Papers by Keyword: Digital Holography

Abstract: The development and fabrication of novel composite materials requires accurate investigation of their mechanical properties. Although various approaches are well-established for investigation of linear elastic properties, there are only few methods that can be applied for study of nonlinear ones. In this report we describe and compare the performance of two different experimental approaches aimed for investigation of nonlinear elastic properties of glassy polymers and polymer-based composites.

Abstract: In phase shifting interferometry phase shift is applied by various ways, but applying it with high accuracy, especially by LD current modulation, is not easy. In order to determine the accurate phase shift a new method has been proposed that the value of LD current corresponding to π/2 phase shift can be determined by phase shifting digital holography. The measured data of standard in surface shape measurement were used for calibration, and the obtained value was confirmed to cause noise reduction and improvement of holographic reconstructed images in digital holography.

Abstract: Digital holography is a comparatively new observation method for micron-sized particles. It is based on numerical reconstruction of recorded interference fringe. Calculation processes for reconstruction are both time- and memory-intensive. The aim of this study was to develop a faster, more efficient algorithm for digital hologram reconstruction. To this purpose Central Processing Unit (CPU) and Graphics Processing Unit (GPU) programming were implemented. For the problem solving the algorithms’ run-time for both configurations was measured. The results showed that the algorithm using a GPU board is faster and more suitable for reconstruction processes. Thus, it makes possible the accomplishment of real-time analysis.

Abstract: In order to solve the problems of complex process of decryption and high cost when shifting the key codes of optical encrypted watermark, a method of applying double random amplitude-phase encryption to digital watermarking is introduced. The encrypted ESPI watermark is obtained by random amplitude-phase optical encryption based on normal speckle interference. An encrypted Fourier transform-ESPI watermarking scheme and an encrypted digital holography-ESPI watermarking scheme are introduced. Computer Simulation results show the feasibility of the new schemes. The compared results of image processing show that the encrypted ESPI watermark has good compatibility when combined with Fourier transform watermarking and digital holographic watermarking.

Abstract: An improved multi-plane imaging fusion algorithm for 3-D digital holography is presented. Multiple reconstructed images at different distances from single off-axis Fresnel digital hologram are fused using discrete cosine transform (DCT) with different blocks. The zero order term is removed using a Laplacian operator while the conjugate image and dispersed images of defocused objects are eliminated by selecting a simple rectangular window before image fusion. Compared with those fused images obtained directly from the reconstructed images, the fused images qualities are greatly improved and all of the objects will be clearly in focus more quickly than discrete wavelet (DWT) based fusion method.

Abstract: Light-emitting diode (LED) is a kind of short-coherence light source, and it can generate time gating effect and reduce the speckle noises in digital holography. Meanwhile, it can cut down the cost of the setup since LED is cheaper than laser. In this paper, an in-line digital holography setup was designed with LED, and the holograms were reconstructed by four-step phase shifting method. Comparing with the phase image obtained by the laser-based setup, results show that the phase image of USAF test target possesses lower speckle noises with the help of LED. Finally, we reconstruct a series of intensity images with different depths of a coin, and these images are fused to get a synthesized image with more information.

Abstract: Aiming to the special demand of the criminal investigation, a non-invasive and non-contact fingerprint acquisition method is proposed based on digital holography. The off-axis Fresnel digital holography is designed to record the digital hologram. The reconstruction of the complex amplitude from fingerprint is analyzed, and the phase aberration is corrected by the surface fitting based on the least square approach. In the scene of the crime, the fingerprint of suspects is easily left on some smooth surfaces. In the experiments, the CD-ROM disk with fingerprint information is used as the sample. The results show that the amplitude and phase images can be obtained and combined to capture more information of latent fingerprints, which demonstrates digital holography is effective for the acquisition of latent fingerprints and can be applied to the criminal investigation field.

Abstract: The optical sparse aperture imaging system consists of several small apertures for high resolution imaging. The incoherent light from each small aperture will form an image together strictly at the same focal plane, while the phase error will destroy such co-phase condition. The phase error is caused by deployment of small aperture and should be diminished. We applied digital holography technology to detect the wavefront of this system. The theoretical analysis and experiment are presented to demonstrate successful reconstruction of phase error.

Abstract: The reconstruction quality of in-line holography suffers from the superposition of twin images, which blurs the details and degrades the quality of the object wavefront reconstruction. We present an iterative reconstruction method to eliminate twin image and truthfully retrieve the object wavefront. This algorithm has a better elimination effect and more rapid rate of convergence than other phase retrieval methods. An experimental setup was built with dual cameras recording the holograms simultaneously, thus this technique can be employed for investigating fast dynamic phenomina. The effectiveness of the proposed method is validated using different samples.

Abstract: According to the holographic optical theory, based on the method of rotating reference light polarization plane, through the simultaneous solution of light intensity equations transformed by the hologram, the digital holographic nondestructive testing of two-dimensional stress field is introduced. This technology does not require additional experimental means and numerical method for separate fringes, determining fringe order and solving stress. It is a convenient, accurate and non-destructive measurement of two-dimensional stress field. The paper first introduces the basic theory of digital holographic photo-elastic method, and then verifies it by experiments and simulation. Light intensity images are obtained through the comparative experiments and theoretical solutions. The results prove the strong feasibility of the method in experiments, and lay the foundation for further experimental study.