JP2011075850A - Multilayer film laminar diffraction grating and spectrometer - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a multilayer film laminar diffraction grating that can be used in a wide wavelength band. <P>SOLUTION: A multilayer film structure 20, in which a low density material layer and a high-density material layer are laminated alternately is uniformly formed on a diffraction surface of the multilayer film laminar diffraction grating 10. The multilayer film structure 20 is stratified into a plurality of (five) layers in the film thickness direction which are a first layer 21, a second layer 22, a third layer 23, a fourth layer 24 and a fifth layer 25 formed sequentially, in this order starting from the top. Each of the first layer 21 to the fifth layer 25 is made up of the low-density material layer and the high density material layer. The length of the period of the multilayer film (the thickness of the low-density material layer and the thickness of the high-density material layer) differs in each of the first layer 21 to the fifth layer 25, and the length of period is set, such that it is larger on the first layer 21 side (the side where the light is incident) and smaller on the fifth layer 25 side (the substrate 11 side). <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a multilayer laminar diffraction grating structure capable of performing spectroscopy in the X-ray region, and a spectroscope using the structure.

  The diffraction grating, for example, has a function to split light in a wide wavelength range from infrared to X-ray, and outputs a single wavelength light at the same time, and outputs a range of wavelengths of light at a position corresponding to each wavelength. It is used in spectroscopes such as multicolor meters. In particular, in the X-ray region, there is no substance that becomes an optical material such as a lens or a prism effective in this wavelength region, so that the diffraction grating is effective. In this case, a laminar diffraction grating that has a high reflectance on the surface is widely used. The laminar diffraction grating has a configuration in which a number of grooves having a rectangular cross section are formed on a plane (diffraction surface). The characteristics of a laminar diffraction grating depend on the grating constant (period length in which grooves are formed), the groove depth, the ratio of the peak width to the grating constant (duty ratio), and the reflective material of the diffraction surface. Is determined.

A multilayer laminar diffraction grating having a configuration in which a multilayer film (optical multilayer film) is formed on its surface (diffraction surface) is known as a particularly improved diffraction efficiency of a laminar diffraction grating. The multilayer film is a film having a structure in which two material layers having different optical constants are alternately and periodically laminated. The multilayer film used in the X-ray region includes a low-density material (for example, SiO ₂ ) layer, It has a configuration in which a high-density material (for example, Co) layer having a higher density is formed alternately. The multilayer film is used for obtaining a high reflectance in the X-ray reflection optical system. In this case, the multilayer film is used for enhancing the diffraction efficiency in the laminar diffraction grating. In order to increase the reflection efficiency in the X-ray reflection optical system, the film thickness configuration of the low-density material layer and the high-density material layer in the multilayer film is optimized so as to cause Bragg reflection (Bragg condition is satisfied). On the other hand, as described in Non-Patent Document 1, in the multilayer laminar type diffraction grating, the film thickness configuration is set so as to match the configuration of the diffraction grating (extended Bragg condition).

  However, since the incident angle and diffraction angle satisfying this extended Bragg condition differ depending on the wavelength, it has been generally difficult to obtain a multilayer laminar diffraction grating that can be used in a wide wavelength band. On the other hand, Non-Patent Document 2 describes a configuration in which a usable band is substantially expanded by dividing the diffraction surface and adapting each region to the extended Bragg condition for different wavelengths. Further, a multilayer laminar diffraction grating that can be used in a wide band (wavelength: 0.2 to 2 nm) particularly in the soft X-ray region by making the grating intervals not equal intervals, but a patent document 1.

  A configuration in which such a multilayer laminar diffraction grating is used in a spectroscope (monochromator) is described in Patent Document 1. This configuration is shown in FIG. In this monochromator 90, incident light (soft X-ray) 101 that has passed through an incident slit 91 is reflected by a concave mirror 92, enters a multilayer laminar diffraction grating 93, and is diffracted at different diffraction angles for each wavelength. . Thereafter, the diffracted soft X-rays are reflected by the plane mirror 94 and output as the output light 102 from the output slit 95. Here, by rotating the multilayer laminar diffraction grating 93 and changing the incident angle and the emission angle of the soft X-ray, the output wavelength is scanned, and by rotating the plane mirror 94 in synchronization with this rotation, Soft X-rays having this wavelength are output from the exit slit 95 as output light 102.

