Photoelastic Constants Research Articles

Acoustooptic Properties of Cs3Bi2I9 Crystals

Cs3Bi2I9 crystals were grown, and their longitudinal-wave acoustooptic properties were studied. The crystals were found to possess a large acoustooptic figure of merit and photoelastic constants.

Diffraction of guided optical waves by surface acoustic waves in GaN

We report on acousto-optical diffraction of the guided optical modes (λ=633 nm) in GaN layers grown on (0001) sapphire substrates. The diffraction of both transverse electric (TE) and transverse magnetic (TM) modes has been observed. The dependence of the diffraction efficiency on the surface acoustic wave (SAW) power is in good agreement with Raman-Nath theory. The values of acousto-optic figure of merit, M2, and effective photoelastic constants p have been determined. For the SAW propagating in [11̄00] direction, the extracted values are M2=1.54×10−15 s3/kg, p=0.061 (TE modes) and M2=1.95×10−15 s3/kg, p=0.066 (TM modes). These values of M2 correspond to 1 and 1.3 of the acousto-optic figure for fused quartz. The obtained results demonstrate the potential of GaN-based structures for the development of blue–ultraviolet acousto-optical devices.

Modelling and characteristics of photoelastic waveguides in Si1−xGex/Si heterostructures

The modelling of the strain, refractive index and optical mode intensity profiles of photoelastic waveguide structures in Si1−xGex/Si heterojunctions are presented. Strain profiles due to the difference in the thermal expansion of Si1−xGex and SiNy are produced by depositing SiNy stripes on the heterostructure surface. The corresponding strain-induced refractive index changes are modelled by finite element analysis. The photoelastic constants are calculated and are used to find the strain-induced refractive index profiles in the waveguides. It is shown that these photoelastic waveguides exhibit a low degree of birefringence because they are oriented along the [100] crystal axis. Optical mode profiles are generated from finite difference calculations which show that there are three distinct guiding regions under each SiNy stressor stripe; these vary with stripe width. Experimental results show good agreement with the model, and both show that the modal characteristics of the photoelastic waveguides are determined by the SiNy stripe width.

Enhancement of photoelastic constant of optical thin film waveguide assisted by surface acoustic wave

In the present research, we proposed a method of controlling the photoelastic constant using surface acoustic waves, which had not previously been reported, and carried out experimental studies thereof. A Bragg diffraction was carried out to determine the photoelastic constants of Ta 2O 5. As a result, it is confirmed that the photoelastic constant of a Ta 2O 5 thin film undergoing a sputtering process, during which surface acoustic waves were excited on the substrate, was about 2.19–2.27 times larger than those of thin films on which surface acoustic waves were not excited.

Acoustooptical and elastic properties of laminated KY(MoO4)2 crystals

Data on acoustic (absorption and velocity of sound), optical (refractive index and optical absorption coefficient), and photoelastic (coefficients of acoustooptical quality and photoelastic constants) properties of KY(MoO4)2 crystals are obtained. It is shown that, not only does the anisotropy of binding forces lead to a significant anisotropy of acoustic and photoelastic properties, but it also determines anomalously high elastic nonlinearity in the direction of the Y-axis perpendicular to cleavage planes.

Fabrication of a thin film phase grating assisted by surface acoustic waves

Nakagawa et al. found in fabricating the Ta2O5 amorphous thin film by sputtering, that the refractive index and the photoelastic constant of the thin film are emphasized by the “diffused-out” electric field of the surface acoustic wave and that there, a phase grating is generated in which the thin film thickness, as well as the internal refraction index, vary periodically. This phenomenon is new and very interesting. This study intends to apply the power of surface acoustic waves. A thin film phase grating is fabricated, the mechanism of generation is analyzed, and engineering applications to optical devices are tested. Large variations of 1.78% at the maximum in the film thickness and 5.9% in the refraction index are obtained. The fabrication of a precise two-dimensional grating is easy. © 1999 Scripta Technica, Electron Comm Jpn Pt 3, 82(12): 26–33, 1999

The photoelastic constant and internal stress around micropipe defects of 6H-SiC single crystal

Hexagonal silicon carbide (6H-SiC) single crystals made by a modified Lely method contain a ‘micropipe’ which is one kind of serious defects degrading device performance. The micropipe accompanies strong internal stress around itself. We determined the photoelastic constant in the plane of (00·1) 6H-SiC and then estimated the magnitude of the internal stress around the micropipes. The photoelastic constant was 2.73 brewster at λ=546 nm. The internal stress around the micropipe was estimated to be 113∼166 MPa.

