Measurement of certain types of spatial coherence functions allows us to obtain three-dimensional (3-D) images of many spectral components for usual objects under illumination of white light. We have developed some of these techniques, which are regarded as combination of incoherent holography and Fourier transform spectroscopy. We illustrate the principle of the basic technique, and then report on advances in alternative techniques. Recent experimental and theoretical achievements are shown to demonstrate the performance of the techniques.
In this research, two-wave coupling in photorefractive lithium niobate crystal has been used to do imaging enhancement of digital holography (DH) system. The image bearing beam of in-line DH system has been incident and interfered with a reference beam that was emerged from the same laser on a LiNbO3 crystal. With certain angles between both beams, the energy of the reference beam was transferred to the image bearing beam then resulted the enhancement of the reconstructed image of the DH system. By using the suitable intensity of laser beam with a right PR crystal, the image from an in-line DH imaging system would be improved.
We present a method to obtain a set of spectral component of three-dimensional images based on measurements of hyperbolic volume interferogram. The method uses an improved two-wavefront folding interferometer incorporating with a single detector of high sensitivity. The method may apply to usual polychromatic objects because it is kind of incoherent holography combined with Fourier transform spectroscopy. First experimental result of the method is shown to demonstrate the capability to acquire continues spectral profile of three-dimensional polychromatic object.
In this paper we propose a modern technique to evaluate the shape changes of solder paste by using double-view in-line digital holography. We observed the transformation of three different kinds of solder paste composition: pure solder paste, solder paste mixed with 0.02%, 0.05%, 0.10% graphene (GPN) and 0.02%, 0.05%, 0.10% graphene oxide (GPNO), respectively. The shape of the solder pastes was investigated at different melt temperatures (i.e. 200°C, 250°C, and 300°C) for 30 seconds using a collimated beam propagating through the solder paste, then being double reflected on a mirror and second incident on another sides of the solder paste. The double images bearing beams were recorded with a CCD sensor simultaneously. The single recorded digital hologram from double view technique was reconstructed using digital holography. The results show that the double-view technique provides reliably data. Moreover, it would be developed for observing more than two images by single holography writing in the future.
In this paper, we discuss the digital holography (DH) experiment in our optical and communication laboratory course for undergraduate students at Physics department, KMITL. The purposes of DH experiment are presenting our students the meaning and advantage of DH and its applications. The Gabor configurations of in-line DH has been set up for recording a number of samples, which were placed on different distances, simultaneously. Then, the images of all objects have been numerical reconstructed by using computer. The students have been learned that all of reconstructed images have been got from only one time recording, while using the conventional recording technique, sharp images of different objects have been gotten from different recording time. The students also have been learned how to use DH technique for investigation some different kinds of samples on their own of interested such as a human hair or a fingerprint. In our future work, our DH system will be developed to be a portable apparatus for easily showing to children in different areas.
A four-dimensional impulse response function for the digital holographic three-dimensional imaging spectrometry has been fully derived in closed form. Due to its factorizing nature of the mathematical expression of four-dimensional impulse response function, three-dimensional spatial part of impulse response function directly corresponds to threedimensional point spread function of in-line digital holography with rectangular aperture. Based on these mathematical results, this paper focuses on the investigation of spectral resolution and three-dimensional spatial resolution in digital holographic three-dimensional imaging spectrometry and digital holography. We found that the theoretical prediction agree well with the experimental results. This work suggests a new criterion and estimate method regarding threedimensional spatial resolution of in-line digital holography.
We have studied a method to obtain both three-dimensional (3-D) spatial information and spectral information of a usual polychromatic object by a fully passive interferometric technique that is strongly coupled with digital signal processing1- 6. Our method can be used for a vast range of wavelengths, because no special imaging devices, such as lenses, are required. In addition, coherent light sources are not necessary. A hyperbolic-type volume interferogram6 is one type of the volume interferogram, which is used for retrieve the object information, and an interferometer to measure directly this volume interferogram has been introduced3. This paper introduces a method to measure the hyperbolic-type volume interferogram with high sensitivity in fully interferometric 3-D imaging spectrometry. This is accomplished by coupling of interferometer to measure directly the hyperbolic-type volume interferogram and heterodyne detection system7 for broadband light. We also report a preliminary experimental result based on the interferometer to measure directly the hyperbolic-type volume interferogram.
A brief review is presented for recent progress in a fully interferometric technique to obtain a set of spectral components of three-dimensional images for usual polychromatic objects. The review includes a principle of method and experimental demonstrations in which the measured object is regarded as spatially incoherent in each spectral component. We also suggest that some alternative ways to realize the same results having different characteristics based on modified synthetic aperture techniques.
This paper presents a new method of digital holographic three-dimensional imaging spectrometry. The method is based on the measurement of new type of volume interferogram, called Rotated-Hyperbolic-type volume interferogram, obtained with the existing interferometer. We report the first demonstration of the method in which a monochromatic point source is used as the measured object. The results include 3-D spatial information and spectral information of a monochromatic point source. This experimental result corresponds to the impulse response function defined over a four dimensional (x, y, z, k) space. As a result, the method is confirmed to have the superior imaging characteristics in the z direction.
We have studied a method to obtain both three-dimensional (3-D) spatial information and spectral information of a usual polychromatic object simultaneously by making use of a specifically designed two-wavefront folding interferometer and signal processing, including synthetic aperture technique, spectral decomposition, and 3-D image retrieval. The method uses only interferometric techniques and signal processing applied to the interferogram generated by propagated light from the measured object1-2. We call the method the digital holographic 3-D imaging spectrometry. The method is based on measurement of 5-D interferogram. By applying synthetic aperture technique and spectral decomposition to that 5-D interferogram, one obtains a set of complex holograms of different spectral components. From these holograms, 3-D images of multiple spectral components have been retrieved on the basis of the propagation law applied to the 2-D cross-spectral densities. Decomposed continuous spectrum of each light source is also shown to demonstrate a potential applicability to identify materials of a particular part of object under illumination of white light. This paper reports experimental results in retrieving the spectral components of 3-D images of the spatially incoherent light source distribution. The results for depth imaging properties are also demonstrated.
An interferometric method, called digital multispectral holography, to obtain three-dimensional (3D) multispectral
images of spatially incoherent, polychromatic source distributions is presented. Each 3D spectral image is retrieved
separately from a 3D spatial coherence function that is synthesized from interferograms measured with a two-axes
wavefront folding interferometer. Numerical demonstration incorporated with spatially extended polychromatic source
distribution, located at nearfield positions, shows that the 3D information of each spectral component is successfully
retrieved by the method.
Like a volume holography reproduces color images of three-dimensional (3D) objects, it is possible to obtain simultaneously both spectral information and 3D spatial information of polychromatic source objects in terms of a certain interferometry to measure 3D spatial coherence function. This paper shows the outline of that idea. An analysis of the depth resolution is also presented.
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