A laser system comprises a high-Q nonlinear optical resonator, a cavity comprising an amplifying element and a dispersive element, an optical delay line adapted to tune the length of the cavity, and a large pass-band filter adapted to tune the cavity's central oscillation wavelength, the nonlinear optical resonator being selected with a linewidth (LWR) comparable to the cavity free-spectral range (FSRC). There is provided a method for generating highly stable pulse streams, comprising providing a cavity comprising an amplifying element and a dispersive element; selecting a high-Q nonlinear optical resonator with a linewidth (LWR) comparable to the cavity free-spectral range (FSRC); tuning the length of the cavity; and tuning the cavity's central oscillation wavelength.