Femtosecond Laser Processing and Evaluation of Broadband THz Anti-Reflection Structures

We fabricate terahertz anti-reflection structures on the surface of high-resistivity silicon via femtosecond laser processing. We measure its spectral properties by terahertz time-domain spectroscopy, and find a broadband increase in transmissivity over 0.3 - 2.5 THz. We investigate the observed spectral characteristics of this transmission by using numerical simulation. We successfully reproduce the observed result for all frequencies, including a previously undocumented high-frequency drop-off, when the model includes additional material losses. We believe these effects to be induced by the laser-ablation fabrication process.