Short pulse generation and mode control of broadband terahertz quantum cascade lasers

TL;DR

This paper introduces a waveguide engineering method for broadband terahertz quantum cascade lasers that achieves ultra-short pulses, wide frequency emission, and effective mode suppression, advancing terahertz laser technology.

Contribution

The study presents a novel side-absorber technique to control modes and generate ultra-short pulses in broadband terahertz quantum cascade lasers.

Findings

Achieved up to 1 THz bandwidth in emission.

Generated 2.5 ps ultra-short pulses.

Demonstrated octave spanning emission from 1.63 to 3.37 THz.

Abstract

We report on a waveguide engineering technique that enables the generation of a bandwidth up to 1 THz and record ultra-short pulse length of 2.5 ps in injection seeded terahertz quantum cascade lasers. The reported technique is able to control and fully suppress higher order lateral modes in broadband terahertz quantum cascade lasers by introducing side-absorbers to metal-metal waveguides. The side-absorbers consist of a top metalization set-back with respect to the laser ridge and an additional lossy metal layer. In continuous wave operation the side-absorbers lead to octave spanning laser emission, ranging from 1.63 to 3.37 THz, exhibiting a 725 GHz wide at top within a 10 dB intensity range as well as frequency comb operation with a bandwidth of 442 GHz. Numerical and experimental studies have been performed to optimize the impact of the side-absorbers on the emission properties and to determine the required increase of waveguide losses. Furthermore, these studies have led to a better understanding of the pulse formation dynamics of injection-seeded quantum cascade lasers.