a plane wave with no phase turbulence while illuminating a recording surface of the X-ray microscope with a plane wave (reference wave) emitted from the Fresnel's zone plate (complex illumination function). Therefore, conventionally, a portion of a plane wave disturbed by the Fresnel's zone plate is used as a sample illumination wave, which is also one factor of making it difficult to obtain an image of high resolution.
The present invention was made in light of the above problems, and it is an object of the present invention to provide a Fresnel's zone plate having a complex illumination function capable of improving resolution even when the outermost opaque band width cannot be reduced and an X-ray microscope with no objective lens, using the Fresnel's zone plate as a complex illumination lens.
In order to achieve the above object, a Fresnel zone plate according to claim 1 having a complex illumination function is characterized in that a transmission window is formed in the Fresnel zone plate such that a portion of a plane wave vertically applied onto the upper surface of the Fresnel zone plate directly and vertically enters a sample disposed below the Fresnel zone plate without being disturbed by the Fresnel zone plate, the Fresnel zone plate being formed by concentrically arranging an opaque band and a transparent band alternately in a radial direction from the center on a flat transparent substrate.
A Fresnel zone plate according to claim 2 having a complex illumination function is characterized in that a portion of the Fresnel zone plate is excised in an axial direction such that a portion of a plane wave vertically applied onto the upper surface of the Fresnel zone plate directly and vertically enters a sample disposed below the Fresnel zone plate without being disturbed by the Fresnel zone plate, the Fresnel zone plate being formed by concentrically arranging an opaque band and a transparent band alternately in a radial direction from the center on a flat transparent substrate.
A Fresnel zone plate according to claim 3 having a complex illumination function is characterized in that a transmission window is formed in the Fresnel's zone plate and a portion of the Fresnel's zone plate is excised in an axial direction such that a portion of a plane wave vertically applied onto the upper surface of the Fresnel's zone plate directly and vertically enters a sample disposed below the Fresnel's zone plate without being disturbed by the Fresnel's zone plate, the Fresnel's zone plate being formed by concentrically arranging an opaque band and a transparent band alternately in a radial direction from the center on a flat transparent substrate.
The Fresnel's zone plate having a complex illumination function according to claim 1 or 3, wherein the transmission window is formed by not disposing the opaque band.
The Fresnel's zone plate having a complex illumination function according to claim 1 or 3, wherein the transmission window is formed by providing a face-excised portion in the transparent substrate.
The Fresnel's zone plate having a complex illumination function according to any one of claims 1, 3, 4 and 5, wherein the transmission window is polygonal.
The Fresnel's zone plate having a complex illumination function according to any one of claims 1, 3, 4 and 5, wherein the transmission window is circular.
The Fresnel's zone plate having a complex illumination function according to any one of claims 1, 3, and 4 to 7, wherein two or more transmission windows are formed.
The Fresnel's zone plate having a complex illumination function according to claim 1 or 3, wherein two or more transmission windows are formed, and at least one of the transmission windows is formed by not disposing the opaque band while at least one of the transmission windows is formed by providing a face-excised portion in the transparent substrate.
The Fresnel's zone plate having a complex illumination function according to claim 1 or 3, wherein two or more transmission windows are formed, and at least one of the transmission windows is polygonal while at least one of the transmission windows is circular.
The Fresnel's zone plate having a complex illumination function according to claim 1 or 3, wherein two or more transmission windows are formed, at least one of the transmission windows is formed by not disposing the opaque band while at least one of the transmission windows is formed by providing a face-excised portion in the transparent substrate, and at least one of the transmission windows is polygonal while at least one of the transmission windows is circular.
The Fresnel's zone plate having a complex illumination function according to claim 2 or 3, wherein the excised portion of the Fresnel's zone plate is an approximately half of the Fresnel's zone plate that is zoned by a straight line passing through the approximate center of the Fresnel's zone plate.
The Fresnel's zone plate having a complex illumination function according to claim 2 or 3, wherein the excised portion of the Fresnel's zone plate is a part of the Fresnel's zone plate that is zoned by a polygon including a part of a circumference of the Fresnel's zone plate.
The Fresnel's zone plate having a complex illumination function according to claim 2 or 3, wherein the excised portion of the Fresnel's zone plate is a part of the Fresnel's zone plate that is zoned by a part of a circumference of the Fresnel's zone plate and a circular arc.
