JP2017156245A - Spectroscopic apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain the clear interferogram and the precise spectral characteristic of an internal component of a measurement object while suppressing the influence of light reflected on a surface of the measurement object.SOLUTION: A spectroscopic apparatus includes: a split optical system that splits light from a measurement object into two in a first axial direction, thereby forming first and second measurement light; optical path length difference providing means that provides the optical path difference that changes continuously along a second axial direction orthogonal to the first axial direction between the first and second measurement light; an imaging optical system that forms linear interference light on an imaging surface by condensing the first and second measurement light, which is provided with the optical path length difference that changes continuously, in the first axial direction; an interference light detection unit including a plurality of pixels arranged at predetermined cycles; a processing unit that obtains the spectrum based on the light intensity of the interference light detected in the interference light detection unit; a conjugated plane imaging optical system including a conjugated plane common to the split optical system disposed between the measurement object and the split optical system; and an amplitude type diffraction grating disposed on the conjugated plane. A light-transmission part of the amplitude type diffraction grating passes internal diffusion light while attenuating the polarized light derived from surface reflection light.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a spectroscopic measurement apparatus that qualitatively or quantitatively measures a measurement target by using spectral characteristics of the measurement target.

  One of the methods for measuring biological components such as glucose (blood glucose) and cholesterol contained in blood is light emitted from biological components inside the subject site when the subject site is irradiated with light. There is a method for qualitatively and quantitatively measuring biological components from the spectral characteristics of the above (Patent Document 1). In this method, it is not necessary to collect blood, and measurement can be performed noninvasively.

  In this method, light that passes through the skin of the site to be examined and enters the interior, is refracted and reflected by biological components, and is diffused to the outside (internally scattered light) is fixed as a phase shifter through the objective lens. The light is guided to the mirror and the movable mirror, and the light reflected by these two mirrors is caused to interfere on the image plane. The movable mirror is moved by a piezo element or the like, and a phase difference corresponding to the amount of movement of the movable mirror is generated between the light reflected by the fixed mirror and the light reflected by the movable mirror. For this reason, as the movable mirror moves, the intensity of the interference light between the light reflected by the movable mirror and the light reflected by the fixed mirror changes to form a so-called interferogram. A spectral characteristic (spectrum) of the internally scattered light is acquired by Fourier transforming the interferogram.

  In the measurement method described above, the light quantity distribution of the interference light on the imaging plane is affected by the difference in diffraction angle depending on the texture (surface condition) of the region to be examined. In other words, the light intensity distribution of the internally scattered light on the imaging surface varies depending on the refractive index distribution of the region to be examined and the optical texture, so this light intensity distribution is the amount of interference light that depends on the concentration of biological components. It is superimposed on the distribution, and the concentration of the biological component cannot be measured accurately.

  On the other hand, an image of the object plane is once formed on an image plane optically conjugate with the object plane by a conjugate imaging optical system, and the object light beam is spatialized by an amplitude type diffraction grating placed on the conjugate image plane. Have been proposed (Patent Document 2, Non-Patent Document 1). According to this method, it is possible to eliminate the influence of the difference in texture of the region to be examined on the light amount distribution of the internally scattered light on the imaging plane. Here, the amplitude type diffraction grating is an arrangement in which a light transmitting portion and a light shielding portion are alternately arranged in the light collecting axis direction (imaging line direction), and the interval (period) of the light transmitting portions, the light collecting axis direction, and the interference. The length in the axial direction (vertical and horizontal lengths) is very small, from several tens of μm to several hundreds of μm, and is also called a multiple slit.

Japanese Patent Laid-Open No. 2001-123456 ([0003], FIG. 3) International Publication WO2014 / 054708

Ichiro Ishimaru “High-definition Fourier spectral tomographic imaging using conjugate-resolution super-resolution grating”, Abstracts of Annual Meeting of Optical Society of Japan 2012 (Optics & Photonics Japan 2012)

  In recent years, an attempt has been made to mount a spectroscopic measurement device on an unmanned aerial vehicle called a drone, and to perform a wide-area measurement of components contained in an object to be measured, such as components contained in plankton in the sea and leaves of forest trees. In this case, the sunlight incident on the sea surface and the leaves of the trees enters the sea and the inside of the leaves, is reflected by the plankton in the sea and the components inside the leaves, and then the light emitted to the outside (internally scattered light) Measured with a spectrometer.

  When measuring the above-mentioned biological components such as glucose and cholesterol in blood, the near-infrared light excellent in skin permeability is irradiated as a measurement light to the test site. For this reason, much of the measurement light can enter the inside of the test site. On the other hand, in the case of sunlight incident on the surface of the sea or the leaves of trees, most of the sunlight is reflected on the surface of the sea or leaves, and less light enters the sea or inside the leaves of the trees. For this reason, the light reflected from the surface of the sea and leaves (surface reflected light) is superimposed on the internally scattered light that should be received by the spectroscopic measurement device, and the internal components of plankton and leaves in the sea are accurately measured. Can not do it.

  The problem to be solved by the present invention is to acquire a clear interferogram and high-accuracy spectral characteristics of the internal components of the object to be measured while suppressing the influence of light reflected from the surface of the object to be measured. .

