Late-time target response measured with terahertz impulse ranging

Time-domain impulse-scattering measurements of freely propagating single cycle terahertz radiation from dielectric targets is measured in the far field with subpicosecond resolution. Initial specular reflection as well as late-time response of the targets is observed to approximately 100 times the initial pulse width. Measured scattered fields agree well with the calculated scattering for early- and late-time response in both the time and frequency domains. The data is fit to both an inverse Fourier transform of numerically calculated frequency domain scattering as well as an intuitive model based on physical optics (PO). The PO picture is verified directly in the time domain and surface wave propagation velocities are measured.