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

## TL;DR

This paper introduces a tapered quantum cascade laser that achieves high output power and low beam divergence, making it suitable for advanced mid-infrared laser applications.

## Contribution

The novel integration of a tapered waveguide with a Fabry–Perot structure significantly enhances output power and beam quality in quantum cascade lasers.

## Key findings

- The optimized tapered QCL achieved 2.76 W output power with 13.01° divergence in pulsed operation.
- Tapered devices showed nearly 10-fold higher output power and over 200% better WPE than non-tapered QCLs.
- The laser maintained 1.34 W output power and 8.2% WPE under room temperature continuous wave operation.

## Abstract

In this work, we present a high-performance tapered quantum cascade laser (QCL) designed to achieve both high output power and low divergence angle. By integrating a tapered waveguide with a Fabry–Perot structure, significant improvements of tapered QCL devices in both output power and beam quality are demonstrated. The optimized 50 µm wide tapered QCL achieved a maximum output power of 2.76 W in pulsed operation with a slope efficiency of 3.52 W/A and a wall-plug efficiency (WPE) of 16.2%, while reducing the divergence angle to 13.01°. The device maintained a maximum power of 1.34 W with a WPE exceeding 8.2%, measured under room temperature and continuous wave (CW) operation. Compared to non-tapered Fabry–Perot QCLs, the tapered devices exhibited a nearly 10-fold increase in output power and over 200% improvement in WPE. This work provides a promising pathway for advancing mid-infrared laser technology, particularly for applications requiring high power, low divergence, and temperature stability.