Semiconductor mode-locked laser with external feedback: emergence of multi-frequency pulse trains with an increasing number of modesKathy Lüdge, Lina Jaurigue, Benjamin Lingnau, Soizic Terrien and Bernd KrauskopfEur. Phys. J. B, 92 4 (2019) 89DOI: https://doi.org/10.1140/epjb/e2019-90662-4