Polarization diffraction element and polarization analyzer

Abstract

To provide a polarization diffraction element and a polarization analysis device capable of accurately determining a polarization trajectory from a diffraction image obtained in short time.SOLUTION: A polarization analysis device includes: a polarization diffraction element which has a structure having a characteristic as a polarization diffraction grating in which the optical anisotropy is periodically modulated in a radiation direction from one point on a plane. The direction of the lattice vector of the polarization diffraction grating changes continuously in a predetermined angular range of 90 to 360° centered on the one point.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a polarization diffraction element and an ellipsometer equipped with the polarization diffraction element. [Background technology]

[0002] Measuring the polarization state, which is the oscillation mode of the electric field of light, is an important technology in modern times. For example, polarized light incident on a material with optical anisotropy undergoes a phase shift depending on the direction of vibration of the light wave, and the transmitted and reflected light is usually elliptically polarized (circularly polarized light and linearly polarized light can be considered special forms of elliptically polarized light). Therefore, when analyzing the properties of a material using light (such as film thickness or optical constants), it is necessary to accurately identify the elliptically polarized state. Polarized light is also used in a variety of fields, including optical communications, optical storage media, image displays, and optical pressure applications, and there is a demand for methods to accurately analyze the polarization state.

[0003] Conventionally, in polarization analysis, an analyzer that transmits only light with a specific vibration direction is rotated, and the trajectory of elliptically polarized light is measured from the intensity of the transmitted light at each rotation angle. For example, in ellipsometry, linearly polarized light is irradiated onto a film-like sample, and the reflected light that passes through a rotating analyzer is received to analyze the polarization state and measure physical properties such as film thickness and optical constants.

[0004] Means for simultaneously detecting polarized light in multiple vibration directions are also being considered. For example, Patent Document 1 (JP 2007-263593 A) describes an apparatus that includes a polarizer patterned so that the direction of transmitted polarized light differs in each region, and a light-receiving element that can independently receive the intensity of light that has passed through each region, and that can measure the phase difference and principal axis direction of light that has passed through a film-like sample.

[0005] Patent Document 2 (Japanese Patent No. 5109112) describes an ellipsometry system that determines the azimuth angle and ellipticity of elliptically polarized light of incident light by configuring a polymer layer in which a diffraction grating is formed by periodically modulating the molecular orientation structure, with lattice vectors in multiple different directions. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Laid-Open No. 2007-263593 [Patent Document 2] Patent No. 5109112 specification Summary of the Invention [Problem to be solved by the invention]

[0007] In conventional systems that use a rotating analyzer to analyze elliptically polarized light, it is difficult to miniaturize the device configuration, and cost control is also difficult due to the use of expensive optical elements. Furthermore, since it takes a certain amount of time to analyze the polarization state, it is not suitable for analyzing dynamically changing polarization.

[0008] In Patent Document 1, a patterned polarizer is used to measure light transmitted through a substrate or film sample, but the sample must have a certain area due to the device configuration. Also, although the phase difference and the principal axis can be determined by estimating the locus of the ellipse from the measured values, the locus of the ellipse cannot be measured directly.

[0009] Patent Document 2 describes the use of a diffraction grating with a constant molecular orientation and periodically modulated orientation order through interference exposure with polarized light to measure the azimuth angle and ellipticity of polarized light incident on the diffraction grating. In this case, multiple exposure is used to form a diffraction grating with multiple lattice vectors with different orientations, and the elliptical trajectory can be determined in a manner similar to that achieved with a rotating analyzer. However, forming the diffraction grating described in Patent Document 2 requires the use of complex exposure optics during manufacturing. Furthermore, the fabrication method described in Patent Document 2 makes it difficult to multiplex multiple lattice vectors in-plane with high precision and density. Furthermore, when determining the trajectory from multiple points on the trajectory of elliptically polarized light, errors in the measurements make it impossible to accurately plot the trajectory.

[0010] When the light to be measured has a wavelength distribution with a certain width, it is desirable to be able to determine the polarization state for each wavelength.

[0011] An object of the present invention is to provide a polarization diffraction element that can be manufactured by a simple method and that can accurately measure the trajectory of polarized light in a short period of time, and an apparatus that includes this element. [Means for solving the problem]

[0012] The first configuration of the present invention has a structure having characteristics as a polarization diffraction grating in which optical anisotropy is periodically modulated in the radial direction from one point in a plane, The direction of the grating vector of the polarization diffraction grating changes continuously within a predetermined angle range of 90 to 360 degrees around the one point. It is a polarized diffraction element.

[0013] By using the above-mentioned polarizing diffraction element, ring-shaped or arc-shaped diffracted light can be obtained, and this can be used to accurately analyze the shape of elliptically polarized light.

[0014] The above-mentioned polarization diffraction element is a plurality of annular or arc-shaped regions having optical anisotropy; A plurality of annular or arc-shaped regions having optical isotropy, are arranged concentrically and alternately around the one point, It may also be a polarizing diffraction element.

