Experimental investigations of second‐harmonic spectra and Langmuir wave collapse

1991 ◽  
Vol 3 (9) ◽  
pp. 2558-2567 ◽  
Author(s):  
Faiz Dahmani ◽  
Djamel Ghobrini ◽  
Malek EL‐Mahdaoui
Keyword(s):  
Second Harmonic ◽  
Langmuir Wave ◽  
Experimental Investigations ◽  
Wave Collapse

scholarly journals Combination of Phase Matching and Phase-Reversal Approaches for Thermal Damage Assessment by Second Harmonic Lamb Waves

Materials ◽  
2018 ◽  
Vol 11 (10) ◽  
pp. 1961 ◽  
Author(s):  
Weibin Li ◽  
Shicheng Hu ◽  
Mingxi Deng
Keyword(s):  
Lamb Wave ◽  
Lamb Waves ◽  
Second Harmonic ◽  
Experimental Investigations ◽  
Phase Matching ◽  
Study Phase ◽  
Linear Wave ◽  
Material Degradation ◽  
Promising Alternative ◽  
Phase Reversal

It is known that measurement and extraction of the tiny amplitude of second harmonic Lamb waves are the main difficulties for practical applications of the nonlinear Lamb wave technique. In this study, phase-reversal approaches and phase matching technique are combined to build up the second-harmonic generation (SHG) of Lamb waves. A specific Lamb wave mode pair, which satisfied phase matching conditions, is selected to ensure the generation of cumulative second harmonic waves. Lamb wave signals with the same frequency but in reverse phase, propagating in the given specimen, are added together to counteract the fundamental waves, and simultaneously to enhance the signals of the second harmonic generated. The obtained results show that the phase-reversal approach can enhance the signals of second harmonic Lamb waves, and effectively counteract that of the fundamental waves. The approach is applied to assess the thermal-induced material degradation in the stainless steel plates. Distinctions of the acoustic nonlinearity parameters under different degraded levels are clearly shown in an improved repeatable and reliable manner, while those of linear wave velocity in the specimens are neglectable. The experimental investigations performed indicate that the proposed approach can be taken as a promising alternative for assessment of material degradation in its early stages.

Impossibility of Zakharov's short-wavelength modulational instability in plasmas with intense Langmuir turbulence

2002 ◽  
Vol 68 (1) ◽  
pp. 1-25 ◽  
Author(s):  
V. I. EROFEEV
Keyword(s):  
Experimental Data ◽  
Short Wavelength ◽  
Modulational Instability ◽  
Langmuir Wave ◽  
Traditional Theory ◽  
Langmuir Turbulence ◽  
Wave Dissipation ◽  
Physical Reason ◽  
Electron Diffusion ◽  
Wave Collapse

An analysis of two experimental observations of Langmuir wave collapse is performed. The corresponding experimental data are shown as evidence against the occurrence of collapses. The physical reason preventing the collapses is found to be the nonresonant electron diffusion in momentum. In this process, plasma thermal electrons are efficiently heated at the expense of wave energy, therefore intense collisionless wave dissipation takes place. The basic reason for the underestimation of nonresonant electron diffusion in the traditional theory is shown to be the substitution of a real plasma by a plasma probabilistic ensemble.A study of nonresonant electron diffusion refraining from ensemble substitution is performed. It is shown that its intensity is sufficient for suppression of Zakharov's short-wavelength modulational plasma instability [Zakharov, V. E., Sov. Phys. JETP35, 908 (1972)]. This explains the nonoccurrence of Zakharov's Langmuir wave collapse in experiments.

