Terahertz radiation enhancement in gallium arsenide nano-hole array under low power optical pump

Though accelerating photocarriers by the semiconductor surface electric field is the simplest way to generate broadband terahertz pulses, the weak THz power under low optical pump hinders its application in these compact systems. Here, we report a ⟨100⟩ semi-insulating gallium arsenide nano-hole array under above-the-bandgap excitation, which boosts terahertz emission power up to 5.75 folds of bare gallium arsenide with a 32 mW pump. The nano-structured array lifts the absorption of the optical pump and localizes the photocarriers near the surface of gallium arsenide, benefiting the transient photocurrents and thus the THz power. Interestingly, the enhancement is poorly related to the terahertz frequency, and the power difference of the emitted THz wave under the TE and TM pumps is greatly smoothed. In addition, the THz emission enhancement of the nanoscale hole arrays favors a low-power pump. The demonstration shown here provides a potential route for advancing the weak THz power of surface emission, which will promote the application of the surface emitting THz source in the practical THz systems employing compact femtosecond lasers.