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Multimodal optical microscopy combines different optical and physiological principles working together to obtain rich perspectives from a single biological event. In this paper, the recent advances in multimodal microscopy systems based on off-axis digital holography and transport-of-intensity equation are reviewed. Both methods used the common-path configuration, and realized simultaneous quantitative phase and fluorescence imaging in 3D space. Feasibility checks with fluorescent micro-beads and live plant cells are presented. The results show that both methods are capable of fast acquisition of the quantitative phase and fluorescence information with digital refocusing ability.

Spatiotemporal information about light pulse propagation obtained with femtosecond temporal resolution plays an important role in understanding transient phenomena and light–matter interactions. Although ultrafast optical imaging techniques have been developed, it is still difficult to capture light pulse propagation spatiotemporally. Furthermore, imaging through a three-dimensional (3-D) scattering medium is a longstanding challenge due to the optical scattering caused by the interaction between light pulse and a 3-D scattering medium. Here, we propose a technique for ultrafast optical imaging of light pulses propagating inside a 3D scattering medium. We record an image of the light pulse propagation using the ultrashort light pulse even when the interaction between light pulse and a 3-D scattering medium causes the optical scattering. We demonstrated our proposed technique by recording converging, refracted, and diffracted propagating light for 59 ps with femtosecond temporal resolution.

We have proposed a new configuration of the single-shot, dual-wavelength, common-path, off-axis DHM system. The proposed system is used for decoupling the refractive index and thickness of a biological specimen.

Sound is an important invisible physical phenomenon that needs to be explained in several physical and biological processes, along with visual phenomena. For this purpose, multiparameter digital holography (DH) has been proposed to visualize both features simultaneously due to the phase and amplitude reconstruction properties of DH. In this paper, we present a brief review on sound field imaging techniques with special focus on the multiparameter imaging capability of DH for visualizing sound and visual features. The basic theory and several experimental results with very high-speed recordings are also presented to demonstrate sound field imaging for the audible range as well as in the ultrasound range.

Upregulation of N-type Ca2+ channel dependent subunits increases functional connections and synchronization for pain formation., Sustained neuropathic pain from injury or inflammation remains a major burden for society. Rodent pain models have informed some cellular mechanisms increasing neuronal excitability within the spinal cord and primary somatosensory cortex (S1), but how activity patterns within these circuits change during pain remains unclear. We have applied multiphoton in vivo imaging and holographic stimulation to examine single S1 neuron activity patterns and connectivity during sustained pain. Following pain induction, there is an increase in synchronized neuronal activity and connectivity within S1, indicating the formation of pain circuits. Artificially increasing neuronal activity and synchrony using DREADDs reduced pain thresholds. The expression of N-type voltage-dependent Ca2+ channel subunits in S1 was increased after pain induction, and locally blocking these channels reduced both the synchrony and allodynia associated with inflammatory pain. Targeting these S1 pain circuits, via inhibiting N-type Ca2+ channels or other approaches, may provide ways to reduce inflammatory pain.

The demand for single-shot and common-path holographic systems has become increasingly important in recent years, as such systems offer various advantages compared to their counterparts. Single-shot holographic systems, for example, reduce computational complexity as only a single hologram with the object information required to process, making them more suitable for the investigation of dynamic events; and common-path holographic systems are less vibration-sensitive, compact, inexpensive, and high in temporal phase stability. We have developed a single-shot common-path off-axis digital holographic setup based on a beam splitter and pinhole. In this paper, we present a concise review of the proposed digital holographic system for several applications, including the quantitative phase imaging to investigate the morphological and quantitative parameters, as a metrological tool for testing of micro-optics, industrial inspection and measurement, and sound field imaging and visualization.

Integrated multimodal cross-sectional or volumetric imaging techniques give us fruitful information to understand the behavior or status of target objects such as biological samples. Most of the reported systems for this purpose are either time consuming due to scanning or use additional reference beams such as in interferometry. Therefore, fast, simple, highly efficient, and powerful multimodal imaging systems that can perform cross-sectional imaging with simple algorithms are worth to be investigated. In this paper, a multimodal technique for cross-sectional quantitative phase and fluorescence imaging with computational microscopy is presented. We combine cross-sectional fluorescence and quantitative phase imaging by using the transport of intensity equation (TIE) and numerical wave propagation. The amplitude and phase of the fluorescence light wave with partially spatial coherence are obtained from three defocused intensity patterns. The proposed hybrid imaging system is simple, compact, and non-iterative. We present experimental results of microbeads and fluorescent proteinlabeled living cells of the moss Physcomitrella patensto demonstrate the performance of the proposed imaging system.

