JP2017078645A - Optical coherence tomography device and optical coherence tomography method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce a measuring time, reduce the size of the device, and improve spatial resolution in a z-axis direction (optical axis direction).SOLUTION: An optical coherence tomography device comprises: an optical complex amplitude measuring instrument (17) that acquires optical complex amplitude information that is a result of measurement of the optical complex amplitude of a reflection signal light that is formed of multiple scattered light generated through irradiation of a measurement sample (OB) with a laser beam; and a computer (21) that calculates a result of output from a virtual 4f optical system formed by multiplying the acquired optical complex amplitude information by a transfer function of a 4f imaging optical system and performing the Fourier conversion on a result of the multiplication.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an optical tomography measurement apparatus and an optical tomography measurement method for measuring a tomography of an object.

  Confocal Laser Scanning Microscope (CLSM) [Non-Patent Document 1] places a pinhole at a position conjugate with the focal point of the objective lens to remove noise light (scattered light) generated from outside the focus. To do. In such a confocal optical system, the contrast of desired signal light reflected from the focal point is increased, and the spatial resolution is improved as compared with a normal optical microscope. Along with this, spatial resolution in the optical axis (z-axis) direction that does not exist in the conventional optical microscope is generated, so that optical tomography or three-dimensional measurement is possible.

  Due to these features, CLSM is used in a wide range of fields such as inspection of fine products such as MEMS (Micro Electro Mechanical Systems) in the industrial field, and observation of biopolymers such as proteins in the medical and life science fields. In addition, research [Non-Patent Document 2] has been conducted in which CLSM is used to observe living bodies as they are. From the above, it can be said that CLSM is a very important and high-profile technology.

  However, the conventional CLSM has the following problems. First, when a three-dimensional image is obtained by CLSM, the irradiation optical system or sample must be mechanically scanned in all the x, y, and z directions by using a galvanometer mirror or an automatic stage. Is a point.

  In order to solve this problem in the xy direction, a method using a spin disk (Nipou disk) in the pinhole portion [Non-Patent Document 3] or a method using a combination of a microlens array and a pinhole array [Non-Patent Document] 4] etc. are proposed.

  In the z-axis direction, there is a method of performing high-speed scanning with parallel flat glass [Non-Patent Document 5], but there is no method that can completely eliminate scanning in the z-axis direction at this stage. Another problem is that the obtained signal light intensity and the spatial resolution in the z-axis direction are in a trade-off relationship. In normal CLSM, the resolution in the z-axis direction is determined by the numerical aperture (NA) of the objective lens and the pinhole diameter. That is, the z-axis resolution is improved by using an objective lens having a higher numerical aperture NA and a pinhole having a smaller diameter.

  However, when the pinhole diameter is made very small, the obtained light intensity is remarkably lowered and detection becomes impossible. Therefore, it is necessary to secure a certain pinhole diameter. Therefore, in practice, even if a high NA objective lens is used, the resolution in the z-axis direction is limited. Below, two typical conventional methods for performing scanning in the z-axis direction in CLSM will be described.

(Irradiation optics and mechanical scanning system)
FIG. 14 shows a conceptual diagram of a system for mechanically scanning the irradiation optical system and the sample. This method is the most basic, and the conceptual diagram shown in FIG. 14 is a general basic configuration of CLSM. In this method, an irradiation optical system composed of an objective lens or the like or the measurement sample itself is mechanically scanned by an automatic stage or the like, and the condensing position on the measurement sample is moved stepwise along the z axis. As described above, this method is the most basic method and has an advantage that an additional optical element is unnecessary. However, there is a problem that the scanning speed is limited due to mechanical scanning.

(Method using parallel flat glass)
FIG. 15 shows a conceptual diagram of a method using parallel flat glass. In this method, the focal position on the z-axis can be step-moved directly without mechanically scanning the measurement sample. In principle, when a parallel plate glass having a thickness d and a refractive index n is inserted between the objective lens and the measurement sample, the focal position is displaced by z = d × (1-1 / n) due to the effect of refraction. You are taking advantage of that. Actually, a plurality of parallel flat glass plates having different thicknesses are arranged side by side on the circumference of the disk and rotated at high speed to realize high-speed step movement of the focal point. In contrast to mechanically scanning the measurement sample with an automatic stage or the like, this method is characterized in that scanning on the z-axis can be performed at a higher speed. However, there are problems such as an increase in the size of a system using a disk on which a plurality of parallel plates are arranged and a decrease in measurement accuracy due to vibrations generated by rotating the disk at a high speed.

