Photoelastic Constants Research Articles

A comparison of photoelastic constants of disk- and square-shaped glasses using the heterodyne method: An empirical approach

A comparison of photoelastic constants of disk- and square-shaped glasses using the heterodyne method: An empirical approach

Characterization of photoelastic materials by Mach–Zehnder interferometry: Application to trigonal calcium galogermanate (CGG) crystals

We explore piezooptic and photoelastic properties of Ca3Ga2Ge4O14 (CGG) crystals. A Mach–Zehnder interferometry technique is utilized to determine a complete set of the piezooptic tensor constants πim, with particular attention to the measurement accuracy, reliability, and uncertainty resolution in the piezooptic measurements. For these reasons, independent piezooptic constants or their combinations were determined by performing interferometric measurements for different geometries of piezooptic coupling using samples of both principal (direct) and non-principal (X/45°) crystallographic cuts. Basing on the results of piezooptic measurements, a complete set of photoelastic tensor constants pim and the acousto-optic performance (figure of merit M2) of CGG crystals were evaluated. The obtained piezooptic, photoelastic, and acousto-optic characteristics of CGG crystals are compared with those of other crystals of the langasite group, langasite and CTGS (Ca3TaGa3Si2O14). A comparative analysis reveals a correlation between the values of the piezooptic or photoelastic constants and the lattice parameters for this group of crystals. High optical quality and optical transparency in the UV region of the spectrum up to 260 nm together with extremely high mechanical resistance to uniaxial compression (≤2000 kg/cm2) opens up the possibility for specific application of CGG crystal as an optical material for piezooptic sensors of high uniaxial compression. The presented piezooptic interference technique along with methodological and metrological approaches paves the way for accurate and unambiguous characterization of photoelastic crystal materials of trigonal symmetry.

Exploring of anisotropy of acousto-optic interaction in lead molybdate crystals

The dependence of the elastic and acousto-optic properties of lead molybdate crystals on the direction of the wave vector and the polarization of acoustic and optical waves has been studied. The effective photoelastic constants were determined by the Dixon method for various geometries of the Bragg light diffraction. The dependence of the acousto-optic quality factor on the direction of the wave vector of longitudinal acoustic waves in the symmetry plane has been studied in detail. It is shown that in this case the largest and smallest values of the acousto-optic quality factor are observed when light is diffracted by pure longitudinal waves in this plane. It is also shown that the values of the acousto-optic quality factor in lead molybdate crystals are practically the same as in paratellurite crystals.

Acoustic properties, elasticity, and equation of state of glycerol under pressure.

We employed high-pressure Brillouin scattering to study the pressure dependencies of acoustic modes of glycerol up to 14GPa at 300K. We observed longitudinal acoustic velocities and transverse acoustic velocities for the first time from 5 to 14GPa. The results allow the determination of a complete set of elastic properties and an accurate determination of the pressure-volume (P-V) equation of state (EOS). EOS parameters, K0 = 14.9 ± 1.8GPa and K'0 = 5.6 ± 0.5, were determined from fits to the data from ambient pressure to 14GPa. Direct volume measurements of the P-V EOS are consistent with those determined by Brillouin scattering. A deviation from a Cauchy-like relationship for elastic properties was observed, and the pressure dependencies of the photoelastic constants and relaxation times were documented from 5 to 14GPa. These results have broad implications for glass-forming liquids, viscoelastic theory, and mode coupling theory.

Анизотропия упругих и фотоупругих свойств кристаллов CaМоО4

The anisotropy of the elastic and photoelastic properties of calcium molybdate crystals has been studied for Bragg diffraction of light by longitudinal acoustic waves propagating in the (001) plane. It is shown that the efficiency of the acousto-optic interaction can be characterizedby the introduced acousto-optic efficiency coefficient, which is determined from the elasticand photoelastic constants of the crystal. A strong dependence of the coefficients of the acousto-optic quality and the acousto-optic efficiency on the direction of propagation of acousticwaves in the investigated plane is revealed.

Оценки диэлектрических и оптических характеристик бинарных 3D- и 2D-соединений IV группы

Using the Harrison’s bond orbital model for the IV group 3D and 2D com-pounds analytical expressions of the high- and low-frequency dielectric suscepti-bilities and dielectric constants, linear electrooptical coefficient, photoelastic con-stants and pressure dependences of the dielectric constants are obtained.

