JP7033968B2 - Spectrometer, hyperspectral measurement system, and spectroscopic method - Google Patents

Description

The present invention relates to a spectroscopic device used to simultaneously acquire spectra from multiple points on a target.

A measurement system such as a hyperspectral camera is used to continuously and simultaneously acquire multiple points in a wide range of wavelength bands, such as the properties and physical properties of the target to be measured.

As shown in FIG. 5, such a hyperspectral camera 200A includes a slit mechanism S in which a plurality of slits are arranged in the slit width direction and provided at predetermined intervals, a collimating lens L1, a diffraction grating G1, and a condenser lens. Some are provided with L2 and a plurality of CMOS image sensors D provided side by side in the slit width direction (see Patent Document 1). This is configured so that the light incident from each slit forms a diffraction image in the corresponding CMOS image sensor.

That is, it is possible to improve the spatial resolution by making it possible to collectively acquire spectra for a plurality of points of the target, or to shorten the imaging time as compared with scanning type imaging using a single-line CCD.

By the way, in a spectroscope for hyperspectral imaging, there is a trade-off relationship between the fineness of an image (spatial resolution) and the amount of information in the spectrum (wavelength range / resolution), and a design that balances the two according to the application is made. You will need it.

However, in the case of the conventional technique using only one diffraction grating as described above, in the case of a design in which spatial resolution is prioritized, not only the amount of information in the spectrum but also another limitation arises.

Specifically, when trying to increase the dispersion of light by the diffraction grating so that an imaging image with finer wavelength decomposition can be obtained, the diffraction image of a certain slit corresponds not only to the CMOS image sensor but also to the adjacent CMOS. An image sensor will also form an image. In such a case, a part of the diffraction image of the adjacent slits overlaps on each CMOS image sensor, and the respective diffraction images cannot be separated and imaged, so that spectroscopic measurement becomes impossible.

Therefore, it is necessary to limit the range in which the target is imaged and the wavelength resolution so that the diffraction images of the slits do not overlap.

Furthermore, in order to prioritize spatial resolution and reduce the amount of spectral information, it is necessary to use a diffraction grating with a coarse lattice spacing. When such a diffraction grating is used, 0th-order diffracted light (non-diffraction) is used on the detector. There is also a problem that the slit image of the light) overlaps with the spectral image due to the diffracted light.

Japanese Patent Application Laid-Open No. 2015-137873

The present invention has been made in view of the above-mentioned problems, and it is necessary to simultaneously acquire multipoint spectral information with a plurality of slits without sacrificing wavelength resolution, and to separate and image the diffraction image of each slit. It is an object of the present invention to provide a spectroscopic device that enables.

That is, the spectroscopic device according to the present invention is a spectroscopic device that disperses the light from the target and incidents the dispersed light on the detector, and a plurality of slits on which the light from the target is incident are formed in the slit width direction. A slit mechanism formed side by side, a collimating optical element that parallelizes light that has passed through the plurality of slits, a first diffraction grid provided so that light that has passed through the collimating optical element is incident, and the first diffraction grid. A second diffraction grid provided so that light dispersed for each wavelength is incident via the diffraction grid, and a condensing optical element that collects the light passing through the second diffraction grid into the detector. The first diffraction is obtained when the light path from the slit mechanism to the detector is viewed along the traveling direction because the grid spacing of the first diffraction grid and the grid spacing of the second diffraction grid are different. The feature is that the direction of diffraction based on the 0th-order diffracted light in the lattice and the direction of diffracted based on the 0th-order diffracted light in the second diffractive lattice are configured to be different from each other. do.