S. W. Paddock, “Confocal Laser Scanning Microscopy” BioTechniques. 27, 992 (1999). Y. Hwang et al., “In vivo analysis of THz wave irradiation induced acute inflammatory response in skin by lasers-canning confocal microscopy” Opt. Express 22, 11465 (2014). G. Q. Xiao et al., “A Real-Time Confocal Scanning Optical Microscope” Proc. SPIE 0809, 107 (1987). H. J. Tiziani et al., “Three-dimensional analysis by a microlens-array confocal arrangement” Appl. Opt. 33, 567 (1994). Mitsuhiro Ishihara and Hiromi Sasaki, “High-speed three-dimensional measurement using non-scanning multi-beam confocal imaging system,” Journal of Precision Optics 64, 1022 (1998). I. Yamaguchi et al., “Phase-shifting digital holography” Opt. Lett., 22, 1268 (1997). K. Matsushima et al., “Band-Limited Angular Spectrum Method for Numerical Simulation of Free-Space Propagation in Far and Near Fields” Opt. Express 17, 19662 (2009). A. Okamoto, K. Kunori, M. Takabayashi, A. Tomita, and K. Sato, "Holographic diversity interferometry for optical storage," Opt. Express, Vol. 19, 13436 (2011).

  In any of the conventional methods described above, when a plurality of positions on the z-axis are measured (when a plurality of tomographic images are obtained), some kind of scanning is necessary, and a plurality of measurements are required. That is, there is a fundamental problem that even if the scanning time can be increased by improving the technology in the scanning mechanism, it cannot be completely eliminated. As a result, real-time measurement of a moving measurement sample such as a living organism is very difficult. Even if the real-time measurement is possible, a very high-speed machine operation unit or calculation processing unit is essential, and it cannot be said that it is practical when considering practical use.

  Further, since additional parts are required for scanning in the z-axis direction, the size of the optical system is increased. In addition, in all these conventional methods, it is possible to improve the spatial resolution on the z-axis by reducing the pinhole diameter, but in actuality, unnecessary noise light (reflected light from a non-measurement surface) and At the same time, the signal light is lost. This is because noise in the photodetector (noise such as shot noise and dark current) dominates and causes a significant reduction in the signal-to-noise ratio (SNR). Therefore, it is necessary to secure a certain pinhole diameter, and there is a problem that the spatial resolution in the z-axis direction is sacrificed.

In summary, the main problems of the conventional CLSM are the following three points.
(1) Mechanical scanning is essential on the z axis, and measurement time increases.
(2) The size of the system increases because additional parts are required for z-axis scanning.
(3) Spatial resolution in the z-axis direction is sacrificed due to the balance with the SNR of the photodetector.

  The present invention has been made in view of the above problems, and its purpose is to reduce the measurement time, downsize the apparatus, and improve the spatial resolution in the z-axis direction (optical axis direction). It is to realize an optical tomography measuring apparatus.

  In order to solve the above-described problem, an optical tomography measurement apparatus according to aspect 1 of the present invention is an optical tomography measurement apparatus that measures a tomography of an object, from multiple scattered light generated by irradiation of laser light on the object. An optical complex amplitude information acquisition unit that acquires optical complex amplitude information that is a result of measuring the optical complex amplitude of the reflected signal light, and the obtained optical complex amplitude information is multiplied by the transfer function of the 4f imaging optical system, and the multiplication is performed. An arithmetic processing unit that calculates an output result of the virtual 4f optical system formed by performing Fourier transform on the result.

  According to the above configuration, by shifting the defocus position of the virtual 4f optical system, it is possible to selectively extract only the reflected component from a position on an arbitrary z axis (optical axis) in the reflected signal light. it can. This virtual 4f optical system can eliminate or reduce scanning in the optical axis direction and eliminate mechanical z-axis scanning. For this reason, measurement time can be reduced, the apparatus can be downsized, and the spatial resolution in the z-axis direction (optical axis direction) can be improved.

  In the optical tomography apparatus according to aspect 2 of the present invention, in the aspect 1, the virtual 4f optical system further multiplies the result obtained by performing the Fourier transform on the multiplication result by a transfer function of a virtual pinhole. It may be formed. According to the above configuration, since the noise removal due to the pinhole is performed on the virtual optical system, the pinhole diameter can be further reduced.

  In the optical tomography measuring apparatus according to aspect 3 of the present invention, in the aspect 1 or 2, a galvanometer mirror may be disposed on the laser beam path between the object and the optical complex amplitude information acquisition unit. According to the above configuration, by changing the angle of the galvanometer mirror, the condensing position on the measurement surface of the object can be displaced. In accordance with this, scanning on the xy plane can be performed by moving the position of the pinhole in the virtual optical system on the xy plane.

  In the optical tomography measuring apparatus according to aspect 4 of the present invention, in the aspect 1 or 2, a phase type spatial light modulator is disposed on the path of the laser light between the object and the optical complex amplitude information acquisition unit. May be. According to the above configuration, the same effect as when the angle of the galvanometer mirror is changed can be obtained by giving the phase-type spatial light modulator a steady phase distribution that displaces the optical axis by a predetermined angle. .

  An optical tomographic measurement apparatus according to aspect 5 of the present invention is configured by a plurality of minute lenses on the path of the laser light between the object and the optical complex amplitude information acquisition unit in the aspect 1 or 2. A microlens array may be arranged. According to the above configuration, light waves are collected at a plurality of positions on the measurement surface of the object. Then, for example, by arranging a plurality of pinholes in the virtual optical system so as to coincide with each condensing position, it is possible to collectively measure the xy plane.

