Abstract

The generation of broadband terahertz radiation from photoconductive antennas has been an active research field in recent years due to the availability of high power, ultrafast laser sources. By exploring parameters such as antenna geometry¹ and electrode spacing², broadband and high field emitters have been investigated. Since the efficient coupling of the incident optical pulse will allow for higher peak-field terahertz emitters, recent works are now moving in this direction³. Laser ablation using femtosecond sources has been shown to increase the optical absorption in 6H-SiC as well as extending the optical absorption range in silicon⁴. In this work we present results on the terahertz generation from a laser ablated, 50 um bow-tie antenna fabricated on SI-GaAs⁵. The antennas are measured using a terahertz time domain spectrometer, with an incident pulse width of 45 fs and pulse energies up to 25 nJ. For a direct comparison we have measured an identical antenna on a pristine SI-GaAs substrate. We observe a terahertz peak enhancement of more than 60% for the ablated sample, with a minor bandwidth increase of approximately 0.2 THz. The micro-scale periodic structure produced by laser ablation provides an enhancement of the absorption properties, and therefore terahertz output, of the photoconductive antenna, which can be extended to all antenna geometries.

© 2014 Optical Society of America