Further, the spectroscopic method according to the present invention includes a slit mechanism in which a plurality of slits to which light from a target is incident are arranged side by side in the slit width direction, and a collimating optical element for parallelizing the light passing through the plurality of slits. A first diffraction grid provided so that light passing through the collimating optical element is incident, and a second diffraction grid provided so as to incident light dispersed for each wavelength via the first diffraction grid. And a light-collecting optical element that collects light that has passed through the second diffraction grid into the detector, and the lattice spacing of the first diffraction grid and the grid spacing of the second diffraction grid are different. In a spectroscopic method using an apparatus, when the optical path from the slit mechanism to the detector is viewed along the traveling direction, the direction of diffraction with respect to the 0th-order diffracted light in the first diffraction grid and the direction of diffraction. It is characterized in that the optical paths are set so that the directions to be diffracted with respect to the 0th-order diffracted light in the second diffractive lattice are different from each other.

In such a case, the light of each wavelength separated by the first diffraction grating is not imaged as it is by the detector, but the light of each separated wavelength is wavelength-dispersed by the second diffraction grating. After making it smaller, an image can be formed by the detector.

Therefore, even if the wavelength resolution is increased, the width dimension of the diffraction image formed by the detector in the slit width direction can be reduced to separate and form an image. From these facts, it is possible to prevent the diffraction images of the slits from overlapping on the detector without sacrificing the wavelength resolution.

Further, since the spectroscopic device of the present invention uses two diffraction gratings, it is possible to make it difficult for the 0th-order diffracted light (non-diffraction light) to reach the detector. It is possible to prevent the problem of overlapping with the slit image due to diffraction.

Therefore, since the problem caused by the 0th-order diffracted light does not occur, it is possible to design the spectroscopic device purely considering the trade-off between the fineness of the image and the amount of information in the spectrum. Therefore, since the parameters to be considered in the optical design are reduced, the degree of freedom in design is increased, and it is easy to realize a preferable relationship between the fineness of the image and the amount of information in the spectrum.

Further, since the spectra of a plurality of points of the target can be acquired by the plurality of slits, the time required for measurement and imaging can be shortened.

In addition, in the optical path from the slit mechanism to the detector, the second diffraction grating is provided so that light dispersed for each wavelength is incident via the first diffraction grating. The 0th-order diffracted light transmitted without being dispersed in the first diffraction grating is less likely to be incident on the second diffraction grating, and as a result, it is less likely to reach the detector. Therefore, it is possible to improve the measurement accuracy of the light dispersed by the detector.

As a configuration of an optical system that can improve the wavelength resolution and prevent the diffraction images of each slit from overlapping on the detector, the longest wavelength to be measured included in the light from the target is λ _max , λ. The wavelength of _max wavelength light is β 1 max, the wavelength of light with λ _max wavelength is β _{2 max} , and the wavelength of light from the target is β 2 max. Of these, the shortest wavelength was defined as λ _min , the diffraction angle formed by light having a wavelength of λ _min in the first diffraction grid was β _{1 min} , and the diffraction angle formed by light having a wavelength of λ _min in the second diffraction grid was β _{2 min} . In some cases, those configured to satisfy | β _2max -β _{2min | <| β 1max -β 1min} | can be mentioned.

When the focal distance of the condensing optical element is f and the slits are provided at predetermined intervals I, the lattice spacing of the first diffraction grating and the lattice spacing so as to satisfy f (sinβ _{2max -sinβ 2min} ) <I. If the lattice spacing of the second diffraction grating is set, it is possible to take an image in a separated state without generating a portion where the diffraction images of the slits overlap.

In order to prevent the transmitted light of the first diffraction grating that has not been dissected from entering the detector, to prevent the mixing of light outside the wavelength to be measured, and to prevent the measurement accuracy from being adversely affected, the second diffraction The grating may be arranged outside the passing range of the 0th-order diffracted light generated by the first diffraction grating.

Of the light incident from each slit diffracted by each diffraction grating, the one with the strongest intensity is incident on the detector so that a large light receiving output can be obtained and the S / N ratio can be improved. The -1st order diffracted light generated by the 1st diffraction grating is incident on the 2nd diffraction grating, and the -1st order diffracted light generated by the 2nd diffraction grating is incident on the condensing optical element. It suffices if it is configured as follows.

