Abstract

Segmented KTP waveguides can efficiently generate second-harmonic (SH) light through quasiphase matching. Highly efficient interaction was attributed to domain reversal in the ion exchanged segments forming the waveguide. Four techniques are described which demonstrate that, in conditions producing high efficiency SH generators, the ion exchange does indeed produce domain reversal. The toning procedure uses a high resolution negative liquid electrostatic toner. Domain reversed segments on the c^--face develop positive charge on cooling and attract toner particles, while nonreversed segments repel the toner. The piezoelectric measurements utilize oscillatory force applied to KTP held between a flat plate and a needle. The piezoelectric voltage from the needle dominates the back surface. Uninverted planar waveguides produce an increased voltage, relative to an undiffused surface, while inverted waveguides yield a significantly reduced voltage. In the surface SHG experiment, 266-nm radiation is generated at the air–KTP interface. Domain inversion shifts the phase of the SHG beam by 180°C, and interference of the SHG beam with a variable-phase reference beam allows determination of domain orientation. The etchant KOH:KNO₃ selectively attacks the negative face (c^-) of KTP. Unexchanged regions are etched to a depth of 1–2 µm, while the domain reversed segments stand out from the surface unetched.

© 1991 Optical Society of America