Broadband THz imaging in gas and multiple quantum-well media

We discuss two schemes of ultrafast THz imaging, both constituting non-perturbative response of either gas or solidstate media to the THz bias fields and thus offering very sensitive detection of the latter. In the first approach, we utilize air-breakdown plasma for space-time mapping of the THz field. In the second approach, we THz-induce strong electroabsorption response in the multiple quantum-well sample of thickness much smaller than the wavelength of the THz bias. As such, ultrabroadband imaging of the quasi single-cycle THz pulses can be possible.