Incoherent beam combination of mid-wave infrared quantum cascade lasers

摘要

Quantum cascade laser (QCL) emitting in the mid-wave infrared atmospheric windows (3 to 5 μm) will beof immediate use to several civilian applications, including airborne self-defense protection system andtrace gas sensing and free space optical communications. When the output power of a single QCL is toolow, the beams of different lasers can be combined by incoherent beam combining. For incoherent beamcombining the laser beams are arranged side by side on the aperture of the laser system and combine inthe farfield. Incoherent beam combining has been applied very successfully to diode lasers with highrobustness and reliability due to it is neither limited to any number of lasers nor to any laser characteristics.This technique is demonstrated to be compatible with QCLs in this work. In this paper, the method ofincoherent beam combination of 4 independent QCL emitters with a 0.1 W continuous wave power at roomtemperature each is studied. Results show that the incoherent power superposition of mid-infrared QCLscan be achieved by beam combining with an efficiency of not less than 90%. The output farfielddivergence angle is about 5 mrad, which is consistent with the farfield divergence angle of the four subbeams.