A simple arbitrary phase-step digital holographic reconstruction approach without blurring using two holograms

This work presents a simple approach for arbitrary phase-step digital holography using two holograms without ambiguity. Using this approach, a magnitude-contrast image is reconstructed without dc term and twin-image blurring, but the phase-contrast image is filled with phase distortion. Computer simulations are carried out to verify the proposed approach, and optical experiments are performed to validate it. The advantages, benefits and limitations of the proposed method compared to conventional two-step phase-shifting methods are also discussed herein.     

Multi-wavelengths digital holography: reconstruction, synthesis and display of holograms using adaptive transformation

A method based on spatial transformations of multiwavelength digital holograms and the correlation matching of their numerical reconstructions is proposed, with the aim to improve superimposition of different color reconstructed images. This method is based on an adaptive affine transform of the hologram that permits management of the physical parameters of numerical reconstruction. In addition, we present a procedure to synthesize a single digital hologram in which three different colors are multiplexed. The optical reconstruction of the synthetic hologram by a spatial light modulator at one wavelength allows us to display all color features of the object, avoiding loss of details.     

Dual-wavelength digital holographic phase reconstruction based on a polarizationmultiplexing configuration

We present a polarization-multiplexing off-axis Mach–Zehnder configuration for dual-wavelength digital holography to achieve phase imaging in one shot. In this configuration, two orthogonal linear-polarized waves with respect to different wavelengths are employed to record respective holograms synchronously, where two recording waves transmit independently through the same optical paths of the interferometer, and by installing two analyzer polarizers each to filter off either of two wavelengths, and filtering through the other, the holograms are acquired, respectively, by a pair of CCDs at the same time. The unwrapped phase image of a grating with groove depth 7.1 μm is retrieved via spatial frequency filtering.     

Quantitative phase-contrast microscopy by a lateral shear approach to digital holographic image reconstruction

Combining the concept of lateral shear interferometry (LSI) within a digital holography microscope, we demonstrate that it is possible to obtain quantitative optical phase measurement in microscopy by a new single-image-processing procedure. Numerical lateral shear of the reconstructed wavefront in the image plane makes it possible to retrieve the derivative of the wavefront and remove the defocus aberration term introduced by the microscope objective. The method is tested to investigate a silicon structure and a mouse cell line.     

Method for superposing reconstructed images from digital holograms of the same object recorded at different distance and wavelength

A method for allowing direct perfect superimposition and comparison of Fresnel-transform reconstructions of digital holograms recorded of the same object at different distances and wavelengths is proposed and demonstrated. The method takes into account the dependence of the reconstruction pixel on the distance and the wavelength by the Fresnel-transform algorithm. The method avoids the need for image scaling at the end of the reconstruction process that usually is performed in multi-wavelength digital holography. Demonstration is given by superposing the numerical reconstructions of holograms recorded at different distances and wavelengths. The method can be potentially very useful for real-time monitoring in biological processes or for recognition and ranging by multiple wavelengths of a target with fast movements or finally for very fast investigation and study of very fast processes.     

Optimum holographic optical element lens recorded by visible laser beams for an infrared two-dimensional vertical-cavity surface-emitting laser array

We have designed an optimum holographic optical element (HOE) lens recorded by visible laser beams for an infrared two-dimensional vertical-cavity surface-emitting laser (VCSEL) array. The hologram computer-aided design tool that we have developed is used for the optimum design. The optimum HOE has both high light efficiency and a small amount of aberration. An Nd:YAG laser operated at 532 nm and an 8 x 8 VCSEL array operated at 850 nm are used for HOE recording and reconstruction, respectively. The designed lens is experimentally demonstrated, and the experimental results of the lens almost agree with the numerical results.     

