JP2018054450A - Reflection spectrum measurement method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To acquire the two-dimensional reflection spectrum of a test object with high accuracy utilizing interference spectroscopy.SOLUTION: Provided is a method for measuring each of the power spectrum A of multi-wavelength near-infrared light emitted from a light source L and reflected by a standard reflector and the power spectrum B of multi-wavelength near-infrared light emitted from the light source L and reflected by the skin of a human or a substance attached to the surface of the human skin as a test object 11 by interference spectroscopy, and finds a reflection spectrum of the test object 11 from the power spectra A and B. In measurement of the power spectrum A, a standard reflector having reflectance close to the human skin is used as the standard reflector. In measurement of the power spectra A and B, an optical path length difference and a sampling interval suitable for the acquisition of a spectrum of the wavelength region and wavelength resolution sufficient for the analysis of a skin surface composition are used, and the power spectra A and B are measured within a time in which human actions are restrictable.SELECTED DRAWING: Figure 7

Description

  The present invention relates to a method for measuring a reflection spectrum using two-dimensional Fourier spectroscopy.

  When performing beauty counseling, it is often performed that a subject's face is photographed with a camera, and the contour of the face, unevenness, skin color, and the like are evaluated based on the image. When photographing such a face, unevenness of the face causes unevenness in the way the illumination is applied, shadows appear in the image, and accurate evaluation of spots, freckles, etc. on the skin surface may be hindered. Therefore, in order to provide an optimal illumination environment for the face of the subject, an apparatus has been proposed in which the entire face and the entire body are covered with a casing, an enclosure, and the like, and a light source is irradiated in the interior (see Patent Document 1). .

  Patent Document 2 also describes a face photographing apparatus used for photographing a subject's face. This apparatus includes a housing that accommodates a portion of the entire face of a subject and that has a substantially spherical space, at least two light sources that irradiate light into the space of the housing, and the entire face that is irradiated with light from the light source. And imaging means for photographing the portion. One or a plurality of light sources are arranged at symmetrical positions of the subject on the spherical surface.

  Apart from these techniques, a spectroscopic measurement device that can measure biological components non-invasively and with high accuracy has been proposed (see Patent Document 3). In this document, near infrared light is irradiated with a palm as a measurement object, and a near infrared light spectrum is acquired two-dimensionally by interferometry. According to the apparatus described in the same document, it is described in the same document that, for example, a near-infrared two-dimensional spectroscopic image of a blood vessel region on the surface of a biological membrane can be acquired more clearly by recognizing a vein pattern.

JP 2004-251750 A JP 2009-245393 A JP 2008-309707 A

  In the skin evaluation technique described in Patent Documents 1 and 2, when trying to obtain a near-infrared light two-dimensional spectrum described in Patent Document 3, the measurement may be accurate depending on the measurement conditions of interference spectroscopy. May not be possible.

  Therefore, an object of the present invention is to improve the technique of near-infrared two-dimensional spectroscopy using interference spectroscopy.

  As a result of intensive studies by the inventor to solve the above-mentioned problems, it has been found that it is effective to control the measurement conditions of the reference power spectrum necessary for obtaining the reflection spectrum.

The present invention has been made on the basis of the above-mentioned findings. The power spectrum A of multi-wavelength near-infrared light emitted from a light source and reflected by a standard reflector, and the human spectrum as a subject emitted from the light source. The power spectrum B of multi-wavelength near-infrared light reflected by the skin or human skin surface deposit is measured by near-infrared two-dimensional Fourier spectroscopy, and the reflection spectrum of the subject is determined from the power spectra A and B. A method of seeking
In the measurement of the power spectrum A, a standard reflector having a reflectance close to that of human skin is used as the standard reflector.
In the measurement of the power spectra A and B, using the optical path length difference and the sampling interval suitable for acquiring the spectrum of wavelength range and wavelength resolution sufficient for the analysis of the skin surface composition, the power spectrum A within the time that can limit the human movement. And the above-mentioned subject is solved by providing the measuring method of a reflection spectrum which measures B and B.

  According to the present invention, a two-dimensional reflection spectrum of a subject using interference spectroscopy can be acquired within a predetermined time with high accuracy.

FIG. 1 is a schematic diagram showing a measurement system for measuring a spectrum in the measurement method of the present invention. FIG. 2 is a schematic system configuration diagram of the spectroscopic system used in the present invention. FIG. 3 is a diagram illustrating an irradiation distribution of object light on the reflection surfaces of the fixed mirror unit and the movable mirror unit. 4A is a diagram showing an interferogram, and FIG. 4B is a waveform diagram of a spectrum obtained by Fourier transforming the interferogram shown in FIG. 4A. FIGS. 5A to 5C are diagrams for explaining the generation principle of the interferogram. FIGS. 6A to 6C are explanatory diagrams showing the operation of the phase shifter. FIG. 7 is a reflection spectrum (absorbance display) obtained in Example 2. FIG. 8 is a reflection spectrum (absorbance display) obtained in Comparative Example 1. FIG. 9 is a schematic diagram illustrating a measurement system for measuring a reflection spectrum in the third embodiment. FIG. 10 is a graph showing the relationship between the reflection spectrum acquired in Example 3 and the angle θ. FIGS. 11A and 11B are calibration curves showing the relationship between the wavelength and the angle θ acquired in Example 3, respectively. 12A is an image showing the intensity distribution of water absorbance after angle correction obtained in Example 3, and FIG. 12B shows the intensity distribution of water absorbance before angle correction. It is an image. FIG. 13 is a schematic diagram showing a measurement system for measuring a spectrum in the measurement method of Example 4. FIG. 14 is a graph showing the near-infrared light transmission characteristics of the optical filter used in Example 4. FIG. 15 is a graph showing a spectrum after the light of the light source used in Example 4 has passed through the optical filter. FIG. 16 is a graph showing the power spectrum of near-infrared light obtained in Example 4. FIG. 17 is a reflection spectrum (absorbance display) obtained in Example 4 using an optical filter. FIG. 18 is a reflection spectrum (absorbance display) obtained in Example 4 without using an optical filter.

