Interference image acquisition device and method for acquiring interference image

Abstract

To provide a device that can easily and stably set the position of a focus surface of a target object when an interference image of the target object is to be acquired.SOLUTION: An interference image acquisition device 1 includes a light source 11, a beam splitter 12, a reference side mirror 13, a piezoelectric element 14, a stage 15, an objective lens 16, a focal point variable lens 17, an imaging unit 18, a housing 30, a supporting unit 31, and an operation unit 40. The focal point variable lens 17 is set on an optical path of an interference light from the beam splitter 12 to the imaging surface of the imaging unit 18, and adjusts the position of a focus surface F to be conjugated to the imaging surface of the imaging unit 18 on an optical path of a first light beam from the beam splitter 12 as a branch unit to the beam splitter 12 as a multiplexer unit. The housing 30 fixes the relative positional relation between the beam splitter 12 and the supporting unit 31 and makes the beam splitter and the supporting unit mechanically integrated with each other.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to an interference image acquisition device and an interference image acquisition method.

Background Art

[0002] Non-Patent Document 1 and Non-Patent Document 2 introduce various configuration examples of an interference image acquisition device capable of acquiring an interference image of an object. The interference image acquisition device includes a light source, a two-beam interferometer that branches the light output from this light source into two beams and then combines the two beams to output interference light, and an imager having an imaging surface that receives the interference light output from this two-beam interferometer. In the two-beam interferometer, an object is disposed on the optical path of either one of the two beams. The imager can acquire an interference image of the object on the focus surface conjugate to the imaging surface.

[0003] Also, this interference image acquisition device can also obtain a phase image or the like of the object by the phase shift method based on the interference image of the object. The interference image acquisition device sets the optical path length difference between the two beams in the two-beam interferometer to a plurality of different set values, acquires an interference image of the object by the imager in each state, and obtains a phase image or the like based on these acquired plurality of interference images.

Prior Art Documents

Non-Patent Documents

[0004]

Non-Patent Document 1

Non-Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0005] Conventional interference image acquisition devices adjust the physical distance between a two-beam interferometer and an object in order to set the position of the focus plane on the object (i.e., the relative positional relationship between the object and the focus plane). Adjustment of the physical distance between the two-beam interferometer and the object can be achieved by moving the two-beam interferometer. However, the Z-stage for moving the two-beam interferometer is large and expensive, and the power consumption for driving the Z-stage is high. Also, when the two-beam interferometer is attached to the Z-stage in a cantilever beam method and the two-beam interferometer is moved, mechanical vibration is large.

[0006] In an interference image acquisition device, if there is mechanical vibration when the imager acquires an interference image, the relative position of the focus plane with respect to the object fluctuates, and the acquired interference image will contain noise. Non-Patent Document 1 does not describe a configuration for stabilizing the relative position of the focus plane with respect to the object. Non-Patent Document 2 describes that it is necessary to strictly control the fluctuation of the optical path length difference due to mechanical vibration to be smaller than the wavelength, but does not describe a specific configuration for that.

[0007] Also, in an interference image acquisition device, it is also conceivable to move the object without moving the two-beam interferometer. However, also in this case, the Z-stage for moving the object is large and expensive, and the power consumption for driving the Z-stage is high. Also, for example, when repeatedly acquiring interference images of living cells while injecting a chemical solution into the living cells, or when acquiring an interference image of a MEMS (Micro Electro Mechanical Systems) element to measure the minute movement of the MEMS element, there are cases where it is not preferable to move the object (living cells, MEMS element).

[0008] The present invention has been made to solve the above problems, and an object thereof is to provide an apparatus and a method capable of easily and stably setting the position of a focus plane in an object when acquiring an interference image of the object.

Means for Solving the Problems

[0009] The interference image acquisition apparatus of the present invention includes: (1) a two-beam interferometer that branches incoherent light output from a light source into a first light beam and a second light beam by a branching unit, and combines, by a multiplexing unit, the first light beam reflected or transmitted by an object disposed on the optical path of the first light beam and supported by a support unit and the second light beam reflected by a reference-side mirror to output interference light; (2) an imager having an imaging surface that receives the interference light output from the two-beam interferometer and acquires an interference image of the object; and (3) a focus plane position adjustment unit provided on the optical path of the interference light from the multiplexing unit to the imaging surface and that adjusts the position of a focus plane conjugate to the imaging surface on the optical path of the first light beam from the branching unit to the multiplexing unit. Further, the relative positional relationship among the branching unit, the multiplexing unit, and the support unit is fixed.

[0010] On one aspect of the interference image acquisition apparatus of the present invention, it is preferable that the optical path length difference between the optical path length of the first light beam reflected at the position of the focus plane and the optical path length of the second light beam reflected by the reference-side mirror in the two-beam interferometer is equal to or less than the coherence length of the light output from the light source. Alternatively, it is preferable that the two-beam interferometer is provided with an object-side mirror that reflects the first light beam transmitted through the object, and the optical path length difference between the optical path length of the first light beam reflected by the object-side mirror and the optical path length of the second light beam reflected by the reference-side mirror is equal to or less than the coherence length of the light output from the light source.

[0011] On one aspect of the interference image acquisition apparatus of the present invention, it is preferable that the focus plane position adjustment unit includes a focus-variable lens with a variable focal length, and it is also preferable that it includes a mechanism for changing the optical path length of the interference light from the multiplexing unit to the imaging surface, and it is also preferable that it includes a mechanism for changing the position of one or more lenses disposed on the optical path of the interference light from the multiplexing unit to the imaging surface.

[0012] In one aspect of the interference image acquisition device of the present invention, it is preferable that the interference image acquisition device further includes a reference side mirror position adjustment unit that adjusts the position of the reference side mirror in a direction perpendicular to the reflecting surface of the reference side mirror. Further, in a state where the focus surface is adjusted to a fixed position by the focus surface position adjustment unit, when the reference side mirror is adjusted to each of a plurality of positions by the reference side mirror position adjustment unit, it is preferable that the interference image acquisition device further includes an arithmetic unit that obtains a phase image or an intensity image of the object based on the interference image acquired by the imager. Furthermore, the focus surface position adjustment unit scans the position of the focus surface along the optical path of the first light beam, the imager acquires an interference image at each position of the scan of the focus surface, and the arithmetic unit obtains a phase image or an intensity image based on the interference image at each position of the scan of the focus surface, and it is preferable that a three-dimensional image of the object is obtained based on these phase images or intensity images.

