Removal of Spectral Distortion Due to Echo for Ultrashort THz Pulses Propagating Through Multilayer Structures with Thick Substrate

Given the wide range of applications of time-domain spectroscopy, and particularly THz time-domain spectroscopy, the modelling of a probe pulse propagating through a multilayered structure is often required. Due to the fact that the multilayers are usually grown on a substrate much thicker than the other layers, the transmission of a probe pulse includes a series of echo pulses caused by the multiple reflections at the substrate interfaces over a long time. However, experiments often measure only a small time window and construct the transmitted spectrum only from the first transmitted pulse. Due to the fact that typical substrates lead to times of crossing comparable to the spectral bandwidth, the first transmitted pulse’s spectrum and the full transmitted spectrum can importantly differ. It is therefore important to theoretically model the transmission without the echo, to be able to make a direct comparison with experimental results. Here, we propose a method to elegantly and easily theoretically remove the echo from the transmission spectrum. The spectrum of the transmitted pulse without echo will be produced analytically without additional numerical steps.