Observation device and observation method

Abstract

The observation device (1) of the present application is provided with a light source section (10), an irradiation optical system (20), an imaging optical system (30), a modulation section (40), an imaging section (50), an analysis section (60), a beam splitter (71, 72), and a mirror (73, 74). The analysis section (60) obtains the real part of a function χ(t) = log[1 + U ref (t) / U obj (t)] defined by time-series data I ref (t) of an intensity image of the object light at the imaging surface of the imaging section (50) and time-series data I obj (t) of an intensity image of the reference light at the imaging surface, based on time-series data I(t) of an intensity image of the interference light at the imaging surface and time-series data I ref (t) of an intensity image of the reference light at the imaging surface. Furthermore, the analysis section (60) obtains the imaginary part of the function χ(t) from the real part of the function χ(t) using the Kramers-Kronig relation, and further obtains U obj (t). Thus, an observation device capable of using a camera with a low frame rate as the imaging section when observing a moving observation target is realized.

Description

Technical Field

[0001] This disclosure relates to observation apparatus and observation methods. Background Technology

[0002] The observation device described in Patent Document 1 and Non-Patent Document 1 branches the light output from the light source and uses it as object light and reference light. It combines the object light passing through the moving object with the reference light whose light frequency is shifted by a heterodyne frequency, and causes heterodyne interference between the object light and the reference light. Moreover, this observation device can obtain time-series data of the complex amplitude image of the object light at the camera's imaging surface based on time-series data of the intensity image of the interference light reaching the camera's imaging surface.

[0003] Such an observation device requires a higher-speed camera to be used when the object being observed moves faster and the frame rate is higher. For example, when this observation device is used to observe cells (the object being observed) flowing along the flow path in a flow cytometer at a speed of several m / s, a high-speed camera with a frame rate of over 100 kfps is preferred.

[0004] Existing technical documents

[0005] Patent documents

[0006] Patent Document 1: International Publication No. 2013 / 065796

[0007] Non-patent literature

[0008] Non-patent literature 1: H.Iwai, T.Yamauchi, M.Miwa, Y.Yamashita, "Doppler-spectrallyencoded imaging of translational objects", Optics Communications, Vol.319, pp.159-169 (2014)

[0009] Non-patent literature 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

[0010] The problem that the invention aims to solve

[0011] However, when using high-speed cameras, the image data acquired through photography becomes enormous, requiring larger storage units and placing a heavier burden on data processing. Furthermore, high-speed cameras are more expensive.

[0012] Furthermore, Non-Patent Document 2 describes a technique that can obtain phase images equivalent to those of the prior art even when the sampling period of the space is increased (i.e., when the pixel pitch of the camera's imaging surface is increased). However, this technique cannot reduce the frame rate of the camera when observing a moving object.

[0013] The purpose of this implementation is to provide an observation device and method that can use a low-speed camera as the imaging unit when observing a moving object.

[0014] means for solving problems

[0015] The implementation is an observation device. The observation device includes: (1) a light source for outputting light; (2) an interference optical system that branches the light output from the light source and serves as object light and reference light, and combines the object light passing through the moving object to be observed with the reference light and outputs it; (3) a modulation unit that is disposed on the optical path of the object light or reference light between the branch and the combined beam of the interference optical system, and shifts the optical frequency of the object light or reference light by an amount of heterodyne frequency f0; (4) an imaging unit that has an imaging surface disposed at a position where the object light output from the interference optical system forms an image of the object to be observed, and acquires an intensity image of the interference light generated by the object light and reference light output from the interference optical system and reaching the imaging surface; and (5) a resolution unit that, based on the time series data of the intensity image of the interference light of the imaging surface, obtains the time series data of the complex amplitude image of the object light of the imaging surface, and the modulation unit sets the maximum value of the Doppler shift of the object light reaching the imaging surface based on the interaction with the object to be observed to be Δf. max When the heterodyne frequency f0 is set as Δf max The above describes the analysis unit (a) based on the time series data I(t) of the intensity image of the interference light from the imaging surface and the time series data I of the intensity image of the reference light from the imaging surface. ref (t), obtain: the time series data U of the complex amplitude image of the object light from the camera surface. obj (t) and time series data U of the complex amplitude image of the reference light of the imaging surface. ref The function χ(t) defined by (t) is log[1+U obj (t) / U ref(b) Using the Kramer-Kronig relation, the imaginary part of the function χ(t) is obtained from the real part of the function χ(t), and (c) Based on the function χ(t), the time series data U of the complex amplitude image of the object light on the imaging surface is obtained. obj (t).

[0016] The implementation method is an observation method. The observation method uses the light source, interference optical system, modulation unit, and imaging unit described above. (a) When the maximum value of the Doppler shift of the object light arriving at the imaging surface based on the light frequency of the object being observed is Δf... max At that time, the heterodyne frequency f0 is set as Δf by the modulation unit. max The above describes the time-series data of the intensity image of the interference light on the imaging surface obtained by the imaging unit, and (b) the time-series data I(t) based on the intensity image of the interference light on the imaging surface and the time-series data I(t) of the intensity image of the reference light on the imaging surface. ref (t), obtain: the time series data U of the complex amplitude image of the object light from the camera surface. obj (t) and time series data U of the complex amplitude image of the reference light of the imaging surface. ref The function χ(t) defined by (t) is log[1+U obj (t) / U ref (c) Using the Cramer-Kroni relation, the imaginary part of the function χ(t) is obtained from the real part of the function χ(t). (d) Based on the function χ(t), the time series data U of the complex amplitude image of the object light on the imaging surface is obtained. obj (t).

