The observation of “neutral” birefringence line in LiNbO₃crystals under torsion

Torsion method for measuring piezooptic coefficients

“…In this case a quarter wave plate was placed behind the sample. The birefringence the stress components, which have been used in the interpretation of [16], become too crude, thus explaining the corresponding lack of accuracy.…”

“…It is also interesting to recall that the distribution of optical birefringence in LiNbO 3 crystals has been studied earlier in one of our works [16] for the experimental geometry (M x , k||Z). The analysis shows that the latter effect is governed by the same piezooptic coefficient 14 π .…”

“…The analysis shows that the latter effect is governed by the same piezooptic coefficient 14 π . However, the cross section of the sample used in [16] normal to the torsion axis had a square shape. The piezooptic coefficient evaluated from these results is equal to attributed to the fact that the experiments of [16] dealt with a square-shaped crystalline sample, instead of a circular cross section needed for this aim.…”

Relations for optical indicatrix parameters in the conditions of crystal torsion

“…As shown in our works [6][7][8][9][10], application of the torsion [6,7,9,10] or bending [7,8,10] stresses leads to some spatial distribution of the optical birefringence and the angle of optical indicatrix rotation in crystals. In particular, when a crystal is twisted around Z axis, a special point of zero induced birefringence is observed in the geometrical centre of XY cross section of a sample, corresponding to the zero shear stress components 13  and…”

Determination of piezooptic coefficient Pi/14/ of LiNbO3 crystals under torsion loading

“…As shown in our earlier works [5][6][7][8][9], the application of torsion [5,6,8,9] or bending [6,7,9] stresses would lead to specific distributions of the optical birefringence and the optical indicatrix rotation in crystals. Under the torsion around a Z axis, a special point of zero induced birefringence has been revealed in the geometrical centre of a sample of XY cross section, which corresponds to a zero shift stress components 13  and 23  .…”