Measurement of Fractional Optical Vortex by a Ring-Type Multi-Pinhole Interferometer

2012 ◽  
Vol 433-440 ◽  
pp. 6339-6344 ◽  
Author(s):  
Gong Xiang Wei ◽  
Yun Yan Liu ◽  
Sheng Gui Fu ◽  
Ping Wang
Keyword(s):  
Fourier Transform ◽  
Topological Charge ◽  
Linear Part ◽  
Azimuthal Angle ◽  
Optical Vortex ◽  
Far Field ◽  
Diffraction Intensity ◽  
Intensity Pattern ◽  
Ring Type ◽  
The Fourier Transform

We presented a method for measuring the topological charge of a Fractional optical vortex (FOV) by a ring-type multi-pinhole interferometer (RMPI). We retrieved the sampled phase of the FOV passing through a ring-type multi-pinhole plate from the Fourier transform of a single far-field diffraction intensity pattern, and found the phase of FOV around the center approximately be linear with the azimuthal angle, the slope of the phase to the azimuthal angle at the linear part is equal to the topological charge of the FOV. Thus we proposed a method for measuring the l state and determining orbital angular momentum (OAM) of a FOV based on the property.

Phase Analyse of Non-Vortical and Vortical Beams in Fractional Fourier Transform System

2014 ◽  
Vol 602-605 ◽  
pp. 3648-3651
Author(s):  
Zhi Ping Dai ◽  
Zhen Jun Yang
Keyword(s):  
Fourier Transform ◽  
Intensity Distribution ◽  
Topological Charge ◽  
Fractional Fourier Transform ◽  
Phase Distribution ◽  
Dark Region ◽  
Strong Intensity ◽  
Beam Parameters ◽  
The Fourier Transform ◽  
Phase Analyse

The phase of vortical beams is very different from that of non-vortical beams. The phase of non-vortical and vortical beams in fractional Fourier transform system is investigated by selecting different parameters of the anomalous vortical beam. It is found that although the intensity distribution is similar except nearby the Fourier transform plane for the non-vortical and the vortical beams, the phase distribution is very different even the beam parameters are the same except the topological charge. The different phases bring different intensity distributions especially at the Fourier transform plane, i.e the center of non-vortical beams is a very strong intensity peaks, however the center of vortical beams is a dark region.

scholarly journals Analysis of Sound Waves with Semi Perforated Pipe

2019 ◽  
Vol 2 (3) ◽  
pp. 704-710
Author(s):  
Burhan Tiryakioglu
Keyword(s):  
Boundary Condition ◽  
Fourier Transform ◽  
Wave Equation ◽  
Pipe Wall ◽  
Far Field ◽  
Sound Waves ◽  
Hopf Equation ◽  
Hopf Method ◽  
The Fourier Transform ◽  
Perforated Pipe

The paper presents analytical results of radiation phenomena at the far field and solution of the wave equation with adequate boundary condition imposed by the pipe wall. An infinite pipe with perforated part is considered. The solution is obtained by using the Fourier transform technique in conjunction with the Wiener-Hopf Method. Applying the Fourier transform technique, the boundary value problem is described by Wiener Hopf equation and then solved analytically.

scholarly journals Dynamic RCS Estimation according to Drone Movement Using the MoM and Far-Field Approximation

2021 ◽  
Vol 21 (4) ◽  
pp. 322-328
Author(s):  
Dong-Yeob Lee ◽  
Jae-In Lee ◽  
Dong-Wook Seo
Keyword(s):  
Fourier Transform ◽  
Cross Section ◽  
Method Of Moments ◽  
Iterative Process ◽  
Rotation Angle ◽  
Field Approximation ◽  
Far Field ◽  
Impedance Matrix ◽  
The Matrix ◽  
The Fourier Transform

Micro-Doppler signatures from the rotating propellers of a drone can be utilized to distinguish the drone from clutter or airborne organisms with similar radar cross section (RCS) levels, such as birds and bats. To obtain the micro-Doppler signatures of a drone, calculation or measurement of the electric field scattered from the rotating propellers is essential. In this paper, using the relative angle concept and far-field approximation, we propose a way to rapidly estimate the dynamic RCS of a drone with several propellers according to its movement. In addition, based on the fact that the shape of the propeller does not change even if it rotates, we construct an impedance matrix only once and apply the matrix to the method of moments instead of the iterative process of calculating the impedance matrix and inverse matrix for each rotation angle of the propeller. Finally, by using the Fourier transform of the results from the proposed method, the rotation frequencies of the propellers according to the movement of the drone can be obtained.

scholarly journals Research of far-field diffraction intensity pattern in hot atomic Rb sample

2015 ◽  
Vol 23 (5) ◽  
pp. 5468 ◽  
Author(s):  
Ying Zhang ◽  
Xuemei Cheng ◽  
Xunli Yin ◽  
Jintao Bai ◽  
Pei Zhao ◽  
...  
Keyword(s):  
Far Field ◽  
Diffraction Intensity ◽  
Intensity Pattern

Zum kollektiven Anteil des Plasma-Mikrofeldes

1968 ◽  
Vol 23 (10) ◽  
pp. 1488-1498
Author(s):  
K. Hunger ◽  
R.W. Larenz
Keyword(s):  
Fourier Transform ◽  
Dipole Moment ◽  
Space Charge ◽  
Long Range ◽  
Field Distribution ◽  
Computer Experiments ◽  
Far Field ◽  
Nearest Neighbour ◽  
Charge Fluctuations ◽  
The Fourier Transform

