Double modulated differential THz-TDS for thin film dielectric characterization

Terahertz differential time-domain spectroscopy (DTDS) is a new technique that uses pulsed terahertz radiation to characterize the optical properties of thin dielectric films. Characterizing thin films in the GHz to THz range is critical for the development of new technologies in integrated circuitry, photonic systems and micro-electro-mechanical systems. There are potential applications for gene and protein chips. This paper shows how DTDS can be combined with double modulation in the pump-probe system to improve sensitivity by an order of magnitude. An iterative algorithm is presented to estimate the optical properties of a given thin film. The technique is experimentally verified using 1-mm-thick samples of silicon dioxide on silicon. q 2002 Elsevier Science Ltd. All rights reserved.