Controlling image size as a function of distance and wavelength in Fresnel-transform reconstruction of digital holograms

A method for controlling the size of amplitude and phase images reconstructed from digital holograms by the Fresnel-transform method is proposed and demonstrated. The method can provide a constant reconstruction pixel width in the reconstructed image plane, independent of the recording and reconstruction distance. The proposed method makes it possible to maintain the size of an object for a sequence of digital holograms recorded at different distances and, therefore, to subtract phase maps for an object recorded at different distances. Furthermore, the method solves the problem of superimposition in multiwavelength digital holography for color display and holographic interferometry applications.     

Wave front reconstruction of Fresnel off-axis holograms with compensation of aberrations by means of phase-shifting digital holography

Off-axis holograms recorded with a CCD camera are numerically reconstructed in amplitude by calculating through the Fresnel–Kirchhoff integral. A phase-shifting Mach–Zehnder interferometer is used for recording four-quadrature phase-shifted off-axis holograms. The basic principle of this technique and its experimental verification are described. We show that the application of this algorithm allows for the suppression of the zero order of diffraction and of the twin image and that the contrast of the reconstructed images can be further enhanced by digital compensation of the aberrations introduced by the holographic recording system     

Pulsed digital holographic interferometry by using a flexible fiber endoscope

A system based on digital holographic interferometry in combination with a flexible fiber endoscope is described. A Q-switched pulsed laser is used. Two digital holograms of the test object, corresponding to the two laser pulses, are captured at separate video frames of a CCD-camera, transferred in a frame grabber and further processed in a PC. If the object undergoes a deformation during the interval between the two laser pulses (usually in the range of 5–600 μs), a fringe pattern will result from the difference between the two holograms. This fringe pattern has the information needed to evaluate quantitatively the amount of the deformation. A compact system has been developed to be used for various applications, both mechanical and biological, where measurements need to be performed at “hidden” surfaces or inside more or less closed objects. The quality of the results obtained by using mechanical objects is usually better than for biological objects. This can be explained easily by the fact that a biological surface is much more complex, in particular some parts of the surface may reflect the light well whereas some other parts may absorb it. Experimental results are presented.     

Fast reconstruction of multiple off-axis holograms based on a combination of complex encoding and digital spatial multiplexing

An algorithm is proposed for the fast reconstruction of off-axis digital holograms based on a combination of complex encoding(CE) and spatial multiplexing(SM). In this algorithm, every two off-axis holograms recorded in sequence are first assembled into a CE hologram using the CE method, and then four of the CE holograms are again encoded into one complex spatial multiplexing(CSM) hologram based on the SM algorithm. It is demonstrated that the eight holograms encoded into such one CSM hologram can be quickly reconstructed by performing a two-dimensional(2D) Fourier transform(FT) on the CSM hologram. Using this method, the eight 2D FTs required for the reconstruction of the eight holograms in the conventional spatial filtering methods can be simplified to a process with only one 2D FT, which can largely improve the computation efficiency with the     

Temporal phase retrieval from a complex field in digital holographic interferometry

We describe a novel method of processing complex phasors in digital holographic interferometry (DHI). Unlike the commonly used digital phase subtraction method that operates on the phase itself, the proposed method operates on the complex phasor instead. Two temporal phase retrieval algorithms are developed in which the complex phasor of each pixel is measured and analyzed as a function of time. The developed algorithms are demonstrated in profile measurement of step heights. Experimental results show that the proposed phase retrieval algorithms for DHI perform well compared with conventional methods.     

Light transmission through a circular metallic grating under broadband radial and azimuthal polarization illumination

We studied the characteristics of a circular metallic grating illuminated by broadband radial and azimuthal polarizations. We demonstrated that this scenario is the cylindrical analogue of a one-dimensional Cartesian grating illuminated by TM and TE polarizations. We measured the transmission spectra of this structure and observed strong polarization selectivity and, specifically, a resonance for radial polarization excitation, indicating a strong coupling to surface plasmons. The structure may be attractive for applications where pure radial polarization is needed, such as tight focusing, material processing, and particle trapping.     

