An intra-cavity optical parametric oscillator including means for providing a non-linear loss for suppressing relaxation oscillations, wherein the means for providing the non-linear loss are variable. The laser resonator may be delimited by the back-facet HR coating (16) of an end-pumped laser gain medium (14) and an output coupler (18). The laser comprises an intra-cavity optical parametric oscillator with a non-linear crystal (24), the singly resonant OPO which is signal-resonant comprises a mirror (26) and the common output coupler (18) and a dichroic beam splitter (22) reflecting the signal radiation and transmitting the laser fundamental. The amplitude of circulating laser fundamental may be stabilized inside the laser resonator by a feedback loop comprising a photodetector (38), a controller (40) and an optical modulator (3) in the resonator.