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We show experimentally that the combination of soft-edged gain and index guiding can lead to resonant excess quantum noise. Resonances with excess noise factors close to 100 are observed in end-pumped Nd3+:YVO4 lasers for cavity lengths in which two modes experience similar gain. An associated increase in the relaxation oscillation damping rate demonstrates that the fluctuation enhancement is indeed caused by excess quantum noise and not by dynamic instabilities.

We demonstrate that the transverse eigenmodes in a waveguide that combines a parabolic index guide with a Gaussian gain guide can be highly nonorthogonal. The excess-noise factor K that arises from this nonorthogonality exhibits resonant features with maximum values that can easily reach K approximately 400 . This simple model applies directly to stable-cavity microchip lasers with focused gain.