Estimates of the dielectric and optical characteristics for the IV group 3D- and 2D-binary compounds

Using the Harrison's bond orbital model for the IV group 3D- and 2D-compounds analytical expressions of the high- and low-frequency dielectric suscepti-bilities and dielectric constants, linear electrooptical coefficient, photoelastic con-stants and pressure dependences of the dielectric constants are obtained. Keywords:: dielectric susceptibility and permittivitiy, photoelectric coefficient.

Photoelasticity of a MgO single crystal from polarized Brillouin scattering spectroscopy.

MgO is a crystalline solid with significant practical and theoretical value in many fields. Brillouin scattering has long been regarded as a reliable method for accurately measuring the elasticity and photoelasticity of crystals; however, its practical application in photoelasticity has been stagnant. In this paper, three independent photoelastic constants of MgO have been measured for the first time by polarized Brillouin scattering spectroscopy and we have defined a scattering factor containing three photoelastic constants to connect with the Brillouin peak intensity. Accordingly, the ratios of |p11/p44| = 2.87 (1), |p12/p44| = 0.53 (2), and |p12/p11| = 0.18 (1) were accurately determined by comparing the intensities of transverse and longitudinal acoustic modes within the same spectrum. Then, a standard sample of CaF2 crystals was adopted to calculate the corresponding peak intensity of MgO to achieve the absolute values (|p44| = 0.085 (1), |p11| = 0.244 (4) and |p12| = 0.045 (3)). Finally, all three constants were confirmed to be negative. These first-hand Brillouin scattering results can eliminate the long-standing discrepancies of the photoelastic constants of MgO. A standard process for the simultaneous measurement of elasticity and photoelasticity through Brillouin scattering was also constructed.

Stress-induced and photo-induced birefringences in As2S3 glass

The birefringence in As2S3 glass that is induced by either uniaxial stress or illumination with linearly-polarized light (ħω = 2.0 and 2.3 eV) is comparatively studied using a specially-designed phase meter operating at a wavelength of 633 nm (∼2.0 eV). The photoelastic constant of As2S3 is negative (−6 × 10−12 Pa−1): the refractive index parallel to an applied uniaxial stress becomes smaller, which is contrastive to that (+3.5 × 10−12 Pa−1) in SiO2 glass. On the other hand, the photoinduced birefringence in As2S3 is also negative; i.e., the refractive index in the direction parallel to the electric field of excitation light becomes smaller than the perpendicular. These resembling features with comparable magnitudes of the stress- and photo-induced birefringences imply common structural origin. We propose that the negative birefringences can be understood by a unified model that assumes anisotropically-aligned segmental layer structures which are produced by mechanical and photo-structural atomic motions.

Properties and structure of ternary BaO−SnO−P2O5 glasses

Series of Ba/Sn phosphate glasses (33 and 40 mol% P2O5) are investigated by 31P MAS NMR and neutron diffraction to clarify the effects of substituting Sn with Ba. The structural parameters are related to glass properties, among them to the photoelastic constant (PEC). Different from the increase of the Sn−O coordination number to four in Zn/Sn phosphate glasses (33 mol% P2O5) the NSnOs of 3.2 and 3.4 do not change with substituting Sn with Ba. The stacking of layer-like entities of Sn or Ba oxygen polyhedra is suggested to cause the first scattering peak at 12 nm−1. Non-bridging oxygens shared by two or more Ba2+ lead to stiff networks with increasing BaO content which is accompanied with increasing Tg, decreasing thermal expansion, and better corrosion resistance. The slopes of the compositional dependence of the PEC of the Ba/Sn glasses are smaller than reported for Zn/Sn glasses which corresponds to the constant NSnOs.

Colorless SnO- and Sb2O3-containing borate and borosilicate glasses with small photoelastic and high refractive properties

We examined the relationship between optical properties and structures of 5s2-type cations such as Sn2+- and Sb3+-containing borate and borosilicate glass. Linear evolutions were observed for the compositional dependences of density, glass transition temperature, refractive index, and photoelastic constant in visible transparent oxide glasses. The structural information was provided using vibrational spectroscopy to elucidate polyhedral units of the borate and borosilicate systems. A weak ligand field around a Sn2+ close to tetrahedral borate unit, which is supported by applying density functional theory calculation, might lead to a blueshift of optical bandgap keeping small photoelastic constant and high refractive index.

