A Broadband Pulsed External-Cavity Quantum Cascade Laser Operating near 6.9μm

We report an external cavity quantum cascade laser (EC-QCL) operating near 6.9 μm using the Littman–Metcalf configuration. The EC-QCL works in a pulsed mode and can be tuned continuously from 1340 to 1640 cm^-1 by only tilting the tuning mirror. The fine tuning ability of the EC-QCL is demonstrated by measuring the absorption spectrum of water in the ambient air with a lock-in amplifier.