Characterization of third-harmonic generation in Fibonacci optical superlattices

A Fibonacci optical superlattice (FOS) made from a single crystal with a quasiperiodic laminar ferroelectric domain structure was proposed to realize a third-harmonic generation (THG) process. Due to its quasiperiodic structure, a FOS can provide more plentiful reciprocal-lattice vectors to compensate for the mismatch phase in optical parametric processes, which causes most of third-harmonic peaks labeled by the corresponding reciprocal-lattice vector indices. Numerical calculation shows that the THG spectrum exhibits a self-similarity property in real space. Effects of the phase mismatch of second-harmonic generation and THG, the bandwidth, and the relative intensity of the second harmonic peak on THG are discussed. We also found THG peaks for which the quasi-phase-matching condition in THG process is not completely satisfied. The physical origins of the phenomenon are presented and discussed.