Room-Temperature Continuous-Wave Operation of a Tunable External Cavity Quantum Cascade Laser

A room-temperature cw operation of a tunable external cavity (EC) quantum cascade laser (QCL) at an emitting wavelength of 4.6 µm is presented. Strain−compensation combined with two-phonon resonance in an active region design promises low threshold current density. A very low threshold current density of 1.47 kA/cm² for an EC−QCL operated in cw mode is realized. Single-mode cw operation with a side-mode suppression ratio of 20 dB and a wide tuning range of over 110 cm^-1 are achieved. Moreover, an even wider tuning range of over 135 cm⁻¹ is obtained in pulsed mode at room temperature.