Theoretical analysis of acoustic transients in lithium niobate electro-optic modulators

Abstract

Acoustic transients generated by high-voltage pulses in a transversely excited LiNbO3 Pockels cell are theoretically investigated. The theory treats explicitly the piezoelectric generation and propagation of the acoustic waves, and their interaction with the laser-beam polarization. Expressions for the strain fields and the strain-induced change in index of refraction are derived for short-voltage-pulse excitations. Numerical results are presented for a square- and a Gaussian-pulse excitation. These theoretical predictions are found to be in good agreement with the experimental observations: The waves propagating in the direction perpendicular to the applied electric field have the largest effect on the laser-light polarization. The damping of these acoustic waves is a straightforward application of these results and leads to an increase in the repetition rate of an Nd3+:YLF regenerative amplifier by over an order of magnitude. This work further illustrates the importance of using short-pulse excitations for minimizing the strain-induced birefringence effects for typical laser-beam geometries.