Distributed strain sensing, employing apodized π-phase shifted FBG: Application in power transformer oil breakdown detection

Early detection of power transformer oil breakdown can save the transformer and power grid from any potential damages. In this article, a novel distributed strain sensing system based on apodized π-phase-shifted Fiber Bragg Grating (FBG) is presented in order to detect power transformer oil breakdown. The main objective is to detect high-frequency acoustic waves and ultra-small strains resulting from partial discharge (PD) occurrence. To this end, optical fiber under various time and position dependent strain conditions is simulated by employing transfer matrix method. Strain is incorporated in the equations by employing photo-elastic constants. For a single FBG sensor case employing a laser at a fixed wavelength of 1550 nm, it is shown that incorporation of a π phase shift drastically increases the sensitivity, reaching values as high as 60 %/0.1μstrain in reflected light intensity. However, maximum measurable strain is limited to only 0.25 μstrain. Afterwards, a suitable Gaussian apodization function is applied to the FBG which drastically increased the strain measurement range to almost 0.45 μstrain by a complete suppression of sidelobes in the reflected light spectrum. It is shown that the proposed system is capable of detecting high-frequency PD-induced acoustic waves of up to 500 kHz.

Anisotropy of elastic and photoelastic properties of lithium niobate crystals

The elastic and photoelastic constants of lithium niobate crystals and the attenuation coefficients of acoustic waves at room temperature have been determined by the Bragg diffraction of light by sound. The components of the photoelasticity tensor were determined by the modified Dixon method. The obtained values of the constants were used to determine the anisotropy of the effective elastic and photoelastic constants with a change in the direction of propagation of acoustic waves in the (100) symmetry plane, for different directions of the wave vector and polarization of light relative to the sound wave vector. It is shown that, for certain geometries of the Bragg light diffraction, there is a correlation between the orientation dependences of the effective elastic and photoelastic constants in the investigated plane. The results of the study can be used to analyze the anisotropy of the photoelastic properties of lithium niobate crystals and determine the diffraction geometry with the highest efficiency of Bragg light diffraction.

Dielectric and optical properties of the cubic SiC, GeC and SnC monocrystals: Model estimations

Within the scope of the Harrison's bond orbital model analytical expressions of the high- and low-frequency dielectric susceptibilities and dielectric constants, linear electrooptical coefficient, photoelastic constants and pressure dependences of the dielectric constants are obtained for the cubic carbides of the group IV elements. Keywords: dielectric susceptibility, dielectric constants, electrooptical coefficient, photoelastic constant.

Диэлектрические и оптические свойства кубических монокристаллов SiC, GeC и SnC: модельные оценки

Within the scope of the Harrison’s bond orbital model analytical expressions of the high- and low-frequency dielectric susceptibilities and dielectric constants, linear electrooptical coefficient, photoelastic constants and pressure dependences of the dielectric constants are obtained for the cubic carbides of the group IV elements.

Logan Hargrove and nonlinear acoustics

Logan Hargrove became involved in nonlinear acoustics as a master’s student at Oklahoma State University under George Thurston, research that led to the 1957 JASA paper “Nonlinear Properties of Circular Orifices.” His involvement continued as a doctoral student under Egon Hiedemann at Michigan State University, where he published the 1960 JASA letter “Fourier Series for the Finite Amplitude Sound Waveform in a Dissipationless Medium.” The letter was part of his research on the use of optical methods to characterize sound fields, which culminated in Hargrove and Achyuthan’s 1965 Physical Acoustics series chapter “Use of Light Diffraction in Measuring the Parameter of Nonlinearity of Liquids and the Photoelastic Constants of Solids.” Following his subsequent employment at Bell Laboratories, where he worked primarily in optics and reported the first demonstration of a mode-locked laser, Logan became a scientific officer at the Office of Naval Research and began funding basic research in nonlinear acoustics. This presentation provides an overview of the research projects and graduate students in nonlinear acoustics that were funded by Logan at UT Austin for nearly three decades. Part of Logan’s legacy is that many students he funded perform research in nonlinear acoustics to this day.

