JP2014215175A - X-ray waveguide - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an X-ray waveguide capable of improving the selective permeation performance of an X-ray beam.SOLUTION: The X-ray waveguide comprises: a core having a periodic structure including regions a, b and c in which two basic structures with different refractive index real parts are periodically arranged; and two clads holding the core therebetween. An X-ray total reflection critical angle on a boundary face between the clad and the periodic structure is larger than a Bragg angle due to a structural period of the core, and a total reflection critical angle on a boundary face between the basic structures with different refractive index real parts forming the periodic structure of the core is smaller than the Bragg angle. A difference of the refractive index real parts between the basic structures of the regions is larger in a direction from the region a having the smallest difference between the refractive index real parts of the two basic structures toward the region b in contact with one of the clads. A difference of the refractive index real parts between the basic structures of the regions is larger in a direction from the region a toward the region c in contact with the other of the clads, or is the same.

Description

  The present invention relates to an X-ray waveguide that guides X-rays, and more particularly to an X-ray waveguide that uses a periodic structure as a core.

When dealing with electromagnetic waves with short wavelengths of several tens of nanometers or less, the difference in refractive index with respect to electromagnetic waves between different substances is as small as 10 ^-4 or less. In order to control such electromagnetic waves, large spatial optical systems have been used and are still mainstream. As a main part constituting the spatial optical system, there is a multilayer film reflecting mirror in which materials having different refractive indexes are alternately laminated, and plays various roles such as beam shaping, spot size conversion, wavelength selection and the like.

  In recent years, research has been conducted on X-ray waveguides that confine electromagnetic waves in a core surrounded by a clad and propagate them in order to reduce the size and increase the performance of the optical systems, which are the mainstream. (Non-Patent Document 1).

  In addition, the present inventors have proposed a type of waveguide composed of a core having a periodic structure and a clad that confines X-rays in the core by total reflection (Patent Document 1).

JP 2012-073232 A

Salditt, T .; Kruger, S .; P. Fuhse, C .; & Ba¨htz, C.I. High-transmission planar x-ray waveguides. “Physical Review Letters”. 100 (2008).

  However, the conventional X-ray waveguide has a problem to be improved.

  In NPL 1, in order to reduce the X-ray waveguide loss, the 0th-order mode having the smallest propagation angle among waveguide modes is mainly used. In an X-ray band electromagnetic wave, the refractive index difference (real part) between materials is extremely small, so that the propagation angle of the 0th-order mode is small, and as a result, it is necessary to produce a very small core in the X-ray waveguide. . Therefore, the area of X-rays to be propagated is reduced, the X-ray beam emitted from the X-ray waveguide is small, and the spatial range of spatial coherence, which is one of the features of the waveguide, is limited.

  In the X-ray waveguide of Patent Document 1, an X-ray waveguide using a periodic structure as a core is disclosed. In this X-ray waveguide, the waveguide mode that resonates with the periodicity of the core (hereinafter referred to as “transmission mode of X-ray beam” due to the waveguide mode that does not resonate with the periodicity of the core) Because of the high transparency of the X-ray beam caused by the periodic resonance waveguide mode), it can be transmitted selectively. As a result, it is possible to extract an X-ray beam having a wide spatial coherence compared to other single mode X-ray waveguides. However, there is a demand for further improving the selective transmission performance of the X-ray beam.

  The present invention has been made in view of such background art, and can further increase the difference in propagation loss coefficient between the periodic resonant waveguide mode and the uniform waveguide mode, and is derived from the periodic resonant waveguide mode. An X-ray waveguide capable of improving the selective transmission performance of an X-ray beam without lowering the transmission intensity of the X-ray beam is provided.

An X-ray waveguide according to the present invention that solves the above-described problems includes a core composed of a periodic structure formed by a plurality of regions in which two basic structures having different real refractive index portions are periodically arranged, and the core And an X-ray waveguide comprising two clads for confining X-rays in the core,
The critical angle of total reflection of X-rays at the interface between the cladding and the periodic structure is larger than the Bragg angle due to the structural period of the core, and the refractive index actual that forms the periodic structure of the core The critical angle for total reflection at the interface of the basic structure with different parts is smaller than the Bragg angle,
Of the plurality of regions, from the region a where the difference in the real part of the refractive index between the two basic structures is the smallest,
The difference in the real part of the refractive index between the basic structures in the region increases in the direction toward the region b including the interface between one of the two claddings and the periodic structure,
The difference in the real part of the refractive index between the basic structures in the region increases or does not differ in the direction from the region a toward the region c including the interface between the other of the two claddings and the periodic structure. It is characterized by.

  According to the present invention, the difference between the propagation loss coefficients of the periodic resonant waveguide mode and the uniform waveguide mode can be further increased, and without reducing the transmission intensity of the X-ray beam derived from the periodic resonant waveguide mode. An X-ray waveguide that can improve the selective transmission performance of a ray beam can be provided.

It is the schematic which shows one Embodiment of the X-ray waveguide of this invention. It is a figure which shows the comparison of the conventional X-ray waveguide and the X-ray waveguide of this invention. It is a figure which shows the comparison of the conventional X-ray waveguide and the X-ray waveguide of this invention. It is the schematic which shows one Embodiment of the curved X-ray waveguide of this invention. It is a figure which shows the comparison of the conventional X-ray waveguide and the curved X-ray waveguide of this invention. It is a figure which shows the comparison of the conventional X-ray waveguide and the curved X-ray waveguide of this invention. It is a figure which shows the result of an Example and a comparative example.

  Hereinafter, the present invention will be described in detail.

