In electrohyphen;optic applications of the mixed crystal K(DxH1minus;x)2PO4(KDPhyphen;KDast;P), strainhyphen;induced refractive index variations result in beam depolarization and transmitted wavehyphen;front distortion. Here the combined linear stresshyphen;optic and electrohyphen;optic effects in crystals of KDPhyphen;KDast;P oriented perpendicular to thecaxis are analyzed and it is shown that while the depolarization is caused by the induced birefringence, the wavehyphen;front distortion is due to average index shifts. Furthermore, the birefringence is determined by the shear stress in thexyplane of the crystal while the average index shift depends only on the normal stresses. For depolarization losses of 0.1percnt;ndash;1percnt; and wavehyphen;front distortion of 0.1ndash;1lgr;, the critical range of stress is 105ndash;106Pa. Measured depolarization loss and wavehyphen;front distortion profiles of 5, 16, and 27 cm K(DxH1minus;x)2PO4crystals for 0le;xle;0.98 are also presented. Using the analysis described above it is shows that the maximum internal stresses in these crystals are within the critical range, but that the areahyphen;averaged stresses are substantially lower. It is found that crystals from different locations along the length of a boule can have similar strain birefringence and wavehyphen;front distortion profiles indicating that the growth conditions which generate the internal strain persist throughout a significant portion of the growth history of the boule. It is also observed that the most highly strained crystals come from near the seed cap. Finally, potential sources of strain in KDast;P are discussed and thermodynamic and structural arguments are given which suggest that inhomogeneities in the H/D ratio are a potential source of the strain in KDast;P. thinsp;
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