DIGITAL HOLOGRAPHY DEVICE AND DIGITAL HOLOGRAM GENERATION METHOD

Abstract

A generation method of a digital hologram includes steps of emitting coherent light from a coherent light source, imaging a hologram that is an interference pattern of an object beam and a reference beam due to the emission light from the light source, and setting a plurality of wavelengths of the illumination light that generates the hologram detected by the detector, and wherein the plurality of wavelength are specified by the wavelength setting step based on a magnification percentage X of a conjugate image set up by a user not to disturb visibility of an image when a real image and the conjugate image reconstructed by a predetermined calculation means relative to structures of observation targets are superimposed to a corresponding real image so that a shortest wavelength λ.sub.min and a longest wavelength λ.sub.max satisfy the expression λ.sub.max/λ.sub.min≧(1/X+1).

Claims

1. A digital holography device comprising: a) a light source that emits a coherent light; b) a detector that images a hologram that is an interference pattern of an object beam and a reference beam due to emitted light from said light source; and c) a wavelength setting means that sets up a plurality of wavelengths of an illumination light to generate a hologram being imaged by said detector; wherein the wavelength setting means specifies the plurality of wavelength, which are set up by the wavelength setting means based on a magnification percentage X set up by a user not to disturb a visibility thereof when a real image reconstructed by the preset calculation means and the conjugate image relative to a structure of the observation targets so that a shortest wavelength λ.sub.min and a longest wavelength λ.sub.max satisfy an expression λ.sub.max/λ.sub.min≧(1/X+1).

2. A digital holography device comprising: a) a light source that emits a coherent light; b) a detector that images a hologram that is an interference pattern of an object beam and a reference beam due to emitted light from said light source; and c) a wavelength setting means that sets up a plurality of wavelengths of an illumination light to generate a hologram being imaged by said detector; wherein said wavelength setting means specifies said plurality of wavelengths so that a shortest wavelength λ.sub.min and a longest wavelength λ.sub.max satisfy an expression λ.sub.max/λ.sub.min≧1.3.

3. The digital holography device, according to claim 2, wherein: said wavelength setting means specifies said plurality of wavelengths so that a shortest wavelength λ.sub.min and a longest wavelength λ.sub.max satisfy an expression 1.3≦λ.sub.max/λ.sub.min≦2.0.

4. A digital holography device, according to claim 1, wherein: said wavelength setting means is a switching element connected to a plurality of said light sources through an optical fiber and is used by switching the connected plurality of light sources.

5. A digital holography device, comprising: a) two light sources that emit coherent light beam together, wherein each emission wavelength λ.sub.1 and wavelength λ.sub.2 satisfy λ.sub.2/λ.sub.1≧1.3; and further comprising: b) a detector that images a hologram that is an interference pattern of a object beam and a reference beam due to each emitted light relative to said respective light sources; c) a wavelength setting means that specifies plurality of wavelengths of the illumination light, which generates a hologram being imaged by the detector; and d) a phase-restoration element that restores a phase by a light propagation calculation based on the hologram imaged relative to said both light sources.

6. A method of generation of a digital hologram, comprising steps of: a) emitting a coherent light from a light source; b) imaging a hologram that is an interference pattern of an object beam and a reference beam due to emitted lights from said light source by a detector; and c) specifying a plurality of wavelengths of illumination lights that generate a hologram being imaged by the detector; wherein the plurality of wavelength is specified by the wavelength specifying step based on a magnification percentage X set up by a user not to disturb a visibility thereof when a real image reconstructed by the preset calculation means and the conjugate image relative to a structure of the observation targets so that a shortest wavelength λ.sub.min and a longest wavelength λ.sub.max satisfy an expression λ.sub.max/λ.sub.min≧(1/X+1).

7. A method of generation of a digital hologram, comprising steps of: a) emitting a coherent light from a light source; b) imaging a hologram that is a interference pattern of a object beam and a reference beam due to emitted lights from; and c) specifying a plurality of wavelengths of illumination lights that generate a hologram being imaged by the detector; wherein said wavelength setting means specifies said plurality of wavelengths so that a shortest wavelength λ.sub.min and a longest wavelength λ.sub.max satisfy an expression λ.sub.max/λ.sub.min≧1.3.

