Circular dichroism spectrometer and polarizing element used therein

Abstract

To provide a circular dichroic spectrometry device that is fast and accurate.SOLUTION: A circular dichroic spectrometry device irradiates an object to be measured with clockwise circular polarized light and counterclockwise circular polarized light and performs spectrometry of the transmission light or reflection light thereof for each polarization direction and comprises: a light source which emits luminous flux including a plurality of wavelength components; a polarizing element which spatially divides and converts the luminous flux into the clockwise circular polarized light and counterclockwise circular polarized light respectively; and a spectrometry unit which receives clockwise circular polarized light and counterclockwise circular polarized light transmitted through or reflected by the object to be measured respectively to perform spectrometry.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a circular dichroism spectrometer used for analysis in the fields of chiral chemistry, asymmetric chemistry, etc., and a polarization element used therefor.

Background Art

[0002] In recent years, there has been an urgent need to establish a treatment method for neurodegenerative diseases based on protein denaturation, called conformational diseases such as Alzheimer's disease and Parkinson's disease. In this field, in order to accurately grasp protein denaturation, it is essential to analyze the optical activity of chiral molecules, and for this purpose, circular dichroism spectroscopy (circular dichroism spectrum) measurement technology is used.

[0003] Circular dichroism spectroscopy measurement technology is particularly indispensable in fields such as the analysis of asymmetric synthesis where three-dimensional anisotropy and higher-order structures are important, the structural analysis of proteins, and the analysis of molecular self-assembly. This technology measures the wavelength dispersion of the difference in absorbance of a substance for left and right circularly polarized light, and information reflecting the chirality and helical structure in the structure of substances and molecules can be obtained in any wavelength band from deep ultraviolet to the terahertz region.

[0004] Currently popular circular dichroism spectrometers employ a pre-spectrometer method using a monochromator to generate left and right circularly polarized light for each wavelength. For this reason, a long time (about several minutes to ten-odd minutes) is required to acquire spectral data, and even when a relatively slow change on the order of seconds occurs in the measurement target, it may be overlooked. Therefore, circular dichroism measurement using a single wavelength based on high-speed time resolution utilizing pulse excitation has been studied. However, in this method, circular dichroism is measured only at a single wavelength in the thermally excited state by a single pulse of light, so significant restrictions occur in the measurement conditions.

[0005] On the other hand, in recent years, research and development of a circular dichroism spectrometer using a polarization diffraction grating that simultaneously causes wavelength dispersion and polarization adjustment has been underway. For example, there is a method of irradiating a sample with white light, separating the transmitted light into right-handed circularly polarized light and left-handed circularly polarized light using a polarization diffraction grating, and analyzing each spectrum (Patent Document 1, Non-Patent Documents 1 and 2). Furthermore, a technique for adjusting the wavelength dispersion of each circularly polarized light using a prism to improve the accuracy has also been studied (Patent Document 2).

Prior Art Documents

Patent Documents

[0006]

Patent Document 1

Patent Document 2

Non-Patent Documents

[0007]

Non-Patent Document 1

Non-Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0008] However, although it can be said that the circular dichroism spectroscopic measurement technique solves the problems of the prior art in terms of high speed, the light incident on the sample must be linearly polarized rather than circularly polarized, and thus there is a problem that errors occur in the measurement.

Means for Solving the Problems

[0009] A circular dichroism spectroscopic measurement device according to an aspect of the present invention is a circular dichroism spectroscopic measurement device that irradiates a measurement object with right-handed circularly polarized light and left-handed circularly polarized light, and spectroscopically measures the transmitted light or reflected light for each polarization direction, and includes a light source that emits a light beam including a plurality of wavelength components, a polarization element that spatially divides the light beam and converts it into right-handed circularly polarized light and left-handed circularly polarized light respectively, and a spectroscopic measurement unit that receives the right-handed circularly polarized light and left-handed circularly polarized light transmitted or reflected by the measurement object and performs spectroscopic measurement.

[0010] It may further include a correction member that corrects the optical path for each wavelength of the first-order diffracted light by the polarization element and irradiates the measurement object.

[0011] In the circular dichroism spectroscopic measurement device, the polarization element may be provided with a first polarization diffraction grating having a locally optical axis that continuously rotates in the lattice vector direction and a second polarization diffraction grating having a locally optical axis that continuously rotates in the direction opposite to the lattice vector direction with the same period as the first polarization diffraction grating, facing each other on the same plane.