[0015] The above-mentioned polarization diffraction element is The film comprises a material (liquid crystal polymer material) containing a photosensitive liquid crystal polymer, and regions in which the liquid crystal polymer is oriented in a predetermined direction and regions in which the liquid crystal polymer is oriented randomly are alternately arranged. It may also be a polarizing diffraction element.

[0016] By controlling the orientation of the photosensitive liquid crystal polymer, a polarization diffraction element with a simple structure can be provided by a simple method.

[0017] A second aspect of the present invention is a polarization analyzer including the above-described polarization diffraction element and a light receiving element having a light receiving surface parallel to the polarization diffraction element, the light receiving surface being positioned a predetermined distance away from the polarization diffraction element in the normal direction of the polarization diffraction element.

[0018] This polarization analyzer can measure the state of polarization incident on the polarization diffraction element for each wavelength with a single image capture. [Effects of the Invention]

[0019] According to the present invention, the polarization state can be accurately analyzed from a diffraction image captured at one time, improving the efficiency of analysis, enabling changes in the polarization state over time to be observed, and enabling the analysis device to be made smaller. [Brief explanation of the drawings]

[0020] The present invention will be more clearly understood from the following description of preferred embodiments with reference to the accompanying drawings. However, the embodiments and drawings are merely for illustration and explanation, and should not be used to define the scope of the present invention, which is defined by the appended claims. In the accompanying drawings, the same part numbers in multiple drawings indicate the same parts. [Figure 1] 1 is a plan view schematically illustrating the configuration of a polarization diffraction element according to an embodiment of the present invention. [Figure 2A] 1 is a schematic diagram showing a diffraction grating in which the orientation of a liquid crystalline polymer is periodically modulated in one direction. [Figure 2B] FIG. 2B illustrates a periodic modulation of the refractive index in the diffraction grating of FIG. 2A. [Figure 3] 2B is a schematic diagram showing first-order diffracted light by the diffraction grating of FIG. 2A. FIG. [Figure 4] 2B is a graph showing the thickness dependency of the diffraction efficiency of the diffraction grating of FIG. 2A. [Figure 5]2B is a graph showing that the change in the diffraction efficiency of first-order diffracted light according to the angle between the oscillation direction of the electric field and the grating vector in the diffraction grating of FIG. 2A varies depending on the thickness of the diffraction grating. [Figure 6A] 1 is a plan view schematically illustrating the configuration of a polarization diffraction element according to an embodiment of the present invention. [Figure 6B] 6C is a diagram schematically showing annular first-order diffracted light generated by the polarization diffraction element of FIG. 6B. FIG. [Figure 7A] 6B is a plan view schematically showing the configuration of a polarization diffraction element according to a different embodiment from that shown in FIG. 6A. FIG. [Figure 7B] FIG. 10 is a plan view schematically showing the configuration of a polarization diffraction element according to yet another embodiment. [Figure 7C] FIG. 10 is a plan view schematically showing the configuration of a polarization diffraction element according to yet another embodiment. [Figure 8A] FIG. 2 is a plan view showing a polarizing diffraction element in the form of a circular divided element, which is a modified example of the polarizing diffraction element shown in FIG. [Figure 8B] FIG. 10 is a plan view showing a semicircular polarization diffraction element as another modified example. [Figure 8C] FIG. 10 is a plan view showing a sector-shaped polarization diffraction element as yet another modified example. [Figure 9] 1 is a diagram showing the configuration of an ellipsometer according to an embodiment of the present invention; [Figure 10A] FIG. 1 is a diagram showing the configuration of an optical system of an ellipsometer in the prior art. [Figure 10B] 1 is a diagram showing the configuration of an optical system of an ellipsometer including a polarization analyzer according to the present invention. [Figure 11A] 1 is a crossed Nicol image of the polarizing diffraction element fabricated in the example, taken by a polarizing microscope. [Figure 11B] For reference, this is a crossed Nicol image taken by a polarizing microscope of an element fabricated with a longer modulation period than the polarizing diffraction element of FIG. 11A. [Figure 12] FIG. 1 is a diagram showing the configuration of an optical system used to inspect the performance of a polarization diffraction element. [Figure 13]1A and 1B are diagrams showing diffraction images of (A) linearly polarized light, (B) elliptically polarized light, and (C) circularly polarized light, obtained by the polarization diffraction element of the example. [Figure 14] FIG. 14 is a diagram showing the diffracted light intensity distribution with respect to the azimuth angle obtained from the diffraction image shown in FIG. [Figure 15A] This is a diffraction image of polarized light using an LED as a light source. [Figure 15B] 15B is a graph showing the distribution of diffracted light intensity with respect to the azimuth angle obtained from the diffraction image of FIG. 15A. [Figure 16] 10 is a graph showing a change in the diffracted light intensity distribution depending on the wavelength of polarized light. [Figure 17] 1 is a three-dimensional overhead view of the diffraction intensity distribution with respect to the polarization azimuth angle, dispersed by wavelength, displayed using the polarization analyzer of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0021] [Polarized diffraction element] The polarized diffraction element of the present invention has a structure having the properties of a polarized diffraction grating in which optical anisotropy is periodically modulated in the radial direction from a single point (radiation center) in a plane, and the direction of the grating vector of the polarized diffraction grating changes continuously within a predetermined angular range, preferably from 90 to 360°, around the single point.

