Tesis sobre el tema "Interference fringe"

To reduce the environmental errors, a snapshot phase-shifting interference microscope (SPSIM) has been developed for surface roughness measurement. However, fringe-print-through (FPT) error widely exists in the phase-shifting interferometry (PSI). To ensure the measurement accuracy, we analyze the sources which introduce the FPT error in the SPSIM. We also develop a FPT error correction algorithm which can be used in the different intensity distribution conditions. The simulation and experiment verify the correctness and feasibility of the FPT error correction algorithm. (C) 2017 Optical Society of America

In the context of this work, a computer program is developed for the simulation of the interference fringe patterns of laboratory-scale pool-fires of organic fuels. With the help of this simulation tool, the formation as well as the dynamics of typical structural components in the interference fringe patterns in the flame neck and the flame plume are modelled. A model conception for the formation of the interference fringe patterns in the flame plume is developed. The temperature field is modelled as a relatively cold convection column, into which a large amount of statistically distributed hot volume elements with gaussian temperature distribution is inserted. The simulation with this model conception shows the typical structure of the measured interference fringe patterns in the flame plume with good congruence. The physical meaning of the velocity of the interference fringe pattern shift within the areas of the flame neck and the flame plume is examined. It is shown in particular that the temporally averaged shifting velocity in vertical direction in the flame neck can be identified as a temporally averaged ascent rate of the flame gases within the region of the thermal boundary layer. For the flame plume, the shifting velocity can be interpreted as a flow velocity averaged over time and the line of sight.

Par une methode de projection de franges d'interferences modulees sur l'objet, une detection electrique directe de la phase du moire realise une mesure de haute precision en interpolant les franges de moire

The terms &lsquo
ground-probing radar&rsquo
, &lsquo
ground penetrating radar (GPR)&rsquo
, &lsquo
sub-surface radar&rsquo
or &lsquo
surface-penetrating radar (SPR)&rsquo
refer to various techniques for detecting and imaging of subsurface objects. Among those terms GPR is preferred and used more often. In this thesis, the depth and the position of the buried circular cylinder are determined by a GPR system which comprises of an optical fiber sensor (OFS). The system is a combination of OFS, GPR and optical communication link. In order to determine the depth and the position, first of all the electric field distribution at the OFS is obtained by integrating the Green&rsquo
s function over the induced current distribution. Those distributions are observed for different frequency and depth values. The voltages inside the distribution are measured by OFS. By changing the depth of the cylinder and the frequency of the system, various plots showing x axis displacement versus measured voltages are obtained. Those plots are related to interference fringe patterns. The position and the depth of the cylinder are obtained using interference fringe patterns. All of the studies mentioned are performed in MATLAB R2007b program. The noises of the system due to OFS are extracted using OPTIWAVE OPTISYSTEM 7.0 program. By adding those noises to the measured voltage values, the operating frequency of the system is observed.

Cette thèse présente l'étude théorique et expérimentale du contrôle des phénomènes de propagation cohérente d'impulsions ultracourtes dans un milieu résonant optiquement dense. Dans une première partie, nous décrivons les phénomènes élémentaires des effets de propagation. Dans un second temps, nous développons l'idée de contrôler par un champ fort, les propriétés transitoires d'une autre impulsion faible et résonante qui se propage simultanément dans le milieu. Le champ fort induit des modifications transitoires dans le milieu, qui modifient par rayonnement le champ de l'impulsion résonante qui se propage. Nous étudions enfin une configuration où les deux impulsions, polarisées orthogonalement, excitent de manière résonante un système à quatre niveaux dégénérés. Deux chemins interfèrent modulant ainsi l'énergie de l'impulsion transmise. La combinaison des déplacements lumineux et de ces interférences, permet de contrôler aussi bien le gain que la forme temporelle de l'impulsion
The topic of this work deals with theoretical and experimental study of the control of ultrashort pulse coherent propagation in optically dense medium. First, we describe the basics of propagation phenomena. Secondly, we study the idea of using a strong driving pulse, to control the transient properties of a weak resonant pulse simultaneously propagating in the medium. The strong field induces transient modifications in the medium, which modify the electric field of the weak resonant propagating pulse. Finally, we study a configuration where two orthogonally polarized pulses, excite resonantly a four level system degenerated two by two. With the strong field mixing the states, the emission and absorption path of the weak field have similar contribution. The two paths interfere thus modulating the transmitted pulse energy. The interplay of the light shift and the interference enables us to control the gain and the pulse temporal shape as well