[0012] The light beam may be linearly polarized.

[0013] In the circular dichroism spectroscopic measurement device, the period of rotation of the locally optical axis in the first polarization diffraction grating and the second polarization diffraction grating may be 0.2 μm or more and 100 μm or less.

[0014] In the circular dichroism spectroscopic measurement device, the thickness of the first polarization diffraction grating and the second polarization diffraction grating may be 0.1 μm or more and 300 μm or less.

[0015] In the circular dichroism spectrometer, the correction member may be composed of a chromatic dispersion material that inversely corrects the difference in diffraction angles depending on the wavelength of the first-order diffracted light.

[0016] In the circular dichroism spectrometer, a condensing element may be further provided to change the optical path of either one or both of the right-handed circularly polarized light beam or the left-handed circularly polarized light beam so that the light beams of the right-handed circularly polarized light and the left-handed circularly polarized light that are spatially separated overlap entirely or partially inside or on the reflection surface of the measurement target.

[0017] A polarizing element according to one aspect of the present invention is a polarizing element used in the circular dichroism spectrometer, and includes a first polarization diffraction grating having a local optical axis that continuously rotates in the lattice vector direction, and a second polarization diffraction grating having a local optical axis that continuously rotates in the direction opposite to the lattice vector direction with the same period as the first polarization diffraction grating, and the two are provided to face each other on the same plane.

[0018] In the polarizing element, the rotation period of the local optical axis in the first polarization diffraction grating and the second polarization diffraction grating may be 0.2 μm or more and 100 μm or less.

[0019] In the polarizing element, the thicknesses of the first polarization diffraction grating and the second polarization diffraction grating may be 0.1 μm or more and 300 μm or less.

Advantages of the Invention

[0020] According to one aspect of the present invention, it is possible to irradiate a measurement target with right-handed circularly polarized light and left-handed circularly polarized light simultaneously and in a spatially separated state, and further measure the spectral distributions of the right-handed circularly polarized light and the left-handed circularly polarized light in a spatially separated state. As a result, high-speed and accurate circular dichroism spectroscopy measurement becomes possible.

Brief Description of the Drawings

[0021]

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Embodiments for Carrying Out the Invention

[0022] Hereinafter, embodiments according to one aspect of the present invention (hereinafter, the present embodiments) will be described in detail with reference to the drawings.

[0023] FIG. 1 shows a block diagram of the circular dichroism spectroscopic measuring apparatus of the present embodiment. In order to more clearly show the characteristics of the optical path, a block diagram (FIG. (a) thereof) viewed from the grating direction (Y-axis) of the polarization element and a block diagram (FIG. (b) thereof) viewed from the grating vector direction (X-axis) direction are shown together.

[0024] In FIG. 1, reference numeral 1 denotes a light source, which is a device that emits a light beam including a plurality of wavelength components. The light source 1 may be a white light source that evenly includes light of all wavelengths in the visible light region. Alternatively, it may be a light source having a wavelength distribution such as Gaussian in a part of the band. Further, it may be a combination of a plurality of monochromatic lights of a specific wavelength. Furthermore, it may be a light source including light outside the visible light region, such as ultraviolet light, infrared light, or even terahertz waves. In the present embodiment, it is assumed that the light beam is linearly polarized.

[0025] Reference numeral 2 denotes a polarization element, which is an element that generates diffracted light having wavelength dispersion in the X-axis direction in the figure with respect to the light beam and has a function of converting it into circular polarization by separating the right-handed and left-handed directions in the Y-axis direction. The detailed configuration and operation of the polarization element 2 will be described later.

[0026] In the present embodiment, only one of the first-order diffracted lights of the light beam transmitted through the polarization element 2 is finally used for circular dichroism spectroscopic measurement. However, since the period of the diffraction grating of the polarization element 2 is constant, the diffraction angle varies depending on the wavelength (λ1>λ2>··>λ n ) that constitutes the light beam. That is, the longer the wavelength, the larger the diffraction angle. The wavelength dispersion generated here is used for the spectroscopic measurement described later. On the other hand, if there is a difference in the diffraction angle, an optical path shift occurs between the long wavelength and the short wavelength before reaching the spectroscopic measurement units 6a and 6b. If this shift is large, there is a risk of causing an error in the spectroscopic analysis. Therefore, each optical path is corrected so that light of all wavelengths reaches the spectroscopic measurement units 6a and 6b, for example, by using a correction member to parallelize the optical path for each wavelength.