  In order to solve the above-described problem, an optical tomography measurement method according to aspect 6 of the present invention is an optical tomography measurement method for measuring a tomography of an object, from multiple scattered light generated by laser light irradiation on the object. An optical complex amplitude information acquisition step for acquiring optical complex amplitude information that is a result of measuring the optical complex amplitude of the reflected signal light, and multiplying the acquired optical complex amplitude information by the transfer function of the 4f imaging optical system, And an arithmetic processing step for calculating an output result of the virtual 4f optical system formed by subjecting the result to Fourier transform. According to the said method, the effect similar to the said aspect 1 can be acquired.

  According to one embodiment of the present invention, it is possible to reduce the measurement time, reduce the size of the apparatus, and improve the spatial resolution in the z-axis direction (optical axis direction).

It is a figure which shows the structure of the optical tomography measuring apparatus which concerns on Embodiment 1 of this invention, (a) shows the structure of the optical tomography measuring apparatus in a measurement process, (b) is measurement position control by a virtual 4f optical system. And show the regeneration process. It is a figure which shows the structure of the optical tomography measurement apparatus which concerns on Embodiment 2 of this invention, (a) shows the structure of the optical tomography measurement apparatus in a measurement process, (b) is measurement position control by a virtual 4f optical system. And show the regeneration process. It is a figure which shows the structure of the optical tomography measurement apparatus which concerns on Embodiment 3 of this invention, (a) shows the structure of the optical tomography measurement apparatus in a measurement process, (b) is measurement position control by a virtual 4f optical system. And show the regeneration process. It is a figure which shows the structure of the optical tomography measurement apparatus which concerns on Embodiment 4 of this invention, (a) shows the structure of the optical tomography measurement apparatus in a measurement process, (b) is measurement position control by a virtual 4f optical system. And show the regeneration process. (A) is a figure which shows the optical model in a measurement process, (b) is a figure which shows the optical model in measurement position control and a reproduction | regeneration process. It is a figure which shows the parameter which concerns on the optical model shown in FIG. It is a graph (Iz curve) which shows normalized reproduction | regeneration intensity | strength. It is a schematic diagram of the measurement object comprised with the some cover glass. (A) is a figure which shows the reproduction intensity image in yz surface, (b) is a figure which shows the reproduction intensity profile on az axis. It is a figure which shows the structure of the experimental optical system used in experiment. It is a graph (Iz curve) which shows normalized reproduction | regeneration intensity | strength. (A) is a figure which shows the reproduction | regeneration intensity | strength profile at the time of scanning an object along az axis, (b) is the reproduction | regeneration intensity | strength at the time of collectively measuring the information on az axis with the virtual 4f imaging optical system. It is a figure which shows an image, (c) is a figure which shows the reproduction | regeneration intensity | strength profile at that time. (A) is a figure which shows the reproduction | regeneration intensity | strength image in the yz surface at the time of measuring the information on z-axis by lump by Embodiment 1-4 of this invention which used what overlapped two cover glasses. (B) is a figure which shows the reproduction intensity profile at that time. It is a figure which shows the general basic composition (system which mechanically scans an irradiation optical system and a sample) of conventional CLSM. It is a figure which shows another structure (system using a parallel plate glass) of the conventional CLSM.

  The embodiment of the present invention will be described with reference to FIGS. Hereinafter, for convenience of explanation, components having the same functions as those described in the specific items may be denoted by the same reference numerals and description thereof may be omitted.

[Outline of Embodiment of the Present Invention]
As will be described later, the optical tomographic measurement apparatus according to the embodiment of the present invention aims to improve the measurement time of the confocal laser scanning microscope (CLSM) and the spatial resolution in the z-axis direction.

  In the optical tomography measuring apparatus according to the embodiment of the present invention, a measurement sample (along the optical axis direction) is irradiated via an irradiation optical system constituted by an objective lens and the like as in a normal confocal laser scanning microscope (CLSM). (Assuming an object having a plurality of reflecting surfaces). At this time, the laser light is multiple-scattered by a plurality of reflecting surfaces. In ordinary CLSM, only the reflection component from the measurement surface (objective lens condensing surface) of the multiple scattered light is used as a signal. However, in the optical tomographic measurement apparatus according to the embodiment of the present invention, the entire multiple scattered light Is detected as reflected signal light.

  Thereafter, the complex amplitude of the detected reflected signal light is multiplied on the computer by the transfer function of the 4f imaging optical system, Fourier-transformed, and then multiplied by the virtual pinhole transfer function (pinhole function). . At this time, by shifting the defocus position of the virtual 4f imaging optical system (virtual 4f optical system), only the reflected component from the position on an arbitrary z-axis is selectively extracted from the reflected signal light. can do. This virtual 4f optical system can eliminate or reduce scanning in the optical axis direction and eliminate mechanical z-axis scanning. At the same time, since the noise removal by the pinhole is performed on the virtual 4f optical system, the pinhole diameter can be further reduced.