Optical noise reduction by reconstructing positive and negative images from Fourier holograms in coaxial holographic storage systems

A technique for reconstructing positive and negative images from an identical intensity-modulated hologram is demonstrated theoretically and experimentally by use of a coaxial holographic storage system. Negative images are obtained by adding a phase-modulated dc component of signal beam on reading. By comparing positive and negative images, the bit error rate (BER) is improved by two orders of magnitude. This technique can reduce optical noise of reconstructed images to attain low BERs.     

Wave-front reconstruction from a sequence of interferograms recorded at different planes

We present a method by which the phase and the amplitude of a wave front are obtained by processing a sequence of intensity patterns recorded at different planes. We do not use any reference wave, as one does for holography. Simulations and experimental results are presented.     

Determination of optical field generated by a microlens using digital holographic method

In the paper, application of the digital holographic method for full field characterization of the beam generated by microlenses is considered. For this goal, the laboratory setup was designed based on Mach-Zehnder interferometry with the additional reference channel. The beam generated by a microlens was imaged by an afocal system and intensity distributions or interferograms (holograms) were registered by CCD camera. The digital holography using one image allows us to determine microlens parameters, i.e., focal length, aberrations, and shape. The optimum conditions to determine the surface shape of a microlens using holographic method have been found. We compare obtained results with geometrical and interferometric measurements. We show the advantage of digital holography for a shape microlens determination (improved accuracy), aberrations, and focal length (characterization facility). Through optimum refocusing, the digital holography gives more precise shape. The paper is accompanied with computer simulations and the experimental measurement data for geometrical, interferometric, and holographic methods.     

Objective evaluation of images reconstructed from digital in-line Fresnel holograms by using coherent background elimination

Quality of images reconstructed from in-line Fresnel holograms using elimination of a coherent background is quantitatively studied through computer simulation and experiment. The coherent background is digitally calculated by averaging an intensity of a recorded hologram. The results show that in spite of the fact that virtual image is still intact, the background elimination can resolve images with quality comparable to the phase-shifting technique.     

Reconstruction from computer-generated holograms displayed by a line printer

Experimental results are shown of optically reconstructed images from computer-generated holograms made with only binary-quantized levels in the real parts of the Fourier-transform complex disturbance of a signal and displayed by a line printer. Relatively good images having no distortion due to the high-pass filtering effect are reconstructed from computer generated holograms multiplied by the random phase factor. Reconstruction is also possible from the present holograms for signals having various degrees of light intensity.     

Generation of three-dimensional optical structures by dynamic holograms displayed on a twisted nematic liquid crystal display

Reconstruction of computer generated holograms (CGHs) addressed on a spatial light modulator (SLM) is an effective way to dynamically generate designed light field distributions. Based on the classic Gerchberg–Saxton (GS) algorithm, we proposed a technique, which can greatly reduce the computation cost to about 60 % in calculating CGHs for three-dimensional (3D) structures but with little degradation of reconstructed light field compared with the classic GS algorithm. The CGHs calculated by our method were displayed on a twisted nematic liquid crystal display, working as a phase-only-modulation SLM, and 3D structures of optical fields, e.g., 3D array of optical traps and vortices, were reconstructed with high efficiency and high quality. Besides, the possibility for 3D holographic display or projection was also demonstrated with this algorithm by reconstruction several images simultaneously in distinct axial planes.     

Optical representation of binary data based on both intensity and phase modulation with a twisted-nematic liquid-crystal display for holographic digital data storage

We propose a method of representing binary data by modulating both the intensity and the phase of beams with a twisted-nematic liquid-crystal display. With our method it is possible to reduce the dc component of the data image and thus improve the beam-intensity uniformity at the holographic recording plane when one is recording Fourier-plane holograms to obtain maximal areal storage density in disk-shaped storage media. The feasibility of our method is demonstrated experimentally.