[0027] The correction member may be a correction member 3 made of an optical member such as a prism formed of a chromatic dispersion material that inversely corrects the difference in diffraction angles. Also, if the distances between the polarization element 2 and the spectroscopic measurement units 6a and 6b are relatively short, a correction member 30 having a variable slit structure as shown in FIG. 2 may be used to partially align the optical paths. That is, if the slit width is narrowed, wavelength resolution can be obtained, but if the diffracted light on the long-wavelength and short-wavelength sides spreads to some extent, kerare may occur at the periphery. At worst, the wavelength distribution accuracy decreases. If the slit width is widened, a portion where the light of each wavelength overlaps (whitens) is formed at the center, and the influence of kerare can be reduced. However, on the other hand, the wavelength resolution decreases. Since the wavelength resolution and the wavelength distribution accuracy are in a trade-off relationship in this way, the optimum value of the slit width may be appropriately adjusted according to the properties of the measurement object. Furthermore, the correction member may be configured to use the prism or the like in combination.

[0028] The light beam whose optical path is aligned by the correction member 3 is irradiated onto the measurement object 40 held by the sample holder 4. In FIG. 1, the light beam that has passed through the measurement object 40 is separated by the separation unit 5 into a right-handed circularly polarized light beam and a left-handed circularly polarized light beam, and each reaches the spectroscopic measurement units 6a and 6b. The spectroscopic measurement units 6a and 6b may be multi-channel spectrometers that analyze the spectra included in the respective polarizations.

[0029] Right-handed circularly polarized light in which dispersion has occurred at wavelengths λ1 to λ n enters the spectroscopic measurement unit 6a, and left-handed circularly polarized light in which dispersion has similarly occurred enters the spectroscopic measurement unit 6b. The spectroscopic measurement units 6a and 6b measure the spectra in the respective circular polarizations and transfer the information to the computer 7. The computer 7 clarifies the wavelength dispersion of the difference in absorbance with respect to the left and right circular polarizations from this information and calculates the circular dichroism.

[0030] Specific calculation means are shown below. First, in a state where the measurement object 40 is not placed in the sample holder 4, the spectral intensity I R (λ) of right-handed circularly polarized light and the spectral intensity I LMeasure (λ). This is called the background spectrum intensity. Next, place the measurement target 40 in the sample holder 4, and measure the transmitted spectrum intensity I R ’(λ) of right-handed circularly polarized light and the transmitted spectrum intensity I L ’(λ) of left-handed circularly polarized light. Once these four spectra are measured, the absorbances A R (λ) and A L (λ) are calculated by the following calculation formulas respectively.

Equation

[0031] In circular dichroism spectrum measurement, it is common to represent the difference in absorbance of the left and right circularly polarized lights by the ellipticity angle θ. That is, from the absorbances of the left and right circularly polarized lights obtained by the above formula, the ellipticity angle θ is calculated using the following formula at each wavelength λ (= λ1, λ2 ··· λ n ), and the circular dichroism spectrum can be derived.

Equation

[0032] The computer 7 receives the outputs of the spectroscopic measurement units 6a and 6b, and performs spectroscopic measurement for a preset spectral update time for a preset spectral intensity integration time of the left and right circularly polarized lights. From the integrated spectral intensity obtained by this measurement, the circular dichroism spectrum is calculated using the background spectral intensity measured and saved in advance. The result is displayed on the monitor and the data is further saved. By the above process, the change in the circular dichroism spectrum can be measured and recorded sequentially at high speed.

[0033] In addition, in order to correct the temporal fluctuation of the output of the light source 1, the light emitted from the light source 1 can be split into two, one of which is used for spectroscopic measurement and the other is used as a reference light for correcting the temporal fluctuation, that is, the so-called "double-beam method" can be applied. In this case, by using the diffracted light on the opposite side (+1st order light) not used in FIG. 5 described later as the reference light, high-precision and high-speed measurement can be performed.

