Electro-optic and piezo-optic tuning of second-order nonlinear processes in crystals

Abstract

The power-handling capability of crystals utilized for second harmonic generation (SHG) and other nonlinear frequency conversions has until recently been limited to a few watts of average output power, chiefly because of two conditions, namely, thermal instability and thermal gradients. Now, techniques have been invented that correct these conditions with a resulting order of magnitude increase in the average output power produced by SHG. This paper presents the theory for two techniques that solve the problem of thermal instability, namely, electro-optical tuning (EOT) and piezo-optical tuning (POT). Beam shaping, which prevents thermal gradients, will be treated in a separate paper. In this paper, the general physical theory is discussed both for EOT and POT. The equation for the phase-match condition is given. Interactive effects of temperature change ΔT, the applied electric field (E), and the stress field σ on a fixed-position crystal are treated. The general equations for EOT and POT are developed. Examples of the effect on SHG in cesium dideuterium arsenate (CD*A) are given. Using these techniques, with beam shaping to be described in a separate paper, 35 W of average output power at 0.53 μ has already been demonstrated.