The spectroscopic measurement device according to the present invention, which has been made to solve the above problems,
a) a splitting optical system that splits light from the object to be measured into two in a predetermined first axis direction to form first measuring light and second measuring light;
b) Optical path length difference providing an optical path length difference that continuously varies along the second axis direction, which is a direction orthogonal to the first axis direction, between the first measurement light and the second measurement light. Means,
c) Condensing the first measurement light and the second measurement light to which the continuously changing optical path length difference is provided in the first axis direction to form linear interference light on the image plane. An image optical system;
d) an interference light detection unit that detects the intensity of the interference light, and includes a plurality of pixels arranged at a predetermined period in the second axis direction on the imaging plane;
e) Processing for obtaining an interferogram of a component included in the object to be measured based on the light intensity of the interference light detected by the interference light detection unit, and acquiring a spectrum by Fourier transforming the interferogram And
f) a conjugate plane imaging optical system having a conjugate plane in common with the divided optical system, disposed between the object to be measured and the divided optical system;
g) an amplitude diffraction grating having a plurality of light-transmitting portions and a plurality of light-shielding portions arranged in the conjugate plane and periodically arranged in the first axis direction;
With
An optical element in which at least some of the plurality of light transmitting parts pass light emitted from the inside of the measurement object while attenuating polarized light derived from the surface reflected light reflected on the surface of the measurement object. It is comprised from these.

  In the spectroscopic measurement device, light incident on the surface of the object to be measured enters the inside of the object to be measured, is reflected by components contained therein, and is emitted to the outside of the object to be measured (internal (Scattered light) passes through the transmission part of the amplitude-type diffraction grating and is given a spatial periodic change, and then is divided into a first measurement light and a second measurement light by a splitting optical system, and then the optical path length difference An optical path length difference that continuously changes between the first measurement light and the second measurement light is applied by the applying unit. Then, the interference light of the first measurement light and the second measurement light is formed on the imaging surface by the imaging optical system, and the intensity of the interference light is detected by the interference light detection unit arranged on the imaging surface, A spectrum is acquired by the processing unit. At this time, at least a part of the translucent portion of the amplitude type diffraction grating attenuates polarized light derived from the surface reflected light reflected by the surface of the object to be measured, and the inside emitted from the object to be measured Since the optical element is configured to allow the scattered light to pass therethrough, it is possible to reduce the ratio of the surface reflected light of the object to be measured that occupies the light toward the split optical system.

  The optical element includes a first linearly polarizing plate disposed so that a transmission axis direction is the first axial direction, and a second linearly polarized light disposed such that the transmission axis direction is the second axial direction. One or more types of linearly polarizing plates selected from a plate and a third linearly polarizing plate arranged so that the direction of the transmission axis is different from both the first and second axis directions Can be used.

  When the light incident on the surface of the object to be measured is non-polarized light such as sunlight, when the incident angle (= reflection angle) is within a predetermined angle range, the surface reflected light contains almost P-polarized light component. However, it is known that the S polarization component becomes dominant. The P-polarized light component is a linearly polarized light component whose electric field vibration direction is perpendicular to the incident surface (a surface including incident light and reflected light), and the S-polarized light component is vertical polarized light whose electric field vibration direction is parallel to the incident surface. Ingredients. On the other hand, the internally scattered light emitted from the inside of the object to be measured is almost maintained in a non-polarized state. Therefore, when the light incident on the object to be measured is non-polarized light, the surface reflected light is incident so that the transmission axis of the linearly polarizing plate is perpendicular to the incident surface and the incident angle is in a predetermined angle range. If the spectroscopic measurement device is installed in any direction, most of the polarized light derived from the surface reflected light (that is, the S-polarized light component) cannot pass through the light transmitting portion composed of the linearly polarizing plate, so that the surface reflected light is attenuated. be able to. In this case, when all of the light transmitting parts are composed of linear polarizing plates having the same transmission axis direction, and the spectroscopic measurement device is installed in such a direction that the transmission axes of these linear polarizing plates are perpendicular to the incident surface, It is possible to prevent the polarized light derived from the reflected light from passing through the light transmitting part.

  Further, in the spectroscopic measurement apparatus, the plurality of light transmitting portions are arranged such that a transmission axis direction is the first axis direction and a transmission axis direction is the second axis. A second linearly polarizing plate arranged to be in a direction, or the plurality of translucent portions are arranged so that a direction of a transmission axis is in the first axis direction. The direction of the transmission axis is different from either the first axial direction or the second axial direction with any one of the second linearly polarizing plates arranged so that the direction of the plate and the transmission axis is the second axial direction. It is preferable to comprise from the 3rd linearly-polarizing plate arrange | positioned in this way.

  In the above configuration, by setting the direction of the transmission axis of the linearly polarizing plate constituting the translucent part to an appropriate direction, a part of the translucent part is derived from polarized light derived from surface reflected light and internally scattered light. It is possible to allow both of the polarized light to pass through and the remaining light transmitting part to pass only the polarized light derived from the internally scattered light and not allow the polarized light derived from the surface reflected light to pass. For example, a part of the linearly polarizing plate constituting the light transmitting part passes the P-polarized component of the internally scattered light, and the remaining linearly polarizing plate passes the S-polarized component of the surface reflected light and the S-polarized component of the internally scattered light. When the direction of the transmission axis is set, the intensity of the P-polarized light component detected by some pixels of the interference light detector, the intensity of the surface reflected light from the light intensity of the S-polarized light component detected by the remaining pixels, The intensity of the scattered light can be obtained, and the intensity (spectral characteristic) of each surface reflected light for each wavelength and the intensity (spectral characteristic) for each wavelength of the internal scattered light can be obtained.