[0017] The effects of the invention

[0018] According to the observation apparatus and observation method described in the embodiments, a low-speed camera can be used as the imaging unit when observing a moving object. Attached Figure Description

[0019] Figure 1 This is a diagram showing the structure of the observation device 1.

[0020] Figure 2 This is a diagram showing an example of the structure of the illumination optical system 20 and the imaging optical system 30 of the observation device 1.

[0021] Figure 3 This is a diagram showing the structure of the observation device 1A in a modified example.

[0022] Figure 4 This is a diagram showing the real part of the original image.

[0023] Figure 5 This is a diagram showing the imaginary part of the original image.

[0024] Figure 6 It is a graph showing the frequency distribution of the intensity image I(t) of the interference light on the imaging surface of the imaging unit 50.

[0025] Figure 7 I shows the camera surface of the camera unit 50. obj (t), I ref (t), I cross (t) and I cross * (t) Plots of their respective frequency distributions.

[0026] Figure 8 It shows that from Figure 6 I is obtained by taking an existing example of the frequency range [0kHz, 80kHz]. cross A graph of the frequency distribution of (t).

[0027] Figure 9 This illustrates the I obtained by using an embodiment employing the KK relation. cross A graph of the frequency distribution of (t).

[0028] Figure 10 It is a diagram showing the image of the rigorous solution.

[0029] Figure 11 This is a diagram showing an image obtained from an existing example.

[0030] Figure 12 This is a diagram showing images obtained from an embodiment.

[0031] Figure 13 This is a graph showing the difference between the complex amplitude image obtained from the existing example and the image of the rigorous solution.

[0032] Figure 14 This is a graph showing the difference between the complex amplitude image obtained by the embodiment and the image of the rigorous solution. Detailed Implementation

[0033] Hereinafter, embodiments of the observation apparatus and observation method will be described in detail with reference to the accompanying drawings. Furthermore, in the description of the drawings, the same reference numerals are used to denote the same elements, and repeated descriptions are omitted. The present invention is not limited to these examples.

[0034] Figure 1 This diagram shows the structure of the observation device 1. The observation device 1 includes: a light source unit 10, an illumination optical system 20, an imaging optical system 30, a modulation unit 40, an imaging unit 50, a resolving unit 60, beam splitters 71 and 72, and reflectors 73 and 74. The components arranged in the optical path from the light source unit 10 to the imaging unit 50 are optically connected. The imaging unit 50 is electrically connected to the resolving unit 60.

[0035] The observation device 1 is, for example, suitable for observing cells (object of observation 2) flowing in one direction along the flow path in a flow cytometer. The object of observation 2 moves between the illumination optical system 20 and the imaging optical system 30.

[0036] The following description, using an orthogonal xyz coordinate system, illustrates the observation device 1. The z-axis is set parallel to the optical axes of the illumination optical system 20 and the imaging optical system 30. Assuming the object 2 moves in a direction perpendicular to the z-axis, the x-axis is set parallel to this direction of movement. The y-axis is set perpendicular to both the x-axis and the z-axis.

[0037] The light source unit 10 outputs light to be illuminated to the object 2. The light source unit 10 outputs temporally and spatially coherent light, such as a He-Ne laser light source. The light source unit 10 preferably includes a beam expander, thereby outputting collimated light with an enlarged beam diameter.

[0038] Beam splitter 71 is optically connected to light source unit 10. Beam splitter 71 splits the light arriving from light source unit 10 into two branches, outputting one branch as object light to illumination optical system 20, and outputting the other branch as reference light to modulation unit 40.

[0039] The illumination optical system 20 is optically connected to the beam splitter 71. The illumination optical system 20 receives the object light arriving from the beam splitter 71 and illuminates the object 2 being observed.

[0040] The imaging optical system 30 receives light (transmitted light, scattered light, etc.) generated on the object 2 by the object light irradiated by the illumination optical system 20, and forms an image of the object 2 on the imaging surface of the imaging unit 50 by the received object light.

[0041] The modulation unit 40 is optically connected to the beam splitter 71. The modulation unit 40 receives reference light arriving from the beam splitter 71 and shifts the optical frequency of the reference light by an amount of heterodyne frequency f0.

[0042] The modulation unit 40 may, for example, include 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 through a first modulation signal and outputs the diffracted reference light to the second acousto-optic element 42.

[0043] The second acousto-optic element 42 diffracts the reference light arriving from the first acousto-optic element 41 through the second modulation signal, and outputs the diffracted reference light to the reflector 73. The reference light output from the second acousto-optic element 42 is reflected sequentially by the reflector 73 and the reflector 74, and arrives at the beam splitter 72.