[0022] This polarizing diffraction element may be a polarizing diffraction element in which a plurality of annular or arc-shaped regions having optical anisotropy and a plurality of annular or arc-shaped regions having optical isotropy are concentrically arranged alternately around the single point.

[0023] FIG. 1 is a schematic plan view for illustrating the configuration of a polarization diffraction element 1 of the present invention. In the illustrated example, polarization diffraction element 1 has first regions I and second regions II, each having different optical anisotropy, arranged alternately in a concentric pattern around a point O. For example, the first regions I may exhibit optical isotropy, while the second regions II may exhibit optical anisotropy. On a line passing through point O, the element functions as a diffraction grating whose optical anisotropy is periodically modulated, and its grating vector k can be oriented in the direction of any rotation angle (indicated in the figure by the rotation angle θ from the x-axis direction).

[0024] The above-described polarization diffraction element 1 may be a film- or plate-like member having an optical structure that is axially symmetric with respect to a normal line passing through a point O on the surface. Such an optical element can be easily obtained, for example, by controlling the orientation of a photosensitive (photoreactive) liquid crystalline polymer.

[0025] FIG. 2A is a schematic diagram illustrating a diffraction grating formed by periodic modulation of the orientation of a liquid crystalline polymer in the direction of a single lattice vector k. In the figure, alignment regions A, in which the liquid crystalline polymer L is oriented substantially parallel to the direction of the lattice vector k, and random regions R, in which the liquid crystalline polymer L is randomly oriented, are alternately arranged in a striped pattern. In such a diffraction grating, the refractive index n is modulated in a rectangular pattern, as shown in FIG. 2B. When laser light is incident on this diffraction grating from the normal direction (z direction in FIG. 2A), positive and negative first-order diffracted light (hereinafter sometimes referred to as first-order light) depending on the orientation period of the liquid crystalline polymer are generated on both sides of the zero-order light, as shown schematically in FIG. 3.

[0026] When polarized light is incident on this diffraction grating, the change in diffraction efficiency, which depends on the polarization direction and the thickness of the diffraction grating, can be calculated as follows.

[0027] In Figure 2A, if the width Λ (the fundamental vector length of lattice vector k) of one orientation region A and one random region R combined is one period π, then an arbitrary position x in the lattice vector k direction (x-axis direction) in Figure 2A is δ = πx / Λ in the coordinate system shown in Figure 2B.

[0028] In the figure, the refractive index in the x-axis direction is n x , the refractive index in the y-axis direction is n y Then, in the random orientation region R, n x = n y ≡ n ave This becomes: On the other hand, in the uniaxially oriented region A, where the molecular orientation direction is parallel to the x-axis direction, n x > n ave > n y This becomes:

[0029] The first-order light generated by light incident on this diffraction grating corresponds to the first spatial frequency component when the phase modulation of this rectangular grating (diffraction grating) is Fourier expanded, and can be analytically calculated using the first kind of Bessel function. The diffraction efficiency of the positive and negative first-order light generated when linearly polarized light (p-polarized light) is incident in the x-axis direction is expressed as the phase difference ΔΦ x of ΔΦ x = kd Δn x cos(δ) As, η p = J1 2 (ΔΦ x ) Here, k is the wave number, and there is a relationship between k and the wavelength λ of the incident light, k = 2π / λ. Also, d is the thickness of the grating. Also, Δn x corresponds to the amplitude of the first spatial frequency component (or the amount of change in refractive index) when the rectangular refractive index modulation is Fourier expanded. Similarly, the diffraction efficiency of the positive and negative first-order light generated when linearly polarized light (s-polarized light) in the y-axis direction is incident is calculated by the phase difference ΔΦ y of ΔΦ x = kd Δn y cos(δ) As, η s = J1 2 (ΔΦ y ) It should be noted that, from the relationship of the periodic modulation of the refractive index shown in FIG. 2B, Δn x and Δny have opposite signs.

[0030] Figure 4 shows the birefringence Δn (Δn x and Δn y This figure shows the dependence of the diffraction efficiency on the grating thickness d, calculated using the Bessel function above, for p-polarized and s-polarized incident light, when the difference between the grating thickness d and the grating thickness d is 0.16 and the wavelength is 633 nm. As shown, the diffraction grating efficiency for positive and negative first-order light in a diffraction grating with a periodic orientation distribution can be higher for s-polarized incident light or higher for p-polarized incident light as the grating thickness d changes.