(Basic configuration)
FIG. 1 is a schematic view showing an embodiment of the X-ray waveguide of the present invention. In FIG. 1, an X-ray waveguide of the present invention includes a core 101 formed of a periodic structure formed by a plurality of regions in which two basic structures having different real refractive index portions are periodically arranged, and the core 101. And two clads 102 for confining X-rays in the core. A plurality of regions are configured by a region a103, a region b104, and a region c105, and the region a103 is sandwiched between the region b104 and the region c105. Of the plurality of regions, a region including an interface between one of the two claddings 102 and the periodic structure body from a region a103 having the smallest difference in real part of refractive index between the two basic structures. The difference in the real part of the refractive index between the basic structures in the region in the direction toward b104 increases, and the region a103 moves toward the region c105 including the interface between the other of the two claddings 102 and the periodic structure. The difference in the real part of the refractive index between the basic structures in the region in the direction is large or there is no difference.

  Further, in the X-ray waveguide of the present invention, as described later, the X-ray total reflection critical angle at the interface between the cladding and the periodic structure is larger than the Bragg angle due to the structural period of the core. And the total reflection critical angle in the interface of the basic structure in which the said refractive index real part which forms the periodic structure of the said core differs is smaller than the said Bragg angle, It is characterized by the above-mentioned.

(X-ray)
In the present invention, X-rays are electromagnetic waves in a wavelength band where the real part of the refractive index of a substance is 1 or less. Specifically, in the present invention, the X-ray refers to an electromagnetic wave having a wavelength of 100 nm or less including extreme ultraviolet light (Extreme Ultra Violet (EUV) light). Unlike the frequency band of electromagnetic waves (visible light and infrared rays) having a wavelength longer than the wavelength of ultraviolet light, the X-rays are different because the outermost electrons of a substance are extremely high and cannot respond to such short-wavelength electromagnetic wave frequencies. It is known that the real part of the refractive index of a substance is smaller than 1. The refractive index n of a substance for such X-rays is generally expressed by the following formula:

The amount of deviation δ from 1 in the real part and the imaginary part related to absorption

It is expressed using In general, unless δ and the intrinsic energy absorption edge contribute, δ and

Is proportional to the electron density ρ _e of the material. Therefore, in general, a substance having a higher electron density has a smaller refractive index real part. The real part of the refractive index is

It becomes. As described above, the refractive index of a substance with respect to X-rays is represented by a complex number. In this specification, the real part is referred to as a refractive index real part and the imaginary part is referred to as a refractive index imaginary part. In the X-ray band, the substance whose refractive index real part is 1 at maximum is a vacuum, and a gas typified by air has almost the same refractive index as that of vacuum, but the refractive index of almost all substances other than gas is real. The part has a value smaller than 1. In the present specification, the terms “component”, “material”, and “substance” also apply to gases such as vacuum and air.

(Relationship between core and clad)
The X-ray waveguide of the present invention guides the X-ray by confining the X-ray in the core by total reflection at the interface between the core and the clad. In order to realize this total reflection, in the X-ray waveguide of the present invention, the real part of the refractive index of the core at the interface between the core and the clad is larger than the real part of the refractive index of the clad. The total reflection critical angle at this time is expressed as θ _c-total with the angle from the interface.

(Containment relationship)
By confining the X-ray having the electric field intensity distribution resonating with such a periodic structure in the core by the clad, a waveguide mode resonating with the periodicity can be formed to guide the X-ray (periodic resonance waveguide). mode). On the other hand, the core of the X-ray waveguide according to the present invention is not an infinite periodic structure, but a periodic structure having a finite thickness sandwiched between clads. There is a waveguide mode (uniform waveguide mode) in the case of a uniform medium having an average refractive index.

  In contrast to the uniform waveguide mode, the periodic resonant waveguide mode in which the X-ray waveguide of the present invention appears has less loss than the uniform waveguide mode and has a uniform phase. The X-ray waveguide of the present invention is designed to satisfy the following conditions in order to form the above-described periodic resonant waveguide mode in addition to the uniform waveguide mode by total reflection at the interface between the cladding and the core ( (See FIG. 1).

The total reflection critical angle θ from the direction parallel to the film surface, where n _{clad is} the real part of the refractive index of the material on the clad side and n _core is the real part of the refractive index of the material on the core side at the interface between the clad and the core _c-total (°) is n _clad <n _core ,

It is expressed.

When the structural period of the periodic structure forming the core is d, the Bragg angle θ _B (°) is defined as follows regardless of the presence or absence of multiple diffraction in the core.

λ is the wavelength of X-rays. The physical property parameter of the substance constituting the X-ray waveguide of the present invention, the structure parameter of the waveguide, and the wavelength of the X-ray need to satisfy the following equations.

In the present invention, it is necessary that another condition is satisfied. When the periodic structure is composed of a plurality of components having different real parts of the refractive index, it is necessary to consider X-ray reflection at the interface between the components. In order for the X-ray waveguide of the present invention to function, multiple reflections originating from the periodic structure must occur. When total reflection occurs at the interface of the material constituting the periodic structure, for example, for a one-dimensional periodic structure, X-rays are confined in the component having the highest refractive index among the materials forming the laminated structure. As a result of the multiple interference being inhibited, the object of the present invention cannot be achieved. In other words, the unit constituting the periodic structure functions as a multi-total reflection X-ray waveguide, resulting in the same structure as a conventional flat plate waveguide. Therefore, it is necessary that the total reflection critical angle at the interface between components having different real parts of the refractive index forming the periodic structure of the core is smaller than the Bragg angle. This can be expressed as follows using mathematical formulas. When the total reflection critical angle between different components of the real part of the refractive index constituting the periodic structure of the core is an angle θ _c-multi (°), the following equation is satisfied.

