Measurements of the linear (Pockels) electro-optical coefficient of wurtzite GaN are reported. The values for the electro-optic coefficients r33 and r31 are 1.91±0.35 and 0.57 ±0.11 pm/V at 633 nm, respectively, in agreement with extrapolations from measured second-harmonic generation coefficients (χ33(2)=−20±6 pm/V and χ31(2)=10±3 pm/V) suggesting that the dominant contributions are electronic in origin. Measurements were performed using a Mach–Zehnder interferometer with LiNbO3 as a reference material. Piezoelectric effects were also observed.
A large photoinduced refractive-index change (as great as Dn=0.21+/-0.04) is obtained in lead silicate glasses by irradiation with the frequency-quadrupled output of a Q -switched YAG laser (266 nm). An approximately exponential relationship is found between the photoinduced refractive-index change and the lead cation mole fraction over the composition range from 18.7% to 57%. The induced refractive-index change is permanent and shows no decay after heating to 360 degrees C during 1 h. Dispersion of the refractive-index change suggests that the photosensitivity is associated with changes in the intrinsic glass absorption edge.
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