We report the observation of the quantum effects of competing ${\mathrm{\chi }}^{\mathrm{}\left(2\right)\mathrm{}}$ nonlinearities. We also report classical signatures of competition, namely, clamping of the second-harmonic power and production of nondegenerate frequencies in the visible. Theory is presented that describes the observations as resulting from competition between various ${\mathrm{\chi }}^{\mathrm{}\left(2\right)\mathrm{}}$ up-conversion and down-conversion processes. We show that competition imposes hitherto unsuspected limits to both power generation and squeezing. The observed signatures are expected to be significant effects in practical systems.

DOI:https://doi.org/10.1103/PhysRevA.55.4511