JP4316991B2 - Refractive index measuring device and concentration measuring device - Google Patents

Description

  The present invention relates to a technique for accurately measuring the refractive index of a sample by low coherence interferometry, and also relates to a technique for calculating the concentration of glucose or the like contained in the sample from the measured refractive index of the sample. It is.

  Conventionally, as a means for measuring the concentration of a sample and the thickness of a transparent thin film, a method of measuring the refractive index by a low coherence interference method has been used. Low coherence interferometry uses a light source with low coherence, such as white light or a super luminescent diode, and superimposes the light transmitted through or reflected by the measurement object and the reference light. , Which uses the fact that interference occurs only when the time-of-flight difference between the two lights is almost zero, the optical path length of the reference light is changed by moving the reference mirror, and the reference mirror when the interference signal is observed is changed. The refractive index of the sample is measured from the position.

  As an optical measurement system using the low coherence interferometry, for example, the one shown in Patent Document 1 can be cited. The optical measurement system described here includes a light source that irradiates light to a measurement object, a beam splitter and an objective lens that are sequentially disposed between the light source and the measurement object, a light source, and the measurement object. A reference mirror arranged on one side of the beam splitter on the straight line passing through the beam splitter and intersecting the connecting straight line, and a detector arranged on the other side of the beam splitter are provided. Here, the reference mirror is movable, and the refractive index and the like of the measurement object can be measured from the displacement of the reference mirror and the signal obtained from the detector. The above method is known as a general configuration when using low coherence interferometry.

  In Non-Patent Document 1, the refractive index of a glucose solution is obtained using femtosecond pulse interferometry, which is an interferometry using a femtosecond laser as a low coherence light source, and the glucose concentration is calculated from the measured value. ing. FIG. 5 shows an outline of the configuration of the optical system with reference to Non-Patent Document 1. The light beam emitted from the femtosecond laser 501 as the light source reaches the beam splitter 502. The beam splitter 502 splits the light beam into straight light and reflected light. The reflected light from the beam splitter 502 enters the sample 503, passes through the sample 503, is reflected by the fixed mirror 504, and the transmitted component at the beam splitter 502 enters the detector 505. Further, the light traveling straight in the beam splitter 502 is incident on the movable mirror 506, reflected and incident again on the beam splitter 502, and the reflected component is incident on the detector 505.

  Here, when two light beams interfere with each other by the detector 505, an interference signal is observed. Since a low-coherence light source is used as the light source, an interference signal is observed by the detector 505 when the flight times of the two light beams are approximately equal. When the light traveling straight in the beam splitter 502 passes through the sample 503, a flight time delay occurs depending on the refractive index of the sample 503. Therefore, the position of the movable mirror 506 is displaced by an amount corresponding to the delay amount. Interfering signals are observed. The refractive index of the sample can be obtained from the displacement amount of the movable mirror 506 at this time. Here, it is known that the refractive index of the glucose solution is proportional to the concentration, and the concentration of the sample can be calculated from the obtained refractive index.

Japanese Patent Laid-Open No. 10-2855 (FIG. 1) Hori, “Development of Glucose Concentration Measurement Method Using Femtosecond Pulse Interferometry”, Proceedings of the 64th Japan Society of Applied Physics, 2003, p.915

  However, in the optical measurement in the conventional low-coherence interferometry, it is an indispensable condition to set the optical path lengths until the light beams divided into two by the beam splitter each go to the detector. For this reason, the amount of movement of a movable stage such as a movable mirror needs to be controlled with very strict accuracy. Further, since it is necessary to provide a stage scanning range necessary for optical measurement, the arrangement of each device is also restricted. Furthermore, since a mechanical operation of moving the stage occurs in the measurement, vibration occurs at that time, which greatly affects the measurement accuracy.

  Therefore, in the present invention, in order to eliminate the above-mentioned problems caused by the prior art, an apparatus capable of measuring the refractive index without being affected by vibration or the like without requiring a mechanical operation in the measurement using the low coherence interferometry. The purpose is to provide.