[0013] The interference image acquisition method of the present invention includes: (1) an interference step of, in a two-beam interferometer, branching incoherent light output from a light source into a first light beam and a second light beam by a branching unit, and combining, by a combining unit, the first light beam reflected or transmitted by an object supported by a support unit and disposed on the optical path of the first light beam and the second light beam reflected by a reference side mirror to output interference light; (2) an imaging step of acquiring an interference image of the object by an imager having an imaging surface that receives the interference light output from the two-beam interferometer; and (3) a focus surface position adjustment step of adjusting the position of a focus surface conjugate to the imaging surface on the optical path of the first light beam from the branching unit to the combining unit by a focus surface position adjustment unit provided on the optical path of the interference light from the combining unit to the imaging surface. Further, the interference step, the imaging step, and the focus surface position adjustment step are performed in a state where the relative positional relationship among the branching unit, the combining unit, and the support unit is fixed.

[0014] In one aspect of the interference image acquisition method of the present invention, in the interference step, in a two-beam interferometer, it is preferable that the optical path length difference between the optical path length of the first light beam reflected at the focus plane position and the optical path length of the second light beam reflected by the reference side mirror is equal to or less than the coherence length of the light output from the light source. Alternatively, in the interference step, in a two-beam interferometer, an object-side mirror for reflecting the first light beam that has passed through the object is provided, and it is preferable that the optical path length difference between the optical path length of the first light beam reflected by the object-side mirror and the optical path length of the second light beam reflected by the reference side mirror is equal to or less than the coherence length of the light output from the light source.

[0015] In one aspect of the interference image acquisition method of the present invention, it is preferable that the focus plane position adjustment unit includes a focus variable lens with a variable focal length, and it is also preferable that it includes a mechanism for changing the optical path length of the interference light from the multiplexing unit to the imaging plane, and it is also preferable that it includes a mechanism for changing the position of one or more lenses arranged on the optical path of the interference light from the multiplexing unit to the imaging plane.

[0016] In one aspect of the interference image acquisition method of the present invention, it is preferable that the interference image acquisition method further includes a reference side mirror position adjustment step for adjusting the position of the reference side mirror in a direction perpendicular to the reflection surface of the reference side mirror. Further, in a state where the focus plane is adjusted to a certain position in the focus plane position adjustment step, it is preferable that it further includes a calculation step for obtaining a phase image or an intensity image of the object based on the interference image obtained in the imaging step when the reference side mirror is adjusted to each of a plurality of positions in the reference side mirror position adjustment step. Furthermore, in the focus plane position adjustment step, the position of the focus plane is scanned along the optical path of the first light beam, in the imaging step, an interference image is obtained at each position of the focus plane scan, and in the calculation step, a phase image or an intensity image is obtained based on the interference image at each position of the focus plane scan, and a three-dimensional image of the object is obtained based on these phase images or intensity images.

Advantages of the Invention

[0017] According to the present invention, when acquiring an interference image of an object, the position of the focus plane in the object can be easily and stably set.

Brief Description of Drawings

[0018]

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[0019] Hereinafter, embodiments for carrying out the present invention will be described in detail with reference to the accompanying drawings. In the description of the drawings, the same elements are denoted by the same reference numerals, and redundant descriptions are omitted. The present invention is not limited to these examples, but is shown by the claims, and is intended to include all modifications within the meaning and scope equivalent to the claims.

[0020] (First Embodiment) FIG. 1 is a diagram showing the configuration of an interference image acquisition apparatus 1 according to the first embodiment. The interference image acquisition apparatus 1 according to the first embodiment includes a light source 11, a beam splitter 12, a reference side mirror 13, a piezo element 14, a stage 15, an objective lens 16, a focus-variable lens 17, an imager 18, a housing 30, a support portion 31, and a calculation unit 40. The interference image acquisition apparatus 1 of the present embodiment has a Michelson interferometer as a two-beam interferometer, and acquires an interference image of an object 90.

[0021] The object 90 is not limited to a specific cell or biological sample, and is arbitrary. For example, as the object 90, cultured cells, immortalized cells, primary cultured cells, cancer cells, adipocytes, liver cells, cardiomyocytes, neurons, glial cells, somatic stem cells, embryonic stem cells, pluripotent stem cells, iPS cells, and cell masses (colonies or spheroids) made from the above cells can be mentioned. Further, as the object 90, not only biological objects but also industrial samples such as glass, semiconductor elements, resin materials, liquid crystals, polymer compounds, and metal materials can be mentioned.

[0022] The light source 11 outputs spatially or temporally incoherent light. The light source 11 is, for example, a lamp-based light source such as a halogen lamp, an LED (Light emitting diode) light source, an SLD (Super luminescent diode) light source, an ASE (Amplified spontaneous emission) light source, or the like. It is preferable that the wavelength bandwidth of the light output by the light source 11 is about 1 nm to 3 nm. If the wavelength band is too wide, it becomes difficult to optically adjust the device for obtaining interference. Conversely, if the wavelength band is too narrow, the adverse effects of interference due to multiple reflections and stray light appear in the interference image. Therefore, it is preferable to narrow the wavelength bandwidth to about 1 nm to 3 nm.

[0023] The beam splitter 12 is optically coupled to the light source 11 and constitutes a Michelson interferometer which is a two-beam interferometer. The beam splitter 12 may be a half mirror having a transmittance to reflectance ratio of 1:1. The beam splitter 12 is a branching portion that branches the light output from the light source 11 into a first light beam and a second light beam, and is also a combining portion that combines the first light beam and the second light beam to output interference light.

[0024] The beam splitter 12 as the branching portion branches the light output from the light source 11 into two, outputs the first light beam toward the object 90, and outputs the second light beam toward the reference side mirror 13. The beam splitter 12 as the combining portion inputs the first light beam that has reached from the object 90, inputs the second light beam that has reached after being reflected by the reference side mirror 13, combines the input first light beam and second light beam, and outputs the interference light toward the objective lens 16.

[0025] The reference mirror 13 is optically coupled to the beam splitter 12 and has a reflecting surface perpendicular to the second light beam reaching from the beam splitter 12. The piezo element 14 and the stage 15 are a reference mirror position adjuster that adjusts the position of the reference mirror 13 in a direction perpendicular to the reflecting surface of the reference mirror 13. The stage 15 is movable with respect to the fixed part, and simultaneously moves the reference mirror 13 and the piezo element 14 on the movable part with respect to the fixed part. Since the stage 15 only needs to be able to mechanically move the reference mirror 13 and the piezo element 14, the required load capacity is about 5 g. Therefore, as the stage 15, a small, inexpensive, low power consumption, and highly stable one can be used. The stage 15 has a relatively wide movable range and low position adjustment accuracy. The stage 15 is suitable for roughly adjusting the position of the reference mirror 13.

[0026] The piezo element 14 has a relatively narrow movable range and high position adjustment accuracy. The piezo element 14 is suitable for finely adjusting the position of the reference mirror 13. The piezo element 14 can precisely adjust the optical path length difference (i.e., phase difference) between the two light beams in the two-beam interferometer. The piezo element 14 can determine the position of the reflecting surface of the reference mirror 13 with a resolution less than the wavelength. In the two-beam interferometer, the optical path length difference between the two light beams is variable.