The Fresnel's zone plate having a complex illumination function according to any one of claims 2, 3, 13 and 14, wherein portions of the Fresnel's zone plate are excised in two or more positions.
The Fresnel's zone plate having a complex illumination function according to claim 2 or 3, wherein portions of the Fresnel's zone plate are excised in two or more positions, and at least one of the excised portions is a part of the Fresnel's zone plate that is zoned by a polygon including a part of a circumference of the Fresnel's zone plate while at least one of the excised portions is a part of the Fresnel's zone plate that is zoned by a part of the circumference of the Fresnel's zone plate and a circular arc.
An X-ray microscope with no objective lens, using one or more Fresnel's zone plate(s) each having a complex illumination function according to any one of claims 1 to 16 as a complex illumination lens.
According to the invention of claim 1, by forming a transmission window in the Fresnel's zone plate, it is possible to allow a perfect plane wave with no phase turbulence (for example, a plane wave of soft X-ray) to vertically enter a sample disposed below the Fresnel's zone plate. Therefore, the phase of the plane wave entering the sample has no turbulence as in the case of using a Fresnel's zone plate of the type that makes a portion of a wave emitted from the Fresnel's zone plate enter the sample as a plane wave. As a result, it is possible to improve the resolution without reducing the width of the outermost opaque band of the Fresnel's zone plate. Therefore, it is possible to obtain an image of such high resolution as exceeding 0.1 μm by reducing the width of the outermost opaque band as small as possible, and forming a transmission window.
According to the invention of claim 2, by excising a portion of the Fresnel's zone plate in the axial direction, it is possible to allow a perfect plane wave with no phase turbulence to vertically enter a sample disposed below the Fresnel's zone plate. Therefore, as in the above case, no phase turbulence occurs in the plane wave entering the sample, so that it is possible to improve the resolution without reducing the width of the outermost opaque band. Therefore, by reducing the width of the outermost opaque band as small as possible and making the plane wave enter the Fresnel's zone plate and the region created by excising a portion of the Fresnel's zone plate, it is possible to obtain an image of such high resolution as exceeding 0.1 μm.
According to the invention of claim 3, by forming a transmission window in the Fresnel's zone plate and excising a portion of the Fresnel's zone plate in the axial direction, it is possible to allow a perfect plane wave with no phase turbulence to vertically enter a sample disposed below the Fresnel's zone plate. Therefore, likewise the above, the phase of the plane wave entering the sample has no turbulence, so that it is possible to improve the resolution without reducing the width of the outermost opaque band. Therefore, by reducing the width of the outermost opaque band as small as possible and making the plane wave enter the Fresnel's zone plate and the region created by excising a portion of the Fresnel's zone plate, it is possible to obtain an image of such high resolution as exceeding 0.1 μm.
According to the invention of claim 4, the transmission window is formed by not disposing an opaque band. Therefore, it is possible to easily form the transmission window.
According to the invention of claim 5, the transmission window is formed by providing a face-excised portion in the transparent substrate. Therefore, it is possible to reduce the production cost by reducing the material for the transparent substrate required for production of the Fresnel's zone plate.
According to the invention of claim 6, the transmission window is in a polygonal shape. Therefore, the shape of the transmission window may be appropriately adapted to the shape of the sample.
According to the invention of claim 7, the transmission window is in a circular shape. Therefore, it is possible to easily form the transmission window.
According to the invention of claim 8, two or more transmission windows are formed. Therefore, it is possible to allow a perfect plane wave with no phase turbulence to vertically enter two or more samples, or two or more positions in a sample.
According to the invention of claim 9, two or more transmission windows are formed, and at least one of the transmission windows is formed by not disposing an opaque band while at least one of the transmission windows is formed by providing a face-excised portion in the transparent substrate. Therefore, it is possible to allow a perfect plane wave with no phase turbulence to vertically enter two or more samples, or two or more positions in a sample; it is possible to easily form the transmission window; and it is possible to reduce the production cost by reducing the material for the transparent substrate required for production of the Fresnel's zone plate.
According to the invention of claim 10, two or more transmission windows are formed, and at least one of the transmission windows is polygonal while at least one of the transmission windows is circular. Therefore, it is possible to allow a perfect plane wave with no phase turbulence to vertically enter two or more samples, or two or more positions in a sample; the shape of the transmission window may be appropriately adapted to the shape of the sample; and it is possible to easily form the transmission window.
