Determining thickness independently from optical constants by use of ultrafast light

We show that the application of ultrafast techniques, especially terahertz time-domain spectroscopy, allows simultaneous measurements of material thickness and optical constants from transmission measurements, by analyzing not only the phase difference between the main terahertz pulse through the medium but also the subsequent multireflection pulse (an echo) from the medium. Such a method provides a fast and precise characterization of the optical properties and can extract thickness information and hence other optical constants in a broad bandwidth. It may have applications in science and engineering such as in situ film thickness and quality monitoring, optical constants measurement, medical imaging, noninvasive detection, and remote sensing.