[0044] The frequency of the first modulation signal applied to the first acousto-optic element 41 and the frequency of the second modulation signal applied to the second acousto-optic element 42 are slightly different from each other. For example, the frequency of the first modulation signal is 40MHz, and the frequency of the second modulation signal is 40.040MHz, with a difference of 40kHz. The first modulation signal and the second modulation signal are both sine waves.

[0045] Furthermore, the modulation unit 40 is not necessarily composed of only two elements: the first acousto-optic element 41 and the second acousto-optic element 42. That is, the modulation unit 40 only needs to have the function of shifting the optical frequency of the reference light by a predetermined heterodyne frequency. The modulation unit 40 can be composed of one modulation element or it can have three or more modulation elements. In addition, the modulation unit 40 can also be arranged in the optical path of the object light to shift the optical frequency of the object light by the heterodyne frequency.

[0046] Beam splitter 72 is optically connected to imaging optical system 30, receiving object light arriving from imaging optical system 30. Additionally, beam splitter 72 is optically connected to mirror 74, receiving reference light arriving from mirror 74. Beam splitter 72 combines these received object light and reference light coaxially, causing heterodyne interference between the two beams to form interference light. The optical system from beam splitter 71 to beam splitter 72 constitutes an interference optical system.

[0047] The camera unit 50 is optically connected to the beam splitter 72. The camera unit 50 receives interference light caused by the object light and reference light output from and arriving at the beam splitter 72. The imaging surface of the camera unit 50 is positioned at the location where the image of the observed object 2 is formed by the object light output from and arriving at the imaging optical system 30. The image formed here can be a real image of the observed object 2 or a Fourier transform image. The camera unit 50 acquires an intensity image of the interference light caused by the object light and reference light output from and arriving at the imaging surface.

[0048] 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. Based on the time-series data of the intensity image of the interference light on the imaging surface of the imaging unit 50, the analysis unit 60 calculates the time-series data of the complex amplitude image of the object light on the imaging surface.

[0049] The analysis unit 60 includes: an input unit for inputting data of the intensity image of the interference light from the camera unit 50; a storage unit (e.g., hard disk drive, RAM, etc.) for storing the input data of the intensity image of the interference light and data of the complex amplitude image of the processing result; a processing unit (e.g., CPU, DSP, FPGA, etc.) for processing the data; and a display unit (e.g., liquid crystal display, etc.) for displaying the intensity image of the interference light and the complex amplitude image of the processing result. The analysis unit 60 is, for example, a computer, a smart device, or cloud computing.

[0050] Figure 2 This is a diagram illustrating an example of the structure of the illumination optical system 20 and the imaging optical system 30 of the observation device 1. The diagram shows the convergence or collimation of object light by the lenses constituting the illumination optical system 20 or the imaging optical system 30, with dashed lines representing observations along the y-axis and solid lines representing observations along the x-axis.

[0051] The illumination optical system 20 includes lenses 21 and 22. Lens 21 is a cylindrical lens. The rear focal point of lens 21 coincides with the front focal point of lens 22. The rear focal point of lens 22 is located at the position through which the object 2 is observed.

[0052] When viewed along the y-axis, as indicated by the dashed line, the object light output from the beam splitter 71 is converged by lens 21 and then input as diverging light into lens 22, where it is collimated. When viewed along the x-axis, as indicated by the solid line, the object light output from the beam splitter 71 is either not converged by lens 21 or divergently input into lens 22, where it is converged.

[0053] Therefore, the illumination optical system 20 can focus the object light onto a linear region in a direction perpendicular to the movement direction (x-axis direction) of the observed object 2 (y-axis direction). That is, the illumination optical system 20 can simultaneously illuminate the observed object 2 from various directions (multi-directional).

[0054] The imaging optical system 30 includes lenses 31 to 34. Lenses 32 to 34 are cylindrical lenses. The front focal point of lens 31 is located at the position through which the object 2 is observed. The rear focal point of lens 31 is located on surface FP. Surface FP is the surface through which the Fourier transform image of the object 2 is formed by lens 31.

[0055] The front focal point of lens 32 is located on surface FP. The rear focal point of lens 32 is located at the position of lens 33. The front focal point of lens 33 is located on surface FP. The rear focal point of lens 33 is located on the imaging surface of imaging unit 50. The front focal point of lens 34 is located at the position of lens 33. The rear focal point of lens 34 is located on the imaging surface of imaging unit 50.

[0056] When viewed along the y-axis, as indicated by the dashed line, the object light emitted from the object 2 is collimated by lens 31 and converged by lens 33. When viewed along the x-axis, as indicated by the solid line, the object light emitted from the Fourier transform surface FP is collimated by lens 32 and converged by lens 34.

[0057] Therefore, the imaging optical system 30 can set the observation object 2 and the imaging surface of the imaging unit 50 to a Fourier transform positional relationship with each other about a direction parallel to the movement direction of the observation object 2 (x-axis direction). In addition, it can set the observation object 2 and the imaging surface of the imaging unit 50 to a conjugate positional relationship with each other about a direction perpendicular to the movement direction of the observation object 2 (y-axis direction).

