Variable shape mirror

Abstract

To prevent a reduction in the optical output of a semiconductor light emitting device.SOLUTION: A variable shape mirror 10A comprises: a first substrate 14 that has a first surface 24 and a second surface 26 on the opposite side of the first surface 24, and is formed of a piezo single crystal material; a first electrode that is provided on the first surface 24 and has a reflection surface 12; a plurality of second electrodes that are provided on the second surface 26; a second substrate 16 that has a third surface 28 joined to the plurality of second electrodes and a fourth surface 30 on the opposite side of the third surface 28, and is formed of the piezo single crystal material; a third electrode that is provided on the fourth surface 30; and a power supply 22A that applies voltage between the first electrode and the plurality of second electrodes and between the plurality of second electrodes and the third electrode.SELECTED DRAWING: Figure 5

Description

[Technical field]

[0001] (CROSS REFERENCE TO RELATED APPLICATIONS) This application claims priority to Japanese Patent Application No. 2021-163085, filed on October 1, 2021, the entire contents of which are incorporated herein by reference.

[0002] (Technical field) The present disclosure relates to deformable mirrors. [Background technology]

[0003] X-ray analysis technology is widely used in academic and industrial fields. In recent years, the development of X-ray microscopes has progressed rapidly, and resolutions of less than 50 nm have been reported. Since X-rays have an extremely short wavelength compared to visible light, it is expected that a resolution of less than 1 nm can be achieved in principle. To further improve the resolution of X-ray microscopes, it is essential to improve the performance of the X-ray optical system that focuses or images the X-rays.

[0004] Optical elements used in X-ray optical systems include a compound refractive lens that utilizes refraction, a Fresnel zone plate that utilizes diffraction, and a grazing incidence total reflection mirror that utilizes reflection. Among these, the grazing incidence total reflection mirror has the advantages of high X-ray utilization efficiency and low chromatic aberration. Furthermore, as an optical system without coma aberration, there is an AKB (Advanced Kirkpatrick-Baez) mirror optical system that uses four grazing incidence total reflection mirrors (see, for example, Patent Document 1). In addition, in order to make the optical characteristics of the X-ray optical system variable, a shape-variable mirror is also used in which a piezoelectric element is attached to the total reflection mirror and the shape of the reflection surface is controlled by the amount of deformation of the piezoelectric element (see, for example, Patent Document 2). [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Patent No. 6478433 [Patent Document 2] Patent Publication No. 2021-21897 Summary of the Invention [Problem to be solved by the invention]

[0006] The shape precision required for the reflective surface of an X-ray mirror is extremely strict; for example, a shape precision of about 1 nm is required for a mirror size of about 100 mm. This is because the wavelength of X-rays is extremely short compared to visible light. Achieving such shape precision is not easy even with the most advanced ultra-precision processing technology; it requires repeated ultra-high-precision shape measurements and ultra-precision correction processing based on the measurement results, which means that manufacturing an X-ray mirror takes an extremely long time and is extremely costly.

[0007] The present disclosure has been made in view of the above problems, and one of its exemplary objectives is to provide a technique for precisely adjusting the shape of a reflecting surface. [Means for solving the problem]

[0008] A deformable mirror according to one embodiment of the present disclosure comprises a first substrate having a first surface and a second surface opposite the first surface and made of a piezoelectric single crystal material, a first electrode provided on the first surface and having a reflective surface, a plurality of second electrodes provided on the second surface, a third surface joined to the plurality of second electrodes, and a fourth surface opposite the third surface and made of a piezoelectric single crystal material, a third electrode provided on the fourth surface, and a power source that applies voltage between the first electrode and the plurality of second electrodes, and between the plurality of second electrodes and the third electrode.

[0009] Any combination of the above components, or mutual substitution of the components or expressions of the present disclosure between methods, systems, etc., are also valid aspects of the present disclosure. Effect of the Invention

[0010] According to the present disclosure, the reflective surface of the mirror can be precisely adjusted. [Brief description of the drawings]

[0011] [Figure 1] 1 is a cross-sectional view showing a schematic configuration of a variable-shape mirror according to an embodiment. [Diagram 2] 1 is a top view illustrating a schematic configuration of a variable-shape mirror according to an embodiment. [Diagram 3] 4 is a graph showing an example of the deformation amount of a reflecting surface of a deformable mirror. [Figure 4] 11 is a graph showing an example of the relationship between the applied voltage and the deformation amount of a deformable mirror. [Diagram 5] FIG. 11 is a cross-sectional view illustrating a schematic configuration of a variable-shape mirror according to a modified example. [Figure 6] FIG. 11 is a cross-sectional view illustrating a schematic configuration of a variable-shape mirror according to a modified example. [Figure 7] 10 is a side view illustrating a method for supporting the deformable mirror. FIG. [Figure 8] 13 is a graph showing the time stability of the deformable mirror. [Figure 9] 9(a) and 9(b) are graphs showing an example of the relationship between the voltage applied to the deformable mirror and the amount of deformation. [Figure 10] 1 is a graph showing an example of a shape error of a reflecting surface of a deformable mirror. [Figure 11] 1 is a perspective view showing a schematic configuration of an X-ray microscope according to an embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] Before describing the present disclosure in detail, an overview will be provided. The present disclosure relates to an X-ray mirror that reflects X-rays, and to a shape-variable mirror that variably controls the shape of the reflecting surface using a piezoelectric material. An X-ray optical system for converging or imaging X-rays uses a curved mirror with a concave or convex reflecting surface. The shape accuracy of the reflecting surface required in the X-ray optical system is about 1 nm (2 nm in PV (Peak-to-Valley)), and it is not easy to achieve this even with the application of cutting-edge ultra-precision processing technology. The present disclosure aims to achieve a shape accuracy of 1 nm by variably controlling the shape of a reflecting surface that has been finished with a shape accuracy of, for example, 2 nm to 5 nm (4 nm to 10 nm in PV) rather than by processing alone, and to achieve a shape accuracy of 1 nm by a combination of processing and deformation. According to the present disclosure, the processing accuracy of the reflecting surface can be reduced, thereby reducing the time and cost required for manufacturing the curved mirror.

