Rare-earth solid-state laser emits mid-infrared pulses at 7 microns
A 0.7 % praseodymium-doped lanthanum trichloride (Pr3+:LaCl3) laser operating at room temperature produces pulsed 7.2-µm output, report scientists from the Naval Research Laboratory (Washington, DC) and Loyola College of Maryland (Baltimore, MD). The 3 ¥ 8 ¥ 15-mm Pr3+:LaCl3 crystal is end-pumped by a thulium-doped YAG laser operating at 2.02 µm, with a peak pum¥energy of roughly 30 mJ for room-temperature operation. Peak power of the microsecond-regime output pulses from the Pr3+:LaCl3 system is estimated at 100 W. The four-level laser system involves direct excitation to the 3F2 level, transition to the lower energy 3H6 level, followed by an upconversion process that populates the 3F3 level. Lasing occurs with the subsequent transition to the 3F2 level. Efficiency is lowered with 2.0-µm pumping because it populates the lower laser level. Future development of 1.49-µm diode laser array pumps may directly populate the upper level, optimizing performance.