[0027] The objective lens 16 is optically connected to the beam splitter 12, inputs the interference light reaching from the beam splitter 12, and outputs the interference light toward the focus variable lens 17.

[0028] The variable focus lens 17 is optically connected to the objective lens 16, receives the interference light that has reached from the objective lens 16, and outputs the interference light toward the imager 18. The focal length of the variable focus lens 17 is variable. The variable focus lens 17 is a focus plane position adjustment unit provided on the optical path of the interference light from the beam splitter 12 as a multiplexing unit to the imaging surface of the imager 18, and adjusts the position of the focus plane F that is conjugate to the imaging surface of the imager 18 on the optical path of the first light beam from the beam splitter 12 as a branching unit to the beam splitter 12 as a multiplexing unit.

[0029] The imager 18 is optically coupled to the variable focus lens 17, has an imaging surface that receives the interference light that has reached from the variable focus lens 17, and acquires an interference image of the object 90. The imager 18 is an image sensor such as, for example, a CCD area image sensor and a CMOS area image sensor.

[0030] The support unit 31 supports the object 90. The support unit 31 may be in the shape of a plate on which the object 90 is placed, and is preferably in the shape of a container when the object 90 is living cells in a culture solution. Further, the support unit 31 may be a part of the housing 30 or may be integrated with the housing 30. The housing 30 fixes the relative positional relationship between the beam splitter 12 (branching unit, multiplexing unit) and the support unit 31 and mechanically integrates them. Further, in addition to the beam splitter 12 and the support unit 31, the housing 30 preferably fixes the relative positional relationships among the light source 11, the fixing part of the stage 15, the objective lens 16, and the variable focus lens 17. The housing 30 is preferably a rigid body, and is preferably made of, for example, metal.

[0031] The arithmetic unit 40 is electrically connected to the imager 18, instructs the imager 18 of the exposure timing (that is, the timing of acquiring the interference image), and receives the data of the interference image acquired by the imager 18. Based on this interference image, the arithmetic unit 40 can obtain a phase image or an intensity image of the object 90.

[0032] The arithmetic unit 40 is also electrically connected to the piezoelectric element 14, and by applying an electrical signal to the piezoelectric element 14, the piezoelectric element 14 is extended to adjust the position of the reference side mirror 13. The arithmetic unit 40 is also electrically connected to the stage 15, and by applying an electrical signal to the stage 15, the stage 15 is moved to adjust the positions of the piezoelectric element 14 and the reference side mirror 13. Further, the arithmetic unit 40 is also electrically connected to the focus variable lens 17, and by applying an electrical signal to the focus variable lens 17, the focal length of the focus variable lens 17 is adjusted.

[0033] The arithmetic unit 40 may be a computer or a tablet. The arithmetic unit 40 includes an interface for inputting or outputting electrical signals among the piezoelectric element 14, the stage 15, the focus variable lens 17, and the imager 18 respectively. The arithmetic unit 40 includes a display unit (for example, a liquid crystal display, etc.) for displaying interference images, phase images, intensity images, as well as measurement conditions and measurement results. The arithmetic unit 40 includes an input unit (for example, a keyboard, a mouse, etc.) for receiving inputs such as measurement conditions. The arithmetic unit 40 includes a storage unit (for example, a hard disk drive, a ROM, a RAM, etc.) for storing measurement conditions, measurement results, programs for measurement, etc. Further, the arithmetic unit 40 includes a control unit (for example, a CPU, etc.) for performing predetermined processing according to a program.

[0034] The calculation unit 40 gives instructions for extending the piezoelectric element 14, moving the stage 15, adjusting the focal length of the focus variable lens 17, and exposing the imager 18 by digital timing control. The element used for timing control is preferably a microcontroller or a signal generation board with a built-in multi-channel DA (Digital-to-analog) converter. Generally, the output of a DA converter is a low-power voltage signal, but by using an appropriate power amplifier, a voltage signal with sufficient power can be given to the piezoelectric element 14 or the stage 15. Also, when the focus variable lens 17 changes its focal length according to the input current value, by using an appropriate voltage-current conversion amplifier together with the DA converter, the current signal output from this voltage-current conversion amplifier can be used as the input signal to the focus variable lens 17.

[0035] Generally, the output current value from the voltage-current conversion amplifier (i.e., the input current value to the focus variable lens) is proportional to the input voltage value to the voltage-current conversion amplifier (i.e., the output voltage value from the DA converter). The refractive power (diopter value) of the focus variable lens is proportional to the input current value to the focus variable lens. The amount of change in the position of the focus plane F conjugate to the imaging plane of the imager 18 is a function of the refractive power (diopter value) of the focus variable lens. Therefore, from these relationships, the position of the focus plane F is a function of the output voltage value from the DA converter.

[0036] A focus-variable lens capable of adjusting the focal length over ±1 diopter or more has been put into practical use and is commercially available. As shown in FIG. 22, between the imaging surface of the imager 18 and the object 90, a tube lens 23 with a focal length f1, a focus-variable lens 17 having a refractive power of ΔD diopter, and an objective lens 16 with a focal length f2 are arranged. Also, let the distance between the imaging surface of the imager 18 and the tube lens 23 be L1, the distance between the tube lens 23 and the focus-variable lens 17 be L2, the distance between the focus-variable lens 17 and the objective lens 16 be L3, and the distance between the objective lens 16 and the object 90 be L4. In such an optical system, the position of the object 90 conjugate with the imaging surface of the imager 18 becomes the corrected focus position. This corrected focus position can be obtained approximately by ray tracing calculation.

[0037] In ray tracing calculation, for example, a method using the ABCD matrix can be used. Let the height of the ray on the optical axis at the incident surface (in the case of FIG. 22, for the sake of convenience, the imaging surface of the imager 18 is called the incident surface because the ray is traced backward from the imaging surface of the imager 18) be r1, the angle of the ray be θ1, the height of the ray on the optical axis at the object surface which is the exit surface be r2, and the angle of the ray be θ2. Then, the incident surface and the exit surface are related by the following formula (1).

[0038]

Equation

[0039] Here, M1 in the above formula (1) is a propagation matrix representing the free-space propagation from the imaging surface of the imager 18 to the tube lens 23. M2 is a propagation matrix representing the refraction at the tube lens 23. M3 is a propagation matrix representing the free-space propagation from the tube lens 23 to the focus-variable lens 17. M4 is a propagation matrix representing the refraction at the focus-variable lens 17. M5 is a propagation matrix representing the free-space propagation from the focus-variable lens 17 to the objective lens 16. M6 is a propagation matrix representing the refraction at the objective lens 16. Also, M7 is a propagation matrix representing the free-space propagation from the objective lens 16 to the object 90. The propagation matrices M1 to M7 are each represented by the following formula (2).

