Experimental investigation on the h-shaped pulse with leading edge in a Raman fiber laser

We report the experimental investigation on the h-shaped pulse with leading edge in a Raman fiber laser. Based on the nonlinear polarization rotation (NPR) technology, we successfully obtain the h-shaped pulse with leading edge in the all -fiber Raman fiber laser. After that, we experimentally study different affecting factors of pump power and polarization state on the leading edge, even the origin of it. Through adjusting the polarization state or increasing pump power, the leading edge can be extended up to 3907.71 ns or 3554.5 ns respectively without pulse collapse, showing an amazing stability and ultra-wide tunability. Finally, the corresponding spectra show that a left side peak always exists and gets stronger along with the extension of leading edge. After employing a home -made Lyot filter, we confirm that the leading edge is derived from the left side peak. Our work will contribute to the understanding of the h-shaped pulse with leading edge in soliton dynamics and its specific application in the material processing.