In this presentation, we briefly review the fluorescence and the phase imaging techniques based on computational imaging such as digital holography and transport of intensity equation. These techniques uses an image sensor to capture the hologram or the intensity distribution and it enables more faster recording than the point-scanning methods. The presented techniques have also an advantage to refocus the images by applying an appropriate distance. Some experimental results are provided to show the effectiveness of the methods. Multimodal three-dimensional imaging is also presented.

The authors review three-dimensional (3D) trajectory of minute object by parallel phase-shifting digital holography. Parallel phase-shifting digital holography is a technique capable of single-shot recording of a complex amplitude distribution of object wave from a dynamic object. The authors constructed an inverted microscope based on parallel phase-shifting digital holography. The microscope consisted of a continuous-wave laser, a Mach–Zehnder interferometer, a polarization imaging camera, and a magnification optical system. A high-speed polarization imaging camera was employed to record motion picture of holograms of the dynamic specimen. Motion picture of the holograms of a minute alum crystal sinking down in the solution of alum was recorded by the microscope at the rate of 60 frames per seconds (FPS). Refocused images of the crystal were successfully obtained for all of the sinking time. The 3D trajectory of the crystal was derived from the refocused images. Also, the authors constructed an inverted and vertical microscope based on parallel phase-shifting digital holography. A Volvox swimming in a water as a living microbe was recorded by the microscope at the rate of 1000 FPS. The 3D trajectory of the microbe curvedly moving in the area of 500 μm × 500 μm × 500 μm was successfully demonstrated from the reconstructed images of the microbe.

In this work, we evaluate quantitatively the three-dimensional fluorescence imaging based transport of intensity equation (TIE). In the TIE-based fluorescence imaging, phase information from the recorded defocus fluorescence images is retrieved by solving the phase retrieval algorithm. From the retrieved phase data and their corresponding fluorescence image, the complex function can reconstructed. Focus images at different distances can be obtained after applying numerical inverse Fresnel propagation of complex function. For the quantitative evaluation of retrieved focus images, we calculate cross correlation coefficients to check intensity conservation.

A single-shot common-path off-axis self-interference dual-wavelength digital holographic microscopic (DHM) system based on a cube beam splitter is demonstrated to expand the phase range in a stepped microstructure and for simultaneous measurement of the refractive index and physical thickness of a specimen. In the system, two laser beams with wavelengths of 532 nm and 632.8 nm are used. These laser beams are combined to transilluminate the object under study, then the object beam is divided into two beams by using a beam splitter oriented in such a way that both the beams propagate in almost the same direction, with an appropriate lateral separation between them. One of the object beams is spatially filtered at its Fourier plane, using a pinhole to generate a reference spherical beam free from the object information. The reference beam interferes with the object beam to form a digital hologram at the faceplate of the image sensor. The phase information is extracted from a single recorded digital hologram using the phase aberration compensation method that is based on principal component analysis (PCA). Owing to the common-path configuration, the system shows high temporal phase stability and it is less vibration-sensitive compared to counterparts such as a Mach–Zehnder type DHM. The performance of the dual-wavelength DHM system is verified in two different application fields by conducting the experiments using microsphere beads and living plant cells.

A single-shot common-path off-axis multi-wavelength digital holographic microscopic (MW-DHM) system for phase imaging of biological specimens is proposed. The DHM system is based on a cube beam splitter which divides the object beam into two beams: one beam is spatially filtered at its Fourier plane to make a reference spherical beam and another beam acts as the object beam. Three wavelengths: 473, 532, and 632.8 nm are used to illuminate the object under observation. The obtained experimental results on various objects corroborate the imaging capability of the proposed single-shot common-path off-axis multi-wavelength MW-DHM system. The proposed system may open new possibilities in bio-imaging and real-time simultaneous measurement of various parameters including the thickness, refractive index, etc.

