A laser (12, 18) with a laser resonator (13), the laser resonator (13) having a non-linear optical loop mirror (1, 1′), NOLM, which is adapted to guide counter-propagating portions of laser pulses, and to bring the counter-propagating portions of laser pulses into interference with each other at an exit point (4) of the NOLM (1, 1′). The non-linear optical loop mirror (1, 1′) has a non-reciprocal optical element (7, 7′).