High-resolution Holographic Imaging Research Articles

Single-shot dual-wavelength telecentric in-line-and-off-axis hybrid digital holography with non-prior reconstruction

Dual-wavelength in-line-and-off-axis hybrid digital holography (iohDH) can achieve high-resolution holographic dynamic imaging. However, it requires the prediction of the diffraction distance and the complex amplitude of the reference beam, which is time consuming and results in complications and accuracy limitations. While telecentric imaging technique can obtain nondiffractive images without predicting the diffraction distance, it also can even eliminate spherical aberration and astigmatic aberration. Therefore, a dual-wavelength telecentric iohDH is proposed to realize non-prior high-resolution reconstruction in a single shot. Employing the dual-wavelength telecentric iohDH, our approach acquires the focused in-line-and-off-axis hologram using a color camera in a single shot. In this case, we perform wavelength conversion on the phase and low-frequency information about the off-axis hologram as constraints for in-line iteration. Then, the in-line amplitude constraints are performed in the spatial and frequency domains until the algorithm converges. Compared to the state-of-the-art dual-wavelength iohDH, our approach can streamline the reconstructed processes without demanding a priori information of the diffraction distance and the complex amplitude of the reference beam. More importantly, our approach enables higher quality and efficient reconstruction under the telecentric system. We verified our approach using simulations and experiments, and the results indicate that our approach can allow the amplitude and phase reconstruction with high resolution in a single shot.

Reconstructing Polarization Multiplexing Terahertz Holographic Images with Transmissive Metasurface

There is a growing trend towards the development of high resolution and multiplexing metasurface holograms. In this paper, we propose the reconstruction of polarization multiplexing terahertz (THz) holographic images based on transmissive metasurface. The metasurface composed of all-dielectric meta-atoms is designed as a multi-foci metalens and the focal points of the metalens are utilized as the pixels of a reconstructed image. We analyze the effects of focal length and phase pixel number of the metalens on focal point to achieve high-resolution holographic images. In addition, by switching the polarization of incident lights, holographic images with different patterns are reconstructed on its focal plane. Such high-resolution and polarization multiplexing metasurface holograms is promising for applications in THz communications, information engineering, and encryption.

Realization of tunable index-near-zero modes in nonreciprocal magneto-optical heterostructures.

Epsilon-near-zero (ENZ) metamaterial with the relative permittivity approaching zero has been a hot research topic for decades. The wave in the ENZ region has infinite phase velocity (v=1/ε μ), but it cannot efficiently travel into the other devices or air due to the impedance mismatch or near-zero group velocity. In this paper, we demonstrate that the tunable index-near-zero (INZ) modes with vanishing wavenumbers (k = 0) and nonzero group velocities (vg ≠ ~0) can be achieved in nonreciprocal magneto-optical systems. The INZ modes have been experimentally demonstrated in the photonic crystals at Dirac point frequencies, and that impedance-matching effect has been observed as well [Nat. Commun.8, 14871 (2017)10.1038/ncomms14871]. Our theoretical analysis reveals that the INZ modes exhibit tunability when changing the parameters of the one-way (nonreciprocal) waveguides. Moreover, owing to the zero-phase-shift characteristic and decreasing vg of the INZ modes, several perfect optical buffers are proposed in the microwave and terahertz regimes. The theoretical results are further verified by the numerical simulations using the finite element method. Our findings may open new avenues for research in the areas of ultra-strong or -fast nonlinearity, perfect cloaking, high-resolution holographic imaging, and wireless communications.

Generalized optimization framework for pixel super-resolution imaging in digital holography.

The imaging quality of in-line digital holography is challenged by the twin-image and aliasing effects because sensors only respond to intensity and pixels are of finite size. As a result, phase retrieval and pixel super-resolution techniques serve as two essential ingredients for high-fidelity and high-resolution holographic imaging. In this work, we combine the two as a unified optimization problem and propose a generalized algorithmic framework for pixel-super-resolved phase retrieval. In particular, we introduce the iterative projection algorithms and gradient descent algorithms for solving this problem. The basic building blocks, namely the projection operator and the Wirtinger gradient, are derived and analyzed. As an example, the Wirtinger gradient descent algorithm for pixel-super-resolved phase retrieval, termed as Wirtinger-PSR, is proposed and compared with the classical error-reduction algorithm. The Wirtinger-PSR algorithm is verified with both simulated and experimental data. The proposed framework generalizes well to various physical settings and helps bridging the gap between empirical studies and theoretical analyses.

