Abstract

Ultrafast mode-locked fiber lasers, owing to their high peak power and short pulse widths, have driven applications in imaging, industrial machining and nonlinear optics. Taking these systems to the mid-infrared wavelengths (2-20 um) allows access to other fields such as sensing and frequency comb based metrology, due to molecules absorbing light strongly at these wavelengths. However the performance of mode-locked fiber lasers in the mid-infrared has been limited with no demonstration of femtosecond scale pulses, and little evidence for a direct pulse measurement [1, 2]. At best an intensity autocorrelation of a 6 ps pulse was measured [3], but it did not reveal the true pulse shape or any phase information. Here we demonstrate the first mode-locked fiber laser operating at wavelengths >2.1 μm, producing 497 fs pulses with a peak power of 6.4 kW, with the field completely characterized using a Frequency Resolved Optical Gating (FROG) technique. This marks the first femtosecond-level fiber laser in the mid-infrared and highlights fluoride lasers as a strong candidate for ultrafast mid-infrared sources.

© 2015 IEEE