Non-interferometric three-dimensional (3D) fluorescence imaging techniques for bio-applications are presented. For bioapplications, the efficient illumination is very important to avoid the damage of living cells. We have proposed a method to obtain the complex amplitude of the fluorescence light wave with partially coherence by using the transport of intensity equation (TIE). We will show some experimental results of the reconstructed fluorescence distributions of fluorescence beads and living plant cells by TIE.

We demonstrate the performance of nonlocal means (NLM) and its related adaptive kernel-based methods for speckle denoising for the intensity and phase images acquired from the digital speckle pattern interferometric (DSPI) and digital holographic interferometric (DHI) techniques, respectively. The speckle denoise capabilities of NLM and its variant denoising methods such as NLM-average (NLM-av), NLM-local polynomial regression (NLM-PLR), and NLM-shape adaptive patches (NLM-SAP), and various NLM-reprojection schemes are implemented on simulated. Their performances are quantified on the basis of two metric criteria – peak signal-to-noise ratio (PSNR) and the image quality index (Q). The effectiveness of these denoising methods is compared with other existing speckle denoising methods. The obtained results suggest that these denoising methods have the ability to denoise speckles from the DSPI/DHI fringes and provide better visual and quantitative results.

Phase-shifting interferometry is a highly accurate technique for obtaining phase distribution from the recorded fringe patterns. Generally, phase-shifting interferometry requires recording several fringe patterns with varying phase shifts experimentally and during the acquisition, the object must be stable. Also, the atmospheric turbulence and mechanical conditions should also remain constant during this time. These requirements limit the use of these phase-shifting interferometric techniques in dynamic event studies. In the present work, we introduce Riesz transformed based digital four-step phase-shifting interferometer to obtain phase distribution from a single recorded fringe pattern. All the experimental phase-shifting setups necessary to realize the phase-shifting are removed. The idea is based on the recording of a single fringe pattern, and computes its Riesz transform at first, second and third-orders. The obtained Riesz transform components are combined to generate three π/2 phase-shifted fringe patterns, and then, the phase distribution is obtained from these phase-shifted fringe patterns. The performance of this method is demonstrated first by using numerical simulation and the quantitative appraisal is given by using image quality index. Further, we apply this technique on a real fringe pattern recorded in digital speckle pattern interferometry (DSPI). The obtained results reveal that our method provides a simple and accurate solution for phase evaluation, therefore, makes it suitable for real-time measurements.

In this manuscript, the astigmatism of the waveguide combiner with a pair of symmetry HOEs was analyzed. The light field can be predicted by the modified convolution formulation of Fresnel diffraction when the information of light passes through the astigmatism causing element. Then the astigmatism can be corrected. The theory was experimentally proved by the system with a phase-only SLM and a diffraction planar waveguide. Furthermore, the image quality of astigmatism corrected phase-type CGHs can be improved via the iteration process. Since the coherence of light source was employed, the temporal averaging method was utilized to avoid speckle noise.

A method for single pixel imaging suitable for high definition imaging is demonstrated. The experimental system consists of a laser with two dimensional scanning, a digital micro-mirror device, a condenser lens, and a photo detector. It is shown that the system can output an image with 1024 X 1024 pixels.

A new type of functional optical microscope system called three-dimensional (3D) stimulation and imaging-based functional optical microscopy (SIFOM) is proposed, to the best of our knowledge. SIFOM can precisely stimulate user-defined targeted biological cells and can simultaneously record the volumetric fluorescence distribution in a single acquisition. Precise and simultaneous stimulation of fluorescent-labeled biological cells is achieved by multiple 3D spots generated by digital holograms displayed on a phase-mode spatial light modulator. Single-shot 3D acquisition of the fluorescence distribution is accomplished by common-path off-axis incoherent digital holographic microscopy in which a diffraction grating with a focusing lens is displayed on another phase-mode spatial light modulator. The effectiveness of the proposed functional microscope system was verified in experiments using fluorescent microbeads and human lung cancer cells located at various defocused positions. The system can be used for manipulating the states of cells in optogenetics.