[0031] Figure 5 shows the diffraction efficiency of first-order diffracted light based on the diffraction characteristics described above. When the grating thickness d1 is 0.5 μm, the diffracted light intensity is maximized when the azimuth angle of the linearly polarized light of the incident light is ±90° (x-axis direction) and minimized when it is 0° (y-axis direction). That is, the diffracted light intensity is maximized when the lattice vector k and the electric field vector E, which indicates the polarization direction, have a relationship E / / k. When the grating thickness d2 is 2.8 μm, the diffracted light intensity is maximized when the azimuth angle of the linearly polarized light of the incident light is 0° (y-axis direction) and minimized when it is ±90° (x-axis direction). That is, the diffracted light intensity is maximized when the lattice vector k and the electric field vector E have a relationship E⊥k. It can also be seen that the diffracted light intensity has a gentle distribution at angles intermediate between the two.

[0032] FIG. 6A is a schematic diagram illustrating the configuration of a polarization diffraction element 1 according to one embodiment of the present invention. In this polarization diffraction element 1, regions R in which the liquid crystalline polymer L is randomly oriented and regions A in which it is oriented in the radial direction (the direction of the radius) are alternately arranged in a concentric pattern around a center point O. Although the illustration is simplified, in reality, the liquid crystalline polymer L is densely distributed in each region R and O, and the width of each region is narrow. Therefore, when viewed in any direction on a line passing through the center point O (the illustration shows lattice vectors k1, k2, and k3 as examples), the element functions as a diffraction grating in which the random regions R and the oriented regions A are alternately distributed. The diffraction characteristics, when viewed in terms of a region with a microscopic width in the circumferential direction, can be explained in the same way as the striped diffraction grating described above ( FIG. 2A ).

[0033] 6B is a diagram schematically showing a diffraction image when laser light is incident on the polarization diffraction element. In this polarization diffraction element 1, the direction of the grating vector k is the radial direction from the center point O, that is, the radial direction of a circle centered at point O, and changes continuously. Therefore, the position of the first-order diffracted light formed by the diffraction grating in each grating vector direction (for example, the direction of vectors k1, k2, and k3 shown in FIG. 6A) also changes continuously along the rotation direction, and the first-order diffracted light is observed as annular diffracted light.

[0034] When polarized light is incident on the polarization diffraction element 1 from the normal direction (directly above: z direction in FIG. 6A), the diffraction grating, which exhibits periodic modulation of optical properties in one dimension, as shown in FIG. 2A, exhibits maximum or minimum diffracted light intensity only when the polarization oscillation direction is parallel or perpendicular to the lattice vector k. At intermediate intensities, even if it is determined that the polarization oscillation direction is tilted with respect to the lattice vector k, it is impossible to determine whether the tilt angle is positive or negative. In contrast, the polarization diffraction element 1 shown in FIG. 6A allows the lattice vector to be oriented in any direction, as exemplified by k1, k2, and k3 in the figure, so the polarization oscillation direction can be parallel or perpendicular to any of the lattice vectors of the polarization diffraction element 1. Therefore, the polarization direction can be identified by determining at which rotation angle θ the maximum intensity is observed in the diffraction image (see FIG. 6B).

[0035] [Method of manufacturing a polarization diffraction element] The polarization diffraction element 1 described above can be manufactured by a simple method, for example, by using a liquid crystalline polymer having photoreactive (photocrosslinkable) side chains. The manufacturing method involves first dissolving a material containing a photoreactive liquid crystalline polymer in a solvent, and then coating and drying the solution on a transparent substrate to form a film. When this film is irradiated with linearly polarized ultraviolet light, axially selective photocrosslinking occurs in a direction parallel to the polarization direction of the ultraviolet light. Next, when the film is annealed at the transition temperature from the solid phase to the liquid crystalline phase, the side chains of the liquid crystalline polymer are oriented parallel to the crosslinked portions, and the liquid crystalline polymer can be aligned parallel to the polarization direction of the ultraviolet light.

[0036] To manufacture the diffraction element 1 shown in Figure 6A, linearly polarized ultraviolet light is converted into radially polarized light by a radial polarizer (radial polarization conversion element) and irradiated onto a film. At this time, a mask with a concentric line-space pattern (ring-space pattern) is placed between the film and the radial polarizer, and the above-mentioned exposure and annealing process is performed to obtain a polarization diffraction element 1 in which the liquid crystalline polymer is randomly oriented in the masked areas and radially oriented in the areas irradiated with ultraviolet light.

[0037] The polarization diffraction element 1 utilizes the liquid crystal properties of the polymer material to form a highly oriented state and exhibit large optical anisotropy. Furthermore, the formation of a crosslinked structure through a photoreaction ensures the heat resistance required for application as an optical element.

