Chirp-Managed, High-Energy, Low-Repetition Mamyshev Oscillator Based on Hollow Core Fiber

Abstract

Mamyshev oscillator (MO) represents a powerful mode-locking technique to produce high energy and ultrashort pulses from a fiber system. However, it is challenging to achieve low repetition rates directly from an oscillator while fully exploiting the outstanding characteristics of MOs due to the constraint of large dispersion and high nonlinearity of conventional solid-core fibers. Here, a new method of combining a low-dispersion and low-nonlinearity hollow-core fiber (HCF) with the MO is proposed to overcome the problem, achieving a reduction in repetition rate from 20 to 1 MHz and realizing sub-50 fs pulses. Furthermore, the HCF provides anomalous dispersion and offers chirp management in the 1 MHz MO, effectively improving the pulse energy from 381 nJ (20 MHz all-normal-dispersion MO) to 514 nJ. The influence of intracavity chirp management is investigated by numerical simulations. To the best of our knowledge, it is the first time of realizing high-energy sub-50 fs pulses at 1 MHz repetition rate directly from an oscillator. The maximum peak power of the output pulses is more than 100 times higher than the previously reported low-repetition ultrafast fiber lasers. This high-performance laser has good potential for applications such as high-precision micromachining, high-order nonlinear microscopy imaging, and femtosecond-laser-assisted chemical ionization mass spectroscopy.