According to the invention of claim 11, two or more transmission windows are formed, at least one of the transmission windows is formed by not disposing an opaque band while at least one of the transmission windows is formed by providing a face-excised portion in the transparent substrate, and at least one of the transmission windows is polygonal while at least one of the transmission windows is circular. Therefore, it is possible to allow a perfect plane wave with no phase turbulence to vertically enter two or more samples, or two or more positions in a sample. Also, it is possible to easily form the transmission window; it is possible to reduce the production cost by reducing the material for the transparent substrate required for production of the Fresnel's zone plate; the shape of the transmission window may be appropriately adapted to the shape of the sample; and it is possible to easily form the transmission window.
According to the invention of claim 12, the excised portion of the Fresnel's zone plate is approximately a half of the Fresnel's zone plate that is zoned by a straight line passing the approximate center of the Fresnel's zone plate. Therefore, the excised Fresnel's zone plate may also be used as a complex illumination lens for an X-ray microscope. In other words, two Fresnel's zone plates having higher resolution can be produced from one Fresnel's zone plate, so that the production cost for the Fresnel's zone plates can be reduced. Also, production of the Fresnel's zone plate is facilitated compared to the case where a transmission window is formed in the Fresnel's zone plate.
According to the invention of claim 13, the excised portion of the Fresnel's zone plate is a part of the Fresnel's zone plate that is zoned by a polygon including a part of circumference of the Fresnel's zone plate. Therefore, it is possible to appropriately allow a perfect plane wave with no phase turbulence to vertically enter the sample in accordance with the shape of the sample.
According to the invention of claim 14, the excised portion of the Fresnel's zone plate is a part of the Fresnel's zone plate that is zoned by a part of the circumference of the Fresnel's zone plate and a circular arc. Therefore, it is possible to easily produce the Fresnel's zone plate.
According to the invention of claim 15, portions of the Fresnel's zone plate are excised in two or more positions. Therefore, it is possible to allow a perfect plane wave with no phase turbulence to vertically enter two or more samples, or two or more positions in a sample.
According to the invention of claim 16, portions of the Fresnel's zone plate are excised in two or more positions, and at least one of the excised portions is a part of the Fresnel's zone plate that is zoned by a polygon including a part of the circumference of the Fresnel's zone plate while at least one of the excised portions is a part of the Fresnel's zone plate that is zoned by a part of the circumference of the Fresnel's zone plate and a circular arc. Therefore, it is possible to allow a perfect plane wave with no phase turbulence to vertically enter two or more samples, or two or more positions in a sample. Also, it is possible to appropriately allow a perfect plane wave with no phase turbulence to vertically enter the sample in accordance with the shape of the sample, and it is possible to easily produce the Fresnel's zone plate.
According to the invention of claim 17, there is provided an X-ray microscope with no objective lens, using a Fresnel's zone plate having a complex illumination function according to any one of claims 1 to 16 as a complex illumination lens. Therefore, it is possible to obtain an image of such high resolution as exceeding 0.1 μm.
By designing the portion to be excised to be substantially a half of the Fresnel zone plate, the excised Fresnel zone plate may also be used as a complex illumination lens of the X-ray microscope. In other words, two Fresnel zone plates having higher resolution can be produced from one Fresnel zone plate, so that the production cost of Fresnel zone plates can be reduced. This is also advantageous in that production of Fresnel zone plate is facilitated compared to the case where a transmission window is formed in the Fresnel zone plate.
In the following, embodiments of the present invention will be described based on the attached drawings.
The transparent substrate 2 is made of a material that easily transmits X-ray, for example, SiN (silicon nitride). The shape and dimension of the transparent substrate 2 are not particularly limited, however, in the present embodiment, it is formed into a flat-plate shape having a circular cross section in the horizontal direction, measuring about 0.625 mm in diameter, and about 0.5 μm in thickness.
The opaque bands 3 are portions that fail to transmit X-ray and the like, and are formed on the transparent substrate 2, for example, by arranging flat plates of Ta concentrically. In the present example, the innermost radius (radius of inner most opaque band 3) is about 7.071 μm, the zone number (total of the number of opaque bands 3 and the number of transparent bands 4) is about 1952, and the zone width of the outermost shell (line width of the outermost opaque band 3) is about 80 nm so as to improve the resolution. The material that forms the opaque bands 3 is not particularly limited, and any material may be used instead of Ta insofar as it does not transmit X-ray. The Fresnel's zone plate 1 may be produced by fine processing techniques (for example, sputtering deposition, ion beam sputtering, electron beam lithography).
