Observation device and observation method

Abstract

This observation device 1 is provided with a light source unit 10, a radiating optical system 20, an image-forming optical system 30, a modulation unit 40, an imaging unit 50, an analysis unit 60, beam splitters 71, 72, and mirrors 73, 74. The analysis unit 60 determines the real part of the function χ(t) = log [1 + Uobj(t) / Uref(t)], defined by time-sequence data Uobj(t) for a complex amplitude image of object light on an imaging surface of the imaging unit 50 and time-sequence data Uref(t) for a complex amplitude image of reference light on the imaging surface, such determination made on the basis of time-sequence data I(t) for an intensity image of interfering light on the imaging surface and time-sequence data Iref(t) for an intensity image of reference light on the imaging surface. Then, the analysis unit 60 determines the imaginary part of χ(t) on the basis of the real part of χ(t) using a Kramers–Kronig relation, and further determines Uobj(t). In this way, an observation device is realized that can utilize a camera with a low frame rate as the imaging unit when a moving observation subject is to be observed.

Description

[Technical field]

[0001] The present disclosure relates to an observation device and an observation method. [Background technology]

[0002] The observation device described in Patent Document 1 and Non-Patent Document 1 splits light output from a light source into object light and reference light, combines the object light that has passed through a moving observation object with the reference light whose optical frequency has been shifted by the heterodyne frequency, and causes heterodyne interference between the object light and the reference light. Then, this observation device can obtain time series data of a complex amplitude image of the object light on the imaging plane based on time series data of an intensity image of the interference light that has reached the imaging plane of the camera.

[0003] Such an observation device requires a camera with a higher frame rate as the object to be observed moves faster. For example, this observation device is used in a flow cytometer to observe cells (objects to be observed) flowing at a speed of several meters per second along a flow path. In this case, it is desirable to use a high-speed camera with a frame rate of more than 100 kfps. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] International Publication No. 2013 / 065796 [Non-patent literature]

[0005] [Non-Patent Document 1] H. Iwai, T. Yamauchi, M. Miwa, Y. Yamashita, "Doppler-spectrally encoded imaging of translational objects", Optics Communications, Vol.319, pp.159-169 (2014) [Non-Patent Document 2] Y. Baek, K. Lee, S. Shin, Y. Park, "Kramers-Kronig holographic imaging for high-space-bandwidth product", Optica, Vol.6 No.1, pp.45-51 (2019) Summary of the Invention [Problem to be solved by the invention]

[0006] However, when a high-speed camera is used, the amount of image data obtained by imaging becomes huge, the capacity of the storage unit for storing the data becomes large, and the load of data processing becomes large. Moreover, high-speed cameras are expensive.

[0007] Non-Patent Document 2 describes a technique that can obtain a phase image equivalent to that obtained in the past even when the spatial sampling period is increased (i.e., when the pixel pitch on the imaging surface of the camera is increased). However, this technique does not enable the frame rate of the camera to be reduced when observing a moving object.

[0008] An object of the embodiments is to provide an observation device and an observation method that can use a low-speed camera as an imaging unit when observing a moving observation target. [Means for solving the problem]

[0009] The embodiment is an observation device. The observation device includes: (1) a light source that outputs light; (2) an interference optical system that splits the light output from the light source into object light and reference light, and combines and outputs the object light and reference light that have passed through a moving observation object; (3) a modulation unit that is provided on the optical path of the object light or reference light between the splitting and combining of the interference optical system and that shifts the optical frequency of the object light or reference light by a heterodyne frequency f0; (4) an imaging unit that has an imaging surface that is located at a position where an image of the observation object is formed by the object light output from the interference optical system and that acquires an intensity image of the interference light of the object light and the reference light that have been output from the interference optical system and reached the imaging surface; and (5) an analysis unit that obtains time series data of a complex amplitude image of the object light on the imaging surface based on time series data of the intensity image of the interference light on the imaging surface, and the modulation unit calculates a maximum value of a Doppler shift amount of the optical frequency based on the interaction between the object light that reaches the imaging surface and the observation object by Δf max When the heterodyne frequency f0 is Δf max With the above in mind, the analysis unit (a) obtains time-series data U obj (t) and the time series data U of the complex amplitude image of the reference light on the imaging plane ref (t) and the function χ(t)=log[1+U obj (t) / U ref The real part of the intensity image of the interference light on the imaging plane I(t) and the real part of the intensity image of the reference light on the imaging plane I ref (b) calculate the imaginary part of the function χ(t) from the real part of the function χ(t) using the Kramers-Kronig relation; and (c) calculate the time series data U of the complex amplitude image of the object light on the imaging plane based on the function χ(t). obj Find (t).