  As a result, in the optical tomography measuring apparatus according to the embodiment of the present invention, the measurement speed is improved by about 10 to 1000 times and the spatial resolution is improved by about 1.5 to 5 times compared with the conventional CLSM. Also, by combining the optical tomography apparatus according to the embodiment of the present invention with a method using a combination of a microlens array and a micropinhole array, two-dimensional scanning is eliminated, and three-dimensional measurement is completely integrated. It is also possible.

Embodiment 1
FIG. 1 is a diagram showing a configuration of an optical system 1a (optical tomography measuring apparatus) according to Embodiment 1 of the present invention. FIG. 1 (a) shows the configuration of the optical system 1a in the measurement process, and FIG. 1 (b) shows the measurement position control and reproduction process by the virtual 4f optical system.

  As shown in FIG. 1A, the optical system 1a includes a laser 11, an objective lens 12, a pinhole 13, an imaging lens 14, a BS (beam splitter) 15, an objective lens 16, an optical complex amplitude measuring instrument (light). A complex amplitude information acquisition unit) 17 and a computer (arithmetic processing unit) 21;

  The laser 11 emits laser light (light wave). The objective lens 12 has a function of condensing the laser light emitted from the laser 11. The pinhole 13 has a function of removing noise light (scattered light) generated from outside the focus. The imaging lens 14 has a function of converting the light wave that has passed through the pinhole 13 into parallel light. The BS 15 transmits parallel light emitted from the imaging lens 14 and has a function of changing an optical path of a light wave of reflected signal light, which will be described later, toward the optical complex amplitude measuring device 17.

  The objective lens 16 has a function of collecting the parallel light that has passed through the BS 15 and irradiating the measurement sample (object) OB. The optical complex amplitude measuring instrument 17 has a function of acquiring optical complex amplitude information that is a result of measuring the optical complex amplitude of reflected signal light composed of multiple scattered light generated by irradiation of laser light on an object.

  The computer 21 multiplies the acquired optical complex amplitude information by the transfer function of the 4f imaging optical system, performs Fourier transform, and further multiplies the transfer function of the virtual pinhole (pinhole function). The virtual 4f optical system is formed above and has a function of executing processing for calculating the output result of the virtual 4f optical system.

  In this embodiment, the measurement sample OB is assumed to be an object having a plurality of reflecting surfaces along the optical axis direction (z-axis direction) of the irradiated laser light, but is not necessarily limited to such a sample. The measurement surface SUF1 indicates the original measurement surface (focal plane of the objective lens 16), and the measurement surface SUF2 indicates the measurement surface (non-focal plane) after movement.

  Comparing the optical system 1a of the present embodiment with the optical system shown in FIGS. 14 and 15, in the optical system 1a, a pinhole (see FIGS. 14 and 15) immediately before the photodetector (optical complex amplitude measuring device 17). There is no pinhole b) and a lens (Lb shown in FIGS. 14 and 15) in front of the pinhole b), and the processing is performed by the virtual optical system on the computer 21. The optical system 1a is different in that there is no mechanism for scanning in the z-axis direction such as an automatic stage.

  Hereinafter, a specific operation principle of the optical system 1a will be described with reference to FIG. The optical system 1a measures the reflected signal light reflected from the measurement sample OB by the real optical system (measurement process), controls the measurement position on the z-axis by the virtual optical system, and reflects light from the non-measurement surface. Can be divided into two processes (measurement position control and regeneration process).

  Here, the virtual optical system means that “the same processing as the real optical system is performed on a computer by multiplying the original optical complex amplitude information read as digital data by an optical transfer function”. .

(Measurement process)
The light wave emitted from the laser 11 is collected by the objective lens 12 and passes through the pinhole 13. Thereafter, the light wave that has passed through the pinhole 13 is converted into parallel light by the imaging lens 14. Then, the parallel light is condensed again by the objective lens 16 arranged on the measurement sample OB side, and enters the measurement sample OB. Here, for simplicity of explanation, the measurement sample OB is assumed to be an object having a plurality of reflection surfaces along the optical axis direction, but is not necessarily limited to such a sample. At this time, the reflected light from the measurement sample OB is divided into a light wave reflected from the objective lens focal position in the sample and a plurality of light waves reflected from other positions (non-focal positions). These light waves are collected as reflected signal light, and measured as digital data (light complex amplitude information) by the optical complex amplitude measuring instrument 17 [In the conventional CLSM, only the light wave reflected from the focal position of the objective lens is used as the signal light. ].

  The optical complex amplitude measuring instrument 17 can use general phase shift digital holography [Non-patent Document 6] or the like, but is not particularly limited as long as it can measure a spatial complex amplitude distribution of a light wave.

