Linear Electro-Optic Effects in KH_2PO_4 and Its Isomorphs

The linear electro-optic coefficients of KH2PO4 and a number of its isomorphs have been measured at room temperature using dc voltages. The results at 546 nm are as follows: r63 = 10.3±0.1×10−12 m/V for KH2PO4, 10.9±0.1×10−12 m/V for KH2AsO4, and 13.0±0.2×10−12 m/V for RbH2AsO4; r41 = 8.77±0.14×10−12 m/V for KH2PO4, 24.5±0.4×10−12m/V for NH4H2PO4, 12.5±0.4×10−12 m/V for KH2AsO4, and 8.8±0.4×10−12 m/V for KD2PO4 which was about 90% deuterated. A transverse modulator based on a single 45° Y-cut crystal of NH4H2PO4 is proposed which requires only 45 V rms for 50% amplitude modulation of 632.8 nm light.