[0013] In the present disclosure, instead of attaching a piezoelectric element to an X-ray mirror, the surface of a piezoelectric material itself is used as a reflecting surface, thereby simplifying the structure and enabling more precise control of the shape of the reflecting surface. In addition, by deforming the piezoelectric material in a direction perpendicular to the reflecting surface, it is possible to control the shape with a higher spatial frequency. In one example of the present disclosure, a piezoelectric single crystal material such as lithium niobate (LN) or lithium tantalate (LT) is used as the piezoelectric material for deforming the reflecting surface, rather than a piezoelectric ceramic material such as lead zirconate titanate (PZT). By using a piezoelectric single crystal material, the amount of deformation can be changed linearly with respect to the applied voltage, enabling stable control of the amount of deformation.

[0014] Hereinafter, the embodiments of the present disclosure will be described in detail with reference to the drawings. In the description, the same elements are given the same reference numerals, and duplicated descriptions will be omitted as appropriate. In addition, in order to facilitate understanding of the description, the dimensional ratios of the components in each drawing do not necessarily match the actual dimensional ratios.

[0015] FIG. 1 is a cross-sectional view showing a schematic configuration of a deformable mirror 10 according to an embodiment. The deformable mirror 10 has a reflecting surface 12 onto which X-rays 40 are obliquely incident, and is configured so that the shape of the reflecting surface 12 is variable. The surface roughness (Rms) of the reflecting surface 12 is extremely small, for example, 0.5 nm or less, and preferably 0.2 nm or less. In addition, the angle θ between the optical axis of the X-rays 40 and the reflecting surface 12 is very small, for example, about 1 to 10 milliradians (mrad). By reducing the surface roughness of the reflecting surface 12 and reducing the angle θ at which the X-rays 40 are incident, the X-rays 40 can be reflected with a high efficiency of about 80% to 90%.

[0016] The deformable mirror 10 includes a first substrate 14, a second substrate 16, a reflective electrode 18, a plurality of control electrodes 20a, 20b, 20c, 20d, 20e, 20f, 20g, and 20h (collectively referred to as control electrodes 20), and a power source 22.

[0017] 1, the direction perpendicular to both the incident optical axis and the reflected optical axis of X-rays 40 incident on and reflected by the deformable mirror 10 is defined as the x direction. The thickness direction of the first substrate 14 and the second substrate 16 is defined as the z direction, and the direction perpendicular to both the x direction and the z direction is defined as the y direction. Note that the coordinate axes shown in the figure are set to facilitate understanding of the explanation, and do not limit the orientation of the deformable mirror 10 during use.

[0018] The first substrate 14 is made of a piezoelectric material, for example, a piezoelectric single crystal material such as lithium niobate (LN) or lithium tantalate (LT). The first substrate 14 has a first surface 24 and a second surface 26 opposite to the first surface 24. A reflective electrode 18 is provided on the first surface 24, and a plurality of control electrodes 20a to 20h are provided on the second surface 26. The first substrate 14 deforms in response to a voltage applied between the reflective electrode 18 and the plurality of control electrodes 20a to 20h. The first substrate 14 is configured to expand and contract in the thickness direction (z direction) in response to a voltage applied in the thickness direction (z direction), and the thickness (height) from the second surface 26 to the first surface 24 changes. For example, a 36 degree Y-cut LN substrate can be used as the first substrate 14. The thickness of the first substrate 14 is, for example, 0.1 mm or more and 10 mm or less, and preferably 0.2 mm or more and 2 mm or less.

[0019] The first surface 24 is configured to have the same shape accuracy and surface roughness as the reflecting surface 12. The shape accuracy (PV) of the first surface 24 is, for example, 10 nm or less, and preferably 2 nm or more and 5 nm or less. The surface roughness (Rms) of the first surface 24 is, for example, 0.5 nm or less, and preferably 0.05 nm or more and 0.2 nm or less. The shape accuracy and surface roughness of the first surface 24 can be achieved by performing a known precision processing such as EEM (Elastic Emission Machining) after rough processing such as cutting or mechanical polishing. The shape of the first surface 24 can be measured by a pencil beam method using X-rays, a visible light interferometer, an X-ray interferometer, an autocollimator, or the like. The first surface 24 is, for example, a convex or concave surface that is arc-shaped, elliptical, hyperbolic, or parabolic, and has a curvature only in one direction (for example, the y direction). In the example of FIG. 1, the first surface 24 is a concave surface. The first surface 24 may be a flat surface or a curved surface having curvatures in two directions (for example, the x direction and the y direction). The second surface 26 is, for example, a polished flat surface.

[0020] The second substrate 16 is a member for supporting the first substrate 14. The second substrate 16 has a third surface 28 and a fourth surface 30 opposite to the third surface 28. The third surface 28 and the fourth surface 30 are, for example, polished flat surfaces. The third surface 28 is bonded to the plurality of control electrodes 20a to 20h and is fixed to the first substrate 14 via the plurality of control electrodes 20a to 20h. The fourth surface 30 is fixed to a jig or the like for positioning the deformable mirror 10. The material of the second substrate 16 is not particularly limited, but for example, a single crystal material such as silicon, quartz, or sapphire can be used. The material of the second substrate 16 may be the same piezoelectric material as the first substrate 14, or may be the same piezoelectric single crystal material as the first substrate 14. By making the first substrate 14 and the second substrate 16 out of the same material, deformation of the reflecting surface 12 caused by the difference in thermal expansion coefficient due to the difference in materials can be suppressed. It should be noted that, when the first substrate 14 is thick, for example, 5 mm or thicker, the deformable mirror 10 does not need to include the second substrate 16.