Second harmonic electromagnetic emission via Langmuir wave coalescence

1996 ◽  
Vol 3 (1) ◽  
pp. 149-159 ◽  
Author(s):  
A. J. Willes ◽  
P. A. Robinson ◽  
D. B. Melrose
Keyword(s):  
Second Harmonic ◽  
Langmuir Wave ◽  
Electromagnetic Emission

scholarly journals Engineering gallium phosphide nanostructures for efficient nonlinear photonics and enhanced spectroscopies

Nanophotonics ◽  
2021 ◽  
Vol 0 (0) ◽  
Author(s):  
Gianni Q. Moretti ◽  
Emiliano Cortés ◽  
Stefan A. Maier ◽  
Andrea V. Bragas ◽  
Gustavo Grinblat
Keyword(s):  
Magnetic Dipole ◽  
Bound States ◽  
Gallium Phosphide ◽  
Second Harmonic ◽  
Periodic Array ◽  
Experimental Investigations ◽  
Point Dipole ◽  
Quality Factors ◽  
Cell Conversion ◽  
Elliptical Cylinders

Abstract Optical resonances arising from quasi-bound states in the continuum (QBICs) have been recently identified in nanostructured dielectrics, showing ultrahigh quality factors accompanied by very large electromagnetic field enhancements. In this work, we design a periodic array of gallium phosphide (GaP) elliptical cylinders supporting, concurrently, three spectrally separated QBIC resonances with in-plane magnetic dipole, out-of-plane magnetic dipole, and electric quadrupole characters. We numerically explore this system for second-harmonic generation and degenerate four-wave mixing, demonstrating giant per unit cell conversion efficiencies of up to ∼ 2 W−1 and ∼ 60 W−2, respectively, when considering realistic introduced asymmetries in the metasurface, compatible with current fabrication limitations. We find that this configuration outperforms by up to more than four orders of magnitude the response of low-Q Mie or anapole resonances in individual GaP nanoantennas with engineered nonlinear mode-matching conditions. Benefiting from the straight-oriented electric field of one of the examined high-Q resonances, we further propose a novel nanocavity design for enhanced spectroscopies by slotting the meta-atoms of the periodic array. We discover that the optical cavity sustains high-intensity fields homogeneously distributed inside the slot, delivering its best performance when the elliptical cylinders are cut from end to end forming a gap, which represents a convenient model for experimental investigations. When placing an electric point dipole inside the added aperture, we find that the metasurface offers ultrahigh radiative enhancements, exceeding the previously reported slotted dielectric nanodisk at the anapole excitation by more than two orders of magnitude.

scholarly journals The Influence of Wave Nonlinearity on Cross-Shore Sediment Transport in Coastal Zone: Experimental Investigations

2020 ◽  
Vol 10 (12) ◽  
pp. 4087
Author(s):  
Yana Saprykina
Keyword(s):  
Energy Transfer ◽  
Sediment Transport ◽  
Second Harmonic ◽  
Breaking Waves ◽  
Wave Transformation ◽  
Experimental Investigations ◽  
Harmonic Amplitude ◽  
Linear Wave ◽  
Coastal Zones ◽  
Non Linear

On the basis of field experiment data, the main features of influence of non-linear wave transformation scenarios on cross-shore sediment transport in coastal zones were investigated. The bottom deformations due to the non-linear wave transformation follow the specific scenario. The increase in the second non-linear harmonic amplitude leads to the erosion of the underwater slope at the distances corresponding to this process, with the subsequent accumulation of sandy material closer to the shore at distances where the amplitude decreases during the backward energy transfer to the first harmonic. This can be explained by the change in the phase shift between harmonics during non-linear wave transformation. The second harmonic maximum provides the point near which the bottom deformations occur in different directions. Scenarios of non-linear wave transformation in which backward energy transfer from the second non-linear harmonic to the first is close to the shoreline will contribute to the transport and accumulation of the sediment on the coast. These scenarios are more characteristic of “small waves”. The scenario without a periodical exchange of wave energy between non-linear harmonics (with an increase in the second harmonic only) that is characteristic of large storm waves and plunging breaking waves will lead to the erosion of the underwater bottom profile.

Evidence for Langmuir wave collapse in the interplanetary plasma

1992 ◽  
Vol 19 (12) ◽  
pp. 1303-1306 ◽  
Author(s):  
Paul J. Kellogg ◽  
K. Goetz ◽  
R. L. Howard ◽  
S. J. Monson
Keyword(s):  
Langmuir Wave ◽  
Wave Collapse ◽  
Interplanetary Plasma
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