[0010] The embodiment is an observation method. The observation method uses the light source, the interference optical system, the modulation unit, and the imaging unit having the above configuration, and (a) calculates a maximum value of a Doppler shift amount of the optical frequency due to an interaction between the object light reaching the imaging plane and the object to be observed as Δf max Then, the heterodyne frequency f0 is changed by the modulation section to Δf maxAs described above, the imaging unit obtains time series data of the intensity image of the interference light on the imaging plane, and (b) time series data U of the complex amplitude image of the object light on the imaging plane. obj (t) and the time series data U of the complex amplitude image of the reference light on the imaging plane ref (t) and the function χ(t)=log[1+U obj (t) / U ref The real part of the intensity image of the interference light on the imaging plane I(t) and the real part of the intensity image of the reference light on the imaging plane I ref (c) calculating the imaginary part of the function χ(t) from the real part of the function χ(t) using the Kramers-Kronig relation; and (d) calculating the time series data U of the complex amplitude image of the object light on the imaging plane based on the function χ(t). obj Find (t). Effect of the Invention

[0011] According to the observation device and observation method of the embodiment, a low-speed camera can be used as an imaging unit when observing a moving observation target. [Brief description of the drawings]

[0012] [Figure 1] FIG. 1 is a diagram showing the configuration of an observation device 1. As shown in FIG. [Diagram 2] FIG. 2 is a diagram showing an example of the configuration of the irradiation optical system 20 and the imaging optical system 30 of the observation device 1. As shown in FIG. [Diagram 3] FIG. 3 is a diagram showing the configuration of an observation device 1A of a modified example. [Figure 4] FIG. 4 is a diagram showing the real part of the original image. [Diagram 5] FIG. 5 is a diagram showing the imaginary part of the original image. [Figure 6] FIG. 6 is a diagram showing the frequency distribution of the intensity image I(t) of the interference light on the imaging plane of the imaging section 50. As shown in FIG. [Figure 7] FIG. 7 is a diagram showing the frequency distributions of Iobj(t), Iref(t), Icross(t) and Icross *(t) on the imaging plane of the imaging section 50. [Figure 8] FIG. 8 is a diagram showing the frequency distribution of Icross(t) obtained by the conventional example of extracting the frequency range [0 kHz, 80 kHz] from FIG. [Figure 9] FIG. 9 is a diagram showing the frequency distribution of Icross(t) obtained by an embodiment using the KK relational expression. [Figure 10] FIG. 10 is a diagram showing an image of the exact solution. [Figure 11] FIG. 11 is a diagram showing an image obtained by the conventional example. [Figure 12] FIG. 12 is a diagram showing an image obtained by the embodiment. [Figure 13] FIG. 13 is a diagram showing the difference between a complex amplitude image obtained by a conventional example and an image of the exact solution. [Figure 14] FIG. 14 is a diagram showing the difference between a complex amplitude image obtained by the embodiment and an image of the exact solution. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] Hereinafter, embodiments of the observation device and the observation method will be described in detail with reference to the accompanying drawings. In the description of the drawings, the same elements are given the same reference numerals, and duplicated explanations will be omitted. The present invention is not limited to these examples.

[0014] 1 is a diagram showing the configuration of an observation device 1. The observation device 1 includes a light source unit 10, an irradiation optical system 20, an imaging optical system 30, a modulation unit 40, an imaging unit 50, an analysis unit 60, beam splitters 71 and 72, and mirrors 73 and 74. The components arranged on the optical path from the light source unit 10 to the imaging unit 50 are optically connected. The imaging unit 50 and the analysis unit 60 are electrically connected.

[0015] The observation device 1 can be suitably used, for example, in observing cells (observation object 2) flowing in one direction along a flow path in a flow cytometer. The observation object 2 moves between an irradiation optical system 20 and an imaging optical system 30.

[0016] In the following, the observation device 1 will be described using an xyz Cartesian coordinate system as shown in the figure. The z-axis is set in a direction parallel to the optical axis of the irradiation optical system 20 and the imaging optical system 30. The observation object 2 is assumed to move in a direction perpendicular to the z-axis, and the x-axis is set in a direction parallel to the direction of movement. The y-axis is set in a direction perpendicular to both the x-axis and the z-axis.

[0017] The light source unit 10 outputs light to be irradiated onto the observation object 2. The light source unit 10 outputs temporally and spatially coherent light, and includes, for example, a He-Ne laser light source. The light source unit 10 preferably includes a beam expander, thereby outputting collimated light with an expanded beam diameter.

[0018] The beam splitter 71 is optically connected to the light source unit 10. The beam splitter 71 splits the light arriving from the light source unit 10 into two beams, outputs one of the beams to the irradiation optical system 20 as object light, and outputs the other beam to the modulation unit 40 as reference light.

[0019] The irradiation optical system 20 is optically connected to the beam splitter 71. The irradiation optical system 20 receives the object light arriving from the beam splitter 71, and irradiates the observation object 2 with the object light.

[0020] The imaging optical system 30 receives light (transmitted light, scattered light, etc.) generated by the object of observation 2 when the object light is irradiated onto the object of observation 2 by the irradiation optical system 20, and forms an image of the object of observation 2 on the imaging plane of the imaging section 50 using this received object light.

[0021] The modulation unit 40 is optically connected to the beam splitter 71. The modulation unit 40 receives the reference light arriving from the beam splitter 71, and shifts the optical frequency of this reference light by the heterodyne frequency f0.