[0038] [Photoreactive liquid crystal polymer materials] The liquid crystalline polymer material (material containing a liquid crystalline polymer) used in the manufacture of the polarization diffraction element of the present invention is not particularly limited, but may be, for example, a material containing a liquid crystalline polymer having side chains that have photoreactive groups and form dimers via at least one hydrogen bonding site, and side chains that do not have photoreactive groups and form dimers via at least one hydrogen bonding site. As an example, the liquid crystalline polymer material may be a material consisting of a polymer containing at least one side chain represented by the following chemical formula 1 and at least one side chain represented by the following chemical formula 2:

[0039] [ka] Here, m=0, 1, n=1 to 3, c=0, 1, X=none, O, CH2, N=N, C=C, C≡C, COO, OCO, R1, R2 respectively represent H or an alkyl group, an alkyloxy group, or a halogen. [ka] Here, p=0, 1, d=0, 1, Y=none, O, CH2, N=N, C=C, C≡C, COO, OCO, R3, R4 are H or alkyl group, alkyloxy group, halogen, respectively.

[0040] The side chain having the structure shown in Chemical Formula 1 is a liquid crystalline polymer having a photoreactive carboxyl group at the side chain terminal. This photoreactive polymer has a structure that allows the carboxyl group at the side chain terminal to dimerize through hydrogen bonding, even though it does not contain a mesogenic group like the materials of the prior art. Side chains having the structure shown in Chemical Formula 2 are preferably used, and this side chain also has a carboxyl group at the side chain terminal, and has a structure that allows the carboxyl group at the side chain terminal to dimerize through hydrogen bonding, allowing the liquid crystalline phase to be expressed.

[0041] The photoreactive liquid crystalline polymer material may be a copolymer of the above-mentioned photoreactive side chain and non-photoreactive side chain, or a mixture of these polymers. The photoreactive side chain and non-photoreactive side chain may be contained in a molar ratio of, for example, 9:1 to 1:9. Furthermore, a crosslinking agent for improving heat resistance may be contained within a range that does not impair liquid crystallinity, and the material may be copolymerized with a non-liquid crystal monomer.

[0042] The above-mentioned photoreactive liquid crystalline polymer material is dissolved in an appropriate solvent (e.g., 1,4-dioxane), applied to a transparent substrate, dried, and then irradiated with polarized ultraviolet light by the above-mentioned method, followed by annealing at 110 to 140°C and cooling, thereby producing the polarized diffraction element of the present invention.

[0043] The photoreactive liquid crystalline polymer material used in the present invention is not limited to the above examples. For example, a liquid crystalline polymer having a photocrosslinkable mesogen in the side chain may be used. The solvent, concentration, and dissolution method for dissolving the photoreactive polymer liquid crystal are not particularly limited and are appropriately selected depending on the substrate used and drying time. Methods for uniformly applying the solution include spin coating, gravure coating, and comma coating, but are not particularly limited and are appropriately selected depending on the required area, substrate shape, precision, etc. The substrate is not particularly limited as long as it is transparent, but a transparent substrate material with a low intrinsic birefringence is preferred to maximize the functionality of the functional polymer layer. Examples of transparent substrate materials with such properties include inorganic materials such as various types of glass and quartz, and organic materials such as polymethyl methacrylate, polycarbonate, norbornene-based polymers, cellulose-based polymers, and polyester-based polymers. The shape of the substrate is not particularly limited, and a plate, film, etc. can be selected appropriately depending on the application.

[0044] [Modification of Polarization Diffraction Element] In the above explanation, a polarized diffraction element 1 is described in which an orientation region A in which the liquid crystal polymer L is oriented in the radial direction and a random region R in which the liquid crystal polymer L is oriented randomly are periodically modulated. However, the present invention is not limited to this, and various configurations in which the optical properties are modulated can be used. 7A shows a modified example of a polarization diffraction element 1 that utilizes periodic modulation of the orientation of the liquid crystal polymer, in which the liquid crystal polymer is oriented in a direction perpendicular to the radius in orientation region A, and overall is oriented approximately along the circumferential direction (strictly speaking, the tangent direction of the circle). Such a polarization diffraction element 1 can be formed by exposing the film to ultraviolet light in the above-described manufacturing method, converting linearly polarized light into azimuthal polarized light using a polarization conversion element, and exposing the light through a mask.

[0045] 7B and 7C are schematic diagrams showing another embodiment of the polarization diffraction element 1. In this example, the polarization diffraction element 1 is formed by carving grooves in the radial direction (FIG. 7B) or circumferential direction (FIG. 7C) into a film or plate made of an optically isotropic material. In practice, grooves can be formed by laser processing, a nanoimprint process, or the like, with minute groove spacing at a subwavelength period that produces form birefringence.