[0058] With the illumination optical system 20 and imaging optical system 30 having such a structure, the analysis unit 60 is able to obtain time-series data of the complex amplitude image of the object light on the imaging surface. 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.

[0059] Furthermore, the analysis unit 60 can obtain a complex amplitude image (real image) for each object light irradiation direction of the object 2 observed by the irradiation optical system 20 by performing Fourier transform and other processing on the time series data of the intensity image of the interference light obtained by the imaging unit 50, and can obtain the three-dimensional distribution of the refractive index of the object 2 observed (see Patent Document 1 and Non-Patent Document 1).

[0060] In addition, Figure 2 The diagram also shows a neutral density filter 35 inserted into the optical path of the object light, and a shield 36 that can be inserted into the optical path of the object light. The neutral density filter 35 adjusts the intensity of the object light reaching the imaging surface of the imaging unit 50. When the shield 36 is inserted into the optical path, it prevents the object light from incident on the imaging surface of the imaging unit 50. When an intensity image of the interference light is obtained through the imaging unit 50, the shield 36 is removed from the optical path of the object light. Their functions will be explained later.

[0061] In such an observation device 1, let the velocity of the object 2 being observed be V, and let the wavenumber component of the light emitted by the object before interacting with it along the x-axis be k. x in Let k be the wavenumber component of the light emitted by the object after it interacts with the observed object 2 along the x-axis. x out At this time, the Doppler shift Δf of the light frequency of the object light caused by the interaction with the observed object 2 is expressed by the following equation (1).

[0062]

[0063] Let the numerical aperture of the final stage lens 22 of the illumination optical system 20 be NA. in Let the numerical aperture of the primary lens 31 of the imaging optical system 30 be NA. out Let the wavelength of the light be λ. At this point, the maximum value of the Doppler offset Δf is Δf.max The minimum value of the Doppler offset Δf is expressed by the following equation (2). min Expressed by the following equation (3). Therefore, the Doppler shift Δf of the light frequency of the object light reaching the imaging surface of the imaging unit 50 is distributed in [-Δf max ,Δf max Within the range of ].

[0064]

[0065]

[0066] Let U be the time series data of the complex amplitude image of the object light on the imaging surface of the imaging unit 50. obj (t). Let the time series data of the complex amplitude image of the reference light of the imaging surface of the imaging unit 50 be U. ref (t). U ref (t) is expressed using the heterodyne frequency f0, as follows.

[0067] U ref (t)=U0·exp(-i2πf0t)

[0068] The time-series data I(t) of the intensity image of the interference light acquired by the imaging unit 50 is represented by the following equations (4) and (5) (5a) to (5d)). Furthermore, i is the imaginary unit, π is pi, and t is the time variable. Labels indicating the position of each image are omitted.

[0069]

[0070] I obj (t)=|U obj (t)| 2 (5a)

[0071] I ref (t)=|U ref (t)| 2 (5b)

[0072]

[0073]

[0074] I obj (t)(Equation (5a)) in [-2Δf max ,2Δf max The range of ] has a frequency component. If U0 does not change in time, then I ref (t)(Equation (5b)) has only the DC component. cross (t)(Equation (5c)) in [-Δfmax +f0,Δf max The range of +f0] has frequency components. cross * (t)(Equation (5d)) in [-Δf max -f0,Δf max The range of [-f0] has frequency components.

[0075] If I cross (t) or I cross * The frequency range of (t) is not the same as that of I. obj If the frequency ranges of (t) overlap, then I can be measured. cross (t) or I cross * (t) time series data. Additionally, time series data U of the complex amplitude image of the object's light can be obtained according to equation (5c) or equation (5d). obj (t).

[0076] In order to make I cross (t) or I cross * The frequency range of (t) is not the same as that of I. obj The frequency ranges of (t) overlap, so the heterodyne frequency f0 needs to be set to f0≥3Δf max Here, when f0 = 3Δf max At that time, the maximum frequency of the time series data I(t) of the intensity image of the interference light is 4Δf. max Therefore, according to Nyquist's sampling theorem, if the sampling frequency is twice the maximum frequency (8Δf)... max If the frame rate is set to obtain the time-series data I(t) of the intensity image of the interference light through the camera unit 50, then the time-series data U of the complex amplitude image of the object light can be reproduced with high precision. obj (t).

[0077] The observation apparatus and method described below can improve the processing performed by the analysis unit 60, thereby reducing the frame rate of the time-series data I(t) of the intensity image of the interference light acquired by the imaging unit 50 to less than 8Δf. max .

[0078] Time-series data U of the complex amplitude image of object light using the imaging surface of camera 50 obj (t) and the time series data U of the complex amplitude image of the reference light of the imaging surface of the imaging unit 50. ref (t), define the function β(t) as expressed in equation (6) below. In addition, using the function β(t), define the function χ(t) as expressed in equation (7) below.