The primary diffractive light generated by the first diffraction grating is incident on the second diffraction grating, and the primary diffracted light generated by the second diffraction grating is incident on the condensing optical element. If this is the case, it is possible to prevent the loss due to diffraction as much as possible and to obtain a large light receiving output for each wavelength component in the detector.

In order to enable the spectroscopic device according to the present invention to be compactly configured, the collimating optical element and the condensing optical element are composed of a lens, and the first diffraction grating and the second diffraction grating are provided. May be transparent.

A hyperspectral measurement system including the spectroscopic device according to the present invention and the detector can simultaneously image a plurality of points and obtain a spectroscopic imaging image having high wavelength resolution.

According to the spectroscopic apparatus according to the present invention, wavelength separation is realized by two diffraction gratings having different lattice spacings, and the diffraction images of the slits imaged on the detector do not have overlapping portions. The wavelength dispersion can be adjusted.

The schematic diagram which shows the hyperspectral measurement system which concerns on 1st Embodiment of this invention. The schematic diagram which shows the relationship between the incident angle and the diffraction angle in each diffraction grating of 1st Embodiment. A slit image of the slit mechanism of the first embodiment. A diffraction image formed on the detector surface of the first embodiment. Schematic diagram showing a conventional hyperspectral measurement system.

The hyperspectral measurement system 200 according to the first embodiment of the present invention will be described with reference to FIGS. 1 to 4.

The hyperspectral measurement system 200 of the first embodiment is used for, for example, microspectroscopy imaging and Raman spectroscopic imaging. The target T to be measured is two-dimensionally imaged, and spectral information is simultaneously obtained for each image pickup point. It is configured to be.

That is, as shown in FIG. 1, in the hyperspectral measurement system 200, a spectroscopic device 100 in which reflected light, scattered light, fluorescence, etc., which are light from the target T, are incident and the light is diffracted, and the spectroscopic device 100 are used. A two-dimensional detector D, in which a diffraction image to be formed is imaged and the image is imaged, is provided. The two-dimensional detector D has a two-dimensional imaging surface such as a CMOS imaging sensor or a CCD.

As shown in FIG. 1, the spectroscopic device 100 is parallelized by a slit mechanism S, which is a shielding plate having a plurality of slits formed therein, a collimating optical element L1 for parallelizing light passing through the slits, and a collimating optical element L1. The light passing through the first diffraction grating G1 to which the light is incident, the second diffraction grating G2 to which the light passing through the first diffraction grating G1 is incident, and the light passing through the second diffraction grating G2 are collected and collected on the detector D. It is provided with a light-collecting optical element L2 for forming an image with.

The spectroscopic device 100 is configured as a transmission optical system, and the collimating optical element L1 and the condensing optical element L2 are each composed of a lens optical system.

The slit mechanism S has a plurality of slits formed as shown in the slit image of FIG. 2, and is formed by arranging them at least at predetermined intervals in the slit width direction. In the first embodiment, for example, four slits are provided in an array, and there are a total of four slits, two in the slit width direction (vertical direction of the paper surface) and two in the slit length direction (left and right direction of the paper surface). The slit width of each slit is, for example, 100 μm.

The first diffraction grating G1 and the second diffraction grating G2 are transmission type, respectively, and the lattice spacing is slightly different. In the first embodiment, the lattice spacing of the first diffraction grating G1 is 1250 l / mm, whereas the lattice spacing of the second diffraction grating G2 is 1240 l / mm. As shown in FIG. 1, the 0th-order diffracted light (non-diffraction light) of the first diffraction grating G1 is arranged so as not to be incident on the second diffraction grating G2. In other words, the second diffraction grating G2 is arranged with respect to the outside of the pass range of the non-diffraction light generated by the first diffraction grating G1.

