Single-stage GaSe OPCPA delivering high-energy few-cycle pulses at 11 µm wavelength – INVITED Martin Bock, Dennis Ueberschaer, Pia Fuertjes and Uwe Griebner EPJ Web Conf., 287 (2023) 08002 Published online: 18 October 2023 DOI: 10.1051/epjconf/202328708002