Various embodiments described herein relate to a laser source for producing a pulsed laser beam comprising a plurality of ultrashort optical pulses having a variable repetition rate. In one embodiment, the laser source comprises a fiber oscillator, which outputs optical pulses and a pulse stretcher disposed to receive the optical pulses. The optical pulses have an optical pulse width. The pulse stretcher has dispersion that increases the optical pulse width yielding stretched optical pulses. The laser source further comprises a fiber amplifier disposed to receive the stretched optical pulses. The fiber optical amplifier has gain so as to amplify the stretched optical pulses. The laser source includes an automatically adjustable grating compressor having dispersion that reduces the optical pulse width. The grating compressor automatically adjusts this dispersion for different repetition rates.