JP2008191547A - Multilayer nonuniform pitch grooves concave diffraction grating and diffraction grating spectroscope - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a polychromator which separates a plurality of light rays of desired wavelengths, included in soft X-ray which is made incident to the apparatus in the range of several keVs and focuses on a detector or a photosensitive material face. <P>SOLUTION: The difference in the directions of incident light at an incident slit, through which the soft X-ray to be measured is introduced to the polychrometor and at respective points on a diffraction grating surface, and the difference in the incident light and the vertical direction of the diffraction grating surface due to the curvature of the surface of the diffraction grating are used; the local incident angle at the respective points on the surface of the diffraction grating is varied, as far much possible, in the range in which the resolution of energy is unaffected; the position of the incident slit, the radius of curvature of the concave diffraction grating, structural materials of a multilayer film and the length of period of the film are decided so that the incident light simultaneously satisfies the formulae of the diffraction grating and extended-Bragg conditions, at any position on the diffraction grating surface in a predetermined photon energy range. Furthermore, the grooves of diffraction grating are nonuniform so that the diffracted light in meridian plane is focused substantially on a straight line. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention is a spectroscopic device that spatially disperses light having a wavelength included in soft X-ray light incident on a spectroscopic device using a diffraction grating in a soft X-ray region and forms an image on a detector or a photosensitive material surface. It relates to a certain multicolor meter (polychromator).

  The spectroscopic device is a general term for devices having a spectroscopic function, and is broadly classified into a multicolor meter and a monochromator. The former is a device that can measure or use many wavelengths at once, and the latter is a device that can extract or measure a single wavelength.

  It has been performed more than half a century ago to increase the reflectance of incident light by depositing several layers of thin films of various substances on the surface of a substrate that becomes a reflecting mirror. Such an optical thin film is called a multilayer film. A multilayer film used to increase the reflectance of incident light in the soft X-ray region is usually a regular deposition of several tens to hundreds of two types of materials. Angle, average refractive index of multilayer film (weighted average value based on the thickness of each of the refractive indices of two kinds of materials), film period length (value of the sum of the thicknesses of two kinds of substances) Given the known “Bragg condition”. When a soft X-ray multilayer film is used to increase the diffraction efficiency of a diffraction grating, the angle direction of light incident on the diffraction grating and diffracted light from the diffraction grating depends on the diffraction conditions of the diffraction grating (diffraction grating equation) In addition, it is necessary to satisfy the interference conditions (extended Bragg conditions) of the multilayer diffraction grating at the same time, and a spectroscopic device without a mechanical movable mechanism can satisfy these conditions only for one wavelength. In the prior art, in order to continuously satisfy these conditions within a certain wavelength range, an auxiliary optical and mechanical mechanism is required, and the efficiency advantage of using the multilayer film is eliminated. (Non-Patent Documents 1, 2 and 3).

In the soft X-ray region of several keV region, the diffraction of the diffraction grating deposited with a soft X-ray multilayer film compared to the conventional diffraction grating having a metal single layer film such as gold or platinum on the surface. Efficiency has increased by one to three orders of magnitude, and obtaining diffraction efficiency of 10% or more is no longer difficult. Further, as a result of technological advancement of the soft X-ray detector, in many fields of use, if a diffraction efficiency of several percent or more is obtained in a spectroscopic system composed of one diffraction grating, it can be sufficiently put into practical use.
M. Koike, T. Namioka, E. Gullikson, Y. Haradad, S. Ishikawa, T. Imazono, S. Mrowka, N. Miyata, M. Yanagihara, JH Underwood, K. Sano, T. Ogiwara, O. Yoda , S. Nagai, “Varied-line-spacing laminar-type holographic grating for the standard soft X-ray flat-field spectrograph,” Proc. SPIE, 4146, 163-170 (2000). M. Koike and T. Namioka, "Optimization and evaluation of varied line spacing plane grating monochromators for third generation synchrotron light sources," J. Electron Spectroscopy and Related Phenomena, 80, 303-308 (1996). M. Ishino, PA Heimann, H. Sasai, M. Hatakeyama, H. Takenaka, K. Sano, EM Gullikson, and M. Koike, “Multilayer laminar-type diffraction gratings achieving high diffraction efficiencies in the 1-8 keV region, ”Applid Optics, 45, 6741-6745 (2006).