[0040]

Number

[0041] Figures 23 to 25 illustrate the behavior of paraxial rays in the vicinity of the object 90 by calculating the propagation matrix of the above formula (2). Assuming L1 = 200 mm, L2 = 50 mm, L3 = 150 mm, f1 = 200 mm, and f2 = 9.0 mm, the refractive power ΔD of the focus-variable lens 17 was varied within the range of ±2 diopters (DP). Figure 23 represents the paraxial rays when the refractive power of the focus-variable lens 17 is -2 DP. Figure 24 represents the paraxial rays when the refractive power of the focus-variable lens 17 is 0 DP. Figure 25 represents the paraxial rays when the refractive power of the focus-variable lens 17 is +2 DP. In these figures, the horizontal axis represents the position in the optical axis direction, and the vertical axis represents the position in the radial direction. When the refractive power of the focus-variable lens 17 is 0, since this optical system is an imaging optical system for an infinite object distance system, as shown in Figure 24, the virtual light emerging from the imaging surface of the imager 18 forms an image on the focal plane of the objective lens 16. On the other hand, when the refractive power of the focus-variable lens 17 is positive (convex lens), as shown in Figure 25, the imaging position approaches the objective lens 16. Conversely, when the refractive power of the focus-variable lens 17 is negative (concave lens), as shown in Figure 23, the imaging position moves away from the objective lens 16.

[0042] Based on the calculation of the propagation matrix of the above equation (2), the relationship between the refractive power of the focus-variable lens 17 and the imaging position on the object 90 side is shown in a graph in Fig. 26. In Fig. 26, the calculation results are represented by a solid line, and the results of actually measuring the amount of change in the imaging position in the optical system of Fig. 22 (L1 = 200 mm, L2 = 50 mm, L3 = 150 mm, f1 = 200 mm, f2 = 9.0 mm) are represented by black circles. Thus, in the optical system of Fig. 22, it can be confirmed that when using the objective lens 16 with f2 = 9 mm and the focus-variable lens 17 of ±2 DP, the imaging position on the object 90 side can be changed in the range of +0.12 mm to -0.22 mm. Also, when the modulation range of the refractive power of the focus-variable lens 17 is a minute amount, the relationship between the refractive power and the focus position on the object 90 side can be approximately proportional.

[0043] In the two-beam interferometer, the optical path difference between the optical path length of the first beam reflected at the position of the focus plane F and the optical path length of the second beam reflected by the reference-side mirror 13 is made to be equal to or less than the coherence length of the light output from the light source 11. When such a condition is satisfied, due to the interference between the first beam and the second beam input to the beam splitter 12 as the combining section, the imager 18 can acquire a clear interference image of the object 90 at the position of the focus plane F. For example, the coherence length of the light output from a halogen lamp that can be used as the light source 11 is about 1 μm, the coherence length of the light output from an LED light source is about 3 μm, and the coherence length of the light output from an SLD light source or an ASE light source is 10 to 50 μm.

[0044] The reference-side mirror position adjustment section (piezo element 14 or stage 15) adjusts the position of the reference-side mirror 13 according to the change in the position of the focus plane F due to the change in the focal length of the focus-variable lens 17, so that the optical path difference is made equal to or less than the coherence length. When the required adjustment width is larger than the movable distance of the piezo element 14 during the position adjustment of the reference-side mirror 13 (for example, when the scanning range of the focus plane F is large in order to obtain a three-dimensional image of the object 90), it is preferable to use the stage 15.

[0045] Next, a method for acquiring an interference image using the interference image acquisition apparatus 1 of the present embodiment will be described. The method for acquiring an interference image of the present embodiment includes an interference step, an imaging step, and a focus plane position adjustment step.

[0046] In the interference step, in a two-beam interferometer, the incoherent light output from the light source 11 is split into a first light beam and a second light beam by the beam splitter 12 (branching unit), and reaches the object 90 that is supported by the support unit 31 and disposed on the optical path of the first light beam. The first light beam and the second light beam that has reached from the reference-side mirror 13 are combined by the beam splitter 12 (combining unit), and interference light is output from the beam splitter 12. In the imaging step, an interference image of the object 90 is acquired by the imager 18 having an imaging surface that receives the interference light output from the two-beam interferometer. In the focus plane position adjustment step, the position of the focus plane F that is conjugate to the imaging surface of the imager 18 is adjusted on the optical path of the first light beam from the beam splitter 12 as the branching unit to the beam splitter 12 as the combining unit by the focus variable lens 17 provided on the optical path of the interference light from the beam splitter 12 as the combining unit to the imaging surface of the imager 18. The method for acquiring an interference image of the present embodiment performs the interference step and the imaging step in a state where the relative positional relationship between the beam splitter 12 (branching unit, combining unit) and the support unit 31 is fixed.

[0047] Further, the method for acquiring an interference image of the present embodiment also includes a reference-side mirror position adjustment step. In the reference-side mirror position adjustment step, the position of the reference-side mirror 13 in the direction perpendicular to the reflection surface of the reference-side mirror 13 is adjusted by the reference-side mirror position adjustment unit (piezo element 14 or stage 15). Further, the method for acquiring an interference image of the present embodiment also includes a calculation step. In the calculation step, the phase image or intensity image of the object 90 is obtained based on the interference image acquired in the imaging step by the calculation unit 40, and further, the three-dimensional image of the object 90 is obtained.

[0048] FIG. 2 is a timing chart for explaining an operation example of the interference image acquisition apparatus 1 according to the first embodiment. This figure explains the operation when obtaining the three-dimensional image of the object 90. In this figure, in order from the top, the amount of expansion of the piezoelectric element 14, the exposure instruction signal to the imager 18, the position of the focus plane F, and the position of the movable part of the stage 15 are shown.

[0049] The focal length of the focus variable lens 17 is changed stepwise at a constant period by the signal given from the arithmetic unit 40 to the focus variable lens 17, and thereby, the position of the focus plane F is changed stepwise at a constant period (focus plane position adjustment step). Also, the movable part of the stage 15 is moved stepwise at a constant period by the signal given from the arithmetic unit 40 to the stage 15, and thereby, the position of the reference side mirror 13 is changed stepwise at a constant period (reference side mirror position adjustment step). These stepwise changes in the position of the focus plane F and the position of the reference side mirror 13 are performed in cooperation with each other.

[0050] Thereby, the optical path length difference between the optical path length of the first light beam reflected at the position of the focus plane F and the optical path length of the second light beam reflected at the reference side mirror 13 is made to be equal to or less than the coherence length of the light output from the light source 11. Between the beam splitter 12 (branching unit, multiplexing unit) and the support unit 31, the relative positional relationship is fixed by the housing 30, and there is no mechanical movable part. Therefore, the two-beam interferometer is extremely stable, and the amount of variation in the optical path length difference per second can be made several nm or less.