8. A digital holography device, according to claim 7, wherein: said wavelength setting means that specifies said plurality of wavelengths so that a shortest wavelength λ.sub.min and a longest wavelength λ.sub.max satisfy an expression 1.3≦λ.sub.max/λ.sub.min≦2.0.

9. A method of generation of a digital hologram comprising steps of: preparing two light sources that emit coherent light beam together, wherein each emission wavelength λ1 and wavelength λ2 satisfy an expression λ2/λ1≧1.3; and further comprising: imaging a hologram that is an interference pattern of a object beam and a reference beam due to each emitted light relative to said both light sources; and performing a phase restoration by a light propagation calculation based on the hologram imaged relative to said both light sources.

10. A digital holography device, according to claim 1, wherein: said wavelength setting means is a switching element connected to a plurality of said light sources through an optical fiber and is used by switching the connected plurality of light sources.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0057] FIG. 1 is a schematic block diagram illustrating a measurement system comprising a digital holography device according to the aspect of the Embodiment of the present invention.

[0058] FIG. 2 is a flow-chart illustrating the processings performed by the measurement system referring to FIG. 1.

[0059] FIG. 3 is a flow-chart illustrating an example of the hologram imaging processing.

[0060] FIG. 4 is a flow-chart illustrating an example of the phase information calculation processing.

[0061] FIG. 5 is simulation results of an object image of an observation target having a variety of sizes, which is reconstructed by the measurement system referring to FIG. 1.

[0062] FIG. 6 is a schematic diagram illustrating the difference of the diffract angle of the incident light depending on the difference between pitch widths of the diffraction grating.

[0063] FIG. 7A is a schematic view illustrating a phenomenon in which a real image and a conjugate image reconstructed by a lightwave propagation calculation are superimposed to each other.

[0064] FIG. 7B is a schematic view illustrating a phenomenon in which a real image and a conjugate image reconstructed by a lightwave propagation calculation are superimposed to each other.

[0065] FIG. 8 is an explanation view illustrating that the light path is different between the high-frequency component and the low-frequency component, which is needed for phase restoration.

[0066] FIG. 9 is a graph illustrating a relationship between the original wavelengths λ.sub.A, λ.sub.B and the combined wavelength λ.sub.AB relative to the phase unwrapping.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0067] Reference will now be made in detail to embodiments of the invention. Wherever possible, same or similar reference numerals are used in the drawings and the description to refer to the same or like parts or steps. The drawings are in simplified form and are not to precise scale. The word ‘couple’ and similar terms do not necessarily denote direct and immediate connections, but also include connections through intermediate elements or devices. For purposes of convenience and clarity only, directional (up/down, etc.) or motional (forward/back, etc.) terms may be used with respect to the drawings. These and similar directional terms should not be construed to limit the scope in any manner. It will also be understood that other embodiments may be utilized without departing from the scope of the present invention, and that the detailed description is not to be taken in a limiting sense, and that elements may be differently positioned, or otherwise noted as in the appended claims without requirements of the written description being required thereto.

[0068] Various operations may be described as multiple discrete operations in turn, in a manner that may be helpful in understanding embodiments of the present invention; however, the order of description should not be construed to imply that these operations are order dependent.

[0069] FIG. 1 is a schematic block diagram illustrating a measurement system comprising a digital holography device according to the aspect of the Embodiment of the present invention. The measurement system comprises a digital holography device 100, a workstation 1 that is communicably connected to the digital holography device 100.

[0070] [Structure of the Digital Holography Device 100]

[0071] The digital holography device 100 that is a microscope comprises the number N of laser diode (LD) 101(1)-101(N), a switching element 102 (corresponds to the wavelength setting means of the present invention), an irradiation element 103, a detector 104 and an interface (I/F) 105.

[0072] Any LD101(1)-101(N) is a light source that oscillates and emits coherent beam and oscillation wavelengths λ1-λN thereof are specified to be longer in order. Such LD101(1)-101(N) are connected to the switching element 102 via an optical fiber.