Further, as shown in FIG. 3, when the optical path from the slit mechanism S to the detector D is viewed along the traveling direction, the direction of diffraction with respect to the 0th-order diffracted light in the first diffraction grating G1 and the above-mentioned first. The direction in which the second diffraction grating G2 is diffracted with respect to the 0th-order diffracted light is configured to be different from each other. That is, the light incident on the first diffraction grating G1 in the optical path from the slit mechanism S to the detector D is diffracted to the left with reference to the 0th-order diffracted light (non-diffraction light). On the other hand, the light incident on the second diffraction grating G2 is diffracted to the right with reference to the 0th-order diffracted light (non-diffraction light) generated by the second diffraction grating G2.

In other words, in the first embodiment, the first diffraction grating G1 and the second diffraction grating G2 are present on the same side of the normal line with respect to the face plate portion of the diffraction grating at the light incident point of the grating. The light diffracted in such a manner finally reaches the detector D. Specifically, the strongest first-order diffracted light in the first diffraction grating G1 is made to be incident on the second diffraction grating G2. Further, the second diffraction grating G2 is configured so that the strongest first-order diffracted light is incident on the condensing optical element L2.

In this way, after the light incident from each slit is dispersed in the first diffraction grating G1, each dispersed light is further diffracted in the second diffraction grating G2 so that the dispersion of the dispersed light becomes smaller. It is configured. As a result, as shown in FIG. 4, the diffraction image of each slit on the D surface of the detector is imaged in a state of being separated into each wavelength component while making no overlapping portion.

Next, as shown in FIG. 4, the incident angle and the diffraction angle of the first diffraction grating G1 and the second diffraction grating G2 are satisfied so that there is no overlapping portion in the diffraction image of each slit. The relationship will be described with reference to FIG.

Here, the incident angle of the incident light on the first diffraction grid G1 is α ₁ , the longest measurement target wavelength included in the light from the target T is λ _max , and the light having a wavelength of λ _max is the first diffraction. The diffraction angle formed by the lattice G1 is β _{1 max} , the incident angle at which light having a wavelength of λ _max is incident on the second diffraction lattice G2 is α 2 _max , and the diffraction angle formed by light having a wavelength of λ max is β 2 _{max .} , The diffraction angle formed by the light having a wavelength of λ _max in the second diffraction grid G2 is β 2 _max , the shortest wavelength to be measured included in the light from the target T is λ _min , and the light having a wavelength of λ _min is described above. The diffraction angle formed by the first diffraction grid G1 is β _{1 min} , the incident angle at which light having a wavelength of λ _min is incident on the second diffraction grid G2 is α _{2 min} , and the light having a wavelength of λ _min is formed by the second diffraction grid G2. Let the angle be β _2min . Further, the lattice spacing of the first diffraction grid G1 is Λ ₁ , the grid spacing of the second diffraction grid G2 is Λ ₂ , the diffraction order of the diffracted light generated by the first diffraction grid G1 is m ₁ , and the diffraction order is generated by the second diffraction grid G2. Let the diffraction order of the diffracted light be m ₂ and the focal distance f of the condensing optical element L2.

Further, for the first diffraction grating G1, the grating equations are Λ ₁ (sin α ₁ + sin β _{1 min} ) = m ₁ λ _min and Λ ₁ (sin α ₁ + sin β 1 _max ) = m ₁ λ _max . From these equations, the diffraction angles of each wavelength, β _{1 min} and β 1 _max , can be obtained.

Similarly, for the second diffraction grating G2, the grating equations are Λ ₂ (sin α _{2 min} + sin β _{2 min} ) = m ₂ λ _min and Λ ₂ (sin α 2 max + sin _β 2 _max ) = m ₂ λ _max . From these equations, β _2in and β 2 max, which are the diffraction angles of each wavelength, can be obtained.

Further, the separation distance D in the slit width direction between the diffraction images of each slit on the detector D can be expressed as D = f (sinβ _{2max -sinβ 2min} ). The grid spacing of each diffraction grating is set so that this value D is smaller than the slit spacing I.