[0051] During the period when each of the focus plane F and the reference side mirror 13 is set to each position and stabilized, the amount of expansion of the piezoelectric element 14 is set stepwise in four steps by the signal given from the arithmetic unit 40 to the piezoelectric element 14, and thereby, the position of the reference side mirror 13 is set stepwise in four steps (reference side mirror position adjustment step). At this time, the position of the reference side mirror 13 is set so as to be different by λ / 8 each by the piezoelectric element 14, and the phase difference between the first light beam and the second light beam at the time of multiplexing is set so as to be different by π / 2 each. λ is the wavelength of the light output from the light source 11.

[0052] A period in which each of the focus plane F and the reference-side mirror 13 is set at each position, and during which the phase difference between the first light beam and the second light beam at the time of beam combination is set to each value by the piezoelectric element 14 and is stable. During this period, the first light beam and the second light beam are combined by the beam splitter 12 as a beam combining unit, and interference light is output (interference step). Then, an interference image of the object on the focus plane F is acquired by the imager 18 according to the exposure instruction signal given from the arithmetic unit 40 (imaging step).

[0053] The stepwise change in the position of the focus plane F by changing the focal length of the focus variable lens 17 and the stepwise change in the position of the reference-side mirror 13 by moving the stage 15 are performed in synchronization with the change in the expansion amount of the piezoelectric element 14 and the exposure of the imager 18, and are performed during the intervals (vertical broken lines in FIG. 2) of the expansion cycle of the piezoelectric element 14 that sets the phase difference in four steps stepwise. The exposure instruction signal given to the imager 18 is synchronized with the change in the expansion amount of the piezoelectric element 14. The stepwise change in the position of the focus plane F by changing the focal length of the focus variable lens 17, the stepwise change in the position of the reference-side mirror 13 by moving the stage 15, and the stepwise change in the phase difference by the piezoelectric element 14 are performed during the period when the imager 18 is not exposing.

[0054] Let the interference image obtained when the position of the reference-side mirror 13 is set stepwise in four steps and the phase difference between the first light beam and the second light beam at the time of beam combination is the initial phase be I0, the interference image obtained when the phase difference is "initial phase + π / 2" be I1, the interference image obtained when the phase difference is "initial phase + π" be I2, and the interference image obtained when the phase difference is "initial phase + 3π / 2" be I3. During the period when each of the focus plane F and the reference-side mirror 13 is set at each position and stabilized, four interference images I0 to I3 are acquired by the imager 18. The data of these interference images are sent from the imager 18 to the arithmetic unit 40.

[0055] In the arithmetic unit 40, an amplitude image A and a phase image φ of the object 90 on the focus plane F are obtained by performing a predetermined calculation based on the received interference images I0 to I3 (arithmetic step). The amplitude image A is represented by the following equation (3). The phase image φ is represented by the following equation (4). arg is an operator for obtaining the argument of a complex number. i is the imaginary unit. Further, a complex amplitude image of the object 90 on the focus plane F is also obtained from these amplitude image and phase image. Furthermore, a three-dimensional image of the object 90 is obtained from the amplitude image or the phase image obtained at each position of the focus plane F scanned in the optical axis direction. Note that these images are functions of pixel positions, and the calculations are performed for each pixel (arithmetic step).

[0056] [Number]

[0057] [Number]

[0058] For example, the time interval for changing the extension amount of the piezo element 14 can be set to 10 ms, the waiting time until stabilization after changing the extension amount of the piezo element 14 can be set to 3 ms, and the exposure time of the imager 18 can be set to 3 ms. In this case, 100 interference images can be acquired per second. When obtaining a set of amplitude image and phase image from four interference images, 25 sets of amplitude image and phase image can be obtained per second.

[0059] In this embodiment, the relative positional relationship between the beam splitter 12 (branching unit, multiplexing unit) and the support unit 31 is fixed, and there is no mechanically movable part. Therefore, the two-beam interferometer is extremely stable, and the amount of fluctuation in the optical path length difference per second can be suppressed to a small value. When acquiring the interference image of the object, the position of the focus plane F on the object can be easily and stably set. Further, conventionally, feedback control was necessary to maintain the phase difference between the first light beam and the second light beam at a constant value during multiplexing. However, in this embodiment, the feedback control can be made unnecessary, so that the apparatus can be configured at low cost and the operation of the apparatus can be facilitated.

[0060] (Second Embodiment) FIG. 3 is a diagram showing the configuration of the interference image acquisition apparatus 2 according to the second embodiment. Compared with the configuration of the interference image acquisition apparatus 1 according to the first embodiment shown in FIG. 1, the interference image acquisition apparatus 2 according to the second embodiment shown in FIG. 3 is different in that it includes objective lenses 21 and 22, and is different in that it includes a tube lens 23 instead of the objective lens 16. The interference image acquisition apparatus 2 according to the present embodiment has a Linnik interferometer, which is a type of Michelson interferometer, as a two-beam interferometer, and acquires an interference image of the object 90.

[0061] The objective lens 21 is provided on the optical path of the first light beam between the beam splitter 12 and the object 90. The objective lens 21 is optically coupled to the beam splitter 12 and is also optically coupled to the object 90. The objective lens 21 outputs the first light beam reaching from the beam splitter 12 toward the object 90, and outputs the first light beam reaching from the object 90 toward the beam splitter 12.

[0062] The objective lens 22 is provided on the optical path of the second light beam between the beam splitter 12 and the reference side mirror 13. The objective lens 22 is optically coupled to the beam splitter 12 and also optically coupled to the reference side mirror 13. The objective lens 22 outputs the second light beam reaching from the beam splitter 12 toward the reference side mirror 13, and outputs the second light beam reaching from the reference side mirror 13 toward the beam splitter 12.

[0063] The focus variable lens 17 is provided on the optical path of the interference light between the beam splitter 12 and the tube lens 23. The focus variable lens 17 is optically coupled to the beam splitter 12 and also optically coupled to the tube lens 23. The focus variable lens 17 outputs the interference light reaching from the beam splitter 12 toward the tube lens 23.

[0064] Let the diopter adjustable range of the focus variable lens 17 be ±ΔD, and the focal length of the tube lens 23 be f0 (1 / f0 diopter), and assume that these two lenses are arranged close to each other. Actually, due to the thickness of the focus variable lens 17 and its peripheral fixtures, the distance between the tube lens 23 and the focus variable lens 17 is about 50 mm. At this time, as described above, the position of the focus plane F can be scanned by changing the refractive power of the focus variable lens 17. For example, f2 = 9 mm, f1 = 200 mm, ΔD = 2 m -1 Then, as shown in FIG. 26, the position of the focus plane F can be scanned in the range of +0.12 mm to -0.22 mm in the optical axis direction.

[0065] A combination of a focus variable lens and another lens integrated may be used. There is a commercially available lens that combines a focus variable lens with an infinity-corrected objective lens that does not use a tube lens in a relatively low magnification region. For example, there is a commercially available lens with a magnification of 2 times and a working distance that can be adjusted within a few mm range.

