Comment: Phase noise power spectral density (PN-PSD) of the QCL mode spacing extracted electrically using a bias T in free-running mode and phase-locked to an external reference. PN-PSD of frequency reference is also recorded. Device: FSWP-26, Phase Noise Analyser Company: Rhode & Schwarz Uploaded by: Atif Shehzad Affiliation: Laboratoire Temps-Frequence, Institut de Physique, Universite de Neuchatel, Avenue de Bellevaux 51, 2000 Neuchatel, Switzerland Contact: atif.shehzad@unine.ch Upload date: 20-02-2020