Abstract

For a general wavevector direction in biaxial media, there are two orthogonal extraordinary waves that propagate.¹ General expressions for Type I conversion efficiency from an extraordinary fundamental wave to two orthogonal extraordinary second-harmonic (SH) waves are derived for arbitrary wavevector directions with respect to the principal coordinate system of biaxial media. The derived expressions for phase-matching include the fact that the walk-off angle between the Poynting vector and wavevector is different for each wave; i.e., there are three walk-off angles to consider. Two new parameters are introduced which modify the phase-matching conditions and which are functions of the permitivity tensor, wavevector, and walk-off angles. These expressions reduce to the condition for uniaxial media. The fundamental and SH extraordinary waves deviate as they propagate. Therefore, the effective overlap region is reduced due to this walkoff effect, lowering the conversion efficiency. The derived general expressions for Type I conversion efficiency include the directional dependence of the walk-off angles on the wavevector. The results are applicable in the limit of low conversion efficiency. Numerical calculations will be presented for specific materials. This work was supported by the NSF under grant no. ECS-9158022.

© 1993 Optical Society of America