W. K. Warburton, “On the diffraction properties of multilayer coated plates”, Nuclear Instruments and Methods in Physics Research, A291, p. 278, 1990 T.A. Imazono, M.M. Ishino, M .; Koike, H.C. Sakai, and K.K. Sano, “Fabrication and evaluation of a wide-band multilayer-type holographic grafting for use with the soft X-ray flat field spectrograph. 46, p. 7054, 2007

JP 2006-133280 A

  However, in such a multilayer laminar diffraction grating, the wavelength band that can be handled by a single multilayer laminar diffraction grating is not yet sufficient. For example, in a spectrometer using this, since the incident angle and diffraction angle are set for each wavelength, the incident angle cannot be used constant for all wavelengths. For this reason, in order to use as a monochromator, as shown in FIG. 9, there is a complicated mechanism in which the multilayer laminar diffraction grating 93 and the plane mirror 94 are rotated in synchronization to adjust the incident angle and the outgoing angle. Necessary.

  That is, it has been difficult to obtain a multilayer laminar diffraction grating that can be used in a wide wavelength band.

  The present invention has been made in view of such problems, and an object thereof is to provide an invention that solves the above problems.

In order to solve the above problems, the present invention has the following configurations.
The multilayer laminar diffraction grating of the present invention has a diffraction grating structure formed by arranging a plurality of grooves having a rectangular cross section on a diffraction surface on a substrate, and includes a low density material layer and the low density material layer. A diffracted light obtained by diffracting incident light incident on the diffractive surface is provided with a multilayer film structure formed by alternately and periodically laminating high-density material layers having higher densities than the diffractive surface. A multilayer laminar type diffraction grating that outputs a low-density material layer and a high-density material layer, each of which has a different periodic length and has an extended Bragg condition on the diffraction grating structure. The periodic length in the plurality of layers is set to be small on the substrate side and to be large on the side on which the incident light is incident.
In the multilayer laminar diffraction grating of the present invention, the plurality of layers include diffraction efficiency by one layer, and transmission of the incident light and the diffracted light by all layers closer to the incident light than the one layer. The product with the rate is set to be uniform.
In the multilayer laminar diffraction grating according to the present invention, the grooves of the diffraction grating structure have unequal spacings on the diffraction surface, and imaging of output light from a spectrometer using the multilayer laminar diffraction grating The groove interval is set according to the characteristics.
The multilayer laminar diffraction grating of the present invention is characterized in that the diffraction surface is concave.
The spectrometer of the present invention is characterized in that the multilayer laminar diffraction grating is used.
The spectroscope of the present invention is characterized by outputting non-monochromatic incident light having a spread in at least one direction so as to form an image for each wavelength on the output surface.
The spectroscope of the present invention is characterized in that the multilayer laminar diffraction grating having a planar diffraction surface and a concave mirror are combined.
The spectroscope according to the present invention is characterized in that the reflecting surface of the concave mirror is formed with the same structure in the film thickness direction as the multilayer film structure.

  Since the present invention is configured as described above, a multilayer laminar diffraction grating that can be used in a wide wavelength band can be obtained, and a spectrometer capable of outputting light in a wide wavelength band can be obtained using the multilayer laminar diffraction grating. be able to.

