The fluoride fiber laser with the longest emission wavelength, the Ho(3+)-transition at 3.9 mum in the attenuation minimum of the 3-5-mum atmospheric window, is characterized. After reviewing the importance of fluoride fibers due to their low phonon energies, we describe room-temperature fluorescence and laser action with liquid-nitrogen cooling. Continuous-wave laser action at 3.9 mum is presented for the 640- and the 890-nm pump ranges. A shift of the emission wavelength is achieved by varying the resonator mirrors. Laser characteristics and temperature dependence are discussed.
We report on an upconversion cascade laser in an erbium-doped ZBLAN fiber emitting simultaneously on the three transitions 4 S 3/2 ! 4 I 9/2 at 1.7 mm, 4 I 11/2 ! 4 I 13/2 at 2.7 mm, and 4 I 13/2 ! 4 I 15/2 at 1.6 mm. At moderate pump powers, the laser transition at 1.6 mm supports 2.7-mm lasing and permits a slope efficiency at 2.7 mm of 15% versus launched pump power. Above the threshold of upconversion lasing at 1.7 mm, the slope efficiency at 2.7 mm increases to 25.4%. Taking pump excited-state absorption into account, this value represents more than 90% of the theoretical slope efficiency. A transversely single-mode output power of 99 mW is achieved at 2.7 mm.
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