[0046] 8A, 8B, and 8C are schematic plan views for illustrating another embodiment of the polarization diffraction element 1. In the polarization diffraction element 1 shown in FIG. 1, FIG. 6A, and FIGS. 7A to 7C, each region is formed in an annular shape, but if necessary, the polarization diffraction element 1 may have the shape of a divided circle (for example, a sector or semicircle). If the lattice vector k is continuously distributed in an azimuth angle range of 90° or more, the azimuth angle of the polarization can be determined from the diffraction intensity distribution of the polarized light incident on the diffraction element 1.

[0047] In the polarization diffraction element 1 of the present invention, the fundamental vector length (width Λ shown in the figure) of the radial grating vector k is determined appropriately depending on the wavelength of the light used, but may be, for example, 1 to 100 μm. The radius of the polarization diffraction element 1 is not particularly limited, but may be 2 to 10 mm. The thickness d of the polarization diffraction element 1 (excluding the thickness of the transparent substrate) may be 0.1 to 10 μm.

[0048] [Optical device] The optical device of the present invention includes the polarization diffraction element of the present invention in an optical system. As an example, the polarization analyzer of the present invention includes the polarization diffraction element of the present invention and a light-receiving element having a light-receiving surface parallel to the polarization diffraction element, the light-receiving surface being positioned a predetermined distance away from the polarization diffraction element in the normal direction of the polarization diffraction element. For example, as shown in FIG. 9, the polarization analyzer 100 may include a polarization diffraction element 1, a light-receiving element 2, a lens 3 that forms an image of the diffracted light formed by the polarization diffraction element 1 on the light-receiving surface of the light-receiving element 2, and a processing device 4 that analyzes the intensity distribution of the diffracted light received by the light-receiving element 2 and displays it as necessary.

[0049] This polarization analyzer 100 can accurately determine the polarization state from the intensity distribution of the diffracted light received by the light receiving element 2. Because this intensity distribution can be obtained by a single image capture, even if the polarization state changes over time, the change in the state can be observed over time. Furthermore, even if the polarized light is made up of light of multiple wavelengths (when the polarized light has a wavelength distribution with a certain width), the polarization state can be analyzed for each wavelength as needed.

[0050] This ellipsometer 100 can be used for a variety of purposes. For example, FIG. 10A is a schematic side view of the optical system of a conventional ellipsometer 200. In this device, light from a light source is converted into polarized light by a polarizer 6 and irradiated onto a thin film sample 8 on a base 7. The reflected light passes through a rotating analyzer 9 and is received by a light-receiving element 2. The polarization state is analyzed by a processing device 4, and ellipsometric parameters used to estimate the refractive index and thickness are derived. In contrast, as shown in FIG. 10B, if the light reflected from the thin film sample 8 is analyzed by a ellipsometer 100 equipped with the polarizing diffraction element 1 of the present invention, the polarization state can be analyzed by capturing a diffraction image only once. This enables measurements to be performed in a short time, and changes in the polarization state over time can be analyzed from continuously captured data. Furthermore, even when multi-wavelength light is used, analysis can be performed for each wavelength. [Example]

[0051] [Preparation of photoreactive liquid crystalline materials] (Monomer 1) 4-(6-hydroxyhexyloxy)cinnamic acid was synthesized by heating p-coumaric acid and 6-chloro-1-hexanol under alkaline conditions. This product was esterified with a large excess of methacrylic acid in the presence of p-toluenesulfonic acid to synthesize Monomer 1 shown in Chemical Formula 3. [ka]

[0052] (Monomer 2) 4-(6-hydroxyhexyloxy)benzoic acid was synthesized by heating 4-hydroxybenzoic acid and 6-chloro-1-hexanol under alkaline conditions. This product was then esterified with a large excess of methacrylic acid in the presence of p-toluenesulfonic acid to synthesize monomer 2 shown in chemical formula 4. [ka]

[0053] (polymer) Monomer 1 and monomer 2 were dissolved in 1,4-dioxane in a molar ratio of 1:9, and polymerized with AIBN as a reaction initiator to obtain a photosensitive polymer, which exhibited a liquid crystal phase.

[0054] [Manufacturing of polarization diffraction elements] The polymer was dissolved in 1,4-dioxane to prepare a solution. This solution was applied to a glass substrate using a spin coater and dried at room temperature to produce a 2.9 μm-thick film. Next, ultraviolet light from a high-pressure mercury lamp was converted to linearly polarized UV light through a Glan-Taylor prism and further converted to radially polarized UV light through a radial polarizer. The light was then irradiated onto the substrate through a mask with a concentric line-space pattern (line width / space width: 12.5 μm / 12.5 μm). After irradiation, the substrate was heated at 110°C for 5 minutes to induce self-organized molecular orientation. The polarization diffraction element of the present invention was then cooled to room temperature. The front retardation value of this polarization diffraction element was 158.3 nm at a wavelength of 633 nm and 137.5 nm at a wavelength of 550 nm. This diffraction element exhibits a characteristic in which the diffracted light intensity is maximized when the lattice vector k and the electric field vector E are orthogonal (E⊥k relationship).