[0066] Even in this embodiment, the same operational effects as those of the first embodiment are achieved. In addition, in this embodiment, since it has the configuration of a Linnik interferometer, an objective lens with a high numerical aperture can be used, and an interference image with high resolution can be obtained.

[0067] (Third Embodiment) FIG. 4 is a diagram showing the configuration of the interference image acquisition device 3 according to the third embodiment. Compared with the configuration of the interference image acquisition device 2 according to the second embodiment shown in FIG. 3, the interference image acquisition device 3 according to the third embodiment shown in FIG. 4 is different in that it includes a stage 24 and different in the configuration of the support portion that supports the object 90. The interference image acquisition device 3 of this embodiment has a Linnik interferometer which is a type of Michelson interferometer as a two-beam interferometer, and acquires an interference image of the object 90.

[0068] The stage 24 moves the objective lens 22 provided on the optical path of the second light beam between the beam splitter 12 and the reference side mirror 13 along the optical path. By appropriately setting the position of the objective lens 22, the stage 24 can make the position conjugate to the imaging surface of the imager 18 coincide with the reflecting surface of the reference side mirror 13. The arithmetic unit 40 is electrically coupled to the stage 24, and moves the stage 24 by applying an electrical signal to the stage 24 to adjust the position of the objective lens 22.

[0069] As shown in FIG. 5, the object 90 is, for example, living cells placed in a container 80 together with a culture solution. FIG. 5 is a diagram for explaining the mode of supporting the object 90 in the interference image acquisition device 3 according to the third embodiment. By placing a lid 81 on the container 80 as a support portion for supporting the object 90, the internal space of the container 80 is sealed. Also, an object side mirror 82 is disposed outside the bottom of the container 80. The bottom and the lid 81 of the container 80 are transparent at the wavelength of the light output from the light source 11. For example, the bottom and the lid 81 of the container 80 are made of quartz glass.

[0070] The object-side mirror 82 reflects the first light beam that has passed through the object 90. The object-side mirror 82 may be provided on the inner surface of the bottom of the container 80, but is preferably provided outside the bottom of the container 80. In this case, the bottom of the container 80 exists between the reflecting surface of the object-side mirror 82 and the object 90. That is, the object-side mirror 82 has a reflecting surface at a position spaced apart from the object 90. The object-side mirror 82 may be fixed to the outside of the bottom of the container 80, or may be a separate body from the container 80. Further, the object-side mirror 82 may be fixed to the housing 30.

[0071] The first light beam output from the beam splitter 12 as a branching portion passes through the objective lens 21, the lid 81, and the bottom of the container 80, and is reflected by the object-side mirror 82. The first light beam reflected by the object-side mirror 82 passes through the bottom of the container 80, the lid 81, and the objective lens 21, and reaches the beam splitter 12 as a combining portion. By positioning the focus plane F on the optical path of this first light beam within the range where the object 90 exists, the imaging device 18 can acquire an interference image of the object 90.

[0072] In the two-beam interferometer, the optical path difference between the optical path length of the first light beam reflected by the object-side mirror 82 and the optical path length of the second light beam reflected by the reference-side mirror 13 is set to be equal to or less than the coherence length of the light output from the light source 11. When such a condition is satisfied, the imaging device 18 can acquire a clear interference image of the object 90 due to the interference between the first light beam and the second light beam input to the beam splitter 12 as a combining portion.

[0073] FIG. 6 is a timing chart for explaining an operation example of the interference image acquisition apparatus 3 according to the third embodiment. This figure explains the operation when obtaining a three-dimensional image of the object 90. In this figure, the elongation amount of the piezo element 14, the exposure instruction signal to the imaging device 18, and the position of the focus plane F are shown in order from the top.

[0074] During the period before time t0, the focal length of the focus variable lens 17 is adjusted by a signal given from the arithmetic unit 40 to the focus variable lens 17, whereby the focus plane F is positioned on the reflecting surface of the object side mirror 82. Also, the position of the reference side mirror 13 is adjusted by a signal given from the arithmetic unit 40 to the stage 15, whereby the optical path length difference between the optical path length of the first light beam reflected by the object side mirror 82 and the optical path length of the second light beam reflected by the reference side mirror 13 is made to be equal to or less than the coherence length of the light output from the light source 11. Thereby, a clear interference image with appropriate contrast is acquired by the imager 18.

[0075] At time t0, the focal length of the focus variable lens 17 is adjusted by a signal given from the arithmetic unit 40 to the focus variable lens 17, whereby the focus plane F is positioned on the inner surface of the bottom of the container 80. Thereafter, the same operations as those described in the first embodiment are performed. However, in this embodiment, after time t0, the stages 15 and 24 do not move. By such operations, the amplitude image and the phase image of the object 90 at each position of the focus plane F scanned in the optical axis direction are obtained, and further, a three-dimensional image of the object 90 is obtained.

[0076] Also in this embodiment, the same effects as those of the second embodiment are achieved. In addition, in this embodiment, when scanning the position of the focus plane F in the optical axis direction, only the focal length of the focus variable lens 17 is changed stepwise, so that it is more reliable, less expensive, and can be made lighter. Further, in this embodiment, when the object 90 is a living cell, the interference image and the like of the living cell can be acquired while culturing the living cell in an environment suitable for culturing the living cell.

[0077] (Modification example) The present invention is not limited to the above-described embodiments, and various modifications are possible. For example, the two-beam interferometer is not limited to a Michelson interferometer or a Linnik interferometer, and may be another type of interferometer (for example, a Mach-Zehnder type).

[0078] The focus plane position adjuster provided on the optical path of the interference light from the beam splitter 12 as a multiplexer to the imaging surface of the imager 18 is not limited to the focus variable lens 17, and any device can be used as long as it can adjust the position of the focus plane F on the optical path of the first light beam from the beam splitter 12 as a branching unit to the beam splitter 12 as a multiplexer. Also, a plurality of focus plane position adjusters may be provided.

[0079] For example, the focus plane position adjuster may include a mechanism for changing the optical path length of the interference light from the beam splitter 12 to the imaging surface of the imager 18. Examples of such an interference optical path length changing mechanism include a mechanism for moving the imager 18 along the optical path of the interference light, and an electro-optical element whose refractive index changes according to an applied electrical signal.

[0080] Also, for example, the focus plane position adjuster may include a mechanism for changing the position of one or more lenses (for example, the objective lens 16 or the focus variable lens 17 in the first embodiment, the tube lens 23 or the focus variable lens 17 in the second or third embodiment) arranged on the optical path of the interference light along the optical path of the interference light. When a telecentric optical system is configured on the optical path of the interference light, a plurality of lenses constituting the telecentric optical system may be integrally moved along the optical path of the interference light.