[0022] The modulation section 40 can include, for example, a first acousto-optic element 41 and a second acousto-optic element 42. The first acousto-optic element 41 diffracts the reference light arriving from the beam splitter 71 using a first modulation signal, and outputs the diffracted reference light to the second acousto-optic element 42.

[0023] The second acousto-optic element 42 diffracts the reference light arriving from the first acousto-optic element 41 by the second modulation signal, and outputs the diffracted reference light to the mirror 73. The reference light output from the second acousto-optic element 42 is reflected by the mirror 73 and the mirror 74 in order, and reaches the beam splitter 72.

[0024] The frequency of the first modulated signal provided to the first acousto-optic element 41 and the frequency of the second modulated signal provided to the second acousto-optic element 42 are slightly different from each other. For example, the frequency of the first modulated signal is 40 MHz, and the frequency of the second modulated signal is 40.040 MHz, and the difference between the two is 40 kHz. Each of the first modulated signal and the second modulated signal is a sine wave.

[0025] The modulation section 40 does not necessarily have to be composed of two, the first acousto-optic element 41 and the second acousto-optic element 42. In other words, the modulation section 40 only needs to have a function of shifting the optical frequency of the reference light by a predetermined heterodyne frequency, and the modulation section 40 may be composed of one modulation element or may include three or more modulation elements. The modulation section 40 may also be disposed on the optical path of the object light and shift the optical frequency of the object light by the heterodyne frequency.

[0026] The beam splitter 72 is optically connected to the imaging optical system 30 and receives the object light arriving from the imaging optical system 30. The beam splitter 72 is also optically connected to a mirror 74 and receives the reference light arriving from the mirror 74. The beam splitter 72 combines the received object light and reference light, outputs them coaxially, and causes heterodyne interference between the two lights to produce interference light. The optical system from the beam splitter 71 to the beam splitter 72 constitutes an interference optical system.

[0027] The imaging unit 50 is optically connected to the beam splitter 72. The imaging unit 50 receives interference light due to the object light and reference light output from the beam splitter 72 and reaching the imaging unit 50. The imaging surface of the imaging unit 50 is disposed at a position where an image of the observation object 2 is formed by the object light output from the imaging optical system 30 and reaching the imaging unit 50. The image formed here may be a real image or a Fourier transform image of the observation object 2. The imaging unit 50 acquires an intensity image of interference light due to the object light and reference light output from the beam splitter 72 and reaching the imaging surface.

[0028] The analysis unit 60 is electrically connected to the imaging unit 50. The analysis unit 60 receives data of the intensity image of the interference light acquired by the imaging unit 50. The analysis unit 60 obtains time series data of the complex amplitude image of the object light on the imaging plane based on time series data of the intensity image of the interference light on the imaging plane of the imaging unit 50.

[0029] The analysis unit 60 includes an input unit that inputs data of the intensity image of the interference light from the imaging unit 50, a storage unit (e.g., a hard disk drive, RAM, etc.) that stores the input data of the intensity image of the interference light and data of the complex amplitude image resulting from the processing, etc., a calculation unit (e.g., a CPU, a DSP, an FPGA, etc.) that processes the data, etc., and a display unit (e.g., a liquid crystal display, etc.) that displays the intensity image of the interference light and the complex amplitude image resulting from the processing, etc. The analysis unit 60 is, for example, a computer, a smart device, or cloud computing.

[0030] 2 is a diagram showing an example of the configuration of the irradiation optical system 20 and the imaging optical system 30 of the observation device 1. In this diagram, the action of converging or collimating the object light by each lens constituting the irradiation optical system 20 or the imaging optical system 30 is shown by a dashed line as viewed in the y-axis direction and by a solid line as viewed in the x-axis direction.

[0031] The irradiation optical system 20 includes lenses 21 and 22. Of these lenses, the lens 21 is a cylindrical lens. The rear focal point of the lens 21 coincides with the front focal point of the lens 22. The rear focal point of the lens 22 is at a position through which the observation object 2 passes.

[0032] When viewed in the y-axis direction, as indicated by the dashed lines, the object light output from beam splitter 71 is converged by lens 21 and then input to lens 22 as divergent light, and is collimated by lens 22. When viewed in the x-axis direction, as indicated by the solid lines, the object light output from beam splitter 71 is input to lens 22 without being converged or diverged by lens 21, and is converged by lens 22.

[0033] As a result, the irradiation optical system 20 can condense and irradiate the object light onto a linear region in a direction (y-axis direction) perpendicular to the movement direction (x-axis direction) of the observation object 2. In other words, the irradiation optical system 20 can irradiate the observation object 2 with the object light from various directions (multiple directions) simultaneously.

[0034] The imaging optical system 30 includes lenses 31 to 34. Of these lenses, lenses 32 to 34 are cylindrical lenses. The front focal point of the lens 31 is at a position through which the observation object 2 passes. The rear focal point of the lens 31 is on a plane FP. The plane FP is a plane on which a Fourier transform image of the observation object 2 is formed by the lens 31.

[0035] The front focal point of lens 32 is on the plane FP. The rear focal point of lens 32 is at the position of lens 33. The front focal point of lens 33 is on the plane FP. The rear focal point of lens 33 is on the imaging plane of imaging unit 50. The front focal point of lens 34 is at the position of lens 33. The rear focal point of lens 34 is on the imaging plane of imaging unit 50.