[0073] The switching element 102 switches the LD101(1)-101(N), which is used as the light source of the illumination light 120, according to the directive from the workstation 1.

[0074] The irradiation element 103 irradiates the illumination light 120, as specified above, toward the object 110. In addition, in a practical measurement, the illumination light 120 passes through the (culture) plate and culture medium other than the object 110, so such components should be also made of light transmissive material.

[0075] The detector 104 images the interference pattern due to the illumination light 120 emitted from the irradiation element 103 as a hologram. The hologram is a record of the interference pattern emerging from the object beam (arc lines depicted in the right-side of the object 110 in FIG. 1) which is the light wave diffracted by the object 110 and the reference wave (straight lines in the right-side of the object 110) which is the not-diffracted light wave (including transmitted light). The detector 104 can be brought into reality by e.g., CCD (charge-coupled devices) image sensor.

[0076] (Structure of the Workstation 1)

[0077] The workstation 1 is practically a true computer comprising a CPU central processing unit) connecting a memory 12, a monitor made of LCD (liquid crystal display) and so forth, an input element 16 including a mouse and a memory storing element 20 each other. Subsequently, the above memory comprises a volatile memory such as RAM (access memory), and the memory storing element 20 comprises non-volatile memory such as a ROM (read only memory), a flash memory, a EPROM (erasable programmable ROM), EEPROM® (electrically EPROM), a HDD (hard disc drive), a SSD (solid state drive) and so forth. An imaging control-data analysis program 21 is installed to the memory storing element 20. Each element that the imaging control-data analysis program 21 comprises is a feasible functional means when CPU 10 reads out the program into the memory 12 and execute. In addition, the memory storing element 20 stores OS (operating system) 29.

[0078] The workstation 1 comprises an interface (I/F) 18 that is operative to connect directly to the outside devices and to the outside devices through a network such as a LAN (local area network), and connects to the digital holography device 100 through the network cable NW (or wireless LAN) from I/F18. In addition, the workstation 1 can connect multiple digital holography devices 100. In addition, the workstation 1 can connect directly multiple digital holography devices 100 via USB cable and so forth.

[0079] The imaging control-data analysis program 21 is an application software for controlling imaging by the digital holography device 100, reconstructing the image of the object 110 by the predetermined operation processing based on the imaged hologram, and displaying the reconstructed image on the monitor 14 as an image.

[0080] Referring to FIG. 1, in accordance with the imaging control-data analysis program 21, the imaging parameter setting element 31, the imaging directive element 32, the hologram acquisition element 33, the phase information calculation element 34, the image generation element 35, the display control element 36 and the hologram memory storing element 37. In addition, the imaging control-data analysis program 21 needs not always be a simplex program, and can be a functional part of elements of the digital holography device 100.

[0081] [Processing Flow in the Measurement System]

[0082] Referring to FIG. 2-FIG. 4, hereinafter, the inventor sets forth a flow of the processings executed by the measurement system including the digital holography device 100 according to the aspect of the present Embodiment.

[0083] First, referring to FIG. 2, the inventor sets forth the flow of the basic processings executed by the imaging control-data analysis program 21. Once the imaging control-data analysis program 21 starts, the user first is requested to input the value of the central wavelength λ.sub.mid of the hologram imaging. The input value of the central wavelength λ.sub.mid can be not only an arbitrary input value, but also any selected value of the number N of LD101(1)-101(N) pre-installed to the digital holography device 100 of the present invention. Once the user inputs the central wavelength λ.sub.mid through the input element 16 (Step S11), the imaging control-data analysis program 21 requests, subsequently, to input the value of the area magnification ratio X.sup.2 of the conjugate image (magnification percentage X). Similarly, not only an arbitrarily value can be input, but also the value can be selected from the list of the pre-registered values displayed on the monitor 14. Once the user inputs the value of the area magnification ratio X.sup.2 (or magnification percentage X) through the input element 16 (Step S12), the imaging parameter setting element 31 of the imaging control-data analysis program 21 selects a plurality of the LD light sources from the LD101(1)-101(N) as the central wavelength λ.sub.mid to satisfy the above expression 9. Specifically, if the selected light sources are LD101(J1)-101(J2), the wavelength λ.sub.J1 of LD101(J1)-wavelength λ.sub.J2 LD101(K2) satisfies

λ.sub.J2/λ.sub.J1≧1/X+1,

average(λ.sub.J1, . . . ,λ.sub.J2)≈λ.sub.mid.

