Low-voltage light-amplitude modulation

An ammonium¿dihydrogen¿phosphate 45° ycut composite crystal is described, requiring 40 V r.m.s. for 50% intensity modulation. Equations are derived for the retardation produced between the ordinary and extraordinary ray as a function of applied voltage along the yaxis and incident light direction in the xz plane. The electro-optic coefficient r41 is calculated from these equations, and a d.c. value of 23.06 × 10¿12 m/V at 6328 Å and 20° C is given.