THz GaAs photonic crystals*

THz GaAs photonic crystals were fabricated by reactive ion etching. The $\langle $100$\rangle $ semi-insulating GaAs had an n-doped epi-layer that was used to generate THz radiation from coherent plasma oscillations initiated by femtosecond laser excitation. The emitted THz radiation was detected by electro-optic detection with a ZnTe crystal. When the laser beam was brought to a line focus at normal incidence, emitted THz radiation was observed whose spectrum consisted of sharp peaks. These peaks are attributed to guided slab modes being diffracted at the $\Gamma $ points of the photonic crystals.