We present an interactive simulation software to help to teach and learn the holography concept. The education interface was developed in the Java platform. The Holographic Interface is a computer assisted learning that can be used in classrooms or for distance education. The binary holograms are numerically generated and reconstructed in the virtual optical laboratory. Several procedures are shown. The interface has been implemented with di↵erent options such as addition, subtraction, multiplexing and some properties of holography. Moreover, the software was designed to simultaneously visualize the 2D object, the generated hologram and the recovered image. We have taken into account the students’ suggestions in this version in Java.
Single-pixel imaging employs structured illumination to record images with very simple light detectors. It can be an alternative to conventional imaging in certain applications such as imaging with radiation in exotic spectral regions, multidimensional imaging, imaging with low light levels, 3D imaging or imaging through scattering media. In most cases, the measurement process is just a basis transformation which depends on the functions used to codify the light patterns. Sampling the object with a different basis of functions allows us to transform the object directly onto a different space. The more common functions used in single-pixel imaging belong to the Hadamard basis or the Fourier basis, although random patterns are also frequently used, particularly in ghost imaging techniques. In this work we compare the performance of different alternative sampling functions for single pixel imaging, all of them codified with a digital micromirror device (DMD). In particular, we analyze the performance of the system with Hadamard, cosine, Fourier and noiselet patterns. Some of these functions are binary, some others real and other complex functions. However, all of them are codified with the same DMD by using different approaches. We perform both numerical and experimental tests with the different sampling functions and we compare the performance in terms of the efficiency and the signal-to-noise ratio (SNR) of the final images.
The complete phase and amplitude information of biological specimens can be easily determined by phase-shifting digital holography. Spatial light modulators (SLMs) based on liquid crystal technology, with a frame-rate around 60 Hz, have been employed in digital holography. In contrast, digital micro-mirror devices (DMDs) can reach frame rates up to 22 kHz. A method proposed by Lee to design computer generated holograms (CGHs) permits the use of such binary amplitude modulators as phase-modulation devices. Single-pixel imaging techniques record images by sampling the object with a sequence of micro-structured light patterns and using a simple photodetector. Our group has reported some approaches combining single-pixel imaging and phase-shifting digital holography. In this communication, we review these techniques and present the possibility of a high-speed single-pixel phase-shifting digital holography system with phase-encoded illumination. This system is based on a Mach-Zehnder interferometer, with a DMD acting as the modulator for projecting the sampling patterns on the object and also being used for phase-shifting. The proposed sampling functions are phaseencoded Hadamard patterns generated through a Lee hologram approach. The method allows the recording of the complex amplitude distribution of an object at high speed on account of the high frame rates of the DMD. Reconstruction may take just a few seconds. Besides, the optical setup is envisaged as a true adaptive system, which is able to measure the aberration induced by the optical system in the absence of a sample object, and then to compensate the wavefront in the phasemodulation stage.
We present an alternative optical method to estimate the temperature during the cooling process of a liquid using digital holographic interferometry (DHI). We make use of phase variations that are linked to variations in the refractive index and the temperature property of a liquid. In DHI, a hologram is first recorded using an object beam scattered from a rectangular container with a liquid at a certain reference temperature. A second hologram is then recorded when the temperature is decreased slightly. A phase difference between the two holograms indicates a temperature variation, and it is possible to obtain the temperature value at each small point of the sensed optical field. The relative phase map between the two object states is obtained simply and quickly through Fourier-transform method. Our experimental results reveal that the temperature values measured using this method and those obtained with a thermometer are consistent. We additionally show that it is possible to analyze the heat-loss process of a liquid sample in dynamic events using DHI.
Refractive index, temperature, pressure, velocity and many other physical magnitudes of phase objects in the refraction less limit are of great interest in engineering and science. Optical tomography is a technique used to estimate these magnitudes. For axially symmetrical phase objects the tomographic reconstruction can be carried out from just one projection when using Abel transform. However, for noisy projections the reconstruction shows low quality. This quality can be improved when using the Kalman filter to compute the inverse Abel Transform. In this paper a tomographic reconstruction method for syntectic axially symmetrical phase objects using Kalman filter is presented.
Phase wrapping is an intermediate step ffor interferometry analysis. When phase is smooth, its unwrapping can be carried out fitting local planes with finite extension at each point of the phase gradient. We propose a method easy to implement that spends the same computation time than those techniques based on basis functions.
We present a comparison of some methodologies that exist for directional filtering of fringe patterns. An important task in fringe image processing is the noise filtering. The implementation of linear filters is not always a proper procedure in the presence of high density fringes because the signal and noise are mixed in Fourier space. The objective of this report is to carry out a comparison of existing procedures to determine which of them provides a better image estimation. The techniques considered in this work are: Regularized Filters (RQCF), Oriented spatial filter masks (OSFM), Second-Order Oriented partial differential equations (SOPDE) and Directional filters (DF). To compare these techniques, we analyze their performance for different noise levels, using synthetic fringe images.
The present paper discusses an improvement for the method by division of cells which is used in multiplexed computer generated holograms (CGH's). Such improvement allows increasing the final number of codified images into a single hologram. Some important properties of images are saved because they will be the key to perform the adequate operations involved in the reconstruction process. The experimental results demonstrate the effectiveness of the suggested procedure.
A new technique useful to store several images in a detour computer generated hologram, is described. The method basically works as follows: every hologram cell is sectioned in vertical segments, which then are used to encode different objects, one per subcell. In the reconstruction all images appear simultaneously in the same diffraction order. Also, by the use of spatial filters at the hologram plane, it is possible to select any desired image. The method allows encoding up to 4 objects. The experimental results demonstrate the effectiveness of the suggested procedure.
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