Excitation of individual Raman Stokes lines of up-to ninth order using rectangular shaped optical pulses at 530 nm

We demonstrate the selective excitation of Raman Stokes lines of up-to 9th order with relatively high extinction ratio pumped by rectangular shaped optical pulses at 530 nm of 100 ns duration. The rectangular shaped optical pulses at 530 nm were generated by frequency doubling of an adaptively pulse shaped fiber MOPA operating at 1060 nm. This kind of pulse shape is optimal for frequency conversion since all parts of the pulse experiences the same Raman gain. Therefore, it is possible for a pulse to transfer all of its energy through sequential frequency Raman shifts to successive order Stokes components. Consequently, by adjusting the pump power it is possible to achieve selective excitation of the Raman shift with little residual pump powers. Here, we have achieved extinction ratio as much as 15 dB from successive Stokes lines by coupling 530 nm light in a 1 km long Pirelli Freelight fiber. In addition, we were able to obtain up-to 9th order Stokes shift by launching 5 W of average pump power to the Raman gain medium. Maximum Stokes shifted power of 54 mW was recorded for a launched pump power of 5W. We attribute this to the large background loss of silica fibre in the visible region.