[0036] When viewed in the y-axis direction, as shown by the dashed lines, the object light emitted from the observation object 2 is collimated by lens 31 and converged by lens 33. When viewed in the x-axis direction, as shown by the solid lines, the object light emitted from the Fourier transform plane FP is collimated by lens 32 and converged by lens 34.

[0037] As a result, the imaging optical system 30 can place the object to be observed 2 and the imaging plane of the imaging section 50 in a Fourier transform positional relationship with each other in the direction parallel to the movement direction of the object to be observed 2 (x-axis direction), and can place the object to be observed 2 and the imaging plane of the imaging section 50 in a conjugate positional relationship with each other in the direction perpendicular to the movement direction of the object to be observed 2 (y-axis direction).

[0038] When the illumination optical system 20 and the imaging optical system 30 have such a configuration, the analysis unit 60 can obtain time series data of a complex amplitude image of the object light on the imaging plane. The complex amplitude image obtained here is a Fourier transform image in the x-axis direction and a real image in the y-axis direction.

[0039] In addition, the analysis unit 60 performs processing such as Fourier transform on the time series data of the intensity image of the interference light acquired by the imaging unit 50, thereby obtaining a complex amplitude image (real image) for each direction in which the object light is irradiated onto the object 2 to be observed by the irradiation optical system 20, and can obtain a three-dimensional distribution of the refractive index of the object 2 to be observed (see Patent Document 1 and Non-Patent Document 1).

[0040] 2 also shows a neutral density filter 35 inserted in the optical path of the object light, and a shield 36 that can be inserted in the optical path of the object light. The neutral density filter 35 adjusts the intensity of the object light that reaches the imaging surface of the imaging section 50. The shield 36, when inserted in the optical path, prevents the object light from entering the imaging surface of the imaging section 50. When the imaging section 50 acquires an intensity image of the interference light, the shield 36 is removed from the optical path of the object light. The roles of these will be described later.

[0041] In such an observation device 1, the speed of movement of the observation object 2 is V, and the wave number component in the x-axis direction of the object light before interacting with the observation object 2 is k x in The wave number component in the x-axis direction of the object light after interacting with the object of observation 2 is k x out In this case, the amount of Doppler shift Δf of the optical frequency of the object light generated by interaction with the observation object 2 is expressed by the following formula (1).

number

[0042] The numerical aperture of the final lens 22 of the irradiation optical system 20 is NA in The numerical aperture of the first lens 31 of the imaging optical system 30 is NA out The wavelength of light is λ. In this case, the maximum value of the Doppler shift Δf is Δf max is expressed by the following equation (2), and the minimum value of the Doppler shift amount Δf is min is expressed by the following formula (3). Therefore, the Doppler shift amount Δf of the optical frequency of the object light arriving at the imaging surface of the imaging unit 50 is [-Δf max ,Δf max ] range.

number

number

[0043] The time series data of the complex amplitude image of the object light on the imaging plane of the imaging unit 50 is expressed as U obj The time series data of the complex amplitude image of the reference light on the imaging plane of the imaging unit 50 is expressed as U ref Let (t). U ref (t) is expressed by using the heterodyne frequency f0 as follows: U ref (t) = U0 exp(-i2πf0t) It is expressed as:

[0044] Time series data I(t) of the intensity image of the interference light acquired by the imaging section 50 is expressed by the following formulas (4) and (5) (formulas (5a) to (5d)). Note that i is the imaginary unit, π is the ratio of the circumference of a circle to its diameter, and t is a time variable. Variables representing positions in each image are omitted.

number

number

[0045] I obj (t) (Eq. (5a)) is [-2Δf max ,2Δf max ] range. ref (t) (equation (5b)) has only a DC component if U0 does not change over time. cross (t) (Eq. (5c)) is [-Δf max +f0,Δf max +f0] range. cross * (t) (Eq. (5d)) is [-Δf max -f0,Δf max -f0] range.

[0046] I cross (t) or I cross * (t) frequency range is I obj If it does not overlap with the frequency range of (t), then I cross (t) or I cross * Furthermore, the time series data of the complex amplitude image of the object light U can be obtained from equation (5c) or (5d). obj (t) can be obtained.

[0047] I cross (t) or I cross * (t) frequency range is I obj In order to avoid overlapping with the frequency range of (t), the heterodyne frequency f0 should be f0 ≥ 3Δfmax Here, f0=3Δf max Then, the maximum frequency of the time series data I(t) of the intensity image of the interference light is 4Δf max Therefore, according to the Nyquist sampling theorem, the maximum frequency is twice (8Δf max If the image capturing unit 50 captures time series data I(t) of the intensity image of the interference light at a frame rate of 1 / 2, the time series data U(t) of the complex amplitude image of the object light is obtained. obj (t) can be reproduced with high accuracy.

[0048] The observation device and observation method described below improve the processing by the analysis unit 60 to thereby increase the frame rate when the imaging unit 50 acquires the time series data I(t) of the intensity image of the interference light by 8Δf max It is possible to make it lower.

