Gain and saturation intensity of the green Ho:ZBLAN upconversion fiber amplifier and laser

The gain and saturation intensity of the green Ho-doped fluorozirconate (ZBLAN) glass fiber amplifier and laser, pumped in the red (643 /spl les/ /spl lambda//sub p/ /spl les/ 649 nm;
⁵
F
₅
/spl larr/
⁵
I/sub 8/), have been measured. For a 2.4-μm core diameter fiber 45 cm in length, the single-pass gain at 543.4 nm exceeds 12 dB for 90 mW of pump power at 643.5 nm. The saturation power for the
⁵
F
₄
,
⁵
S
₂
/spl rarr/
⁵
I/sub 8/ lasing transition was determined from gain measurements to be 970 /spl plusmn/ 175 μW, which corresponds to a saturation intensity of 19.8 /spl plusmn/ 3.5 kW /spl middot/ cm/sup -2/, and a stimulated emission cross section approximately one order of magnitude larger than theoretical estimates.