Using the features of the photoelastic effect to measure the parameters of optoelectronic devices

The features of the photoelastic effect are discussed and it is shown that they can be used to measure the parameters of a laser and a photodetector, which are the main units of any optoelectronic product. A brief review of the known methods for measuring the parameters of a laser and a photodetector is carried out, and some limitations in their application are noted. The possibility of using the features of the photoelastic effect for measuring the parameters of the inertia of the photodetector is theoretically substantiated. A formula for calculating the response at the output of an acousto-optic processor to a rectangular input action is derived and used to separately estimate the time of crossing the optical beam by an elastic wave packet and the inertia of the photodetector. It has also been proven that by choosing a short input action, the features of the photoelastic effect can be used to determine the configuration of the cross section of the laser beam and the law of the distribution of the power flux density in it. The results of theoretical studies have been tested by numerical calculations and confirmed by experimental measurements.

Force chain structure in a rod-withdrawn granular layer

When a rod is vertically withdrawn from a granular layer, oblique force chains can be developed by effective shearing. In this study, the force-chain structure in a rod-withdrawn granular layer was experimentally investigated using a photoelastic technique. The rod is vertically withdrawn from a two-dimensional granular layer consisting of bidisperse photoelastic disks. During the withdrawal, the development process of force chains is visualized by the photoelastic effect. By systematic analysis of photoelastic images, force chain structures newly developed by the rod withdrawing are identified and analyzed. In particular, the relation between the rod-withdrawing force [Formula: see text], total force-chains force [Formula: see text], and their average orientation [Formula: see text] are discussed. We find that the oblique force chains are newly developed by withdrawing. The force-chain angle [Formula: see text] is almost constant (approximately [Formula: see text] from the horizontal), and the total force [Formula: see text] gradually increases by the withdrawal. In addition, [Formula: see text] shows a clear correlation with [Formula: see text].

Visualization and Quantification of Stresses at the Ends of Short Fibers Embedded in Epoxy Resin

The photoelastic effect was used to visualize and quantify stresses at the end of fibers embedded in birefringent epoxy resin. A method was proposed allowing not to only quantify the differences in main principal stress for a single loading state, but to allow monitoring the evolution of local stress throughout the micro-mechanical experiment. It was found that the ends of fibers foster the formation of shear stresses which influence the principal stress distribution. Typically, star-shaped principal stress distributions were found at the ends of fibers. Finite Element simulations of the tests were in good agreement with the experimental evidence.

On the use of photoelastic effect and plane strain or plane stress approximations for the description of thermal lensing

Correct use of the photoelastic effect for the description of thermally induced refractive index change is discussed and the analytical relations between thermo-optic coefficients at zero stresses and zero strains are found for all classes of cubic crystals. These relations may be useful for the investigation of thermal effects in very promising sesquioxide class m3 laser crystals. An accepted set of elasto-optical coefficients of the YAG crystal and an alternative one found in the literature were used in numerical simulations. Significant differences in the calculated thermo-optic coefficients and induced birefringence are found using different sets of these coefficients. Misunderstandings related with the so-called photoelastic coefficients are resolved and new expressions for these coefficients are found. It is shown that the incorrect use of these coefficients for different pump beam distributions can lead to significant discrepancies for thermally induced birefringence. It is also shown that common use of the generalized thermo-optic coefficients significantly overestimates the values of optical power of thermal lenses when they are applied to the laser rods with lengths several times longer than their diameter.