[0021] The reflective electrode 18 is provided on the first surface 24 and has a reflective surface 12 on which the X-rays 40 are obliquely incident. The reflective electrode 18 has a thickness of, for example, 10 nm or more and 100 nm or less, and preferably has a thickness of 30 nm or more and 70 nm or less. The reflective electrode 18 is provided, for example, so as to cover the entire first surface 24 and have a uniform thickness over the entire first surface 24. Since the reflective electrode 18 has a uniform thickness, the reflective surface 12 has a shape corresponding to the first surface 24 and has the same shape accuracy and surface roughness as the first surface 24. Nickel (Ni), chromium (Cr), rhodium (Rh), platinum (Pt), gold (Au), etc. can be used as the material of the reflective electrode 18. The reflective electrode 18 may be composed of a metal thin film of a single material, or may be composed of a laminate of multiple metal thin films of different materials. The reflective electrode 18 may have, for example, an adhesive layer of Cr, Ti or the like in contact with the first surface 24, and a reflective layer of Rh, Pt, Au or the like formed on the adhesive layer. The reflective electrode 18 can be formed by using a vapor deposition method or a sputtering method.

[0022] The reflecting surface 12 may be configured to function as a total reflection mirror based on the total reflection phenomenon, or may be configured as a multilayer mirror utilizing Bragg reflection. When the reflecting surface 12 is configured as a multilayer mirror, the reflecting electrode 18 may include a multilayer film in which a plurality of first layers made of heavy elements and a plurality of second layers made of light elements are alternately and periodically stacked. Molybdenum (Mo), rhodium (Rh), tungsten (W), platinum (Pt), etc. can be used as the heavy elements constituting the first layer, and beryllium (Be), carbon (C), silicon (Si), etc. can be used as the light elements constituting the second layer. The number of layers in the multilayer film is, for example, about 10 to 100. The thickness of each of the first layer and the second layer is about 1 nm to 10 nm. The reflecting electrode 18 may be configured as a so-called multilayer film super mirror, and may be configured so that the periodic length of the multilayer film (the sum of the thicknesses of the first layer and the second layer) changes in the depth direction. In other words, at least one of the thickness of each of the plurality of first layers and the thickness of each of the plurality of second layers constituting the reflective layer of the multilayer film may vary depending on the position in the thickness direction.

[0023] The reflective electrode 18 includes a material having electrical conductivity, and preferably includes a material having high electrical conductivity. When the reflective electrode 18 is composed of a metal thin film of a single material, the metal material constituting the reflective electrode 18 can provide electrical conductivity. When the reflective electrode 18 is configured as a multilayer mirror, the multilayer mirror can be provided with high electrical conductivity by combining a first layer (e.g., W) and a second layer (e.g., C) having electrical conductivity. When the multilayer mirror is composed of a material having low electrical conductivity, for example, when the first layer is tungsten carbide (WC) and the second layer is boron carbide (B4C), the reflective electrode 18 can be provided with electrical conductivity by using a metal material having high electrical conductivity, such as Cr, as an adhesive layer between the first surface 24 of the first substrate 14 and the multilayer mirror. That is, the electrical conductivity of the adhesive layer may be higher than that of the reflective layer. When the electrical conductivity of the reflective layer is high, the electrical conductivity of the adhesive layer may be lower than that of the reflective layer. That is, the electrical conductivity of the reflective layer may be higher than that of the adhesive layer.

[0024] The control electrode 20 is provided between the first substrate 14 and the second substrate 16, and is joined to the second surface 26 and the third surface 28. The control electrodes 20a to 20h are arranged at intervals in a predetermined direction (for example, the y direction). The width w of the control electrodes 20a to 20h in the predetermined direction (for example, the y direction) is, for example, 0.5 mm to 10 mm, and preferably 1 mm to 6 mm. The interval d of the control electrodes 20a to 20h in the predetermined direction (for example, the y direction) is, for example, 0.1 mm to 5 mm, and preferably 0.5 mm to 4 mm. The pitch p (the sum of the width w and the interval d) of the control electrodes 20a to 20h in the predetermined direction (for example, the y direction) is, for example, 1 mm to 15 mm, and preferably 1.5 mm to 10 mm.

[0025] The control electrodes 20a-20h are configured, for example, so that the width w, interval d, and pitch p in a predetermined direction (e.g., y direction) are constant. At least one of the width w, interval d, and pitch p of the control electrodes 20a-20h may be configured to be different from one another. For example, when the angle θ of the X-rays 40 obliquely incident on the reflecting surface 12 varies depending on the location in the predetermined direction (e.g., y direction), the pitch p of the control electrodes 20a-20h may be made different from one another so that the effective pitch p×θ when viewed from the X-rays 40 is constant.

[0026] The control electrode 20 is made of a metal material, and for example, nickel (Ni), chromium (Cr), copper (Cu), silver (Ag), gold (Au), etc. can be used. The control electrode 20 can be formed by forming a first metal film on the second surface 26, forming a second metal film on the third surface 28, and then bonding the first metal film and the second metal film, for example, by using a vapor deposition method or a sputtering method. There is no particular restriction on the method for bonding the first metal film and the second metal film, and any metal bonding technique can be used. As an example, a solid-phase bonding technique such as room temperature bonding or diffusion bonding can be used. In addition, the first metal film and the second metal film may be bonded using a binder material such as a conductive adhesive or metal nanoparticles. The thickness of the control electrode 20 is not particularly limited, but is, for example, 100 nm or more and 1000 nm or less.