  In the soft X-ray region having a photon energy of several keV in which the diffraction grating spectroscope has not been practically used in the spectroscopic measurement using a conventional laboratory light source, the present invention is a soft X having a certain photon energy width incident on the spectroscopic device. The present invention provides a polychromator (polychromator) which is a spectroscopic device capable of separating linear light according to energy and forming an image on a detector or a photosensitive material surface.

  In order to solve the above problems, the present invention provides a difference in the direction of incident light at each point of the entrance slit and the surface of the diffraction grating where the soft X-ray light to be measured is introduced into the polychromator, and the diffraction grating. Utilizing the difference in perpendicular direction between the incident light and the diffraction grating surface due to the curvature of the surface, the local incidence angle at each point on the diffraction grating surface is changed as much as possible within a range that does not affect the energy resolution, and is constant The incident slit within the photon energy range of, so that the diffraction condition of the diffraction grating (diffraction grating equation) and the diffraction grating Bragg condition (extended Bragg condition) are simultaneously satisfied at any position on the diffraction grating surface. , The radius of curvature of the concave diffraction grating, the constituent material of the multilayer film, the film period length, and the like. Further, the diffraction grating grooves are non-uniformly spaced so that diffracted light in the meridian plane (perpendicular plane with respect to the diffraction grating surface; xy plane in FIG. 1) forms an image on substantially the same straight line.

  The diffraction grating and the spectroscopic device using the same according to the present invention are detectors having a position resolution of one or more dimensions for each photon energy of soft X-ray light within a certain photon energy range without mechanical moving parts. It can be measured simultaneously.

  There are various methods for producing a multilayer concave diffraction grating. (1) A multilayer film is formed on a substrate polished on a concave surface, and then a groove pattern is formed by a holographic method using laser light, and this is used as a mask for etching. (2) A groove pattern is formed on the substrate by holographic method using a laser beam, and then this pattern is used as a mask to form an ion beam. A laminar type groove is formed by etching, and then a multilayer film is deposited. (3) A blazed-type diffraction grating groove is formed in a soft metal formed on a substrate by a mechanical engraving method. Thereafter, there is a method of forming a multilayer film. Any method may be used when generating the multilayer diffraction grating according to the present invention.

  As described in Non-Patent Document 1, when the diffraction grating substrate is concave and the groove intervals are unequal, the polychromator (polychromator) can be composed of one diffraction grating, and the desired measurement can be performed. Diffracted light having a wavelength forms an image on a straight line. Furthermore, as described in Non-Patent Document 2, when the diffraction grating substrate is flat and the groove interval is unequal, the polychromator (polychromator) can be composed of a diffraction grating and a single concave mirror. The diffracted light having a desired measurement wavelength is also imaged on a straight line. However, in the latter case, when a metal single layer deposition is added to the concave mirror, it is used under conditions that cause total reflection with an oblique incident angle of 0.5 degrees or less, or the concave mirror has multiple specifications corresponding to each section of the diffraction grating. It is necessary to partially deposit the film. Therefore, the most suitable form for carrying out the present invention is the multicolor meter described in Non-Patent Document 1.

  Here, taking a multicolor meter having the configuration described in Non-Patent Document 1 as an example, a quantitative diffraction grating and multicolor meter design will be described (see FIG. 1). In the diffraction grating, an unevenly spaced groove pattern is formed on a substrate by a holographic method, and then a laminar type groove is formed based on this pattern.

