Efficient gain-switched operation of a Tm-doped silica fiber laser

摘要

We present the results from experiments relating to angain-switched Tm-doped silica fiber laser in which a gain-switchednNd:YAG laser is used to pump the 3H5 energy levelnof the Tm3+ dopant ion. This fiber laser configuration is thenfirst example to our knowledge of a moderate energy gain-switched fibernlaser which is pumped with a low-repetition-rate high-energy pulsednlaser. For a near-optimized cavity, the gain-switched fiber lasernproduces a maximum pulse energy of 1.46 mJ at a maximum linear slopenefficiency of 20% and a total optical-to-optical efficiency (withnrespect to the launched energy) of 19%. At low pump energies, the slopenefficiency is approximately 40%, however, saturation of the output pulsenenergy is observed with the increase in the launched pump energy. Wenalso present results from a numerical model that simulates 3Hn5-band pumping and includes all of the known pumpnexcited-state absorption (ESA) mechanisms and, in addition, fourncross-relaxation mechanisms have also been included. The calculationsnestablish that the pump ESA mechanism contributes only a small lossnfactor to the overall efficiency of the laser when the Tm-doped silicanfiber laser is pumped at low pump energies, however, as the pump energynis increased, losses due to pump ESA limit the amount of output energynfrom the fiber laser. The loss mechanism is mainly attributed to pumpnESA from the 3H4 upper laser level to the combinedn3F2,3 energy level at low launched pump energiesnbecause of the large absorption cross section for this transition andnthe relatively long lifetime of the 3H4 energynlevel. For harder pumping conditions, the majority of the excited statenpopulation resides in the 1G4 level, inhibiting innsome laser configurations gain-switching of the fiber laser untilncessation of the pump pulse itself