  The present invention will be described below based on preferred embodiments with reference to the drawings. The present invention relates to a method of irradiating a subject with near infrared light and measuring a spectrum of reflected light. Near-infrared light is an electromagnetic wave having a wavelength ranging from about 800 nm to about 2500 nm.

  The subject to be measured in the present invention is human skin or / and human skin surface deposits. There is no particular limitation on the skin part, and any part of the body can be provided to the subject as long as the measurement is not hindered. For example, the face, arms, back, legs, etc. can be measured, but the face is preferred. Examples of human skin surface deposits include sebum, sweat, cosmetics, and dirt.

  The measurements of the present invention are performed for non-medical purposes. Specific examples of non-medical purposes include beauty counseling, selection of cosmetics for users, development of cosmetics, development of diapers and sanitary products, development of clothing, development of skin cleaning products, and information exchange means for communication with customers The development of such as, but not limited to.

  The subject may have a flat surface (that is, a two-dimensional shape) as an outer surface to be measured, or a three-dimensional shape having irregularities.

The measurement method of the present invention relates to measuring a reflection spectrum of near-infrared light irradiated on a subject and obtaining a reflection spectrum on a measurement target surface in the subject two-dimensionally. To obtain a reflection spectrum two-dimensionally means, for example, that a measurement target surface (this surface may be a perfect two-dimensional surface or a three-dimensional surface having irregularities) at an arbitrary position. The coordinates are (x _i , y _i ) (i is the number of coordinates on the surface to be measured and takes a number from 1 to n), and the near infrared light at the coordinates (x _i , y _i ) When the reflection spectrum in the wavelength region is P _i , it means obtaining the reflection spectra P ₁ to P _n at all coordinates from (x ₁ , y ₁ ) to (x _n , y _n ). Therefore, the higher the number of coordinates (x _i , y _i ) included in the unit area, the higher the resolution can be measured.

  In the present invention, the power spectrum A of the multi-wavelength near infrared light emitted from the light source and reflected by the standard reflector, and the power of the multi-wavelength near infrared light emitted from the light source and reflected by the subject. The spectrum B is measured by near-infrared two-dimensional Fourier spectroscopy, which is interferometry. As the subject, human skin is used as described above. Then, the reflection spectrum of the subject is measured from the power spectra A and B. When obtaining the reflection spectrum of the subject from the power spectra A and B, the formula for calculating the power spectrum B / power spectrum A can be used.

  The subject is placed under multi-wavelength near infrared light illumination emitted from a light source. The light source is not particularly limited as long as it can emit multi-wavelength near infrared light. An example of such a light source is a halogen lamp having a continuous spectrum in the near infrared wavelength region.

  At the time of measurement, a spectroscopic system including a light source and a detector is arranged, and these and a subject constitute a measurement system. An example of the measurement system is shown in FIG. As shown in the figure, the arrangement position of the detector in the spectroscopic system 10 is not particularly limited as long as it can detect the reflected light of the near infrared light irradiated from the light source L to the subject 11. In general, it is preferable to place the spectroscopic system 10 in front of the subject 11 in terms of accurate reflection spectrum measurement. As the detector provided in the spectroscopic system 10, a device known in the technical field can be used as a device capable of detecting near-infrared light, and examples thereof include InGaAs and PbSe. In particular, an InGaAs / GaAsSb type-II quantum well light-receiving element is preferable. As the light source L, for example, a ring-shaped light source can be used. In this case, the subject 11 adjusts the positional relationship so that the subject 11 is positioned inside the ring-shaped light source L.

  In FIG. 1, the subject 11 is arranged at the irradiation position of near-infrared light emitted from the light source L. In this arrangement state, the power spectrum B is measured. On the other hand, when the power spectrum A is measured, a standard reflector (not shown) may be disposed at the position where the subject 11 is disposed instead of the subject 11. The standard reflector is used to generate a reference light with respect to the light reflected by the subject 11, whereby the relative reflectance of the subject with respect to the reflectance of the reference standard reflector can be obtained. .

