Tapered Quantum Cascade Laser Achieving Low Divergence Angle and High Output Power.

Area of Science:

• Optoelectronics
• Laser Physics
• Materials Science

Background:

• Quantum cascade lasers (QCLs) are crucial for mid-infrared applications.
• Improving output power and beam quality in QCLs remains a key challenge.
• Existing Fabry-Perot QCLs often suffer from high divergence angles and limited power.

Purpose of the Study:

• To design and demonstrate a high-performance tapered quantum cascade laser (QCL).
• To achieve significant improvements in both output power and beam divergence.
• To explore the integration of a tapered waveguide with a Fabry-Perot structure for enhanced performance.

Main Methods:

• Fabrication of a 50 µm wide tapered QCL incorporating a Fabry-Perot structure.
• Characterization of device performance under pulsed and continuous wave (CW) operation.
• Comparison of the tapered QCL performance against non-tapered Fabry-Perot QCLs.

Main Results:

• Maximum pulsed output power of 2.76 W achieved with a slope efficiency of 3.52 W/A.
• Wall-plug efficiency (WPE) reached 16.2% in pulsed mode and exceeded 8.2% in CW operation.
• Divergence angle reduced to 13.01°, with CW operation maintaining 1.34 W at room temperature.
• Nearly 10-fold increase in output power and over 200% WPE improvement compared to non-tapered devices.

Conclusions:

• The integrated tapered waveguide and Fabry-Perot structure significantly enhances QCL performance.
• The developed tapered QCL offers a viable solution for high-power, low-divergence mid-infrared applications.
• This advancement paves the way for improved laser technology in demanding fields requiring temperature stability and high beam quality.