In order to solve these problems, the refractive index measuring device and the concentration measuring device according to the present invention employ the following means. That is, the refractive index measuring apparatus of the present invention includes a light output unit including a light source that outputs low-coherence light, a light splitting unit that splits a linearly polarized light beam output from the light output unit into two light beams, Of the two light beams divided by the light splitting means, only one of the light beams is incident on the sample, the measurement light incident on the sample, the lens for collecting the reference light not incident on the sample, and the lens Light intensity detection means for detecting the intensity of the collected light, a liquid crystal element that changes the speed of the light beam passing according to the voltage, and the orientation direction of the liquid crystal molecules in the element by applying a voltage to the liquid crystal element, comprising a liquid crystal driving circuit for changing to a substantially vertical direction from the direction parallel to light rays, a refractive index measurement apparatus according to the interference optical system for causing interference multiplexes the reference light and the measurement light, the said reference light to the liquid crystal element input And to modulate, and measuring the applied voltage of the liquid crystal element, the measurement light and the refractive index of the sample from the interference signal of the reference light detected in the light intensity detecting means.

Further, it is desirable that the liquid crystal element is a homogeneously aligned liquid crystal element.

Furthermore , it is desirable that the homogeneously aligned liquid crystal element has a direction equal to the polarization direction of the incident light.

The liquid crystal element is a split type liquid crystal element composed of a substrate having a surface on which an electrode having an area sufficiently larger than a beam diameter of a light beam is disposed and a surface on which the electrode of the area is not disposed on the same surface, The measurement light is incident on the surface of the split liquid crystal element where the electrode is not disposed, the reference light is incident on the surface of the split liquid crystal element where the electrode is disposed, and is modulated, It is desirable to measure the refractive index of the sample from the voltage applied to the split liquid crystal element and the interference signal between the measurement light and the reference light detected by the light intensity detection means.

  In the refractive index measuring apparatus of the present invention, it is desirable that both the measuring light and the reference light pass through a polarizer having an arbitrary polarization axis before entering the light intensity detecting means.

In the refractive index measuring apparatus of the present invention, at least two types of solutions can be separately placed in the sample cell in which the sample is placed, and at least the sample and the reference solution are separately placed in the sample cell. It is desirable to pass through the liquid.

  The sample in the present invention is more useful when it is an aqueous solution and the reference solution is pure water.

  Further, it is desirable that the light output means in the present invention outputs linearly polarized light.

  Moreover, it is desirable that the light source in the present invention outputs linearly polarized light.

  The light source in the present invention is preferably a super luminescent diode, a femtosecond laser, or a light emitting diode.

  In addition, the sample in the present invention is more useful when the sample is a glucose solution, blood, or urine, and the solute in the sample is glucose.

  Further, the concentration measuring apparatus of the present invention is characterized in that the refractive index of a sample is measured by any one of these refractive index measuring apparatuses, and the concentration of a substance in the sample is calculated.

(Function)
In a refractive index measurement device and a concentration measurement device that measure the refractive index of a sample using low coherence interferometry, the time of flight of a light beam used for reference out of two beams divided by a light splitting means is not mechanical. In addition, by changing electrically using a liquid crystal element, it is not necessary to adjust a device that requires high accuracy, and measurement with high accuracy is possible because there is no influence of vibration or the like. Also, until now, the mirror was made movable and the reflected light from the mirror was used as the reference light, so there were great restrictions on the arrangement of the equipment. By using a liquid crystal element that can use transmitted light, it can be used in various situations such as downsizing. Device configuration is possible.

  As described above, the refractive index measuring device and the concentration measuring device of the present invention have the effects described below.

  A light beam from a low-coherence light source such as a super luminescent diode is split into two by a light splitting means, one light beam is incident on the sample, and the other light beam is used as a reference light beam. In a refractive index measuring device and concentration measuring device using low coherence interferometry that measures the refractive index of a sample, mechanical operations such as moving a reflecting mirror are performed when changing the time of flight of a light beam used for reference. However, by using a liquid crystal element electrically, it is not necessary to adjust equipment that requires high accuracy, and there is no influence of vibration when moving the stage. Concentration measurement is possible.

  Further, the space of the scanning range of the stage, which was necessary for measurement in the case of mechanical operation, is unnecessary, and further, a configuration without using a mirror or a beam splitter is possible by using a liquid crystal element that transmits light. Therefore, it is possible to configure the apparatus according to various situations such as downsizing.

  DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, exemplary embodiments of a refractive index measuring device and a concentration measuring device using the present invention will be described with reference to the drawings.

