Abstract

This paper presents an experimental study of third optical harmonic generation processes in synthetic opal. Excitation was provided by ultrashort (∼10−13 s) laser pulses (λ = 1026 and 513 nm) with a high repetition rate (105 Hz), high peak power (up to 1 GW), and low pulse energy (10−5 J). The third optical harmonic intensity was shown to depend significantly on the diameter of the silica spheres, which determines the spectral position of the band gaps in the opal photonic crystal. The highest efficiency of the nonlinear optical conversion of excitation light to the third optical harmonic was observed when the excitation or optical harmonic wavelength was close to the spectral position of the band gap of the photonic crystal. This behavior can be accounted for by the presence of surface photon (Tamm) states of the optical field in opal photonic crystals in the spectral region corresponding to the band gap of the photonic crystal. The presence of photon Tamm states leads to the formation of high spectral intensity regions localized near the surface of the photonic crystal. This causes a considerable increase in nonlinear optical conversion efficiency, in particular, in the case of the third optical harmonic generation in the centrosymmetric structure of opal lattices.

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