[0027] The power supply 22 applies a DC voltage between the reflective electrode 18 and the control electrode 20. In FIG. 1, the power supply 22 is connected to only one control electrode 20a to avoid complication of the drawing, but the power supply 22 is connected to each of the multiple control electrodes 20a to 20h. The power supply 22 is configured to independently control the voltage applied to each of the multiple control electrodes 20a to 20h. The power supply 22 applies a DC voltage that is variable within a range of, for example, −1 kV to +1 kV. The power supply 22 individually variably controls the voltage applied to each of the multiple control electrodes 20a to 20h, thereby controlling the amount of deformation of the first substrate 14 at the positions corresponding to each of the multiple control electrodes 20a to 20h, and variably controlling the shape of the reflective surface 12.

[0028] FIG. 2 is a plan view showing a schematic configuration of the variable-shape mirror 10 according to the embodiment. FIG. 1 corresponds to the cross section taken along the line AA in FIG. 2. The first substrate 14 and the second substrate 16 have a rectangular shape that is long in the y direction and short in the x direction. The length Lx1 of the first substrate 14 in the x direction is larger than the beam size of the obliquely incident X-rays 40, and is, for example, 5 mm or more and 50 mm or less, and, for example, 10 mm or more and 30 mm or less. The length Ly of the first substrate 14 in the y direction is determined according to the beam size and angle θ of the obliquely incident X-rays 40, and is, for example, 20 mm or more and 200 mm or less, and, for example, 50 mm or more and 150 mm or less.

[0029] The length Lx2 in the x direction of the second substrate 16 is greater than the length Lx1 in the x direction of the first substrate 14, and is, for example, 10 mm or more and 100 mm or less. By making the length Lx2 in the x direction of the second substrate 16 greater than the length Lx1 in the x direction of the first substrate 14, the control electrode 20 provided on the third surface 28 of the second substrate 16 is exposed, and the connection between the power source 22 and the control electrode 20 can be easily established. The length in the y direction of the second substrate 16 is the same as the length Ly in the y direction of the first substrate 14. The length in the y direction of the second substrate 16 may be greater or smaller than the length Ly in the y direction of the first substrate 14.

[0030] Each of the multiple control electrodes 20a-20h is formed in a strip shape extending in the x direction on the third surface 28. The length in the x direction of the multiple control electrodes 20a-20h is greater than the length Lx1 in the x direction of the first substrate 14 and is equal to, for example, the length Lx2 in the x direction of the second substrate 16. The length in the x direction of the multiple control electrodes 20a-20h may be smaller than the length Lx2 in the x direction of the second substrate 16.

[0031] Each of the multiple control electrodes 20a-20h is bonded to the first substrate 14 at a bonding region 32 indicated by a dashed line in the center of the first substrate 14 in Fig. 2. The length Lx3 in the x direction of the bonding region 32 is smaller than the length Lx1 in the x direction of the first substrate 14. The length Lx3 in the x direction of the bonding region 32 is larger than the beam size in the x direction of the obliquely incident X-rays 40, and is, for example, 3 mm or more and 30 mm or less, for example, 5 mm or more and 20 mm or less. The length Lx3 in the x direction of the bonding region 32 may be the same as the length Lx1 in the x direction of the first substrate 14.

[0032] FIG. 3 is a graph showing an example of the deformation amount of the reflecting surface 12 of the deformable mirror 10. FIG. 3 shows the deformation amount of the reflecting surface 12 when the height of the reflecting surface 12 when no voltage is applied to the control electrodes 20a to 20h is set as a reference and the applied voltages of the control electrodes 20a to 20h are 100V, 200V, 300V, 400V, and 500V. The applied voltages of the control electrodes 20a to 20h are alternately positive and negative in a predetermined direction (for example, the y direction), and a positive voltage is applied to the odd-numbered control electrodes 20a, 20c, 20e, and 20g, and a negative voltage is applied to the even-numbered control electrodes 20b, 20d, 20f, and 20h. The vertical axis of the graph represents the deformation amount [nm] in the thickness direction (z direction), and the horizontal axis of the graph represents the position [mm] in the predetermined direction (y direction). In the embodiment of FIG. 3, the width w of the plurality of control electrodes 20a to 20h in the y direction is 2 mm, and the interval d is 1 mm.

[0033] As shown in FIG. 3, the convex and concave portions of the deformed reflecting surface 12 are generated at intervals of about 3 mm, and it can be seen that the reflecting surface 12 can be deformed to correspond to the positions of the plurality of control electrodes 20a to 20h arranged at a pitch of 3 mm. According to the example of FIG. 3, the reflecting surface 12 can be deformed at a spatial frequency of 6 mm. In a conventional deformable mirror that uses PZT as a piezoelectric element and deforms the piezoelectric element in a direction along the reflecting surface, the spatial frequency was limited to 20 to 30 mm. Therefore, according to this embodiment, shape control with a higher spatial frequency than the conventional one is possible. Note that if the pitch p of the plurality of control electrodes 20a to 20h is made smaller than 3 mm and set to 1.5 mm (for example, the width w is 1 mm and the interval d is 0.5 mm), the reflecting surface 12 can be deformed at a spatial frequency of 3 mm.

[0034] When ±500V is applied to each of two adjacent control electrodes 20 (e.g., control electrodes 20a and 20b), the difference in height between the convex and concave portions is about 20 nm, which is a smaller maximum deformation amount than when PZT is used as the piezoelectric material. However, this deformation amount is sufficient to correct a shape error of about 5 nm (about 10 nm in PV).

