Quantum cascade lasers for the mid-infrared spectral range: Devices and applications

Quantum cascade lasers emitting at lambda about 5 µm based on different active region designs are investigated. Using lattice-matched GaInAs/ AlInAs on InP substrates the maximum peak optical power as well as the maximum pulsed-mode operating temperature is enhanced by incorporating AlAs blocking barriers together with strain-compensating InAs layers into the active regions. Further improvement is achieved by employing strain-compensated GaInAs/ AlInAs quantum wells for which maximum pulsed-mode operating temperatures in excess of 350 K are observed. High-reflectivity coated devices mounted substrate-side down show a maximum continuous-wave operating temperature of 194 K. Also the normalized relative intensity noise is investigated. Finally, a comparison trace-gas sensing experiment employing one of the present quantum cascade lasers and a lead-chalcogenide laser is presented. Detecting the P (25) absorption line of CO, higher stability is obtained using a quantum cascade laser.