A new, to the best of our knowledge, configuration of common-path off-axis digital holography is proposed for simultaneous evaluation of out-of-plane and in-plane displacements of the vibrating object. The object is illuminated from two different directions, and each illumination interferes with its corresponding reference beam generated near the object, resulting in two independent holograms that are spatially multiplexed in a single camera image. Two multiplexed holograms, at undeformed and deformed states of the object, are recorded and processed to obtain the out-of-plane and in-plane displacements simultaneously. The proposed digital holographic system has the advantage of a simple and compact optical setup, is less sensitive to environmental disturbances, and has high temporal phase stability. The two-dimensional ( z , x ) full-field amplitude and phase vibration analysis of a perfect specularly reflecting surface are also demonstrated by the proposed holographic system. The experimental results authenticate the feasibility of the proposed system and reveal its unique advantages. The proposed digital holographic system, owing to simple and compact geometry and providing several advantages over other two-channel holographic systems, may find a wide range of applications in investigating real-time dynamic phenomena.

This paper proposes a binocular holographic floating display. The device consists of two phase-modulation spatial light modulators (SLM) and a dihedral corner reflector array (DCRA) element. The conjugate images of the SLMs generated by the DCRA become the system’s exit pupils. Exit pupils that are larger than the pupils of human eyes are arranged to locate at the position of observer's eyes. Therefore, the dimension of the SLM will not limit the viewing angle, although the pixel pitch of the SLM still limits the maximum field of view. For the laser light source, the resolution of the images can achieve 3 arc minutes when the distance between images and DCRA is less than 20 cm. The full-color display function is also performed in the proposed device.

Measurement of surface shape and refractive index for moving transparent objects is critical in various fields. A parallel phase-shifting digital holography system that can record and reconstruct the phase information of moving transparent objects using two high-resolution polarization imaging cameras was presented. In the developed system, two polarization imaging cameras with 3.45 µm pixel pitch passed through the object in different directions. These two polarization imaging cameras were controlled by LabVIEW and worked synchronously. The proposed system can obtain the object's integral phase distributions in different directions, which is more effective for measuring an asymmetric object. In the experiment, the resolution of the system was confirmed by using a transmission-type test target. Besides, the dynamic phase measurement of an irregularly shaped transparent object was completed to verify the proposed system's effectiveness.

Digital holography provides a method of the 3-D recording and numerical reconstruction by a simple optical system and a computer. Quantitative measurement and numerical refocusing are major characteristics. So far, many physical parameters such as amplitude, phase, polarization, fluorescence, and spectra can be obtained independently. Recently, multimodal imaging that can obtain simultaneously two or more physical parameters by combining digital holographic microscope and other optical microscopes such as a fluorescence optical microscope and a Raman scattering microscope has emerged. In this review, physical parametric imaging techniques based on digital holography are presented and then these techniques are enhanced to develop multimodal imaging based on digital holography.

A Hamiltonian-based ray tracing technique is applied to the evaluation of the performance of cloaking devices with arbitrary shapes based on full-mesh representation. The constitutive parameters of cloaking devices are calculated by the finite element method. The cloaking characteristics of a double cylindrical cloaking device and a huge cloaking device with a completely arbitrary shape are evaluated. The numerical results showed that fine mesh structure is required for better cloaking performance. The full-mesh representation is useful for fabrication design.

The extraction of multi-dimensional information from a biological specimen in the single examination is always beneficiary for extending the in-depth understanding of the specimen. This leads to increase the demand of multimodal imaging systems in recent years. Several multimodal imaging systems have been developed according to the requirements. We have developed multimodal imaging systems based on digital holography, for retrieving simultaneously the quantitative phase and 3D fluorescence imaging of the biological specimen, enabling to extract the specimen’s structural and functional information in a single examination. We have developed the multimodal system by integrating the coherent and incoherent digital holographic microscopes for retrieving simultaneously the phase and 3D fluorescence imaging, respectively.

Computational ghost imaging (CGI) is one of several attractive techniques for optical measurement because it can determine two-dimensional structures of target objects without using an image sensor. However, conventional CGI is not suitable for practical use in terms of measurement time. In this paper, we report on reducing the optical measurement time in CGI and propose a new CGI implementation. The proposed method utilizes the wide bandwidth of laser diodes. We can obtain a set of speckle patterns required in computational ghost imaging in a significantly shorter time by changing emission patterns. Consequently, this method is suitable for high-speed measurements. The concept of the method is described and verified by numerical analysis. Further, optical setup for the experimental verification is assembled. As verified with experiments and signal processing, the proposed method can provide reconstructed images of targets.