[0035] 4 is a graph showing an example of the relationship between the applied voltage and the deformation amount of the deformable mirror 10. As shown in FIG. 4, there is a high degree of linearity between the applied voltage and the deformation amount. In addition, no hysteresis is observed, as exists in piezoelectric ceramic materials such as PZT, and no drift is observed, in which the deformation amount changes over time even when the applied voltage is fixed. Therefore, according to the deformable mirror 10 of this embodiment, the deformation amount can be uniquely determined according to the applied voltage, and the shape of the reflecting surface 12 can be stably controlled with high reproducibility.

[0036] According to this embodiment, the shape of reflecting surface 12 can be variably controlled while irradiating reflecting surface 12 with X-rays 40, so that the shape of reflecting surface 12 can be adjusted afterwards to be optimal for the X-ray optical system in which deformable mirror 10 is incorporated. For example, by measuring the shape of reflecting surface 12 by a pencil beam method using X-rays, it is possible to precisely measure and adjust the shape of reflecting surface 12 on the spot in a state in which deformable mirror 10 is incorporated into the X-ray optical system.

[0037] 5 is a cross-sectional view showing a schematic configuration of a deformable mirror 10A according to a modified example. This modified example differs from the above-mentioned embodiment in that the second substrate 16 is made of a piezoelectric material and a back electrode 34 is provided on the fourth surface 30 of the second substrate 16. In this modified example, the second substrate 16 is made deformable in response to an applied voltage, and the second substrate 16 is deformed in the same manner as the first substrate 14, thereby suppressing unintended curvature of the reflecting surface 12 caused by the difference in the amount of deformation between the first substrate 14 and the second substrate 16. This modified example will be described mainly with respect to the differences from the above-mentioned embodiment, and the description of the commonalities will be omitted as appropriate.

[0038] The deformable mirror 10A includes a first substrate 14, a second substrate 16, a reflective electrode 18, a plurality of control electrodes 20a to 20h, a power source 22A, and a rear surface electrode .

[0039] The back electrode 34 is provided on the fourth surface 30 of the second substrate 16. The back electrode 34 is provided, for example, so as to cover the entire fourth surface 30. The back electrode 34 is made of a metal material, and for example, nickel (Ni), chromium (Cr), copper (Cu), silver (Ag), gold (Au), etc. can be used. The back electrode 34 can be formed by a vapor deposition method or a sputtering method. The thickness of the back electrode 34 is not particularly limited, but is, for example, 10 nm or more and 1000 nm or less, and preferably 30 nm or more and 200 nm or less.

[0040] The power supply 22A applies a DC voltage between the reflective electrode 18 and the control electrode 20, and also applies a DC voltage between the rear electrode 34 and the control electrode 20. In the example of FIG. 5, the power supply 22A is connected so that the potentials of the reflective electrode 18 and the rear electrode 34 are common. In a further modified example, a second power supply that applies a DC voltage between the rear electrode 34 and the control electrode 20 may be used in addition to a first power supply that applies a DC voltage between the reflective electrode 18 and the control electrode 20. In other words, the first applied voltage between the reflective electrode 18 and the control electrode 20 and the second applied voltage between the rear electrode 34 and the control electrode 20 may be individually controllable.

[0041] 5, the direction of the electric field applied to the first substrate 14 and the direction of the electric field applied to the second substrate 16 are upside down. For example, when a positive voltage is applied to the control electrode 20, an electric field is applied to the first substrate 14 from the second surface 26 to the first surface 24, and an electric field is applied to the second substrate 16 from the third surface 28 to the fourth surface 30. The second substrate 16 is disposed so that the polarization direction is upside down relative to the first substrate 14. By reversing the polarization directions of the first substrate 14 and the second substrate 16, the deformation directions when upside down electric fields are applied to the first substrate 14 and the second substrate 16 can be made the same.

[0042] According to this modification, the structure of the deformable mirror 10A can be made symmetrical in the thickness direction (e.g., z direction) with respect to the control electrode 20, so that deformation of the reflective surface 12 due to temperature changes can be more suitably suppressed. In addition, the deformation amounts of the first substrate 14 and the second substrate 16 in the x direction, y direction, and z direction when a voltage is applied can be made the same. As a result, the difference between the deformation amounts of the first substrate 14 and the second substrate 16 can suppress bending of the deformable mirror 10A like a bimetal. According to this modification, the shape of the reflective surface 12 can be controlled more stably and with higher reproducibility.

[0043] Fig. 6 is a cross-sectional view showing a schematic configuration of a variable-shape mirror 10B according to a modified example. In this modified example, the second substrate 16 is removed from the variable-shape mirror 10 shown in Fig. 1. The variable-shape mirror 10B includes a first substrate 14, a reflective electrode 18, a plurality of control electrodes 20a-20h, and a power supply 22. The first substrate 14, the reflective electrode 18, the plurality of control electrodes 20a-20h, and the power supply 22 are configured in the same manner as in the above-described embodiment.

[0044] FIG. 7 is a side view showing a schematic diagram of a method for supporting the deformable mirror 10B. The deformable mirror 10B can be supported by three points using three supports 50a, 50b, and 50c that are in point contact with the deformable mirror 10B. Support spheres 52a, 52b, and 52c are provided at the tips of the supports 50a to 50c, respectively, and the support spheres 52a to 52c are in point contact with the deformable mirror 10B. By supporting the deformable mirror 10B by three points using the supports 50a to 50c, the deformation of the deformable mirror 10B due to the point contact can be predicted with high accuracy by a simulation such as the finite element method. In addition, the three points where the supports 50a to 50c are in contact can be selected so that the deformation of the deformable mirror 10B based on the simulation becomes a desired shape.

