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Spectral properties of quantum cascade lasers: from noise analysis to stabilization
Responsable du projet Thomas Südmeyer
Stephane Schilt
   
Collaborateur Lionel Tombez
   
Résumé Quantum cascade lasers (QCL) constitute the most versatile laser source in the mid-infrared and have wide applications in high-resolution molecular spectroscopy, such as trace gas sensing for environmental monitoring, safety or industrial process control. An important property of a laser source for such applications is its spectral purity. A precise knowledge of the frequency noise properties of QCLs has recently become of particular relevance in conjunction with the possibility to link a QCL to an optical frequency comb to make an absolute frequency reference in the mid-infrared. In this context, the achievement of a narrow-linewidth QCL would benefit to many applications.
Our group has recently shown QCLs operating at low frequency noise in free-running mode at room temperature, and studied a surprising temperature behavior for the first time: while the frequency noise is nearly unchanged above 200K, it drastically increases at lower temperature with an exponential dependence [Tombez et al, Opt. Express 20, 6851-6859, (2012)]. In this project, we want to understand the origins of this noise behavior. This includes identifying the important experimental parameters impacting the frequency noise in QCLs and understanding the underlying mechanisms leading to frequency fluctuations.
In a second phase, we want to exploit the low-noise properties of a QCL and explore new possibilities to further reduce its frequency noise significantly by active stabilization. For this purpose, we propose to use a crystalline (MgF2) ultra-high-Q micro-resonator as a frequency reference and to lock the QCL on a resonance of this cavity to reduce its frequency noise. This would provide a stable and narrow-linewidth mid-infrared laser in a compact arrangement that could benefit to many spectroscopic applications.
Any improvement of the spectral purity of mid-infrared laser sources will have a notable impact on many applications where low optical phase noise is important, for instance in high-resolution spectroscopy (trace gas sensing), but also in metrology, sensing or in free-space optical communications. Moreover, a QCL stabilized onto a micro-resonator can lead to substantially more compact systems than traditional approaches based on standard reference cavities.
   
Mots-clés Lasers à cascade quantique, Micro-résonateur, Stabilisation, Bruit de fréquence
   
Type de projet Recherche fondamentale
Domaine de recherche Physique, Lasers, Infrarouge
Source de financement FNS - Encouragement de projets (Div. I-III)
Etat Terminé
Début de projet 1-10-2012
Fin du projet 31-3-2014
Budget alloué 115'320.00
Contact Stephane Schilt