3D fluorescence imaging based on incoherent digital holography is very useful in the biological field. We have proposed a common-path and off-axis incoherent digital holography using a diffraction grating embedded with a lens to make the self-interference pattern. Based on the observation of the fluorescence image, active illumination of the holographic method is more efficient to avoid unwanted exposure to another area. We present the feasibility experiment to show the potential characteristics of our proposed system.

In this Letter, a concept of new multi-parameter imaging that can acquire visual and audio data of dynamic object phenomena simultaneously by a holographic technique is proposed. Temporal intensity distributions give us visual information of the dynamic events. The temporal profile of the phase distribution can give different information of the dynamic events, such as audio data. These two physical data can express the dynamic events with multi-parameters in various dimensions. The proposed imaging approach has potential in several applications in physics and life science research. Two experimental demonstrations such as static object and broken glass with visual and sound features are provided to show the effectiveness of the proposed concept.

Significance: Parallel phase-shifting digital holographic microscope (PPSDHM) is powerful for three-dimensional (3D) measurements of dynamic specimens. However, the PPSDHM reported previously was directly fixed on the optical bench and imposed difficulties case, thus it is required to modify the specification of the microscope or transport the microscope to another location. Aim: We present a modularized PPSDHM. We construct the proposed PPSDHM and demonstrate the 3D measurement capability of the PPSDHM. Approach: The PPSDHM was designed as an inverted microscope to record transparent objects and modularized by integrating the optical elements of the PPSDHM on an optical breadboard. To demonstrate the effectiveness of the PPSDHM, we recorded a 3D motion-picture of moving Volvoxes at 1000 frames/s and carried out 3D tracking of the Volvoxes. Results: The PPSDHM was practically realized and 3D images of objects were successfully reconstructed from holograms recorded with a single-shot exposure. The 3D trajectories of Volvoxes were obtained from the reconstructed images. Conclusions: We established a modularized PPSDHM that is capable of 3D image acquisition by integrating the optical elements of the PPSDHM on an optical breadboard. The recording capability of 3D motion-pictures of dynamic specimens was experimentally demonstrated by the PPSDHM.

From its inception holography has proven an extremely productive and attractive area of research. While specific technical applications give rise to 'hot topics', and three-dimensional (3D) visualisation comes in and out of fashion, the core principals involved continue to lead to exciting innovations in a wide range of areas. We humbly submit that it is impossible, in any journal document of this type, to fully reflect current and potential activity; however, our valiant contributors have produced a series of documents that go no small way to neatly capture progress across a wide range of core activities. As editors we have attempted to spread our net wide in order to illustrate the breadth of international activity. In relation to this we believe we have been at least partially successful. This Roadmap is organized under three headings: Materials, Applications and Concepts . We hope this structure is not misleading as in some cases the contributions do not fit neatly under any single heading and in several cases, there is significant overlap between articles listed in all the three sections. Significantly, some articles discuss work in areas not traditionally addressed side by side with others. We sincerely hope our approach will lead to an increase in awareness and a cross-fertilization in this wonderful field. Materials development and characterisation have always been of critically importance for the development of holography. The Roadmap begins with Wang et al (section 1) who briefly discuss novel materials for use in dynamic holographic displays. Tomita (section 2) then describes the development of nanocomposite photopolymers. Neipp and Frances (section 3) discuss the recording of holographic waveguides, while Gallego and Pascual (section 4) discuss shrinkage effects arising in photopolymers. Marovina et al (section 5) describe recent photorefractive materials and devices. Bruder et al (section 6) then discuss industrial-scale material production and volume holographic optical elements (vHOEs) fabrication. Under the heading of Applications, Kostuk (section 7) leads with the use of non-imaging HOES for solar energy conversion. Odinokov (section 8) discussed holographic data storage (HDS) and security issues. Matoba et al (section 9) reviews some advances in Multimodal 3D data acquisition using digital holography (DH). Wachulak (section 10) describes the performance of extreme ultraviolet (EUV) and soft x-ray (SXR) holography and tomography employing compact short wavelength sources. Gorelaya et al (section 11) then discuss holographic wavefront sensors (WFS) and next Chmelik (section 12), describes advance in incoherent holographic microscopy (HM). Ferrara and Coppola (section 13) describe the applications of digital polarized holography in the sciences. Márquez and Beléndez (section 14) discuss the use of liquid crystal on silicon (LCoS) microdisplays for use in HDS systems. Yang and Yuste (section 15) discuss the two-photon holographic imaging and manipulation of neural activity in vivo. Finally, in this section, Bianco and Zanutta (section 16) describe the use of holography in astronomical spectrographs. Under the heading Concepts, we begin with the description by Falldorf (section 17) of DH employing the spatial coherence function. Healy et al (section 18) describe the performance of autofocus in holographic imaging. Zhurminsky et al (section 19) discuss interference lithography for the fabrication of nanostructures. Situ and Wang (section 20) examine the applications of deep learning (DL) in DH. Abdurashitov and Tuchin (section 21) examine digital focusing in laser speckle contrast imaging (LSCI). Petrov (section 22) introduces ultrafast digital techniques and spatio-temporal metrology and Nomura (section 23) describes the evolution from the concepts of conventional DH to wide-sense DH. To conclude Morim and Saravanamuttu (section 24) describe the fabrication of functional 3D waveguide microstructures with nonlinear waves of light.