  Conventional standard reflectors used so far for interference spectroscopy generally have a reflectivity of 100% or close to the wavelength range of the light to be irradiated. In contrast, in the present invention, a standard reflector with a known reflectance having a reflectance close to that of human skin is used as the standard reflector. The reflectance of human skin is usually in the range of 3% to 30%, although there is some variation depending on the body part, race, and the like. Therefore, the reflectance of the standard reflector used in the present invention is preferably 3% or more and 30% or less, and more preferably 10% or more and 20% or less. The reflectance of the standard reflector is a value measured in a wavelength range of 1000 nm to 2500 nm, and the reflectance is a value measured by an total luminous flux measurement system using an integrating sphere.

  By using a standard reflector with known reflectance having a reflectance close to that of human skin as the standard reflector, the power spectrum B is more precise than when using a standard reflector having a reflectance of 100% or close to it. As a result of the study of the present inventor, it has been found that it is possible to measure the As described above, the reflectance of the near infrared light of the skin is about 3% to about 30%. By using a reflector with the same reflectance as the standard plate, the power spectrum with the optimum light quantity for skin measurement. A and power spectrum B can be acquired. On the other hand, when a reflector having a reflectance of 100% is used, the power spectrum A cannot be acquired because the detection range of the detector is exceeded when photographing is performed with a light amount suitable for skin measurement. There is. For this reason, measurement with a light amount suitable for the measurement of the 100% reflector is necessary, and skin measurement with a sufficient light amount is difficult, so that the SN (signal / noise ratio) of the power spectrum B tends to decrease.

  Examples of the material constituting the standard reflecting plate having the reflectance in the above range include resin, paper, carbon paper, model skin, artificial skin, plastic plate, plate uniformly coated with inorganic particles, glass plate, metal mesh, etc. Is mentioned. Among resins, Spectralon (manufactured by Labsphere) is particularly desirable because it has a constant reflectance over a wide wavelength range. Spectralon is an article obtained by pressing and baking polytetrafluoroethylene powder. As the paper, black and gray drawing paper and the like are preferably used. As the carbon paper, carbon paper, plastic carbon paper, carbonless paper and the like are preferably used. As model skin, bioskin, excised skin and the like are preferably used. As the plastic plate, thermoplastic resins such as polypropylene, polyethylene, and polyvinyl chloride, and thermosetting resins are preferably used. As the plate uniformly coated with inorganic particles, a plate uniformly coated with barium sulfate, titanium dioxide, calcium carbonate, silicon dioxide and the like is preferably used. As the metal mesh, a mesh of metal wires such as gold and aluminum is preferably used.

  In the present invention, in order to measure the power spectrum A and the power spectrum B, these spectra are acquired two-dimensionally using interference spectroscopy. For the two-dimensional acquisition of the power spectrum A and the power spectrum B, for example, the spectroscopic system 10 shown in FIG. 2 can be used. The spectroscopic system 10 shown in the figure includes a splitting optical system that separates reflected light of near-infrared light irradiated from a light source onto a standard reflector or a subject into first and second light, and first and second And an optical path length difference expansion / contraction means for expanding / contracting the optical path length difference between the first and second lights. The two-dimensional acquisition method of the reflection spectrum using the spectroscopic system 10 shown in the figure is as follows.

  A group of rays such as scattered light and fluorescent light emitted radially from various bright directions from a bright spot of the standard reflector or subject 11 when light is emitted from the light source L to the standard reflector or subject 11. 2 (also referred to as “object light”) is incident on the objective lens 12 which is one member constituting the spectroscopic system 10 shown in FIG. 2 and is converted into a parallel light beam. The objective lens 12 is configured to be movable in the optical axis direction by a lens driving mechanism 13. The lens driving mechanism 13 is for scanning the in-focus position of the objective lens 12 and can be constituted by, for example, a piezo element.

  The light beam after passing through the objective lens 12 does not need to be a completely parallel light beam. The light beam after passing through the objective lens 12 only needs to be spread to such an extent that a light beam generated from one bright spot can be divided into two or more. However, in order to obtain higher spectroscopic measurement accuracy, it is desirable to use a parallel beam as much as possible.

  The parallel light beam that has passed through the objective lens 12 reaches the phase shifter 14. The phase shifter 14 functions as an optical path length difference expansion / contraction means. The phase shifter 14 includes a rectangular plate-like fixed mirror portion 15 and a columnar movable mirror portion 16 inserted into an opening (not shown) at the center thereof. The surfaces of the fixed mirror unit 15 and the movable mirror unit 16 are optically flat, and are optical mirror surfaces that can reflect the wavelength range of light to be measured by the spectroscopic system 10.

  In the following description, among the light beams that reach the phase shifter 14, the light beams that reach the reflection surface of the fixed mirror unit 15 and are reflected are the fixed light beam groups, and the light beams that reach the reflection surface of the movable mirror unit 16 and are reflected. It is also called a movable ray group. These members constitute a split optical system that separates the reflected light of the near infrared light irradiated from the light source onto the standard reflector or the subject into the first and second lights.

  The fixed mirror unit 15 and the movable mirror unit 16 are installed on a drive stage (not shown). The drive stage is composed of, for example, a piezoelectric element having a capacitance sensor, and can advance and retract along the direction of arrow A in response to a control signal from the control unit 17. Thereby, the movable mirror part 16 moves along the arrow A direction with an accuracy according to the wavelength of light.