It is a figure which shows the cross-section of the multilayer laminar type | mold diffraction grating used as the 1st Embodiment of this invention. It is a figure which shows the cross-section of the multilayer film structure provided in the diffraction surface of the multilayer laminar type | mold diffraction grating used as the 1st Embodiment of this invention. It is the spectrum of the diffraction efficiency of the multilayer laminar type diffraction grating which becomes the 1st embodiment of the present invention computed by the simplified model. It is the spectrum of the diffraction efficiency of the multilayer laminar type diffraction grating used as the 1st embodiment of the present invention computed by simulation. It is a figure which shows the structure of the spectrometer used as 2nd Embodiment. It is the result of calculating | requiring the light ray distribution and intensity distribution for every wavelength in the output surface of the spectrometer used as 2nd Embodiment by the ray tracing method. It is the spectrum of the diffraction efficiency computed about the multilayer laminar type spherical diffraction grating in the spectroscope which becomes a 2nd embodiment. It is a figure which shows the structure of the spectrometer used as 3rd Embodiment. It is a figure which shows the structure of an example of the spectrometer using the conventional multilayer laminar type diffraction grating.

  Hereinafter, a multilayer laminar diffraction grating according to an embodiment of the present invention will be described. Here, the basic structure of this multilayer laminar diffraction grating is the first embodiment, and a modification of this multilayer laminar diffraction grating is applied to a multicolor meter (spectrometer) according to the second embodiment. Further, a modified example of this multicolor meter will be described below as a third embodiment.

(First embodiment)
The first embodiment is a multilayer laminar diffraction grating having a planar diffraction surface. FIG. 1 shows a cross-sectional structure in a direction perpendicular to the groove formed on the diffraction surface of the multilayer laminar diffraction grating 10, and FIG. 2 shows an enlarged cross-sectional view of the multilayer film structure 20. The multilayer laminar diffraction grating 10 diffracts light in the soft X-ray region by a diffraction surface and separates it. In the following, the case where the shape of the diffraction surface before forming the grooves (engaged lines) of the diffraction grating is a plane is referred to as a planar shape, and the case where the shape is a concave shape (curved surface) is a concave shape (curved surface). Etc.).

1, the upper surface of the substrate 11 (diffraction surface) has a plurality of grooves are formed, the pitch (lattice constant: length g ₂ and the sum of the length g ₁ of the crest of the valley of the groove) is σ and groove depth are h. α is the incident angle of the incident light 15 (soft X-ray) measured from the normal line (dashed line) of the diffraction surface, and β is the diffraction angle of the diffracted light 16. In α and β, the counterclockwise direction from the normal is positive and the clockwise direction is negative. In this case, the diffraction order is represented by m _G. Here, the lattice constant σ is the reciprocal of the marking density (the number of grooves per unit length). This configuration is a general diffraction grating structure.

  Here, quartz or the like can be used as the material of the substrate 11. In order to form the above structure (diffraction grating structure) on this, for example, after forming a groove pattern with a photoresist using photolithography, an ion beam etching method or the like is performed using this as a mask to obtain a depth of h. Only the substrate 11 is etched. If σ is uniform on the diffractive surface, the photoresist can be exposed using an interference pattern of two beams of laser light and used as the mask.

  On the diffractive surface of the multilayer laminar diffraction grating 10, a multilayer film structure 20 in which low-density material layers 31 and high-density material layers 32 are alternately stacked is provided as in the case described in Patent Document 1. It is formed like this. Both the material constituting the low density substance layer 31 and the material constituting the high density substance layer 32 may be a single element or a compound. However, it is preferable that the density ratio between the high-density material layer 32 and the low-density material layer 31 is large in order to increase the diffraction efficiency. As shown in FIGS. 1 and 2, the multilayer film structure 20 is hierarchized into a plurality (five) in the film thickness direction. The first layer 21, the second layer 22, the third layer 23, A fourth layer 24 and a fifth layer 25 are sequentially formed. Each of the first layer 21 to the fifth layer 25 includes a low-density material layer 31 and a high-density material layer 32. In each of the first layer 21 to the fifth layer 25, the cycle length (low density) The thickness of the material layer 31 and the high-density material layer 32 is different, the period length is large on the first layer 21 side (incident light incident side), and the period length is on the fifth layer 25 side (substrate 11 side). Is set to be small. In each layer of the first layer 21 to the fifth layer 25, the period length is constant. Since FIG. 2 is a diagram showing an outline of the multilayer film structure, the period length and the number of layers in each layer are different from actual ones.