  When the conditions described above are satisfied, the waveguide mode confined by total reflection at the interface between the clad and the core can be localized in the core. Effective propagation angle measured from the direction parallel to the membrane

Is represented by the following equation using a wave number vector (propagation constant) k _z in the propagation direction of the waveguide mode and a wave number vector k ₀ in vacuum.

  As described above, in the X-ray waveguide of the present invention, only the waveguide mode X-rays that resonate with the period of the regular structure due to multiple interference can be selectively propagated with low loss. This X-ray is in phase over the entire thickness of the core, that is, becomes a spatially coherent X-ray, and has a small divergence angle determined by the wavelength of the X-ray and the core structural period from the end face of the waveguide. It is emitted at.

  Even if the dimension of the X-ray waveguide of the present invention for confining X-rays is a one-dimensional structure in which a film-like core is sandwiched between clads, a core whose cross section perpendicular to the waveguide direction is a circle or a rectangle is used. It may be two-dimensionally surrounded by a clad. In the two-dimensional confinement type waveguide, X-rays are confined two-dimensionally in the waveguide, so that the divergence is suppressed compared to the one-dimensional confinement type, and an X-ray beam having a small beam size can be extracted.

(Clad material)
The total reflection critical angle θ _c− from the direction parallel to the film surface when the real part of the refractive index of the clad side material at the interface between the clad and the core is n _clad and the real part of the refractive index on the core side is n _{core. The total} (°) is expressed by Expression (A) as n _clad <n _core . The clad material of the X-ray waveguide of the present invention can be configured by other structural parameters and physical property parameters of the waveguide satisfying the formula (A). For example, when a multilayer film in which WO ₃ and B ₄ C are stacked with each other with a structural period of 15 nm is used as the region b or c, the clad can be made of Au, W, Ta, or the like.

  By adopting such a configuration, the X-ray waveguide of the present invention can resonate with periodicity, phase-control, form a periodic resonant waveguide mode with little loss, and guide X-rays.

(core)
The X-ray waveguide of the present invention is characterized in that a periodic structure made of a plurality of substances having different real parts of the refractive index is used for the core. Since the core has a periodic structure, the waveguide mode formed in the waveguide resonates with the periodic structure. Such a periodic structure of different real part of the refractive index, when the number of periods is infinite, forms a photonic band between the propagation constant and the angular frequency of the X-ray and has a specific mode that resonates with the periodicity of the core. Only X-rays can exist in this structure.

  The periodic structure is a structure in which basic structures are periodically arranged, a one-dimensional periodic structure in which they are stacked with a layered structure as a basic structure, and a two-dimensional periodic structure in which they are arranged with a cylindrical structure as a basic structure A three-dimensional periodic structure in which the cage structure is arranged as a basic structure can be exemplified. The waveguide mode formed in the waveguide of the present invention is caused by multiple reflection corresponding to each dimension of the periodic structure of the periodic structure. Such a mode is formed by periodicity, and the positions of the antinodes and nodes of the X-ray electric field distribution and electric field intensity distribution coincide with the positions in the respective substance regions constituting the basic structure. At that time, the propagation loss of the waveguide mode in which the electric field intensity of the X-ray is concentrated on the material having a large real part of the refractive index of the periodic structure is smaller than that of other waveguide modes. Can be taken out.

  Although the periodic structure in the present invention is different from a crystal in a strict sense, it can indicate the direction of the periodic arrangement of the basic structure in the same manner as the crystal orientation defined by the crystal. The crystal orientation of the periodic structure can be measured by X-ray diffraction or electron diffraction as with the crystal.

The characteristics of the X-ray waveguide of the present invention will be described using FIG. 2 in comparison with the conventional X-ray waveguide. In the X-ray waveguide of the present invention, the core is composed of the regions a, b, and c, and the region a is sandwiched between the regions b and c. Further, the difference in the real part of the refractive index between the components having different real parts of the refractive index forming the regions b and c is larger than the difference in the real part of the refractive index similarly defined in the region a (FIG. 2c). The features of the X-ray waveguide of the present invention will be described in comparison with the case where the core has a single periodic structure (in the case of only the region a, FIG. 2a). Here, as an example, the region a is composed of Al ₂ O ₃ and B ₄ C, the regions b and c are composed of WO ₃ and B ₄ C, and the X-ray waveguide is sandwiched between W claddings. It explains using the result of the simulation experiment by the finite element method. The total number of periods of the periodic structure is 100 and the structure period is 15 nm. In addition to the simulation experiment method used here, the X-ray waveguide of the present invention can be designed using a conventionally known theoretical examination or simulation method.

  FIG. 2 b shows the electric field intensity distribution of the waveguide mode formed when the core is only the region a. The electric field intensity distribution formed by the periodic resonant waveguide mode and the uniform waveguide mode (hereinafter referred to as the proximity waveguide mode) that has the closest propagation angle and the next lowest propagation loss coefficient after the periodic resonant waveguide mode. It can be confirmed that the electric field strength increases or decreases in accordance with the distribution of the real part of the refractive index of the periodic structure. However, the envelope functions of the two electric field strength distributions are different. In the periodic resonant waveguide mode, an envelope function having a convex portion at the center of the core is formed by resonance with the periodicity, whereas in the proximity waveguide mode, the upper and lower sides of the core are An envelope function having one convex portion at a time is formed (FIG. 2b).

  In the X-ray waveguide of the present invention, a region b having a large difference in the real part of the refractive index is formed in a portion corresponding to the skirt of the envelope function of the electric field intensity distribution in the periodic resonant waveguide mode (portion where electric field is relatively not concentrated) c is arranged so as to sandwich the region a (FIG. 2c).

