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 30degC. 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 15degC. This gain chip enabled CW room temperature EC tuning with output powers in excess of 20 mW over 172 cm -1.