We constructed a parallel-phase-shifting digital holographic microscopy (PPSDHM) system using an inverted magnification optical system, and succeeded in three-dimensional (3D) motion-picture imaging for 3D displacement of a microscopic object. In the PPSDHM system, the inverted and afocal magnification optical system consisted of a microscope objective (16.56 mm focal length and 0.25 numerical aperture) and a convex lens (300 mm focal length and 82 mm aperture diameter). A polarization-imaging camera was used to record multiple phase-shifted holograms with a single-shot exposure. We recorded an alum crystal, sinking down in aqueous solution of alum, by the constructed PPSDHM system at 60 frames/s for about 20 s and reconstructed high-quality 3D motion-picture image of the crystal. Then, we calculated amounts of displacement of the crystal from the amounts in the focus plane and the magnifications of the magnification optical system, and obtained the 3D trajectory of the crystal by that amounts.

We present a digital holography using high dynamic range (HDR) imaging to improve quality of the reconstructed image of digital holography. The technique extends the dynamic range of the digitally recorded hologram using multiple holograms recorded with different exposures. We numerically and experimentally demonstrated the technique based on an off-axis digital holography system. In the numerical simulation and experiment, the quality of the reconstructed images by the proposed technique is higher than that by the conventional digital holography without HDR imaging.

To improve the reconstructed image quality in a 3D display system using binary phase modulator, we propose two successive methods that are a modified iterative Fresnel algorithm for designing the binary phase pattern and the intensity addition for the speckle reduction. Numerical and experimental results show the effectiveness of the proposed methods by increasing the number of iteration for optimizing the binary phase distribution and the number of intensity addition.

To extract effectively the absorber information embedded in a homogeneous scattering medium in the transmission geometry, a method of taking the ratio of the output intensity in a measured medium to that in a reference medium is evaluated. The reference medium is a virtual one with the same scattering coefficient distribution as that of the measured medium, but with a uniform absorption coefficient distribution. Numerical results show that the proposed method can enhance the output signal by extracting the ballistic-like component. We also apply a backprojection method to reconstruct the single absorber using many pairs of input and output intensity ratio distributions. The reconstruction position error and the quantitative measurement of absorption coefficient are discussed.

Sound field imaging techniques have been found very useful for acoustic designs. Building on this idea, innovative techniques are needed and presented in this paper, where we report on developed imaging of the sound field radiated from speakers by parallel phase-shifting digital holography. We adopted an ultrasonic wave radiated from a speaker for an object. The phase distribution of the light wave was modulated by the sound field radiated from the speaker. The modulated phase distribution was recorded in the form of multiplexed phase-shifted holograms at the frame rate of 100,000 fps. A 40,000 Hz sound field radiated from a speaker is used as an observation target. Our proposed method can implement the imaging of the sound field successfully. Also, in order to demonstrate the digital refocusing capability of digital holography, we set two speakers, whose difference in depth positions was 6.6 cm, as a long-depth object. We demonstrated the digital refocusing on the two speakers along with the capability of measuring the positions of the objects. Furthermore, we succeeded in imaging of 40,000 Hz and 41,000 Hz sound fields radiated from the two speakers. The presented experimental results showed that parallel phase-shifting digital holography is very useful and suitable for sound field imaging.

