Power enhancement of terahertz photoconductive antenna with optical nanoantenna arrays

Abstract

THz time domain spectroscopy is an emerging biosensing technique. Photon energy of terahertz wave is relevant to the intermolecular modes of molecules. The unique signatures on THz range help identify poly-morphs, biochemical and skin cancers. However high water absorption limit biomedical applications due to the low power of THz sources. This work presents a nanoplasmonic photoconductive antenna (NP-PCA) integrating plasmonically matched optical nanoantenna arrays for high power terahertz emission. Plasmonic resonance of optical nanoantenna arrays is matched to excitation wavelength of optical pulse, 800nm. Optical nanoantenna arrays concentrate the pump beam and enhance electric field around optical nanoantenna arrays. The local field enhancement generates high photocurrent, which also induces high power THz radiation. The NP-PCA has achieved by hierarchical patterning using e-beam, photo lithography and lift-off process. The electrodes have bow-tie antenna shape with 15μm electrode gap and 90° apex. Reflective intensity from optical nanoantenna arrays is measured with micro-spectrometer with a reflective type. THz time-domain waveforms are measured by using conventional optoelectronic sampling method. As a result, Spectral power of the PCA increases 2.6 times when optical nanoantenna arrays plasmonically resonate at the excitation wavelength. THz enhancement change with the plasmonic resonance wavelength.