[0081] The light source 11 may not be provided in the housing 30 and may be separate therefrom. In the latter case, for example, light output from a separately provided light source may be guided by an optical fiber, and parallel light may be output from a collimator provided at the light output end of the optical fiber toward the beam splitter 12.

Example

[0082] (First Embodiment) In the first embodiment, an apparatus having the same configuration as the interference image acquisition apparatus 1 of the first embodiment shown in FIG. 1 was used. The light source 11 used was an LED that outputs light with a central wavelength of 630 nm and a wavelength bandwidth of 30 nm, and the light output therefrom was narrowed to a narrow band with a central wavelength of 632 nm and a wavelength bandwidth of 1 nm. The focus variable lens 17 used had a magnification of 2 and was a lens capable of adjusting the working distance within a few millimeters.

[0083] FIG. 7 is a photograph of the object used in the first embodiment. An object with a metal washer placed on a 100-yen coin of Japan was used, and the first light beam reflected from the surface of this object and the second light beam reflected by the reference mirror 13 were combined to obtain an interference image in the range surrounded by the white rectangular frame in this photograph. The range surrounded by the white rectangular frame includes one Chinese character engraved on the 100-yen coin and a part of the metal washer around it.

[0084] First, the focus variable lens 17 was used to align the focus plane F with the bottom surface of the object (the surface of the area of the 100-yen coin where no Chinese character is engraved), and the position of the reference mirror 13 was adjusted by the stage 15 so that interference fringes could be obtained by the imager 18, thereby making the optical path length difference between the optical path length of the first light beam and the optical path length of the second light beam less than or equal to the coherence length of the light.

[0085] Thereafter, according to the timing chart shown in FIG. 2, the focus variable lens 17 was used to scan the position of the focus plane F along the optical path of the first light beam, and in cooperation with this, the stage 15 was used to scan the position of the reference mirror 13. At each position of the focus plane F during the scanning, the phase difference between the first light beam and the second light beam at the time of beam combination was changed in four steps by the piezo element 14, and four interference images I0 to I3 were obtained by the imager 18. The scanning of the position of the focus plane F was performed in 2-μm steps over a distance of 1000 μm, and 500 sets of interference images I0 to I3 were obtained.

[0086] FIG. 8(a) is a diagram showing an interference image I0 near the bottom surface of the object obtained in the first embodiment. FIG. 8(b) is a diagram showing an image representing the difference between the interference image I0 and the interference image I2 near the bottom surface of the object obtained in the first embodiment. FIG. 9(a) is a diagram showing an interference image I0 near the upper surface of the object obtained in the first embodiment. FIG. 9(b) is a diagram showing an image representing the difference between the interference image I0 and the interference image I2 near the upper surface of the object obtained in the first embodiment. Since the interference images I0 and I2 differ in phase difference by π, the difference between the two becomes an image in which interference fringes are emphasized.

[0087] FIG. 10(a) is a diagram showing an amplitude image near the bottom surface of the object obtained in the first embodiment. FIG. 10(b) is a diagram showing an amplitude image near the upper surface of the object obtained in the first embodiment. These amplitude images of the object were obtained from the four interference images I0 to I3 by the above formula (1).

[0088] FIG. 11 is a diagram showing an image of the three-dimensional image of the object obtained in the first embodiment as viewed from a certain direction. The amplitude image at each position of the scanning of the focus plane F was used as a Z-stack image, and the three-dimensional image of the object was obtained by three-dimensionally displaying this Z-stack image using 3D rendering software.

[0089] FIG. 12(a) is a diagram showing a phase image near the bottom surface of the object obtained in the first embodiment. FIG. 12(b) is a diagram showing an enlarged phase image of the region indicated by the rectangular frame in FIG. 12(a). This phase image of the object was obtained from the four interference images I0 to I3 by the above formula (2).

[0090] As shown in these figures, high-precision interference images, amplitude images, and phase images of the object were obtained at each position in the scanning direction from the bottom surface of the object (the surface of the 100-yen coin where no Chinese characters are engraved) to the upper surface (the upper surface of the metal washer), and the three-dimensional shape of the object could be visualized.

[0091] Also, as shown in the phase image of Fig. 12, the contour lines of the phase with a half-wavelength (315 nm) period can be clearly confirmed. By analyzing these contour lines, it was possible to quantify the fine nano-scale unevenness on the object while moving the focus plane F over 1 mm for the entire scan. Thus, since the mechanical stability is extremely high, the phase shift method can be realized with sufficient accuracy simply by changing the elongation amount of the piezo element, and the feedback control for phase difference stabilization, which was conventionally required, can be made unnecessary.

[0092] (Second Embodiment) In the second embodiment, the same apparatus as in the first embodiment was used, and a Kimwipe (registered trademark) manufactured by Nippon Paper Crecia Co., Ltd. was used as the object. At each position of the scan of the focus plane F, an interference image of the object was acquired to obtain an amplitude image and a phase image, and a three-dimensional image of the object was obtained.

[0093] In the second embodiment, the scan of the position of the focus plane F was performed in 1-μm steps over a distance of 200 μm, and 200 sets of interference images I0 to I3 were acquired. An amplitude image was obtained from each set of interference images I0 to I3, and a three-dimensional image of the object was obtained.

[0094] Figs. 13 and 14 are diagrams showing the amplitude images at each position in the scanning direction of the object obtained in the second embodiment. Let the amount of movement of the focus plane F from the start of the scan be z. Fig. 13(a) shows the amplitude image at the position where z = 40 μm, and Fig. 13(b) shows the amplitude image at the position where z = 70 μm. Fig. 14(a) shows the amplitude image at the position where z = 100 μm, and Fig. 14(b) shows the amplitude image at the position where z = 130 μm.

[0095] Fig. 15 is a diagram showing an image of the three-dimensional image of the object obtained in the second embodiment as viewed from a certain direction. The amplitude image at each position of the scan of the focus plane F was used as a Z-stack image, and the three-dimensional image of the object was obtained by three-dimensionally displaying this Z-stack image using 3D rendering software.

[0096] As shown in these figures, not only the reflective surface such as the metal of the object in the first embodiment but also the rough surface such as the wiper of the object in the second embodiment can obtain high-precision interference images, amplitude images, and phase images at each position in the scanning direction, and the three-dimensional shape of the object can be visualized.

[0097] (Third Embodiment) In the third embodiment, an apparatus having the same configuration as the interference image acquisition apparatus 3 of the third embodiment shown in FIG. 4 was used. The light source 11 used was an LED that outputs light with a central wavelength of 532 nm, and the light output therefrom was narrowed to a wavelength bandwidth of 3 nm. The focus variable lens 17 used was capable of modulating the refractive power within a range of up to ±2 diopters. The objective lens 21 used had a focal length of 9 mm. The tube lens 23 used had a focal length of 200 mm. The distance between the tube lens 23 and the imager 18 was set to 200 mm. The distance between the tube lens 23 and the focus variable lens 17 was set to 50 mm. The distance between the focus variable lens 17 and the objective lens 21 was set to 150 mm.

