Appl. Phys. Lett. 106, 131107 (2015)

Spectroscopy techniques require the sweeping of emission frequency across molecular lines to gather information about a sample. Although electrical frequency tuning of terahertz quantum cascade lasers (QCLs) has been demonstrated, it is always accompanied by an unwanted change in output power and to date only limited tunability has been achieved. Now, Dana Turčinková and co-workers from Switzerland and France have demonstrated continuous electrical tuning of a single-mode QCL operating at 3 THz.

The devices were made of a GaAs/Al0.15Ga0.85 material system and based on a two-section interdigitated third-order distributed feedback (DFB) cavity. The two sections were independently pumped with electrical currents. The measurements were performed in pulsed operation at a heat-sink temperature of 10 K. The effective index of the DFB lasing mode decreased with increasing current difference between the two sections. It followed that the laser wavelength, determined by the Bragg diffraction condition, decreased concomitantly. As an example, a continuous tuning over a frequency range of 4 GHz was achieved for a fixed optical output power of 0.7 mW. The tuning range is expected to improve by using another active-region design with a higher gain or stronger Stark effect.