  The phase shifter 14 is disposed so that the reflecting surfaces of the fixed mirror unit 15 and the movable mirror unit 16 are inclined by 45 degrees with respect to the optical axis of the parallel light flux from the objective lens 12. The drive stage (not shown) moves the movable mirror unit 16 while maintaining the inclination of the reflecting surface of the movable mirror unit 16 with respect to the optical axis at 45 degrees. With such a configuration, the amount of movement of the movable mirror unit 16 in the optical axis direction is 1 / √2 of the amount of movement of the drive stage. Further, the optical path length difference that gives a relative phase change between the two light beams of the fixed light beam group and the movable light beam group is twice the amount of movement of the movable mirror unit 16 in the optical axis direction.

  If the fixed mirror unit 15 and the movable mirror unit 16 are arranged obliquely in this way, a beam splitter for branching the light beam is not necessary, and the utilization efficiency of the object light can be increased. In addition, since the movable mirror unit 16 is tilted, the amount of movement of the movable mirror unit 16 in the optical axis direction with respect to the amount of movement of the drive stage is reduced, so that the influence of deterioration of the stage movement error on the spectral measurement accuracy can be reduced.

  The fixed ray group and the movable ray group that reach the phase shifter 14 and are reflected by the reflecting surfaces of the fixed mirror unit 15 and the movable mirror unit 16 are converged by the imaging lens 22 and enter the imaging plane of the detection unit 18. . This portion constitutes an imaging optical system for guiding the first and second lights to substantially the same point to form an interference image. The detection unit 18 is composed of, for example, a two-dimensional CCD camera provided with a light receiving element composed of a plurality of pixels. This light receiving element functions as means for detecting the light intensity of the interference image. The light receiving elements are two-dimensionally arranged in a plane, whereby a two-dimensional distribution of the reflection spectrum on the surface of the subject can be acquired. The reflecting surface of the fixed mirror unit 15 and the reflecting surface of the movable mirror unit 16 are configured in parallel with an accuracy that does not deviate the focusing positions of the two light beam groups on the imaging surface of the detecting unit 18.

  The optical action of the spectroscopic system 10 having the above configuration will be described. First, a group of light rays whose initial phases are not necessarily aligned, such as fluorescence and scattered light, are focused on one point as a wave whose phases are aligned on the imaging surface of the detection unit 18 via the objective lens 12 and the imaging lens 22. Description will be made based on an optical model for forming a bright spot image (interference image).

  As described above, the light beam reflected by the standard reflector or one bright spot of the subject 11 reaches the surfaces of the fixed mirror portion 15 and the movable mirror portion 16 of the phase shifter 14 via the objective lens 12. At this time, as shown in FIG. 3, the light beam group reaches the surface of the fixed mirror unit 15 and the surface of the movable mirror unit 16 in two parts. It should be noted that the light beam group that has reached the surface of the fixed mirror unit 15, that is, the fixed light beam group, and the light beam group that has reached the surface of the movable mirror unit 16, that is, the light amount of the movable light beam group is substantially equal. Although the surface area is set, it is possible to equalize the light quantity by adjusting the relative light quantity difference by installing a neutral density filter in the light path of one or both of the fixed ray group and the movable ray group. is there.

  The light beam groups reflected on the surfaces of the fixed mirror unit 15 and the movable mirror unit 16 enter the imaging lens 22 as a fixed beam group and a movable beam group, respectively, and form an interference image on the imaging surface of the detection unit 18. At this time, the light beam group reflected by the standard reflector or the subject 11 includes light of various wavelengths (and the initial phase of the light of each wavelength is not necessarily aligned), so the movable mirror unit 16 is moved. By changing the optical path length difference between the fixed light beam group and the movable light beam group, a waveform of an imaging intensity change (interference light intensity change) called an interferogram as shown in FIG. 4A is obtained. That is, an interferogram obtained by interference spectroscopy is acquired for each pixel provided in the detection unit 18. FIG. 4A is an interferogram in one pixel of the detection unit 18. In FIG. 4A, the horizontal axis indicates the optical path length difference between the fixed light beam group and the movable light beam group as the movable mirror unit 16 moves, and the vertical axis indicates the imaging intensity at one point on the imaging surface. .

  By performing Fourier transform on each acquired interferogram, it is possible to acquire, for each pixel, spectral characteristics that are relative intensities for each wavelength of light reflected by a standard reflection plate or one bright spot of the subject 11 (FIG. 4 (b)). Then, by obtaining spectral characteristics in all the pixels of the detection unit 18, the power spectrum A of multi-wavelength near infrared light emitted from the light source L and reflected by the standard reflector, and the multiple reflected by the subject 11. Two-dimensional spectroscopic measurement of the power spectrum B of near-infrared light having a wavelength is performed. The generation of the interferogram and the acquisition of the spectrum by Fourier transform of the interferogram are performed by the control unit 17 as a processing unit, or by an arithmetic unit (not shown) connected to the control unit 17. Done.

  Here, the principle of generating the interferogram will be described. First, the relationship between the optical path length difference and the interference light intensity when the measurement wavelength is a single wavelength will be described with reference to FIGS. 5A to 5C, the horizontal axis indicates the relative optical path length difference between the fixed light beam group and the movable light beam group accompanying the movement of the movable mirror unit, and the vertical axis indicates the connection in one pixel of the detection unit. The image intensity is shown.