(First embodiment)
FIG. 1 is an example of the first embodiment of the present invention. In FIG. 1, a linearly polarized light beam emitted from a light source 101 such as a super luminescent diode driven by a drive circuit 109 is incident on the collimator lens 102. Here, the light source 101 is not limited to a super luminescent diode, and is a light source that emits low coherence light with low coherence, such as white light, a light emitting diode, or a femtosecond laser. If the light beam emitted from the light source 101 is not linearly polarized light depending on the type of light source, a polarizer or the like is disposed so that linearly polarized light is emitted. The collimator lens 102 converts incident light rays into parallel light, and changes the arrangement according to the spread angle of the light rays to change the distance from the light source. Next, the light beam that has been collimated by the collimator lens 102 enters the light splitting unit 103. Here, in this embodiment, an aperture is used as the light splitting means 103 and split into two light beams. Other examples of the light splitting means 103 include a diffraction grating, a prism, and a combination of them with a reflector. Next, one of the two light beams split by the light splitting means 103 enters the sample 104. In the present embodiment, the sample 104 is a glucose solution. Here, when the light beam passes through the sample 104, the speed of light decreases due to the refractive index of the glucose solution. If the refractive index of the glucose solution is _ng , the speed c ₁ when the light beam passes through the sample 104 is
c ₁ = c / _ng
It becomes. At this time, c is the speed of light in vacuum. That is, assuming that the optical path length when passing through the sample is L, the delay time T ₁ of the flight time of the light beam by passing through the sample 104 is
T ₁ = ( _ng −1) · L / c
It becomes. Next, the light beam that has passed through the sample 104 enters the polarizer 106, and only the component of the incident light beam in the direction of the transmission axis of the polarizer 106 is transmitted. Next, the light beam that has passed through the polarizer 106 enters the condenser lens 107 and is condensed on the light receiving portion of the light receiver 108.

Further, of the two light beams split by the light splitting means 103, the other light beam enters the liquid crystal element 105. Here, the liquid crystal element 105 is a homogeneously aligned liquid crystal element, and the alignment direction is the same as the polarization direction of incident light. The liquid crystal element 105 is driven by the liquid crystal drive circuit 110, and the speed of the light beam passing through the liquid crystal element changes according to the voltage applied to the liquid crystal element 105 from the liquid crystal drive circuit 110. This is because the refractive index of the liquid crystal element 105 as a whole changes as the alignment direction of the liquid crystal molecules in the element changes from a parallel direction to a substantially vertical direction with respect to the light beam by the voltage applied to the liquid crystal element 105. is there. Here, when the refractive index when the refractive index is the minimum is n _lcd1 and the refractive index when the refractive index is the maximum is n _lcd2 , the speed c ₂ when the light beam passes through the liquid crystal element 105 is
_{c / n lcd2 <c 2 <} c / n lcd1
It becomes. That is, _assuming that the gap of the liquid crystal element 105 is L _lcd , the delay time T ₂ of the flight time of the light beam by passing through the liquid crystal element 105 is
(N _lcd1 −1) · L _lcd / c <T ₂ <(n _lcd2 −1) · L _lcd / c
It becomes. Here, T _lcd1 = (n _lcd1 −1) · L _lcd / c and T _lcd2 = (n _lcd2 −1) · L _lcd / c. Next, the light beam that has passed through the liquid crystal element 105 enters the polarizer 106, and only the component of the incident light beam in the transmission axis direction of the polarizer 106 is transmitted. Next, the light beam that has passed through the polarizer 106 enters the condenser lens 107 and is condensed on the light receiving portion of the light receiver 108.

  The light receiver 108 outputs a change in the intensity of the received light as a voltage change, and a signal detected by the light receiver is input to a computing unit 111 such as a PC. The computing unit 111 also controls the liquid crystal driving circuit 110 as a controller.

At this time, regarding the two light beams incident on the light receiver 108, an interference signal is observed only when the flight time of the light beams from the light source 101 to the light receiver 108 until reaching the light receiver 108 is substantially equal. For example, when there is a deviation in the flight time of two light beams, the light intensity detected by the light receiver 108 is constant by adding the two light beams, but the two light beams interfere with each other. if you did this,
Maximum or minimum peaks are observed.