In a periodic structure having a large difference in the real part of the refractive index, the intensity of multiple reflection due to the periodicity is increased and a resonance effect with the periodicity can be obtained, so that it is relatively concentrated in the regions b and c. An envelope function that is modulated into a periodic resonant waveguide mode and a proximity guided mode is formed (FIG. 2d). In the regions b and c, a material (WO ₃ ) having a high electron density is used in order to make the difference in the real part of the refractive index larger than that in the region a. The absolute value of the average refractive index imaginary part increases and the absorption loss increases. Because of the shape of the envelope function of the electric field strength in the case of the X-ray waveguide having only the region a (FIG. 2b), the proximity waveguide mode is more concentrated in the regions b and c than the periodic resonance waveguide mode. As a result, the difference between the two propagation loss coefficients becomes larger than that of the conventional X-ray waveguide.

FIG. 3 summarizes the results of a simulation experiment when the end portion of the region a having a period of 100 is replaced with regions b and c to form the X-ray waveguide of the present invention. The number of periods in regions b and c is the same, and the total N is summarized as a parameter. When N = 0 is only the region a (in the case of only a periodic structure composed of Al ₂ O ₃ and B ₄ C), N = 100 is when the region a is completely replaced by the regions b and c ( (In the case of only a periodic structure composed of WO ₃ and B ₄ C). The propagation loss coefficient (μ _R ) and transmittance (T _R ) of the periodic resonant waveguide mode and the propagation loss coefficient (μ _p ) and transmittance (T _p ) of the proximity waveguide mode are summarized.

Than when it is confirmed that mu _R increases as going replaces the region a in the region b and c (as N increases) (Fig. 3a), the value of mu _p - [mu] _R is N = 0 (Fig. 3b). That is, the propagation loss of the periodic resonant waveguide mode is increased, but the difference of the propagation loss from the adjacent waveguide mode is increased, and it is understood that the selective transmission performance of the periodic resonant waveguide mode is improved as compared with the conventional case. In an X-ray waveguide using a periodic structure as a core, the transmittance T _R of the periodic resonant waveguide mode and the selective transmission performance T _R / T _p are in a trade-off relationship. The selective transmission performance of the resonant waveguide mode is evaluated using the following formula (B).

Here, L is the length of the waveguide. From this equation, it can be seen that if the value of μ _p −μ _R is large, the selective transmission performance can be maintained or improved even if L is shortened. If L is short, it will increase the T _R. In the X-ray waveguide design, set the transmittance T _R of the periodic resonant waveguide mode required, it calculates a selected permeability T _{R /} T _p to be T _R and mu _R and mu _p-function To evaluate.

FIGS. 3c and 3d show the results of evaluating T _R / T _p against N when T _R = 10 ⁻² and T _R = 10 ⁻³ are set, respectively. At N = 50, both T _R / T _p are maximum, and it can be seen that this condition is preferable for the design value of the X-ray waveguide of the present invention. Further, in the case of T _R = 10 ⁻³ , the increase rate of T _R / T _{p with} respect to N = 0 (conventional X-ray waveguide) is larger, and when T _R is reduced, the X-ray waveguide of the present invention is reduced. It can be seen that the selective transmission performance of the periodic resonant waveguide mode becomes remarkable. This can also be seen from equation (B).

  Further, when the two basic structures constituting the region b of the X-ray waveguide of the present invention are s and t, the real part of the refractive index of the basic structure s in contact with the cladding is the refractive index of the basic structure t. When two basic structures that are smaller than the real part and constitute the region c are u and v, the refractive index real part of the basic structure u that is in contact with the cladding is larger than the refractive index real part of the basic structure v. Is preferably small.

(Material for periodic structures)
The periodic structure used for the core of the X-ray waveguide of the present invention is not particularly limited as long as it satisfies the above-described configuration of the waveguide of the present invention. A multilayer film produced by sputtering or vapor deposition, a periodic structure produced by a conventional semiconductor process such as photolithography, electron beam lithography, etching process, lamination, bonding, or the like can be used. Further, a mesostructured film or mesoporous material film formed by self-assembly can be used as the periodic structure of the core. It can be said that these are almost the only materials when using a periodic structure of two or more dimensions. This is because in the semiconductor process described above, it is almost impossible to form a two-dimensional or higher periodic structure having a period of about several tens of nanometers. In addition, oxidation degradation can be prevented by using an oxide as a material constituting the periodic structure.

  Since the difference in the refractive index of the core material contributes to the gap interval dependency of the modulation of the waveguide mode, the refractive index of the core material can be appropriately selected according to the required waveguide characteristics.

(Curved X-ray waveguide)
As another embodiment of the X-ray waveguide of the present invention, the core and the clad have a curved portion, and the curved portion of the core includes at least one of the region a, the region b, and the region c. The crystal orientation of at least part of the region a, at least part of the region b, and at least part of the region c is continuously changed along the X-ray propagation direction. A curved X-ray waveguide characterized in that

Further, in an X-ray waveguide including the core constituting the waveguide and a portion where the shape of the clad is curved, a circle defining a radius of curvature of an interface between one of the two clads and the core When the y-axis is defined in the normal direction from the interface toward the outside of the circle O with the center of O as the origin, the region a, the region b, and the region c are arranged in this order in the direction of increasing y. Have been
The difference between the real part of the refractive index of the region a and the difference between the real part of the refractive index of the region c are the same,
The difference in the real part of the refractive index of the region b is larger than the difference in the real part of the refractive index of the region a,
A curved X-ray waveguide characterized in that the difference in the real part of the refractive index in the region b is larger than the difference in the real part of the refractive index in the region c is preferable.

