Repetition-Rate and Wavelength Flexible Femtosecond Laser Pulse Generation

Abstract

Compared to mode-locked oscillators, gain-switched diodes (GSD) have the key advantage of repetition-rate agility. Yet, large pulse duration and poor coherence of the GSD pulses greatly limit their applications. Here, a GSD-pumped Raman fiber amplifier is demonstrated, which can effectively generate femtosecond laser pulses with both repetition-rate and wavelength agility. It is proved that both nonlinear optical gain and single-frequency seed in the fiber amplifier play critical roles for improving the coherence of the generated laser pulses. In the experimental demonstration, pumped by 1065 nm GSD pulses, the nonlinear fiber amplifier can generate highly coherent 1121 nm femtosecond Raman pulses with up to 80.2% conversion efficiency. The Raman pulses can maintain high performance within the repetition-rate tuning range from 1 to 150 MHz. The potential for generating 1178 nm femtosecond Raman pulses is also demonstrated with an optical conversion efficiency of 63.8%. This all-fiber based femtosecond laser with both repetition-rate and wavelength agility is a promising light source for applications such as nonlinear microscopy and micromachining.