The multilayer film structure 20 (the first layer 21 to the fifth layer 25) can be formed by, for example, a sputtering method. In this case, the sputtering time is adjusted by appropriately switching between a target made of the material constituting the low-density substance layer 31 (for example, SiO ₂ ) and a target made of the material constituting the high-density substance layer 32 (eg, Co). Thus, the thickness of each layer can be adjusted.

  For example, Non-Patent Document 1 and Patent Document 1 describe the setting of the above parameters when the multilayer film structure 20 is not hierarchized and is configured with a single period length over the entire film thickness direction. Has been. First, in this case, the diffraction condition in the diffraction grating structure is given by the following equation. Here, λ is the wavelength of incident light (soft X-ray).

In the case of a multilayer laminar type diffraction grating, the effect of diffraction by the multilayer film structure 20 is also added, so that the following expression must also be satisfied (extended Bragg condition). Here, _MM is the interference order of the multilayer film.

  Here, D is the periodic length of the multilayer film in the multilayer film structure 20, and δ is the average refractive index of the multilayer film structure 20 (complex refraction of the low-density material layer 31 and the high-density material layer 32 in consideration of the film thickness ratio). Δ = 1−n, where n is the weighted average of the real part of the rate. The refractive index n in the soft X-ray region is a value smaller than 1 and very close to 1.

  The groove depth h is expressed by the following equation depending on the phase matching conditions in the diffracted light from the bottom and top of the groove.

For example, the lattice constant σ and 1/2400 (mm), + 1st-order diffracted orders mG of the diffraction grating, the diffraction order _{m M} of the multilayer film structure 20 and +1 order, a wavelength λ 0.33nm (3757eV), the angle of incidence Consider the case where α is 88.65 °. The low density material layer 31 in the multilayer film structure 20 is made of SiO ₂ , the high density material layer 32 is made of Co, and the thickness ratio of the high density material layer 32 to the periodic length in the multilayer film structure 20 is made 0.4. In this case, the period length satisfying both the expressions (1) and (2) is 5.00 nm, the diffraction angle β is −87.361 °, and the groove depth h is 2.341 nm.

  According to the simulation, when the number of periods in the multilayer structure 20 is 24 and the groove depth h is 3.0 nm, the diffraction efficiency is 42.4% at the maximum when the wavelength λ is 0.33 nm, half of The value width is 0.018 nm (208 eV). The width at which the maximum diffraction efficiency of 10% is obtained instead of the half width is 0.028 nm (321 eV). These values are 1/10 or less of the wavelength and are extremely small in practical use. Thus, when the period length is single, the peak value of the diffraction efficiency is high, but the half width of the diffraction efficiency is small, so that the usable wavelength band is extremely narrow.

Therefore, in the multilayer laminar diffraction grating 10, the multilayer film structure 20 is hierarchized, and the periodic lengths of the multilayer films in the first layer 21 to the fifth layer 25 are changed. Here, each layer (the first layer 21 to the fifth layer 25) is set so that the extended Bragg condition (2) is satisfied at the wavelength to be output (diffracted). Here, as shown in FIG. 2, the periodic length is set to be large on the first layer 21 side on the upper side and to be small on the fifth layer 25 on the lower side. Accordingly, the wavelengths optimized by the first layer 21, the second layer 22, the third layer 23, the fourth layer 24, and the fifth layer 25 are respectively λ ₁ , λ ₂ , λ ₃ , λ ₄ , λ ₅ (λ ₁ > λ ₂ > λ ₃ > λ ₄ > λ ₅ ). In this configuration, long-wavelength light having a large absorption in the multilayer structure 20 is diffracted in a layer near the surface, and short-wavelength light having a small absorption in the multilayer structure 20 is diffracted in a lower layer. The

  However, when the multilayer film structure 20 has such a hierarchical structure, for example, light incident on the fifth layer 25 is light transmitted through the first layer 21 to the fourth layer 24, and light diffracted by the fifth layer 25 is The light passes through the first layer 21 to the fourth layer 24 and is emitted. Therefore, in this case, it is necessary to consider the influence of the first layer 21 to the fourth layer 24 on the light incident on the fifth layer 25 and the light diffracted by the fifth layer. That is, for the incident light and diffracted light of the i-th layer, it is necessary to consider the influence of absorption from the first layer to the (i-1) -th layer. That is, when considering the diffraction efficiency of a specific wavelength by a certain layer, the diffraction efficiency of this layer alone and the transmission of incident light and diffracted light by all layers above this layer (incident light side) The product of the rate is calculated, and it is preferable that this is uniform in each hierarchy. For this purpose, it is necessary that the following equation holds.