[0079]

[0080] χ(t)=log[1+β(t)] (7)

[0081] Re[χ(t)], which is the real part of the function χ(t), is expressed by the following equation (8). As shown in equation (8), Re[χ(t)] can be based on the time series data I(t) of the intensity image of the interference light of the imaging surface of the imaging unit 50 and the time series data I of the intensity image of the reference light of the imaging surface of the imaging unit 50. ref (t) is obtained. Since I(t) and I... ref Since all (t) can be measured, Re[χ(t)] can be obtained from their measured values.

[0082]

[0083] Time series data I of the reference light intensity image ref (t) Under the condition that the time does not change during or before the measurement, for example, it is possible to change the time before or after the measurement, such as Figure 2 As shown, in the interference optical system, a shield 36 is inserted in the optical path of the object light so that only the reference light reaches the imaging surface of the imaging unit 50 for measurement. Furthermore, in equation (8), the reference light intensity image corresponding to the time series data I(t) of the interference light intensity image is referred to as the time series data I of the reference light intensity image that does not change over time. ref (t).

[0084] Additionally, referencing the time-series data of the light intensity image I ref (t) In cases where it varies over time, for example, it can also be as follows: Figure 3 As shown in the structure of the observation device 1A, a beam splitter 75 is provided in the optical path of the reference light in the interference optical system. A portion of the reference light is branched off and extracted by the beam splitter 75, and time-series data I of the intensity image of the extracted reference light is obtained by another second imaging unit 51. ref (t).

[0085] Time-series data I of the intensity image of the reference light acquired by the second camera unit 51 ref (t), can be compared with the time series data I of the intensity image of the reference light obtained by the camera unit 50 when only the reference light reaches the camera unit 50. ref (t) are equal. The second camera unit 51 may also have the same structure as the camera unit 50.

[0086] Im[χ(t)], the imaginary part of the function χ(t), has a relationship with Re[χ(t)] expressed by the Kramer-Kronig relation (hereinafter referred to as the "KK relation") in equations (9) and (10). Therefore, Im[χ(t)] can be obtained from Re[χ(t)] using equation (10). Thus, the function χ(t) can be obtained, and therefore, the time series data U of the complex amplitude image of the object light can be obtained from the function χ(t) using equations (6) and (7). obj (t).

[0087]

[0088]

[0089] Here, the relationship between Re[χ(t)] and Im[χ(t)], expressed by equations (9) and (10) above, will be explained. When β(t) satisfies equation (11), χ(t) can be Taylor expanded as shown in equation (12). That is, χ(t) can be expanded as a power of β(t).

[0090] |β(t)|<1 (11)

[0091]

[0092] To satisfy equation (11) above, the transmittance and reflectance of beam splitter 71 or beam splitter 72 can be set to appropriate values. Alternatively, to satisfy equation (11) above, it can also be done as follows: Figure 2 As shown, the object light is attenuated by a light-reducing filter 35 disposed in the optical path of the object light in the interference optical system. The light-reducing filter 35 is preferably disposed in the optical path of the collimated object light (for example, between lens 32 and lens 33, or between beam splitter 71 and lens 21).

[0093] Generally, the convolution theorem holds between two functions f1(t) and f2(t). That is, when the Fourier transform of f1(t) is taken as F1(ω) and the Fourier transform of f2(t) is taken as F2(ω), the product of f1(t) and f2(t) is equal to the Fourier transform of the convolution of F1(ω) and F2(ω).

[0094] According to the convolution theorem and equation (12) above, when the Fourier transform B(ω) of β(t) satisfies B(ω<0)=0, the Fourier transform X(ω) of χ(t) satisfies X(ω<0)=0. That is, when B(ω)=0 in the range of ω<0, it is: when ω<0, X(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 relation expressed by equations (9) and (10) above.

[0095] To satisfy B(ω<0)=0, the heterodyne frequency f0 set by the modulation unit 40 is set as Δf. max That's all. That is, as can be seen from equation (6) above, when U... obj The frequency range of (t) is [-Δf max ,Δf max Offset U ref When the heterodyne frequency f0 of (t) is equal to the amount of the offset, it is sufficient to ensure that there are no negative frequency components after the offset.

[0096] If f0 is set to be less than 3Δf max This allows for the acquisition of time-series data I(t) of the intensity image of the interference light through the camera unit 50 at a lower frame rate than existing technologies, and high-precision reproduction of time-series data U of the complex amplitude image of the object light. obj (t). For example, let f0 = Δf max At that time, 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 camera 50 is 4Δf max That's it. This is half the frame rate required by current technology.

[0097] Furthermore, preferably, I(t) and I(t) obtained by the camera unit 50 are respectively... ref (t), perform a Fourier transform, expand the frequency region after the Fourier transform and perform padding processing to assign a specified value (e.g., 0) to the expanded region, and perform an inverse Fourier transform after the padding processing, and use the processed data in equation (8).

[0098] Furthermore, preferably, for U obtained from χ(t) obj (t) Perform a Fourier transform, then perform a cropping process to extract a portion of the frequency region, and then perform an inverse Fourier transform. Use the processed data for subsequent processing.

