Mode-locked oscillators are fantastic scientific instruments. Today, femtosecond pulses are now in demand for applications outside physics and chemistry laboratories, most notably for precision materials processing and nonlinear optical microscopy in biomedical laboratories and clinics. These applications require short pulses with high peak power and excellent beam quality. However, they also require devices that are cheap, reliable, and – crucially -- flexible. For example, synchronization of pulses with scanning optics is crucial for high efficiency machining and imaging alike. Lasers in materials processing are often required to exhibit pulse-on-demand operation in order to deposit energy only in specific locations. In biology, such behavior would enable region-of-interest monitoring, allowing e.g. ultrahigh resolution monitoring of a neuronal circuit’s dynamics. This kind of behavior is not compatible with the regular pulse train of a mode-locked oscillator.
To this end, we seed an ultrafast fiber amplifier with a gain-switched diode. This a robust, integrated device that can be electronically triggered at virtually any repetition rate, or on-demand, yielding partially-coherent, ~10 ps duration pulses. Remarkably, a single Mamyshev regenerator (nonlinear spectral broadening in fiber followed by offset spectral filtering) allows isolation of a coherent component of the diode pulse. After subsequent nonlinear pulse shaping, amplification to the µJ-regime, and linear compression, we obtain transform-limited ~140-fs pulses with 13 MW peak power. As will be discussed, such a source cannot replace all mode-locked oscillators (e.g., for frequency comb applications), but is extremely attractive for the key mainstream applications of ultrashort pulses.