In this paper, we propose an optical multimodal biometric encryption technique which uses digital holography (DH) for multiple biometric recording and successive optical encryption methods, by means of keys generated from biometric data. Physiological biometrics, such as fingerprints or iris scans, along with behavioral biometrics such as voice, are recorded simultaneously as multimodal biometrics, using multi-parameter off-axis DH. Moreover, multiple biometrics embedded in the same holograms are encrypted using the Fresnel domain double random phase encoding method, in which keys are generated from biometric data via a phase retrieval algorithm. By employing the decryption procedure for this encoding method, along with the correct keys and reconstruction parameters of DH, the original multimodal biometrics can be successfully retrieved . The proposed method provides multimodal biometrics with a higher level of security by availing itself of the advantages of optical techniques. Our proposed multimodal biometric security scheme is demonstrated and validated by the results of the optical recording and encryption of biometric data presented below.

Lensless, interferenceless coded aperture correlation holography (LI-COACH) is an incoherent computational optical technique for three-dimensional (3D) imaging. In direct imaging, the image of the object is generated by a lens, whereas the LI-COACH is an indirect imaging technique that consists of two steps: one-time point spread hologram (PSH) training and then many times imaging of multiple-point objects. In the one-time training step, a point object moves in the object space along the optical axis. Light emitted from the point is modulated by a quasi-random phase mask, and the PSH library is recorded. In the imaging step, an object is mounted within the axial boundaries of the PSH library, and the object holograms are recorded using the same quasi-random phase masks. The 3D image of the object is reconstructed by the cross correlation of the object holograms with the PSH library. In this study, the entire PSH library is digitally synthesized from a single PSH, recorded at one plane only. The recorded PSH is scaled by magnification factors corresponding to the various axial planes. The reconstruction results from the synthetic PSH library are comparable with those from the recorded PSH library. The proposed approach can reduce the time of the training step in LI-COACH.

We present a multimodal imaging system based on simple off-axis digital holography, for simultaneous recording and retrieval of cross-sectional fluorescence and quantitative phase imaging of the biological specimen. Synergism in the imaging capabilities can be achieved by incorporating two off-axis digital holographic microscopes integrated to record different information at the same time. The cross-sectional fluorescence imaging is realized by a common-path configuration of the single-shot off-axis incoherent digital holographic system. The quantitative phase imaging, on the other hand, is achieved by another off-axis coherent digital holographic microscopy operating in transmission mode. The fundamental characteristics of the proposed multimodal system are confirmed by performing various experiments on fluorescent beads and fluorescent protein-labeled living cells of the moss Physcomitrella patens lying at different axial depth positions. Furthermore, the cross-sectional live fluorescence and phase imaging of the fluorescent beads are demonstrated by the proposed multimodal system. The experimental results presented here corroborate the feasibility of the proposed system and indicate its potential in the applications to analyze the functional and structural behavior of biological cells and tissues.

pA stable multimodal system is developed by combining two common-path digital holographic microscopes (DHMs): coherent and incoherent, for simultaneous recording and retrieval of three-dimensional (3-D) phase and 3-D fluorescence imaging (FI), respectively, of a biological specimen. The 3-D FI is realized by a single-shot common-path off-axis fluorescent DHM developed recently by our group. In addition, we accomplish, the phase imaging by another single-shot, highly stable common-path off-axis DHM based on a beam splitter. In this DHM configuration, a beam splitter is used to divide the incoming object beam into two beams. One beam serves as the object beam carrying the useful information of the object under study, whereas another beam is spatially filtered at its Fourier plane by using a pinhole and it serves as a reference beam. This DHM setup, owing to a common-path geometry, is less vibration-sensitive and compact, having a similar field of view but with high temporal phase stability in comparison to a two-beam Mach-Zehnder-type DHM. The performance of the proposed common-path DHM and the multimodal system is verified by conducting various experiments on fluorescent microspheres and fluorescent protein-labeled living cells of the mossitalicPhyscomitrella patens/italic. Moreover, the potential capability of the proposed multimodal system for 3-D live fluorescence and phase imaging of the fluorescent beads is also demonstrated. The obtained experimental results corroborate the feasibility of the proposed multimodal system and indicate its potential applications for the analysis of functional and structural behaviors of a biological specimen and enhancement of the understanding of physiological mechanisms and various biological diseases./p.