  FIGS. 5A to 5C show the relationship between the optical path length difference of three types of monochromatic light (λa> λb> λc) having different wavelength lengths and the interference light intensity. The phase shift origin shown in the vicinity of the center in FIG. 5 (indicated by the alternate long and short dash line in FIG. 5) indicates that the reflecting surface of the movable mirror unit 16 shown in FIG. 6B matches the reflecting surface of the fixed mirror unit 15. Say. When the reflecting surfaces of the movable mirror unit 16 and the fixed mirror unit 15 are coincident, there is no relative phase difference between the fixed light beam group and the movable light beam group. That is, the light beams of these two light beam groups reach each other in phase on the imaging plane, and thus strengthen each other. For this reason, bright bright spots are formed on the imaging surface, and the imaging intensity is increased.

  On the other hand, when the movable mirror unit 16 is moved from the position shown in FIG. 6B to cause a relative optical path length difference between the fixed light beam group and the movable light beam group, the optical path length difference is reduced by half. When the wavelength (λ / 2) becomes an odd number multiple, the destructive interference condition is satisfied, so that the imaging intensity is reduced. When the optical path length difference is an integral multiple of one wavelength, the interference condition between the two light beams is intensified, and the imaging intensity increases. Therefore, when the movable mirror unit 16 is moved from FIG. 6A to FIG. 6B to the state of FIG. 6C and the optical path length difference is sequentially changed, the imaging intensity due to the interference phenomenon between the two light beams is It will change periodically. As shown in FIGS. 5A to 5C, the cycle of the imaging intensity change is long for light having a long wavelength, and is short for light having a short wavelength.

  In a spectroscopic system that measures multi-wavelength light, changes in the intensity of interference light having various lengths of wavelengths are detected as a change in luminance value. This is the interferogram shown in FIG. At the phase shift origin where there is no relative optical path length difference between the fixed beam group and the movable beam group, the two light beams intensify without depending on the wavelength. It becomes strength. However, when the optical path length difference is increased, the period of intensity change of each wavelength does not match, so that the imaging intensity does not increase even when the intensity changes of multiple wavelengths are added. For this reason, in the interferogram, a change in imaging intensity is observed in which the luminance value gradually decreases as the optical path length difference increases. In this way, since the interferogram is a waveform in which single-wavelength imaging intensity changes of a single wavelength are added, spectral characteristics that are relative intensities for each wavelength can be obtained by Fourier transforming this waveform data. Can do.

  Thus, when the power spectra A and B are acquired two-dimensionally, the reflection spectrum at each position on the surface of the subject 11 is calculated. As described above, the calculation formula of power spectrum B / power spectrum A can be used for the measurement of the reflection spectrum. Thereby, a reflection spectrum is acquired two-dimensionally. This operation is performed, for example, in the control unit 17 provided in the spectroscopic system 10 illustrated in FIG. 2 or in an arithmetic unit (not shown) connected to the control unit 17.

In the measurement of the power spectrum B in the above measuring method, it is advantageous to increase the wavelength resolution in the near infrared light wavelength region by increasing the optical path length difference. In two-dimensional Fourier spectroscopy, for example, when analyzing the amount of moisture contained in the skin and its distribution two-dimensionally according to the method of the present invention for the analysis of the skin surface composition of a human subject, It is common to pay attention to the absorption band of water in the wavelength range of near infrared light used for the analysis. Such absorption bands are near 1450 nm containing OH stretching harmonics of water and 1950 nm containing OH stretching and coupling sounds of water. In order to accurately measure the absorption in these absorption bands, a wavelength resolution of 100 nm or less is required. Incidentally, the wavelength resolution is expressed by the following equation (1).
Wavelength resolution = (wavelength) ² / maximum optical path length difference (1)
Therefore, in order to obtain a wavelength resolution of 100 nm or less in a measurement wavelength range of 1000 nm or more and 2000 nm or less, which is an example of a wavelength range sufficient for analysis of the skin surface composition, the optical path length difference is preferably set to 40 μm or more, and 80 μm It is more preferable to set the above. This optical path length difference is a value obtained by multiplying the previously described movement amount (stroke length) of the movable mirror section 16 by √2. This is because the movable mirror unit is installed at 45 degrees, and may vary depending on the installation angle of the movable mirror unit.

  In measuring the power spectrum B, it is preferable to measure the interferogram at a sampling interval that is half or less of the wavelength of the spectrum to be measured. Specifically, in order to obtain a power spectrum in the wavelength range of 1000 nm to 2000 nm, which is the measurement range, it is preferable to sample the interferogram at an interval narrower than 500 nm, corresponding to half of the shortest wavelength of 1000 nm. .

  As described above, in the measurement of the power spectrum B, it is preferable to obtain an optical path length difference of 40 μm or more and an interferogram sampling interval of 500 nm or less. However, an increase in the optical path length difference or a shortening of the sampling interval is not possible. This leads to an increase in the number of points constituting the interferogram, that is, an increase in the number of images to be taken, resulting in an increase in measurement time. If the subject moves during this measurement time, the accuracy of the measurement is greatly reduced. Therefore, in order to increase the accuracy of the measurement, it is desirable that the subject is stationary during the measurement. However, when the subject to be measured is a human subject, the time during which the subject human subject can limit his / her movement (hereinafter, this time is referred to as “quiescible time”) is finite, so it is long. Setting the measurement time leads to deterioration of measurement accuracy.

