Laser diode-pumped holmium-doped fluorozirconate glass fiber laserin the green (Λ~544-549 nm): power conversion efficiency, pumpacceptance bandwidth, and excited-state kinetics

摘要

The green (544-549 nm) Ho-doped fluorozirconate (ZBLAN) glassnfiber laser, pumped in the red (Λ~6;15 nm) by a high-power (~30nmW) InGaAlP laser diode or a ring dye-laser, has been characterized withnregard to power conversion efficiency, fiber core-diameter and length,ncavity output coupling, and pump acceptance bandwidth. Fibers doped withn~1200 ppm (by weight) of Ho and having core diameters of 1.7, 3, and 11nΜm, and lengths ranging from 12.5 to 86 cm, have been studied innFabry-Perot resonators having output couplings ranging from 1.545 ton96%. For a 1.7-Μm core-diameter fiber, 21 cm in length, thenthreshold-launched pump power for the diode-pumped fiber laser is 1.9nand 3.5 mW for cavity output couplings of 1.5% and 24%, respectively.nThese values are the lowest for any upconversion-pumped fiber lasernreported to date. Also, the noise and threshold-pumping power propertiesnof the diode-pumped fiber laser are superior to those for itsndye-laser-pumped counterpart. The highest laser slope efficiencyn(>22% with respect to launched pump power) was measured for a 3-Μmncore-diameter fiber and a cavity output coupling of 24%. The spectralninterval over which the launched threshold pump power for this laser isn<10 mW is almost 20 nm (637-656 nm). Studies of the fiber lasernwaveform as a function of pump power reveal competition for populationnbetween the 5S2 and 5F4nstates and among the Stark sublevels of the 5F4nmanifold. Also, measurements of the output power on individual lasernlines of the 5F4, 5S2→n5I8 (ground) transitions of Ho3+:ZBLANnas a function of pump power demonstrate the existence of a lossnmechanism at the fiber laser wavelength, presumably due to absorptionnfrom ground or the 5Iy, 6S2nor 5F4 excited states of the ion