The multilayer film is a soft X-ray multilayer film formed by laminating a set of layers composed of a light compound (SiO ₂ etc.) layer and a heavy element (Mo etc.) or heavy compound layer many times. And

To maximize the diffraction efficiency of incident light 1) Diffraction conditions of diffraction grating (diffraction grating equation)

2) Bragg condition of multilayer diffraction grating

It is necessary to satisfy. Expression (2) is sometimes called an extended Bragg condition. here,
λ is the wavelength of the incident light, α and β are the incident angle of the incident light and the diffraction angle of the diffracted light measured from the perpendicular to the surface of the light diffraction grating, and the counterclockwise direction is a positive angle (see FIG. 3). Here, α and β represent α ₀ and β ₀ for the principal ray whose incident point is the diffraction grating center. The incident angle α at other points is different from α ₀ (see FIG. 2). For this reason, when viewed at a local point on the diffraction grating surface (a point other than the center of the diffraction grating), the wavelengths satisfying the expressions (1) and (2) are different. The wavelengths R _α and R _β are respectively

And n is an average refractive index of the multilayer film (a weighted average value based on the film thickness of the real part of the complex refractive index of the two substances used in the multilayer film), δ = n−1. Further, m _G and m _C in the equations (1) and (2) are the diffraction order of the diffraction grating and the interference order of the multilayer film, respectively, but in this embodiment, it is assumed that m _G = m _C = 1.

  Furthermore, the optimum groove depth h is

It becomes. Also, the optimum duty ratio (DR) is that the groove depth is h, the width of the convex part, and the width of the concave part are g ₁ and g ₂ respectively. (Duty ratio means that the groove of the laminar diffraction grating is a rectangular wave shape. Is indicated by the value of a / σ in FIG. 7),

It becomes. Actually, it is determined by calculating the diffraction efficiency around the numerical value given by Equation (5).

A spherical diffraction grating, which is a type of concave diffraction grating, where the grating grooves are non-uniformly spaced, the imaging characteristics of the diffraction grating are the radius of curvature (R), the lattice constant (σ), and the nonuniformly spaced grooves are parameters n ₂ , It is represented by n ₃ and n ₄ . Using these three parameters, if the groove at the center of the diffraction grating is zero, the groove number at the point where the value in the y-axis direction on the diffraction grating surface is w is

Given in.

  First, the effective grating constant (groove interval at the center of the diffraction grating) s, which is a basic parameter, is 1/2400 mm, and the diffraction order m of the diffraction grating is the + 1st order. The range of the photon energy of the soft X-ray to be measured is 1610 to 1770 eV, and the wavelength range is 0.70 to 0.77 nm. Furthermore, the principal ray direction of incident light (the ray direction incident on the diffraction grating center) is 87 °, and the distance (r) between the entrance slit (or light emitting point) and the diffraction grating center is 150 mm. The image plane on which the spectral spectrum is imaged is perpendicular to the tangent plane at the center of the diffraction grating, and the distance (L) between the intersection of the image plane and the tangent plane at the center of the diffraction grating and the center of the diffraction grating is 407mm. Furthermore, the size of the diffraction grating was set to a width of 50 mm (y-axis direction) and a height of 30 mm (z-axis direction).

The optimization of the imaging characteristics was determined by the ray tracing method exactly as in the diffraction grating of ordinary metal thin film deposition. As a result, the radius of curvature of the spherical diffraction grating is 4320 mm, and the parameters of the unevenly spaced grooves are n ₂ = -8.66870 × 10 ^-4 mm ^-1 , n ₃ = -1.49594 × 10 ^-5 mm ^-2 , n ₄ = -1.61648 × 10 ^-7 mm ^-3

The material pair of the multilayer film consists of heavy material Mo and light material SiO ₂ , the ratio of the thickness of the heavy material layer is 0.4, and diffraction is performed at the center of the diffraction grating at the wavelength in the middle of the wavelength range to be measured (about 0.7 nm) The period length D is determined so as to increase the efficiency. In this example, D = 6 nm was set based on such consideration.