When the present inventor examined the resting time, the upper limit of the resting time was found to be about 5 seconds. The measurement time is expressed by the following formula (2).
Measurement time = optical path length difference / sampling interval / detector sampling frequency (2)
From equation (2), the sampling frequency, optical path length difference, and sampling interval of the detector can be set so that the measurement time is shorter than the predetermined restable time. Specifically, the results of calculating the relationship between the optical path length difference, the sampling interval, and the measurement time when using the detector with the highest sampling frequency (sampling frequency 320 Hz) currently available in the near-infrared region. Table 1 shows. The border corresponding to 40 μm corresponding to the lower limit of the optical path length difference and 500 nm corresponding to the upper limit of the sampling interval is indicated by a bold line. Furthermore, the background of the cell whose measurement time is within 5 seconds is shown in gray. By searching Table 1 for a region that satisfies all of the lower limit of the optical path length difference, the upper limit of the sampling interval, and the upper limit of the measurement time, a preferable optical path length difference region is set to 40 to 800 μm and a preferable sampling interval is set to 25 to 500 nm. It turned out to be necessary. More preferably, in the relational expression of the optical path length difference, the sampling interval, and the detector sampling frequency, the following expression (3) is satisfied from the expression (2) under the condition that the measurement time is within 5 seconds and the sampling frequency is 320 Hz. is necessary.
Sampling interval (nm) ≧ optical path length difference (μm) /1.6 (3)
Here, the optical path length difference region is 40 μm or more, and the sampling interval is 500 nm or less.

  When the power spectrum B is measured under the above-described conditions, the power spectrum A separately measured at the same optical path length difference and sampling interval as the power spectrum B and the power spectrum B are used as described above. Calculate the reflection spectrum. At this time, prior to the calculation, by multiplying the power spectrum A by the reciprocal of the reflectance of the standard reflector used for the measurement of the power spectrum A, the power spectrum C of the reflector having a reflectance of 100% is virtually calculated. It is preferred to perform additional steps. Specifically, when the reflectance of the standard reflector is 10%, the power spectrum C is calculated by multiplying the power spectrum A by 10 which is the reciprocal of 0.1. And it is preferable to calculate a reflection spectrum from the ratio of the power spectrum C and the power spectrum B obtained in this way. By performing this additional step, the finally obtained reflection spectrum can be made even more accurate.

  The measurement method of the present invention as described above is used to evaluate the distribution of skin surface deposits or skin moisture for non-medical purposes using, for example, human skin or human skin surface deposits as a subject. This is useful when measuring a reflection spectrum. Examples of human skin surface deposits include, but are not limited to, cosmetics applied to the surface of human skin.

  As mentioned above, although this invention was demonstrated based on the preferable embodiment, this invention is not restrict | limited to the said embodiment. For example, in the above-described embodiment, a ring-shaped light source is used as the near-infrared light source, but the shape of the light source is not limited to this. Moreover, near infrared light irradiation may be direct or indirect. For example, the light sources described in Patent Documents 1 and 2 described above can be used.

  Hereinafter, the present invention will be described in more detail with reference to examples. However, the scope of the present invention is not limited to such examples. Unless otherwise specified, “%” means “mass%”.

[Example 1]
Using the apparatus shown in FIGS. 1 and 2, the reflection spectrum of a human face in the near-infrared light wavelength range was measured two-dimensionally. The measuring device is as follows.
・ Apparatus: Imaging type 2D Fourier spectroscopy system (Aoi Electronics Co., Ltd.)
・ Light source: Ring illumination (halogen bulb x 20 (Mitsubishi Electric), ring diameter φ350mm)
Objective lens: Fixed focus lens (F1.4, 16mm, Edmund Optics)
・ Spectroscopic system:
Conjugate plane lattice: aperture width 30 μm, light shielding width 30 μm
Lens in spectroscopic unit: φ25mm, focal length: 100mm
Stroke length of movable mirror: 50 μm (Optical path length difference: 70.7 μm)
Acquisition number: 320 Sampling interval: 220.97nm
・ Detection system:
Camera: CV-N800 (Sumitomo Electric Industries, Ltd., 320 x 256 pixels)
Exposure time: 2.5 msec, Frame rate: 320 Hz
Integration count: 1 time Measurement time: 1 second

  A standard reflector is arranged at the position of the spectroscopic system, light source, and subject as shown in FIG. 1, and the image is taken, and the power spectrum of multi-wavelength near infrared light emitted from the light source and reflected by the standard reflector A was measured by interferometry. As the standard reflector, Spectralon manufactured by Labsphere with a reflectance of 10% was used. Next, the standard reflector is removed, a human face is placed at the position where the standard reflector is placed instead, and the power spectrum B of multi-wavelength near-infrared light reflected by the face is measured by interference spectroscopy. . The face was fixed with a chin stand and a forehead stand, and measurement was performed 10 times every second. The reflection spectrum obtained from the power spectrum A and the power spectrum B obtained had a sharpness that fell when it exceeded 5 seconds from the start of measurement. This was considered to be the effect of human movement. From this result, it was concluded that the upper limit of the time during which the subject can rest is 5 seconds.