[0099] Next, the simulation results will be explained. Here, it is assumed that... Figure 1 and Figure 2 The structure of the observation device shown allows the original image to be parallel to the xy plane. Figure 4 , Figure 5 The object light moves along the x-axis. The maximum value Δf of the Doppler shift of the light reaching the imaging surface of the camera unit 50 is measured. max Set the frequency to 40kHz, and also set the heterodyne frequency f0 of the modulation section 40 to 40kHz. Figure 4 This is a diagram showing the real part of the original image. Figure 5 This is a diagram showing the imaginary part of the original image. The original image has 256×512 pixels.

[0100] Figure 6 It is a graph showing the frequency distribution of the intensity image I(t) of the interference light on the imaging surface of the imaging unit 50. Figure 7 I shows the camera surface of the camera unit 50. obj (t), I ref (t), I cross (t) and I cross * (t) Plots of their respective frequency distributions.

[0101] I obj (t) has frequency components in the range [-80kHz, 80kHz], with a peak at 0kHz. ref The frequency distribution of (t) is constant in time and has only a DC component.

[0102] I cross (t) has frequency components in the range [0kHz, 80kHz], with a peak at a frequency of 40kHz. cross * (t) has frequency components in the range [-80kHz, 0kHz], with a peak at a frequency of -40kHz. cross (t) and I cross * (t) their respective frequency ranges and I obj The frequency ranges of I(t) overlap. Therefore, I cross (t) and I cross * (t) cannot be with I obj (t) were measured separately.

[0103] Figure 8 It shows that by from Figure 6 I obtained from existing examples of frequency range [0kHz, 80kHz] cross A graph of the frequency distribution of (t). Figure 9 This illustrates an embodiment of I obtained using the KK relation. crossA graph of the frequency distribution of (t). In the existing example, I obj The frequency distribution of (t) overlaps with the original I. cross The frequency distribution of (t). In contrast, in the embodiment, there is no I. obj The influence of the frequency distribution of (t) is used to obtain the original I. cross Frequency distribution of (t).

[0104] Figure 10 It is a diagram showing the image of the rigorous solution. Figure 11 This is a diagram showing an image obtained from an existing example. Figure 12 This is a diagram showing images obtained from an embodiment. Figures 10-12 Each image is the real part of a complex amplitude image obtained when the direction of the object light irradiated by the irradiation optical system 20 to the original image is set to 34° relative to the z-axis.

[0105] Figure 13 This is a graph showing the difference between the complex amplitude image obtained from the existing example and the image of the rigorous solution. Figure 14 This is a graph showing the difference between the complex amplitude image obtained from the embodiment and the image of the rigorous solution. Figure 13 and Figure 14 Each image is an image of the square of the absolute value of the difference between two images. In the existing example, the error is large. In contrast, in the embodiment, there is almost no error.

[0106] As described above, according to this embodiment, when observing a moving object, a camera with a lower frame rate than existing methods can be used as the imaging unit. For example, according to this embodiment, the same information (image quality) can be obtained at half the frame rate compared to existing methods.

[0107] Therefore, it is possible to reduce the amount of image data acquired through imaging, thereby reducing the storage capacity required for data storage and lowering the data processing load. Furthermore, inexpensive cameras can be used as the imaging unit. Conversely, if a high-speed camera, as required by existing methods, is used as the imaging unit, the throughput (number of observations per second) of the observed object can be increased by two times, and the number of sampling records per device can be increased by two times.

[0108] The observation device and observation method are not limited to the above-described embodiments and structural examples, and can be modified in various ways.

[0109] The observation apparatus of the above embodiment comprises: (1) a light source for outputting light; (2) an interference optical system that branches the light output from the light source and serves as object light and reference light, and combines the object light passing through the moving object to be observed with the reference light and outputs it; (3) a modulation unit that is disposed on the optical path of the object light or reference light between the branch and the combined beam of the interference optical system, and shifts the optical frequency of the object light or reference light by an amount of heterodyne frequency f0; (4) an imaging unit that has an imaging surface disposed at a position where the object light output from the interference optical system forms an image of the object to be observed, and acquires an intensity image of the interference light generated by the object light and reference light output from the interference optical system and reaching the imaging surface; and (5) a resolution unit that, based on the time series data of the intensity image of the interference light at the imaging surface, obtains the time series data of the complex amplitude image of the object light at the imaging surface, and the modulation unit sets the maximum value of the Doppler shift of the object light reaching the imaging surface based on the interaction with the object to be observed as Δf. max When the heterodyne frequency f0 is set as Δf max The above, in the analysis section, includes (a) time-series data I(t) based on the intensity image of the interference light from the imaging surface and the time-series data I(t) based on the intensity image of the reference light from the imaging surface. ref (t), obtain: the time series data U of the complex amplitude image of the object light from the camera surface. obj (t) and time series data U of the complex amplitude image of the reference light of the imaging surface. ref The function χ(t) defined by (t) is log[1+U obj (t) / U ref (b) Using the Cramer-Kroni relation, the imaginary part of the function χ(t) is obtained from the real part of the function χ(t), and (c) Based on the function χ(t), the time series data U of the complex amplitude image of the object light on the imaging surface is obtained. obj (t).