[0034] Here, the configuration and operation of the polarization element 2 in the present embodiment will be described in detail. FIG. 3 shows the configuration of the polarization element 2 in the present embodiment. In FIG. 3, the polarization element 2 includes a (first) polarization diffraction grating 2a having a local optical axis 20a that continuously rotates in the X-axis (lattice vector k) direction, and a local optical axis 20b that continuously rotates in the opposite direction of the X-axis (lattice vector xk direction) with the same period as the polarization diffraction grating 2a. The (second) polarization diffraction grating 2b is provided facing each other on the same plane. In any of the polarization diffraction gratings, the distance at which the local optical axis rotates 360° corresponds to the interval between the diffraction gratings. Here, the local optical axes 20a and 20b shown as ellipses in FIG. 3 represent uniaxial anisotropy of the refractive index, and the major axis of this ellipse means the slow axis and the minor axis means the fast axis, respectively.

[0035] Generally, the interference electric field of circularly polarized light rotating in opposite directions has periodicity in which the polarization azimuth angle of linearly polarized light with equal magnitudes continuously rotates. Assuming that such an interference electric field is generated on the surface of the photo-aligned liquid crystal thin film, the local optical axis is oriented along this electric field distribution. At this time, a diffraction grating is formed in which the magnitudes are the same and the direction of birefringence (Δn) continuously rotates in the lattice vector (k) direction. Such a diffraction grating is known as a polarization hologram by orthogonal circularly polarized light.

[0036] When the refractive index modulation (Δn) within this grating is decomposed into components as shown in Fig. 4, it is considered equivalent to the superposition of opposed blazed gratings for left and right circular polarizations. Therefore, as shown in Fig. 5, the left and right circular polarization components contained in the incident light have the property (polarization separation property) of being separated and diffracted into the ±1st order diffracted lights respectively. Since linearly polarized light is considered to be the sum of left and right circularly polarized lights with equal amplitudes, when this linearly polarized light is incident, accurate left and right circularly polarized lights are simultaneously generated with equal efficiency for both the ±1st order diffracted lights.

[0037] Explaining this diffraction characteristic based on the coupled-wave theory is as follows. That is, since the rotating electric field component (circular polarization component) of the incident light couples to the periodically rotating birefringence modulation (modulation of the local optical axis) that forms the diffraction grating, the ±1st order diffracted lights become those in which only pure left and right circular polarization components are diffracted respectively, and the non-harmonic components are diffracted as higher-order lights. For this reason, this ±1st order diffracted light is applied to the measurement of the circular dichroism spectrum. However, since the ±1st order diffracted lights are spatially separated, it is not possible to obtain left and right circularly polarized lights within the same spot.

[0038] Therefore, in the present embodiment, as shown in Fig. 3, by arranging polarization diffraction gratings 2a and 2b having lattice vectors in opposite directions facing each other, this problem is solved. That is, as shown in Fig. 5, the wavelength dispersion (λ1~λ n ) of the diffraction angle occurs parallel (in the X-axis direction) along the lattice vector in each polarization diffraction grating. At this time, it has no influence in the vertical (Y-axis) direction separated in the polarization direction. As a result, spectroscopically separated left and right circularly polarized lights can be generated simultaneously in four quadrants. By irradiating this light onto the measurement target 40 and post-spectroscopically analyzing the emitted light, the circular dichroism spectrum can be obtained as described above.

[0039] The polarization diffraction gratings 2a and 2b are not particularly limited as long as they are diffraction gratings having birefringence. They may be those utilizing the structural birefringence formed by a resin subjected to nanoimprinting of a pattern as shown in Example 3. Further, they may be those in which glass, quartz, sapphire, etc. are used as an optical substrate and fine processing is performed thereon to develop structural birefringence. Further, they may be those using the birefringence generated by the alignment of polymer molecules. Preferably, they may be those utilizing the alignment distribution of liquid crystal molecules.

[0040] As described above, in the present embodiment, by arranging the grating vectors (k) of the special polarization diffraction gratings 2a and 2b to face each other as shown in FIG. 3, it becomes possible to spatially expand the left and right circularly polarized lights developed for each wavelength at the same time. The experimental results of actually observing the spatially expanded light beam are shown in Example 1 described later.

[0041] The period of the diffraction grating is preferably 0.2 μm or more and 100 μm or less. As described above, the period of the rotation (360° rotation) of the local optical axis (such as liquid crystal molecules) in the polarization diffraction grating 2a and the polarization diffraction grating 2b corresponds to the period (Λ) of the diffraction grating. If the period of the diffraction grating is long, the diffraction angle becomes small and the accuracy of spectroscopic analysis decreases. Conversely, if it is short, the long wavelength side may exceed the diffraction limit.