Crystal Symmetry Dependence of the Polarization of Brillouin Scattered Light

The Brillouin scattering is the light scattering by the phonons in the solid. It is very useful for studying the structural phase transition in the crystal and measuring the elastic and photoelastic constants of the materials. To accomplish these goals, one has to be able to determine the linkage between the polarization of the scattered light and the phonon modes which can also provide insight into the origin of the phase transition. In our paper, we calculated the scattering factors using elastic equations, photoelastic relation and radiation equations for an orthorhombic crystal. The results are summerized in the Chart. From the Chart provided below one can easily find the correspondence of the phonon mode to the polarization of the scattered light.

Mechanical and photoelastic properties of oriented poly-4-methyl-1-pentene investigated by Brillouin spectroscopy

The elastic constants C11, C13, C33 and C44 of oriented poly-4-methyl-1-pentane (P4M1P) films were measured with Brillouin scattering. The photoelastic constants p11, p13, p31 and p33 were measured by evaluating the integral intensities of the phonon lines. The correlation of the photoelastic constants p13 and p31 with the degree of stretching was determined by evaluating the relative integral intensities of the Brillouin lines with the phonon propagation vector into and perpendicular to the stress direction. The other photoelastic constants were measured by comparing the angle-dependent relative integral intensities of the transverse and longitudinal Brillouin lines. The elastic constants, as well as birefringence, were surprisingly found to be unaffacted by further stretching of the sample above the necking region. The density was constant for all degrees of stretching. The photoelastic constants p11 and p33 showed significant variation during deformation. The results have been compared with former measurements of polypropylene (PP) by Cavanaugh and Wang. Because the elastic constants are unchanged during deformation, the modulation of the intensities is due to the variation of the photoelastic constants for this material.

Photoelasticity for the investigation of internal stress in BGO scintillating crystals

Quality control of scintillating crystals production requires the on-line monitoring of the state of internal stress levels. The determination of the photoelastic constant in crystals is fundamental in this measurement, rendered necessary by the crystal fragility, a limiting factor in the construction of calorimeters (radiation detectors consisting in large arrays of crystals). In this work high-density BGO (Bismuth Germanate Bi 3Ge 4O 12) crystals for calorimeters have been studied by means of photoelasticity. A test bench, based on a circular polariscope, an image acquisition system, a data processing unit and a suitable mechanical loading unit have been developed and applied to crystal sample testing. The results provide new data on photoelasticity of BGO and outline the basic features for the construction of an apparatus for on-line inspection of crystal quality.

Photoelasticity and quadratic permittivity of wide-gap semiconductors

Expressions for the photoelastic constants are obtained on the basis of an analogy between the photoelastic and elastic properties of semiconductor crystals. Calculations were performed for wide-gap semiconductors (silicon carbide and boron, aluminum, and gallium nitrides) with sphalerite and wurtzite structures. The quadratic permittivity is also calculated for hexagonal structures.

Optical and acousto-optical properties of Nd:phosphate glasses

Nd 3+-doped potassium barium aluminum phosphate (KBAP) glasses have been synthesized with a Nd concentration of 4%. The glasses are characterized for their optical and acousto-optical properties and these properties are compared with fused quartz and LiNbO 3. The refractive index of this glass varies from 1.976 to 1.523 in the wavelength range 200–2500 nm, with a value of 1.612 at 633 nm. The acoustic velocity and the photoelastic constant are 7.31 × 10 5 cm/s and 0.226 respectively. Acousto-optic figures of merit of this material are comparable to those of quartz. It has been concluded that these glasses can be effectively used at high frequencies for wideband acousto-optic deflector and modulator applications.

Polarization properties of the flint glass fiber

To realize stable characteristics of a current sensor using the Faraday effect in an optical fiber, it is necessary to prevent the influence of birefringent effect on light passing the fiber, which is caused by photo-elastic effect and/or lack of axial symmetry of its structure. The flint glass fiber manufactured from flint glass with very small photo-elastic constant, which has circular core and satisfies the single ode condition,has been developed to solve this problem. This paper reports results of a study to clarify polarization properties of the fiber and to consider a method for highly stabilizing the polarization. From experiments to investigate the relationship between state of polarization of light inserted to the fiber and that emitted from another end, it was confirmed that the birefringence due to the photo-elastic effect and the lack of symmetry are negligibly small. It also became known that the azimuth angle of polarization of the emitted light depends on the shape of the curve of the fiber. Namely, a rotation of the polarization plane is equal to the amount of line integral of the torsional rate along the curve. A countermeasure is necessary for this phenomenon, because characteristics of the current sensor may be influenced if the flint glass fiber coil is deformed by environmental factors. From a consideration of the mechanism of the phenomenon, it is inferred that the problem can be solved by reciprocating light in the fiber to stabilize the polarization. The effect of this method is confirmed experimentally. >

