A new method for measuring electrooptic constants at high frequencies

The frequency dependence of some electrooptic tensor coefficients of KDP, LiIO₃, and benzil was measured by means of a lock-in amplifier. The technique was also used above the upper frequency limit of the lock-in amplifier. This was achieved by modulating the high frequency voltage at a fixed low frequency and inserting a fast demodulator into the receiving circuit. The resolution in phase shift was 10⁻⁵ degree and when modulated about 10⁻⁴ degree.