[0084] According to the aspect of the present Embodiment, the object 110 of the imaging target is a colony of the induced pluripotent stem cell such as ES cells and iPS cells and so forth. And the inventor sets forth as given the value of the area magnification ratio X.sup.2 of the conjugate image is 10 (√10 as magnification percentage). The reason for the decision is that when the object 110 of the observation targets is the cell colony, the area between the real image and the superimposed conjugate image thereon, which is approximately 10 times as large as the real image, can be satisfactory to provide the clear shape-image based on the result of a preliminary experiment. On the other hand, if the difference between the shortest wavelength λmin and the longest wavelength λ.sub.max is too big, as set forth before, a part of the diffracted light is going out of the detection plane, so that such incident can be an factor to lessen the degree of accuracy of phase restoration. The imaging parameter setting element 31 selects the light source LD101(J1)-101(J2) giving the expression of 1.3(=1/√10+1)≦λ.sub.max/λ.sub.min=λ.sub.J2/λ.sub.J1≦2.0 at the step S13 under considering such conditions. In addition, the wavelength input by the user at the above step can be the shortest wavelength λmin or the longest wavelength λ.sub.max instead of the central wavelength λ.sub.mid. In addition, in the case of cell observation, a visible region (approximately 600 nm) is appropriate to avoid a low wavelength region concerned about a toxicological effect or a far-infrared region concerned about heat generation due to absorption of light, but such value is not particularly an issue in regard to the below explanation.

[0085] In such way, a hologram imaging processing is executed (Step S14) following section of the light source to be used. Referring to FIG. 3, the inventor set forth further detail of the above step.

[0086] First of all, j=J1 (J1≦j≦J2) is given (Step S101) and the imaging parameter setting element 31 specifies the wavelength of the illumination light 120 (referring to FIG. 1) emitted from the irradiation element 103 as λj (Step S102). Subsequently, the imaging directive element 32 directs the digital holography device 100 to image a hologram image of λj (Step S103). The above directive by the imaging directive element 32 is sent to an I/F105 of the digital holography device 100 from the I/F18 as the imaging directive signal (Step S104).

[0087] Once the I/F105 installed to the digital holography device 100 receives the above imaging directive signal, the switching element 102 switched the light source for the illumination light 120 to the number j of LD101(j) (Step S105). Subsequently, the irradiation element 103 irradiates the illumination light 120 toward the object 110 (Step S106). Then, the interference pattern between the diffracted object beam by the object 110 and the non-diffracted reference wave is imaged by the detector 104 (Step 107). The imaged hologram data is sent to the I/F18 of the workstation 1 via I/F/105 (Step 108).

[0088] Once the I/F18 installed to the workstation 1 receives the above hologram data, the hologram acquisition element 33 acquires the received hologram data and stores in the hologram memory storing element 37 (Step S109). The hologram memory storing element 37 collectively stores a plurality of hologram data (J2−J1+1 according to the aspect of the present Embodiment) applied for the phase information calculation processing, set forth later, and reconstruction of the object image every measurement targets designated by the user.

[0089] Once the hologram data is stored, the imaging parameter setting element 31, subsequently, increments j (Step S110) and unless the value j is beyond the maximum value J2 (Step 111), the processing turns back to right before the Step 102 and then the steps S102-S111 are executed relative to the next wavelength λ.sub.j.

[0090] On the other hand, following the incrementation result at the step S110, if j is bigger than j2 (Yes at Step 111), such decision means that the hologram data corresponding to all light wavelengths between λ.sub.J1-λ.sub.J2 set up at the step S100 are in order.

[0091] Referring to FIG. 2 again, once the hologram imaging processing (Step S14) in such way is completed, the phase information calculation element 34 subsequently executes the phase information calculation processing to the respective hologram data (Step S15). The inventor sets forth the detail of the processing at the present step later referring to FIG. 4.

