Characterization of harmonic generation spectra in three-component Fibonacci optical superlattices

The second-harmonic generation (SHG) and third-harmonic generation (THG) processes in a three-component Fibonacci optical superlattice (TCFOS) are studied. The TCFOS is made from a single crystal with quasiperiodic laminar ferroelectric domain structure. It is found that the TCFOS can provide more reciprocal vectors to compensate phase mismatch in optical parametric processes, which results in more intense peaks in the SHG and THG spectra of the quasiperiodic superlattice. The intense SHG and THG peaks can be labeled with three indices. In real space, the SHG and THG spectra exhibit self-similarity which is inherent to the superlattice. In reciprocal space, the self-similarity is destroyed due to the dispersion effect of the optical material. Dependence of the THG peak intensity within the TCFOS on the second-harmonic phase mismatch and the third-harmonic phase mismatch is discussed and presented. Numerical calculations show that an efficient THG can be achieved when THG quasi-phase-matching condition is satisfied even though the SHG is quasi-phase-mismatched. [S0163-1829(98)06940-9].