A frequency doubling electro-optic modulation system for pockels effect measurements: Application in LiNbO3

A novel system is presented which is capable of measuring with high accuracy the linear (Pockels) electro-optic effect by means of a new dynamic (ac) method. This method is based on the observation of the photodetected output obtained from a Senarmont-type ellipsometric system with an ac (modulating) voltage being applied onto the electro-optic sample under test. This observation is made on a high sensitivity oscilloscope and allows us to determine accurately the null point of the system by locating the position of the analyzer that produces in the output a characteristic and abrupt doubling of the (modulation) frequency. By locating this frequency doubling position without and with electric field one can finally determine the corresponding electro-optic coefficients. Theoretical analysis and considerations of practical interest are presented in the article and show that the system in question can ensure reduced errors and increased sensitivity. Also, experimental evidence in support of the expected performance is obtained by implementing and applying the system for the measurement of the composite electro-optic coefficient r(c) of LiNbO3 for various temperatures in the range of 17-20 degrees C. (C) 1997 American Institute of Physics.