Carlos Hernández-GarcíaPhotonics and Laser Applications GroupUniversity of Salamanca Xinhua XiePhoton Science DivisionPaul Scherer Institute Oliver HecklChristian Doppler Laboratory for Mid-IR Spectroscopy and Semiconductor OpticsUniversity of Vienna Christoph Eisenmenger-Sittner Institute of Solid State Physics – Functional Materials Karin Whitmore Amalio Fernandez-Pacheco Chicon