Transverse-mode astigmatism in a diode-pumped unstable resonator Nd:YVO(4) laser

We have observed a sizable astigmatism in the output beam from a diode-pumped unstable resonator Nd:YVO(4) laser operating in a single polarization and a single-longitudinal and transverse mode. The anisotropic index of refraction of the vanadate crystal has been identified as the source of this astigmatism. A theoretical prediction of the eigenmode astigmatism based on this index anisotropy is consistent with our experimental measurements.