Double-mode external cavity quantum cascade lasers

Tunable double-mode external cavity (EC) quantum cascade lasers (QCLs) based on a dual-Littrow and a dual-Littman configuration are reported. An otherwise multi-mode emitted Fabry-Perot (FP) QCL with no anti-reflective facet coating is used as the gain chip. In the dual-Littrow setup, a widely course double-mode tuning range of 400 nm for the spectral range between 4450 and 4850 nm in pulsed operation is achieved by rotating the diffraction gratings, whereas in the dual-Littman configuration a course double-mode tuning range of 330 nm for the spectral range between 4460 and 4790 nm is reached by rotating the mirrors. In both cases, a fine continuous tuning range over 10 nm is reached by modulating the injection current in a few ms without moving any part. The linewidth and maximum optical power of the dual-Littrow setup are determined to be 0.08 cm(-1) and 40 mW, whereas these values for the dual-Littman configuration are found to be 0.01 cm(-1) and 35 mW, respectively. N2O is used as target molecule to evaluate the absorption features of the lasers. To the best of our knowledge, it is the first demonstration of such double-mode EC-QCLs.