Single Hologram Research Articles

Measurement of cell volume using in-line digital holography.

The measurement of the volume of blood cells is important for clinical diagnosis and patient management. While digital holography microscopy has been used to obtain such information, previous off-axis setups usually involve a separated reference beam and are thus not very easy to implement. Here, we use the simple in-line Gabor setup without separation of a reference beam to measure the shape and volume of cells mounted on glass slides. Inherent to the in-line holograms, the reconstructed phase of the object is affected by the virtual image noise, producing errors in the cell volume measurement. We optimized our approach to use a single hologram without phase retrieval, increasing distance between cell and hologram plane to reduce the measurement error of cell volume to less than 6% in some instances. Therefore, the in-line Gabor setup can be a useful and simple tool to obtain volumetric and morphologic cellular information.

High Efficiency Polarization‐Encoded Holograms with Ultrathin Bilayer Spin‐Decoupled Information Metasurfaces

AbstractInformation metasurfaces, including digital coding and programmable metasurfaces, have reformed the design theory of metasurfaces from effective medium to coding pattern, and bridged the physical and digital world. Metasurface hologram has shown great potential in imaging and manipulating electromagnetic waves. In this work, bilayer information metasurfaces are proposed to achieve polarization‐encoded holograms in microwave regime. The designed metasurfaces consist of 3‐bit spin‐decoupled meta‐atoms, which possess ultrathin profiles (0.14λ0) and high cross‐polarization transmittance (over 0.8). The incident wave, which is right‐handed circularly polarized or left‐handed circularly polarized, is encoded with code “0” or “1”. The spin‐decoupled design is combined with diffuse scattering and holographic technology. Based on this, a novel algorithm is proposed to generate coding sequences according to the code of incident wave, to achieve different functionalities for corresponding circularly polarized channels. In this way, polarization‐encoded holograms, including diffuse scattering holograms (code “00”), single channel holograms (code “01” or “10”), and spin‐selective holograms (code “11”), are achieved. Simulated and measured results show that the maximum imaging efficiency can reach up to 65.1%, verifying the high efficiency of this holographic technology. This work is expected to open a way of realizing more complicated and higher efficiency information metasurface holography.

Single-shot common-path off-axis digital holography: applications in bioimaging and optical metrology [Invited

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.

Exploiting a holographic polarization microscope for rapid autofocusing and 3D tracking.

We report a fast autofocusing and accurate 3D tracking scheme for a digital hologram (DH) that intrinsically exploits a polarization microscope setup with two off-axis illumination beams having different polarization. This configuration forms twin-object images that are recorded in a digital hologram by angular and polarization multiplexing technique. We show that the separation of the two images on the recording plane follows a linear relationship with the defocus distance and indicates the defocus direction. Thus, in the entire field of view (FOV), the best focus distance of each object can be directly retrieved by identifying the respective separation distance with a cross-correlation algorithm, at the same time, 3D tracking can be performed by calculating the transverse coordinates of the two images. Moreover, we estimate this linear relationship by utilizing the numerical propagation calculation based on a single hologram, in which the focus distance of one of the objects in the FOV is known. We proved the proposed approach in accurate 3D tracking through multiple completely different experimental cases, i.e., recovering the swimming path of a marine alga (tetraselmis) in water and fast refocusing of ovarian cancer cells under micro-vibration stimulation. The reported experimental results validate the proposed strategy's effectiveness in dynamic measurement and 3D tracking without multiple diffraction calculations and any precise knowledge about the setup. We claim that it is the first time that a holographic polarization multiplexing setup is exploited intrinsically for 3D tracking and/or fast and accurate refocusing. This means that almost any polarization DH setup, thanks to our results, can guarantee accurate focusing along the optical axis in addition to polarization analysis of the sample, thus overcoming the limitation of the poor axial resolution.

Recordable-Time Extension of Digital Light-in-Flight Recording by Holography Using a Polarization-Imaging Camera

Digital light-in-flight recording by holography is a powerful tool for observing ultrashort light pulse propagation as a motion picture. However, the recordable time of the technique has been limited by the lateral length of the image sensor used for the recording of the hologram, and no technique for extending the recordable time has been reported yet. Then, to extend the recordable time of digital light-in-flight recording by holography, we proposed a technique that records two holograms as a single hologram using double reference light pulses with an image sensor. In this technique, the image sensor is spatially divided into multiple micro-areas. Each micro-area consists of 2 × 1 pixels and records 1 pixel of each of the two holograms. We employed a polarization-imaging camera in order to implement the proposed technique to extend the recordable time. This technique is a new application of the polarization-imaging camera. We experimentally succeeded in extending the recordable time for the first time using the proposed technique. Specifically, we recorded the motion picture of the ultrashort light pulse propagation for 1.04 ps.

