Study on the algorithm of computational ghost imaging based on discrete fourier transform measurement matrix

We have developed a model and realized an algorithm for the calculation of the coefficient of coherent (direct) transmission of light through a layer of liquid crystal (LC) droplets in a polymer matrix. The model is based on the Hulst anomalous diffraction approximation for describing the scattering by an individual particle and the Foldy-Twersky approximation for a coherent field. It allows one to investigate polymer dispersed LC (PDLC) materials with homogeneous and inhomogeneous interphase surface anchoring on the droplet surface. In order to calculate the configuration of the field of the local director in the droplet, the relaxation method of solving the problem of minimization of the free energy volume density has been used. We have verified the model by comparison with experiment under the inverse regime of the ionic modification of the LC-polymer interphase boundary. The model makes it possible to solve problems of optimization of the optical response of PDLC films in relation to their thickness and optical characteristics of the polymer matrix, sizes, polydispersity, concentration, and anisometry parameters of droplets. Based on this model, we have proposed a technique for estimating the size of LC droplets from the data on the dependence of the transmission coefficient on the applied voltage.     

Three-dimensional fourier transform NMR imaging. High-resolution chemical-shift-resolved planar imaging

A conventional high-resolution NMR spectrometer has been adapted for a three-dimensional imaging experiment which involves two spatial coordinates plus chemical shift. One dimension has far greater digital resolution than the other two, and when it is used to encode the chemical shifts it is possible to obtain separate slice images showing the distribution of each chemical species within the imaging plane. The method is illustrated using a tube phantom containing ethanol and water, in this case the ethanol gives sufficiently narrow finewidths that it is possible to obtain a separate image from the individual transitions of each multiplet.     

IR spectral depth profiling using fourier transform photothermal beam deflection

FTIR photothermal beam-deflection spectroscopy (PBDS) was used to make spectral depth-profiling measurements with synthetic bilayer samples of polyethylene/nitrocellulose, with a commercial plastic having surface printing and with a single human hair. A Digilab interferometer modified to operate at several scan speeds was used to record the spectra, without the cell-resonance problems found with photoacoustic spectroscopy (PAS). The utility of spectral depth profiling is discussed; significant S/N improvements seem to be needed and, with either PBDS or PAS, a wider range of modulation frequencies is required for the methods to be useful.     

The use of the fast fourier transform in high resolution spectroscopy

Journal of Applied Spectroscopy -     

快速Hartley变换的应用

FFT的出现使得对信号进行卷积,相关和功率谱计算之速度发生了数量级的变化,同时减小了计算误差.多年以来,许多人致力于进一步提高其计算速度.我们利用快速Hartley变换(FHT)进行以上计算,使速度提高了近一倍.设有一N点实函数序列f(τ),其离散形式的Hartley变换(DHT)H(γ)的定义为     

Modified fourier transform profilometry for the measurement of 3-D steep shapes

Analysing the principle of Fourier transform profilometry (FTP) for the measurement of 3-D object shapes and improved Fourier transform profilometry (IFTP) for the measurement of 3-D steep object shapes, the disadvantage of IFTP is discussed. Through the measurable slope of the height variation normal to grating line can be extended to nearly three times in IFTP, and phase-shift error is introduced. In this paper modified Fourier transform profilometry (MFTP) is described for the measurement of 3-D steep object shapes, which gets rid of the disadvantage of IFTP by utilizing the nature of FTP. The measuring precision and the measureable steepness can be ensured in this way.     

The Marple algorithm for the autoregressive spectral estimates of the SMMW fourier transform spectroscopy data

The Marple algorthm for the autoregressive spectral estimates has been applied to the SMMW Fourier transform spectrum analysis. The experimental results have shown that this method yields AR spectra with three times higher resolution than the FFT method does. The improvements obtained from the Marple algorithm over the maximum entropy algorithm include higher resolution, less bias in the spectral peak frequency estimation and absence of observed spectral line splitting. The effects of the structure of the spectral lines and the noise on the resolution are discussed.Projects supported by National Natural Science Foundation of China     

Application of wavelet transform to 3D shape measurement

A new method for analyzing the phase distributions of deformed grating images on the surface of three-dimensional (3D) object to obtain its shape information has been presented. In the conventional technique, Fourier transform profilometry (FTP), there is an intrinsic problem of extracting the fundamental frequency component if the deformation of the grating pattern is either considerable or complicated, which will definitely bring bad influence to the analysis' accuracy. That means FTP is not appropriate to deal with the complex surfaces of 3D objects. The approach that we here introduce to solve this problem is to utilize Gabor wavelet transform (GWT), a tool excelling for its multiresolution in time-frequency domain, to analyze the phase distributions.     