According to the spectroscopic device 100 and the hyperspectral measurement system 200 of the first embodiment configured in this way, there is no overlapped portion of the diffraction images of the slits imaged on the detector D. , Multipoint spectral information can be acquired without limiting the measurement range.

Further, the spectra of a plurality of points of the target T can be simultaneously imaged, and the imaging can be performed in a short time.

In addition, the -1st order diffracted light diffracted by the 1st diffraction grating G1 is configured to be incident on the 2nd diffraction grating G2, and is outside the passing range of the 0th order diffracted light generated by the 1st diffraction grating G1. Since the second diffraction grating G2 is arranged on the second diffraction grating G2, light that is not wavelength-separated by the first diffraction grating G1 does not enter the second diffraction grating G2. Therefore, even in the detector D, such light that is not wavelength-separated does not reach, so that the measurement accuracy of the wavelength-separated light can be prevented from being adversely affected.

Therefore, the problem itself that the spectral image due to diffracted light and the slit image due to non-diffractive light overlap on the detector D cannot occur, so only the trade-off relationship between the fineness of the image and the amount of information in the spectrum is considered. Then, it becomes possible to configure the dispersion device 100 having the dispersion characteristics according to the application and the purpose.

Other embodiments will be described.

In the optical path from the slit mechanism to the detector, the primary diffraction light generated by the first diffraction grating is incident on the second diffraction grating, and the primary diffraction light generated by the second diffraction grating is incident on the focusing optical element. It may be configured.

Even in such an embodiment, the dispersion of the diffracted light emitted from the second diffraction grating can be reduced without sacrificing the wavelength resolution as in the first embodiment.

Therefore, it is possible to eliminate overlapping portions of the diffracted light of each slit so that the measurement cannot be performed.

Although the hyperspectral measurement system configured as a transmission type optical system and the spectroscopic device are shown in the first embodiment, they may be configured as, for example, a reflection type optical system. For example, the collimating optical element and the condensing optical element may be configured by using a concave mirror or the like.

Similarly, the first diffraction grating and the second diffraction grating may be configured as a reflection type diffraction grating.

Further, the plurality of slits formed in the slit mechanism are not limited to those formed and arranged in an array, and for example, a plurality of slits may be formed by arranging a plurality of slits in the width direction of the slits. The number may be plural, and the number is not particularly limited.

A diffraction grating other than the first diffraction grating and the second diffraction grating may be further provided in the optical path from the slit mechanism to the detector D. Further, the second diffraction grating does not necessarily have to be a diffraction grating immediately before the incident on the detector D.

In each embodiment, the optical path from the slit mechanism to the detector D is composed of the first-order diffracted light or the first-order diffracted light having the strongest intensity in each diffraction grating. For example, the optical path is the first diffracted light. The second-order diffracted light generated in the grating may be configured to be incident on the second diffraction grating. That is, an optical path may be formed by using diffracted light of an arbitrary order so that the signs of the order of the diffracted light generated in each diffraction grating are aligned.

Further, if it is configured to satisfy | β _2max -β _{2min | <| β 1max -β 1min} |, it is possible to prevent the detector D from having a portion that overlaps with the diffraction image of each slit. It becomes.

The spectroscopic device and the hyperspectral measurement system according to the present invention are not limited to the use of imaging, and may be used, for example, for simultaneous measurement of spectral information at multiple points on a target. Further, the present invention is not limited to microscopic measurements such as microscopes and Raman spectroscopic analysis, but may be targeted to macroscopic measurements such as multispectral cameras and hyperspectral cameras. In addition, it may be used as a hyperspectral camera mounted on an artificial satellite.

In addition, various embodiments may be combined or modified as long as it does not contradict the gist of the present invention.

