In this introduction, we provide an overview of the papers that were accepted for publication in feature issue on ultrafast phenomena and terahertz (THz) waves. This presents cutting-edge research highlights recent developments THz technology.

The progress on terahertz imaging at Capital Normal University in Beijing is presented. Our works on Terahertz Imaging include the active and passive imaging. For the active terahertz imaging, the pulse and continue wave terahertz imaging are studied, respectively. The active terahertz pulse imaging is based on the terahertz time-domain spectroscopy (THz-TDS). A practical focus-plane imaging sy...

We report the first coherent excitation of intramolecular vibrational modes via the nonlinear interaction of a TeraHertz (THz) light field with molecular liquids. A terahertz-terahertz-Raman pulse sequence prepares the coherences with a broadband, high-energy, (sub)picosecond terahertz pulse, that are then measured in a terahertz Kerr effect spectrometer via phase-sensitive, heterodyne detectio...

We discuss the design and operation of widely-tunable terahertz sources based on Cherenkov intra-cavity difference-frequency generation in mid-infrared quantum cascade lasers. Laser chips are integrated into a Littrow-type external cavity system. Devices demonstrate continuous terahertz emission tuning at room temperature with a record tuning range from 1.2 THz to 5.9 THz and peak power output ...

The terahertz gap lies between the infrared and millimeter regions of the electromagnetic spectrum. Terahertz (THz) waves, or T-rays, bridge the gap between electronics and photonics, have novel properties and interact uniquely with many materials. Various rotational, vibrational and translational modes of molecules are within the THz range (0.1–10 THz). Since these modes are unique to a partic...

A bistatic terahertz impulse ranging system has permitted the full isolation and direct measurements of the surface wave loss and dispersion for terahertz frequencies on a dielectric cylinder. This system permits ranging investigations with variable bistatic angles between the source and detector. Direct, frequency dependent comparisons of surface wave loss and propagation velocity are compared...

Recently, air plasma, produced by focusing an intense laser beam to ionize atoms or molecules, has been demonstrated to be a promising source of broadband terahertz waves. However, simultaneous broadband and coherent detection of such broadband terahertz waves is still challenging. Electro-optical sampling and photoconductive antennas are the typical approaches for terahertz wave detection. The...

We demonstrate for the first time the ability to perform time resolved imaging of terahertz (THz) waves propagating within a photonic crystal (PhC) slab. For photonic lattices with different orientations and symmetries, we used the electrooptic effect to record the full spatiotemporal evolution of THz fields across a broad spectral range spanning the photonic band gap. In addition to revealing ...

We experimentally investigated the spectral fingerprints of high e xplosive cyclo-1,3,5trimethylene-2,4,6-trinitramine (RDX) in terahertz frequency region. A home-made terahertz time-domain spectroscopy ranging from 0.2 THz~3.4 THz was deployed. Furthermore, two sample pellets (RDX pellet and polyethylene pellet), which were concealed in an opaque envelop, could be identified by using terahertz...

Broadband horn antennae are presented that efficiently couple terahertz radiation between sub-wavelength metal-metal waveguides and free space. Sub-picosecond terahertz pulses were coupled into and out from sub-wavelength parallel-plate waveguides by using the horn antennae in a terahertz time-domain spectrometer. Monolithic antennae were fabricated at the facets of metal-metal terahertz quantu...