[Example 2]
Using the apparatus shown in FIG. 1 and FIG. 2, the reflection spectrum of the palm of the human in the near-infrared light wavelength range was measured two-dimensionally. The measuring device is as follows.
・ Apparatus: Imaging type 2D Fourier spectroscopy system (Aoi Electronics Co., Ltd.)
・ Light source: Ring illumination (halogen bulb x 20 (Mitsubishi Electric), ring diameter φ350mm)
Objective lens: Fixed focus lens (F1.4, 16mm, Edmund Optics)
・ Spectroscopic system:
Conjugate plane lattice: aperture width 30 μm, light shielding width 30 μm
Lens in spectroscopic unit: φ25mm, focal length: 100mm
Stroke length of movable mirror: 50 μm (Optical path length difference: 70.7 μm)
Acquisition number: 640 sheets Sampling interval: 110.49 nm
・ Detection system:
Camera: CV-N800 (Sumitomo Electric Industries, Ltd., 320 x 256 pixels)
Exposure time: 2.5 msec, Frame rate: 320 Hz
Integration count: 1 time Measurement time: 2 seconds

Specifically, a spectroscopic system, a light source, and a standard reflector are arranged at the position of the subject as shown in FIG. 1, and imaging is performed. The multi-wavelength near infrared light emitted from the light source and reflected by the standard reflector is obtained. The light power spectrum A was measured by interferometry. As a standard reflector, Spectralon (SRS-10-020) manufactured by Labsphere with a reflectance of 10% was used. Next, a human palm was placed in place of the standard reflector, and the power spectrum B of multi-wavelength near-infrared light reflected by the palm was measured by interference spectroscopy. A lotion (Sophina Beaute (registered trademark) lotion moist type manufactured by Kao Corporation) is applied to a part of the palm, and a power spectrum B1 for the application part and a power spectrum B2 for the non-application part are applied. Each was measured. The measurement time was 5 seconds or less. FIG. 7 shows a reflection spectrum (absorbance display) at an arbitrary pixel obtained from the obtained power spectrum A and power spectra B1 and B2. The reflection spectrum (absorbance display) was calculated from the relationship of A = −log ₁₀ (power spectrum B1 / (power spectrum A * 10)), A = −log ₁₀ (power spectrum B2 / (power spectrum A * 10)). . As shown in the figure, the absorption peak around 1450 nm including the OH stretching overtone of water is different between the applied part and the non-applied part of the lotion, and the skin surface composition can be analyzed by the measurement method of the present invention. It turns out that it is possible.

[Comparative Example 1]
In Example 1, Spectralon (SRS-99-020) having a reflectance of 99% was used as the standard reflector. Except this, it carried out similarly to Example 1, and obtained the reflection spectrum (absorbance display) of the application part and non-application part of the lotion in the palm. The result is shown in FIG. As shown in the figure, the peak of the absorption peak in the vicinity of 1450 nm including the OH stretching overtone of water is crushed, and it can be seen that it is difficult to distinguish between the application part and the non-application part of the lotion.

Example 3
Using the apparatus shown in FIG. 1 and FIG. 2, the moisture content of the skin of the human face was measured. The measurement was performed by measuring the absorbance of water at a wavelength of 1450 nm two-dimensionally and imaging the measurement result. The measuring device is as follows.
・ Apparatus: Imaging type 2D Fourier spectroscopy system (Aoi Electronics Co., Ltd.)
・ Light source: Ring illumination (halogen bulb x 20 (Mitsubishi Electric), ring diameter φ350mm)
Objective lens: Fixed focus lens (F1.4, 16mm, Edmund Optics)
・ Spectroscopic system:
Conjugate plane lattice: aperture width 30 μm, light shielding width 30 μm
Lens in spectroscopic unit: φ25mm, focal length: 100mm
Stroke length of movable mirror: 50 μm (Optical path length difference: 70.7 μm)
Sampling interval: 110.49 nm
・ Detection system:
Camera: CV-N800 (Sumitomo Electric Industries, Ltd., 320 x 256 pixels)
Exposure time: 2.5 msec, Frame rate: 320 Hz
Integration count: 1 time Measurement time: 2 seconds

  Specifically, a spectroscopic system, a light source, and the back of a human hand as a model subject were installed as shown in FIG. As shown in FIG. 9, the skin of the back of the hand as the plane portion S was rotated by 10 ° between 0 ° and 90 ° with respect to the spectroscopic system, and photographing was performed. The reflection spectrum (absorbance display) for each angle θ is shown in FIG. The angle θ is an angle formed between the normal line N of the optical axis X and the plane portion S. FIGS. 11A and 11B show reflection spectra (absorbance display) with respect to angles at 1000 nm with no water absorption and 1450 nm with water absorption. From the results shown in FIGS. 11A and 11B, it was found that the absorbance increased monotonously with respect to the angle at 1000 nm. On the other hand, at 1450 nm, it had a maximum near 60 °. Both of them could be fitted with a cubic polynomial. Based on the polynomial at 1000 nm and the absorbance at 1000 nm, the skin angle can be estimated. Furthermore, it is possible to correct the change in absorbance due to the angle from the relationship between the angle thus obtained and the polynomial at 1450 nm.