The Holtsmark microfield evaluation is rediscussed. It is shown that in the usual computation of the Fourier transform a term is neglected which has the dimension of a dipole moment density. This term occurs only for long range forces (here Coulomb ones) and remains undetermined in the limit of an infinitely large system without interaction. Furthermore, it is sensitive to deviations from ergodicity. The true microfield distribution results as a Holtsmark distribution centered at the generally nonvanishing far field. As the distribution of the latter is Gaussian the complete distribution results as a convolution of the Holtsmark distribution with that of the far field. The parameter of the Gaussian far field distribution is computed for a non interacting plasma consisting of N charges, by taking into account explicitely the collective field of space charge fluctuations. The formulae arrived at with respect to the microfield as well as the micropotential suggest to perform numerical computer experiments (HUNGER, LARENZ and WILKE, to be published). For an interacting plasma, the far field is obtained qualitatively. It agrees with the microfield of HUNGER and LARENZ (1961). The far field dominates the Holtsmark nearest neighbour field at plasma conditions kT/e2n1/3 > 1.

Generation of a double-ring perfect optical vortex by the Fourier transform of azimuthally polarized Bessel beams

2019 ◽  
Vol 44 (6) ◽  
pp. 1504 ◽  
Author(s):  
Yansheng Liang ◽  
Shaohui Yan ◽  
Minru He ◽  
Manman Li ◽  
Yanan Cai ◽  
...  
Keyword(s):  
Fourier Transform ◽  
Optical Vortex ◽  
Bessel Beams ◽  
Double Ring ◽  
The Fourier Transform

scholarly journals Generation of Perfect Optical Vortices by Using a Transmission Liquid Crystal Spatial Light Modulator

2017 ◽  
Vol 2017 ◽  
pp. 1-10 ◽  
Author(s):  
Nelson Anaya Carvajal ◽  
Cristian H. Acevedo ◽  
Yezid Torres Moreno
Keyword(s):  
Liquid Crystal ◽  
Topological Charge ◽  
Spatial Light Modulator ◽  
Propagation Distance ◽  
Optical Vortex ◽  
Optical Vortices ◽  
Light Modulator ◽  
Intensity Pattern ◽  
Fourier Plane ◽  
Spiral Phase

We have experimentally created perfect optical vortices by the Fourier transformation of holographic masks with combination of axicons and spiral functions, which are displayed on a transmission liquid crystal spatial light modulator. We showed theoretically that the size of the annular vortex in the Fourier plane is independent of the spiral phase topological charge but it is dependent on the axicon. We also studied numerically and experimentally the free space diffraction of a perfect optical vortex after the Fourier back plane and we found that the size of the intensity pattern of a perfect optical vortex depends on the topological charge and the propagation distance.

scholarly journals Fourier Splitting Method for Kawahara Type Equations

2014 ◽  
Vol 2014 ◽  
pp. 1-4 ◽  
Author(s):  
Pablo U. Suárez ◽  
J. Héctor Morales
Keyword(s):  
Fourier Transform ◽  
Analytical Solutions ◽  
Linear Part ◽  
Splitting Method ◽  
Operator Method ◽  
Conserved Quantities ◽  
Kawahara Equation ◽  
Nonlinear Part ◽  
The Fourier Transform ◽  
Exponential Operator

In this work, we integrate numerically the Kawahara and generalized Kawahara equation by using an algorithm based on Strang’s splitting method. The linear part is solved using the Fourier transform and the nonlinear part is solved with the aid of the exponential operator method. To assess the accuracy of the solution, we compare known analytical solutions with the numerical solution. Further, we show that as t increases the conserved quantities remain constant.

scholarly journals Strain Sensitivity Enhancement of Broadband Ultrasonic Signals in Plates Using Spectral Phase Filtering

2021 ◽  
Vol 11 (6) ◽  
pp. 2582
Author(s):  
Lucas M. Martinho ◽  
Alan C. Kubrusly ◽  
Nicolás Pérez ◽  
Jean Pierre von der Weid
Keyword(s):  
Fourier Transform ◽  
Guided Waves ◽  
Strain Level ◽  
Energy Concentration ◽  
Short Time Fourier Transform ◽  
Time Frequency ◽  
Frequency Representation ◽  
The Fourier Transform ◽  
Short Time ◽  
Sensitivity Gain

The focused signal obtained by the time-reversal or the cross-correlation techniques of ultrasonic guided waves in plates changes when the medium is subject to strain, which can be used to monitor the medium strain level. In this paper, the sensitivity to strain of cross-correlated signals is enhanced by a post-processing filtering procedure aiming to preserve only strain-sensitive spectrum components. Two different strategies were adopted, based on the phase of either the Fourier transform or the short-time Fourier transform. Both use prior knowledge of the system impulse response at some strain level. The technique was evaluated in an aluminum plate, effectively providing up to twice higher sensitivity to strain. The sensitivity increase depends on a phase threshold parameter used in the filtering process. Its performance was assessed based on the sensitivity gain, the loss of energy concentration capability, and the value of the foreknown strain. Signals synthesized with the time–frequency representation, through the short-time Fourier transform, provided a better tradeoff between sensitivity gain and loss of energy concentration.

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