Frequency and intensity noise of a grating-tuned external-cavity quantum cascade laser

Year: 2026

Authors: La Penna I., Gabbrielli T., Rimoldi C., Mazzotti D., Faist J., Consolino L., Borri S., De Natale P., Cappelli F.

Autors Affiliation: European Lab Nonlinear Spect, LENS, Via Carrara 1, I-50019 Sesto Fiorentino, FI, Italy; Ist Nazl Ottica, CNR, INO, Largo Fermi 6, I-50125 Florence, FI, Italy; Swiss Fed Inst Technol, Inst Quantum Elect, Zurich, Switzerland.

Abstract: Quantum cascade lasers (QCLs) are semiconductor-heterostructure devices known for their emission in the mid-infrared and THz spectral regions. Due to their operating regime, their intrinsic linewidth is significantly narrower compared to bipolar semiconductor lasers. Here, we demonstrate that by implementing an external-cavity (EC) configuration based on a commercial diffraction grating, we have successfully induced a Fabry-P & eacute;rot QCL to emit on a single mode with a broadly-tunable wavelength in the range 4.29-4.44 & micro;m. This very simple setup enhances the laser performance in terms of threshold current and emitted power. A detailed noise analysis has been carried out, which demonstrates that the EC configuration positively impacts the laser operation. In particular, the intrinsic linewidth is substantially reduced (by a factor of similar to 5), the full linewidth is also decreased (depending on the integration timescale), and the relative intensity noise is slightly reduced. These characteristics, which hold within the whole tuning range, make the EC-QCL a good candidate for spectroscopy applications where broad tunability and narrow linewidth are highly demanded. (c) 2026 Optica Publishing Group under the terms of the Optica Open Access Publishing Agreement

Journal/Review: OPTICS EXPRESS

Volume: 34 (10)      Pages from: 18375  to: 18383

More Information: The authors acknowledge financial support by the European Union’s NextGenerationEU Programme with the I-PHOQS Infrastructure [IR0000016, ID D2B8D520, CUP B53C22001750006] Integrated infrastructure initiative in Photonic and Quantum Sciences; by the European Union’s Research and Innovation Programme Horizon Europe with the Laserlab-Europe Project [G.A. n. 871124] and the MUQUABIS Project [G.A. n. 101070546] Multiscale quantum bio-imaging and spectroscopy; by the European Union’s QuantERA II [G.A. n. 101017733] – QATACOMB Project Quantum correlations in terahertz QCL combs; by the Italian ESFRI Roadmap (Extreme Light Infrastructure-ELI Project); by the Italian Ministero dell’Universita e della Ricerca (project PRIN-2022KH2KMT QUAQK); by ASI and CNR under the Joint Project Laboratori congiunti ASI-CNR nel settore delle Quantum Technologies (QASINO) (Accordo Attuativo n. 2023-47-HH.0); by the European Partnership on Metrology with the 23FUN04 COMOMET project [Funder ID 10.13039/100019599].
KeyWords: Single-mode; Linewidth; Spectroscopy; Comb
DOI: 10.1364/OE.586860