  A standard reflector is arranged at the position of the spectroscopic system, the light source, and the subject as shown in FIG. 1, and photographing is performed. A power spectrum A of multi-wavelength near infrared light emitted from the light source and reflected by the standard reflector. Was measured by interferometry. As the standard reflector, Spectralon made by Labsphere having a reflectance of 10% was used. Next, a human face was placed in place of the standard reflector, and photographing was performed. From the obtained absorbance at 1000 nm of each pixel, the angle of each pixel was calculated based on the 1000 nm polynomial. Based on the 1450 nm polynomial, the absorbance at 1450 nm was corrected from the angle of each pixel obtained. The difference in absorbance between 1450 nm and 1000 nm was calculated, and an intensity image was created (FIG. 12 (a)). Compared with no angle correction (FIG. 12 (b)), it can be seen that the unevenness of the intensity at the uneven portion such as the nose has been eliminated by the angle correction.

Example 4
Using the apparatus shown in FIGS. 2 and 13, the moisture content in the skin of the human face after applying the skin lotion was measured. In FIG. 13, symbol F represents an optical filter. The measurement was performed by two-dimensionally measuring the water reflection spectrum (absorbance display) in the near-infrared light wavelength region and imaging the measurement result. The measuring device is as follows.
・ Apparatus: Imaging type 2D Fourier spectroscopy system (Aoi Electronics Co., Ltd.)
Light source: Ring illumination (halogen bulb × 20), spectrum of light source is shown in FIG.
Optical filter: one having the transmission characteristics shown in FIG. 14 (dielectric multilayer film, manufactured by Asahi Spectroscopic Co., Ltd.), and the spectrum of the light source after passing through the optical filter is shown in FIG.
Objective lens: Fixed focus lens (F1.4, 16mm, Edmund Optics)
・ Spectroscopic system:
Conjugate plane lattice: aperture width 30 μm, light shielding width 30 μm
Lens in spectroscopic unit: φ25mm, focal length: 100mm
Stroke length of movable mirror 50μm (Optical path length difference: 70.7μm)
Sampling interval: 110.49 nm
・ Detection system:
Camera: CV-N800 (Sumitomo Electric Industries, Ltd., 320 x 256 pixels)
Exposure time: 2.5 msec, Frame rate: 320 Hz
Integration count: 1 time Measurement time: 2 seconds

  A standard reflector is arranged as shown in FIG. 13 at the position of the spectroscopic system, the light source, and the subject, the image is taken, and the power spectrum of multi-wavelength near-infrared light emitted from the light source and reflected by the standard reflector. A was measured by interferometry. As the standard reflector, Spectralon made by Labsphere having a reflectance of 10% was used. Subsequently, the human face immediately after the application of the skin lotion was placed in place of the standard reflector, and the power spectrum B of the multi-wavelength near infrared light reflected on the human face was measured by interference spectroscopy. The result for any one pixel is shown in FIG. The reflection spectrum (absorbance display) obtained from the obtained power spectra A and B is shown in FIG. Further, a reflection spectrum (absorbance display) obtained without using an optical filter is shown in FIG. 18 as a reference example. As is clear from the comparison between FIG. 17 and FIG. 18, in FIG. 17 using the optical filter, absorption peaks are observed both in the vicinity of 1450 nm and 1950 nm, which are characteristic absorption bands of water. On the other hand, in FIG. 18 in which no optical filter is used, an absorption peak to be observed around 1950 nm is not observed.

DESCRIPTION OF SYMBOLS 10 Spectroscopic system 11 Subject 12 Objective lens 13 Lens drive mechanism 14 Phase shifter 15 Fixed mirror part 16 Movable mirror part 17 Control part 18 Detection part 22 Imaging lens L Light source

Claims (6)

  Power spectrum A of multi-wavelength near-infrared light emitted from a light source and reflected by a standard reflector, and multi-wavelength light emitted from a light source and reflected by human skin or a human skin surface deposit as a subject The near-infrared light power spectrum B is converted into a near-infrared light within a wavelength range and a sampling interval suitable for acquiring a spectrum having a wavelength range and wavelength resolution sufficient for analysis of the skin surface composition, and within a time that can limit human movement. A method of obtaining the reflection spectrum of the subject from the power spectra A and B by measuring by two-dimensional Fourier spectroscopy.   The method for measuring a reflection spectrum according to claim 1, wherein the standard reflecting plate has a reflectance of 3% to 30%.   The method for measuring a reflection spectrum according to claim 1 or 2, wherein the optical path length difference is 40 µm or more and 800 µm or less, and the sampling interval is 25 nm or more and 500 nm or less. A step of calculating a power spectrum C by multiplying the power spectrum A by a reciprocal of the reflectance of the standard reflector;
The method for measuring a reflection spectrum according to any one of claims 1 to 3, wherein a reflection spectrum of the subject is obtained from a ratio between a power spectrum C and a power spectrum B.   The method of measuring a reflection spectrum according to any one of claims 1 to 4, wherein the time during which the human movement can be restricted is 5 seconds.   The method for measuring a reflection spectrum according to any one of claims 1 to 5, wherein the subject is a face.