  FIG. 4 shows the photon energy satisfying the extended Bragg condition of the multilayer film corresponding to α (dotted line, right axis) and α corresponding to the incident angle α (dotted line, right axis) at the incident point of the incident light in the meridian plane calculated by this system (solid line, (Left axis) and diffracted light bandpass (full width at half maximum of about ± 40 eV, alternate long and short dash line, left axis). As can be seen from the figure, the photon energy width that can be measured simultaneously is 270 eV from 1540 eV to 1810 eV with respect to the marking line width of 50 mm. Since the inverse dispersion at the detector surface is about 0.08 nm / mm, when the width of one pixel of the detector is 20 mm, the energy decomposition by the detector is 4.9 eV.

  FIG. 4 is a diagram showing a region on the diffraction grating surface effective for incident light having each photon energy on the multilayer spherical diffraction grating surface in the multicolor meter according to the embodiment of the present invention, When the value in the y direction on the diffraction grating surface is 25 mm, it is an effective region (having diffraction efficiency) for light of about 1720 to 1820 eV.

  FIG. 5 shows a ray distribution diagram calculated by the ray tracing method when the aperture size of the entrance slit is 10 μm × 1 mm. The traced wavelengths were measured for three wavelengths of λ ± λ / 100 corresponding to the central wavelength λ and the resolution of 100 shown in each figure. From this figure, the resolution is 436 when the center wavelength is 0.70 nm, and similarly 545 at 0.72 nm, 589 at 0.74 nm, 537 at 0.76 nm, 537 at 0.78 nm, and 484 at 0.78 nm.

  FIG. 5 is a ray distribution diagram created by the ray tracing method for the multicolor meter according to the embodiment of the present invention. WIDTH and HIGH are the width (horizontal position) and height (vertical position) on the image plane. The resolution is expressed as λ / Δλ where the wavelength interval that can be resolved at the wavelength λ is Δλ. Here, the resolution is to trace light beams of three wavelengths of λ−λ / 100 and λ + λ / 100 corresponding to 100. The three images (lines) corresponding to it are visible. In other words, if these three lines are seen separately, it means that there is 100 resolution.

  FIG. 6 is a diagram showing the diffraction efficiency of + 1st order light corresponding to the local incident angle of the multilayer spherical diffraction grating described above. In the calculation, the depth h of the groove was 3 nm, and the duty ratio (D.R.) was 0.5. The incident angles were 86.7776 degrees, 87.0000 degrees, and 87.1173 degrees corresponding to the positions of w = + 25 mm, 0 mm, and -25 mm. As can be seen from the figure, the diffraction efficiency is 0.3 (30%) or more in the wavelength range of 0.69 to 0.77 nm. That is, in FIG. 6, when the incident angles are 86.7777, 87.0000.871173, the peak of diffraction efficiency is seen when the wavelengths are about 0.69 and 0.73.0.77 nm. Is shown.

  As described above, according to the embodiment of the present invention, it is possible to extend the measurable photon energy width when the multilayer spherical diffraction grating is applied to a polychromometer without reducing the resolution.

FIG. 8 shows a diffraction grating spectroscope in which a diffraction grating surface shape is a plane and a concave mirror are combined so that the spectral image points of light rays in a meridian plane of a plurality of wavelengths are formed on a substantially straight line. FIG. The light emitted from the light source point (A) is reflected on the plane mirror surface and is incident on the unevenly spaced groove plane diffraction grating surface, and the reflected light due to the rotation of the grating is incident on the exit slit (B). In the figure, r ₀ ′ is the distance between the unevenly spaced groove plane diffraction grating and the exit slit (B), r _M is the distance between the light source point (A) and the spherical mirror, and D ′ is the spherical mirror and the unevenly spaced groove plane. The distance from the diffraction grating, 2K is the angle between the incident angle and the diffraction angle on the unequal spacing groove plane diffraction grating, θ is the incidence angle on the spherical mirror, α is the incidence angle on the unequal spacing groove plane diffraction grating, β ₀ indicates the diffraction angle on the unevenly spaced groove plane diffraction grating, and r indicates the distance from the unevenly spaced groove plane diffraction grating of the image point of the light source point (A) by the spherical mirror.