[0055] Figure 11A shows a crossed-Nicols image of the above-mentioned polarized diffraction element taken with a polarizing microscope. For reference, Figure 11B shows a polarizing microscope photograph of a reference element fabricated with a line-space pattern of line width / space width of 50 μm / 50 μm. The scale length indicated by the white horizontal bars in the figure is 1 mm. In both figures, the horizontal and vertical directions (the directions of the polarizer and analyzer) appear dark because the orientation direction of the liquid crystal polymer is in the extinction position. In Figure 11B of the reference element with a wide line / space width, it can be seen that the alignment regions A, which appear bright due to their optical anisotropy, and the random regions R, which appear dark due to their optical isotropy, are arranged concentrically and alternately at a regular interval.

[0056] [Polarization analysis experiment] FIG. 12 shows the configuration of the optical system used in the polarization state analysis experiment using the polarization diffraction element 1. Light emitted from a light source 5 (e.g., a tungsten halogen lamp) with a continuous spectrum was passed through a pinhole 10 and collimated using a lens 11 with a focal length of f1. This collimated light was converted to single-wavelength light using a wavelength filter 12 with a transmission center wavelength of 633 nm and a half-width of 10 nm. This light was then converted to linearly polarized light by a linear polarizer 13 (analyzer) with its transmission axis oriented at -45°. The light was then adjusted to linearly polarized light, elliptically polarized light, or circularly polarized light by a quarter-wave plate 14 corresponding to the 633 nm wavelength, and then incident on a polarization analyzer 100 comprising the polarization diffraction element 1, a lens 3, a light-receiving element 2, and a processing device 4. As a result, the circularly diffracted light generated by the light incident on the polarization diffraction element 1 can be captured on the light-receiving surface 2a of the light-receiving element 2 by the Fourier transform effect of the lens 3.

[0057] The right-hand diagram in Figure 13 shows the diffraction images obtained when the angle between the linear polarizer 13 and the quarter-wave plate 14 is changed to 0°, 22.5°, and 45°, and the incident light is adjusted to linearly polarized, elliptically polarized, and circularly polarized (as shown on the left side of the diagram). The original diagram is on an RGB scale, but even in Figure 13, which is displayed in gray, it can be seen that circularly polarized light (C) produces uniform intensity, and that the diffracted light intensity distributions are different for (A) linearly polarized light and (B) elliptically polarized light.

[0058] Figure 14 shows the diffracted light intensity distribution obtained from the diffraction image. The horizontal axis represents the azimuth angle θ in the rotation direction, and the vertical axis represents the diffracted light intensity. The diffracted light intensity distribution is plotted using circles for linearly polarized light, diamonds for elliptically polarized light, and triangles for circularly polarized light. The intensity distribution of linearly polarized light fits relatively well with the calculated value shown by the solid line, and the waveform of the elliptically polarized light graph also matches the calculated value, although the azimuth angle is slightly shifted. Conventionally, measuring the intensity distribution of polarized light required time-consuming measurements using a rotating analyzer. However, by using an analysis device 100 equipped with the polarizing diffraction element 1 of the present invention, the polarization state can be analyzed from the intensity distribution of diffracted light captured in a single image. In the polarizing diffraction element 1 used, the diffracted light intensity is maximized when the vibration direction of the electric field E is perpendicular to the lattice vector k, so the angle θ and the actual polarization azimuth angle are shifted by 90°.

[0059] In the portion indicated by the arrow in Fig. 14 (near θ = 0.9 rad), the plotted data deviates from the curve and appears stepped. When measuring the diffracted light intensity at discontinuous azimuth angle intervals as in Patent Document 3, it was difficult to accurately analyze the polarization state if there were outliers in the measurement data. However, with the analyzer 100 of the present invention, data corresponding to continuous changes in the azimuth angle θ can be collected, and therefore even if there are outliers in some locations, the polarization state can be accurately analyzed from the other data.

[0060] [Polarized light analysis] Polarization analysis using an LED light source was performed using the polarization analyzer 100 of the present invention. However, since LEDs that emit polarized light are not yet commercially available, the light from a white LED was converted to linearly polarized light using the device configuration shown in Figure 12, excluding the quarter-wave plate 14. Specifically, in the device configuration shown in Figure 12, a white LED with an emission peak near 450 nm was used as light source 5. Light emitted from the light source was passed through pinhole 10 and collimated by lens 11, and a wavelength filter 12 with a wavelength of 450 nm (±10 nm) was introduced. The single-wavelength light transmitted through filter 12 was converted to p-polarized light by linear polarizer 13, and the diffracted light intensity distribution was analyzed through polarization diffraction element 1. A CCD camera was used for light receiving element 2. Figure 15A shows the acquired diffraction image, and Figure 15B shows the intensity distribution of the first-order diffracted light, extracted and plotted against the azimuth angle θ.