[0042] The thicknesses of the polarization diffraction grating 2a and the polarization diffraction grating 2b are related to the diffraction efficiency, that is, the intensity of the primary light. However, if it is too thick, it will affect the transmittance of the light beam. The thickness is preferably 0.1 μm or more and 300 μm or less.

[0043] FIG. 6 shows a conceptual diagram of the light beam reaching the spectroscopic measurement units 6a and 6b. The light beams having wavelengths λ1 to λ n diffracted by the polarization diffraction grating 2a are incident on the spectroscopic measurement unit 6a in a dispersed manner. Further, the light beams having wavelengths λ1 to λ n diffracted by the polarization diffraction grating 2b are incident on the spectroscopic measurement unit 6b in a dispersed manner.

[0044] As described above, according to the present embodiment, by using the polarization element 2 composed of the polarization diffraction grating 2a and the polarization diffraction grating 2b, it is possible to irradiate the measurement object 40 with right-handed circularly polarized light and left-handed circularly polarized light simultaneously and in a spatially separated state. Furthermore, the spectral distributions of the right-handed circularly polarized light and the left-handed circularly polarized light can be measured in a spatially separated state. As a result, high-speed and accurate circular dichroism spectroscopic measurement becomes possible.

[0045] In the present embodiment, the correction member 3 or the correction member 30 is used for correcting the optical path of the spectroscopy. However, depending on the specifications of the entire apparatus, these may be omitted. For example, since the polarization diffraction grating 2 itself also has a certain degree of spectroscopic ability as shown in Example 1 (Fig. 8) described later, when the homogeneity of the object is high, white spotting is unnecessary, and the wavelength resolution may be somewhat low, the wavelength dispersion effect of this polarization diffraction grating can be actively utilized. In this case, the correction member may not be used. Also, the spectroscopic measurement units 6a and 6b may be components for consumer devices such as a CCD image sensor, and the cost of the apparatus can be significantly reduced.

[0046] Also, in the present embodiment, the measurement object 40 may be a transmissive liquid such as a solution or a suspension, or a gel. In this case, the sample holder 4 may be a container formed of transparent quartz or resin. When the measurement object 40 is a solid or has a mirror surface such as a metal thin film, the sample holder 4 may be a mechanical component having a clamping function.

[0047] Furthermore, as shown in FIG. 7, a condensing element 31 may be provided so that the light beams of right-handed circular polarization and left-handed circular polarization overlap inside the measurement target 40. In the present embodiment, the condensing element 30 is constituted by a roof-shaped prism. If this condensing element 31 is arranged so that the ridge line of the prism coincides with the splitting line of both polarizations, the light beam of right-handed circular polarization refracts downward on the drawing, and the light beam of left-handed circular polarization refracts upward, and these circular polarizations substantially overlap at the position of the measurement target. As a result, the measurement accuracy for a measurement target with a small size or a measurement target with low uniformity can be improved. After the light beams of both polarizations that have once overlapped leave the measurement target 40, they diverge again and are separated into respective circular polarizations by the separation unit 5. Regarding the overlapping manner of both polarizations, all of them may overlap, or a part of them may overlap. Also, as shown in FIG. 7, both circular polarizations may be refracted in opposite directions to each other, or one of them may be made to travel straight.

[0048] Hereinafter, embodiments of the present invention will be described. (Example 1) In this example, an experiment and results of actually measuring diffracted light by a prototype polarizing element will be described. In this example, the polarizing element was prototyped from two liquid crystal plates having a length × width × thickness of 12 mm × 24 mm × 250 μm. Each liquid crystal plate was provided with a liquid crystal molecule alignment distribution so that the lattice vectors were in opposite directions to each other to form a polarization diffraction grating. These polarization diffraction gratings were bonded together on the same plane in an arrangement where the lattice vectors faced each other to form a polarizing element. In each polarization diffraction grating, the grating period (360° rotation period of liquid crystal molecules) was 2.5 μm. As the light source, a white light source (product number DH-2000-BAL) manufactured by Ocean Optics was used. This white light was irradiated onto the prototyped polarizing element, and the transmitted light was photographed with a CCD camera. The results are shown in FIG. 8.

