Second optical harmonic near the surface of ferroelectric photonic crystals and photon traps

This paper reports on the results of experimental investigations of the generation of the second optical harmonic localized in a thin subsurface layer of ferroelectric photonic crystals and photon traps. To excite the second optical harmonic, a KGW: Yb solid-state pulsed-periodic laser generating the radiation with a wavelength of 1026 nm in a form of pulses $\sim$ 10$^{-13}$ s long with a repetition frequency of 200 kHz at the average power of 0.1–3.5 W and power density of $\sim$ 10$^9$–10$^{12}$ W/cm$^2$ in a spot less than 100 $\mu$m in diameter focused near the surface was used. Ferroelectrics, notably, barium titanate or sodium nitrite, were introduced into the pores between SiO$_2$ nanoglobules. It is established that the maximal conversion efficiency of the exciting radiation into the second optical harmonic was several percents. The generation characteristics of the second optical harmonic near the surface of photonic crystals filled with ferroelectrics are compared with the generation of the second optical harmonic in ferroelectric photon traps of barium titanate ceramics and sodium nitrite microcrystals.