[0061] The polarization diffraction element 1 used has a maximum diffracted light intensity when the vibration direction of the electric field E is perpendicular to the lattice vector k, so the angle θ and the actual polarization azimuth angle are offset by 90°. When this point is kept in mind during analysis, it was easy to detect that the polarization state was linearly polarized light oriented in the horizontal direction (or slightly elliptically polarized light).

[0062] [Polarization spectroscopy] The polarization diffraction element 1 also functions as a spectroscopic element. For example, if the wavelength filter 12 is removed from the device shown in Figure 12, a diffraction image consisting of multiple rings of rainbow colors, red, green, and blue from the outside, is obtained. The angle between the linear polarizer 6 and the quarter-wave plate 7 corresponding to a wavelength of 633 nm is set to 45°. In this case, the light with a wavelength of 633 nm contained in the multi-wavelength light is circularly polarized, and the light with other wavelengths is elliptically polarized. Therefore, by detecting this wavelength-dependent difference in polarization state, the polarization state of each wavelength of the multi-wavelength light can be simultaneously detected from the annular diffracted light intensity distribution.

[0063] Figure 16 plots the light intensity distribution around the circumference of the circularly diffracted light generated on the photodetector when wavelength filters with center wavelengths of 500 nm, 633 nm, and 750 nm are applied. The intensity distribution of 633 nm is close to circularly polarized light, while the polarization of 500 nm and 750 nm is elliptically polarized light, and the directions of the ellipses are orthogonal to each other due to differences in phase shift. In the figure, the solid line represents the predicted polarization state, demonstrating that the elliptical polarization locus for each wavelength can be estimated from the obtained data.

[0064] Using a processing device, it is also possible to convert the diffracted light shown in polar coordinates into Cartesian coordinates. Furthermore, by adding the intensity values ​​for each wavelength, it is possible to display it in the form of a three-dimensional bird's-eye view, as shown in Figure 17. Figure 17 shows a three-dimensional display in which the azimuth angle θ and the radius of the diffraction circle are taken as plane coordinates, and the diffracted light intensity is taken as the vertical axis. Since the diffraction angle involves wavelength dispersion, the light intensity for each wavelength is shown at a specific coordinate on the radial axis. In addition, the original diagram is displayed in color, allowing the polarization state for each wavelength to be easily understood from a single diagram.

[0065] In this way, by recording a single image data acquired by the light receiving element for multi-wavelength light incident on the polarization diffraction element to be measured, it is possible to determine the polarization state for all incident wavelengths. Therefore, by acquiring light reflected from a rapidly changing object at high speed according to the performance of the light receiving element, it is possible to determine the polarization state for each wavelength and its change over time from the stored data. This solves the problem of current ellipsometry and spectroscopic ellipsometry being unable to handle high-speed measurements. It also enables accurate analysis of polarization states used in various optical engineering fields. [Industrial Applicability]

[0066] The polarization diffraction element of the present invention can accurately analyze the polarization state from a diffraction image captured in one shot, and therefore can contribute to improving the performance of various optical devices that use polarized light, such as physical property measuring devices, display devices, communication devices, and optical storage devices, and is of great industrial applicability. [Explanation of symbols]

[0067] 1 Polarized diffraction element 2 Photodetector 3 Lenses 4 Processing equipment 5 light source 6,14 Polarizing elements 7. Circuit Board 8 Thin film samples 9,13 Rotating analyzer 12 Optical Filters A Orientation region R random region k, k1, k2, k3 lattice vectors θ rotation angle (azimuth angle) L liquid crystal molecule I isotropic region AN Anisotropic region

Claims

1. The film includes a film made of a material containing a photosensitive liquid crystal polymer, and has a structure having characteristics as a polarization diffraction grating in which optical anisotropy is periodically modulated in a radial direction from a point in a plane, a plurality of annular or arc-shaped first regions having optical anisotropy, in which the alignment direction of the liquid crystalline polymer changes axially symmetrically around the one point; a plurality of second regions in an annular or arcuate shape in which the liquid crystalline polymer is randomly oriented and which have optical isotropy, are arranged concentrically and alternately around the one point, The direction of the grating vector of the polarization diffraction grating changes continuously within a predetermined angle range of 90 to 360 degrees around the one point. Polarized diffraction element.

2. 2. The polarization diffraction element according to claim 1, wherein in the first region, the liquid crystalline polymer is oriented in radial directions with the one point as a center.

3. 2. The polarization diffraction element according to claim 1, wherein in the first region, the liquid crystalline polymer is oriented along a circumferential direction of a circle centered on the one point.

4. 4. A polarization analyzer comprising: the polarization diffraction element according to claim 1; and a light-receiving element having a light-receiving surface parallel to the polarization diffraction element, the light-receiving surface being disposed at a predetermined distance from the polarization diffraction element in a normal direction of the polarization diffraction element.

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