  The spectral characteristic of the surface reflected light reflects the light incident on the object to be measured, that is, the light source color. On the other hand, the spectral characteristic of the internal scattered light reflects the spectral characteristic of the reflected light of the internal component of the object to be measured (in other words, the spectral characteristic of the absorbed light). Therefore, by performing light source color correction (background correction) using the intensity of the surface reflected light, it is possible to obtain highly accurate spectral characteristics of the internal components.

Moreover, the spectroscopic measurement method according to the present invention made to solve the above problems is
a) The light from the object to be measured is split into two in a predetermined first axis direction by a splitting optical system to form first measuring light and second measuring light;
b) An optical path length difference that continuously changes along a second axis direction that is a direction orthogonal to the first axis direction is provided between the first measurement light and the second measurement light,
c) The first measurement light and the second measurement light, to which a continuously changing optical path length difference is given, are condensed in the first axis direction by an imaging optical system and linearly formed on the imaging surface. Form interference light,
d) detecting the intensity of the interference light using an interference light detector having a plurality of pixels arranged at a predetermined period in the second axis direction on the imaging plane;
e) Spectroscopy that obtains a spectrum by obtaining an interferogram of a component contained in the object to be measured based on the light intensity of the interference light detected by the interference light detection unit and Fourier-transforming the interferogram In the measurement method,
A conjugate plane imaging optical system having a conjugate plane common to the divided optical system is disposed between the object to be measured and the divided optical system, and is periodically arranged in the first axis direction on the conjugate plane. An amplitude type diffraction grating having a plurality of light transmitting parts and a plurality of light shielding parts is arranged, and at least a part of the light transmitting parts is attenuated by polarization reflected from the surface reflected light reflected from the surface of the object to be measured. And an optical element that allows light emitted from the inside of the object to be measured to pass therethrough.

  According to the present invention, the amplitude type diffraction grating is disposed on the common conjugate plane of the split optical system and the conjugate plane imaging optical system, and the light transmitting portion of the amplitude type diffraction grating is reflected by the surface of the object to be measured. Since the optical element that passes the light emitted from the inside of the object to be measured is attenuated while the polarized light derived from the surface reflected light is attenuated, the difference in the texture of the object to be measured is the light quantity distribution of the internally scattered light on the imaging surface. A clear interferogram and high-precision spectral characteristics of the internal components of the object to be measured can be acquired while suppressing the influence on the measurement object.

1 is a perspective view showing an overall configuration of a spectrometer according to a first embodiment of the present invention. The top view of a spectrometer. The side view of a spectrometer. The front view (a) and side view (b) of a multiple slit. The schematic diagram explaining the measurement principle when measuring on the conditions which scattered surface reflected light injects into a spectrometer. The figure which shows the relationship between the incident angle of S polarized light and P polarized light, and a reflectance. The figure for demonstrating the relationship between the S polarization component and P polarization component of surface reflected light and internal scattering light. The figure which shows the result measured using the spectrometer which concerns on this embodiment. The schematic diagram explaining the measurement principle when measuring on the conditions in which surface reflected light directly injects into a spectrometer. 1 is a perspective view showing an overall configuration of a spectrometer according to a first embodiment of the present invention.

  Hereinafter, specific embodiments of a spectroscopic measurement apparatus according to the present invention will be described with reference to the drawings.

[First Embodiment]
<Device configuration>
As shown in FIGS. 1 to 3, the spectroscopic measurement apparatus 100 includes a conjugate plane imaging optical system and an imaging type one-dimensional Fourier spectroscopy optical system. In the conjugate plane imaging optical system, an image of a measurement target (object plane) is optically coupled with an object plane using a lens 11 such as an imaging lens, a wide-angle lens, or a micro objective lens in accordance with a viewing field range and magnification that are observation conditions. Form a conjugate plane. This conjugate plane becomes the object plane of the imaging type one-dimensional Fourier spectroscopic optical system, and the multiple slits 13 are arranged on the conjugate plane. The multiple slits 13 correspond to the amplitude type diffraction grating of the present invention.

  As shown in FIG. 4, the multiple slit 13 has a plurality of light transmitting portions 131 arranged periodically in a predetermined direction. A portion between the light transmitting portion 131 and the light transmitting portion 131 serves as a light shielding portion 132. The direction in which the light transmitting portions 131 of the multiple slits 13 are arranged corresponds to the first axis direction of the present invention. The width of the translucent part 131 is set to be approximately the same as the pixel pitch (pixel size) in the first axis direction of the two-dimensional array device 21 described later. An optical element 131 </ b> A that allows internal scattered light to pass through while attenuating the surface reflected light of the object to be measured is fitted into the plurality of light transmitting portions 131. The optical element 131A includes a first linear polarizing plate in which the direction of the transmission axis coincides with the first axis direction, a second linear polarizing plate in which the direction of the transmission axis coincides with the second axial direction, and the direction of the transmission axis is the first. One or more types of linear polarizing plates selected from the third linear polarizing plates in directions different from the axis and the second axis are used. Which linear polarizing plate is used depends on the type of light incident on the object to be measured (polarized light or non-polarized light), and at what angle to the surface of the object to be measured. Decide whether to install

  The imaging type one-dimensional Fourier spectroscopic optical system is an infinitely corrected imaging optical system composed of an objective lens 15 and an imaging lens 17, and a phase shifter 19 is connected in the vicinity of the optical Fourier transform plane, and the imaging lens 17 is connected. Two-dimensional light receiving array devices 21 are respectively installed on the image plane. The two-dimensional light receiving array device 21 corresponds to the interference light detection unit of the present invention.