[0049] Time series data U of the complex amplitude image of the object light on the imaging plane of the imaging unit 50 obj (t), and time series data U ref Using (t), we define a function β(t) expressed by the following equation (6). Furthermore, using this function β(t), we define a function χ(t) expressed by the following equation (7).

number

number

[0050] The real part of the function χ(t) is Re[χ(t)], which is expressed by the following formula (8). As shown in this formula (8), Re[χ(t)] is obtained by multiplying the time series data I(t) of the intensity image of the interference light on the imaging plane of the imaging unit 50 and the time series data I(t) of the intensity image of the reference light on the imaging plane of the imaging unit 50. ref Based on I(t) and I ref Since both (t) are measurable, Re[χ(t)] can be obtained from these measurements.

number

[0051] Time series data of reference light intensity image I ref In the case where I(t) does not change over time during, before and after the measurement, for example, a shield 36 can be inserted in the optical path of the object light in the interference optical system as shown in Fig. 2 before or after the measurement, so that only the reference light of the object light and the reference light reaches the imaging surface of the imaging section 50. Note that although the time series data I(t) of the intensity image of the reference light does not change over time in the sense of the intensity image of the reference light corresponding to the time series data I(t) of the intensity image of the interference light in equation (8), ref Let's call it (t).

[0052] In addition, the time series data of the reference light intensity image I ref When (t) changes over time, for example, as in the configuration of the observation device 1A shown in FIG. 3, a beam splitter 75 is provided on the optical path of the reference light in the interference optical system, and part of the reference light is branched and extracted by this beam splitter 75, and the time series data I of the intensity image of the extracted reference light is ref The image (t) may be acquired by another second imaging unit 51.

[0053] Time series data I of the intensity image of the reference light acquired by the second imaging unit 51 ref (t) is the time series data I of the intensity image of the reference light acquired by the imaging unit 50 when only the reference light reaches the imaging unit 50. ref The second imaging section 51 may have a similar configuration to the imaging section 50.

[0054] Im[χ(t)], which is the imaginary part of the function χ(t), and the above Re[χ(t)] have a relationship expressed by the Kramers-Kronig relational equations (hereinafter referred to as the "KK relational equations") in the following equations (9) and (10). Therefore, Im[χ(t)] can be obtained from Re[χ(t)] by using equation (10). This allows the function χ(t) to be obtained, and the time series data U of the complex amplitude image of the object light can be calculated from the function χ(t) by using equations (6) and (7). obj (t) can be found.

number

number

[0055] Here, we will explain that Re[χ(t)] and Im[χ(t)] have the relationship expressed by the above formulas (9) and (10). When β(t) satisfies the following formula (11), χ(t) can be expanded in Taylor series as shown in the following formula (12). In other words, χ(t) can be expanded in powers of β(t).

number

number

[0056] To satisfy the above formula (11), the transmittance and reflectance of beam splitter 71 or beam splitter 72 may be set to appropriate values. Alternatively, to satisfy the above formula (11), the object light may be attenuated by a neutral density filter 35 provided on the optical path of the object light in the interference optical system, as shown in Fig. 2. The neutral density filter 35 is preferably provided on the optical path where the object light is collimated (for example, between lens 32 and lens 33, or between beam splitter 71 and lens 21).

[0057] In general, the convolution theorem holds between two functions f1(t) and f2(t). That is, if the Fourier transform of f1(t) is F1(ω) and the Fourier transform of f2(t) is F2(ω), then the product of f1(t) and f2(t) is equal to the Fourier transform of the convolution of F1(ω) and F2(ω).

[0058] From this convolution theorem and equation (12) above, if the Fourier transform B(ω) of β(t) satisfies B(ω<0)=0, then the Fourier transform X(ω) of χ(t) satisfies X(ω<0)=0. In other words, if B(ω)=0 in the range ω<0, then X(ω)=0 in the range ω<0. Since the inverse Fourier transform of the function X(ω) that satisfies X(ω<0)=0 is χ(t), Re[χ(t)] and Im[χ(t)] have the KK relational relationship expressed by equations (9) and (10) above.

[0059] In order to satisfy the condition Β(ω<0)=0, the heterodyne frequency f0 set by the modulation unit 40 is set to Δf max That is, as can be seen from the above formula (6), U obj (t) Frequency range [-Δf max ,Δf max ] to U ref It is sufficient that when the heterodyne frequency f0 of (t) is shifted, there is no negative frequency component after the shift.

[0060] f0 = 3Δf max If the frame rate is less than 1 / 2, the image capturing unit 50 can capture time series data I(t) of the intensity image of the interference light at a frame rate lower than that of the conventional method, and the time series data U(t) of the complex amplitude image of the object light can be obtained. obj (t) can be reproduced with high accuracy. For example, f0=Δf max Then, the maximum frequency of the time series data I(t) of the intensity image of the interference light is 2Δf max Therefore, the frame rate of the image capturing unit 50 is 4Δf max This is half the frame rate that was previously required.

