The invented laser comprises a pulsed source and an optical fiber. The invention allows for generating high efficiency spectral red-shifting of light from short wavelengths (high frequencies) to longer wavelengths (lower frequencies) using Raman amplification produced within the optical fiber. The pulsed source produces a pulsed signal with a low spontaneous noise component and a flat pulse-shape. The optical fiber receives the pulsed signal and perform Raman amplification which is performed by spectrally filtering a pulsed signal and which provides sufficient power to saturate a stage of erbium doped fiber amplification. The pulse signal is used to excite normal chromatic dispersion in the fibers, acting as a nonlinear system for efficient mid-infrared spectral generation.