Compressed off-axis digital holography

The Fourier transform method (FTM), which can reconstruct a wavefront from a single hologram, is widely used in digital holography (DH) as a reconstruction technique. However, the space-bandwidth product (SBP) is limited because of the frequency filtering required. We propose a wavefront reconstruction algorithm based on compressed sensing that can obtain a high SBP for use instead of the FTM. The proposed method can reconstruct a high-SBP wavefront by solving the hologram recording model with total variation regularization. We demonstrate the proposed method’s effectiveness via simulations and experiments. The method can be applied to conventional off-axis DH without alteration and thus can be applied in various fields.

Compressive complex wave retrieval from a single off-axis digital Fresnel hologram for quantitative phase imaging and microlens characterization

A compressive sensing (CS) approach is proposed for the complex wave retrieval algorithm from single off-axis digital Fresnel holography to improve the accuracy of quantitative phase measurement. The linear model of non-linear holographic process used in the complex wave retrieval algorithm is utilized to meet the linearity requirement of the proposed CS implementation presented in this paper. The error in object wave reconstruction due to the approximations used in complex wave retrieval algorithm is compensated by combining it with CS approach. A Mach–Zehnder interferometric geometry in transmission and off-axis mode in the Fresnel domain is used to record the digital hologram. The numerical simulations and experimental results are presented to demonstrate and validate the proof of the concept and to compare CS frame work with conventional complex wave retrieval algorithm. The proposed algorithm is tested for the microlens sample characterization by considering the parameters such as height, diameter and radius of curvature. A Haar wavelet based object wave sparsification is used in the experiment for the prudent phase reconstruction in the CS approach. The proposed method enables an improved and accurate object phase reconstruction, with minimal noise such as distortions or speckles with respect to the conventional complex wave retrieval method.

Off-axis digital holographic multiplexing for rapid wavefront acquisition and processing

Off-axis holographic multiplexing involves capturing several complex wavefronts, each encoded into off-axis holograms with different interference fringe orientations, simultaneously, with a single camera acquisition. Thus, the multiplexed off-axis hologram can capture several wavefronts at once, where each one encodes different information from the sample, using the same number of pixels typically required for acquiring a single conventional off-axis hologram encoding only one sample wavefront. This gives rise to many possible applications, with focus on acquisition of dynamic samples, with hundreds of scientific papers already published in the last decade. These include field-of-view multiplexing, depth-of-field multiplexing, angular perspective multiplexing for tomographic phase microscopy for 3-D refractive index imaging, multiple wavelength multiplexing for multiwavelength phase unwrapping or for spectroscopy, performing super-resolution holographic imaging with synthetic aperture with simultaneous acquisition, holographic imaging of ultrafast events by encoding different temporal events into the parallel channels using laser pulses, measuring the Jones matrix and the birefringence of the sample from a single multiplexed hologram, and measuring several fluorescent microscopy channels and quantitative phase profiles together, among others. Each of the multiplexing techniques opens new perspectives for applying holography to efficiently measure challenging biological and metrological samples. Furthermore, even if the multiplexing is done digitally, off-axis holographic multiplexing is useful for rapid processing of the wavefront, for holographic compression, and for visualization purposes. Although each of these applications typically requires a different optical system or processing, they all share the same theoretical background. We therefore review the theory, various optical systems, applications, and perspectives of the field of off-axis holographic multiplexing, with the goal of stimulating its further development.

Y4-Net: a deep learning solution to one-shot dual-wavelength digital holographic reconstruction.

In this Letter, a deep learning solution (Y4-Net, four output channels network) to one-shot dual-wavelength digital holography is proposed to simultaneously reconstruct the complex amplitude information of both wavelengths from a single digital hologram with high efficiency. In the meantime, by using single-wavelength results as network ground truth to train the Y4-Net, the challenging spectral overlapping problem in common-path situations is solved with high accuracy.

PyHoLo software, a new tool for electron hologram analysis and magnetic investigation

