1. Photonics Institute, Technische Universität Wien, A-1040 Vienna, Austria
2. Christian Doppler Laboratory for Mid-IR Spectroscopy and Semiconductor Optics, University of Vienna, A-1090 Vienna, Austria
3. Istituto di Fotonica e Nanotecnologie-Consiglio Nazionale delle Ricerche (IFN-CNR) and Dipartimento di Fisica-Politecnico di Milano, Piazza Leonardo da Vinci 32, Milano 20133, Italy
4. few-Cycle Inc., 1650 Blvd. Lionel Boulet, J3X 1P7, Varennes, QC Canada
5. Ludwig-Maximilians-Universität München, Department of Physics, Am Coulombwall 1, 85748 Garching, Germany
6. UltraFast Innovations GmbH, Am Coulombwall 1, 85748 Garching, Germany
7. Center for Physical Sciences and Technology, Savanoriu Ave. 231, LT-02300, Vilnius, Lithuania