Abstract
All possible experimental geometries of the piezo-optic effect in crystals of trigonal symmetry are studied in detail through the interferometric technique, and the corresponding expressions for the calculation of piezo-optic coefficients (POCs) πim and some sums of πim based on experimental data obtained from the samples of direct and X/45°-cuts are given. The reliability of the values of POCs is proven by the convergence of πim obtained from different experimental geometries as well as by the convergence of some sums of POCs. Because both the signs and the absolute values of POCs π14 and π41 are defined by the choice of the right crystal-physics coordinate system, we here use the system whereby the condition S14 > 0 is fulfilled (S14 is an elastic compliance coefficient). The absolute value and the sign of S14 are determined by piezo-optic interferometric method from two experimental geometries. The errors of POCs are calculated as mean square values of the errors of the half-wave stresses and the elastic term. All components of the matrix of elasto-optic coefficients pin are calculated based on POCs and elastic stiffness coefficients. The technique is tested on LiTaO3 crystal. The obtained results are compared with the corresponding data for trigonal LiNbO3 and Ca3TaGa3Si2O14 crystals.
Highlights
According to the terminology adopted here, low-symmetry elasto-optic materials are the ones which, in addition to principal components of the tensor of elasto-optic coefficients (ELOCs) pin, have non-principal non-diagonal components, expressed as pin, where i, n = 4, 5, 6
3) crystals belong to 3m symmetry class [15] and their maLithium tantalate
The piezo-optic effect in trigonal LiTaO3 crystals was investigated through the use of the interferometric method
Summary
Only the use of acousto-optic methods prevents the determination of the values and signs of all components of the ELOC matrix with high precision, especially for the crystals in pin matrices that contain such problematic coefficients as p14 , p41 , p25 , p52 , p16 , p61 , p64 , p45 , etc. The absolute values and signs of ELOCs for orthorhombic crystals characterized by the rather simple pin matrix (without problematic coefficients) were completely determined in [17,18] using three methods (acousto-optic, interferometric and polarization-optical methods) including the application, in addition to uniaxial pressure, of the hydrostatic method to the samples. The matrix of pin coefficients for trigonal lithium tantalate crystals LiTaO3 (symmetry class 3m) was filled based on the experimentally determined matrix of piezo-optic coefficients (POCs) π im and the known tensor expression pin = π im Cmn ,.
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