(Measurement position control and regeneration process)
The digital data of the complex amplitude of the reflected signal light measured in the optical measurement process is multiplied by a transfer function of a 4f imaging optical system (virtual 4f optical system) composed of two lenses on a computer. Thereafter, a fast Fourier transform (FFT) is executed to obtain a complex amplitude distribution on the light converging surface (Fourier region). Then, the complex amplitude distribution is multiplied by the transfer function of the virtual pinhole (the same effect as transmitting through the pinhole b in FIGS. 14 and 15). At this time, intensity information of only a desired position on the z-axis can be obtained by shifting (defocusing) one FT lens of the virtual 4f optical system. When defocusing is not performed at all, the intensity information of only the component reflected from the focal position of the objective lens 16 can be obtained in the same way as normal CLSM.

The specific calculation process of the virtual optical system including the virtual 4f optical system is shown below.
(1) Multiply the original complex amplitude (complex amplitude measured in the measurement process) by a transfer function of free space propagation from the input surface to the lens surface.
(2) A lens phase factor exp [ik (dx ² + dy ² ) / f] is added to the phase term of the complex amplitude after propagation in free space (i is an imaginary unit, k is a wave number, dx, dy are xy planes) Upper coordinate position, f is the focal length of the lens).
(3) Multiply the transfer function of free space propagation from the lens surface to the condensing surface.
(4) Multiply the transfer function of free space propagation from the condensing surface to the second lens surface.
(5) The lens phase factor exp [ik (dx ² + dy ² ) / f] is added to the phase term of the complex amplitude after propagation in free space.
(6) Multiply the transfer function of free space propagation from the lens surface to the image plane.
(7) A fast Fourier transform (FFT) is executed to obtain a complex amplitude distribution on the condensing surface.
(8) Multiply the complex amplitude distribution on the condensing surface by the transfer function (pinhole function) of the virtual pinhole.

  Note that the free space propagation calculation method is not particularly limited, and any method such as general Fresnel diffraction integration can be used.

  When it is desired to move the measurement position by Δz (that is, when the virtual 4f optical system is defocused), the propagation distance in (3) or (4) may be a distance obtained by subtracting 2Δz from the original distance. Thereby, it is possible to selectively obtain intensity information only at a position on an arbitrary z-axis. Moreover, it is possible to acquire information at all positions on the z-axis by repeatedly calculating the above process a plurality of times while slightly changing the propagation distance in (3) or (4) [Non-Patent Document]. 6].

  The basic principle described in the first embodiment is for obtaining one-dimensional information only on the z-axis. In Embodiments 2 to 4 to be described below, modes for realizing acquisition of a two-dimensional image or a three-dimensional image of a vertical plane with respect to the optical axis will be described.

[Embodiment 2: A mode in which scanning in the xy direction is realized by a galvanometer mirror]
FIG. 2 is a diagram showing a configuration of an optical system 1b (optical tomography measuring apparatus) according to Embodiment 2 of the present invention. 2A shows the configuration of the optical system 1b in the measurement process, and FIG. 1B shows the measurement position control and reproduction process by the virtual 4f optical system.

  The optical system 1b of the present embodiment is different from the first embodiment in that the galvanometer mirror 18 realizes scanning in the xy direction (direction perpendicular to the optical axis) with respect to the measurement sample OB.

  That is, as shown in FIG. 2A, the optical system 1b of the present embodiment is different from the first embodiment in that the galvano mirror 18 is on the laser beam path between the measurement sample OB and the optical complex amplitude measuring instrument 17. Is arranged.

Here, for simplicity of explanation, scanning in the x-axis direction will be described, but the same applies to the y-axis direction. First, when the galvanometer mirror 18 is displaced by an angle θ = tan ⁻¹ (Δx / f) and then condensed by the objective lens 16, the condensing position on the measurement surface is displaced by Δx. Here, f is the focal length of the objective lens 16. In accordance with this, scanning on the xy plane can be performed by moving the position of the virtual pinhole in the virtual optical system on the xy plane (see FIG. 2B). In this aspect, it is possible to scan the xy plane relatively easily.

[Embodiment 3: A mode in which scanning in the xy direction is realized by a phase modulation spatial light modulator]
FIG. 3 is a diagram showing a configuration of an optical system 1c (optical tomography measuring apparatus) according to Embodiment 3 of the present invention. FIG. 3A shows the configuration of the optical system 1c in the measurement process, and FIG. 3B shows the measurement position control and reproduction process by the virtual 4f optical system.

  The optical system 1c of the present embodiment realizes scanning in the xy direction (direction perpendicular to the optical axis) with respect to the measurement sample OB by a PSLM (Phase-type Spatial Light Modulator) 19. Thus, it differs from the first and second embodiments.

  That is, as shown in FIG. 3A, the optical system 1c of the present embodiment differs from the first and second embodiments in that the PSLM 19 is on the laser beam path between the measurement sample OB and the optical complex amplitude measuring instrument 17. Is arranged.

