Quasipatterns in second-harmonic generation

A cascade of two-dimensional quasipatterns is predicted in intracavity opti cal frequency doubling due to a polarization instability at the fundamental frequency. Amplitude equations derived from a microscopic model of the fre quency conversion process show that quasiperiodic structures of arbitrary o rientational order can be spontaneously selected due to bulk nonlinear effe cts when detuned operation for both fundamental and second: harmonic fields occurs. Multistability and coexistence of patterns and quasipatterns is al so discussed. [S1063-651X(99)50401-7].