Here, when the optical path lengths of the light beam passing through the sample 104 and the light beam passing through the liquid crystal element 105 are equal, the delay time T ₁ of the flight time of the light beam by passing through the sample 104 is
T _lcd1 <T ₁ <T _lcd2
If the above condition is satisfied, an interference signal is observed at a certain voltage value when the voltage applied to the liquid crystal element 105 is changed. At this time, since a correlation is observed between the voltage value at which the interference signal is observed and the refractive index of the sample 104, the refractive index of the sample 104 can be measured. In addition, the glucose concentration proportional to the refractive index can be calculated.

  In actual measurement, an influence such as the container in which the sample 104 is placed and the type of glass of the liquid crystal element 105 is generated. Therefore, there is a difference between the optical path lengths of the light beam passing through the sample 104 and the light beam passing through the liquid crystal element 105. Calibration is necessary before measurement. As a calibration method, for example, as sample 104, pure water is first measured and measured, and the value is used as a reference.

  Further, when the sample 104 is not transparent and includes a scatterer, the observed interference signal does not show a clean peak, and as shown in FIG. 2, a phenomenon occurs in which a plurality of peaks are observed. This is because when passing through a scatterer, the light beam is divided into forward straight light that is hardly affected by scattering and scattered light that has been scattered, and the light path length increases as the number of times the light particles are scattered. This is because an interference signal is detected over a wide range. In this case, the signal that appears first is considered to be an interference signal due to the forward straight light, and by using this signal, measurement can be performed even for the scatterer.

  As described above, the refractive index of a sample can be measured even in a method in which mechanical operation such as stage movement is replaced with electrical operation by a liquid crystal element in low coherence interferometry. By not requiring mechanical operation, it is not necessary to adjust a device that requires very high accuracy, and high accuracy measurement is possible because there is no influence of vibration or the like. Also, until now, the mirror was made movable and the reflected light from the mirror was used as the reference light, so there were great restrictions on the arrangement of the equipment, but by using a liquid crystal element that can use transmitted light, it can be adapted to various situations such as downsizing Device configuration is possible.

  In this embodiment, a glucose solution is used as a sample, and in this case, the polarization axis of light transmitted through the sample is rotated due to the optical rotation of glucose. For this reason, the polarizer 106 is disposed in order to align the polarization directions of the two light beams that reach the light receiver and reduce noise to the interference signal. If the sample has no optical rotation or the scattering in the sample is very small, the polarizer 106 is not necessary.

(Second embodiment)
Next, a second embodiment will be described with reference to FIG. The optical elements and the like are the same as those in the first embodiment. Similar to the first embodiment, a linearly polarized light beam emitted from the low-coherence light source 101 driven by the drive circuit 109 is incident on the collimator lens 102. Depending on the type of light source, when the light beam emitted from the light source 101 is not linearly polarized light, a polarizer or the like is disposed so that linearly polarized light is emitted. Next, the light beam that has been collimated by the collimator lens 102 enters the light splitting unit 103. Here, also in this embodiment, an aperture is used as the light splitting means 103 as in the first embodiment, and split into two light beams. Next, the two light beams split by the light splitting means 103 enter the split-type liquid crystal element 301.

The split-type liquid crystal element 301 is a homogeneously aligned liquid crystal element, and the alignment direction is the same as the polarization direction of the incident light beam, and electrodes are arranged only on the half surface and the surface B of the liquid crystal injection part. When a voltage is applied to the split-type liquid crystal element 301 by the liquid crystal driving circuit 110, the voltage is applied only to the surface B, and the alignment direction of the liquid crystal molecules changes. The surface A without electrodes does not change even when a voltage is applied. Here, the two light beams split by the light splitting means 103 are respectively incident on the surface A and the surface B of the split-type liquid crystal element 301. At this time, a light beam incident on the surface A of the split-type liquid crystal element 301 is a light beam a, and a light beam incident on the surface B is a light beam b.