In the X-ray waveguide of the present invention, the selective transmission performance of the periodic resonance waveguide mode is further improved by using an X-ray waveguide (curved X-ray waveguide) having a curved portion as shown in FIG. 4A. Is possible. In the curved X-ray waveguide of the present invention, its radius of curvature is defined in the coordinate system as shown in FIG. Considering the core and two clads sandwiching it, the origin of the center of the circle O that defines the radius of curvature of the interface between the core and one of the clads, and the y-axis in the normal direction from the interface to the outside of the circle O Define. On the y axis, the interface between the core and the other clad is located at y coordinate = y ₁ which is larger than the y coordinate = y ₀ of the interface between the core and one clad. The radius of curvature R of the curved X-ray waveguide is y ₀ as the radius of the circle O. In FIG. 4b, r represents one of the axes in the cylindrical coordinate system, θ represents one of the axes in the cylindrical coordinate system, z represents one of the axes in the cylindrical coordinate system and the orthogonal coordinate system, and x represents one of the axes in the orthogonal coordinate system.

  In such an X-ray waveguide, at least one of the above crystal orientations formed by a periodic arrangement of basic structures made of materials having different real parts of refractive index, forming the regions a, b and c forming the core. One is continuously changing along the X-ray propagation direction, so that the core constituting the waveguide and the portion where the shape of the cladding is curved are formed. The crystal orientation represents a direction in which a plurality of basic structures are periodically arranged in the periodic structure.

  In the X-ray waveguide including the core constituting the waveguide and the portion where the shape of the cladding is curved in the present invention, the region c, the region a, and the region b are arranged in this order as the value of y is increased. And the difference between the real part of the refractive index in the region a and the region c is the same, and the difference between the real part of the refractive index in the region b is larger than the difference between the real part of the refractive index in the region a and the region c. , Especially noticeable.

  When considering a curved optical element such as the curved X-ray waveguide of the present invention, it is convenient to consider using a cylindrical coordinate system (rθz coordinate system). When converted from a cylindrical coordinate system to an orthogonal coordinate system (xyz coordinate system) and further approximated, the curved X-ray waveguide has a refractive index (complex refractive index) n (y) of y in the orthogonal coordinate system. Along the axis, it is synonymous with an uncurved X-ray waveguide modulated according to the following equation (C).

Similar to FIG. 2, FIG. 5 shows a comparison between the curved X-ray waveguide of the core having only the region a and the curved X-ray waveguide of the present invention. The top of the vertical axis in the figure is the positive direction of the y axis. Here, the regions a and c are composed of Al ₂ O ₃ and B ₄ C, the region b is composed of WO ₃ and B ₄ C, and an X-ray waveguide sandwiched between W claddings is taken as an example. It explains using the result of the simulation experiment by the finite element method. The radius of curvature is 5.0 m, the total number of periodic structures is 100, and the structural period is 15 nm. The difference in the real part of the refractive index between components having different real parts of the refractive index in the region b is larger than the difference in the real part of the refractive index similarly defined in the region a, while the actual refractive index in the region c is different. The difference between the parts is the same as that in the region a. Curved X-ray waveguide of region a only (FIG. 5a) The real part of the refractive index of the X-ray waveguide of the present invention (FIG. 5c) shows the real part of the refractive index modulated according to the equation (C). It has a trend that gradually increases from top to bottom.

  FIGS. 5b and 5d show the electric field strength distributions of the periodic resonant waveguide mode and the proximity waveguide mode formed in the X-ray waveguide having the configuration of FIGS. 5a and 5c. In the case of the core having only the region a, the electric field strength of the periodic resonant waveguide mode is smaller in the direction of the y-coordinate due to the curved X-ray waveguide than the uncurved X-ray waveguide of FIG. While the envelope function of the distribution is shifted, the envelope function of the near-waveguide mode is shifted in the direction in which the y coordinate is large. Therefore, as shown in FIG. 5c, a region b having a larger difference in the real part of the refractive index is arranged in a portion of the core having a relatively large y coordinate, while the difference in the real part of the refractive index in the region c is The configuration is the same as that of the region a.

  By arranging the periodic structure in this way, as shown in FIG. 4d, the envelope function of the electric field strength is higher in the proximity waveguide mode than in the periodic resonance waveguide mode, and the electron density is higher and the loss of X-rays. It shifts to the area | region b with larger. As a result, the difference in the propagation loss coefficient between the periodic resonance waveguide mode and the proximity waveguide mode becomes significant as compared with the X-ray waveguide having only the region a.

FIG. 6 summarizes the results of a simulation experiment in which an X-ray waveguide according to the present invention is formed by replacing a portion where the y coordinate of the region a having a period of 100 is large with the region b. Here, the region c has the same configuration as the region a. The number of periods N and the radius of curvature R of the region b are used as parameters, and are summarized using the same variables and evaluation methods as described in FIG. When N = 0 is only the region a (only in the case of a periodic structure composed of Al ₂ O ₃ and B ₄ C), N = 100 is when the region a is completely composed of the region b (WO ₃ And a periodic structure composed of B ₄ C). 6a and 6b, _{respectively,} T R = ^{10 -2} and _T R = ^{10 -3} when you set, the results of evaluation of the _T R / _{T p} calculated from the formula (B) with respect to N and R FIG. It can be seen that the selective transmission performance is further improved as compared with the uncurved X-ray waveguide of the present invention shown in FIG. Thus, the design value of the X-ray waveguide of the present invention can be determined based on the result of the simulation experiment.

  Hereinafter, the present invention will be described in more detail with reference to examples.

Example 1
In this example, the X-ray waveguide of the present invention uses tungsten as the cladding, a multilayer film made of B ₄ C and Al ₂ O _{3 in the} region a, and a multilayer film made of B ₄ C and WO _{3 in the} regions b and c. It is an example.

  The manufacturing method of the X-ray waveguide of the present embodiment includes the following steps by sputtering.