[0045] In the example of FIG. 7, the reflecting surface 12 faces vertically upward, and the multiple supports 50a-50c contact the second surface 26 of the first substrate 14 or the control electrode 20 to support the deformable mirror 10B. When the reflecting surface 12 faces vertically downward, that is, upside down from FIG. 7, the multiple supports 50a-50c can contact the reflecting surface 12 to support the deformable mirror 10B. When the reflecting surface 12 faces laterally, the multiple supports 50a-50c can contact the side surface of the first substrate 14 to support the deformable mirror 10B. The support method using the multiple supports 50a-50c can also be applied to the deformable mirrors 10 and 10A shown in FIG. 1 or FIG. 5.

[0046] FIG. 8 is a graph showing the time stability of the deformable mirror 10B. FIG. 8 shows the wavefront shape of the X-ray 40 reflected by the deformable mirror 10B when a voltage of 500 V is applied to any one of the control electrodes 20a to 20h. The energy of the obliquely incident X-ray 40 is 14.5 keV, and the deformable mirror 10B is used as an elliptical concave mirror in a Wolter 3 type mirror that combines an elliptical concave mirror and a hyperbolic convex mirror. Graph A shows the time after 1 hour from the voltage application, graph B shows the time after 4 hours from the voltage application, and graph C shows the time after 7 hours from the voltage application. As shown in FIG. 8, the change in the shape of the reflecting surface of the deformable mirror 10B with time is extremely small, and the amount of change in the wavefront with time within the measurement period is about 0.03 rad, which corresponds to a shape change of 0.5 Å. Therefore, the shape of the deformable mirror 10B can be precisely and stably controlled over a long period of time when the deformable mirror 10B is used.

[0047] 9(a)-(b) are graphs showing an example of the relationship between the applied voltage and the deformation amount of the deformable mirror 10B. FIG. 9(a) shows the deformation amount of the reflecting surface 12 with respect to the applied voltage, and it can be seen that the deformation amount of the reflecting surface 12 changes linearly. FIG. 9(b) shows the hysteresis of the deformation amount of the reflecting surface 12 when the applied voltage is changed, and shows the difference between the plot of FIG. 9(a) and the approximation line. As shown in FIG. 9(b), the hysteresis of the deformation amount of the reflecting surface 12 is extremely small, and exists at only about several percent of the deformation amount of the reflecting surface 12. Therefore, the shape of the deformable mirror 10B can be precisely and easily controlled without being concerned about the hysteresis.

[0048] FIG. 10 is a graph showing an example of a shape error of the reflecting surface of the deformable mirror 10B. Graph D shows a shape error before correction when no voltage is applied to the control electrodes 20a-20h, and shows a shape accuracy of about ±2 nm (about 4 nm in PV). Graph E shows a shape error after correction when a voltage is applied to the control electrodes 20a-20h, and a shape accuracy of about ±0.5 nm (about 1 nm in PV) is realized. When the energy of the X-rays 40 is 14.5 keV and the oblique incidence angle θ of the X-rays 40 is about 4 mrad, the shape accuracy required for the reflecting surface 12 is 0.76 nm or less in Rms. The shape accuracy after correction shown in graph E is 0.24 nm in Rms, and therefore the required accuracy is fully achieved. According to this embodiment, wavefront correction with an accuracy exceeding the diffraction limit of the X-rays 40 can be realized, and the diffraction limit can be achieved even when the energy of the X-rays 40 is 45 keV, for example.

[0049] 11 is a perspective view showing a schematic configuration of an X-ray microscope 60 according to an embodiment. The X-ray microscope 60 is an example of an X-ray device that uses X-rays, and has a so-called imaging type microscope configuration. The X-ray microscope 60 includes an illumination optical system 62, a sample holder 64, an imaging optical system 66, and an X-ray detector 68. The X-ray microscope 60 is configured to irradiate a sample 88 with X-rays 92 generated by an X-ray source 90, and to detect an enlarged image of X-rays 96 transmitted through the sample 88 by the X-ray detector 68.

[0050] The X-ray source 90 generates X-rays 92 for observing the sample 88. The type of the X-ray source 90 is not particularly limited, and an X-ray tube, a large-scale synchrotron radiation facility such as Spring-8, an X-ray free electron laser, or the like can be used. When a small device such as an X-ray tube is used as the X-ray source, the X-ray microscope 60 may include the X-ray source 90. On the other hand, when a large device such as a synchrotron radiation facility is used as the X-ray source 90, the X-ray microscope 60 does not need to include the X-ray source 90. The X-ray source 90 is configured to output hard X-rays of, for example, 2 keV or more. The X-ray source 90 may generate monochromatic X-rays monochromatized to a specific wavelength, or may generate continuous X-rays (white X-rays) containing various wavelength components.

[0051] The illumination optical system 62 is disposed between the X-ray source 90 and the sample holder 64. The illumination optical system 62 is configured to focus X-rays 92 from the X-ray source 90 on the sample holder 64. The illumination optical system 62 is configured with so-called Kirkpatrick-Baez (KB) mirrors, and includes a horizontal concave mirror 70 and a vertical concave mirror 72. The horizontal concave mirror 70 and the vertical concave mirror 72 are disposed so that the normal directions of their respective reflecting surfaces are orthogonal to each other. The reflecting surfaces of the horizontal concave mirror 70 and the vertical concave mirror 72 are configured, for example, as elliptical concave curved surfaces having a focal point at the position of the sample holder 64. The illumination optical system 62 may be configured with four curved mirrors, similar to the imaging optical system 66 described later.

