In focus

A paper on the generation of Multi-THz electric fields with simultaneously high fields and high repetition rates has been published in Optics Letters by the group at University of Regensburg. We have demonstrated a compact source of energetic and phase-locked multi-terahertz pulses at a repetition rate of 190 kHz. Difference frequency mixing of the fundamental output of an Yb:KGW amplifier with the idler of an optical parametric amplifier in GaSe and LiGaS2 crystals yields a passively (...)

In the terahertz (THz) frequency range, a semiconductor-based technology platform for ultra-short pulse generation has yet to be realized. A limiting factor is the negative and positive chromatic dispersion of the gain of quantum cascade lasers (QCLs). Here, a novel dispersion compensation scheme based on an off-resonance Gires-Tournois Interferomenter is applied to a THz QCL, greatly reducing the THz pulse duration to a few optical cycles, with stable pulses as short as 4ps. The (...)

A paper on Echo-less photoconductive switches as high resolution detectors has been published in Applied Physics Letters by the group at CNRS-LPA. Photoconductive (PC) switches are powerful and convenient devices for time-resolved spectroscopy, with the ability to operate both as sources and detectors of terahertz (THz) frequency pulses. However, reflection of the emitted or detected radiation within the device substrate itself can lead to echoes that inherently limits the spectroscopic (...)

A paper on evidence of Fermi level pinning at the Dirac point in epitaxial multilayer graphene has has been published in Physical Review B by the group at CNRS-LPA. The authors investigated the temperature-dependent conductivity of epitaxial multilayer graphene using THz time domain spectroscopy and show evidence that the Fermi level in quasi-neutral graphene layers is pinned at the Dirac point by mid-gap states. The authors demonstrated that the scattering mechanisms result from the (...)

A paper on self modulation of QCLs has been published in Scientific Reports by the group at CNR. The authors show a compact architecture to induce both frequency and amplitude self-modulation in a THz QCL. By engineering a microwave avalanche oscillator into the laser cavity, which provides a 10 GHz self-modulation of the bias current and output power, we demonstrate multimode laser emission centered around 3 THz, with distinct multiple sidebands. The resulting microwave amplitude and (...)

The CNRS-LPA partner has demonstrated, in a new publication in Optics Express, a simple method to engineer the beam profile of a Terahertz QCLs. The far-field emission metal-metal QCLs is controlled in directionality and form through planar horn-type shape structures, whilst conserving a broad spectral response. The structures produce a gradual change in the high modal confinement of the waveguides and permit an improved far-field emission profile and resulting in a four-fold increase in (...)

A new type of photoconductive antenna has been realised that eliminates the ’echo’ signals that typically originate from substrate reflections. These new devices will be of use to the time resolved study of the QCL emission. Full details of the work can be found here

The ULTRAQCL project has started! The kick-off meeting for the ULTRAQCL project took place at the Centre Culturel Irlandais in Paris on 29th Nov 2015

A paper on ultrafast THz detectors based on 3D meta-atoms has been published in Optica by the group at University of Paris South. Quantum-well infrared photodetectors (QWIPs) have proved to be an excellent technology as ultrafast THz receivers, given their intrinsic picosecond-range response. (...)

A paper on generating short pulses from QCLs has been published in Optica by the group at CNRS-LPA. The authors bring new insights into the QCL modelocking and show, contrary to popular believe, that the ‘active microwave’ modulation is the key parameter that determines the pulse duration rather (...)