(A) Formation of cladding Tungsten is formed to a thickness of 30 nm on a Si substrate by magnetron sputtering.

(B) Formation of core Regions c are formed by alternately forming films in the order of WO ₃ and B ₄ C by magnetron sputtering. The thicknesses of WO ₃ and B ₄ C are 2.0 nm and 13.0 nm, respectively. WO ₃ and B ₄ C form 25 layers and 25 layers, respectively.

Subsequently, Al ₂ O ₃ and B ₄ C are alternately formed in this order by magnetron sputtering to produce region a. The thicknesses of Al ₂ O ₃ and B ₄ C are 2.0 nm and 13.0 nm, respectively. Al ₂ O ₃ and B ₄ C are formed in 50 layers and 50 layers, respectively.

Subsequently, the region b is formed by alternately forming films in the order of WO ₃ and B ₄ C by magnetron sputtering. The thicknesses of WO ₃ and B ₄ C are 2.0 nm and 13.0 nm, respectively. WO ₃ and B ₄ C form 26 and 25 layers, respectively.

(C) Formation of clad Tungsten is formed on the core to a thickness of 30 nm by magnetron sputtering.

(D) Determination of waveguide length The X-ray waveguide formed on the Si substrate is cut together with the Si substrate by using a dicing apparatus so that the waveguide length becomes 3.4 mm.

The obtained X-ray waveguide has a shape in which the core is sandwiched between clads, and the X-rays are confined in the core by total reflection at the interface between the core and the clad. According to this configuration, the relationship between the period of the multilayer film as the core and the real part of the refractive index of the material forming the core is θ _B <θ _c-total and θ _c-multi <θ _B
Meet. For example, for 8 keV X-rays, θc-total = 0.431 ° (total reflection critical angle at the interface between WO3 and tungsten), θB = 0.296 ° and θc-multi = 0.268 ° (WO3 and B4C X-rays are confined in the core by total reflection at the interface between the cladding and the core, and a periodic resonant waveguide mode can be formed.

  An X-ray is an interference pattern formed by X-rays (energy: 8 keV) incident from the end of the X-ray waveguide and formed by the emitted X-rays emitted from the end of the waveguide behind the waveguide (camera length: 1500 mm). Measure with a two-dimensional detector. The X-ray incident angle corresponding to the propagation angle of the waveguide mode is gradually changed, and the integrated value of the transmitted X-ray intensity is acquired at that time.

  FIG. 7 a shows the result of comparison between Comparative Example 1 and Example 1 described later. Compared with the conventional X-ray waveguide, the peak of the transmitted X-ray intensity by the periodic resonance waveguide mode is sharp, and it can be seen that the selective transmission performance is improved.

(Example 2)
In this example, the cladding is tungsten, the region a is a multilayer film composed of B ₄ C and Al ₂ O ₃ , the region b is a multilayer film composed of B ₄ C and WO ₃ , and the region c is B ₄ C and Al ₂ O _3. It is an example of the X-ray waveguide of this invention using the multilayer film which consists of. The region a and the region c have the same configuration and are not distinguished.

  The manufacturing method of the X-ray waveguide of the present embodiment includes the following steps by sputtering.

(A) Formation of cladding Tungsten is formed to a thickness of 30 nm on a Si substrate by magnetron sputtering.

(B) Formation of cores Regions c and a are formed by alternately forming films in the order of Al ₂ O ₃ and B ₄ C by magnetron sputtering. The thicknesses of Al ₂ O ₃ and B ₄ C are 2.0 nm and 13.0 nm, respectively, and the lowermost layer of the multilayer film is Al ₂ O ₃ . Al ₂ O ₃ and B ₄ C form 90 layers and 90 layers, respectively.

Subsequently, the region b is formed by alternately forming films in the order of WO ₃ and B ₄ C by magnetron sputtering. The thicknesses of WO ₃ and B ₄ C are 2.0 nm and 13.0 nm, respectively, and the lowermost and uppermost layers of the multilayer film are WO ₃ . WO ₃ and B ₄ C form 11 layers and 10 layers, respectively.

(C) Formation of clad Tungsten is formed on the core to a thickness of 30 nm by magnetron sputtering.

(D) Determination of waveguide length The X-ray waveguide formed on the Si substrate is cut together with the Si substrate by using a dicing apparatus so that the waveguide length becomes 4.9 mm.

The obtained X-ray waveguide has a shape in which the core is sandwiched between clads, and the X-rays are confined in the core by total reflection at the interface between the core and the clad. According to this configuration, the relationship between the period of the multilayer film as the core and the real part of the refractive index of the material forming the core is θ _B <θ _c-total and θ _c-multi <θ _B
Meet. For example, for 8 keV X-rays, θc-total = 0.431 ° (total reflection critical angle at the interface between WO3 and tungsten), θB = 0.296 ° and θc-multi = 0.268 ° (WO3 and B4C X-rays are confined in the core by total reflection at the interface between the cladding and the core, and a periodic resonant waveguide mode can be formed.

  An X-ray is an interference pattern formed by X-rays (energy: 8 keV) incident from the end of the X-ray waveguide and formed by the emitted X-rays emitted from the end of the waveguide behind the waveguide (camera length: 1500 mm). Measure with a two-dimensional detector. The X-ray incident angle corresponding to the propagation angle of the waveguide mode is gradually changed, and the integrated value of the transmitted X-ray intensity is acquired at that time.

  FIG. 7 b shows the result of comparison between Comparative Example 1 and Example 2 described later. Compared with the conventional X-ray waveguide, the peak of the transmitted X-ray intensity by the periodic resonance waveguide mode is sharp, and it can be seen that the selective transmission performance is improved.