  The phase shifter 19 includes a first transmissive portion 191 and a second transmissive portion 192 that are semicircular transmissive optical members, and has a substantially disk-like configuration as a whole. The first transmission unit 191 and the second transmission unit 192 are configured by an optical member that can transmit the wavelength band of light measured by this apparatus. The first transmission part 191 is made of an optical member having a constant thickness and having an incident surface and an output surface that are parallel to each other. On the other hand, the second transmissive part 192 is a wedge-shaped optical member having an incident surface that is inclined with respect to the incident surface of the first transmissive part 191 and an output surface that is on the same plane as the output surface of the first transmissive part 191. Become. In the present embodiment, the thickness of the second transmission part 192 gradually decreases from one side to the other side (in FIG. 1, from the front side to the back side), so that the incident surface changes from one side to the other side. It inclines toward the imaging lens 17 side. The imaging lens 17 is a plano-convex cylindrical lens. The imaging lens 17 is formed of a cylindrical convex surface centering on an axis parallel to the second axis, the surface on the phase shifter 19 side projecting toward the phase shifter 19, and the surface on the two-dimensional light receiving array device 21 side. Consists of a plane parallel to the exit surface of the phase shifter 19.

  The objective lens 15 and the phase shifter 19 constitute the split optical system of the present invention, and the phase shifter 19 constitutes the optical path length difference providing means of the present invention. The direction in which the thickness of the second transmission part 192 changes corresponds to the second axial direction of the present invention, and is orthogonal to the first axial direction described above. In the drawings, the first axis is represented as a vertical axis, and the second axis is represented as a horizontal axis, but it may be reversed or an axis other than the horizontal axis or the vertical axis may be used. In short, it suffices if the first axis direction and the second axis direction are orthogonal to each other.

The two-dimensional light receiving array device 21 is composed of a two-dimensional CCD camera having a plurality of pixels arranged at a predetermined pitch in the first axis direction and the second axis direction.
Note that the inclination angle of the incident surface of the second transmission unit 192 depends on the phase shift amount determined by the wave number resolution and the sampling interval in the second axis direction of the pixels of the two-dimensional light receiving array device 21 (the pitch of the pixels arranged in the second axis direction). ), But there is no problem even if it deviates slightly.

<Optical action of the device>
Next, the optical action of the spectrometer 100 will be described with reference to FIG. The spectroscopic measurement apparatus 100 measures both the spectral characteristics of light (internally scattered light) emitted from the inside of the object to be measured and the spectral characteristics of light (surface reflected light) emitted from the surface of the object to be measured. However, the present invention aims to measure the spectral characteristics of the internally scattered light and quantitatively and qualitatively analyze the components contained in the object to be measured. A method for obtaining the characteristics will be described. That is, the measurement target of the spectrometer 100 according to the present embodiment is an internal component of the object to be measured. Hereinafter, a case where the spectral characteristics of plankton in the sea, which is a measurement target, is measured by measuring the sea surface over a wide area will be described as an example. For convenience of explanation, the sea surface is assumed to be a horizontal flat surface.

<Measurement under conditions where sunlight scattered light / diffuse reflected light is incident>
The reflectivity is determined based on the refractive index difference at the interface, as is known from the Fresnel reflection law. It is known that the refractive index of biological systems such as plankton existing in the sea is slightly larger than the refractive index of water (1.33) (for example, refractive index: 1.38). Therefore, the difference in refractive index between plankton and water is very small compared to the difference in refractive index at the sea surface (atmospheric refractive index: 1.0, water refractive index: 1.33). For this reason, the reflectance at the sea surface (surface reflectance) is several hundred times greater than the internal scattering reflectance.

  On the other hand, since various gases and dusts exist in the air, sunlight is scattered and diffused by dusts in the air. Therefore, sunlight is directly incident on the sea surface, and sunlight scattered light and diffused light are incident on the sea surface. The intensity of reflected light (direct surface reflected light) when sunlight directly enters the sea surface is much higher than the intensity of reflected light (scattered surface reflected light) when sunlight scattered or diffused light enters the sea surface. Big.

  When the difference between the intensity of the internal scattered light and the intensity of the surface reflected light is large, it is difficult to measure both the intensity of the internal scattered light and the intensity of the surface reflected light within the dynamic range of the spectrometer 100. Therefore, the spectroscopic measurement apparatus 100 is arranged so that the scattered surface reflected light is incident on the spectroscopic measurement apparatus 100. In the following description, the scattered surface reflected light is simply referred to as surface reflected light.

