Investigation of pulsed image-plane distributions with applications in time domain THz spectroscopy

Time domain THz spectroscopy (THz-TDS) is currently an active research area and may have several industrial applications such as the non-destructive estimation of semi-conductor wafer doping profiles. Several studies of diffraction and propagation of pulses, have reported effects such as spectral shifting, which may have some significance for THz imaging spectroscopy. In this manuscript we examine the spectral and amplitude distributions in the output plane of an imaging system for pulsed light. Several types of limiting aperture and pulse profiles are considered. For simplicity it is assumed that the paraxial approximation is valid. For the pulse profiles considered, we conclude that there is a spectral shift in the on-axis pulse distribution present at the imaging plane. The extent of the on-axis spectral shift is dependent on the initial spatial and temporal pulse profile. The spectral distribution for off axis points however, is dependent on both the initial pulse profile and the type of limiting aperture.