Example 3
In this example, the curved X-ray guide of the present invention using tungsten as the cladding, a multilayer film made of B ₄ C and Al ₂ O _{3 in the} region a, and a multilayer film made of B ₄ C and WO _{3 in the} regions b and c. It is an example of a waveguide.

  The manufacturing method of the X-ray waveguide of the present embodiment includes the following steps by sputtering.

(A) Formation of cladding Tungsten is formed to a thickness of 30 nm on the convex surface of a glass substrate having a radius of curvature R of 0.5 m by magnetron sputtering.

(B) Formation of core Regions c are formed by alternately forming films in the order of WO ₃ and B ₄ C by magnetron sputtering. The thicknesses of WO ₃ and B ₄ C are 2.0 nm and 13.0 nm, respectively, and the lowermost layer of the multilayer film is WO ₃ . WO ₃ and B ₄ C form 5 layers and 5 layers, respectively.

Subsequently, Al ₂ O ₃ and B ₄ C are alternately formed in this order by magnetron sputtering to produce region a. The thicknesses of Al ₂ O ₃ and B ₄ C are 2.0 nm and 13.0 nm, respectively, and the lowermost layer of the multilayer film is Al ₂ O ₃ . Al ₂ O ₃ and B ₄ C form 90 layers and 90 layers, respectively.

Subsequently, the region b is formed by alternately forming films in the order of WO ₃ and B ₄ C by magnetron sputtering. The thicknesses of WO ₃ and B ₄ C are 2.0 nm and 13.0 nm, respectively, and the lowermost and uppermost layers of the multilayer film are WO ₃ . WO ₃ and B ₄ C form 6 layers and 5 layers, respectively.

(C) Formation of clad Tungsten is formed on the core to a thickness of 30 nm by magnetron sputtering.

(D) Determination of waveguide length The X-ray waveguide formed on the glass substrate is cut together with the glass substrate by using a dicing apparatus so that the waveguide length becomes 4.8 mm.

The obtained X-ray waveguide has a shape in which the core is sandwiched between clads, and the X-rays are confined in the core by total reflection at the interface between the core and the clad. According to this configuration, the relationship between the period of the multilayer film as the core and the real part of the refractive index of the material forming the core is θ _B <θ _c-total and θ _c-multi <θ _B
Meet. For example, for 8 keV X-rays, θc-total = 0.431 ° (total reflection critical angle at the interface between WO3 and tungsten), θB = 0.296 ° and θc-multi = 0.268 ° (WO3 and B4C X-rays are confined in the core by total reflection at the interface between the cladding and the core, and a periodic resonant waveguide mode can be formed.

  An X-ray is an interference pattern formed by X-rays (energy: 8 keV) incident from the end of the X-ray waveguide and formed by the emitted X-rays emitted from the end of the waveguide behind the waveguide (camera length: 1500 mm). Measure with a two-dimensional detector. The X-ray incident angle corresponding to the propagation angle of the waveguide mode is gradually changed, and the integrated value of the transmitted X-ray intensity is acquired at that time.

  FIG. 7 c shows the result of comparison between Comparative Example 1 and Example 3 described later. Compared with the conventional X-ray waveguide, the peak of the transmitted X-ray intensity by the periodic resonance waveguide mode is sharp, and it can be seen that the selective transmission performance is improved.

Example 4
In this example, the cladding is tungsten, the region a is a multilayer film composed of B ₄ C and Al ₂ O ₃ , the region b is a multilayer film composed of B ₄ C and WO ₃ , and the region c is B ₄ C and Al ₂ O _3. It is an example of the X-ray waveguide of this invention using the multilayer film which consists of. The region a and the region c have the same configuration and are not distinguished.

  The manufacturing method of the X-ray waveguide of the present embodiment includes the following steps by sputtering.

(A) Formation of clad Tungsten is formed with a thickness of 30 nm on a convex surface of a glass substrate having a curvature radius of 5.0 m by magnetron sputtering.

(B) Formation of cores Regions c and a are formed by alternately forming films in the order of Al ₂ O ₃ and B ₄ C by magnetron sputtering. The thicknesses of Al ₂ O ₃ and B ₄ C are 2.0 nm and 13.0 nm, respectively, and the lowermost layer of the multilayer film is Al ₂ O ₃ . Al ₂ O ₃ and B ₄ C form 60 layers and 60 layers, respectively.

Subsequently, the region b is formed by alternately forming films in the order of WO ₃ and B ₄ C by magnetron sputtering. The thicknesses of WO ₃ and B ₄ C are 2.0 nm and 13.0 nm, respectively, and the lowermost and uppermost layers of the multilayer film are WO ₃ . WO ₃ and B ₄ C form 41 layers and 40 layers, respectively.

(C) Formation of clad Tungsten is formed on the core to a thickness of 30 nm by magnetron sputtering.

(D) Determination of the waveguide length The X-ray waveguide formed on the glass substrate is cut together with the glass substrate by using a dicing apparatus so that the waveguide length becomes 4.4 mm.

The obtained X-ray waveguide has a shape in which the core is sandwiched between clads, and the X-rays are confined in the core by total reflection at the interface between the core and the clad. According to this configuration, the relationship between the period of the multilayer film as the core and the real part of the refractive index of the material forming the core is θ _B <θ _c-total and θ _c-multi <θ _B
Meet. For example, for 8 keV X-rays, θc-total = 0.431 ° (total reflection critical angle at the interface between WO3 and tungsten), θB = 0.296 ° and θc-multi = 0.268 ° (WO3 and B4C X-rays are confined in the core by total reflection at the interface between the cladding and the core, and a periodic resonant waveguide mode can be formed.