  Specifically, as shown in FIG. 5, the light receiving axis L1 (axis extending in a direction orthogonal to the first axis and the second axis) of the spectroscopic measurement apparatus 100 and a horizontal plane in a state where the back is directed to the sun. The spectroscopic measurement apparatus 100 is installed so that an angle (a depression angle) formed is θ [rad.]. Further, the spectroscopic measurement apparatus 100 is installed so as to be in the horizontal direction of either the first axis direction or the second axis direction. Thereby, the lens 11 of the spectroscopic measurement apparatus 100 has a surface reflection whose incident surface (surface including incident light and reflected light) is perpendicular to the sea surface and whose reflection angle is θ1 (= 90−θ [rad.]). Light enters. At the same time, the internally scattered light emitted from the sea enters the lens 11 of the spectroscopic measurement device 100 in the same direction as the surface reflected light. These surface reflected light and internally scattered light are condensed by the lens 11 on a conjugate plane common to the split optical system.

  Multiple slits 13 are arranged on the conjugate plane, and a linear polarizing plate is fitted in the light transmitting part 131 of the multiple slits 13. In this example, a linear polarizing plate in which the direction of the transmission axis is the first axial direction and a linear polarizing plate in which the direction of the transmission axis is the second axial direction are used as the linear polarizing plates. Are alternately fitted in the translucent part 131, the S-polarized light derived from the surface reflected light and the internally scattered light passes through only one of these two types of linearly polarizing plates and does not pass through the other. Further, the P-polarized light derived from the surface reflected light and the internally scattered light passes only through the other of the two types of linearly polarizing plates, and does not pass through the other.

  Non-polarized light such as sunlight can be decomposed into a P-polarized component and an S-polarized component. FIG. 6 shows the relationship between the reflectance and the incident angle of the P-polarized component and the S-polarized component when such non-polarized light is incident on the surface of the object to be measured at a predetermined angle. FIG. 6 is a graph showing the reflectance for each incident angle of P-polarized light and S-polarized light at the interface of water (refractive index 1.33) and air (refractive index 1.00). The reflectance of each polarized light was obtained from an equation according to the Fresnel reflection law. As can be seen from FIG. 6, the reflectance of the S-polarized component is higher than the reflectance of the P-polarized component throughout. On the other hand, when the incident angle is less than about 70 [deg.], The reflectance of the P-polarized component becomes very low, and the Brewster angle is 0%. As shown in FIG. 6, the Brewster angle at the interface between water and air is 53 [deg.].

Brewster's angle refers to the direction of vibration of an electric field when light is incident on the interface between two substances with different refractive indices from one substance (incident side medium) to the other substance (transmission side medium). The linearly polarized light component (P-polarized light) parallel to the surface (the surface including incident light and reflected light) is incident on the inside of the material, and only the linearly polarized light component (S-polarized light) whose electric field vibration direction is perpendicular to the incident surface is reflected. An angle. When the Brewster angle is θ _B , the refractive index of the incident side medium is n ₁ , and the refractive index of the transmission side medium is n ₂ , the angle θ _B is expressed by the following equation.
tan θ _B = n ₂ / n ₁

  Therefore, when the spectroscopic measurement device 100 is installed so that the depression angle θ is 37 [rad.] (= 90-53 [rad.]), The surface reflected light incident on the lens 11 of the spectroscopic measurement device 100 is only the S-polarized light component. It becomes. Therefore, the surface reflected light (the S-polarized component thereof) passes through one linearly polarizing plate together with the S-polarized component of the internally scattered light, but the light passing through the other linearly polarizing plate is only the P-polarized component of the internally scattered light. Become.

  Since the light transmitting portions 131 and the light shielding portions 132 are alternately arranged in the multiple slits 13, the light that has passed through the light transmitting portions 131 is given a spatial periodicity, and is then divided into a split optical system and a plano-convex cylindrical surface. The light enters the two-dimensional light receiving array device 21 through the lens 17. The light incident on the objective lens 15 constituting the split optical system is split into two in the first axis direction by the phase shifter 19 and is emitted as the first measurement light and the second measurement light. As described above, the first transmission part 191 constituting the phase shifter 19 is composed of an optical member having a constant thickness with the incident surface and the output surface parallel, and the second transmission part 192 has a thickness from one side to the other side. Since the optical member gradually decreases toward the first direction, a continuous optical path length difference is given between the first measurement light that has passed through the first transmission part 191 and the second measurement light that has passed through the second transmission part 192. . The first measurement light and the second measurement light are condensed in the first axis direction by the plano-convex cylindrical lens 17 to form interference light on the imaging plane. A large number of pixels constituting the two-dimensional light receiving array device 21 are arranged on the imaging plane, and the intensity of the interference light is detected by these pixels.

  In the pixels of the two-dimensional light receiving array device 21, the intensity of the interference light formed by the light transmitted through the corresponding light transmitting portions 131 is detected. As described above, part of the plurality of translucent portions 131 passes the S-polarized component of the surface reflected light and the S-polarized component of the internally scattered light, and the rest passes only the P-polarized component of the internally scattered light. Therefore, in some pixels, the intensity of the interference light caused by the superposition of the S-polarized component of the surface reflected light and the S-polarized component of the internally scattered light is detected, and in the remaining pixels, the interference light of the P-polarized component of the internally scattered light is detected. Intensity is detected.

  The detection signal of the two-dimensional light receiving array device 21 is input to a control device 25 composed of a personal computer or the like, a plankton interferogram is obtained by a predetermined calculation process, and a spectrum (spectral characteristics) is obtained by Fourier-transforming the interferogram. ) Is obtained. Therefore, in the present embodiment, the control device 25 corresponds to the processing unit of the present invention.

