PRECISE 2ND-HARMONIC GENERATION MAKER FRINGE MEASUREMENTS IN SINGLE-CRYSTALS OF THE DIACETYLENE NP 4-MPU AND EVALUATION BY A 2ND-HARMONIC GENERATION THEORY IN 4X4 MATRIX FORMULATION AND RAY-TRACING/

Accurate second-harmonic generation (SHG) measurements in birefringent single crystals of the asymmetrically substituted diacetylene NP/4-MP U were performed with a 10-ns pulsed laser system with small bandwidth . The measurements show typical oscillations, which overlie the well-k nown Maker fringe pattern. These oscillations can be explained by inte rference between the incident fundamental wave and its reflections at the front and back sides of the crystal. The interference is described by a ray-tracer algorithm, which takes into account the beam profile. Furthermore, because the investigated material is biaxially birefring ent at its principal axes, the theory for SHG proposed by Okamoto et a l. [J. Opt. Sec. Am. B 9, 2083 (1992)] was extended for this case and is written in a compact 4 x 4 matrix formulation. By using the additio nal information of the interference of the fundamental wave, we evalua ted and fitted the measurements with greater accuracy. (C) 1997 Optica l Society of America.