Here, it is assumed that the incident angle to each layer is constant (= α), and the diffraction angle from the i-th layer is β _i . R _i is the diffraction efficiency when the i-th layer is present alone, η _i is a weighted average value corresponding to the film thickness ratio of the extinction coefficient at the wavelength λ _i of the low-density material layer 31 and the high-density material layer 32 It is. _Di is the thickness of the i-th layer (= number of periods × period length). Here, incident light and refraction of diffracted light on the surface of the multilayer structure 20 and reflection and refraction of light of wavelength λ _i in the jth layer (j ≠ i) are ignored. Note that the part represented by exp () on the left side in the equation (6) indicates the transmittance of light of wavelength λ _i in all layers (upper layers) above the i-th layer.

A specific example in which the above conditions are actually set will be described. As described above, the parameters of the diffraction grating are as follows: σ = 1/2400 (mm), incident angle α = 88.65 °, groove depth h = 3.0 nm, diffraction order m _G = + 1, interference order m _M = +1. The low-density material layer 31 is SiO ₂ , the high-density material layer 32 is Co, the ratio of the high-density material layer 32 to the periodic length is fixed at 0.4, the periodic lengths are different in five layers, and λ _i is different. Let Table 1 shows the results of an example of calculating the diffraction efficiency Ri in each layer, the upper layer transmittance in the equation (6), and the value of the equation (6).

  Based on the results of Table 1, the diffraction efficiency of each layer and the absorption rate by the layer above this layer are calculated for each wavelength, and if the sum of each layer is taken, the simplified diffraction efficiency is calculated. A spectrum can be obtained. This characteristic is shown in FIG. On the other hand, FIG. 4 shows a spectrum of diffraction efficiency calculated by performing simulation on the configuration in which the first to fifth layers are sequentially formed as shown in FIG. In the spectrum (FIG. 4) calculated by the simulation, the difference between the peak and the valley is larger than that of the simplified spectrum (FIG. 3). It can be confirmed that a diffraction efficiency of% or more can be obtained.

  Accordingly, the wavelength band of light that can be diffracted and dispersed by the multilayer laminar diffraction grating 10 is widened, that is, the multilayer laminar diffraction grating 10 can be used in a wide wavelength band. By using this, it is possible to obtain a spectrometer capable of outputting light in a wide wavelength band.

(Second Embodiment)
In the second embodiment, a multilayer laminar spherical diffraction grating in which the diffraction surface of the multilayer laminar diffraction grating is a curved surface (spherical shape), and the lattice constant σ is not uniform on this surface, and It is the used multicolor meter (spectrometer). About the structure which makes a diffraction surface the concave shape with a condensing capability, it is the same as that of what is described in the nonpatent literature 2, for example.

  The configuration in which the lattice constant σ is non-uniform, that is, the groove spacing is unequal is the same as that described in Patent Document 1. In this case, a multicolor meter 50 can be configured as shown in FIG. 5 using a multilayer laminar spherical diffraction grating (multilayer laminar diffraction grating) 40 in which the concave shape is a spherical shape. In the multicolor meter 50, non-monochromatic incident light 61 that has passed through the incident slit 51 enters the multilayer laminar spherical diffraction grating 40. The diffracted light 62 diffracted and split by the multilayer laminar spherical diffraction grating 40 is incident on a detector 63 having a planar detection surface here. The slits in the entrance slit 51 are formed in the vertical direction in FIG. 5, and the incident light 61 that spreads in this direction is set so as to form an image on this detection surface (output surface) for each wavelength. In other words, the detection surface is set to be an imaging portion of the output light of the multicolor meter.