[0098] As shown in FIG. 5, the object was a 10% gelatin solution placed in a container 80 with resin beads having a diameter of 1 μm dispersed therein. This simulates floating cells in a culture solution. The lid 81 was a cover glass with a thickness of 170 μm, the thickness of the bottom of the container 80 was 400 μm, and the depth of the internal space of the container 80 was 150 μm.

[0099] For this object, in accordance with the timing chart shown in FIG. 6, first, the focal length of the focus variable lens 17 was adjusted so that the focus plane F was positioned on the reflecting surface of the object-side mirror 82, and the position of the reference-side mirror 13 was adjusted so that a clear interference image with appropriate contrast was acquired by the imager 18. Thereafter, the position of the focus plane F was scanned upward from the inner surface position (z = 0) of the bottom of the container 80 along the optical path of the first light beam by the focus variable lens 17. At each position of the focus plane F during the scanning, the phase difference between the first light beam and the second light beam at the time of multiplexing was changed in four steps by the piezo element 14, and four interference images I0 to I3 were acquired by the imager 18. The scanning of the position of the focus plane F was performed in 0.5-μm steps over a distance of 20 μm, and 40 sets of interference images I0 to I3 were acquired.

[0100] FIGS. 16 and 17 are diagrams showing interference images at the position of z = 7.0 μm of the object acquired in the third embodiment. FIG. 16(a) shows the interference image I0, and FIG. 16(b) shows the interference image I1. FIG. 17(a) shows the interference image I2, and FIG. 17(b) shows the interference image I3. FIG. 18 is a diagram showing a phase image at the position of z = 7.0 μm of the object obtained in the third embodiment. The gray scale corresponds to the phase value (-0.4 radian to +2.0 radians).

[0101] FIGS. 19 and 20 are diagrams showing interference images at the position of z = 10.0 μm of the object acquired in the third embodiment. FIG. 19(a) shows the interference image I0, and FIG. 19(b) shows the interference image I1. FIG. 20(a) shows the interference image I2, and FIG. 20(b) shows the interference image I3. FIG. 21 is a diagram showing a phase image at the position of z = 10.0 μm of the object obtained in the third embodiment. The gray scale corresponds to the phase value (-0.4 radian to +2.0 radians).

[0102] As shown in these figures, high-precision interference images and phase images of the object were obtained at each position in the scanning direction. In addition, a three-dimensional phase image of the object was also obtained.

Explanation of Reference Numerals

[0103] 1, 2, 3… interference image acquisition device, 11… light source, 12… beam splitter, 13… reference side mirror, 14… piezo element, 15… stage, 16… objective lens, 17… focus variable lens, 18… imager, 21, 22… objective lens, 23… tube lens, 24… stage, 30… housing, 31… support part, 40… arithmetic unit, 80… container, 81… lid, 82… object side mirror, 90… object, F… focus plane.

Claims

1. An incoherent light output from a light source is branched into a first light beam and a second light beam by a branching unit, and is supported by a support unit having an object-side mirror disposed inside or outside the bottom, and passes through an object disposed on the optical path of the first light beam and is reflected by the object-side mirror. A two-beam interferometer that combines the first light beam and the second light beam reflected by a reference-side mirror by a combining unit to output interference light; An imager having an imaging surface that receives the interference light output from the two-beam interferometer and acquires an interference image of the object; A focus plane position adjustment unit that adjusts the position of a focus plane conjugate to the imaging surface on the optical path of the first light beam from the branching unit to the combining unit by a focus variable lens provided on the optical path of the interference light from the combining unit to the imaging surface; An interference image acquisition device comprising:

2. In the two-beam interferometer, the optical path difference between the optical path length of the first light beam reflected by the object-side mirror and the optical path length of the second light beam reflected by the reference-side mirror is equal to or less than the coherence length of the light output from the light source. The interference image acquisition device according to claim 1.

3. Further comprising a reference-side mirror position adjustment unit that adjusts the position of the reference-side mirror in a direction perpendicular to the reflecting surface of the reference-side mirror. The interference image acquisition device according to claim 1 or 2.

4. Further comprising an arithmetic unit that obtains a phase image or an intensity image of the object based on the interference image acquired by the imager when the reference-side mirror is adjusted to each of a plurality of positions by the reference-side mirror position adjustment unit in a state where the focus plane is adjusted to a fixed position by the focus plane position adjustment unit. The interference image acquisition device according to claim 3.

5. The focus plane position adjustment unit scans the position of the focus plane along the optical path of the first light beam. The imager acquires an interference image at each position of the scan of the focus plane. The arithmetic unit obtains a phase image or an intensity image based on the interference image at each position of the scan of the focus plane, and obtains a three-dimensional image of the object based on these phase images or intensity images. The interference image acquisition device according to claim 4.

6. In a two-beam interferometer, incoherent light output from a light source is branched into a first light beam and a second light beam by a branching unit, and is supported by a support unit on which an object-side mirror is disposed inside or outside the bottom, and passes through an object disposed on the optical path of the first light beam and is reflected by the object-side mirror. An interference step of combining the first light beam and the second light beam reflected by the reference-side mirror by a combining unit to output interference light; An imaging step of acquiring an interference image of the object by an imager having an imaging surface that receives the interference light output from the two-beam interferometer; A focus surface position adjustment step of adjusting the position of a focus surface conjugate to the imaging surface on the optical path of the first light beam from the branching unit to the combining unit by a focus variable lens provided on the optical path of the interference light from the combining unit to the imaging surface, the focal length of which is variable; An interference image acquisition method comprising the steps of:

7. In the interference step, in the two-beam interferometer, the optical path length difference between the optical path length of the first light beam reflected by the object-side mirror and the optical path length of the second light beam reflected by the reference-side mirror is set to be equal to or less than the coherence length of the light output from the light source. The interference image acquisition method according to claim 6.

8. Further comprising a reference-side mirror position adjustment step of adjusting the position of the reference-side mirror in a direction perpendicular to the reflection surface of the reference-side mirror. The interference image acquisition method according to claim 6 or 7.

9. Further comprising an arithmetic step of obtaining a phase image or an intensity image of the object based on the interference image acquired in the imaging step when the reference-side mirror is adjusted to each of a plurality of positions in the reference-side mirror position adjustment step in a state where the focus surface is adjusted to a fixed position in the focus surface position adjustment step. The interference image acquisition method according to claim 8.

10. The focus surface position adjustment step scans the position of the focus surface along the optical path of the first light beam. The imaging step acquires an interference image at each position of the scan of the focus surface. The arithmetic step obtains a phase image or an intensity image based on the interference image at each position of the scan of the focus surface, and obtains a three-dimensional image of the object based on these phase images or intensity images. The interference image acquisition method according to claim 9.

Images