碩士
國立中興大學
機械工程學系所
102
The present study employs a single interference pattern phase retrieval to collect data on surface profilometry. Since single im- ages have fewer environmental constraints than a multi-step phase shift method, it is possible to glean phase data from the interfer- ence pattern generated by this method using phase measurement techniques. This data can subsequently be converted into a surface profilometry of an object. However, calculating the phase through the Fourier transform method results in frequency leakage, if the edges of the interference pattern lack sufficient continuity or pe- riodicity. This diminishes the resolution of the surface edge profilometry data and leads to differences from the actual profilometry. This study aims to alleviate the loss of resolution problems caused by frequency leakage, by reconstructing the edge fringes using the Papoulis Gerchberg algorithm. By improving the algorithm and comparing the efficiencies of various filters, re- constructions to the initial interference pattern were found to smooth out the edge and increase the speed of convergence, al- lowing for an analysis of different pattern densities. The first portion of the design involved the use of a fringe projection method to project simulated interference patterns, using a five step phase shift method to verify the results of Papoulis Gerchberg calculations and improve the effectiveness of P-G on a single image. The second portion consisted of acquiring surface profilometry by creating interference patterns with green mono- chromatic light, and deriving the phase using a Fourier transform.

Laser interference fringe tomography (LIFT) is within the class of optical imaging devices designed for volumetric microscope applications. LIFT is a very simple and cost-effective three-dimensional imaging device which is able to reliably produce low-quality imagery. It measures the reflectivity as a function of depth within a sample and is capable of producing three-dimensional images from optically scattering surfaces. The first generation of this instrument is designed and prototyped for optical microscopy. With an imaging spot size of 42 μm and a 180 μm axial resolution kernel, LIFT is capable of producing one- and two- dimensional images of various samples up to 1.5 mm thickness. The prototype was built using commercial-off-the-shelf components and cost ~ $1,000. It is possible that with effort, this device can become a reliable, stable, low-quality volumetric imaging microscope to be readily available to the consumer market at a very affordable price. This document will present the optical design of LIFT along with the complete mathematical description of the instrument. The design trade-offs and choices of the instrument are discussed in detail and justified. The theoretical imaging capabilities of the instrument are tested and experimentally verified. Finally, some imaging results are presented and discussed.

碩士
國立臺灣大學
應用力學研究所
103
The main application scenario of this thesis is using Michelson interferometer as the non-destructive testing method, which measures tiny deformation of objects by retrieving the phase of the interference fringes generated due to deformation. To retrieve the deformation induced phase, we measure the interference fringe first and then analyze the phase by a process called phase-unwrapping. Trying to take advantages of the rapid development of CCD/CMOS, which provides a platform to significantly increase the spatial modulation frequency, Fourier transform based phase-unwrapping algorithm was adopted in this thesis. Trying to remove the bottleneck associated with phase-unwrapping, Fourier spectrum of interference fringe obtained with pre-introduced spatial carrier frequency so as to distinguish the correct direction of object deformation, was adopted. This approach first proposed by Mitsuo Takeda in 1981 is similar to the Doppler interferometer that solves the directional ambiguity by providing a frequency shift. The only difference lies on either temporal or spatial frequency was pre-introduced. It is with this pre-introduced spatial frequency shift, retrieving the phase information by using only one interference fringe (intensity map) becomes feasible. More specifically, the above-mentioned approach circumvent the disadvantages associated with phase-shifting algorithms such as the 5,1 phase-shifting algorithm, etc. that require more than one image to analyze the phase information. It is to be noted that retrieve phase map from intensity map with a single intensity map not only saves valuable computation time but also provides us with a platform for dynamic measurement as high-speed camera can be used to record the time-varying interference fringes (intensity maps) first and then compute phase map after the deformation is completed. Furthermore, in dealing with problems related to valid or effective functional domain (domain with valid interference fringes) and regions with vastly different signal-to-noise ratios (SNR), Windowed Fourier Transform (WFT) first proposed by Qian Kemao in 2004 was also introduced in this thesis. For phase unwrapping, this study used Least-Squares method to get the information of measured object rapidly. It is to be noted that this method leads to the use of Fourier transform to solve a Poisson’s equation with Neumann boundary conditions. As Fourier transform algorithm was used in converting the intensity map to the phase map and then perform phase-unwrapping, these algorithms developed in this thesis provides us with an opportunity to adopt the many attempts over the last 50 years in speeding up the computation time associated with Fourier transform. Some of these methods include Fast Fourier Transform (FFT), Sparse Fast Fourier Transform (SFFT) and hardware solution such as Graphic Processing Unit (GPU), etc. All of which can then be integrated to develop an ultrafast phase analysis system, which can found applications potentials ranging from in-situ real-time optical field measurement, production-need driven automatic optical inspection (AOI), etc. This works completed throughout this research include setting the Michelson interferometer, integrating MATLAB and LabVIEW to transfer experimentally induced optical intensity map to computers for signal post-processing, etc. To verify the overall effectiveness of this system, this study analyzed the phase information by measuring the mirror and stainless steel deformation by using the Michelson interferometer set up. The results of unwrapped phase matched the object deformation, successfully validated the accuracy and the feasibility of integrating these algorithms in this thesis.