[0092] Once the phase is restored relative to each hologram data at the step S15, the image generation element 35 reconstructs the object image based on the hologram data following such phase restoration (Step S16). The reconstructed object image (hereafter reconstructed image) is displayed on the monitor 14 by the display control element 36 (Step S17). At this point, the general processings due to the measurement system complete.

[0093] (Flow of the Phase Information Calculation Processing]

[0094] Referring to FIG. 4, one example of the flow of phase information calculation processing at the above step S15 is illustrated. Such phase information calculation processing is executed based on the number (J2−J1+1) of the hologram data stored in the hologram memory storing element 37 at the step 109.

[0095] First, the phase information calculation element 34 converts each hologram to an amplitude image (Step 201). The hologram that is a distribution of intensity values, so the hologram cannot be applied to a Fourier transform used in the propagation calculation set forth later. Therefore, each intensity value is converted to an amplitude value at the present step. The conversion to the amplitude image is performed by calculation of the square root of each pixel value.

[0096] Subsequently, the phase information calculation element 34 specifies a default value of the phase image at the detection plane as j=1, a=1, n=1. The default value of the phase image can be arbitrarily and, for example, all pixel values can be specified as null or each pixel value can be specified randomly. In addition, j (1≦j≦J2) is a discriminator of LD101, which is the light source of the illumination light 120, as well as set forth above, a is a direction value having either 1 or −1, and n (1≦n) is the repetition number of the operation.

[0097] Subsequently, the phase information calculation element 34 updates the amplitude image of λ.sub.j (Step S203). Specifically, the amplitude image obtained by the conversion of the intensity value at the step S201 is substituted. According to the processing referring to FIG. 4, an expression of “update” corresponding to the update of j is used, but if j=j1 is given, the expression of “substitute” is likely more appropriate.

[0098] Subsequently, the phase information calculation element 34 calculates a reverse propagation to the object plane (Step S204).

[0099] Subsequently, the phase information calculation element 34 determines whether or not a value of j+a is in the range of J1-J2 (Step S205). Here, given the value of J2 is 5, the value of j+a is 2 at the first test, so that the decision is “Yes” at the step S205 and consequently the j is incremented (Step S207). In such way, when the repetition of increment results in 5, specifically, J equals to J2, j+1 is 6 that is over J2, so that decision at the step S205 results in “No”. At such stage, the phase information calculation element 34 reverses plus and minus of a (Step S206) and decrements j (Step S207). If the value of j decreases until 1 due to repetition of the decrement at the step S207, the decision at the step S205 results in “No”, so that plus and minus of a reverse again at the step S2067. Consequently, according to the present flow-chart, the reverse of plus and minus of a is repeated followed by reverse repetition of increment and decrement.

[0100] As set forth above, when J=1, j is incremented to give 2 at the step S207. Subsequently, the phase information calculation element 34 updates the phase of the object beam due to λ.sub.j (Step S208). Specifically, relative to the complex wavefront relative to the object plane calculated at the step S204, the phase is converted to the next wavelength (without updating the amplitude). In such way, under the condition in which only the phase is converted to the next wavelength, propagation to the detection plane is calculated (Step S209), and when the sum of differences (i.e., errors) between the calculation result and the actual measurement value, which is the square root of each intensity value of the hologram, is bigger than the threshold value ε (“No” at the step S210), the phase information calculation element 34 increments n (Step S221) and repeats the above processings.

[0101] On the other hand, if the sum of errors is smaller than the threshold value ε (“Yes” at the step S210), the phase information calculation element 34 deems that the satisfactory phase restoration is obtained and ends the phase information calculation processing.

[0102] Simulation results of the object images that are reconstructed according to the above method are illustrated in FIG. 5. All images are simulation results of phase restoration and reverse propagation using the USAF chart hologram model, and the simulation result 51 is illustrating the case when the reverse propagation (400 nm) takes place without phase restoration; the simulation result 52 is illustrating the case when the phase is restored at 400 nm and 520 nm (λ.sub.max/λ.sub.min=1.3) and the reverse propagation takes place with phase restoration; the simulation result 53 is illustrating the case when the phase is restored at 400 nm and 800 nm (λ.sub.max/λ.sub.min=2.0) and the reverse propagation takes place with phase restoration; and the simulation result 54 is illustrating the case when the phase is restored at 400 nm, 520 nm and 800 nm (λ.sub.max/λ.sub.min=2.0, and at three wavelengths) and the reverse propagation takes place with phase restoration. When λ.sub.max/λ.sub.min≧1.3 is given, an remarkable phase restoration is observed. In addition, a positive effect due to increase of the number of wavelengths within such range is found.

