Decoupling of coherent Gaussian beams with general astigmatism.

We show how to decouple a coherent Gaussian beam having general astigmatism (to transform it into a beam having only simple astigmatism, or orthogonal symmetry) by using a single rotated thin cylindrical lens. The resulting coherent orthogonal Gaussian beam may be further transformed into a stigmatic (rotationally symmetric) Gaussian beam by an orthogonal telescopic magnifier. The initial beam parameters must be known; we suggest a procedure for their measurement.