[0061] In addition, I(t) and I ref For each of (t), it is preferable to perform a Fourier transform, a padding process in which the frequency domain is expanded after the Fourier transform and a predetermined value (e.g., 0) is assigned to the expanded domain, and an inverse Fourier transform is performed after the padding process, and the data after these processes are used in equation (8).

[0062] Also, U obtained from χ(t) obj It is preferable to perform a Fourier transform on (t), a cropping process for extracting a part of the frequency domain after the Fourier transform, and an inverse Fourier transform after the cropping process, and use the data after these processes in the subsequent processes.

[0063] Next, the results of the simulation will be described. Here, the configuration of the observation device shown in Fig. 1 and Fig. 2 was assumed, and the original image (Fig. 4, Fig. 5) parallel to the xy plane was moved in the x-axis direction. The maximum value Δf of the Doppler shift amount of the object light arriving at the imaging surface of the imaging unit 50 was max was set to 40 kHz, and the heterodyne frequency f0 by the modulation unit 40 was also set to 40 kHz. Figure 4 is a diagram showing the real part of the original image, and Figure 5 is a diagram showing the imaginary part of the original image. The number of pixels of the original image is 256 × 512.

[0064] 6 is a diagram showing the frequency distribution of the intensity image I(t) of the interference light on the imaging plane of the imaging section 50. FIG. obj (t), I ref (t), I cross (t) and I cross * FIG. 1(t) is a diagram showing the respective frequency distributions.

[0065] I obj (t) has frequency components in the range of [-80kHz, 80kHz] and has a peak at the frequency position of 0kHz. ref The frequency distribution of (t) is constant over time and has only a DC component.

[0066] I cross (t) has frequency components in the range [0 kHz, 80 kHz] and has a peak at a frequency of 40 kHz. cross * (t) has frequency components in the range of [-80kHz, 0kHz] and has a peak at a frequency of -40kHz. cross (t) and I cross * (t) Each frequency range is I obj (t) frequency range. Therefore, I cross (t) and I cross * (t) is I obj It cannot be measured separately from (t).

[0067] FIG. 8 shows the I obtained by the conventional method of extracting the frequency range [0 kHz, 80 kHz] from FIG. cross FIG. 9 is a diagram showing the frequency distribution of I(t) obtained by an embodiment using the KK relation. cross FIG. 1 shows the frequency distribution of the original I cross (t) frequency distribution I obj In contrast, in the embodiment, the frequency distribution of I obj There is no influence of the frequency distribution of (t) and the original I cross The frequency distribution of (t) is obtained.

[0068] Fig. 10 is a diagram showing an image of the exact solution. Fig. 11 is a diagram showing an image obtained by a conventional example. Fig. 12 is a diagram showing an image obtained by an embodiment. Each image in Fig. 10 to Fig. 12 is a real part of a complex amplitude image obtained when the irradiation direction of the object light from the irradiation optical system 20 on the original image is set to 34° with respect to the z-axis.

[0069] Fig. 13 is a diagram showing the difference between a complex amplitude image obtained by the conventional example and an image of the exact solution. Fig. 14 is a diagram showing the difference between a complex amplitude image obtained by the embodiment and an image of the exact solution. Each image in Fig. 13 and Fig. 14 is an image of the square of the absolute value of the difference between the two images. The conventional example has a large error. In contrast, the embodiment has almost no error.

[0070] As described above, according to this embodiment, when observing a moving observation target, a camera with a lower frame rate than the conventional method can be used as an imaging unit. For example, according to this embodiment, it is possible to obtain the same information (image quality) at a frame rate that is half that of the conventional method.

[0071] Therefore, the amount of image data obtained by imaging can be reduced, the capacity of the memory unit required for data storage can be reduced, and the load of data processing can be reduced. Also, an inexpensive camera can be used as the imaging unit. Conversely, if a high-speed camera, which was necessary in the conventional method, is used as the imaging unit, the throughput of observation of the object to be observed (pieces / second) can be doubled, and the number of sample records per device can be doubled.

[0072] The observation device and the observation method are not limited to the above-described embodiment and configuration examples, and various modifications are possible.

[0073] The observation device according to the above embodiment includes: (1) a light source that outputs light; (2) an interference optical system that branches the light output from the light source into object light and reference light, and combines and outputs the object light and reference light that have passed through a moving observation object; (3) a modulation unit that is provided on the optical path of the object light or reference light between the branching and combination of the interference optical system, and shifts the optical frequency of the object light or reference light by a heterodyne frequency f0; (4) an imaging unit that has an imaging surface that is arranged at a position where an image of the observation object is formed by the object light output from the interference optical system, and acquires an intensity image of interference light caused by the object light and reference light output from the interference optical system and reaching the imaging surface; and (5) an analysis unit that obtains time series data of a complex amplitude image of the object light on the imaging surface based on time series data of the intensity image of the interference light on the imaging surface, and the modulation unit calculates a maximum value of a Doppler shift amount of the optical frequency based on the interaction between the object light that reaches the imaging surface and the observation object, by Δf max When the heterodyne frequency f0 is Δf max With the above in mind, the analysis unit (a) obtains time-series data U obj (t) and the time series data U of the complex amplitude image of the reference light on the imaging plane ref (t) and the function χ(t)=log[1+U obj (t) / U ref The real part of the intensity image of the interference light on the imaging plane I(t) and the real part of the intensity image of the reference light on the imaging plane I ref (b) calculate the imaginary part of the function χ(t) from the real part of the function χ(t) using the Kramers-Kronig relation; and (c) calculate the time series data U of the complex amplitude image of the object light on the imaging plane based on the function χ(t). obj Find (t).