Here, the normal direction of the diffractive surface at the center of the multilayer laminar spherical diffraction grating 40 is the x-axis, and the direction orthogonal to the x-axis on the surface including the incident light 61 and the diffracted light 62 is the y-axis, The direction orthogonal to the y axis is taken as the z axis. It is assumed that the grooves (engraving lines) in the multilayer laminar spherical diffraction grating 40 are formed in parallel to the z-axis and aligned in the y-axis direction. In this case, the incident angle α ₀ on the optical axis, the diffraction angle (outgoing angle) β ₀ , and the angle θ formed by the detection surface (output surface) of the detector 63 and the tangential plane of the multilayer laminar spherical diffraction grating 40 are: Each is represented as shown. In the multilayer laminar spherical diffraction grating 40, the distance between the intersection of the tangent plane at the center of the diffractive surface and the image plane and the center of the diffractive surface is L. In the figure, r (distance between the entrance slit 51 and the multilayer laminar spherical diffraction grating 40) and r '(distance between the multilayer laminar spherical diffraction grating 40 and the detector 63), and the concave curvature radius R are as follows. From the relationship with α ₀ , β ₀ , θ, L, etc., the imaging point is set to be on the detection surface of the detector 63.

This imaging characteristic is expressed by using the radius of curvature R of the multilayer laminar spherical diffraction grating 40, the lattice constant σ, and the like. At this time, the groove intervals are unequal, and σ is not uniform. In this case, similarly to the case described in Patent Document 1, when the position in the y-axis direction in the multilayer laminar spherical diffraction grating 40 is represented by w, the groove at the position w is the number of the groove when viewed from the origin. N (w) indicating whether or not can be expressed as a polynomial of w as shown below. Here, n ₂ , n ₃ , and n ₄ are parameters that define unequal intervals, and σ ₀ is a reference value of the lattice constant.

n ₂ , n ₃ , and n ₄ are set so that the imaging characteristics are optimal, that is, light in a predetermined wavelength region is imaged on the detector 63. This setting can be performed using optical simulation. Note that n (w) can be set as appropriate in order to adjust the imaging characteristics, and another approximate expression may be used.

As a specific example, the lattice constant at y = 0 is 1/2400 (mm) with σ ₀ , α ₀ is 88.65 °, r is 236.756 mm, θ = 90 °, and L = 233.5 mm. The multilayer laminar spherical diffraction grating 40 has a width (y-axis direction) of 50 mm and a height (z-axis direction) of 30 mm. In this case, the optimal unequal spacing parameters are n ₂ = −3.332729 × 10 ⁻³ mm ⁻¹ , n ₃ = 1.26818 × 10 ⁻⁵ mm ⁻² , and n ₄ = −7.49441 × 10 ^{− 8} mm ⁻³ .

  FIG. 6 shows the result of the light ray distribution on the detector 63 and its intensity distribution obtained in this case using the ray tracing method. Here, the wavelength (λ) is calculated for four wavelengths of 0.3 nm, 0.4 nm, 0.5 nm, and 0.6 nm, and for each of these wavelengths, a wavelength of λ ± λ / 100 is also calculated. Yes. In this case, the horizontal direction is the dispersion direction, and the intensity (Intensity) indicates the integral value of the light beam in the direction (Height) perpendicular thereto. In the incident light 61, spread in the horizontal direction is limited by the incident slit 51, but spread in the vertical direction. However, at any wavelength, an image is formed in a finite size on the output surface (detection surface). As described above, the multicolor meter 50 can image incident light that is not monochromatic and spreads in at least one direction for each wavelength on the detection surface (output surface).

  The resolution at each wavelength calculated from the result of FIG. 6 is 1471 at the maximum of 0.4 nm, and 389 at the minimum of 0.6 nm. Therefore, it can be confirmed that the image has sufficient resolution in these wavelength ranges. Moreover, since the light of these wavelengths can be output simultaneously from single incident light, it can be used as a multicolor meter.