[0049] Fig. 8(a) shows the diffracted light generated by the polarization element. The 0th-order light is at the center, and the 1st-order diffracted lights (+1st-order light and -1st-order light) with chromatic dispersion are confirmed on the right. Since the difference in polarization cannot be seen from this photograph, the diffracted light was further photographed through a polarization filter. The result is shown in Fig. (b) of the same figure. Focusing on the diffracted light on the left side (-1st-order light), it was confirmed that the right-handed circular polarization is divided into the upper half and the left-handed circular polarization is divided into the lower half.

[0050] (Example 2) In this example, an experiment to verify the time responsiveness of the circular dichroism spectroscopic measurement device of this embodiment and the results thereof will be described. In this embodiment, the light source and the polarization element having the same configuration as in Example 1 were used. A multi-channel spectrometer (product number FLAME-S-UV-VIS-ES) manufactured by Ocean Optics was used for the spectroscopic measurement units (6a, 6b) corresponding to the right-handed circular polarization and the left-handed circular polarization of the 1st-order diffracted light (-1st-order light), respectively.

[0051] A chiral nematic liquid crystal cell that generates selective circular polarization reflection in the wavelength band of 520 nm to 560 nm was used as the measurement object. This liquid crystal cell was fixed to the sample holder 4 and heated while blowing hot air at about 40 °C with a fan equipped with a heater. External appearance photographs before and after heating are shown in Fig. 9. The liquid crystal cell that could be visually seen as green initially decolorized after heating. During heating, the circular dichroism (CD) spectroscopic characteristics were measured using the device of Example 1 at intervals of 300 msec. Sampling this, the change in the spectrum every 4.2 sec was graphed. The time required for one measurement was about 20 sec. The measurement results are shown in Fig. 10. In the figure, the horizontal axis represents the wavelength and the vertical axis represents the circular dichroism (CD) value. In addition, in order to clearly show the time change of the spectrum, the vertical axis is in arbitrary units (arb unit).

[0052] Although the CD spectroscopic characteristics could be measured a total of 6 times in about 20 sec, as is clear from Fig. 10, the CD spectral characteristics changed significantly during this period. In other words, it was demonstrated that the circular dichroism (CD) spectroscopic characteristics that change so rapidly can be measured in real time using the circular dichroism spectroscopic measurement device of this embodiment.

[0053] (Example 3) Fig. 11 shows SEM image photos of a Si master mold for nanoimprinting of a polarization diffraction grating (grating pitch: 6.4 μm) having structural birefringence. The magnification of the left photo is 5000, and the magnification of the right photo is 60000. The left photo shows an area near the boundary of polarization diffraction gratings (corresponding to 2a and 2b) where the local optical axes rotate in opposite directions. In the enlarged image on the right, it was confirmed that grooves with a pitch of approximately 200 nm were formed. By transferring the pattern formed on this master mold to a resin material, a large number of polarization diffraction gratings can be replicated.

Industrial Applicability

[0054] By using the present invention, the optical activity of chiral molecules can be analyzed in real time by quickly and accurately measuring the circular dichroism spectroscopic characteristics. This function can be utilized for the diagnosis and treatment of neurodegenerative diseases based on protein denaturation, such as Alzheimer's disease and Parkinson's disease, which are called conformational diseases.

Explanation of Signs

[0055] 1 Light source 2 Polarizing element 2a, 2b Polarization diffraction gratings 20a, 20b Local optical axes 3 Correction member 30 Correction member (variable slit structure) 31 Condensing element 4 Sample holder 40 Object to be measured 5 Separation unit 6a, 6b Spectroscopic measurement units 7 Computer

Claims

1. A circular dichroism spectroscopic measurement apparatus that irradiates a measurement target with right-handed circularly polarized light and left-handed circularly polarized light and spectroscopically measures the transmitted light or reflected light for each polarization direction, a light source that emits a light beam including a plurality of wavelength components, a polarization element that spatially divides the light beam and converts it into right-handed circularly polarized light and left-handed circularly polarized light respectively, a spectroscopic measurement unit that receives the right-handed circularly polarized light and left-handed circularly polarized light transmitted through or reflected by the measurement target and performs spectroscopic measurement, a correction member that corrects the optical path for each wavelength of the first-order diffracted light by the polarization element and irradiates the measurement target, and a circular dichroism spectroscopic measurement apparatus comprising the same.

