The researchers found that the all-fiber Mamyshev oscillator provides high power and energy

High power/energy ultrafast fiber lasers have broadband applications in material processing, medicine, advanced manufacturing and other fields. Compared with solid-state laser, fiber laser has the advantages of compact system, good flexibility, good heat dissipation and high beam quality. However, the monopulse energy and average power of ultrafast fiber lasers, especially all-fiber structures, still lag behind solid-state lasers due to the serious nonlinear effects inside the fiber. In recent years, Mamyshev oscillators have attracted a lot of research attention due to their potential to produce high-energy ultrafast pulses. A Mamyshev oscillator based on fully polarization-maintaining fiber with a core/cladding diameter of 10/125 μm has been reported by a research group at National University of Defense Technology, achieving a monopulse energy of 153 nJ and a compression pulse width of 73 fs. In addition, by adjusting the cavity parameters, the maximum fifth harmonic mode-locking operation is obtained, with an average output power of 3.4 W and a compression pulse width of 100 fs. Recently, their work entitled "Full polarization-maintaining Fiber Mamyshev Oscillator delivers Pne Joule and Dovar 100 fs Pulses" was published in Ultrafast Science.

In recent years, the pulse energy and average power of ultrafast fiber lasers have been greatly improved based on Mamyshev oscillators with cascaded spectral broadening and offset spectral filtering effects. Continuous light and weak pulses will be blocked in the Mamyshev oscillator. Because the spectrum is sufficiently broadened, the strong pulse can survive in the cavity after two filters with different central wavelengths, and the ultrafast laser with high pulse energy can be obtained. However, most of the previous results adopt spatial structure and introduce a large number of free space units for signal collimation and coupling, which makes the system cumbersome and susceptible to interference.

"Our goal is to achieve a high power/energy ultra-fast fiber laser with an all-fiber structure," explained Professor Can Li. In the ultrafast Science paper, a Mamyshev oscillator based on fully polarization-maintaining fiber with a core/cladding diameter of 10/125μm is reported. In contrast to conventional Mamyshev oscillators, which usually consist of two-stage gain fiber amplifier, there is only one amplifier arm in the proposed laser. Using a passive fiber to widen the spectrum of the other arm alleviates the accumulation of nonlinear phase in the cavity while making the system more compact.

The research team achieved a high-performance ultrafast fiber laser with a single pulse energy of 153 nJ and an average power of 3.4 W, respectively, representing the highest pulse energy and average power recorded for an all-fiber ultrafast laser oscillator with picosecond/femtosecond pulse duration. "By using a fiber with a larger core diameter and a new pulse evolution mechanism with higher nonlinear phase cumulative tolerance, an all-fiber ultrafine laser with higher power/pulse energy can be expected," said Professor Pu Zhou.

This work was supported by the National Natural Science Foundation of China and the Director's Foundation of the State Key Laboratory of Pulsed Power Laser Technology.

Source: Laser Net