A new tool, PyHoLo software, was developed to help automate the process of determining magnetic field B from a series of holograms, registered at different environmental conditions (e.g. for upside and downside orientations of a sample in a specimen holder). This procedure involves translating single holograms into phase shift of electron wave, but also alignment of holograms (i.e. shift, rotation, magnification) and finally calculation of magnetic field in an area selected for investigation. PyHoLo gives functionality for performing all those steps without having to refer to different programs and tools. The workflow and results of this procedure are discussed using as an example sample of FeCuSiB. Program summaryProgram title: PyHoLoCPC Library link to program files:http://dx.doi.org/10.17632/n4rgzbnbpw.1Licensing provisions: GNU General Public License 3Programming language: PythonNature of problem: (1) Determination of electric and magnetic fields in a sample on the basis of electron holograms, registered on transmission electron microscope during off-axis holography experiment. (2) Alignment of electron holograms acquired for different sample orientations and at different external conditions.Solution method: PyHoLo adapts procedures for all steps required to translate experimental holograms into electric and magnetic signals, i.e. restoration of total phase shift, alignment of electron holograms (shift, rotation, magnification, warping), phase separation. There is no need to refer to different tools and programs.Additional comments: PyHoLo requires Python 3.6 or newer and a number of external libraries to work (see README or manual for details). PyHoLo is a constant work in progress, developed by only one person, so it might be a little rough around the edges.

Stackable acoustic holograms

Acoustic holograms can be used to form complex distributions of pressure in 3D at MHz frequencies from simple inexpensive ultrasound sources. The generation of such fields is vital to a diverse range of applications in physical acoustics. However, at present, the application of acoustic holograms is severely hindered by the static nature of the resulting fields. In this work, it is shown that by intentionally reducing the diffraction efficiency of each hologram, it is possible to create stackable acoustic holograms that can be repositioned to reconfigure the combined acoustic field. An experimental test-case consisting of two holograms, each designed to generate a distinct distribution of acoustic foci, is used to demonstrate the feasibility of this approach. Field scans taken for four different positions of the two holograms confirm that the individual patterns for each hologram can be arbitrary translated relative to one another. This allows for the generation of a much greater range of fields from a single transducer than could be created using a single hologram.

Automatic and robust phase aberration compensation for digital holographic microscopy based on minimizing total standard deviation

A totally automatic and robust phase aberration compensation method is proposed for digital holographic microscopy. The correction needs no manual operation or prior knowledge of the recording setup. As the phase aberrations are modeled with orthogonal polynomials, not only phase curvature but also high order aberrations could be corrected with a single hologram. The polynomial coefficients are obtained in an optimization procedure by minimizing the total standard deviation, i.e., the sum of local standard deviation of the compensated phase map. Since both the global and the local phase variations are considered, the proposed method is more accurate and robust than the state-of-the-art numerical methods with the existence of abrupt edges and phase noise. The effectiveness of the proposed method is validated with numerical simulation and the experimental results of mouse osteoblastic MC3T3-E1 living cells and USAF 1951 resolution target.

Non-scanning 2-D Laser Cutting of Polyimide by Using a Computer-Generated Hologram

Laser processing is an effective way for precisely and accurately removing a small region of materials without tool wear. Conventional laser processing, which has a limitation on the processing speed, is performed by scanning a single spot on a target material. For improving its speed, a high-power laser beam can be spatially distributed using a hologram to simultaneously process a two-dimensional area. This technique has been used in experiments such as drilling, patterning, etc. However, as far as we know, due to several difficulties, no experiments have been reported that apply the holographic technique to non-scanning cutting with a single hologram. In this research, we experimentally performed non-scanning 2-D laser cutting of a polyimide film by using a single computer-generated hologram (CGH) and a high-power laser of 120 W. To do this, we designed a CGH to reconstruct twelve lines in a 24 mm × 23 mm area. This was then fabricated with fused silica so that it would not be damaged by the high-power laser. This method makes possible the achievement of a high throughput in a material cutting process by utilizing a high-power laser efficiently.

The Methods and Experiments of Shape Measurement for Off-Axis Conic Aspheric Surface.

The off-axis conic aspheric surface is widely used as a component in modern optical systems. It is critical for this kind of surface to obtain the real accuracy of the shape during optical processing. As is widely known, the null test is an effective method to measure the shape accuracy with high precision. Therefore, three shape measurement methods of null test including auto-collimation, single computer-generated hologram (CGH), and hybrid compensation are presented in detail in this research. Although the various methods have their own advantages and disadvantages, all methods need a special auxiliary component to accomplish the measurement. In the paper, an off-axis paraboloid (OAP) was chosen to be measured using the three methods along with auxiliary components of their own and it was shown that the experimental results involved in peak-to-valley (PV), root-mean-square (RMS), and shape distribution from three methods were consistent. As a result, the correctness and effectiveness of these three measurement methods were confirmed, which are very useful in engineering.

Field-portable microsphere-assisted high resolution digital holographic microscopy in compact and 3D-printed Mach-Zehnder Interferometer

We present a compact and field-portable system for high resolution microsphere-assisted digital holographic microscopy using a 3D-printed Mach-Zehnder interferometer. Microsphere assisted microscopy inserts a glass microsphere between the sample and magnifying objective lens to increase both lateral resolution and magnification factor by acquiring a single hologram. Our system is verified by reconstruction of a grating structure, which has a patterned surface unresolvable by the native imaging system to confirm the resolution enhancement. Furthermore, the system is analyzed for field portability and practically demonstrated for cell visualization and identification by classification of different animal red blood cells. To the best of our knowledge, this is the first report of a low cost and field-portable system for microsphere-assisted digital holographic microscopy.

