Light Diffraction Studies of CdS Phonon Masers: Off-Axis Cavity Structures

1974 ◽  
Vol 52 (14) ◽  
pp. 1239-1245
Author(s):  
J. Vrba ◽  
R. R. Haering
Keyword(s):  
Acoustic Waves ◽  
Mode Conversion ◽  
Light Diffraction ◽  
Acoustic Anisotropy

Light diffraction experiments on CdS phonon masers whose cavity normal is oriented at 15, 30, 45, 60, and 75° to the crystallographic c axis are presented and compared with theory. It is shown that in general the acoustic waves do not propagate along the direction of the cavity normal. An interpretation of the observations requires that one takes into account the acoustic anisotropy and the effect of mode conversion at the cavity walls.

Polarization hysteresis in dielectric films using light diffraction by acoustic waves

1984 ◽  
Vol 44 (5) ◽  
pp. 522-524 ◽  
Author(s):  
Alfred E. Attard ◽  
John F. Kuehls
Keyword(s):  
Acoustic Waves ◽  
Light Diffraction ◽  
Dielectric Films

Tunable Mode Conversion Using Acoustic Waves in Optical Microwires

2014 ◽  
Vol 32 (19) ◽  
pp. 3257-3265 ◽  
Author(s):  
Gil M. Fernandes ◽  
Nelson J. Muga ◽  
Armando Nolasco Pinto
Keyword(s):  
Acoustic Waves ◽  
Mode Conversion

Laser ultrasonic monitoring of reversible/irreversible modification of a real crack under photothermal loading

2020 ◽  
pp. 147592172091516
Author(s):  
Chen-Yin Ni ◽  
Jin-Chao LV ◽  
Yue-Ying Zhang ◽  
Hai-Yan He ◽  
Xi-Feng Xia ◽  
...  
Keyword(s):  
Acoustic Waves ◽  
Crack Detection ◽  
Optical Measurement ◽  
Mode Conversion ◽  
Surface Acoustic Waves ◽  
Equilibrium Temperature ◽  
Laser Ultrasonics ◽  
Loading Cycle ◽  
Detection Techniques ◽  
Significant Difference

We study the responses of laser-generated acoustic waves to localized reversible/irreversible modifications of microscopic asperities on crack surfaces during crack closure, which is an essential process in nonlinear photoacoustic/photothermal crack detection techniques. Our laser ultrasonics technique involves optical measurement of the transmission and mode conversion of the laser-generated surface acoustic waves caused by the crack. Reversible/irreversible modifications of asperities can be achieved via non-contact photothermal loading of the crack. Three photothermal loading cycles were realized in individual succession and were monitored using the laser ultrasonics technique at various experimental locations along the crack. In our experiments, each photothermal loading cycle includes multiple successive subcycles, in which the material is first heated and then cooled to its equilibrium temperature, thereby initiating local closing, followed by opening of the crack. Each subcycle is monitored twice using the laser ultrasonics technique, once each at the end of heating and cooling. Furthermore, each successive subcycle is accomplished at a higher power of heating laser than that of the previous subcycle. Significant differences in the peak-to-peak amplitude of the surface skimming longitudinal acoustic wave, which is excited by mode conversion of the Rayleigh wave by the crack, are revealed during the first cycle of photothermal loading. These differences clearly indicate a partial irreversibility of the mechanical processes occurring in the crack surfaces during subcycles of the first cycle. In a larger temporal scale, irreversible modification of crack surfaces is observed from the significant difference between the experimental results of the first photothermal loading cycle and the subsequent two cycles, whereas a reversible response of the crack surface to thermoelastic loading is observed from the similarity of the measurements accumulated during the two subsequent cycles.

Convolution and correlation using light diffraction from bulk acoustic waves

1975 ◽  
Vol 11 (13) ◽  
pp. 281 ◽  
Author(s):  
J.M. Rouvaen ◽  
E. Bridoux ◽  
R. Torguet ◽  
C. Carles
Keyword(s):  
Acoustic Waves ◽  
Light Diffraction ◽  
Bulk Acoustic Waves

Phonon Transport in Anisotropic Scattering Particulate Media

2003 ◽  
Vol 125 (6) ◽  
pp. 1156-1162 ◽  
Author(s):  
Ravi Prasher
Keyword(s):  
Cross Section ◽  
Acoustic Waves ◽  
Transport Theory ◽  
Mode Conversion ◽  
Anisotropic Scattering ◽  
Phonon Transport ◽  
Isotropic Scattering ◽  
Radiative Transport ◽  
Particulate Media ◽  
Transport Cross Section

Equation of phonon radiative transport (EPRT) is rewritten to include anisotropic scattering by a particulate media by including an acoustic phase function and an inscattering term which makes EPRT exactly same as equation of radiative transport (ERT). This formulation of EPRT is called generalized EPRT (GEPRT). It is shown that GEPRT reduces to EPRT for isotropic scattering and is totally consistent with phonon transport theory, showing that transport cross section is different from the scattering cross section. GEPRT leads to same formulation for transport cross section as given by phonon transport theory. However GEPRT shows that transport cross section formulations as described by phonon transport theory are only valid for acoustically thick medium. Transport cross section is different for the acoustically thin medium leading to the conclusion that mean free path (m.f.p) is size dependant. Finally calculations are performed for two types of scatterers for acoustic waves without mode conversion: (1) acoustically hard Rayleigh sphere; and (2) large sphere in the geometrical scattering regime. Results show that the scattering from these particles is highly anisotropic. It is also shown that for geometrical scattering case isotropic scattering leads to the conclusion of total internal reflection at the particle/medium interface.

Numerical modelling of MHD waves in the solar chromosphere

2005 ◽  
Vol 364 (1839) ◽  
pp. 395-404 ◽  
Author(s):  
Mats Carlsson ◽  
Thomas J Bogdan
Keyword(s):  
Magnetic Field ◽  
Acoustic Waves ◽  
Mode Conversion ◽  
Three Dimensions ◽  
Mhd Waves ◽  
Solar Chromosphere ◽  
Fast Mode ◽  
Reflected Waves ◽  
The Waves ◽  
The Magnetic Field

Acoustic waves are generated by the convective motions in the solar convection zone. When propagating upwards into the chromosphere they reach the height where the sound speed equals the Alfvén speed and they undergo mode conversion, refraction and reflection. We use numerical simulations to study these processes in realistic configurations where the wavelength of the waves is similar to the length scales of the magnetic field. Even though this regime is outside the validity of previous analytic studies or studies using ray-tracing theory, we show that some of their basic results remain valid: the critical quantity for mode conversion is the angle between the magnetic field and the k-vector: the attack angle. At angles smaller than 30° much of the acoustic, fast mode from the photosphere is transmitted as an acoustic, slow mode propagating along the field lines. At larger angles, most of the energy is refracted/reflected and returns as a fast mode creating an interference pattern between the upward and downward propagating waves. In three-dimensions, this interference between waves at small angles creates patterns with large horizontal phase speeds, especially close to magnetic field concentrations. When damping from shock dissipation and radiation is taken into account, the waves in the low–mid chromosphere have mostly the character of upward propagating acoustic waves and it is only close to the reflecting layer we get similar amplitudes for the upward propagating and refracted/reflected waves. The oscillatory power is suppressed in magnetic field concentrations and enhanced in ring-formed patterns around them. The complex interference patterns caused by mode-conversion, refraction and reflection, even with simple incident waves and in simple magnetic field geometries, make direct inversion of observables exceedingly difficult. In a dynamic chromosphere it is doubtful if the determination of mean quantities is even meaningful.

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