In the following, description will be made for an optical system of an X-ray microscope 5 with no objective lens that uses the Fresnel's zone plate 1 as a complex illumination lens. The description centers on principal elements of the X-ray microscope 5 according to an embodiment of the present invention while omitting description for the elements that are essentially provided in a general X-ray microscope.
The X-ray microscope 5 obtains a high-resolution transmission image of an object by using soft X-ray which inflicts little damage on biological samples and has a facility of observing an organism with high resolution and no dying, as an optical source, and the Fresnel's zone plate 1 as a complex illumination lens. As shown in the figure, as to the Fresnel's zone plate 1 used as a complex illumination lens by the X-ray microscope 5, the Fresnel's zone plate 1 is provided with a transmission window 7 so that a portion of a plane wave of soft X-ray vertically applied onto the upper surface of the Fresnel's zone plate 1 will directly and vertically enter a sample 6 disposed below the Fresnel's zone plate 1 without being disturbed by the Fresnel's zone plate 1. The transmission window 7, the size of which is not particularly limited, is formed in accordance with the size of the sample 6 disposed below the Fresnel's zone plate 1. In other words, it is formed into such a size that allows a portion of the plane wave vertically applied from above the Fresnel's zone plate 1 to directly and vertically enter the entire upper surface of the sample 6 without being disturbed under the influence of the Fresnel's zone plate 1.
As shown in
The X-ray microscope 5 has a plate supporting member (not illustrated) for supporting the Fresnel's zone plate 1 serving as a complex illumination lens, and is able to finely adjust the position of the Fresnel's zone plate 1 in the vertical, back-and-forth, and horizontal directions by displacing the plate supporting member.
Also below the Fresnel's zone plate 1, a sample stage 8 for supporting the sample 6 is provided, and by displacing the sample stage 8, the position of the sample 6 can be finely adjusted in the vertical, back-and-forth, and horizontal directions.
Therefore, a user can easily conduct horizontal positioning of the transmission window 7 of the Fresnel's zone plate 1 and the sample 6 on the sample stage 8 by displacing either one or both of the plate supporting part and the sample stage 8.
After positioning the transmission window 7 of the Fresnel's zone plate 1 and the sample stage 8 in this manner, a plane wave of X-ray (soft X-ray) is vertically applied to the upper surface of the Fresnel's zone plate 1 from an optical source which is not illustrated (for example, from a synchrotron optical source having strong directivity), then the plane wave is focused by the Fresnel's zone plate 1, and a point optical source 0 is formed by the focused waves emitted from the Fresnel's zone plate 1. The sample stage 8 is provided with a PH (pinhole) 9 by which diffracted waves of unnecessary orders are removed from the focused waves emitted from the Fresnel's zone plate 1. Then, a reference wave (spherical wave) 10 is emitted from the point optical source 0. The point optical source 0 is formed at the position where the distance from a recording surface (observation surface) 11 is equal to the distance from the recording surface 11 to the sample 6. As an optical source for illuminating the Fresnel's zone plate 1 with soft X-ray, a laser plasma source, an electron beam exciting X-ray tube and the like may be used. Further, application to an optical microscope is possible when visible light is used for the optical source.
On the other hand, the plane wave vertically applied to the transmission window 7 of the Fresnel's zone plate 1 runs straight via the transmission window 7 without being focused by the Fresnel's zone plate 1, and directly and vertically enters, as the sample illumination wave, the upper surface of the sample 6 which is disposed on the same plane as the point optical source 0 and at the same position as the transmission window 7 when seen horizontally. Then, an object wave (spherical wave) 12 is emitted from the sample 6.
Sequentially, the object wave 12 having passed the sample 6 and the reference wave 10 not having passed the sample 6 interfere with each other on the recording surface 11, so that interference fringes are formed on the recording surface 11. The sample 6 and the recording surface 11 are so arranged that complex amplitudes (phase and amplitude) of the object wave 12 and the reference wave 10 in the recording surface 11 are Fourier transform images of complex amplitudes of the sample 6 and the reference wave point optical source 0, respectively, or in other words, a Fourier transform holography optical system is formed. In this manner, a hologram is optically formed by recording information of the complex amplitude (phase and amplitude) of the object wave 12 on the recording surface 11 with the use of the interferential action of light wave.