  An X-ray is an interference pattern formed by X-rays (energy: 8 keV) incident from the end of the X-ray waveguide and formed by the emitted X-rays emitted from the end of the waveguide behind the waveguide (camera length: 1500 mm). Measure with a two-dimensional detector. The X-ray incident angle corresponding to the propagation angle of the waveguide mode is gradually changed, and the integrated value of the transmitted X-ray intensity is acquired at that time.

  FIG. 7d shows the result of comparison between Comparative Example 1 and Example 4 described later. Compared with the conventional X-ray waveguide, the peak of the transmitted X-ray intensity by the periodic resonance waveguide mode is sharp, and it can be seen that the selective transmission performance is improved. In addition, the selective transmission performance is high as compared with the other examples, and it can be seen that appropriately designing the curved X-ray waveguide of the present invention is effective in improving the selective transmission performance.

(Comparative Example 1)
This comparative example is an example of a conventional X-ray waveguide in which the clad is made of tungsten and the core is made only of a multilayer film (region a) made of B ₄ C and Al ₂ O ₃ .

  As a method for producing the X-ray waveguide of this comparative example, the following steps by sputtering are listed.

(A) Formation of cladding Tungsten is formed to a thickness of 30 nm on a Si substrate by magnetron sputtering.

(B) Formation of core Region a is formed by alternately forming films of Al ₂ O ₃ and B ₄ C in this order by magnetron sputtering. The thicknesses of Al ₂ O ₃ and B ₄ C are 2.0 nm and 13.0 nm, respectively, and the lowermost and uppermost layers of the multilayer film are Al ₂ O ₃ . Al ₂ O ₃ and B ₄ C are formed as 101 layers and 100 layers, respectively.

(C) Formation of clad Tungsten is formed on the core to a thickness of 30 nm by magnetron sputtering.

(D) Determination of waveguide length The X-ray waveguide formed on the Si substrate is cut together with the Si substrate by using a dicing apparatus so that the waveguide length becomes 5.4 mm.

The obtained X-ray waveguide has a shape in which the core is sandwiched between clads, and the X-rays are confined in the core by total reflection at the interface between the core and the clad. According to this configuration, the relationship between the period of the multilayer film as the core and the real part of the refractive index of the material forming the core is θ _B <θ _c-total and θ _c-multi <θ _B
Meet. For example, for 8 keV X-rays, θc-total = 0.474 ° (total reflection critical angle at the interface between Al 2 O 3 and tungsten), θB = 0.296 ° and θc-multi = 0.182 ° (Al 2 O 3 and B 4 C X-rays are confined in the core by total reflection at the interface between the cladding and the core, and a periodic resonant waveguide mode can be formed.

  An X-ray is an interference pattern formed by X-rays (energy: 8 keV) incident from the end of the X-ray waveguide and formed by the emitted X-rays emitted from the end of the waveguide behind the waveguide (camera length: 1500 mm). Measure with a two-dimensional detector. The X-ray incident angle corresponding to the propagation angle of the waveguide mode is gradually changed, and the integrated value of the transmitted X-ray intensity is acquired at that time.

  FIG. 7 shows the result of Comparative Example 1 as a comparison with the example.

  The X-ray waveguide according to the present invention can provide an X-ray beam having a uniform phase, and can further adjust waveguide characteristics such as transmittance, Useful in imaging techniques.

101 Core 102 Cladding 103 Region a
104 region b
105 region c

Claims (5)

A core composed of a periodic structure formed by a plurality of regions in which two basic structures having different real refractive indexes are periodically arranged, and two clads for sandwiching the core and confining X-rays in the core An X-ray waveguide comprising:
The critical angle of total reflection of X-rays at the interface between the cladding and the periodic structure is larger than the Bragg angle due to the structural period of the core, and the refractive index actual that forms the periodic structure of the core The critical angle for total reflection at the interface of the basic structure with different parts is smaller than the Bragg angle,
Of the plurality of regions, from the region a where the difference in the real part of the refractive index between the two basic structures is the smallest,
The difference in the real part of the refractive index between the basic structures in the region increases in the direction toward the region b including the interface between one of the two claddings and the periodic structure,
The difference in the real part of the refractive index between the basic structures in the region increases or does not differ in the direction from the region a toward the region c including the interface between the other of the two claddings and the periodic structure. An X-ray waveguide characterized by the above.   The plurality of regions are configured by the region a, the region b, and the region c, and the region a is sandwiched between the region b and the region c. X-ray waveguide.   The core and the clad have a curved portion, and the curved portion of the core includes at least a part of each of the region a, the region b, and the region c, and at least a part of the region a. 2. The crystal orientation of at least a part of the region b and at least a part of the region c continuously changes along the X-ray propagation direction. Or the X-ray waveguide of 2. In the X-ray waveguide including the core constituting the waveguide and a portion where the shape of the clad is curved,
When the y axis is defined in the normal direction from the interface to the outside of the circle O with the center of the circle O defining the radius of curvature of the interface between one of the two claddings and the core as the origin, The region a, the region b, and the region c are arranged in this order in the direction of increasing
The difference between the real part of the refractive index of the region a and the difference between the real part of the refractive index of the region c are the same,
The difference in the real part of the refractive index of the region b is larger than the difference in the real part of the refractive index of the region a,
4. The X-ray waveguide according to claim 2, wherein a difference in the real part of the refractive index in the region b is larger than a difference in the real part of the refractive index in the region c. When the two basic structures constituting the region b are s and t, the refractive index real part of the basic structure s in contact with the cladding is smaller than the refractive index real part of the basic structure t,
And when the two basic structures constituting the region c are u and v, the real part of the refractive index of the basic structure u in contact with the cladding is smaller than the real part of the refractive index of the basic structure v. The X-ray waveguide according to any one of claims 1 to 4, wherein the X-ray waveguide is characterized by the following.

Images