  At this time, the control device 25 determines the intensity of the interference light formed by superimposing the S-polarized component of the surface reflected light and the S-polarized component of the internally scattered light, and the interference light formed by the P-polarized component of the internally scattered light. The amount of surface reflected light and the amount of internally scattered light are obtained based on the intensity of the light, and the interferogram and spectrum of the surface reflected light and the internally scattered light are obtained using these. For example, FIG. 8A shows an example of an interferogram and spectrum of surface reflected light, and FIG. 8B shows an example of an interferogram and spectrum of internally scattered light. Then, the spectrum of the internal scattered light is corrected using the spectrum of the surface reflected light, and the spectral characteristics of the internal component (plankton) are obtained. Hereinafter, a method for obtaining the light amount of the surface reflected light and the light amount of the internally scattered light will be described with reference to FIG.

Of the light incident on the sea surface, the amount of light having a wavelength λ (spectral light amount) is I ₀ (λ), and the surface reflectance (spectral reflectance) of the light having a wavelength λ incident on the sea surface is r ₁ (λ). If the reflectance (spectral reflectance) due to the internal component of light of wavelength λ is r ₂ (λ), the surface reflected light amount I ₁ (λ) of wavelength λ and the internal scattered light amount I ₂ (λ) of wavelength λ are It is expressed by a formula.
Surface reflected light quantity of wavelength λ: I ₁ (λ) = r ₁ (λ) · I ₀ (λ) (1)
Internally scattered light quantity at wavelength λ: I ₂ (λ) = r ₂ (λ) · (1−r ₁ (λ)) · I ₀ (λ) (2)

Further, the reflectances r ₁ (λ) and r ₂ (λ) are represented by the sum of the reflectances of the S-polarized component and the P-polarized component, respectively, as shown below.
r ₁ (λ) = r _1p (λ) + r _1s (λ) (3)
r ₂ (λ) = r _2p (λ) + r _2p (λ) (4)
Then, the light quantities Ip (λ) and Is (λ) of the P-polarized component and S-polarized component of the light of wavelength λ detected by the two-dimensional light receiving array device 21 are expressed by the following equations from equations (1) to (4). expressed.
Ip (λ) = r _1p (λ) · I ₀ (λ) + r _2p (λ) · (1−r _1p (λ) −r _1s (λ)) · I ₀ (λ) (5)
Is (λ) = r _1s (λ) · I ₀ (λ) + r _2s (λ) · (1−r _1p (λ) −r _1s (λ)) · I ₀ (λ) (6)

However, as described above, the spectroscopic measurement apparatus 100 is installed such that the depression angle θ is 37 [rad.], And the surface reflected light near the Brewster angle (53 [rad.]) Is reflected in the spectroscopic measurement apparatus. Since it is incident on the lens 11 of 100, the P-polarized light component is hardly contained in the surface reflected light. On the other hand, the internally scattered light maintains the non-polarized state of the incident light. For this reason,
Reflectance of P-polarized light component: r _1p (λ) = 0 (7)
r _2p (λ) = r _2p (λ) = 1/2 ・ r ₂ (λ) (8)
Can be assumed.

Therefore, when the equations (7) and (8) are substituted into the equations (5) and (6), the light amounts Ip (λ) and Is (λ) of the P-polarized component and the S-polarized component of the detection light are expressed by the following equations: It is represented by
Ip (λ) = 1/2 · r ₂ (λ) · (1−r _1s (λ)) · I ₀ (λ) (9)
Is (λ) = r _1s (λ) · I ₀ (λ) + 1/2 · r ₂ (λ) · (1−r _1s (λ)) · I ₀ (λ) (10)

Solving Equation (9) for r ₂ (λ)
r ₂ (λ) = [2 / (1−r _1s (λ))] · (Ip (λ) / I ₀ (λ)) (11)
It becomes. Also, from Equation (9) and Equation (10),
Is (λ) = r _1s (λ) · I ₀ (λ) + Ip (λ)
Therefore, when this equation is solved for I ₀ (λ),
I ₀ (λ) = (Is (λ) −Ip (λ)) / r _1s (λ) (12)
It becomes.

From the equations (11) and (12), the spectral reflectance r ₂ (λ) of the internally scattered light is expressed by the following equation.
r ₂ (λ) = [2r _1s (λ) / (1−r _1s (λ))] · (Ip (λ) / (Is (λ) −Ip (λ)) (13)
The value of the reflectance r _1s (λ) of the S-polarized component of the surface scattered light can be estimated from the incident angle (90-θ [rad.]) Of the surface reflected light incident on the spectrometer 100 (FIG. 6). reference). Further, the values of Ip (λ) and Is (λ) are obtained from the detection result of the two-dimensional light receiving array device 21. Therefore, by substituting these values into Equation (13), the spectral reflectance r ₂ (λ) of the internally scattered light can be obtained, and the spectral absorptance of the internal component can be obtained from this spectral reflectance r ₂ (λ). (1-r ₂ (λ)) can be obtained. Therefore, the spectral characteristics of the internal component can be obtained using the spectral absorptance of the internal component.