Also in this mode, scanning in the x-axis direction will be described for the sake of simplicity of explanation, but the same applies to the y-axis direction. First, the PSLM 19 is given a steady phase distribution φ = −iksin θdx that displaces the optical axis by an angle θ = tan ⁻¹ (Δx / f) [the galvanometer mirror 18 is displaced by an angle θ = tan ⁻¹ (Δx / f). The same effect as that obtained is obtained. Thereafter, when the light is collected by the objective lens 16, the light collection position on the measurement surface is displaced by Δx. Here, f is a focal length of the objective lens, i is an imaginary unit, k is a wave number, and dx is a coordinate position on the SLM plane. As in the second embodiment, scanning on the xy plane can be performed by moving the position of the virtual pinhole in the virtual optical system on the xy plane by Δx (see FIG. 3B). In this embodiment, it is possible to scan the xy plane without completely mechanical scanning.

[Embodiment 4: A mode of realizing collective measurement of xy plane using a microlens array]
FIG. 4 is a diagram showing a configuration of an optical system 1d (optical tomography measuring apparatus) according to Embodiment 4 of the present invention. 4A shows the configuration of the optical system 1d in the measurement process, and FIG. 4B shows the measurement position control and reproduction process by the virtual 4f optical system.

  The optical system 1c of the present embodiment is different from Embodiments 1 to 3 in that collective measurement of the xy plane is realized using a microlens array 20 composed of a plurality of minute lenses.

  That is, as shown in FIG. 4A, the optical system 1d of the present embodiment is different from the first to third embodiments in that a micro is placed on the laser beam path between the measurement sample OB and the optical complex amplitude measuring instrument 17. A lens array 20 is arranged. In this embodiment, the microlens array 20 is used instead of the objective lens 16 that is disposed immediately before the measurement sample OB of the first embodiment. Thereby, as shown in FIG. 4, light waves are condensed at a plurality of positions on the measurement surface. Then, by arranging a plurality of virtual pinholes in the virtual optical system so as to coincide with each condensing position (virtual pinhole array), it is possible to collectively measure the xy plane. As described above, it is possible to perform exposure over a wide range of the measurement surface while maintaining the confocal effect. At this time, the number of lenses of the microlens array 20 becomes the resolution of the xy plane of the reproduced image, and the interval between the lenses of the microlens array 20 becomes the resolution of the xy plane of the reproduced image. Since scanning is not necessary in this aspect, the measurement speed can be increased compared to the second or third embodiment. Further, as described in [Outline of Embodiment of the Present Invention], in this mode, collective three-dimensional measurement is possible in principle.

[Operation of Optical System of Embodiments 1 to 4]
In the optical systems of the first to fourth embodiments, a light wave reflected from the focal position of the objective lens in the measurement sample OB and a plurality of light waves reflected from other positions (non-focal positions) are collectively converted into reflected signal light. Measure amplitude. Then, the virtual 4f imaging optical system in the virtual optical system on the computer 21 is defocused. Therefore, in the optical systems of the first to fourth embodiments, if complex amplitude measurement is performed only once on the actual optical system, all depth direction information can be obtained by repeated calculation on the computer 21 based on that information. Acquisition is possible, and mechanical scanning on the actual optical system can be eliminated or greatly reduced (measurement speed is improved by about 10 to 1000 times compared to conventional CLSM).

  Further, in the conventional CLSM, the signal light intensity becomes very weak by reducing the pinhole diameter in order to improve the spatial resolution in the z axis, and the SNR (S / N ratio) of the photodetector is lowered. However, in the optical systems of the first to fourth embodiments, since the reflected light from the non-measurement surface by the pinhole is removed on the virtual optical system, the actual photodetector does not exist after passing through the pinhole. Therefore, it is not necessary to consider a decrease in SNR. Even when the signal light intensity becomes very weak, it is possible to avoid a decrease in contrast by performing standardization processing or the like on the computer 21. Therefore, the pinhole diameter can be further reduced, and the spatial resolution in the z-axis can be improved (an improvement of about 1.5 to 5 times compared to the conventional CLSM).

  In addition, as described above, since the z-axis scanning and the removal of the reflected light from the non-measurement surface by the pinhole are simultaneously performed in the virtual optical system, not only an additional element for scanning is unnecessary, Since the pinhole for removing noise light and the condensing lens associated therewith are not required, the fact that the actual optical system is reduced in size compared with the conventional CLSM is also an advantage of the optical systems of the first to fourth embodiments.

  In Embodiment 2 or 3, the spatial resolution in the xy direction may be reduced when the distance from the measurement position is extremely far. This is because the focal position of the objective lens 16 on the z-axis is not actually displaced. Therefore, there is a problem that a wide measurement region in the z-axis direction cannot be secured. This can be solved by combining the methods described in [Background Art]. For example, when it is desired to obtain 500 two-dimensional tomographic images at intervals of 1 μm in the range of 500 μm with respect to the z-axis direction, first, scanning is performed every 25 μm by the method described in [Background Art], and 20 tomographic images are obtained. get. Then, for each tomographic image, virtual scanning is performed at intervals of 1 μm by the optical system of the first to fourth embodiments. Thus, 500 tomographic images can be finally obtained by only 20 mechanical scans and measurements. Even in this case, the measurement time can be improved by about 25 times. In the fourth embodiment, as described above, since the spatial resolution in the xy direction is determined by the distance between the lenses of the microlens array 20, such a problem does not occur.