  In this multilayer laminar spherical diffraction grating 40, the diffraction surface has a spherical shape and the lattice spacing is unequal, so that depending on the incident position of incident light with respect to the multilayer laminar spherical diffraction grating 40, The incident angle is different. This effect will be described below. When the above parameters are used, the incident angle on the diffraction surface of the multilayer laminar spherical diffraction grating 40 at z = 0 and the value of the marking density (lines / mm) obtained from n (w) at this location. Is shown in Table 2 for each value of y.

  Due to this characteristic, the incident angle and the marking density differ for different incident positions. Therefore, in general, diffraction conditions are also different. What is actually detected on the detection surface of the detector 63 is the sum of the light diffracted at each of these points on the diffraction surface of the multilayer laminar spherical diffraction grating 40. The spectrum on the detection surface in this case is shown in FIG. 7 as in FIG. Compared with the case of FIG. 4, which is a planar multilayer laminar diffraction grating, the difference between the peak portion and the valley portion of the spectrum is small and flatter. This is because when such a multilayer laminar spherical diffraction grating 40 is used, the light detected on the detection surface is the sum of the light diffracted on the diffraction surface under different diffraction conditions, and the spectrum is averaged. Because.

  Therefore, the multilayer laminar spherical diffraction grating 40 can be used in a wide wavelength band, and the spectrum of the diffracted light can be more averaged than in the case of the planar type. The same applies to the output light of a multicolor meter (spectrometer) using this.

  In the configuration of FIG. 5, the above-described characteristics are realized by using only the multilayer laminar spherical diffraction grating 40 as the movable part in the optical system. On the other hand, in the conventional monochromator using the diffraction grating, as shown in FIG. 9, a complicated mechanism of interlocking the two optical systems is required. The reason why such a good characteristic can be obtained in the configuration of FIG. 5 is that a hierarchical structure in a multilayer film structure is used, the diffraction surface is concave, and the lattice spacing is unequal.

(Third embodiment)
In the third embodiment, instead of the multilayer laminar spherical diffraction grating 40 in the second embodiment, a multi-layer laminar planar diffraction grating 80 having no light collecting ability is used, and a similar multicolor meter (spectral spectroscopy) is used. Device) 70 is an example of the configuration. FIG. 8 is a diagram showing this configuration.

  In this multicolor meter 70, a multilayer laminar type plane diffraction grating (multilayer laminar type) having the multilayer film structure in the first embodiment and the unequally spaced diffraction grating in the second embodiment. (Diffraction grating) 80 is used. Unlike the multilayer laminar spherical diffraction grating 40 in the second embodiment, since the diffraction surface thereof is a flat surface, the multilayer laminar planar diffraction grating 80 itself does not have an imaging capability.

  In this multicolor meter 70, the non-monochromatic incident light 61 that has passed through the incident slit 71 enters a concave mirror 72 having a concave reflecting surface. Thereafter, this light is diffracted by the multilayer laminar type planar diffraction grating 80, and the diffracted light 62 is incident on a detector 63 having a planar detection surface. The incident angle with respect to the multilayer laminar planar diffraction grating 80 can be adjusted by rotating the multilayer laminar planar diffraction grating 80 as shown.

  In this multicolor meter 70, the imaging action is provided by the concave mirror 72, and the multilayer laminar planar diffraction grating 80 performs only diffraction and spectroscopy. Even if such a configuration is used, it is apparent that the same effects as those of the second embodiment can be obtained. Also, in this case, optimization of diffraction and spectral action (spectrum broadening, etc.) is performed by designing the multilayer laminar planar diffraction grating 80, and the imaging action can be independently adjusted by designing the concave mirror 72. Therefore, the degree of freedom in designing the multicolor meter 70 is increased.

  In order to increase the reflectivity of the concave mirror 72, it is preferable to coat the surface of the concave mirror 72 with gold or platinum having a high reflectivity for soft X-rays. Further, it is more preferable that the multilayer film structure similar to the multilayer laminar type plane diffraction grating 80 and the structure in the film thickness direction are the same, that is, the structure shown in FIG.