Photo-Elastic Constants of Proton-Exchanged LiNbO 3

The acousto optic interaction on proton-exchanged 128°-rotated Y-cut LiNbO3 was investigated to evaluate the photo-elastic constants. The experimental and theoretical analysis using a surface acoustic wave of 200 MHz and a He-Ne laser beam showed that the acoustic power required for 100% diffraction depends on the proton-exchange depth and that the photo-elastic constants of the proton-exchanged layer are 76% of those in unexchanged LiNbO3. The effects of annealing on the photo-elastic constants and the diffraction efficiency were also measured.

Laser picosecond acoustics in double-layer transparent films

By the optical pump-and-probe technique, picosecond acoustic pulses are excited and detected in thin transparent double-layer films of silica and silicon nitride upon opaque chromium substrates. By taking both acoustic and optical multiple reflections into account, one can successfully model the main features of the reflectance variation. The film thicknesses, sound velocities, and photoelastic constants are derived by use of known values of the refractive indices.

Photoelastic constants of germanate glasses containing lead and bismuth oxides

Regression equations which accurately approximate the concentration curves of the photoelastic constants of lead bismuth germanate glasses were obtained and the isolines of the photoelastic constants were plotted and graphically illustrate the change in the properties of the glasses in almost the entire glass-formation region of the PbO-Bi2O3-GeO2 system. The partial values of the photoelastic constants of the oxides, components of these glasses, were determined and are in agreement with the values established for glasses of other systems. The data obtained can be used in planning the compositions of effective optical media for fabrication of light and acoustic lines for acousto-optic instruments and glasses with a zero optical stress coefficient.

Near-resonance acousto-optical interactions in GaAs and InP

Acousto-optical properties of GaAs and InP are thoroughly investigated for photon energies tending to the band gap from below, and the whole set of photoelastic constants is determined as a function of the wavelength λ for λ≤1.06 μm. Figures of merit as high as 1200 times those of silica have been measured. It is shown how one can take advantage of the near-resonance acousto-optical properties of GaAs and InP in device design, in spite of the optical absorption. Such devices could be broadband, fast, compact, and insensitive to light polarization and may involve other direct-gap III-V crystals, adapted to the laser radiation.

Determination of the elastic and photoelastic constants of quartz-type GaPO4 by Brillouin scattering.

The full elastic and photoelastic tensors of quartz-homeotypic ${\mathrm{GaPO}}_{4}$ were measured at room temperature by Brillouin scattering. The phonon spectra were taken in 90\ifmmode^\circ\else\textdegree\fi{} scattering with a computer-controlled triple-pass Fabry-Perot interferometer. The six independent elastic constants show remarkable differences with quartz and berlinite; the value of ${\mathit{c}}_{14}$ is only about one-fourth, while ${\mathit{c}}_{12}$ and ${\mathit{c}}_{13}$ are much larger than in those two homeotypic materials. The photoelastic constants are mostly higher than in quartz.

A brief review of photo-orthotropic elasticity theories

The development of the theory of birefringence of annotropic composites has proceeded mainly along the following directions, strew strain models, analogy, integrated photoelasticity and tensonal nature of birefringence. All these studies have concluded that three independent photoelastic constants are needed to characterize orthotropic model materials. In the literature, there has not been uniformity of notation used in the representations of the results.In this paper, using uniform notation, existing photo-orthotropic clasticity theories are reviewed under three major headings stress-optic laws strain-optic laws and approximate strain-optic laws. The interrelation ships between stress-optic and strain-optic coefficients are brought out Interpretation of isoclinics is discussed. The steps necessary to calibrate a birefringent orthotropic composite are summarized and finally the influence of residual birefringence is also discussed.

Enhancement of Photoelastic Constant of Optical Thin-Film Waveguide Assisted by Surface Acoustic Wave

In the present research, we propose a method of controlling the photoelastic constant using surface acoustic waves. A Bragg diffraction is carried out to determine the photoelastic constants of Nb2O5. As a result, it is confirmed that the photoelastic constant of Nb2O5 thin film undergoing a sputtering process, during which surface acoustic waves were excited on the substrate, was about 3 to 6 times larger than those of thin films on which surface acoustic waves were not excited.