When the light beam a passes through the split-type liquid crystal element 301, the flight time of the light beam is delayed by the refractive index, but the delay amount is constant regardless of the voltage applied to the split-type liquid crystal element 301. The light beam a passes through the split-type liquid crystal element 301 and then enters the sample cell 302. Also in this embodiment, the sample 104 is a glucose solution. Here, as shown in FIG. 4, the sample cell 302 has a structure in which two light beams pass through different paths, and has a structure in which two kinds of samples are put. The sample 104 is put in one, and the pure water is put in the other. Of the reference solution 303 is added. Further, the light beam a is arranged to pass through the sample 104 and the light beam b is arranged to pass through the reference liquid 303. When the light beam a passes through the sample 104, the speed of light decreases due to the refractive index of the glucose solution. As in the first embodiment, assuming that the refractive index of the glucose solution is _ng , the speed of light in vacuum is c, and the optical path length when passing through the sample is L, the flight of light rays by passing through the sample 104 The amount of time delay T ₁ is
T ₁ = ( _ng −1) · L / c
It becomes. In fact, since the light beam also passes through the sample cell 302, a flight time delay occurs even when it passes through the sample cell. Next, the light beam that has passed through the sample 104 enters the polarizer 106, and only the component of the incident light beam in the direction of the transmission axis of the polarizer 106 is transmitted. Next, the light beam that has passed through the polarizer 106 enters the condenser lens 107 and is condensed on the light receiving portion of the light receiver 108.

Further, when the light beam b passes through the split-type liquid crystal element 301, the flight time of the light beam is delayed by the refractive index, and the delay amount depends on the voltage applied to the split-type liquid crystal element 301. Next, the light beam b passes through the split-type liquid crystal element 301, then enters the sample cell 302, and passes through the reference liquid 303. Here, assuming that the refractive index of the reference liquid 303 is n ₀ , the delay time T ₂ of the flight time of the light beam by passing through the reference liquid 303 is
T ₂ = (n ₀ −1) · L / c
It becomes. Next, the light beam that has passed through the reference liquid 303 enters the polarizer 106, and only the component of the incident light beam in the transmission axis direction of the polarizer 106 is transmitted. Next, the light beam that has passed through the polarizer 106 enters the condenser lens 107 and is condensed on the light receiving portion of the light receiver 108.

  The light receiver 108 outputs a change in the intensity of the received light as a voltage change, and a signal detected by the light receiver is input to a computing unit 111 such as a PC. The computing unit 111 also controls the liquid crystal driving circuit 110 as a controller. At this time, with respect to the light rays a and b incident on the light receiver 108, the interference signal is observed only when the flight time of the light rays from the light source 101 until reaching the light receiver 108 is substantially equal. For example, when there is a deviation in the flight time of two light beams, the light intensity detected by the light receiver 108 is constant by adding the two light beams, but the two light beams interfere with each other. In this case, a maximum or minimum peak is observed. That is, as in the first embodiment, when the applied voltage to the split-type liquid crystal element 301 is changed, an interference signal is observed at a certain voltage value. At this time, since a correlation is observed between the voltage value at which the interference signal is observed and the refractive index of the sample 104, the refractive index of the sample 104 can be measured. In addition, the glucose concentration proportional to the refractive index can be calculated.

Here, when the interference signal is observed, the influence of the disturbance can be reduced by making the paths of the light rays a and b as equal as possible, and the modulation width of the split liquid crystal element 301 can be reduced. Highly accurate measurement is possible. In the present embodiment, both the light beam a and the light beam b are incident on the split-type liquid crystal element 301, and only the surface B of the liquid crystal element is modulated, so that elements other than the amount modulated by the liquid crystal molecules, that is, the glass of the liquid crystal element. And the influence of the alignment film and the like can be counteracted. Similarly, by entering the same sample cell 302 and entering the light beam a into the sample and the light beam b into the reference liquid, the influence when passing through the sample cell 302 can be canceled between the light beam a and the light beam b. I can do it. That is, in the flight time of the light beam a and the light beam b, the delay difference occurs only in the modulation by the liquid crystal molecules and the refractive index difference between the sample 104 and the reference liquid 303, and elements other than those necessary for measurement can be canceled. As described above, highly accurate measurement is possible. Further, as in the first embodiment, the scatterer can also be measured in this embodiment.

