Image reconstruction of targets illuminated by terahertz Gaussian beam with phase shift migration technique

2013 ◽  
Author(s):  
Chao Li ◽  
Shengming Gu ◽  
Xiang Gao ◽  
Guangyou Fang
Keyword(s):  
Image Reconstruction ◽  
Phase Shift ◽  
Gaussian Beam ◽  
Migration Technique

Z-TRANSFORM METHOD FOR OPTIMIZATION OF ADD-DROP CONFIGURATION SYSTEM

2015 ◽  
Vol 74 (8) ◽  
Author(s):  
Suzairi Daud ◽  
Kashif Tufail Chaudary ◽  
Mahdi Bahadoran ◽  
Jalil Ali
Keyword(s):  
Phase Shift ◽  
Gaussian Beam ◽  
Communication Technology ◽  
Input Signal ◽  
Ring Resonator ◽  
Incident Light ◽  
Dark Soliton ◽  
Transform Method ◽  
New Approaches ◽  
Configuration System

This paper presents the new approaches of optimization the add-drop configuration system by using Z-transform method. Dark soliton was chosen as the input signal and Gaussian beam was chosen as the control signal for the model proposed. The incident light was said to achieve the maximum resonance with the ring resonator when the phase shift, . The derivation, analyzation, and optimization of the system are typically very important especially for the communication technology.

scholarly journals Estimation of methods for calculating the phase shift of wave fronts of own modes of a confocal resonator

2019 ◽  
Keyword(s):  
Parabolic Equation ◽  
Phase Shift ◽  
Gaussian Beam ◽  
Phase Structure ◽  
Phase Lag ◽  
Topological Phase ◽  
Radiation Beam ◽  
Beam Method ◽  
Gaussian Beam Method ◽  
Laser Interferometers

Background: The redefinition of a unit of length - a meter - through a unit of time and a fundamental constant - the speed of light in vacuum - has opened up the fundamental possibility of a significant reduction in the uncertainty of its reproduction. Now progress in areas such as absolute ballistic gravimetry, control of large-sized aspherical optics, laser interferometry, and the production of electronic components in the semiconductor industry have made this feature extremely relevant. It is known that the measuring scale of laser interferometers used for precision distance measurement is non-linear, since the common-mode surfaces of any real radiation beam are located irregularly in space. To compensate for the effect of this irregularity on the measurement result, it is necessary to know the precision phase structure of real laser beams. Objectives of the work is comparing existing methods for studying the phase structure of optical radiation beams and estimating the distribution of the topological phase shift of a relatively uniform plane wave. Materials and methods:. The well-known theoretical methods for calculating the topological phase shift of in-phase surfaces of an optical beam are considered and compared - the Lommel-Debye method based on the Fresnel-Kirchhoff integral, the modified method based on the Rayleigh-Sommerfeld integral and the Gaussian beam method based on a parabolic equation. Results: Each method performed calculations of the accumulated phase lag of the focused radiation beam when moving the observation plane relative to the focal point. The distribution of the relative change in the distance between the in-phase surfaces in the range of displacements from λ to 106•λ was also calculated. The most adequate physical picture of the phenomenon was obtained by the Gaussian beam method based on a parabolic equation. Conclusion: The results will be used to reduce the systematic error of laser interferometers.

Criteria and Methods for Reliable Three-Dimensional Image Reconstruction

1974 ◽  
Vol 32 ◽  
pp. 330-331
Author(s):  
R. A. Crowther
Keyword(s):  
Image Reconstruction ◽  
Finite Number ◽  
Density Distribution ◽  
Electron Micrographs ◽  
Mathematical Problem ◽  
Three Dimensional ◽  
Ideal Case ◽  
Dimensional Image ◽  
General Object ◽  
The Ideal

The reconstruction of a three-dimensional image of a specimen from a set of electron micrographs reduces, under certain assumptions about the imaging process in the microscope, to the mathematical problem of reconstructing a density distribution from a set of its plane projections.In the absence of noise we can formulate a purely geometrical criterion, which, for a general object, fixes the resolution attainable from a given finite number of views in terms of the size of the object. For simplicity we take the ideal case of projections collected by a series of m equally spaced tilts about a single axis.

Object Wave Determination by Single-Sideband Methods

1973 ◽  
Vol 31 ◽  
pp. 266-267
Author(s):  
Kenneth H. Downing ◽  
Benjamin M. Siegel
Keyword(s):  
Phase Shift ◽  
Carbon Films ◽  
Object Wave ◽  
Electron Wave ◽  
Phase Object ◽  
Heavy Atoms ◽  
Single Sideband ◽  
Thin Carbon ◽  
Additional Phase Shift ◽  
Additional Phase

Under the “weak phase object” approximation, the component of the electron wave scattered by an object is phase shifted by π/2 with respect to the unscattered component. This phase shift has been confirmed for thin carbon films by many experiments dealing with image contrast and the contrast transfer theory. There is also an additional phase shift which is a function of the atomic number of the scattering atom. This shift is negligible for light atoms such as carbon, but becomes significant for heavy atoms as used for stains for biological specimens. The light elements are imaged as phase objects, while those atoms scattering with a larger phase shift may be imaged as amplitude objects. There is a great deal of interest in determining the complete object wave, i.e., both the phase and amplitude components of the electron wave leaving the object.

A Many-Beam Technique for Enhanced Resolution of Partial Dislocations

1972 ◽  
Vol 30 ◽  
pp. 646-647
Author(s):  
J. M. Oblak ◽  
B. H. Kear
Keyword(s):  
Phase Shift ◽  
Field Method ◽  
Dark Field ◽  
Bright Field ◽  
Field Technique ◽  
Weak Beam ◽  
Partial Dislocations ◽  
Enhanced Resolution ◽  
Nickel Base ◽  
Beam Technique

The “weak-beam” and systematic many-beam techniques are the currently available methods for resolution of closely spaced dislocations or other inhomogeneities imaged through strain contrast. The former is a dark field technique and image intensities are usually very weak. The latter is a bright field technique, but generally use of a high voltage instrument is required. In what follows a bright field method for obtaining enhanced resolution of partial dislocations at 100 KV accelerating potential will be described.A brief discussion of an application will first be given. A study of intermediate temperature creep processes in commercial nickel-base alloys strengthened by the Ll2 Ni3 Al γ precipitate has suggested that partial dislocations such as those labelled 1 and 2 in Fig. 1(a) are in reality composed of two closely spaced a/6 <112> Shockley partials. Stacking fault contrast, when present, tends to obscure resolution of the partials; thus, conditions for resolution must be chosen such that the phase shift at the fault is 0 or a multiple of 2π.

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