Heterogeneous High-Performance Quantum-Cascade Laser Sources for Broad-Band Tuning

A heterogeneous high-performance quantum-cascade laser gain chip comprising two bound-to-continuum active region designs emitting at 8.2 and 9.3 mum is presented. Its extrapolated gain spectrum has a full-width at half-maximum (FWHM) of 350 cm ^{- 1}. Though a broad gain bandwidth invariably results in a reduced gain cross section, devices with a high-reflection coated back facet still lase continuous-wave (CW) up to a temperature of 50 ^degC and demonstrates output powers in excess of 100 mW at 30^degC. Such high performance was achieved by designing the waveguide in a buried heterostructure fashion and epi-down mounting on a diamond submount, resulting in a thermal resistance of only 4.8 K/W. In pulsed mode, we reached a peak output power of 1 W at room temperature. Finally, in order to prove the usability for broad-band tuning, this chip was antireflection coated on the front facet with a residual reflectivity of < 2.5 x 10^-3 and used in our external cavity (EC) setup operated at room temperature. In pulsed mode, we were able to tune the gain chip over 292 cm ^-1, which is 25% of center frequency. In CW, we reached a coarse tuning range of 201 cm^-1 (18%) and an output power in excess of 135 mW at the gain maximum at 15^degC. This gain chip enabled CW room temperature EC tuning with output powers in excess of 20 mW over 172 cm ^-1.