Femtosecond Laser Amplification Based on Stimulated Raman Scattering in Optical Fibers

The amplification of femtosecond laser has been experimentally investigated around 1.060 m m wavelength through an optical fiber based on stimulated Raman scattering (SRS) . A passively mode locked Nd:glass laser (model Timebandwidth GLX 200) giving a pulse duration of about 200 fsec at 1.060 m m wavelength and 120 mW average optical power with 100 MHz repetition rate is used as seed signal . Whereas the high repetition rate 88MHz Nd YLF laser operating at 1.053 m m with pulse duration of 120 Psec is used as pump laser of the 15 and 25 m long single mode fiber. The broadening in the time of the pulse is done in the first few meters of the optical fiber and then amplified due to the energy transfer from pump laser source to the seed laser pulse . The results showed that the peak power conversion efficiency exceeds 45% and the on-off peak gain is about 2 dB. The peak wavelength shift is about 0.3 nm when the optical fiber is forward pumping by Nd-YLF laser. The self phase modulation (SPM) leads to compress the laser spectral width from 6.96 nm to 5 nm with small effect on the maximum nonlinear phase shift.