Second-harmonic generation (SHG) spectra of single and coupled porous silicon-based photonic crystal microcavities are studied in both frequency and wave vector domains. For the fundamental field resonant to the microcavity mode the second-harmonic intensity is enhanced by 102 times in comparison with that outside the photonic band gap. SHG spectroscopy in identical microcavities coupled through the intermediate Bragg reflector reveals two SHG peaks if the fundamental field is in resonance with the splitted mode of coupled microcavities. The spatial confinement of the resonant fundamental radiation is directly probed at the microcavity cleavage by scanning near-field optical microscopy.

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Second-harmonic scanning optical microscopy in reflection is used to image at room temperature individual GaInP/GaAs microstructures formed on a GaAs (001) substrate. Second-harmonic images of individual microstructures are recorded along with first-harmonic images for four combinations of polarizations of the pump and second-harmonic radiation with different pump wavelengths in the range of 720–920 nm. We observe different second-harmonic images for different polarization configurations and their evolution when changing the pump wavelength. Comparing the dependencies of the second-harmonic signal from the bare sample surface with those related to the microstructures, we conclude that the second-harmonic radiation detected when illuminating the microstructures originates from the substrate at short wavelengths and directly from the microstructures at ∼900 nm of the pump wavelength. The appearance of the second-harmonic images for different polarization configurations is used to discuss the nonlinear properties of the investigated microstructures.

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