Terahertz imaging with room-temperature terahertz difference-frequency quantum-cascade laser sources.

We demonstrate high-quality non-destructive imaging using a broadband terahertz quantum cascade laser source based on Cerenkov difference-frequency generation. The source exhibited ultra-broadband terahertz emission spectra, as well as a single-lobed Gaussian-like far-field pattern at -30 °C. These features allowed us to build a compact imaging system with a high spatial resolution, from which a nearly theoretical minimum beam spot size was obtained.

Non-ellipsometric detection of terahertz radiation using heterodyne EO sampling in the Cherenkov velocity matching scheme.

A new electro-optic (EO) sampling scheme, which we refer to as "heterodyne EO sampling", for detection of pulsed terahertz (THz) waves is proposed and experimentally demonstrated. In this heterodyne EO sampling scheme, the intensity change in the optical probe pulse induced by a THz field in a nonlinear crystal is measured without any polarization optics. Applied in combination with the non-collinear Cherenkov velocity matching technique, this method allows one to detect pulsed THz waves efficiently and easily using a simpler optical setup as compared to the conventional ellipsometric EO sampling method.

Efficient electro-optic sampling detection of terahertz radiation via Cherenkov phase matching.

We experimentally demonstrate an efficient electro-optic sampling scheme based on Cherenkov phase matching of broadband terahertz radiation with 800-nm femtosecond probe beam in a 0.5 mm-thick LiNbO3 crystal coupled to a Si prism. The electro-optic signal from a Cherenkov-phase-matched LiNbO3 crystal is found to be comparable to that with a 4 mm-thick ZnTe crystal using a collinear phase matching.