Alternative Embodiment

[0103] According to the aspect of the Embodiment as set forth above, adequate light sources LD101(J1)-101(J2) from a number of laser diodes LD101(1)-101(N) corresponding to the central wavelength λ.sub.mid (or the longest wavelength λ.sub.max or the shortest wavelength λ.sub.min) and the magnification percentage X input by the user are selected and used by switching the light sources, but such setting of freedom is not required and when an imaging (observation) target is pre-determined, only a plurality of light sources pre-registered according to the expression 9 is installed to the digital holography device 100 and only such light sources are allowed to be employed. In such scenario, the number of light sources (number of wavelengths) are set to 2 so that the calculation time is shortened, and when such defect of the cell colony and so forth is examined as set forth above, practically and satisfactorily clear image reconstruction can be accomplished.

REFERENCE OF SIGNS

[0104] 10 FPD [0105] 12 Memory [0106] 14 Monitor [0107] 16 Input element [0108] 18 I/F [0109] 20 Memory element [0110] 21 Imaging control-data analysis program [0111] 31 Imaging parameter setting element [0112] 32 Imaging directive element [0113] 33 Hologram acquisition element [0114] 34 Phase information calculation element [0115] 35 Image generation element [0116] 36 Display control element [0117] 37 Hologram memory storing element [0118] 100 Digital holography device [0119] 101(1)-101(N) Laser diode (LD) [0120] 102 Switching element [0121] 103 Irradiation element [0122] 104 Detector [0123] 105 I/F [0124] 110 Object [0125] 120 Illumination light

[0126] It will be further understood by those of skill in the art that the apparatus and devices and the elements herein, without limitation, and including the sub components such as operational structures, circuits, communication pathways, and related elements, control elements of all kinds, display circuits and display systems and elements, any necessary driving elements, inputs, circuits, sensors, detectors, memory elements, processors and any combinations of these structures etc. as will be understood by those of skill in the art as also being identified as or capable of operating the systems and devices and subcomponents noted herein and structures that accomplish the functions without restrictive language or label requirements since those of skill in the art are well versed in related digital holography devices and generation methods for the same, including, computer and operational controls and technologies of radiographic devices and all their sub components, including various circuits and combinations of circuits without departing from the scope and spirit of the present invention.

[0127] Although only a few embodiments have been disclosed in detail above, other embodiments are possible and the inventors intend these to be encompassed within this specification. The specification describes certain technological solutions to solve the technical problems that are described expressly and inherently in this application. This disclosure describes embodiments, and the claims are intended to cover any modification or alternative or generalization of these embodiments which might be predictable to a person having ordinary skill in the art.

[0128] Those of skill would further appreciate that the various illustrative logical blocks, modules, circuits, and algorithm steps described in connection with the embodiments disclosed herein may be implemented as electronic hardware, computer software running on a specific purpose machine that is programmed to carry out the operations described in this application, or combinations of both. To clearly illustrate this interchangeability of hardware and software, various illustrative components, blocks, modules, circuits, and steps have been described above generally in terms of their functionality. Whether such functionality is implemented as hardware or software depends upon the particular application and design constraints imposed on the overall system. Skilled artisans may implement the described functionality in varying ways for each particular application, but such implementation decisions should not be interpreted as causing a departure from the scope of the exemplary embodiments.

[0129] Having described at least one of the preferred embodiments of the present invention with reference to the accompanying drawings, it will be apparent to those skills that the invention is not limited to those precise embodiments, and that various modifications and variations can be made in the presently disclosed system without departing from the scope or spirit of the invention. Thus, it is intended that the present disclosure cover modifications and variations of this disclosure provided they come within the scope of the appended claims and their equivalents.