Object-based digital hologram segmentation and motion compensation.

Digital video holography faces two main problems: 1) computer-generation of holograms is computationally very costly, even more when dynamic content is considered; 2) the transmission of many high-resolution holograms requires large bandwidths. Motion compensation algorithms leverage temporal redundancies and can be used to address both issues by predicting future frames from preceding ones. Unfortunately, existing holographic motion compensation methods can only model uniform motions of entire 3D scenes. We address this limitation by proposing both a segmentation scheme for multi-object holograms based on Gabor masks and derive a Gabor mask-based multi-object motion compensation (GMMC) method for the compensation of independently moving objects within a single hologram. The utilized Gabor masks are defined in 4D space-frequency domain (also known as time-frequency domain or optical phase-space). GMMC can segment holograms containing an arbitrary number of mutually occluding objects by means of a coarse triangulation of the scene as side information. We demonstrate high segmentation quality (down to ≤ 0.01% normalized mean-squared error) with Gabor masks for scenes with spatial occlusions. The support of holographic motion compensation for arbitrary multi-object scenes can enable faster generation or improved video compression rates for dynamic digital holography.

A Joint Transform Correlator Encryption System Based On Complex Amplitude Modulation for Grayscale Images

Aiming at the problem that the joint transform correlator (JTC) encryption system is difficult to perform experiments on encrypted grayscale images, a JTC encryption system based on complex amplitude modulation for grayscale images system is proposed. In this system, the complex amplitude modulation is implemented by means of single pixel hologram coding, so that the encryption of the grayscale image can be completed by using a single spatial light modulator with pure phase in the JTC encryption experiment.

Compressive Holography From Poisson Noise Plagued Holograms Using Expectation-Maximization

Lensless in-line holography is a simple, portable, and cost-effective method of imaging especially for the biomedical microscopy applications. We propose a multiplicative gradient descent optimization based method to obtain multi-depth imaging from a single hologram acquired in this imaging system. We further extend the method to achieve phase imaging from a single hologram. Negative-log-likelihood functional with the assumption of poisson noise has been used as the cost function to be minimized. The ill-posed nature of the problem is handled by the sparse regularization and the upper-bound constraint. The gradient descent optimization requires calculation of the partial derivative of the cost function with respect to a given estimate of the object. A method of obtaining this quantity for holography in both the cases of real object and complex object has been shown. The reconstruction method has been validated using extensive simulation and experimental studies. The comparison with the previously established iterative shrinkage/thresholding algorithm based compressive holography shows that the proposed method has the following advantages: significantly faster convergence rate, better reconstructed image quality and the ability to perform phase imaging.

Phase-error correction in digital holography using single-shot data.

In remote-sensing applications, digital holography data often includes both phase errors from atmospheric turbulence and fully developed laser speckle from rough objects. When processing single-shot data, i.e., data from a single hologram, the high speckle contrast makes it more difficult to correct for atmospheric phase errors compared to scenarios where multiple speckle realizations are available for processing. A Bayesian phase-error correction algorithm [J. Opt. Soc. Am. A34, 1659 (2017)JOAOD60740-323210.1364/JOSAA.34.001659] was recently developed for use with single-shot data. The features of this approach are discussed and used to implement an alternative algorithm based on image-sharpness maximization. Algorithm performance is tested using simulated data for a range of signal-to-noise ratios (SNRs) and turbulence conditions. Using a combination of appropriate parameterization of the phase-error estimates and spatial binning for speckle-contrast reduction, the image-sharpness algorithm achieves performance comparable (better in the high-SNR regime but worse in the low-SNR regime) to the Bayesian approach. Limited experimental results are also presented.

Suppression of zero-order term and twin-image in in-line digital holography by a single hologram

Suppressing zero-order term and twin-image is a crucial technique in in-line digital holography, which can obtain more accurate reconstructed images. A robust and effective algorithm to suppress zero-order term and twin-image in in-line digital holography is proposed in this paper, which combines a phase retrieval method and spatial spectrum filtering in a single hologram. In order to more accurately distinguish the effective information and noise information (zero-order term and twin-images), we propose a synthetic threshold condition of frequency domain and spatial domain in the iterative process. Several experiments have been carried out to validate the effectiveness of the proposed algorithm. The results demonstrate that the proposed algorithm not only has better visual effects, but also has a better accuracy.