Contour plot of the (a) linear polarization fraction, (b) polarization angle, and (c) circular polarization fraction of anisotropically pumped SiO masers as a function of the rate of stimulated emission and the angle θ. Maser simulations were performed with anisotropy parameters of η = 0.1 and at an anisotropy angle perpendicular to the magnetic field and propagation direction. Simulations were performed for an incident radiation-strength of T_b = 0.1 K, but here only a small part of the region sensitive to this parameter is shown. Magnetic field strength and transition angular momentum are indicated. For simulations with J_up >  1 and other magnetic field strengths, see Figs. A.10–A.18 in the Appendix.