Highly efficient one- and two-cascade Raman lasers based on phosphosilicate fibers

Characteristics of one-cascade (1.06 double right arrow 1.24 mum) and two-cascade (1.06 double right arrow 1.24 double right arrow 1.48 mum) phosphorus-doped fiber Raman lasers are studied. The cavities of both lasers are formed by Bragg gratings written directly in the active fiber. Double-cladding Yb3+ and Nd3+ ion fiber lasers with lambda similar to 1.06 mum were employed for pumping. These lasers were pumped, in their turn, by diode laser arrays with lambda similar to 0.98 mum (Yb) and lambda similar to 0.81 mum (Nd). The efficiency of the one-cascade laser with an unprecedentedly short length of 50 in was as high as 65% with 4.8-W pump radiation applied to the input of the laser. The maximum efficiency of the two-cascade Raman fiber laser was 40%. Gratings directly written in the active fiber reduced concentrated losses in laser cavities, which allowed the laser length to be decreased and the lasing threshold power of Raman fiber lasers to be lowered.