It is a bird's-eye view which shows the multicolor meter concerning the Example of this invention. It is a figure explaining the local incident angle on the spherical diffraction grating surface in the multicolor meter concerning the Example of this invention. It is a figure which shows the cross-section of the laminar type | mold multilayer spherical diffraction grating concerning the Example of this invention. It is a figure which shows the area | region on a diffraction grating surface effective with respect to the incident light which has each photon energy on the multilayer film spherical diffraction grating surface in the polychromator concerning the Example of this invention. It is a ray distribution map produced by the ray tracing method about the multicolor meter concerning the Example of this invention. It is a figure which shows the diffraction efficiency of the + 1st order light corresponding to the local incident angle of the multilayer film diffraction grating concerning the Example of this invention. It is a figure which shows the meaning of Duty ratio in Formula (5). It is a figure which shows the diffraction grating spectroscopy apparatus which consists of a diffraction grating with which a diffraction grating surface shape is a plane, and a concave mirror. It is a figure which shows an approximate line (Claim 7).

Explanation of symbols

1: Laminar multilayer spherical diffraction grating 2: Incident beam 3: Diffraction beam 4: Entrance slit 5: Detector surface (imaging surface)
6: Center of curvature radius r ₀ ′ of spherical diffraction grating: Distance r _M between uneven groove plane diffraction grating and exit slit (B) _{M M} : Distance between light source point (A) and spherical mirror D ′: Spherical mirror and non-uniformity Distance 2K from the equidistant groove plane diffraction grating: Angle between the incident angle and diffraction angle on the unequally spaced groove plane diffraction grating θ: Incident angle α on the spherical mirror α: Incident angle β on the unequally spaced groove plane diffraction grating ₀ : Diffraction angle on unevenly spaced groove plane diffraction grating r: Distance of image point of light source point (A) by spherical mirror from unevenly spaced groove plane diffraction grating

Claims (9)

  In a multilayer concave grating having a diffraction grating groove, the radius of curvature of the concave grating, the film period of the multilayer film, so that the maximum diffraction efficiency can be obtained for light in a certain wavelength range incident from one point. Multi-layer diffraction grating in which the average refractive index of the long and multi-layer films simultaneously satisfies the diffraction grating diffraction condition and the extended Bragg condition for one of the incident light wavelengths at each position on the diffraction grating surface. .   2. The multilayer concave diffraction grating according to claim 1, wherein the diffraction grating surface is a spherical surface.   2. The multi-layer concave diffraction grating according to claim 1, wherein the groove intervals are unequal intervals.   2. The multilayer-type concave diffraction grating according to claim 1, wherein the groove intervals are unequal and the diffraction grating surface is spherical.   In a diffraction grating spectrometer using a multilayered diffraction grating, a diffraction grating with a flat diffraction grating surface is combined with a concave mirror so that the spectral image points of rays in the meridional plane of multiple wavelengths are formed on a substantially straight line. A diffraction grating spectrometer.   5. The diffraction grating spectroscopic device using the multilayer concave diffraction grating according to claim 4, wherein the imaging points on the detection surface of the spectrum of the diffracted light beam in the meridional plane having a plurality of wavelengths of the incident light are connected almost linearly. Diffraction grating spectrometer for imaging.   The diffraction grating spectroscope according to claim 6, wherein an angle formed by an approximate straight line of a spectral image point group (focal line) and a direction of a diffracted light beam from the diffraction grating is 90 degrees ± 20 degrees or less.   7. The diffraction grating spectrometer according to claim 6, wherein the multilayer film added to the diffraction grating surface uses a multilayer film diffraction grating deposited on the entire diffraction grating surface under the same film period length and average refractive index conditions. .   7. The diffraction grating spectrometer according to claim 6, wherein the diffraction grating surface is divided into a plurality of sections, and each of the sections uses a multilayer film diffraction grating deposited under different film period length and average refractive index conditions. .