2. A circular dichroism spectroscopic measurement apparatus that irradiates a measurement target with right-handed circularly polarized light and left-handed circularly polarized light and spectroscopically measures the transmitted light or reflected light for each polarization direction, a light source that emits a light beam including a plurality of wavelength components, a polarization element that spatially divides the light beam and converts it into right-handed circularly polarized light and left-handed circularly polarized light respectively, a spectroscopic measurement unit that receives the right-handed circularly polarized light and left-handed circularly polarized light transmitted through or reflected by the measurement target and performs spectroscopic measurement, comprising, the polarization element includes a first polarization diffraction grating having a locally optical axis that continuously rotates in the lattice vector direction, and a second polarization diffraction grating having a locally optical axis that continuously rotates in the direction opposite to the lattice vector direction with the same period as the first polarization diffraction grating. When the optical axis direction of the light beam emitted by the light source is the Z-axis direction, the direction orthogonal to the Z-axis direction and in which wavelength dispersion of the diffracted light occurs is the X-axis direction, and the direction orthogonal to the Z-axis direction and the X-axis direction is the Y-axis direction, the circular dichroism spectroscopic measurement apparatus is formed by laminating them facing each other in the Y-axis direction.

3. The circular dichroism spectroscopic measurement apparatus according to Claim 2, wherein the period of rotation of the locally optical axis in the first polarization diffraction grating and the second polarization diffraction grating is 0.2 μm or more and 100 μm or less.

4. The circular dichroism spectroscopic measurement apparatus according to Claim 2 or Claim 3, wherein the thickness of the first polarization diffraction grating and the second polarization diffraction grating in the Z-axis direction is 0.1 μm or more and 300 μm or less.

5. The circular dichroism spectroscopic measurement apparatus according to any one of Claims 2 to 4, further comprising a correction member that corrects the optical path for each wavelength of the first-order diffracted light by the polarization element and irradiates the measurement target.

6. The circular dichroism spectroscopic measurement apparatus according to Claim 1 or Claim 5, wherein the correction member is composed of a chromatic dispersion material that inversely corrects the difference in diffraction angles depending on the wavelength of the first-order diffracted light.

7. The circular dichroism spectroscopic measurement device according to any one of claims 1 to 3, wherein the light beam emitted from the light source is linearly polarized.

8. The circular dichroism spectroscopic measurement device according to any one of claims 1 to 7, further comprising a condensing element that changes the optical path of either or both of the right-handed circularly polarized light beam and the left-handed circularly polarized light beam so that all or part of the spatially separated right-handed circularly polarized light beam and left-handed circularly polarized light beam overlap at the inside or the reflection surface of the measurement object.

9. A circular dichroism spectroscopic measurement device that irradiates a measurement object with right-handed circularly polarized light and left-handed circularly polarized light, and spectroscopically measures the transmitted light or the reflected light for each polarization direction, a light source that emits a light beam including a plurality of wavelength components, a polarization element that spatially divides the light beam and converts it into right-handed circularly polarized light and left-handed circularly polarized light respectively, a spectroscopic measurement unit that receives right-handed circularly polarized light and left-handed circularly polarized light transmitted or reflected by the measurement object and performs spectroscopic measurement, A polarization element used in the circular dichroism spectroscopic measurement device comprising a first polarization diffraction grating having a local optical axis that continuously rotates in the lattice vector direction, and a second polarization diffraction grating having a local optical axis that continuously rotates in the direction opposite to the lattice vector direction with the same period as the first polarization diffraction grating. When the optical axis direction of the light beam emitted by the light source is the Z-axis direction, the direction orthogonal to the Z-axis direction and in which wavelength dispersion of the diffracted light occurs is the X-axis direction, and the direction orthogonal to the Z-axis direction and the X-axis direction is the Y-axis direction, the first polarization diffraction grating and the second polarization diffraction grating are stacked facing each other in the Y-axis direction.

10. The polarization element according to claim 9, wherein the period of rotation of the local optical axis in the first polarization diffraction grating and the second polarization diffraction grating is 0.2 μm or more and 100 μm or less.

11. The polarization element according to claim 9 or claim 10, wherein the thickness of the first polarization diffraction grating and the second polarization diffraction grating in the Z-axis direction is 0.1 μm or more and 300 μm or less.

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