[0110] The observation method of the above embodiment uses the light source, interference optical system, modulation unit and imaging unit of the above structure, (a) setting the maximum value of the Doppler shift of the object light arriving at the imaging surface based on the light frequency of the object being observed as Δf max At that time, the heterodyne frequency f0 is set as Δf by the modulation unit. max The above describes the time-series data of the intensity image of the interference light on the imaging surface obtained by the imaging unit, and (b) the time-series data I(t) based on the intensity image of the interference light on the imaging surface and the time-series data I(t) based on the intensity image of the reference light on the imaging surface. ref (t), to obtain the time series data U of the complex amplitude image of the object light from the camera surface. obj (t) and time series data U of the complex amplitude image of the reference light of the imaging surface. refThe function χ(t) defined by (t) is log[1+U obj (t) / U ref (c) Using the Cramer-Kroni relation, the imaginary part of the function χ(t) is obtained from the real part of the function χ(t). (d) Based on the function χ(t), the time series data U of the complex amplitude image of the object light on the imaging surface is obtained. obj (t).

[0111] The observation device and method described above can also be configured such that, in the modulation unit, the heterodyne frequency f0 is set to be less than 3Δf. max .

[0112] In the above-mentioned observation device and observation method, the interference optical system may also be configured to include: (1) an illumination optical system that, when illuminating the object object with object light, focuses the object light onto a linear region in a direction perpendicular to the movement direction of the object object; and (2) an imaging optical system that, when forming an image of the object object caused by the object light emitted from the object object on an imaging surface, sets the object object and the imaging surface in a Fourier transform positional relationship with respect to a direction parallel to the movement direction of the object object, and sets the object object and the imaging surface in a conjugate positional relationship with respect to a direction perpendicular to the movement direction of the object object. In the analysis unit, for each illumination direction of the object light to the object object by the illumination optical system, a complex amplitude image is obtained, and a 3D distribution of the refractive index of the object object is obtained.

[0113] In the above-mentioned observation device, it can also be configured such that the analysis unit uses the intensity image of the reference light obtained when only the reference light of the object light and the reference light reaches the imaging surface of the imaging unit in the state where the object light is shielded in the optical path of the interference optical system, and obtains the real part of the function χ(t).

[0114] The above observation method can also be configured to use the intensity image of the reference light obtained by only the reference light of the object light and the reference light reaching the imaging surface of the imaging unit in the state where a shield is set in the optical path of the object light in the interference optical system, and to find the real part of the function χ(t).

[0115] The aforementioned observation device may also be configured to further include: a beam splitter disposed in the optical path of the reference light in the interference optical system, which branches and extracts a portion of the reference light; and a second imaging unit that acquires an intensity image of the reference light extracted by the beam splitter, and a resolution unit using time-series data I of the intensity image of the reference light acquired by the second imaging unit. ref (t), find the real part of the function χ(t).

[0116] The above-described observation method can also be further configured to include: a beam splitter positioned in the optical path of the reference light in the interference optical system, which branches and extracts a portion of the reference light; a second imaging unit that acquires an intensity image of the reference light extracted through the beam splitter; and time-series data I of the intensity image of the reference light acquired through the second imaging unit. ref Find the real part of the function χ(t).

[0117] Industrial availability

[0118] The implementation method can be used as an observation device and observation method, which can use a low-speed camera as the imaging unit when observing a moving object.

[0119] Explanation of reference numerals in the attached figures

[0120] 1, 1A…Observation device; 2…Object to be observed; 10…Light source; 20…Illumination optical system; 21, 22…Lens; 30…Imaging optical system; 31-34…Lens; 35…Neutral neutral density filter; 36…Shielding body; 40…Modulation unit; 41, 42…Acousto-optic element; 50, 51…Image-sensing unit; 60…Resolving unit; 71, 72…Beam splitter; 73, 74…Mirror; 75…Beam splitter.

Claims

1. An observation apparatus, wherein provided are: a light source that outputs light; an interference optical system that branches the light output from the light source and serves as an object light and a reference light, combines the object light that has passed through a moving observation target object and the reference light, and outputs the combined light; a modulation section that is provided on an optical path of the object light or the reference light between branching and combining in the interference optical system, and shifts the optical frequency of the object light or the reference light by an amount of a heterodyne frequency f0; an imaging section that has an imaging surface arranged at a position at which an image of the observation target object is formed by the object light output from the interference optical system, and acquires an intensity image of interference light generated by the object light and the reference light that have reached the imaging surface and output from the interference optical system; and an analysis section that obtains time-series data of a complex amplitude image of the object light at the imaging surface on the basis of time-series data of the intensity image of the interference light at the imaging surface, The modulation section sets a maximum value of a Doppler shift amount of a light frequency based on interaction with the observation object to Δf max The heterodyne frequency f0 is set to Δf max The above and less than 3Δf max , the analysis section, The time series data I(t) of the intensity image of the interference light from the imaging surface and the time series data I(t) of the intensity image of the reference light from the imaging surface. ref (t), to obtain: the time series data U of the complex amplitude image of the object light from the camera surface. obj (t) and the time series data U of the complex amplitude image of the reference light of the imaging surface. ref The function χ(t) defined by (t) is log[1+U obj (t) / U ref The real part of [(t)] obtains an imaginary part of a function χ(t) from a real part of the function χ(t) using a Cramer-Kronig relation, Based on the function χ(t), the time series data U of the complex amplitude image of the object light of the image plane is obtained obj (t).