[0074] The observation method according to the embodiment uses the light source, the interference optical system, the modulation unit, and the imaging unit having the above configuration to (a) calculate the maximum value of the Doppler shift of the optical frequency of the object light arriving at the imaging plane based on the interaction with the object to be observed as Δf max Then, the heterodyne frequency f0 is changed by the modulation section to Δf maxAs described above, the imaging unit obtains time series data of the intensity image of the interference light on the imaging plane, and (b) time series data U of the complex amplitude image of the object light on the imaging plane. obj (t) and the time series data U of the complex amplitude image of the reference light on the imaging plane ref (t) and the function χ(t)=log[1+U obj (t) / U ref The real part of the intensity image of the interference light on the imaging plane I(t) and the real part of the intensity image of the reference light on the imaging plane I ref (c) calculating the imaginary part of the function χ(t) from the real part of the function χ(t) using the Kramers-Kronig relation; and (d) calculating the time series data U of the complex amplitude image of the object light on the imaging plane based on the function χ(t). obj Find (t).

[0075] The observation device and observation method described above are configured to modulate the heterodyne frequency f0 by 3Δf max It may be configured to be less than this.

[0076] In the above observation device and observation method, the interference optical system includes (1) an illumination optical system which, when illuminating the object light onto the observation object, focuses and illuminates the object light onto a linear region in a direction perpendicular to the movement direction of the observation object, and (2) an imaging optical system which, when forming an image of the observation object on the imaging plane by the object light emitted from the observation object, places the observation object and the imaging plane in a Fourier transform positional relationship with each other in the direction parallel to the movement direction of the observation object, and places the observation object and the imaging plane in a conjugate positional relationship with each other in the direction perpendicular to the movement direction of the observation object. The analysis unit may be configured to obtain a complex amplitude image for each direction of illumination of the object light onto the observation object by the illumination optical system, and to acquire a three-dimensional distribution of the refractive index of the observation object.

[0077] In the above observation device, the analysis unit may be configured to obtain the real part of the function χ(t) by using an intensity image of the reference light acquired when, of the object light and the reference light, only the reference light reaches an imaging surface of the imaging unit in a state in which a shield is placed on the optical path of the object light in the interference optical system.

[0078] The above observation method may be configured to obtain the real part of the function χ(t) using an intensity image of the reference light obtained when, of the object light and the reference light, only the reference light reaches an imaging surface of the imaging unit in a state in which a shielding object is placed on the optical path of the object light in an interference optical system.

[0079] The observation device further includes a beam splitter that is provided on an optical path of the reference light in the interference optical system and splits and extracts a part of the reference light, and a second imaging unit that acquires an intensity image of the reference light extracted by the beam splitter, and the analysis unit acquires time-series data I of the intensity image of the reference light acquired by the second imaging unit. ref (t) may be used to find the real part of the function χ(t).

[0080] The above observation method further includes a beam splitter that is provided on the optical path of the reference light in the interference optical system and splits and extracts a part of the reference light, and a second image capturing unit that captures an intensity image of the reference light extracted by the beam splitter, and further includes: acquiring time-series data I of the intensity image of the reference light acquired by the second image capturing unit; ref (t) may be used to find the real part of the function χ(t). [Industrial Applicability]

[0081] The embodiment can be used as an observation device and an observation method that can use a low-speed camera as an image capturing unit when observing a moving observation target. [Explanation of symbols]

[0082] 1, 1A...observation device, 2...observation object, 10...light source unit, 20...irradiation optical system, 21, 22...lens, 30...imaging optical system, 31 to 34...lens, 35...neutral attenuation filter, 36...shield, 40...modulation unit, 41, 42...acousto-optical element, 50, 51...imaging unit, 60...analysis unit, 71, 72...beam splitter, 73, 74...mirror, 75...beam splitter.

Claims

1. A light source that outputs light; an interference optical system that splits the light output from the light source into object light and reference light, combines the object light and the reference light that have passed through a moving observation object, and outputs the combined light; A heterodyne frequency f ０ a modulation section for shifting the an imaging unit having an imaging surface arranged at a position where an image of the observation target is formed by the object light output from the interference optical system, and acquiring an intensity image of interference light caused by the object light and the reference light output from the interference optical system and reaching the imaging surface; an analysis unit that obtains time series data of a complex amplitude image of the object light on the imaging plane based on time series data of an intensity image of the interference light on the imaging plane; Equipped with The modulation unit reduces the maximum value of the Doppler shift amount of the optical frequency due to the interaction between the object light arriving at the imaging surface and the object to be observed to Δf max When the heterodyne frequency f ０ Δf max That is all. The analysis unit is Time series data U of the complex amplitude image of the object light on the imaging plane obj (t) and time series data U of the complex amplitude image of the reference light on the imaging plane ref (t) and the function χ(t) = log[1 + U obj (t) / U ref The real part of the intensity image of the interference light on the imaging plane I(t) is expressed as the time series data I(t) of the intensity image of the reference light on the imaging plane. ref (t) and based on determining the imaginary part of the function χ(t) from the real part of the function χ(t) using the Kramers-Kronig relation; Based on the function χ(t), time series data U of the complex amplitude image of the object light on the imaging plane is calculated. obj Find (t), Observation equipment.