<Measurement under direct sunlight reflected surface light>
When the intensity of sunlight is high, such as in fine weather, the intensity of scattered light and diffused light from dust in the air is also large. The strength of is very small. Therefore, in such a case, as shown in FIG. 9, even if the direct surface reflected light of sunlight is measured under the condition where the light is incident on the spectrometer 100, the surface reflected light and the internal scattered light are measured within the dynamic range. can do.

  Even in the case where measurement is performed under the condition that direct surface reflected light of sunlight is incident on the spectroscopic measurement device 100, the spectroscopic measurement device 100 has a light receiving axis (axis extending in a direction orthogonal to the first axis and the second axis) and a horizontal plane. Install so that the formed angle (Depression angle) is θ [rad.]. The spectroscopic measurement apparatus 100 is installed so as to be in the horizontal direction of either the first axis direction or the second axis direction. Then, measurement is performed in a time zone in which the altitude of sunlight is 90-53 = 37 [rad.]. As a result, the lens 11 of the spectroscopic measurement apparatus 100 receives direct surface reflected light having an incident surface (a surface including incident light and reflected light) perpendicular to the sea surface and a reflection angle of 57 [rad.]. At the same time, the internally scattered light emitted from the sea enters the lens 11 of the spectroscopic measurement device 100 in the same direction as the surface reflected light. These direct surface reflected light and internal scattered light are condensed by a lens 11 on a common conjugate surface with the splitting optical system, passed through a multiple slit 13, an objective lens 15, a phase shifter 19, and a plano-convex cylindrical lens 17 to form a two-dimensional light receiving array. After the intensity of the interference light is detected by the device 21, a spectrum is obtained by a predetermined calculation process in the control device 25.

  In the above description, the sea surface is a horizontal flat surface. However, in actuality, the sea surface is composed of inclined surfaces in various directions by waves. Therefore, even in the time zone when the altitude of sunlight is 33 [rad.], The incident angle (reflection angle) of the surface reflected light reflected by the sea surface varies. Therefore, even when the spectroscopic measurement apparatus 100 is installed at a depression angle other than the above-described angle θ (37 [rad.]), The surface reflected light and the internal scattered light can be taken into the spectroscopic measurement apparatus 100. Even if the altitude of sunlight is other than 37 [rad.], The reflected light and the internally scattered light are transmitted to the spectrometer 100 by setting the depression angle of the spectrometer 100 to an appropriate value. Can be captured. In such a case, the surface reflected light becomes random polarized light including P-polarized light and S-polarized light, but the spectral characteristics of the internal components can be obtained by using the above-described calculation formula.

[Second Embodiment]
As shown in FIG. 10, the spectroscopic measurement apparatus 200 according to the second embodiment is different from the first example in that the spectroscopic optical system is formed of an imaging type two-dimensional Fourier spectroscopic optical system. That is, the spectroscopic measurement apparatus 200 includes a conjugate plane imaging optical system, a multiple slit 113, and an imaging type two-dimensional Fourier spectroscopy optical system. The imaging type two-dimensional Fourier spectroscopic optical system includes an objective lens 115, a reflection type phase shifter 30, an imaging lens 117, a detection unit 121, and a control device 125. The detection unit 121 is constituted by a CCD camera, for example.

  The reflective phase shifter 30 includes a movable mirror unit 301, a fixed mirror unit 302, and a drive mechanism 303 that moves the movable mirror unit 301. The surfaces (reflecting surfaces) of the movable mirror unit 301 and the fixed mirror unit 302 are optically flat and are optical mirror surfaces that can reflect the wavelength band of light to be measured by this apparatus. In the present embodiment, the reflective phase shifter 30 corresponds to an optical path length difference providing unit.

The conjugate plane imaging optical system includes a lens 111 disposed between the multiple slit 113 and the object S to be measured. The conjugate plane imaging optical system and the objective lens 115 have a common conjugate plane, and multiple slits 113 are arranged on the common conjugate plane.
In the above configuration, the light incident on the movable mirror part 301 and the fixed mirror part 302 of the phase shifter 30 through the multiple slits 113 and the objective lens 115 is reflected by the reflecting surfaces of these two mirror parts, and then the imaging lens. The light passes through 117 and is collected and interferes with the light receiving surface of the detection unit 121. The interference light intensity received by the detection unit 121 is input to the control device 125 and subjected to Fourier transform, and then spectral characteristics are acquired.
Even in such a configuration, the same operations and effects as those of the first embodiment described above can be obtained.

The present invention is not limited to the above-described embodiment.
You may comprise all the translucent parts 13 of the multiple slit 13 from the optical element which blocks | prevents passage of the polarization component derived from the surface reflected light of a to-be-measured object, and permeate | transmits the polarization component derived from internal scattered light. For example, in the case where measurement is performed under conditions where the surface reflected light is incident on the spectroscopic measurement device at the Brewster angle, all the light transmitting parts are configured by linearly polarizing plates that transmit the P-polarized component and do not transmit the S-polarized component. According to this configuration, the surface reflected light can be removed from the interference light detected by the interference light detector. Further, in this configuration, the background correction of the internal scattered light can be performed using this information by acquiring in advance information on the intensity and spectral characteristics of the surface reflected light using a spectrophotometer or the like. .