Evaluation of gripping sensor using polyurethane with high photoelastic constant

In this study, the measurement of the gripping force on an object using a photoelastic polyurethane sensor is reported. A small amount of force (0.1–10 N) is detected using polyurethane with a high photoelastic constant of 1000–10 000 (×10–12 Pa−1). The force is detected based on the change in the optical path difference due to birefringence when stress is applied to the polyurethane. The value after correction processing for light-receiving intensity that periodically changed with respect to stress is used to determine the force. This corrected value is obtained from the sum of the absolute values of the time difference of the received voltage. The sensor, installed at the fingertips of the robot hand, is used to lift hard and soft imitation eggs, both of which were successfully lifted using a force of approximately 1 N, as detected by the sensor.

Elasto-optic properties and internal stress analysis for monoclinic and trigonal crystals

We study the elasto-optic behaviour of monoclinic and trigonal crystals. The eigenvalues and eigenvectors of the dielectric impermeability tensor under stress are evaluated by the means of the approximated formulae obtained by Sirotin. The parameters which characterize Bertin's surfaces and fringe patterns in conoscopic observation are determined as functions of either residual or applied stress. Later, the photoelastic constants, and the rotation of the optic plane and optic axes bisector are estimated in order to allow for the evaluation of the residual or applied stress by conoscopic measurements. Finally, we obtain the dependence of the refraction indices on the stress. The knowledge of these crystal properties is mandatory for applications in high physics energy, security, geological prospection and in crystals for photonics and medical applications. The evaluated photoelastic constants allow the development of methodologies for an easy and fast quality control via stress distribution detections by means of conoscopic observation, even for strongly anisotropic crystals. As a case study we apply these results to the cases of monoclinic Lu2(1-x)Y2xSiO5(LYSO) and trigonal LiNbO3 (Lithium Niobate).

Ultrafast laser-induced guided elastic waves in a freestanding aluminum membrane

Ultrafast laser-induced guided acoustic waves in thin, freely suspended films are important for many applications adopting the laser-ultrasonics technique. These waves show unique dispersion relations, leading to minimal propagation losses and acoustic energy confinement. While this principle has been known, the separation of various physical effects in the formation of measured signals involving these guided acoustic waves has not been clearly elaborated. Here, we present a combined experimental and theoretical study on all-optical excitation and detection of these waves in a thin, freestanding aluminum membrane. The acoustic dynamics is excited and measured by using a femtosecond time-resolved pump-probe technique with controlled probing position, enabling spatially resolved detection. The measured signals are compared with an advanced numerical model that we developed earlier [H. Zhang et al., Phys. Rev. Appl. 13, 014010 (2020)], showing excellent agreement. The combination of experiment and simulation allows us to decode various physical effects in the signal formation, including different acoustic field components. Unknown material properties, such as acoustic attenuation coefficients, and the two complex photoelastic constants are quantitatively retrieved by fitting the measured signals. Furthermore, we provide evidence of nonlinear propagation of the excited guided acoustic waves.

Photoelasticity of VO2 nanolayers in insulating and metallic phases studied by picosecond ultrasonics

We use a picosecond ultrasonic technique to evaluate the photoelastic parameters at the wavelength of 1028 nm in epitaxial vanadium dioxide $({\mathrm{VO}}_{2})$ nanolayers grown on c-cut sapphire substrates. In the experiments, we monitor the picosecond evolution of the reflectivity of ${\mathrm{VO}}_{2}$ in insulating and metallic phases under the impact of a picosecond longitudinal strain pulse injected into the nanolayer from the side of the substrate. We show that in a 145-nm-thick granular nanolayer, the temporal features of the reflectivity are clearly dependent on the phase state of ${\mathrm{VO}}_{2}$, showing the change of the photoelastic parameters upon the insulator-metal transition. Analytical consideration and numerical simulations of the optical response to the picosecond strain pulse show that the temporal evolution of the reflectivity strongly depends on the complex photoelastic parameter. The analysis enables us to obtain the values of the photoelastic parameters in the studied nanolayer in both insulating and metallic phases. We find that for a 145-nm film of ${\mathrm{VO}}_{2}$ in an insulating state the imaginary part of the photoelastic constant is negligible. This means that in the insulating phase the strain does not affect the optical absorption of ${\mathrm{VO}}_{2}$. In the metallic phase, the photoelastic parameter of ${\mathrm{VO}}_{2}$ is found to be similar to that typical for metals with positive real and negative imaginary parts. We further show that the optical response to the strain pulse in the layer consisting of disconnected ${\mathrm{VO}}_{2}$ nanohillocks with an average height of 70 nm is governed by their morphology and is different from what is predicted in the plane ${\mathrm{VO}}_{2}$ films.