  As described above, the refractive index of a sample can be measured even in a method in which mechanical operation such as stage movement is replaced with electrical operation by a liquid crystal element in low coherence interferometry. By not requiring mechanical operation, it is not necessary to adjust a device that requires very high accuracy, and high accuracy measurement is possible because there is no influence of vibration or the like. Also, until now, the mirror was made movable and the reflected light from the mirror was used as the reference light, so there were great restrictions on the arrangement of the equipment, but by using a liquid crystal element that can use transmitted light, it can be adapted to various situations such as downsizing Device configuration is possible. Furthermore, by adopting a configuration in which elements other than those necessary for measurement can be canceled as in this embodiment, high-precision measurement can be performed as described above.

  In the embodiment described in the present specification, the optical system configuration is different from the conventional low-coherence interference system by taking advantage of the ability to use the transmitted light. However, the stage movement is also possible in the conventional optical system configuration. The same effect as described above can be obtained by replacing the mechanical operation such as the above with the electrical operation by the liquid crystal element.

It is a figure which shows the structure of the refractive index measuring apparatus in 1st embodiment of this invention. It is a figure which shows the detection signal of the light receiver in embodiment of this invention. It is a figure which shows the structure of the refractive index measuring apparatus in 2nd embodiment of this invention. It is a figure which shows the structure of the sample cell in embodiment of this invention. It is the schematic of the refractive index measuring apparatus in a prior art example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 101 Light source 102 Collimating lens 103 Light splitting means 104 Sample 105 Liquid crystal element 106 Polarizer 107 Condensing lens 108 Light receiver 301 Split type liquid crystal element 302 Sample cell

Claims (12)

A light output means including a light source that outputs low-coherence light, a light splitting means for splitting the linearly polarized light beam output from the light output means into two light beams, and two light beams split by the light splitting means. Of the light beams, only one of the light beams is incident on the sample, and the measurement light incident on the sample, the lens for condensing the reference light not incident on the sample, and the intensity of the light collected by the lens are detected. Light intensity detection means , a liquid crystal element that changes the speed of the light beam that passes according to the voltage, and the orientation direction of the liquid crystal molecules in the element by applying a voltage to the liquid crystal element is substantially perpendicular to the light beam. comprising a liquid crystal driving circuit for changing up, the a refractive index measuring apparatus measuring light and the reference light by multiplexing to interference optical system for causing interference to modulate incident the reference light to the liquid crystal element, the Applied voltage of liquid crystal element When the refractive index measuring apparatus for measuring the measurement light and the refractive index of the sample from the interference signal of the reference light detected in the light intensity detecting means. The refractive index measuring apparatus according to claim 1, wherein the liquid crystal element is a homogeneous alignment liquid crystal element. The refractive index measuring apparatus according to claim 2, wherein the homogeneously aligned liquid crystal element has a direction equal to a polarization direction of incident light. The liquid crystal element is a split type liquid crystal element composed of a substrate having a surface on which an electrode having an area sufficiently larger than a beam diameter of a light beam is disposed and a surface on which the electrode of the area is not disposed on the same surface, The measurement light is incident on the surface of the split liquid crystal element where the electrode is not disposed, the reference light is incident on the surface of the split liquid crystal element where the electrode is disposed, and is modulated, 4. The refractive index of the sample is measured from an applied voltage value to the split-type liquid crystal element and an interference signal between the measurement light and the reference light detected by the light intensity detection unit. 5. The refractive index measuring device according to one item. 5. The measurement light and the reference light are both transmitted through a polarizer having an arbitrary polarization axis before entering the light intensity detection means. The refractive index measuring apparatus as described in 2. Before SL sample can sample cell is put separately at least two solutions to put the At least the sample and the reference liquid are separately placed in the sample cell, said reference light passes through the reference fluid The refractive index measuring device according to any one of claims 1 to 5, wherein The refractive index measurement apparatus according to claim 6, wherein the sample is an aqueous solution, and the reference solution is pure water. The refractive index measurement apparatus according to claim 1, wherein the light output unit outputs linearly polarized light. The refractive index measuring apparatus according to claim 1, wherein the light source outputs linearly polarized light. The refractive index measuring device according to any one of claims 1 to 9, wherein the light source is a super luminescent diode, a femtosecond laser, or a light emitting diode. The refractive index measurement apparatus according to claim 1, wherein the sample is a glucose solution, blood, or urine, and the solute in the sample is glucose. A concentration measuring device that measures the refractive index of a sample by the refractive index measuring device according to any one of claims 1 to 11 and calculates the concentration of a substance in the sample.

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