In summary, the optical systems of Embodiments 1 to 4 have the following three points.
(1) The virtual 4f optical system completely eliminates or greatly reduces scanning on the z axis, and improves the measurement time by about 10 to 1000 times.
(2) The virtual pinhole improves the spatial resolution in the z-axis direction by about 1.5 to 5 times without reducing the SNR of the photodetector (optical complex amplitude measuring device 17).
(3) The actual optical system can be downsized by replacing some real optical processes with virtual optical system processes.

[Effect of the optical system of the first to fourth embodiments]
Below, the effect of the optical system of the said Embodiments 1-4 is shown by both numerical analysis and experiment.

(Operation check by numerical analysis)
FIG. 5 shows an optical model of this analysis, and FIG. 6 shows parameters related to the optical model. In this analysis, the spatial resolution in the z-axis direction of a CLSM (optical tomographic measurement apparatus) to which the present invention is applied was evaluated. Further, in the following, it is shown that information on the z axis can be collectively measured by the effect of CLSM to which the present invention is applied. Specifically, the measurement sample is a mirror (assuming a single reflecting surface) and a plurality of cover glasses used for the preparation sample (ideally assuming a thickness of 0 and assuming a plurality of reflecting surfaces). A measurement simulation was performed. For the free space propagation in the virtual 4f optical system, the angular spectrum method (ASM) [Non-patent Document 7] is used, but as described above, the present invention is not limited to this method. Further, in this analysis, scanning in the y direction is performed by applying steady phase modulation by PSLM, and in order to simplify the analysis, scanning in the x direction is not performed.

  First, a mirror measurement simulation was performed to show that the CLSM to which the present invention is applied has improved spatial resolution in the z-axis direction as compared with that of the conventional CLSM. The mirror was disposed at a position of z = 0 μm. The graph of FIG. 7 shows the normalized reproduction intensity (Iz curve). The vertical axis is the normalized reproduction intensity, and the horizontal axis is the position on the z axis. As can be seen from FIG. 7, the normalized reproduction intensity decreases as the virtual 4f optical system is defocused with z = 0 μm as the peak.

  This indicates that even in the case of a CLSM to which the present invention is applied using a virtual 4f optical system and a virtual pinhole, an optical sectioning characteristic by a confocal effect can be obtained as in the conventional CLSM. Here, the optical sectioning characteristic refers to a characteristic obtained by cutting light that causes pinhole noise from other than the focal plane. Therefore, the full width at half maximum (FWHM) of the Iz curve is the spatial resolution in the z-axis direction. Further, as described above, since the signal strength obtained by reducing the pinhole diameter is remarkably lowered, the conventional CLSM generally secures a pinhole diameter of about 1 to 0.7 AU. In the CLSM to which the present invention is applied, since the optical complex amplitude of the light wave is detected before condensing and virtual pinhole processing is performed on the computer, the pinhole diameter can be reduced. In the case of this analysis, the pinhole diameter was set to 0.016 AU. As a result, the FWHM of the Iz curve when the pinhole diameter was 1 AU (assuming the case of the conventional CLSM) was 1.20 μm, whereas the FWHM at 0.016 AU was 0.74 μm. In other words, it is shown that the CLSM to which the present invention is applied can achieve 1.6 times the spatial resolution improvement in the axial direction (by optimizing the parameters in the virtual optical system such as the condensing lens before the virtual pinhole) It is thought that it can be improved up to about 5 times).

  Next, a measurement simulation assuming an object in which a plurality of cover glasses are stacked will be described. As shown in FIG. 8, four pieces of glass are arranged at intervals of 150 μm. The first sheet is z = 0.0 μm. Then, the object was not scanned on the z axis, and the calculation was repeated while displacing the defocus amount of the virtual 4f optical system. FIG. 9A shows a reproduction intensity image on the yz plane, and FIG. 9B shows a reproduction intensity profile on the z axis. 9A and 9B, it can be seen that the position of the intensity peak coincides with the glass reflecting surface. This result shows that the CLSM to which the present invention is applied can collectively measure in the z-axis direction.

(Operation check by experiment)
In this experiment, the spatial resolution in the z-axis direction is evaluated in the same manner as in the numerical analysis described above, and it is shown that collective measurement of information on the z-axis becomes possible. FIG. 10 shows the experimental optical system used in this experiment. The light source used had a wavelength of 532 nm, the objective lens (OL2) had an NA of 0.4, and a focal depth of 4.45 μm. Further, similarly to the numerical analysis, the operation in the y-axis direction was performed using PSLM. Further, the optical complex amplitude measuring instrument uses a holographic diversity interferometry (HDI) [Non-Patent Document 8] capable of measuring complex amplitude with high accuracy (not necessarily limited to this method). ).

