No abstract

Terahertz (THz) frequency quantum cascade lasers emitting peak powers of >1 W from a single facet in the pulsed mode are demonstrated. The active region is based on a bound-to-continuum transition with a one-well injector, and is embedded into a surface-plasmon waveguide. The lasers emit at a frequency of ∼3.4 THz and have a maximum operating temperature of 123 K. The maximum measured emitted powers are ∼1.01 W at 10 K and ∼420 mW at 77 K, with no correction made to allow for the optical collection efficiency of the apparatus.

The generation of ultrashort pulses from quantum cascade lasers (QCLs) has proved to be challenging. It has been suggested that the ultrafast electron dynamics of these devices is the limiting factor for modelocking and hence pulse formation. Even so, clear modelocking of terahertz (THz) QCLs has been recently demonstrated but the exact mechanism for pulse generation is not fully understood. Here we demonstrate that the dominant factor necessary for active pulse generation is in fact the synchronization between the propagating electronic modulation and the generated THz pulse in the QCL. By using phase resolved detection of the electric field in QCLs embedded in metal-metal waveguides, we demonstrate that active modelocking requires the phase velocity of the microwave round trip modulation to equal the group velocity of the THz pulse. This allows the THz pulse to propagate in phase with the microwave modulation along the gain medium, permitting short pulse generation. Modelocking was performed on QCLs employing phonon depopulation active regions, permitting coherent detection of large gain bandwidths (500 GHz), and the generation of 11 ps pulses centered around 2.6 THz when the above 'phase-matching' condition is satisfied. This work brings an enhanced understanding of QCL modelocking and will permit new concepts to be explored to generate shorter and more intense pulses from mid-infrared, as well as THz, QCLs.

International audienceDispersion compensation is vital for the generation of ultrashort and single cycle pulses from modelocked lasers across the electromagnetic spectrum. It is typically based on addition of an extra dispersive element to the laser cavity that introduces a chromatic dispersion opposite to that of the gain medium. To date, however, no dispersion compensation schemes have been successfully applied to terahertz (THz) quantum cascade lasers for short and stable pulse generation in the THz range. In this work, a monolithic on-chip compensation scheme is realized for a modelocked QCL, permitting THz pulses to be considerably shortened from 16ps to 4ps. This is based on the realization of a small coupled cavity resonator that acts as an 'off resonance' Gires-Tournois interferometer (GTI), permitting large THz spectral bandwidths to be compensated. This novel application of a GTI opens up a direct and simple route to sub-picosecond and single cycle pulses in the THz range from a compact semiconductor source

Miniaturized frequency comb sources across hard-to-access spectral regions, i.e. mid- and far-infrared, have long been sought. Four-wave-mixing based Quantum Cascade Laser combs (QCL-combs) are ideal candidates, in this respect, due to the unique possibility to tailor their spectral emission by proper nanoscale design of the quantum wells. We demonstrate full-phase-stabilization of a QCL-comb against the primary frequency standard, proving independent and simultaneous control of the two comb degrees of freedom (modes spacing and frequency offset) at a metrological level. Each emitted mode exhibits a sub-Hz relative frequency stability, while a correlation analysis on the modal phases confirms the high degree of coherence in the device emission, over different power-cycles and over different days. The achievement of fully controlled, phase-stabilized QCL-comb emitters proves that this technology is mature for metrological-grade uses, as well as for an increasing number of scientific and technological applications.