DESCRIPTION OF SYMBOLS 100, 200 ... Spectrometer 11, 111 ... Lens 13, 113 ... Multiple slit 131 ... Translucent part 132 ... Light-shielding part 131A ... Optical element 15, 115 ... Objective lens 17 ... Imaging lens (plano-convex cylindrical lens)
DESCRIPTION OF SYMBOLS 117 ... Imaging lens 19 ... Phase shifter 191 ... 1st transmission part 192 ... 2nd transmission part 21 ... Two-dimensional light-receiving array device 211 ... Pixel 25, 125 ... Control apparatus 30 ... Phase shifter 301 ... Movable mirror part 302 ... Fixed mirror 303: Drive mechanism

Claims (7)

a) a splitting optical system that splits light from the object to be measured into two in a predetermined first axis direction to form first measuring light and second measuring light;
b) Optical path length difference providing an optical path length difference that continuously varies along the second axis direction, which is a direction orthogonal to the first axis direction, between the first measurement light and the second measurement light. Means,
c) Condensing the first measurement light and the second measurement light to which the continuously changing optical path length difference is provided in the first axis direction to form linear interference light on the image plane. An image optical system;
d) an interference light detection unit that detects the intensity of the interference light, and includes a plurality of pixels arranged at a predetermined period in the second axis direction on the imaging plane;
e) Processing for obtaining an interferogram of a component included in the object to be measured based on the light intensity of the interference light detected by the interference light detection unit, and acquiring a spectrum by Fourier transforming the interferogram And
f) a conjugate plane imaging optical system having a conjugate plane in common with the divided optical system, disposed between the object to be measured and the divided optical system;
g) an amplitude diffraction grating having a plurality of light-transmitting portions and a plurality of light-shielding portions arranged in the conjugate plane and periodically arranged in the first axis direction;
With
An optical element in which at least some of the plurality of light transmitting parts pass light emitted from the inside of the measurement object while attenuating polarized light derived from the surface reflected light reflected on the surface of the measurement object. A spectroscopic measurement device comprising:   The optical element is a first linearly polarizing plate disposed so that a transmission axis direction is the first axial direction, and a second linear polarizing plate is disposed such that the transmission axis direction is the second axial direction. , And one or more types of linearly polarizing plates selected from the third linearly polarizing plates arranged so that the direction of the transmission axis is different from both the first and second axial directions. The spectroscopic measurement apparatus according to claim 1, wherein:   The plurality of light-transmitting portions are arranged such that the direction of the transmission axis is the first axis direction and the first linear polarizing plate is arranged so that the direction of the transmission axis is the second axis direction. The spectroscopic measurement apparatus according to claim 1, comprising two linear polarizing plates.   The plurality of translucent portions are a first linearly polarizing plate disposed so that a transmission axis direction is the first axis direction, and a second linear polarization plate is disposed such that the transmission axis direction is the second axis direction. One of the linear polarizing plates and a third linear polarizing plate disposed so that the direction of the transmission axis is different from both the first axial direction and the second axial direction. The spectroscopic measurement apparatus according to claim 1. a) The light from the object to be measured is split into two in a predetermined first axis direction by a splitting optical system to form first measuring light and second measuring light;
b) An optical path length difference that continuously changes along a second axis direction that is a direction orthogonal to the first axis direction is provided between the first measurement light and the second measurement light,
c) The first measurement light and the second measurement light, to which a continuously changing optical path length difference is given, are condensed in the first axis direction by an imaging optical system and linearly formed on the imaging surface. Form interference light,
d) detecting the intensity of the interference light using an interference light detector having a plurality of pixels arranged at a predetermined period in the second axis direction on the imaging plane;
e) Spectroscopy that obtains a spectrum by obtaining an interferogram of a component contained in the object to be measured based on the light intensity of the interference light detected by the interference light detection unit and Fourier-transforming the interferogram In the measurement method,
A conjugate plane imaging optical system having a conjugate plane common to the divided optical system is disposed between the object to be measured and the divided optical system, and is periodically arranged in the first axis direction on the conjugate plane. An amplitude type diffraction grating having a plurality of light transmitting parts and a plurality of light shielding parts is arranged, and at least a part of the light transmitting parts is attenuated by polarization reflected from the surface reflected light reflected from the surface of the object to be measured. A spectroscopic measurement method comprising: an optical element that allows light emitted from the inside of the object to be measured to pass therethrough.   A part of the plurality of translucent parts is composed of an optical element that transmits a P-polarized light component derived from the surface reflected light and a P-polarized light component derived from the light emitted from the inside of the object to be measured, and the rest are the above-mentioned 6. The spectroscopic measurement method according to claim 5, wherein the spectroscopic measurement method comprises an optical element that transmits an S-polarized light component derived from surface reflected light and an S-polarized light component derived from light emitted from the inside of the object to be measured. Surface reflected light reflected at the Brewster angle on the surface of the object to be measured is incident on the split optical system,
Of the interference light detected by the interference light detector, the intensity of the interference light by the light in which the P polarization component derived from the surface reflected light and the P polarization component derived from the light emitted from the inside of the object to be measured are superimposed. The intensity of the surface reflected light and the intensity of the internal scattered light are calculated from the intensity of the interference light generated by superimposing the S polarized component derived from the surface reflected light and the S polarized component derived from the light emitted from the inside of the object to be measured. The spectroscopic measurement method according to claim 6, wherein the intensity is calculated.

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