[0052] The sample holder 64 holds a sample 88 to be irradiated with X-rays 94 emitted from the illumination optical system 62. The sample holder 64 holds the sample 88 to be observed on the optical path of the X-rays 94. The configuration of the sample holder 64 is not particularly limited, and any configuration for fixing the position of the sample 88 can be used depending on the characteristics of the sample 88. The sample holder 64 includes, for example, a stage device for adjusting the position of the sample 88 with respect to the optical path of the X-rays 94.

[0053] The imaging optical system 66 is disposed between the sample holder 64 and the X-ray detector 68. The imaging optical system 66 is configured to image the X-rays 96 from the sample holder 64 on the X-ray detector 68. The imaging optical system 66 is a so-called AKB (Advanced Kirkpatrick-Baez) mirror optical system, and includes four curved mirrors 74, 76, 78, and 80. The imaging optical system 66 is configured to achieve an image magnification of, for example, about 100 times to 1,000 times.

[0054] The imaging optical system 66 can be configured as a Wolter 1 type mirror that combines, for example, a hyperbolic concave mirror and an elliptical concave mirror. In this case, the first curved mirror 74 is a horizontal hyperbolic concave mirror, and has, for example, a reflective surface composed of a hyperbolic concave surface having a focus at the position of the sample holder 64. The second curved mirror 76 is a vertical hyperbolic concave mirror, and has, for example, a reflective surface composed of a hyperbolic concave surface having a focus at the position of the sample holder 64. The third curved mirror 78 is a horizontal elliptical concave mirror, and has, for example, a reflective surface composed of an elliptical concave surface having a first focus at the position of the X-ray detector 68 and a second focus shared with the first curved mirror 74. The fourth curved mirror 80 is a vertical elliptical concave mirror, and has, for example, a reflective surface composed of an elliptical concave surface having a first focus at the position of the X-ray detector 68 and a second focus shared with the second curved mirror 76.

[0055] In the example of FIG. 11, the four curved mirrors 74-80 are arranged from the sample holder 64 toward the X-ray detector 68 in the order of a horizontal hyperbolic concave mirror, a vertical hyperbolic concave mirror, a horizontal elliptical concave mirror, and a vertical elliptical concave mirror, but the arrangement order is not limited to this. For example, the horizontal hyperbolic concave mirror may be arranged next to the horizontal hyperbolic concave mirror, or the vertical elliptical concave mirror may be arranged next to the vertical hyperbolic concave mirror. The imaging optical system 66 may also be configured as a Wolter 3 type mirror combining an elliptical concave mirror and a hyperbolic convex mirror. In this case, the first curved mirror 74 may be a horizontal elliptical concave mirror, the second curved mirror 76 may be a vertical elliptical concave mirror, the third curved mirror 78 may be a horizontal hyperbolic convex mirror, and the fourth curved mirror 80 may be a vertical hyperbolic convex mirror.

[0056] The X-ray detection unit 68 detects X-rays 98 emitted from the imaging optical system 66. The X-ray detection unit 68 is, for example, an X-ray camera that detects a two-dimensional image of the X-rays 98. The configuration of the X-ray detection unit 68 is not particularly limited, and for example, a direct conversion type or indirect conversion type image sensor (CCD or CMOS sensor) can be used. In order to further increase the resolution, the X-ray detection unit 68 may include an optical element such as a lens for enlarging the visible light image converted by the scintillator, and an image sensor for imaging the enlarged visible light image.

[0057] At least one of the illumination optical system 62 and the imaging optical system 66 includes the deformable mirror 10, 10A, or 10B according to the above-mentioned embodiment or modification. At least one of the horizontal concave mirror 70 and the vertical concave mirror 72 constituting the illumination optical system 62 may be composed of the deformable mirror 10, 10A, or 10B. The deformable mirror 10, 10A, or 10B may be applied only to the horizontal concave mirror 70, only to the vertical concave mirror 72, or both to the horizontal concave mirror 70 and the vertical concave mirror 72. At least one of the four curved mirrors 74 to 80 constituting the imaging optical system 66 may be composed of the deformable mirror 10, 10A, or 10B. The deformable mirror 10, 10A, or 10B may be applied to any one, two, or three of the four curved mirrors 74 to 80, or may be applied to all of them. By using the deformable mirror 10, 10A or 10B in at least one of the illumination optical system 62 and the imaging optical system 66, the time and cost required for manufacturing the mirror can be reduced, while the characteristics of the X-ray optical system can be improved.

[0058] The deformable mirror 10, 10A or 10B according to the present disclosure is preferably applied to the imaging optical system 66, which requires higher accuracy. In particular, it is preferable to apply the deformable mirror 10, 10A or 10B to each of the horizontal curved mirror and the vertical curved mirror that are arranged near the sample holder 64 and serve as the objective lens of the imaging optical system 66. In the configuration of FIG. 11, it is preferable to apply the deformable mirror 10, 10A or 10B to one or both of the first curved mirror 74, which is a horizontal hyperbolic concave mirror, and the second curved mirror 76, which is a vertical hyperbolic concave mirror. In order to increase the resolution of the imaging optical system 66, it is necessary to increase the numerical aperture of the imaging optical system 66, and the shape accuracy of the objective lens that determines the numerical aperture is important. By applying the deformable mirror 10, 10A or 10B to the curved mirror that serves as the objective lens of the X-ray optical system, the performance of the X-ray microscope 60 can be more effectively improved.

[0059] The X-ray microscope 60 may further include an X-ray spectrometer (not shown) disposed between the X-ray source 90 and the illumination optical system 62. The X-ray spectrometer is configured to monochromatize the X-rays 92 from the X-ray source 90. The X-ray spectrometer may be a crystal spectrometer such as a double crystal monochromator, and may be configured to tune the X-ray wavelength by changing the crystal angle. The X-ray microscope 60 can provide XAFS (X-ray Absorption Fine Structure) imaging by making the X-ray wavelength variable. Since the X-ray microscope 60 is configured with an X-ray optical system with little chromatic aberration, it can provide a high-resolution (e.g., 50 nm or less) XAFS image by simply changing the X-ray wavelength.