Imaging biological tissue with high-throughput single-pixel compressive holography

Single-pixel holography (SPH) is capable of generating holographic images with rich spatial information by employing only a single-pixel detector. Thanks to the relatively low dark-noise production, high sensitivity, large bandwidth, and cheap price of single-pixel detectors in comparison to pixel-array detectors, SPH is becoming an attractive imaging modality at wavelengths where pixel-array detectors are not available or prohibitively expensive. In this work, we develop a high-throughput single-pixel compressive holography with a space-bandwidth-time product (SBP-T) of 41,667 pixels/s, realized by enabling phase stepping naturally in time and abandoning the need for phase-encoded illumination. This holographic system is scalable to provide either a large field of view (~83 mm2) or a high resolution (5.80 μm × 4.31 μm). In particular, high-resolution holographic images of biological tissues are presented, exhibiting rich contrast in both amplitude and phase. This work is an important step towards multi-spectrum imaging using a single-pixel detector in biophotonics.

Three-Dimensional High-Resolution Digital Inline Hologram Reconstruction with a Volumetric Deconvolution Method.

The digital in-line holographic microscope (DIHM) was developed for a 2D imaging technology and has recently been adapted to 3D imaging methods, providing new approaches to obtaining volumetric images with both a high resolution and wide field-of-view (FOV), which allows the physical limitations to be overcome. However, during the sectioning process of 3D image generation, the out-of-focus image of the object becomes a significant impediment to obtaining evident 3D features in the 2D sectioning plane of a thick biological sample. Based on phase retrieved high-resolution holographic imaging and a 3D deconvolution technique, we demonstrate that a high-resolution 3D volumetric image, which significantly reduces wave-front reconstruction and out-of-focus artifacts, can be achieved. The results show a 3D volumetric image that is more finely focused compared to a conventional 3D stacked image from 2D reconstructed images in relation to micron-size polystyrene beads, a whole blood smear, and a kidney tissue sample. We believe that this technology can be applicable for medical-grade images of smeared whole blood or an optically cleared tissue sample for mobile phytological microscopy and laser sectioning microscopy.

Water detection in thermal insulating materials by high resolution imaging with holographic radar

The present research is aimed at the application of high resolution holographic images for the detection and characterization of low water content (0.2–1 g) water patches in insulating materials. The images acquired with manual scanning with high frequency (7 GHz) holographic radar with I/Q outputs are compared with a high speed electromechanical scanner with 4 GHz holographic radar. Small patches of the order of 22 mm × 22 mm buried at 18 mm into insulating materials with a low dielectric constant, have been accurately reconstructed with the high frequency holographic radar but they can also be detected with the lower frequency holographic radar at even greater depths.

Wide-field imaging of birefringent synovial fluid crystals using lens-free polarized microscopy for gout diagnosis.

Gout is a form of crystal arthropathy where monosodium urate (MSU) crystals deposit and elicit inflammation in a joint. Diagnosis of gout relies on identification of MSU crystals under a compensated polarized light microscope (CPLM) in synovial fluid aspirated from the patient’s joint. The detection of MSU crystals by optical microscopy is enhanced by their birefringent properties. However, CPLM partially suffers from the high-cost and bulkiness of conventional lens-based microscopy, and its relatively small field-of-view (FOV) limits the efficiency and accuracy of gout diagnosis. Here we present a lens-free polarized microscope which adopts a novel differential and angle-mismatched polarizing optical design achieving wide-field and high-resolution holographic imaging of birefringent objects with a color contrast similar to that of a standard CPLM. The performance of this computational polarization microscope is validated by imaging MSU crystals made from a gout patient’s tophus and steroid crystals used as negative control. This lens-free polarized microscope, with its wide FOV (>20 mm2), cost-effectiveness and field-portability, can significantly improve the efficiency and accuracy of gout diagnosis, reduce costs, and can be deployed even at the point-of-care and in resource-limited clinical settings.