碩士
國立臺灣科技大學
機械工程系
90
This work studies the surface profile reconstruction of silicon wafers based on optical interference fringes. Following the developing of new technologies, leading wafer manufacturers focus their attention on the produce of large scale wafers. Surface flatness is one of the most important factors which affect the quality of wafers. Laser beams and array of capacitances had been applied to the measurement of wafer profiles. Since the position data were collected point by point, both methods were time-consuming in order to have a complete description of wafer surface. Optical interference fringes could be a different approach to deal the problem. At the present time, the interference image from the available optical device cannot cover the whole surface of an 8” wafer. This work studies the possibility of reconstruction of wafer surface profile from local interference diagrams. The results from computer simulation show the success in two specific models. A general solution will rely on the further study in the future.

碩士
國立交通大學
照明與能源光電研究所
107
Signal is often measured in noisy environments. In this work, the signal recovery by using a home-made lock-in amplifier is implemented. A lock-in amplifier is a type of amplifier with a very narrow bandwidth that can extract a signal from an extremely noisy environment. The interference fringes of a Michelson interferometer are applied for determininge the detection limits of our home-made lock-in amplifier operated at 70 kHz. Our experimental results confirm that our lock-in amplifier with a 0.5 ms time constant can effectively extract a signal up to 1480 times smaller than noise components.

碩士
國立臺灣大學
工程科學及海洋工程學研究所
104
This thesis is related to three-dimensional metrology system, a widely used technique that has been applied in monitoring semiconductor elements packing, shape/roughness of optical lenses/mirrors, microelectromechanical devices, panel geometry checking, and the cell morphology. The two most significant performance factors in morphology technique are precision and speed, and the corresponding improvements, i.e. enhancing the measurement accuracy and reducing the processing time can ensure the production quality and lower its costs. Consequently, there are two major aspects in this thesis. One is the accuracy improvement of metrology techniques, and the other is the introduction of a new signal analysis method called Sparse Fourier Transform (SFT) and exploring its applicability in the current fringe analysis techniques. The metrology technique used in this research starts with the Fourier transformation of a single frame of fringe pattern, and reconstruct the object morphology through the phase information obtained from its spectrum. Although the noise effect on the spectrum can be reduced by using this full-field based FT algorithms, there still exist some drawbacks on the accuracy due to either frequency aliasing caused by pixels’ interactions or the imperfect design of the filters. To solve the problem mentioned above, we take the advantage of local spectral analysis used in Windowed Fourier Transform (WFT). Firstly, the original spectrum of fringes pattern is partitioned into many small blocks by a moving window function, and the frequency spectrum of each block is obtained by Fast Fourier Transform (FFT). And then, the final spectrum is achieved by adding up the spectrum of each block. As compared to the conventional full-field FT, this local analysis based technique is simpler in its structure and less affected by aliasing. In addition, by a proper choice of cutoff frequency, this technique can still guarantee an effective noise reduction. By comparing with the experimental pattern obtained from Michelson interferometer and simulated pattern generated on the MATLAB coding, we have proved the WFT’s advantages on the accuracy of morphology reconstruction. It is worth noting that 70% of computer processing time is devoted to FFT of window function, whereas there are only a few non-zero values on the frequency spectrum of window function and exist only on specific coordinates. Hence, the major content of the 2nd part in this thesis is focusing on an efficient processing theory proposed since 2012, i.e. SFT, in dealing with these sparsely distributed spectrum. We’ll systemically introduce the theoretical aspects of SFT, its algorithm’s theoretical structure, the error guarantee of signal recovery, as well as the signal reconstruction technique newly proposed by MIT’s Hassanieh. Besides, by implementing a few MATLAB simulation examples, we also discussed some key technique problems and possible solutions such as spectrum permutation, subsampled FFT and the design of flat window function. It appears that replacing window functions’ FFT by SFT is very likely to greatly reduce the processing time of fringe pattern analysis.