Digital Holographic Technology Research Articles

Measurements of the Characteristics of Transparent Material Using Digital Holography

Digital holography is applied to measure the characteristics of transparent material. A digital hologram recording system to measure the surface of transparent material was established, and the digital holograms of transparent object were obtained in high quality. For postprocessing of hologram, the least-squares phase unwrapping algorithm was used in phase unwrapping, and the phase reconstruction image of transparent object was obtained. The information of material surfaces was measured and the characteristic was presented in 3D visualization. The validation experiment was conducted by NanoMap 500LS system; the results of validation experiment are well satisfied with the measurement by digital holography, which proved the feasibility of digital holographic technology as a good measurement tool for transparent material.

数字全息技术在温度场测量中的应用

数字全息技术在温度场测量中的应用

The Analysis and Research on Digital Holography Signal Based on Wavelet Theory

When introduce the wavelet theory to filter the hologram and the reconstructed image in the digital holography, the noise of the reconstructed image is greatly reduced. In the off-axis digital holography, the zero-order wave is decreased dramatically when after a wavelet filter, at the same time, the speckle noise is also reduced, and it turns out that the resolution of the reconstruction image is improved greatly. The system launches the research thoroughly on the three-dimensional body digital holographic technology, from the theory to the application, from the simulation to the experiment, and has elaborated and analyzed each characteristic of three-dimensional body digital holographic technology. It proposes many kinds of improved effective method of three-dimensional body digital holographic restructuring information, and finally has effectively explored the three-dimensional body digital holographic technology application through the experiment.

基于无透镜数字全息成像的活体细胞培养状态无损监测

A non-invasive detection method for the status analysis of cell culture is presented based on digital holography technology. Lensless Fourier transform digital holography (LFTDH) configuration is developed for living cell imaging without prestaining. Complex amplitude information is reconstructed by a single inverse fast Fourier transform, and the phase aberration is corrected through the two-step phase subtraction method. The image segmentation is then applied to the automatic evaluation of confluency. Finally, the cervical cancer cell TZMbl is employed for experimental validation, and the results demonstrate that LFTDH imaging with the corresponding image post-processing can provide an automatic and non-invasive approach for monitoring living cell culture.

Fast numerical generation and encryption of computer-generated Fresnel holograms

In the past two decades, generation and encryption of holographic images have been identified as two important areas of investigation in digital holography. The integration of these two technologies has enabled images to be encrypted with more dimensions of freedom on top of simply employing the encryption keys. Despite the moderate success attained to date, and the rapid advancement of computing technology in recent years, the heavy computation load involved in these two processes remains a major bottleneck in the evolution of the digital holography technology. To alleviate this problem, we have proposed a fast and economical solution which is capable of generating, and at the same time encrypting, holograms with numerical means. In our method, the hologram formation mechanism is decomposed into a pair of one-dimensional (1D) processes. In the first stage, a given three-dimensional (3D) scene is partitioned into a stack of uniformed spaced horizontal planes and converted into a set of hologram sublines. Next, the sublines are expanded to a hologram by convolving it with a 1D reference signal. To encrypt the hologram, the reference signal is first convolved with a key function in the form of a maximum length sequence (also known as MLS, or M-sequence). The use of a MLS has two advantages. First, an MLS is spectrally flat so that it will not jeopardize the frequency spectrum of the hologram. Second, the autocorrelation function of an MLS is close to a train of Kronecker delta function. As a result, the encrypted hologram can be decoded by correlating it with the same key that is adopted in the encoding process. Experimental results reveal that the proposed method can be applied to generate and encrypt holograms with a small number of computations. In addition, the encrypted hologram can be decoded and reconstructed to the original 3D scene with good fidelity.

High-performance holographic technologies for fluid-dynamics experiments.

Modern technologies offer new opportunities for experimentalists in a variety of research areas of fluid dynamics. Improvements are now possible in the state-of-the-art in precision, dynamic range, reproducibility, motion-control accuracy, data-acquisition rate and information capacity. These improvements are required for understanding complex turbulent flows under realistic conditions, and for allowing unambiguous comparisons to be made with new theoretical approaches and large-scale numerical simulations. One of the new technologies is high-performance digital holography. State-of-the-art motion control, electronics and optical imaging allow for the realization of turbulent flows with very high Reynolds number (more than 10(7)) on a relatively small laboratory scale, and quantification of their properties with high space-time resolutions and bandwidth. In-line digital holographic technology can provide complete three-dimensional mapping of the flow velocity and density fields at high data rates (over 1000 frames per second) over a relatively large spatial area with high spatial (1-10 microm) and temporal (better than a few nanoseconds) resolution, and can give accurate quantitative description of the fluid flows, including those of multi-phase and unsteady conditions. This technology can be applied in a variety of problems to study fundamental properties of flow-particle interactions, rotating flows, non-canonical boundary layers and Rayleigh-Taylor mixing. Some of these examples are discussed briefly.

New technologies for fluid dynamics experiments and optical diagnostics

Modern technologies offer new opportunities for experimentalists in a wide variety of research areas including hydrodynamics. A significant improvement in precision, dynamic range, reproducibility, motion control accuracy, data acquisition rate and information capacity of the experimental datasets over the current state-of-the-art are possible using new approaches and techniques, which may bring the quality of experiments to a new level of standards. Application of these new technologies in experimental diagnostics can help bridge the current quality gap between the observations and the large-scale computational fluid dynamics simulations allowing direct and unambiguous comparison of the data and the modeling results, which is crucial for the code validation. One of the new technologies which is described in this paper is ultra-high performance digital holographic data storage. The state-of-the-art motion control, electronics and optical imaging allow for realization of turbulent flows with very high Reynolds number (>107) in a relatively small laboratory-scale form-factor and quantification of their properties with extremely high spatio-temporal resolutions and bandwidth. Digital holographic technology can provide complete three-dimensional mapping of the flow velocity and density fields at high data rates (over 1000 fps) over large spatial area (∼50 cm) with high spatial (1–10 μm) and temporal (better than a few nanoseconds) resolutions and, therefore, can provide extremely accurate quantitative description of the fluid flows, including those of multiphase and unsteady conditions. These unique experimental and metrological capabilities enable the studies of spatial and temporal properties of the transport of momentum, angular momentum and energy, and the identification of scaling, invariants and statistical properties of the complex multiphase and unsteady turbulent flows. The technology can be applied for investigations of a large variety of hydrodynamic problems including the fundamental properties of non-Kolmogorov turbulence, flow–particle interactions, accelerating and rotating flows, boundary layers, Rayleigh–Taylor instability and turbulent mixing, magneto-hydrodynamics and laboratory astrophysics.