Holographic imaging and interferometry with non-Bragg diffraction orders on volume and surface-relief gratings in lithium niobate and photo-thermoplastic materials

The recording of holographic volume and surface-relief gratings in a photorefractive crystal using a photo-thermoplastic (PTP) holographic camera with an image-bearing signal beam leads to the appearance of two Bragg and two or more non-Bragg diffracted beams that show the transformed images in each beam (rotation and angular amplification of images). Using this real-time mode of interferometry, the hologram is retrieved with a deformed object beam, resulting in the appearance of fringes with a proper phase shift in each of four diffracted beams. This one-shot (one-exposure) phase-shifting interferometry results in clarification of the object wave-front information (for example, from surface deformation) and solution of the sign ambiguity problem. This procedure demonstrates that high-resolution holographic imaging of the PTP holographic camera static deformations in the order of ∼0.1 mm can be revealed on the diffusion reflection surface. In addition, it was demonstrated that using the PTP materials could achieve holographic recording and imaging through phase aberration, with the image appearing in the non-Bragg diffraction order.

Holographic Measurement and Improvement of the Green Bank Telescope Surface

ABSTRACTWe describe the successful design, implementation, and operation of a 12 GHz holography system installed on the Robert C. Byrd Green Bank Telescope (GBT). We have used a geostationary satellite beacon to construct high-resolution holographic images of the telescope mirror surface irregularities. These images have allowed us to infer and apply improved position offsets for the 2209 actuators which control the active surface of the primary mirror, thereby achieving a dramatic reduction in the total surface error (from 390 μm to ∼240 μm, rms). We have also performed manual adjustments of the corner offsets for a few panels. The expected improvement in the radiometric aperture efficiency has been rigorously modeled and confirmed at 43 GHz and 90 GHz. The improvement in the telescope beam pattern has also been measured at 11.7 GHz with greater than 60 dB of dynamic range. Symmetric features in the beam pattern have emerged which are consistent with a repetitive pattern in the aperture due to systematic panel distortions. By computing average images for each tier of panels from the holography images, we confirm that the magnitude and direction of the panel distortions, in response to the combination of gravity and thermal gradients, are in general agreement with finite-element model predictions. The holography system is now fully integrated into the GBT control system, and by enabling the telescope staff to monitor the health of the individual actuators, it continues to be an essential tool to support high-frequency observations.

Reconstruction of high-resolution holographic microscopic images

In in-line holographic microscopy a pinhole illuminates an object and a CCD-detector directly records the hologram in a pixel-pitch-dependent distance. A rapidly calculating exact reconstruction technique using a reorganized hologram with a low number of pixels, the tile superposition technique, is presented. The algorithm is applied on imaging of a 2 microm bead cluster, and it is compared with other reconstruction techniques. The high-contrast image corresponds to an NA of 0.7. A full 4 megapixel reconstruction with a resolution approaching the diffraction limit is possible in less than a minute. The technique is a base for high-resolution wide-field imaging by multispot illumination.

Optical storage of hidden images in ultraviolet-cured polymer dispersed liquid crystals

Among the different methods used to prepare polymer dispersed liquid crystals (PDLCs), polymerization induced phase separation can be successfully exploited to obtain optical recording of high resolution holographic gratings and binary images in these materials. In this paper we report a new method that allows hidden images to be obtained in PDLCs that are not detectable by light in the visible range. The possibility of storing invisible images during the curing process will be described and discussed. The binary images obtained can be detected by illuminating them with low power UV radiation, thus opening the way to interesting applications in the field of optical storage of reserved information.

Demonstration of X-ray Holography with an X-ray Laser

An x-ray hologram was made by means of an x-ray laser and a laser-quality near normal incidence x-ray mirror. The high brightness and large coherence lengths of x-ray lasers now offer the potential for in vitro three-dimensional high-resolution holographic images of dynamically varying biological microstructures.