2. The observation apparatus according to claim 1, wherein the interference optical system includes: an irradiation optical system that condenses and irradiates the object light on a linear region in a direction perpendicular to a moving direction of the observation target object when the object light is irradiated on the observation target object; and an imaging optical system that arranges the observation target object and the imaging surface in a positional relationship in which the observation target object and the imaging surface are Fourier-transformed with respect to a direction parallel to a moving direction of the observation target object and are conjugated with respect to a direction perpendicular to the moving direction of the observation target object when an image of the observation target object generated by the object light emitted from the observation target object is formed on the imaging surface, the analysis section obtains a complex amplitude image for each of irradiation directions of the object light on the observation target object by the irradiation optical system, and acquires a three-dimensional distribution of a refractive index of the observation target object.

3. The observation apparatus according to claim 1 or 2, wherein the analysis section obtains the real part of the function χ(t) using an intensity image of the reference light that is acquired when only the reference light among the object light and the reference light is made to reach the imaging surface of the imaging section in a state in which a shield is provided on an optical path of the object light in the interference optical system.

4. The observation apparatus according to claim 1 or 2, wherein further provided are: a beam splitter that is provided on an optical path of the reference light of the interference optical system, branches a part of the reference light, and takes out the part; and a second imaging section that acquires an intensity image of the reference light taken out by the beam splitter, The analysis section uses the time-series data I of the intensity image of the reference light acquired by the second imaging section ref (t), the real part of the function χ(t) is obtained.

5. An observation method, wherein a light source, an interference optical system, a modulation section, and an imaging section are used, the light source outputs light, the interference optical system branches the light output from the light source and serves as an object light and a reference light, combines the object light that has passed through a moving observation target object and the reference light, and outputs the combined light, the modulation section is provided on an optical path of the object light or the reference light between branching and combining in the interference optical system, and shifts the optical frequency of the object light or the reference light by an amount of a heterodyne frequency f0, the imaging section has an imaging surface arranged at a position at which an image of the observation target object is formed by the object light output from the interference optical system, and acquires an intensity image of interference light generated by the object light and the reference light that have reached the imaging surface and output from the interference optical system, and an analysis section obtains time-series data of a complex amplitude image of the object light at the imaging surface on the basis of time-series data of the intensity image of the interference light at the imaging surface. The modulation section is provided on an optical path of the object light or the reference light between branching from the interference optical system to combining, and shifts the optical frequency of the object light or the reference light by an amount of a heterodyne frequency f0, The imaging section has an imaging surface disposed 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 generated by the object light and the reference light output from the interference optical system and reaching the imaging surface, When a maximum value of a Doppler shift amount of a light frequency based on interaction with the observation object of the object light reaching the imaging surface is Δf max , the heterodyne frequency f0 is set to Δf by the modulation section max , and is less than 3Δf max , time-series data of an intensity image of the interference light of the imaging surface is obtained by the imaging section, The time series data I(t) of the intensity image of the interference light from the imaging surface and the time series data I(t) of the intensity image of the reference light from the imaging surface. ref (t), to obtain: the time series data U of the complex amplitude image of the object light from the camera surface. obj (t) and the time series data U of the complex amplitude image of the reference light of the imaging surface. ref The function χ(t) defined by (t) is log[1+U obj (t) / U ref The real part of [(t)] The imaginary part of the function χ(t) is obtained from the real part of the function χ(t) using the Cramer-Kronig relation, Based on the function χ(t), the time series data U of the complex amplitude image of the object light of the image plane is obtained obj (t).

6. The observation method according to claim 5, wherein The interference optical system includes: an illumination optical system that condenses the object light to a linear region in a direction perpendicular to a moving direction of the observation object when the object light is illuminated to the observation object; and an imaging optical system that forms an image of the observation object generated by the object light emitted from the observation object on the imaging surface, and sets the observation object and the imaging surface in a positional relationship in which they are Fourier-transformed with respect to a direction parallel to the moving direction of the observation object, and in a positional relationship in which they are conjugate with respect to a direction perpendicular to the moving direction of the observation object, a complex amplitude image is obtained for each of the illumination directions of the object light to the observation object by the illumination optical system, and a three-dimensional distribution of the refractive index of the observation object is acquired.

7. The observation method according to claim 5 or 6, wherein The real part of the function χ(t) is obtained using an intensity image of the reference light acquired when only the reference light among the object light and the reference light is made to reach the imaging surface of the imaging section in a state in which a shield is provided on an optical path of the object light in the interference optical system.

8. The observation method according to claim 5 or 6, wherein Further, a beam splitter that branches and takes out a part of the reference light is provided on an optical path of the reference light of the interference optical system, and a second imaging section that acquires an intensity image of the reference light taken out by the beam splitter is used, using the time series data I of the intensity image of the reference light acquired by the second imaging section ref (t), the real part of the function χ(t) is determined.

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