A M HAMED
Articles written in Pramana – Journal of Physics
Volume 94 All articles Published: 16 August 2020 Article ID 0126 Research Article
In this paper, a new concentric Hamming linear aperture is suggested. The point spread function (PSF) is computed for concentric Hamming linear aperture and it is compared with the corresponding circular, conventional Hamming and obstructed Hamming apertures. In addition, the autocorrelation corresponding to the aperture under consideration is computed and plotted. Application of the Hamming linear aperture in the formation of modulated speckle images of Ramses II statues using definite random diffuser is given. A diffuser limited by a circular uniform aperture is the basic element in the formation of ordinary speckle images located in the Fourier plane. Meanwhile,the Fourier spectrum of images of Ramses II multiplied by the ordinary speckle give modulated speckle images. Discrimination between the modulated speckle images is justified by comparing the profiles corresponding to each speckle image. Finally, the speckle contours and correlation of the modulated speckle images compared to the ordinary speckle images are investigated. It is noted that all computation and formation of images and plots are based on fast Fourier transform (FFT) techniques using Matlab codes.
Volume 95 All articles Published: 19 July 2021 Article ID 0122 Research article
Using the same diffuser, linear, quadratic and Hamming apertures can form static speckle images. The distribution of the obtained speckle images using modulated apertures is computed by examining the full width at half maximum (FWHM) of the autocorrelation function of the sampled speckle pattern. The FWHM results are compared with the results obtained with open circular aperture. In addition, the effects of the neighbourhood size over the computed speckle contrast are investigated as a function of speckle size.
Volume 95 All articles Published: 24 November 2021 Article ID 0202 Research Article
Fourier transform (FT) corresponding to the diffuser has a comb function realised from uniform illumination, and hence the speckle image is nearly equal to comb point spread function (PSF). Consequently, the resulted distribution permits computation of the speckle size from the FWHM corresponding to the PSF of the HG$_nm$ annular aperture. In the second method, the numerical autocorrelation of the speckle images using new apertures are computed and the speckle sizes are obtained. The results in both methods are compared with the speckle images obtained using circular aperture. It is noted that, the maximum number of spots produced in the HG$_nm$ modes given by combinations m, n ∈ [0, 5] is (m + 1) (n + 1) = 36 and all images and plots are obtained using Mat-Lab codes.
Volume 96, 2022
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