Continuous wave and Q-switched infrared erbium laser

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Abstract
Upconversion pumping has been demonstrated both experimentally and theoretically to be important in the 2.8-μm 4I11/2–4I13/2 lasing transition in a CaF2 (Er3+) system. A minimum pump threshold of only 2.8 J with a 1-ms Xe lamp pulse has been achieved in CaF2 rods containing 5 mol % of Er3+ ions. A simple theory has been developed to show that upconversion pumping makes possible cw lasing between the 4I11/2 and 4I13/2 states even when the lifetime of the terminal 4I13/2 state is much longer than that of the upper 4I11/2 state. Semi-cw lasing has been experimentally demonstrated by pumping with six ganged photographic flash bulbs fired in sequence, with each bulb having a duration of 15–20 ms. Lasing at 2.8 μm lasted for 80 ms, well beyond 10 and 20 ms lifetimes of the 4I11/2 and 4I13/2 states. The 2.8-μm CaF2 (Er3+) laser has also been Q switched, using a 100-nm thin graphite foil as a shutter.