  In the multilayer laminar type planar diffraction grating 80, the groove interval in the diffraction grating structure may be uniform. Even in this case, it is clear that the spectrum can be broadened.

  In any of the above-described embodiments, the wavelength range of the light to be dispersed is the soft X-ray range, but it is obvious that the same effect can be obtained with light in other wavelength ranges. In such a case, the two material layers constituting the multilayer film are changed to two material layers having different optical constants (refractive indices) in the wavelength region, and the marking density and the like are adapted to the wavelength region, and the same as described above. It can be set as this structure. However, this multilayer laminar diffraction grating and a spectrometer using this are particularly effective in the soft X-ray region where the effect of Bragg diffraction in the multilayer structure is large and the lattice constant is within the range of easy manufacture. is there. In particular, it is particularly effective for X-rays having an energy of about 2 keV to 4 keV (wavelength 0.31 nm to 0.62 nm), which has been difficult to obtain a good spectroscope as shown in the simulation. .

  Further, although the number of layers in the multilayer film structure is five, this number is also arbitrary. Obviously, by increasing this number, a wider band can be achieved and the spectrum becomes more flat. On the other hand, when this number is large, there is a problem that absorption due to the multilayer film structure is increased and manufacturing is difficult. In consideration of these points, the number of layers is appropriately set.

  In the above example, a multicolor meter that is required to have a particularly wide wavelength range has been described. However, it is also clear that a monochromator can be configured using this multilayer laminar diffraction grating.

10, 93 Multilayer laminar diffraction grating 11 Substrate 15, 61, 101 Incident light 16, 62 Diffracted light 20 Multilayer structure 21 First layer 22 Second layer 23 Third layer 24 Fourth layer 25 Fifth layer 31 Low density Material layer 32 High-density material layer 40 Multilayer laminar spherical diffraction grating (multilayer laminar diffraction grating)
50, 70 Multicolor meter (spectrometer)
51, 71, 91 Incident slit 63 Detector 72, 92 Concave mirror 80 Multilayer laminar type plane diffraction grating (multilayer laminar type diffraction grating)
90 Monochromator (spectrometer)
94 Flat mirror 95 Outgoing slit 102 Outgoing light

Claims (8)

A diffraction grating structure in which a plurality of grooves having a rectangular cross section are arranged on the diffraction surface on the substrate is formed, and a low density material layer and a high density material layer having a higher density than the low density material layer are formed. A multilayer laminar diffraction grating is provided that has a multilayer film structure formed by alternately and periodically stacking on the diffractive surface and outputs diffracted light diffracted incident light incident on the diffractive surface side. And
The multilayer structure has a periodic length in which the low-density material layer and the high-density material layer are laminated, and has a periodic length that satisfies an extended Bragg condition with an incident angle and diffraction angle of one wavelength within a desired wavelength range. It consists of multiple hierarchies,
The multilayer laminar diffraction grating according to claim 1, wherein the periodic length in the plurality of layers is set to be small on the substrate side and large on the incident light incident side. The plurality of hierarchies are:
The product of the diffraction efficiency by one layer and the transmittance of the incident light and the diffracted light by all layers closer to the incident light than the one layer is set to be uniform. The multilayer laminar type diffraction grating according to claim 1.   The groove interval in the diffraction grating structure is unequal on the diffraction surface, and the groove interval is set according to the imaging characteristics of the output light of the spectrometer using the multilayer laminar diffraction grating. The multilayer laminar type diffraction grating according to claim 1 or 2, wherein   4. The multilayer laminar diffraction grating according to claim 1, wherein the diffractive surface has a concave shape. 5.   A spectrometer using the multilayer laminar type diffraction grating according to any one of claims 1 to 4.   6. The spectrometer according to claim 5, wherein non-monochromatic incident light having a spread in at least one direction is output so as to form an image for each wavelength on the output surface.   4. A spectroscope comprising a multilayer laminar diffraction grating according to claim 3 and a concave mirror, wherein the diffraction surface is planar.   The spectroscope according to claim 7, wherein the reflecting surface of the concave mirror is formed with the same structure in the film thickness direction as the multilayer film structure.

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