  A mirror and a plurality of cover glasses were used as measurement objects. The experimental procedure is shown below. First, the light wave emitted from the light source is condensed by the objective lens (OL1) and transmitted through the pinhole. The light wave at this point is regarded as an ideal point light source. Then, after collimating by the imaging lens L1, a steady phase distribution is given by PSLM for the y-axis scanning, passes through the imaging lens, and is condensed by the objective lens OL2. The collected light wave is reflected by the measurement sample and becomes reflected signal light. After that, it is reflected by BS2, passes through the imaging lens, and is measured for complex amplitude by HDI. The measured complex amplitude data is calculated and processed as described above.

  FIG. 11 shows the normalized reproduction intensity (Iz curve). It can be seen that the optical sectioning characteristic is obtained as in the numerical analysis. Further, when the pinhole diameter was made smaller than 1 AU (assuming the case of the conventional CLSM), the spatial resolution in the z-axis direction was improved as in the numerical analysis. In this experiment, the pinhole diameter was set to 0.4 AU. As a result, the FWHM of the Iz curve when the pinhole diameter is 1 AU (assuming the case of the conventional CLSM) is 7.20 μm, whereas the FWHM at 0.4 AU is 5.74 μm (this The result can be improved by optimizing the parameters of the virtual optical system as well as the numerical analysis). Therefore, it was demonstrated that CLSM to which the present invention is applied has an effect of improving the spatial resolution in the z-axis direction.

  Next, a reproduction intensity image on the yz plane when the cover glass is used as a measurement object is shown. The cover glass has a thickness of 150 μm (the apparent thickness is about 100 μm because the refractive index is about 1.5).

  FIG. 12A shows a reproduction intensity profile when an object is scanned along the z-axis as in the conventional CLSM. FIG. 12B shows a reproduction intensity image when information on the z-axis is collectively measured by the virtual 4f imaging optical system. FIG. 12C shows the reproduction intensity profile at that time. Comparing these results (both were scanned at intervals of 4 μm), it can be seen that the intensity peaks are identical with the reflective surfaces (front and back surfaces) of the cover glass.

  Further, FIG. 13 shows a reproduction intensity image on the yz plane when information on the z-axis is collectively measured by CLSM to which the present invention is applied, with a measurement object formed by overlapping two cover glasses. This result also shows that the intensity peak coincides with the reflective surface of the cover glass. Based on these results, the effect of enabling collective measurement in the z-axis direction by CLSM to which the present invention is applied was demonstrated [Non-Patent Document 7].

[Additional Notes]
The present invention is not limited to the above-described embodiments, and various modifications are possible within the scope shown in the claims, and embodiments obtained by appropriately combining technical means disclosed in different embodiments. Is also included in the technical scope of the present invention. Furthermore, a new technical feature can be formed by combining the technical means disclosed in each embodiment.

1a to 1d optical system (optical tomography measuring device)
17 Optical Complex Amplitude Measuring Device (Optical Complex Amplitude Information Acquisition Unit)
18 Galvano mirror 19 PSLM (Phase type spatial light modulator)
20 Microlens array 21 Computer (arithmetic processing unit)
OB measurement sample (object)

Claims (6)

An optical tomography measuring device for measuring a tomography of an object,
An optical complex amplitude information acquisition unit that acquires optical complex amplitude information that is a result of measuring the optical complex amplitude of reflected signal light composed of multiple scattered light generated by irradiation of laser light on the object;
A calculation processing unit that calculates the output result of the virtual 4f optical system formed by multiplying the acquired optical complex amplitude information by the transfer function of the 4f imaging optical system and subjecting the multiplication result to Fourier transform; An optical tomography measuring device.   2. The optical tomography measuring apparatus according to claim 1, wherein the virtual 4f optical system is formed by further multiplying a result of performing the Fourier transform on the multiplication result and a transfer function of a virtual pinhole. .   The optical tomography measuring apparatus according to claim 1, wherein a galvanometer mirror is disposed on a path of the laser light between the object and the optical complex amplitude information acquisition unit.   3. The optical tomographic measurement apparatus according to claim 1, wherein a phase type spatial light modulator is disposed on a path of the laser light between the object and the optical complex amplitude information acquisition unit.   3. The microlens array including a plurality of minute lenses is disposed on the laser beam path between the object and the optical complex amplitude information acquisition unit. Optical tomography measuring device. An optical tomography method for measuring a tomography of an object,
An optical complex amplitude information acquisition step for acquiring optical complex amplitude information that is a result of measuring the optical complex amplitude of the reflected signal light composed of multiple scattered light generated by irradiation of laser light on the object;
A calculation processing step of calculating the output result of the virtual 4f optical system formed by multiplying the acquired optical complex amplitude information by the transfer function of the 4f imaging optical system and subjecting the multiplication result to Fourier transform. Optical tomography measurement method characterized by