93 fs pulses from a low repetition rate fiber laser

This paper reports on a passively mode-locked ytterbium-doped fiber laser with a repetition rate as low as 1.8 MHz. The oscillator with a resonator length of 118 m is hybridly mode-locked via nonlinear polarization evolution and saturable absorption in a semiconductor generating chirped 3.8 ps long pulses with a pulse energy of 1.0 nJ. These pulses are dechirped externally to pulse duration of 93 fs. These are the shortest pulses generated by fiber oscillators with repetition rates below 20 MHz.