Early history of fourier transform spectroscopy

This is an attempt to explain how and why the stage was set for the appearance on the scene of Fourier transform spectroscopy (FTS) in the 1950s and not a whit before. The play begins 100 years earlier with Fizeau and Foucault who first produced high path-difference interference phenomena and used them for measuring solar spectrum wavelengths in the near IR. Next, the story unfolds with Michelson's contribution, which led to important discoveries around 1890: the hyperfine structures and widths of atomic lines. Somewhat less well known is the Rubens interferometric technique, presented in 1910, because no such striking results were ever collected; still, it represented a distinct advance over the Michelson one.What is the reason why Michelson, Rubens and Lord Rayleigh (who made no experiments himself but understood all about them) never managed to get together and propose the modern form of FTS? Part of the responsibility we must ascribe to chance; however, sufficient motivation could not be felt as long as basic noise limitations had not been understood and closely approached.     

Curvature measurement using three-aperture digital shearography and fast Fourier transform

Curvature measurement using a three-aperture digital shearography (DS) system is reported in this paper. The outer apertures are covered with wedge plates for introducing shear. Four images by sequentially blocking the outer apertures are used for quantitative measurement. Fourier transform technique is used to determine two sheared slope phase maps from two images at a time representing initial and deformed states. Subtraction of these two-phase maps yields the curvature phase map. Experimental results are presented for a circular diaphragm clamped along the edges and loaded at the center.     

Deconvolution of auger electron spectra for lineshape analysis and quantitation using a fast fourier transform algorithm

A Fast Fourier Transform algorithm for the deconvolution of electron energy loss processes and instrumental broadening functions from Auger lineshapes is presented. This method uses a scaled electron backscatter spectrum at the energy of the Auger transition to approximate the spectral features in the data due to energy-loss processes and instrumental broadening effects (the sample-instrument response function, SIRF). Auger spectra, following deconvolution of the SIRF, show little variation to changes in the scaling of the low energy loss features of this backscatter spectrum, and little sensitivity to the choice of the truncation point of the SIRF in the frequency domain during apodization. Auger transitions for a series of sulfur oxyanions standards are comparable to transitions expected from independent molecular orbital calculations. The areas of the deconvolved oxygen (KLL) and sulfur (LMM) spectra were used to calculate oxygen-to-sulfur atomic ratios which were then corrected using standard theories for electron escape depth, electron impact ionization cross section and backscattering coefficient. These relative atomic ratios agree with the stoichiometry obtained from the molecular formulas of the standard compounds.     

移动式加速器在快中子照相中的应用

介绍了移动式加速器的工作原理、结构和调试过程。该加速器具有体积小、重量轻、束流稳定度高、束斑直径小的特点。移动式加速器是首次在中国工程物理研究院应用于快中子照相。在调试过程中测试了小型移动式加速器的束流稳定性等参数,采用伴随粒子方法测量了直流中子产额。通过移动加速器和数字照相系统的组合,获得了初步图像。     

移动式加速器在快中子照相中的应用

介绍了移动式加速器的工作原理、结构和调试过程。该加速器具有体积小、重量轻、束流稳定度高、束斑直径小的特点。移动式加速器是首次在中国工程物理研究院应用于快中子照相。在调试过程中测试了小型移动式加速器的束流稳定性等参数,采用伴随粒子方法测量了直流中子产额。通过移动加速器和数字照相系统的组合,获得了初步图像。     

Applications of near-infrared spectroscopy to process analysis using fourier transform spectrometer

The applications of near-IR spectroscopy to process analysis using a Fourier transform spectrometer are described. In recent years, process analysis based on near-IR spectroscopy has received keen interest from a growing number of industries. Some configurations of Fourier transform near infrared (FT-NIR) interferometers used for process analysis are introduced as special optical systems for the realization of stable and reproducible performance. Moreover, the applications of NIR spectroscopy to process analysis using FT-NIR spectrometers are overviewed and two examples of applications are described in more detail. Furthermore, process analytical technology (PAT) for the pharmaceutical industry is introduced as a future trend of the application of FT-NIR spectroscopy, and a dual-wavelength system that can combine NIR and IR spectra is discussed as a newly proposed PAT tool for understanding processes.     

Ellipsometry with fourier transform spectrometer: An application to TaSi2 films

Summary Ellipsometric measurements on TaSi₂ polycrystalline films are presented in this paper. The optical functions are directly obtained in the wavenumber range from 400 to 3000 cm⁻¹ using an infrared ellipsometer coupled with a Fourier transform spectrometer. The analysis of the results provides the spectral range where the infrared response has a Drude-like behaviour. Finally, the optical resistivity at zero frequency is evaluated from the Drude parameters.