Femtosecond Pulse Generation by Nonlinear Optical Gain Modulation

Abstract

Many approaches have been explored to generate ultrafast lasers including mode locking, microresonators, electro‐optic modulation, and gain‐switched diodes. Despite much progress, it is still challenging to generate high‐performance ultrafast pulses with wavelength versatility in a simple approach. Herein, a new method is proposed and demonstrated to transform a continuous‐wave (CW) single‐frequency laser into femtosecond‐scale pulses by nonlinear optical gain modulation in a fiber Raman amplifier. The proof‐of‐principle setup generates a stable and highly coherent laser at 1120 nm with a pulse energy of 25.7 nJ, a pulse width of 436 fs, and an optical efficiency of 69.4% by 14 ps gain modulation. Numerical simulation shows that pulse energy scaling to micro‐Joule level is feasible by increasing pump energy. By cascading the conversion process, high‐energy, femtosecond‐scale pulses can be produced over a wide spectral range.