[0060] The deformable mirror 10, 10A, or 10B according to the present disclosure can be applied to any X-ray device, and in particular to an X-ray optical system such as a focusing optical system or an imaging optical system provided in an X-ray device. Examples of the X-ray device include an imaging X-ray microscope as shown in Fig. 11, as well as a scanning X-ray microscope and an X-ray telescope.

[0061] The scanning X-ray microscope may include a focusing optical system that focuses X-rays on a sample holder, and at least one of the X-ray mirrors constituting the focusing optical system may be the deformable mirror 10, 10A, or 10B according to the present disclosure. In the case of a scanning X-ray microscope, the resolution is determined by the beam size of the X-rays focused by the focusing optical system. By using the deformable mirror 10, 10A, or 10B according to the present disclosure, the characteristics of the focusing optical system can be improved, and the resolution of the scanning X-ray microscope can be improved. As the focusing optical system of the scanning X-ray microscope, a horizontal concave mirror 70 and a vertical concave mirror 72 similar to the illumination optical system 62 in FIG. 11 can be used, and at least one of them can be the deformable mirror 10, 10A, or 10B according to the present disclosure. As the focusing optical system of the scanning X-ray microscope, an AKB mirror optical system including four curved mirrors can also be used, and at least one of the four curved mirrors can be the deformable mirror 10, 10A, or 10B according to the present disclosure.

[0062] The X-ray telescope includes an imaging optical system that forms an image of X-rays from an astronomical object to be observed on an X-ray detector, and at least one of the X-ray mirrors constituting the imaging optical system may be the deformable mirror 10, 10A, or 10B according to the present disclosure. As the imaging optical system of the X-ray telescope, for example, an AKB mirror optical system similar to the imaging optical system 66 in FIG. 11 may be used. When the sample 88 in FIG. 11 is regarded as the astronomical object to be observed, a Wolter 1 type imaging optical system may be used in which the first curved mirror 74 and the second curved mirror 76 are parabolic concave mirrors, and the third curved mirror 78 and the fourth curved mirror 80 are hyperbolic concave mirrors. In addition, a Wolter 3 type imaging optical system may be used in which the first curved mirror 74 and the second curved mirror 76 are parabolic convex mirrors, and the third curved mirror 78 and the fourth curved mirror 80 are elliptical concave mirrors. In these cases, at least one of the four curved mirrors can be the deformable mirror 10, 10A or 10B according to the present disclosure.

[0063] The deformable mirror 10, 10A or 10B according to the present disclosure may be used as a wavefront compensation optical element in any X-ray device. When used as a wavefront compensation optical element, the reflecting surface 12, which is a substantially flat surface, is slightly deformed to, for example, have a shape opposite to the wavefront aberration of the obliquely incident X-rays 40, thereby compensating for the wavefront aberration of the incident X-rays 40. The X-rays whose wavefront aberration has been compensated for by the deformable mirror 10, 10A or 10B may be further processed by an X-ray optical element such as a lens or a mirror, may be irradiated onto a sample held by a sample holder, or may be detected by an X-ray detection unit.

[0064] The present disclosure has been described above based on the embodiments. It will be understood by those skilled in the art that the present disclosure is not limited to the above embodiments, that various design changes are possible, that various modifications are possible, and that such modifications are also within the scope of the present disclosure. [Explanation of symbols]

[0065] 10... deformable mirror, 12... reflective surface, 14... first substrate, 16... second substrate, 18... reflective electrode, 20... control electrode, 22... power supply, 24... first surface, 26... second surface, 28... third surface, 30... fourth surface, 40... X-ray.

Claims

1. a first substrate having a first surface and a second surface opposite to the first surface, the first substrate being made of a piezoelectric single crystal material; a first electrode provided on the first surface and having a reflective surface; A plurality of second electrodes provided on the second surface; a second substrate having a third surface bonded to the plurality of second electrodes and a fourth surface opposite to the third surface, the second substrate being made of a piezoelectric single crystal material; a third electrode provided on the fourth surface; a power source that applies a voltage between the first electrode and the plurality of second electrodes, and between the plurality of second electrodes and the third electrode.

2. The deformable mirror according to claim 1 , wherein the first substrate and the second substrate are made of the same material.

3. The deformable mirror according to claim 1 , wherein at least one of the first substrate and the second substrate is made of lithium niobate (LN) or lithium tantalate (LT).

4. The deformable mirror according to claim 1 , wherein a size of the second surface of the first substrate is different from a size of the third surface of the second substrate.

5. The deformable mirror according to claim 1 , wherein a size of the second surface of the first substrate is smaller than a size of the third surface of the second substrate.

6. the second electrodes are arranged in a predetermined direction on the second surface, The variable-shape mirror according to claim 1 , wherein a size of the second surface of the first substrate in a direction perpendicular to the predetermined direction is smaller than a size of the third surface of the second substrate in the direction perpendicular to the predetermined direction.

7. The variable-shape mirror according to claim 1 , wherein each of the second electrodes has a portion that is not bonded to the second surface and is exposed.

8. The deformable mirror according to claim 1 , wherein a thickness of the first substrate is different from a thickness of the second substrate.

9. The deformable mirror according to claim 1 , wherein a thickness of the first substrate is smaller than a thickness of the second substrate.

10. The deformable mirror according to claim 1 , wherein the first substrate has a thickness of 2 mm or less.

Images