2. The modulation unit modulates the heterodyne frequency f ０ 3Δf max The observation device according to claim 1 , wherein the observation device is less than 1 mm in diameter.

3. The interference optical system includes: an illumination optical system that condenses and illuminates the object light onto a linear region in a direction perpendicular to a moving direction of the observation object when illuminating the object light onto the observation object; an imaging optical system that, when forming an image of the observation object by the object light emitted from the observation object on the imaging plane, has a positional relationship between the observation object and the imaging plane that is a Fourier transform relationship with respect to a direction parallel to a moving direction of the observation object, and has a positional relationship between the observation object and the imaging plane that is a conjugate relationship with respect to a direction perpendicular to the moving direction of the observation object; Including, 3 . The observation device according to claim 1 , wherein the analysis section obtains a complex amplitude image for each direction in which the object light is irradiated onto the observation object by the irradiation optical system, and acquires a three-dimensional distribution of the refractive index of the observation object.

4. 4. The observation device according to claim 1, wherein the analysis unit calculates the real part of the function χ(t) by using an intensity image of the reference light acquired when only the reference light of the object light and the reference light reaches the imaging surface of the imaging unit in a state in which a shield is placed on an optical path of the object light in the interference optical system.

5. a beam splitter that is provided on an optical path of the reference light in the interference optical system and that splits and extracts a part of the reference light; and a second image capturing unit that acquires an intensity image of the reference light extracted by the beam splitter, The analysis unit acquires time-series data I of the intensity image of the reference light acquired by the second imaging unit. ref 4. The observation device according to claim 1, wherein the real part of the function χ(t) is calculated using (t).

6. A light source that outputs light; an interference optical system that splits the light output from the light source into object light and reference light, combines the object light and the reference light that have passed through a moving observation object, and outputs the combined light; A heterodyne frequency f ０ a modulation section for shifting the an imaging unit having an imaging surface arranged at a position where an image of the observation target is formed by the object light output from the interference optical system, and acquiring an intensity image of interference light caused by the object light and the reference light output from the interference optical system and reaching the imaging surface; Using The maximum value of the Doppler shift of the optical frequency due to the interaction with the object of observation in the object light arriving at the imaging surface is defined as Δf max Then, the heterodyne frequency f ０ Δf max As described above, the imaging unit obtains time series data of an intensity image of the interference light on the imaging plane, Time series data U of the complex amplitude image of the object light on the imaging plane obj (t) and time series data U of the complex amplitude image of the reference light on the imaging plane ref (t) and the function χ(t) = log[1 + U obj (t) / U ref The real part of the intensity image of the interference light on the imaging plane I(t) is expressed as the time series data I(t) of the intensity image of the reference light on the imaging plane. ref (t) and based on determining the imaginary part of the function χ(t) from the real part of the function χ(t) using the Kramers-Kronig relation; Based on the function χ(t), time series data U of the complex amplitude image of the object light on the imaging plane is calculated. obj Find (t), Observation method.

7. The heterodyne frequency f ０ 3Δf max The observation method according to claim 6, wherein the observation is performed in a range of 100 to 2000 nm.

8. The interference optical system includes: an illumination optical system that condenses and illuminates the object light onto a linear region in a direction perpendicular to a moving direction of the observation object when illuminating the object light onto the observation object; an imaging optical system that, when forming an image of the observation object by the object light emitted from the observation object on the imaging plane, has a positional relationship between the observation object and the imaging plane that is a Fourier transform relationship with respect to a direction parallel to a moving direction of the observation object, and has a positional relationship between the observation object and the imaging plane that is a conjugate relationship with respect to a direction perpendicular to the moving direction of the observation object; Including, 8. The observation method according to claim 6, further comprising obtaining a complex amplitude image for each direction of irradiation of the object light by the irradiation optical system onto the observation object, thereby acquiring a three-dimensional distribution of the refractive index of the observation object.

9. 9. The observation method according to claim 6, further comprising the step of determining a real part of the function χ(t) using an intensity image of the reference light acquired when only the reference light of the object light and the reference light reaches the imaging surface of the imaging unit in a state in which a shield is placed on an optical path of the object light in the interference optical system.

10. a beam splitter that is provided on an optical path of the reference light in the interference optical system and that splits and extracts a part of the reference light, and a second image capturing unit that acquires an intensity image of the reference light extracted by the beam splitter, Time series data I of the intensity image of the reference light acquired by the second imaging unit ref The observation method according to any one of claims 6 to 8, further comprising the step of: determining a real part of the function χ(t) using (t).

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