200 ... Hyperspectral measurement system 100 ... Spectroscopic device S ... Slit mechanism L1 ... Collimating optical element G1 ... First diffraction grating G2 ... Second diffraction grating L2 ... Condensing optics Element D: Detector

Claims (9)

A spectroscopic device that disperses light from a target and incidents the dispersed light onto a detector.
A slit mechanism in which multiple slits that receive light from the target are arranged side by side in the slit width direction,
A collimating optical element that parallelizes the light that has passed through the plurality of slits,
A first diffraction grating provided so that light passing through the collimating optical element is incident, and
A second diffraction grating provided so that light dispersed for each wavelength is incident via the first diffraction grating, and configured to reduce the dispersion of the incident light of each wavelength .
A condensing optical element that collects light that has passed through the second diffraction grating on the detector is provided.
The grid spacing of the first diffraction grating and the grid spacing of the second diffraction grating are different.
When the optical path from the slit mechanism to the detector is viewed along the traveling direction, the direction of diffraction with respect to the 0th-order diffracted light in the first diffraction grating and the 0th-order diffracted light in the second diffraction grating are shown. A spectroscopic device characterized in that the direction to be diffracted as a reference is configured to be different from each other. Of the wavelengths to be measured contained in the light from the target, the longest wavelength is λ _max , the light having a wavelength of λ _max is the diffraction angle formed by the first diffraction grid is β 1 _max , and the light having a wavelength of λ _max is the second diffraction. The diffraction angle formed by the lattice is β _{2 max} , the shortest wavelength of the measurement target wavelengths contained in the light from the target is λ _min , and the diffraction angle formed by the light having a wavelength of λ _min in the first diffraction lattice is β _{1 min} , λ _min . When the diffraction angle formed by the light of the wavelength of 2 in the second diffraction lattice is β _{2 min} ,
The spectroscopic device according to claim 1, which is configured to satisfy | β _2max -β _{2min | <| β 1max -β 1min} |. When the focal length of the condensing optical element is f and the slits are provided at predetermined intervals I,
The spectroscopic device according to claim 2, wherein the lattice spacing of the first diffraction grating and the lattice spacing of the second diffraction grating are set so as to satisfy f (sinβ _{2max -sinβ 2min} ) <I. The spectroscopic device according to claim 1, wherein the second diffraction grating is arranged outside the passing range of the 0th-order diffraction grating generated by the first diffraction grating. The -1st order diffracted light generated by the first diffraction grating is incident on the second diffraction grating,
The spectroscopic device according to claim 1, wherein the -1st order diffracted light generated by the second diffraction grating is configured to be incident on the condensing optical element. The primary diffractive light generated by the first diffraction grating is incident on the second diffraction grating, and the light is incident on the second diffraction grating.
The spectroscopic device according to claim 1, wherein the primary diffracted light generated by the second diffraction grating is configured to be incident on the condensing optical element. The collimating optical element and the condensing optical element are composed of a lens.
The spectroscopic device according to claim 1, wherein the first diffraction grating and the second diffraction grating are transmission type. The spectroscopic device according to any one of claims 1 to 7.
A hyperspectral measurement system comprising the detector. A slit mechanism in which a plurality of slits to which light from a target is incident is arranged side by side in the width direction of the slit, a collimating optical element that parallelizes the light passing through the plurality of slits, and light passing through the collimating optical element is incident. It is provided so that the light dispersed for each wavelength is incident through the first diffraction grid provided so as to be incidental and the light dispersed for each wavelength is small. The second diffraction grid is provided with a light-collecting optical element that collects the light passing through the second diffraction grid into the detector, and the grid spacing of the first diffraction grid and the grid of the second diffraction grid are provided. It is a spectroscopic method using spectroscopic devices with different intervals.
When the optical path from the slit mechanism to the detector is viewed along the traveling direction, the direction of diffraction with respect to the 0th-order diffracted light in the first diffraction grating and the 0th-order diffracted light in the second diffraction grating are shown. A spectroscopic method characterized in that an optical path is set so that the direction to be diffracted as a reference is different from each other.

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