Séminaire Nano

Jeudi 5 Février 2015 à 11h00.

Investigating the coherence properties of terahertz quantum cascade lasers with mode-locked fs-lasers

''Since a couple of decades mode-locked fs-lasers have become a widespread tool in Terahertz (THz) technology where they are exploited in time-domain spectroscopy systems for the generation and coherent sampling of short pulses using photomixers and non-linear crystals [1]. This is thanks to the fact that they can produce trains of pulses with a duration of ~100fs or lower, that is well below one optical cycle at 1 THz frequency. We have shown that this property can be used to coherently sample the electric field amplitude emitted by THz Quantum Cascade Lasers (QCLs) [2,3]. This sampling process can be viewed as a coherent down-conversion from the THz directly into the MHz range and has several applications that will be reviewed in this presentation. After a short introduction and review of the state-of-the-art of THz QCLs, a special emphasis will be given to the application of the sampling technique to study the coherence properties of this family of semiconductor lasers, from the measurement of their frequency noise spectral density [4], to their mode-locking operation [5], to the investigation of recently demonstrated multimode lasers with a spectral bandwidth beyond 1 THz [6]. [1] K. Sakai, “Terahertz optoelectronics”, Springer-Verlag (2005); [2] S. Barbieri, et al. Nature Photon. 4, 636 (2010); [3] M. Ravaro et al. Opt. Lett. 36, 3969 (2011); [4] M. Ravaro et al. Opt. Expr. 5, 25654 (2012); [5] S. Barbieri. et al. Nature Photon. 5, 306 (2011); [6] M. Rösch, et al. Nature Photon.9, 42 (2015).''