High-power, continuous-wave, phase-locked quantum cascade laser arrays emitting at 8 µm

Area of Science:

• Optics and Photonics
• Semiconductor Lasers
• Quantum Cascade Lasers

Background:

• Quantum cascade lasers (QCLs) are crucial semiconductor devices for mid-infrared applications.
• Improving power output and efficiency in QCLs remains a key research objective.
• Phase-locked arrays offer a route to higher power and improved beam quality.

Purpose of the Study:

• To report on a novel eight-element phase-locked quantum cascade laser array.
• To achieve high continuous-wave (CW) power and wall plug efficiency (WPE) at 8 µm.
• To investigate the emission characteristics, including supermode operation and side-mode suppression.

Main Methods:

• Fabrication of an eight-element phase-locked QCL array.
• Characterization of the laser array's power, efficiency, and spectral properties under CW operation.
• Design optimization of the QCL active region for high differential gain and low voltage defect.

Main Results:

• Achieved 8.2 W CW output power from the 8 µm QCL array at room temperature.
• Obtained a WPE of 9.5% for the array, operating primarily in the in-phase supermode.
• Demonstrated single-mode emission with a side-mode suppression ratio of approximately 20 dB.
• Reported a record WPE of 20.4% for a single-element Fabry-Perot laser in pulsed mode.

Conclusions:

• The developed QCL array represents a significant advancement in high-power mid-infrared laser technology.
• The design principles employed are effective for achieving high performance in phase-locked QCL arrays.
• Further improvements in WPE were demonstrated in single-element devices, indicating potential for future array designs.