Through one Fourier transform of the hologram thus obtained by application of the Fourier transform holographic method with the use of a computer not illustrated, an enlarged structure of the sample 6 can be reproduced.
Now, the plane wave vertically entering the sample 6 shown in
Therefore, according to the Fresnel's zone plate 1, since the Fresnel's zone plate is made to function as a beam splitter, a plane wave having phase turbulence due to disturbance by the Fresnel's zone plate will not vertically enter the sample as is the case with the conventional X-ray microscope in which transmitted 0-order light having transmitted the Fresnel's zone plate vertically enters the sample as the sample illumination wave. Accordingly, an image having higher resolution compared with the case of using a conventional Fresnel's zone plate (reproduced image exceeding 0.1 μm) can be obtained.
In the present embodiment, description was made for the case where the transmission window 7 is formed by providing the transparent substrate 2 of the Fresnel's zone plate 1 with a face-excised portion, however, the face-excised portion may not be formed and the opaque band 3 may not be provided at the position corresponding to the sample 6 in the Fresnel's zone plate 1 so that a portion of the plane wave vertically applied to the upper surface of the Fresnel's zone plate 1 directly and vertically enters the sample 6 disposed below the Fresnel's zone plate 1 without being disturbed by the Fresnel's zone plate 1. In this case, however, since the plane wave vertically applied passes the transparent band 4, the phase may be disturbed more or less, to deteriorate the resolution. Therefore, it is more preferred to form the transmission window 7 as described in the present embodiment.
The position, shape, and number of the transmission window 7 are not limited to those of the example shown in
Next, description will be made on a Fresnel's zone plate 13 according to a modification of the embodiment described above. In the following description, different points are mainly described while those having the same structures as in the Fresnel's zone plate 1 are designated by the same reference numerals and description thereof will be omitted.
The position, shape and number of the portion to be excised in the Fresnel's zone plate are not limited to those of the example shown in
The Fresnel's zone plate 13 may be obtained by excising a portion in the axial direction as described above, or by forming into a shape in which a portion of the Fresnel's zone plate is excised in advance; otherwise obtained in any methods without limited to the above methods insofar as it allows a plane wave to vertically enter the sample 6 disposed below the Fresnel's zone plate.
According to the present Fresnel's zone plate 13, it is possible to allow a perfect plane wave with no phase turbulence to vertically enter the sample 6 as in the case of the Fresnel's zone plate 1, so that an image of still higher resolution can be obtained in comparison with the conventional Fresnel's zone plate. Since the Fresnel's zone plate 13 can be fabricated by excising a portion of the Fresnel's zone plate in the axial direction (substantial half in the present embodiment) as described above, it can be fabricated easily and with lower cost compared to the Fresnel's zone plate 1 in which the transmission window 7 is formed.
When a substantial half of the Fresnel's zone plate is excised as described above, the portion excised for producing the Fresnel's zone plate 13 is substantially identical to the Fresnel's zone plate 13. In other words, it is possible to produce two Fresnel's zone plates 13 from one Fresnel's zone plate as shown in
Further, the Fresnel's zone plate may be a Fresnel's zone plate 14 obtained by excising a part of the Fresnel's zone plate and forming the transmission window 7. That is, as shown in
Configurations of the Fresnel's zone plate 1, the Fresnel's zone plate 13 and the X-ray microscope 5 shown in the present embodiment are merely one aspect of the Fresnel's zone plate and X-ray microscope according to the present invention, and it goes without saying that the design may be appropriately changed without departing from the subject matter of the present invention, and may be realized, for example, as an optical microscope using a laser beam as an optical source. The X-ray microscope may use one of the Fresnel's zone plate 1, Fresnel's zone plate 13, and Fresnel's zone plate 14, or may use a plurality of the Fresnel's zone plates. In the latter case, the plurality of the Fresnel's zone plates may be those of different aspects.
The present invention is also applicable to an optical microscope using visible light as an optical source as well as to a Fresnel's zone plate and an X-ray microscope using the Fresnel's zone plate, for example.
| Number | Date | Country | Kind |
|---|---|---|---|
| P2005-121990 | Apr 2005 | JP | national |
| Number | Date | Country | |
|---|---|---|---|
| Parent | 11912013 | US | |
| Child | 11950916 | Dec 2007 | US |
