Electrooptic and piezoelectric measurements in photorefractive barium titanate and strontium barium niobate

We have measured the low-frequency ("unclamped") electrooptic and piezoelectric coefficients in undoped BaTiO
3
and Sr
x
Ba
1-x
Nb
2
O
6
(
x = 0.61
) crystals using interferometric techniques. The contribution of the piezoelectric effect to the Pockels measurements is discussed. For an applied ac electric field in the range 0.1-200 V/cm, the electrooptic and piezoelectric effects are linear in the magnitude of the applied field and independent of its frequency in the range 10 Hz-100 kHz. The unclamped electrooptic coefficients of poled BaTiO
3
single crystals are
r_{13} = 19.5 \pm 1
pm/V and
r_{33} = 97 \pm 7
pm/V, and for strontium barium niobate are
r_{13} = 47 \pm 5
pm/V and
r_{33} = 235 \pm 21
pm/V, all measured at a wavelength of 514.5 nm and at
T = 23\deg
C. For the barium titanate samples the measured Pockels coefficient
r_{c} \equiv r_{33} - (n_{1}/n_{3})^{3} r_{13} = 79 \pm 6
pm/V is in good agreement with the value
r_{c} = 76 \pm 7
pm/V computed from the above values of r
13
and r
33
, where n
1
and n
3
are the ordinary and extraordinary indexes of refraction, respectively. The measured piezoelectric ] coefficient is
d_{23} = +28.7 \pm 2
pm/V for barium titanate, and is
d_{23} = +24.6 \pm 2
pm/V for strontium barium niobate. We also measured the photorefractive coupling of two optical beams in the crystals, and we show that the dependence of the coupling strength on beam polarization is in fair agreement with the measured values of the Pockels coefficients.