Controlling and Phase-Locking a THz Quantum Cascade Laser Frequency Comb by Small Optical Frequency Tuning

TL;DR

This paper introduces a simple method to control and phase-lock THz quantum cascade laser frequency combs using small optical frequency tuning with white light, enhancing stability and potential applications.

Contribution

A novel, straightforward technique for controlling THz QCL combs via small optical frequency tuning with white light, simplifying device stabilization.

Findings

SOFT effectively tunes emission frequencies without destabilizing the laser

The method allows phase stabilization of the QCL comb

Comparison shows SOFT as a viable alternative to current actuators

Abstract

Full phase control of THz emitting quantum cascade laser (QCL) combs has recently been demonstrated, opening new perspectives for even the most demanding applications. In this framework, simplifying the set-ups for control of these devices will help to accelerate their spreading in many fields. We report a new way to control the emission frequencies of a THz QCL comb by small optical frequency tuning (SOFT), using a very simple experimental setup, exploiting the incoherent emission of an ordinary white light emitting diode. The slightly perturbative regime accessible in these condition allows tweaking the complex refractive index of the semiconductor without destabilizing the broadband laser gain. The SOFT actuator is characterized and compared to another actuator, the QCL driving current. The suitability of this additional degree of freedom for frequency and phase stabilization of a THz QCL comb is shown and perspectives are discussed.